⎇ⓥ⺖㗴ฬ㧦ࡄ࡜ࡔ࠻࡝࠶ࠢ㨄✢ࠍ↪޿ߚ㜞࿶ਅߦ߅ߌࠆ XANES ⎇ⓥ⎇ⓥઍ⴫⠪㧦Ṛᴛ ᱞ↵ (ᣣᧄᄢቇᢥℂቇㇱ‛ℂቇ⑼)⎇ⓥᓥ੐⠪㧦㜞ᯅ ඳ᮸ (ᣣᧄᄢቇᢥℂቇㇱ‛ℂቇ⑼)౒ห⎇ⓥ⠪㧦᧻ਅ ⵨੫ (᧲ᶏᄢቇ㐿⊒ᎿቇㇱᖱႎㅢାᎿቇ⑼)‫⎇ޣ‬ⓥ⋡⊛‫ޤ‬⏛ᕈ૕‫⿥ޔ‬વዉ૕‫ޔ‬ඨዉ૕ߩ‛ℂ⊛ᕈ⾰ߦߪ‫ޔ‬ౝㇱߩ㔚ሶ⁁ᘒ߇ᄢ߈ߊ෻ᤋߐࠇࠆ‫⃻ޔ߫߃଀ޕ‬࿷‫ޔ‬ᄙߊߩ⎇ⓥ⠪ߩ⥝๧ࠍᒁ߈ߟߌߡ޿ࠆ㜞᷷⿥વዉ૕ߪ‫౒ޔ‬ㅢߩᕈ⾰ߣߒߡ Cu-O ࡀ࠶࠻ࡢ࡯ࠢ
ࠍ᦭ߒ‫ࠢ࡯ࡢ࠻࠶ࡀߩߎޔ‬ਛߩ Cu ߩ㔚ሶ⁁ᘒ㧔ଔᢙ㧕ߪ‫⚛㉄ޔ‬㊂߿᭴ᚑర⚛ߦࠃࠅᓇ㗀ࠍฃߌ‫ޔ‬޽ࠆଔᢙߩ᧦ઙߩ߽ߣߢ⿥વዉࠍ␜ߔ‫ޔߚ߹ޕ‬㊄ዻ⏛ᕈߩᧄ⾰ࠍ⷗ᭂ߼ࠆߚ߼ߦ♖ജ⊛ߦ⎇ⓥ߇ㅴ
߼ࠄࠇߡ޿ࠆࡋࡆ࡯ࡈࠚ࡞ࡒࠝࡦߣ޿ࠊࠇࠆ‛⾰⟲ߦ߅޿ߡߪ‫ޔ‬વዉ㔚ሶߣዪ࿷㔚ሶߣߩ⋧੕૞↪
߇⏛ᕈߩ⊒⃻ߩᩮᐙߢ޽ࠆߣ⠨߃ࠄࠇ‫ߩߘޔ‬㔚ሶ⁁ᘒߩታ㛎⊛⸃᣿ߪ㊀ⷐߢ޽ࠅ‫ޔߚ߹ޔ‬ᄢ߈ߥᦼᓙ߇ነߖࠄࠇߡ޿ࠆ‫ޕ‬ඨዉ૕߽฽߼ߎࠇࠄߩ‛⾰ߩ‛ℂ⊛ᕈ⾰ࠍ⺞ߴࠆߚ߼ߦߪ‫ޔ‬ర⚛⟎឵ࠍⴕ޿ߘߩ㔚ሶ⁁ᘒ߳ߩᓇ㗀ࠍ⺞ߴࠆߎߣ߇ᄙ޿‫߇ࠈߎߣޕ‬ర⚛⟎឵ߢߪ⟎឵㊂߇㒢ࠄࠇ‫ࠬࡀࡓ࠳ࡦ࡜ޔ‬╬ߩ೽ᰴ⊛ߥലᨐ߇ᷙ౉ߔࠆߚ߼ᧄ⾰߇⷗߃ߡߎߥ޿႐ว߇޽ࠆ‫ޕ‬ߎࠇߦኻߒ‫ޔ‬㜞࿶ജᛛⴚࠍ೑↪ߒߚታ㛎ߢߪ‛⾰ࠍ㕒᳓࿶⊛ߦ࿶❗ߔࠆߎߣߦࠃࠅㅪ⛯⊛ߦේሶ㑆〒㔌╬ߩ᭴ㅧࠍᄌൻߐߖߥ߇ࠄ㔚ሶ⁁ᘒߩᄌൻࠍ⺞ߴࠆߎߣ߇ߢ߈ࠆ‫ޕ‬㜞࿶ਅߩ㔚᳇ᛶ᛫‫ޔ‬Ꮺ⏛₸᷹ቯߦࠃࠆ⿥વዉォ⒖᷷ᐲ TC‫⏛ޔ‬᳇ォ⒖᷷ᐲߩ࿶ജലᨐߥߤ㕖Ᏹߦߚߊߐࠎߩ࿶ജਅߩ‛ᕈ߇ႎ๔ߐࠇߡ޿ࠆ‫ߩ߼ߚࠆߔ㉼⸃ࠍࠄࠇߎޔߒ߆ߒޕ‬㔚ሶ⁁ᘒߦ㑐ߔࠆᖱႎ߇߈ࠊ߼ߡዋߥ޿‫ߦ․ޕ‬㜞᷷⿥વዉ૕ߢߪ࿶ജࠍ߆ߌࠆߎߣߦࠃߞߡ HgBa2Ca2Cu3O10 ߇਎⇇ᦨ㜞ߩ TC= 164 K ࠍ␜ߔߎߣ߇ႎ
๔ߐࠇߡ޿ࠆ߇‫ߦࡓ࠭࠾ࠞࡔޔ‬㑐ߔࠆℂ⸃ߪㅴࠎߢ߅ࠄߕ‫ޔ‬㔚ሶ⁁ᘒߦ㑐ߔࠆታ㛎࠺࡯࠲߽߶ߣࠎ
ߤߥ޿‫ࠇߘޕ‬᡿‫ޔ‬Cu ߩ࿶ജਅߩ㔚ሶ⁁ᘒߦ㑐ߔࠆታ㛎߳ߩᦼᓙߪᄢ߈޿‫ޕ‬㜞࿶ਅߢశቇ⊛ߦ㔚ሶ⁁ᘒࠍ⺞ߴࠆߚ߼ߦߪ‫ޔ‬శቇ⊛᷹ቯߩ߶߆ߦ㨄✢ๆ෼ታ㛎(XANES)߇⠨߃ࠄࠇࠆ‫ߦ․ޕ‬㨄✢ๆ෼ታ㛎ߢߪ․ᕈๆ෼┵ઃㄭߦ⃻ࠇࠆࠬࡍࠢ࠻࡞ߩᓸ⚦᭴ㅧ߇ర⚛ߩ㔚ሶ᭴ㅧ߿
ኻ⒓ᕈࠍᒝߊ෻ᤋߔࠆߎߣ߆ࠄ‫ޔ‬ଔᢙߥߤߩ㔚ሶ⁁ᘒߦ㑐ߔࠆᖱႎ߇ᓧࠄࠇࠆ‫⃻ޕ‬࿷‫ࡦࡕࡗࠗ࠳ޔ‬࠼ࠕࡦࡆ࡞㜞࿶⊒↢ⵝ⟎ࠍ↪޿ࠆߎߣߦࠃߞߡ 100 ਁ᳇࿶એ਄ߩ࿶ജਅߢߩታ㛎߇น⢻ߢ޽ࠆ‫ߎޕ‬ߩࠃ߁ߥᵹࠇߩਛߢ‫⎇ᧄޔ‬ⓥࠣ࡞࡯ࡊ㧔㜞ᯅ㧕ߪ‫⏛ߦߢߔޔ‬ᕈ૕ Yb4As3 ߩ⏛ᕈߩ⿠Ḯࠍ⺞ߴࠆߚ߼ߦ㜞ࠛࡀ⎇㧼㧲ߢ㜞࿶ਅߩ XANES ᷹ቯࠍⴕ޿‫ޔ‬Yb ߩଔᢙߩ࿶ജലᨐࠍ⺞ߴߚ‫ߪ⾰‛ߩߎޕ‬࿶ജਅߢ᭽‫ߥޘ‬㔚᳇⊛࡮⏛᳇⊛᷹ቯ߇ⴕࠊࠇߡ߅ࠅ XANES ᷹ቯ߆ࠄߪ‛ᕈℂ⸃ߩߚ߼ߩၮ␆࠺࡯࠲߇
ᓧࠄࠇߡ޿ࠆ‫ޕ‬⃻࿷‫ޔ‬ᣣᧄᄢቇ㔚ሶ✢೑↪ᣉ⸳ߢߪᵄ㐳นᄌߢࠛࡀ࡞ࠡ࡯ಽ⸃⢻ߦఝࠇߚࡄ࡜ࡔ࠻࡝࠶ࠢ㨄✢ߩᣉ⸳೑↪ߩḰ஻߇ㅴ߼ࠄࠇߡ߅ࠅ‫⎇ᧄޔ‬ⓥߢߪߎߩᣉ⸳ߦ㜞࿶ XANES ᷹ቯࠪࠬ࠹ࡓࠍ᭴▽ߒ‫౒ޔ‬ห೑↪ᣉ⸳ߣߒߡᢛ஻ߔࠆߣหᤨߦ‫⏛ޔ‬ᕈ૕‫⿥ޔ‬વዉ૕‫ޔ‬ඨዉ૕ߩ㔚ሶ⁁ᘒߦ㑐ߔࠆၮ␆࠺࡯࠲ࠍ
⫾Ⓧߔࠆ੐ࠍ⋡⊛ߣߔࠆ‫ޕ‬‫⎇ޣ‬ⓥ᭎ⷐ‫ޤ‬࠳ࠗࡗࡕࡦ࠼ࠕࡦࡆ࡞࠮࡞(DAC)ࠍ↪޿ߚ㜞࿶ਅߩ XANES ᷹ቯߪߔߢߦᶏᄖߢ߽ⴕࠊࠇ‫ߚ߹ޔ‬࿖ౝߢ߽ᚒ‫߇࠲࡯࠺ߥ↪᦭ߡߞࠃߦࡊ࡯࡞ࠣߩޘ‬ᓧࠄࠇߡ޿ࠆ߇㜞࿶ᛛⴚ਄ߩ໧㗴‫ޔ‬㒢ࠄࠇߚࡑࠪ
ࡦ࠲ࠗࡓߩ໧㗴߿࠺࡯࠲ߩ⸃㉼ߩ໧㗴߆ࠄߐ߶ߤㅴዷߒߡ޿ߥ޿ߩ߇⃻⁁ߢ޽ࠆ‫ߦ․ޕ‬㜞࿶ታ㛎ߢߪ࠳ࠗࡗࡕࡦ࠼߇ోᵄ㐳㗔ၞߦࠊߚߞߡㅘ᣿ߢߪߥ޿ߩߢ‫ޔ‬ๆ෼┵ࠍ᷹ቯߢ߈ࠆర⚛߇㒢ࠄࠇߡߊࠆ‫ߥ߁ࠃߩߎޕ‬੐ᖱ߆ࠄ੹߹ߢߩߣߎࠈ㜞࿶ਅߩ XANES ᷹ቯߪ․ቯߩᏗ࿯㘃ర⚛ߦ㒢ࠄࠇࠆߎߣ
߇ᄙ߆ߞߚ‫ߚ߹ޕ‬㜞᷷⿥વዉ૕ਛߩ Cu ߩๆ෼┵ߩࠛࡀ࡞ࠡ࡯㗔ၞߢߪ࠳ࠗࡗࡕࡦ࠼ߪ㨄✢ߦኻߒਇㅘ᣿ߢ޽ࠆߩߢ‫ޔ‬㨄✢ࠍ࠳ࠗࡗࡕࡦ࠼ࠕࡦࡆ࡞ߩ㑆ߩ Be ⵾ߩࠟࠬࠤ࠶࠻ࠍㅘㆊߐߖߡታ㛎ࠍⴕ߁ߎߣࠍ⸘↹ߒߡ޿ࠆ‫ ߼ߚߩߎޕ‬DAC ࠍ⾼౉ߒ Be ࠍࠟࠬࠤ࠶࠻ߣߒߡട࿶⹜㛎ࠍⴕ߁‫ޕ‬࿶ജ᷹ቯߦߪ DAC ౝߦ࡞ࡆ࡯ߩ࠴࠶ࡊࠍ౉ࠇ‫Ⱟߩߘޔ‬శᵄ㐳ࠍ᷹ቯߔࠆߎߣߦࠃߞߡⴕ߁‫Ⱟߩ߼ߚߩߘޕ‬శ᷹ቯࠪࠬ࠹ࡓࠍ᭴▽ߔࠆ‫ޕ‬ᰴߦ‫ޔ‬ᣣᧄᄢቇ㔚ሶ✢೑↪ᣉ⸳ߩࡄ࡜ࡔ࠻࡝࠶ࠢ㨄✢ࡆ࡯ࡓ࡜ࠗࡦߦ XANES ᷹ቯ↪ߩ㨄✢ᬌ಴ࠪࠬ࠹ࡓࠍ᭴▽ߔࠆ‫⹜ޕ‬ᢱߩ೨ᓟߦࡆ࡯ࡓߩᒝᐲࠍ᷹ቯߔࠆᬌ಴ེࠍ߅߈೨ᓟߩᒝᐲᲧ߆ࠄๆ෼ଥ
ᢙࠍ᳞߼ࠆ‫ޕ‬ᄢ᳇࿶ਛߢ޿ߊߟ߆ߩౖဳ⊛ߥ‛⾰ߩࠬࡍࠢ࠻࡞ߩ᷹ቯࠍⴕ߁‫ߦࠄߐޕ‬ૐ᷹᷷ቯ߇ߢ
߈ࠆࠃ߁ߦ 4K ߹ߢ಄ළߢ߈ࠆ಄ಓᯏࠍ⾼౉ߒ‫ޔ‬಄ළ࠹ࠬ࠻ࠍⴕ߁‫ޕ‬ૐ᷷ߢߩ࿶ജ࠹ࠬ࠻߽ⴕ߁‫ޕ‬
DAC ౝߦ࠮࠶࠻ߒߚ⹜ᢱߦߟ޿ߡๆ෼ଥᢙߩ᷹ቯࠍⴕ߁‫ޕ‬㧝㧚 㜞᷷⿥વዉ૕ਛߩ Cu ߩ XANES ࠍ㜞࿶ਅߢ᷹ቯߒ⿥વዉォ⒖᷷ᐲ TC ߣ Cu ଔᢙߣߩ㑐ㅪࠍ⺞ߴࠆ‫ᦨߦ․ޕ‬㜞ߩ TC ࠍ␜ߔ Hg ♽㉄ൻ‛⿥વዉ૕ߦߟ޿ߡ㜞࿶ਅߢ᷹ቯࠍⴕ߁‫ޕ‬Cu ߩ XANESࠍ᷹ቯߔࠆߚ߼ߦ㨄✢ߪ࠳ࠗࡗࡕࡦ࠼ࠍㅢߐߥ޿ߢࠟࠬࠤ࠶࠻ߩ Be ࠍㅘㆊߐߖࠆࠃ߁ߦߔࠆ‫ޕ‬㧞㧚 ࡋࡆ࡯ࡈࠚ࡞ࡒࠝࡦߣ๭߫ࠇࠆ‛⾰⟲ߦߟ޿ߡ㜞࿶ਅߢߩ XANES ᷹ቯࠍⴕ߁‫ޕ‬Yb‫ޔ‬Tm ߩൻว‛ߦߟ޿ߡߪታ❣߇޽ࠆ‫ޕ‬Ce‫ޔ‬Eu ߩൻว‛ߥߤଔᢙᄌൻߦࠃߞߡ㔚᳇⊛࡮⏛᳇⊛ᕈ⾰߇ᄢ߈ߊᄌൻߒᵈ⋡ࠍ㓸߼ߡ޿ࠆ‛⾰ߩ XANES ᷹ቯࠍⴕ߁‫ޕ‬Ce‫ޔ‬Eu ߽㨄✢ߪ࠳ࠗࡗࡕࡦ࠼ࠍㅢߐ
ߥ޿ߢ Be ⵾ߩࠟࠬࠤ࠶࠻ࠍㅘㆊߐߖࠆࠃ߁ߦߔࠆ‫ޕ‬㧟㧚 ࿶ജਅߢඨዉ૕ࡓ㊄ዻォ⒖ࠍ␜ߔ‛⾰ߩ㊄ዻߩଔᢙᄌൻࠍ⺞ߴࠆ‫ޕ‬ඨዉ૕㊄ዻォ⒖ߪ᭽‫ߥޘ‬ⷐ࿃ߢ⿠ߎࠆߎߣ߇⍮ࠄࠇߡ޿ࠆ߇‫ޔ‬ଔᢙࠍ࿶ജਅߢ⺞ߴߚ଀ߪߥߊ‫ޔ‬ォ⒖ᯏ᭴⸃᣿ߦᣂߚߥ
ᖱႎࠍឭଏߢ߈ࠆ‫ޕ‬‫⎇ޣ‬ⓥᬺ❣╬‫ޤ‬࡮⊒⴫⺰ᢥ(1) Ho-Ba-Cu-O ♽ࡃ࡞ࠢ⿥વዉ᧚ᢱߩ⥃⇇㔚ᵹኒᐲߣ᝝ᝒ⏛႐․ᕈ,↰ਛᒄା㧘ᚑᧁ⚩਽㧘ဈ੗⋥㆏㧘᧛਄㓷ੱ㧘ᐔᨋᴰ㧘Ṛᴛᱞ↵: ᣣᧄ㊄ዻቇળ⹹ ╙ 68 Ꮞ ╙ 9 ภ (2004) 693-697(2) Flux motion in Y-Ba-Cu-O bulk superconductors during pulse field magnetization, K.Yoshizawa,
S.Nariki, N.Sakai, M.Murakami, I.Hirabayashi, and T.Takizawa: Superconductor Science andTechnology 17 74-78 (2004)(3) Phase diagrams of the pseudo-binary systems of BaS-Ga2S3 and BaS-In2S3, C. Hidaka, E. Yamagishi
and T. Takizawa:

In press(4) Single Crystal growth of SrIn2VI4 (Ψ=Se,S) Compounds Solidifying through Supercooling, C. Hidaka,
E. Yamagishi and T. Takizawa: Journal of Crystal Growth 275 433-437 (2005)(5) Effect of pinning on the flux motion of Gd-Ba-Cu-O bulk superconductors,
Murakami, T. Takizawa:

Physica C, 392-396 (2003)

K. Yoshizawa, S. Nariki, M.

391-395(6) Radiative and non-radiative processes of Ce related transitions in CaGa2S4 and SrGa2S4, A. Kato, M.
Yamazaki, H. Najafov, K. Iwai, A. Bayramov, C. Hidaka, T. Takizawa and S. Iida: Journal of Physics
and Chemistry of Solids 64 1511-1517 (2003)(7) Determination of a pseudo-binary SrSe--Ga2Se3 phase diagram and single crystal growth of SrGa2Se4
compounds, Chiharu Hidaka, Nobuyasu Makabe and Takeo Takizawa: Journal of Physics and Chemistryof Solids 64 1797-1800 (2003)(8) ESR study of Ce3+ ions doped in the CdIn2S4 lattice, Takeo Takizawa, Hiroyuki Ozawa and Chiharu
Hidaka: Journal of Physics and Chemistry of Solids 64 1807-1810 (2003)(9) Light figure spectroscopy of optically active anisotropic materials Nobuyuki Yamamoto, Nazim
Mamedov, Yonggu Shim, Chiharu Hidaka, Takeo Takizawa, Eiji Niwa and Katashi Masumoto Journalof Physics and Chemistry of Solids 64 1959-1962 (2003)(10) Schottky properties of CuInSe2 single crystals grown by the Horizontal Bridgman method with
controlling Se vapor pressure Hiroki Matsushita, Yukio Tojo and Takeo Takizawa Journal of Physics andChemistry of Solids 64 1825-1829 (2003)(11) Extended Application of Light Figures to Optically Active Materials with Transversally Isotropic
Dielectric Function Nazim Mamedov, Nobuyuki Yamamoto, Yonggu Shim, Yuichiro Ninomiya andTakeo Takizawa

Jpn. J. Appl.Phys. 42 5145-5152 (2003)(12) IIa-III2-VI4 ♽ൻว‛ߩන⚿᥏૞⵾, Ṛᴛᱞ↵㧘ᣣ㜞ජ᥍ ᔕ↪‛ℂ ╙ 71 Ꮞ ╙ 5 ภ (2002)
553-556(13) Flux creep propertiea in Dy-Ba-Cu-O bulk superconductors, H.Enomoto, K.Inoue, S.Nariki,
M.Murakami, T.Takizawa: Physica C 378-381 513--516 (2002)(14) Cu-based multinary compounds and their crystal growth: synthesis processes, phase diagrams andcontrol of vapor pressures, Hiroaki Matsushita, Akinori Katsui and Takeo Takizawa: Journal of Crystal
Growth 237-239 1986-1992 (2002)(15) Single-crystal growth and optical properties of undoped and Ce3+ doped CaGa2S4,

C.Hidaka andT.Takizawa: Journal of Crystal Growth 237-239 2009-2013 (2002)(16) Thermal analysis of chemical reaction processes of chalcopyrite compound semiconductors, HiroakiMatsushita and Takeo Takizawa: IPAP Book Series 1, Japanese Research Review for Pioneering Ternaryand Multinary Compounds in the 21st Century, 11-16 (2002)(17) Single crystal growth of CaGa2S4 and SrGa2S4, Chiharu Hidaka and Takeo Takizawa: IPAP Book
Series 1, Japanese Research Review for Pioneering Ternary and Multinary Compounds in the 21stCentury, 68-72 (2002)(18) Phase diagrams and crystal structures of the CdS-In2S-Ga2S3 system, Kimitaka Asaka, Chiharu Hidaka,
Takeo Takizawa and Hiroaki Matsushita: IPAP Book Series 1, Japanese Research Review for Pioneering
Ternary and Multinary Compounds in the 21st Century, 73-78 (2002)(19) Defect physics of CuInSe2 and CuGaSe2 bulk single crystals grown by the horizontal Bridgman method,
Hiroaki Matsushita and Takeo Takizawa: IPAP Book Series 1, Japanese Research Review for Pioneering
Ternary and Multinary Compounds in the 21st Century, 190-196 (2002)(20) The viscous flux flow and flux creep induced by pulsed magnetic field in YBCO disk, T. Kono, M.
Tomita, M. Murakami and T. Takizawa:

Physica C, 357-360 537-540 (2001)(21) AC susceptibility measurement for Nd-Ba-Cu-O superconductor, Y. Akamatsu, K. Waki, K. Inoue, M.
Murakami and T. Takizawa: Physica C 357-360 541-544 (2001)(22) Two-step transition of (Nd0.33Eu0.33Gd0.33)Ba2Cu3Ox superconductors in high fields, T. Matano, M.
R. Koblischka, M. Muralidar, M. Murakami and T. Takizawa: Physica C 357-360 548-551 (2001)(23) Ac susceptibility of high-Tc superconductor REBa2Cu3Oy, H.Enomoto, K.Inoue, M.Muralidhar,
M.Murakami and T.Takizawa: Physica C 357-360 545-547 (2001)(24) Defect properties of CuInS2 single crystals grown by horizontal Bridgman method with controlling S
vapor pressure, Hiroaki Matsushita, Tomohiro Mihira and Takeo Takizawa: Jpn. Journal of Applied
Physics 40 4789-4793 (2001)(25) Phase diagram of the CaS-Ga2S3 system and melt growth of CaGa2S4 single crystals,
C.Hidaka-Komatsu and T.Takizawa: Journal of Crystal Growth 222-3 574-578 (2001)(26) Growth and Crystallographic Properties of II-III2-VI4 Compounds --- Focusing on the
Sulfides---(Invited), T.Takizawa, C.Hidaka, K.Asaka, T.Isomoto and H.Matsushita: Jpn. Journal ofApplied Physics 39 35-40 (2000) Supp. 39-1 Proc. of 12th ICTMC, R.O.C., 2000
(27) Probing the Interface and Microstructures in CdS/CuInSe2 and InGaAsN/GaAs Heterojunctions by
Synchrotron Radiation (Invited), Y.L.Soo, S.Huang, Y.H.Kao, S.K.Deb, K.Ramanathan and T.Takizawa:
Jpn. Journal of Applied Physics 39 29-34 (2000) Supp. 39-1 Proc. of 12th ICTMC, R.O.C., 2000
(28) Single Crystal Growth of SrGa2S4 by the Self-Flux Method, C.Hidaka and T.Takizawa:

Jpn. Journalof Applied Physics 39 67-68 (2000) Supp. 39-1 Proc. of 12th ICTMC, R.O.C., 2000
(29) Thermal and Crystallographic Analysis of Cd(InxGa{1-x})2S4 Compounds, K.Asaka, C.Hidaka,
T.Takizawa and H.Matsushita: Jpn. Journal of Applied Physics 39 139-140 (2000) Supp. 39-1 Proc. of
12th ICTMC, R.O.C., 2000
(30) Flux Motion in melt-processed YBCO in pulsed magnetic fields, T. Kono, M. Tomita, M. Murakami and
T. Takizawa:

Physica C: Superconductivity, 341-348 2437-2438 (2000)(31) Confirmation of Ba-rich Nd1+xBa2-xCu3O7-į solid solutions, G.Osabe, S.I.Yoo, N.Sakai, T.Higuchi,
T.Takizawa, K.Yasohama and M.Murakami: Supercond. Sci. Technol. 13 637-640 (2000)(32) Flux motion in bulk YBCO induced by pulsed magnetic fields: T.Kohno, M.Tomita, M.Murakami and

T.Takizawa:

Physica C, 341-348 (2000) 2437-2438(33) Ac susceptibility measurements for Nd-Ba-Cu-O superconductor, Y.Akamatsu, K.Waki, K.Inoue,
M.Murakami and T.Takizawa: Supercond. Sci. Technol. 13 802-804 (2000)(34) Superconducting transitions of YBa2Cu3Ox superconductors in high fields, T.Matano, M.R.Koblischka,
B.W.Veal, M.Murakami and T.Takizawa:

Supercond. Sci. Technol. 13 805-806 (2000)(35) V-I characteristics of a melt grown YBCO as revealed by a pulsed field, T.Takizawa, M.Yamazaki and
M.Murakami: Physica B: Physics of Condensed Matter 284-288 845-846(2000)(36) Phase diagram of the SrS - Ga2S3 system and its application to the single crystal growth of SrGa2S4,
C.Komatsu and T.Takizawa: Journal of Crystal Growth 210 677-682 (2000)(37) Thermal analysis and synthesis from the melts of Cu-based quaternary compounds

Cu-III-IV-VI4 andCu2-II-IV-VI4 (II = Zn, Cd; III = Ga, In; IV = Ge, Sn; VI = Se), Hiroaki Matsushita, Takashi Maeda,
Akinori Katsui and Takeo Takizawa: Journal of Crystal Growth 208 416-422 (2000)(38) Pressure Effect on the Antiferromagnetic Transition Temperature in CuFeO2, H. Takahashi, Y.Motegi,
R.Tsuchigane, and M. Hasegawa, J.Magn.Magn.Mat. Vol.272-276 (2004) pp.216-217.
(39) High pressure studies of anomalous electronic states of Y1-xUxPd3,
H.Sato, Y.Onuki, H.Takahashi, N.Mori, J.Phys.:Condens. Matter

G.Oomi, T.Kagayama, Y.Aoki,

Vol.16 (2004) pp.3385-3400.

(40) Pressure effect on a ferromagnetic transition temperature of RuSr2GdCu2O8, J.Shibata, H.Goto,
H.Takahashi, A.Matsushita, Y.Yamada, Physica C Vol.388-389 (2003) pp.235-236.
(41) N.Motoyama, H.Eisaki, S.Uchida, N.Takeshita, N.Mori, T.Nakanishi, H.Takahashi, Electronic phase
diagram of a hole-doped two-leg ladder system, Sr14-xCaxCu24O41, Europhys. Lett. Vol.58 , (2002),
pp.758-763.
(42) Metal to insulator transition of filled skutterudite PrRu4P12 at low temperaturea and high pressures,
I.Shirotani, J.Hayashi, T.Adachi, C.Sekine, T.Kawakami, T.Nakanishi, H.Takahashi, J.Tang,
A.Matsushita, T.Matsumoto, Physica B Vol.322 (2002) pp.408-412.
(43) ࿶ജⵝ⟎ߩ⃻⁁㧘㜞ᯅඳ᮸㧘㜞࿶ജߩ⑼ቇߣᛛⴚ ╙㧝㧞Ꮞ╙㧠ภ (2002) pp.272-279㧚(44) H.Takahashi, H.Takahashi, T.Nakanishi, T.Arima, M.Noguchi, M.Oyanagi, N.Takashita, N.Môri,
High-pressure effect on transport properties of spin-ladder compoundNa1-xCaxV2O5 andCa0.7Li0.3V2O5, J.Magn.Magn.Mat. Vol.226-230, (2001), pp.246-248.
(45) H.Kobayashi, N.Takashita, N.Mori, H.Takahashi, T.Kamimura, Pressure-inducedsemiconductor-metal-semiconductor transitions in FeS, Phys. Rev.B Vol.63, (2001), p.115203.
(46) T.Nakanishi, N.Motoyama, H.Mitamura, N.Takeshita, H.Takahashi, H.Eisaki, S.Uchida, T.Goto,
H.Ishimoto, N.Môri, Pressure and field dependence in the spin-ladder Sr14-xCaxCu24O41,
J.Magn.Magn.Mat. Vol.226-230 , (2001), pp.449-451.
(47) DAC ࠍ↪޿ߚૐ᷷‛ᕈ᷹ቯ㧘㜞ᯅඳ᮸㧘㜞࿶ജߩ⑼ቇߣᛛⴚ ╙ 11 Ꮞ ╙ 3 ภ (2001)
pp.195-202.
(48) T.Nakanishi, H.Takahashi, N.Takeshita, N.Môri, N.Motoyama, H.Eisaki, S.Uchida, H.Fujino, T.Nagata,
J.Akimitsu,Upper critical field of spin-ladder Sr2Ca12Cu24O41, Physica Vol.B281&282,(2000) ,pp.957-958.
(49) I.Shirotani, K.Ohno, C.Sekine, T.Yagi, T.Kawakami, T.Nakanishi, H.Takahashi, J.Tang, A.Matsushita,
T.Matsumoto, Electrical conductivity and superconductivity of LaT4As12 (T=Fe, Ru, and Os) with

skutterudite-type structure., Physica

Vol.B281&282, (2000) ,pp.1021-1023.

(50) H.Hedo, T.Nakama, A.T.Burkov, K.Yagasaki, Y.Uwatoko, H.Takahashi, T.Nakanishi, N.Môri,
Pressure-induced structural-phase transition of CeRu2, Physica Vol.B281&282 , (2000) ,pp.88-89.
(51) S.Miyasaka, H.Takagi, Y.Sekine, H.Takahashi, N.Môri, R.J.Cava, Metal-Insulator transition anditinerant antiferromagnetism in NiS2-xSex pyrite, J.Phys. Soc.Jpn Vol.69, (2000) ,pp.3166-3169.
(52) H.Nozaki, H.Ikuta, Y.Yamada, A.Matsushita, H.Takahashi, I.Hirabayashi, U.Mizutani, Substitution
effect on ferromagnetism in La4Ba2Cu2O10, Phys. Rev.B Vol.62 , (2000) ,pp.9555-9560.
(53) T.Nakanishi, N.Motoyama, H.Mitamura, N.Takeshita, H.Takahashi, H.Eisaki, S.Uchida, N.Mori,
Critical Field of Superconducting Spin-Ladder Sr14-xCaxCu24O41, Int.J.Mod.Phys. Vol.B14, (2000) ,p.3617.
࡮ቇળ⊒⴫(1) H. Tanaka1,2, S. Nariki1, N. Sakai1, M. Murakami1,3, I. Hirabayashi1, T. Takizawa2 㧘
1Superconductivity Research Laboratory, ISTEC, 2Nihon University, 3Shibaura Institute of Technology㧘
MICROSTRUCTURE AND SUPERCONDUCTING PROPERTIES OF Dy-Ba-Cu-O BULKSUPERCONDUCTORS FABRICATED IN VARIOUS OXGEN PARTIAL PRESSURES㧘ᣂẟࠦࡦࡌࡦ࡚ࠪࡦ࠮ࡦ࠲࡯ (ᧇ㣕ࡔ࠶࠮) 㧘ᐔᚑ 16 ᐕ 11 ᦬(2) S. Nariki1, A. Mogi1,2, H. Tanaka1,2, N. Sakai1, M. Murakami1,3, I. Hirabayashi1, T. Takizawa2
1Superconductivity Research Laboratory, ISTEC, 2Nihon University, 3Shibaura Institute ofTechnology)   EFFECT OF Y-Ba-Cu-O-M (M = Zr, Sn AND Ce) ADDITION ON THE
SUPERCONDUCTING PROPERTIES OF MELT-TEXTURED Y123 BULK㧘ᣂẟࠦࡦࡌࡦ࡚ࠪࡦ࠮
ࡦ࠲࡯ (ᧇ㣕ࡔ࠶࠮) 㧘ᐔᚑ 16 ᐕ 11 ᦬(3) Kato, S. Iida, M. Yamazaki, E. Yamagishi, C. Hidaka 㧘T. Takizawa㧘Optical Gain due to the Eu
Transition in the Alloy of Ca1-xEuxGa2S4㧘The 14th International Conference on Ternary andMultinary Compounds㧘ᐔᚑ 16 ᐕ 10 ᦬(4) C. Hidaka, E. Yamagishi㧘T. Takizawa㧘Photoluminescence spectra of rare earth doped CaGa2S4 single
crystals 㧘The 14th International Conference on Ternary and Multinary Compounds㧘ᐔᚑ 16 ᐕ 10᦬(5) S. Nomura, T. Takizawa㧘S. Endo㧘Electronic States of Lanthanide in the Ternary Thiogallate CaGa2S4㧘
The 14th International Conference on Ternary and Multinary Compounds㧘ᐔᚑ 16 ᐕ 10 ᦬(6) E. Yamagishi, C. Hidaka㧘 T. Takizawa㧘Preparation of Ca1-xEuxGa2S4 crystals and theirphotoluminescence, absorption and excitation spectra㧘The 14th International Conference on Ternaryand Multinary Compounds ᐔᚑ 16 ᐕ 10 ᦬(7) ↰ਛᒄା㧘ᚑᧁ⚩਽㧘ဈ੗⋥㆏㧘᧛਄㓷ੱ㧘ᐔᨋᴰ㧘Ṛᴛᱞ↵㧘⒳‫⚛㉄ߩޘ‬ಽ࿶ਅߢ૞⵾ߒߚ
Dy-Ba-Cu-O ♽ࡃ࡞ࠢ᧚ᢱߩ⿥વዉ․ᕈ㧘╙ 65 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘᧲ർቇ㒮ᄢቇ㧘ᐔ
ᚑ 16 ᐕ 9 ᦬(8) ട⮮᦭ⴕ㧘㘵↰⺈ਯ㧘ጊፒ⺈㧘ጊጯᕺ೑㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Ca1-xEuxGa2S4 ᷙ᥏ߩ Eu ㆫ
⒖ߦࠃࠆశቇ೑ᓧ㧘╙ 65 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘᧲ർቇ㒮ᄢቇ㧘ᐔᚑ 16 ᐕ 9 ᦬(9) ㊁᧛㊀ቁ㧘Ṛᴛᱞ↵㧘㆙⮮ਃ㇢,ਃర࠴ࠝࠟ࡟࡯࠻ൻว‛ CaGa2S4 ਛߩ࡜ࡦ࠲ࡁࠗ࠼ర⚛ߩ㔚ሶ⁁ᘒ㧘╙ 65 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘᧲ർቇ㒮ᄢቇ㧘ᐔᚑ 16 ᐕ 9 ᦬

(10) Hiroaki Matsushita, Koji Mitake㧘Takeo Takizawa, Single crystal growth of Cu(Ga,In)Se2 solid
solutions by horizontal Bridgman method with controlling Se vapor pressure and their defect properties㧘
The 14th International Conference on Crystal Growth, ࡈ࡜ࡦࠬ㧘ᐔᚑ 16 ᐕ 8 ᦬(11) C. Hidaka, M. Goto, M. Kubo, T. Takizawa, Phase diagrams of the pseudo-binary systems of BaS-In2S3
and BaS-Ga2S3㧘The 14th International Conference on Crystal Growth, ࡈ࡜ࡦࠬ ᐔᚑ 16 ᐕ 8 ᦬(12) ਭ଻㓷๺㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘BaIn 2S4 ߩන⚿᥏૞⵾㧘╙ 65 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᧲੩Ꮏ⑼ᄢቇ㧘ᐔᚑ 16 ᐕ 3 ᦬(13) ጊጯᕺ೑㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Ca1-xEuxGa2S4 ൻว‛ߩ⊒శ࡮శๆ෼࡮ബ⿠ࠬࡍࠢ࠻࡞㧘╙65 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᧲੩Ꮏ⑼ᄢቇ㧘ᐔᚑ 16 ᐕ 3 ᦬(14) ศᴛసⷙ, ᷓ੗዆ผ, ᚑᧁ⚩਽, ဈ੗⋥㆏, ᧛਄㓷ੱ, ᐔᨋᴰ, Ṛᴛᱞ↵㧘ࡄ࡞ࠬ⌕⏛ㆊ⒟ߦ߅
ߌࠆ㜞᷷⿥㔚ዉ૕ࡃ࡞ࠢ૕ਛߩ⏛᧤᜼േߣ⊒ᾲߩ⹏ଔ㧘⑺ቄૐ᷷Ꮏቇ࡮⿥㔚ዉቇળ, ᐔᚑ 15 ᐕ
12 ᦬(15) ጊጯᕺ೑㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Ca(1-x)EuxGa2S4 ൻว‛ᷙ᥏ߩ૞⵾ߣߘߩశๆ෼෸߮⊒శ․ᕈ㧘ᄙర♽ᯏ⢻᧚ᢱ⎇ⓥળᐕᧃ⻠Ṷળ㧘ᐔᚑ 15 ᐕ 11 ᦬(16) ਭ଻㓷๺㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrIn2S4 ൻว‛ߩන⚿᥏૞⵾㧘ᄙర♽ᯏ⢻᧚ᢱ⎇ⓥળᐕᧃ⻠Ṷળ㧘ᐔᚑ 15 ᐕ 11 ᦬(17) Hironobu TANAKA, Shinya NARIKI, Naomichi SAKAI, Masato MURAKAMI, Izumi
HIRABAYASHI, Takeo TAKIZAWA㧘Field Trapping Properties of Melt-Textured Ho-Ba-Cu-O Bulk
Superconductors with Fine Ho-211 Inclusions The 16th International Symposium on Superconductivity,
ᐔᚑ 15 ᐕ 10 ᦬ 27 ᣣ㨪29 ᣣ(18) ↰ਛᒄା㧘ᚑᧁ⚩਽㧘ဈ੗⋥㆏㧘᧛਄㓷ੱ㧘ᐔᨋᴰ㧘Ṛᴛᱞ↵㧘Ho-Ba-Cu-O ♽ ࡃ࡞ࠢ⿥વዉ
૕ߩ૞⵾෸߮ߘߩ⿥વዉ․ᕈ㧘╙ 64 ࿁ ⑺ቄᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ᐔᚑ 15 ᐕ 8 ᦬ 31p-N-5(19) ศᴛసⷙ㧘ᷓ੗዆ผ㧘ᚑᧁ⚩਽㧘ဈ੗⋥㆏㧘᧛਄㓷ੱ㧘ᐔᨋᴰ㧘Ṛᴛᱞ↵㧘ࡄ࡞ࠬ⏛႐ബ⏛ਅߦ߅ߌࠆ⿥વዉࡃ࡞ࠢ૕ਛߩ⏛᧤᜼േߣ⊒ᾲߩ⹏ଔ㧘ᔕ↪‛ℂቇળ㧘ᐔᚑ 15 ᐕ 8 ᦬ 31p-N-8(20) ጊጯᕺ೑㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Ca(1-x)EuxGa2S4 ൻว‛ߩ⊒శ․ᕈ㧘╙ 64 ࿁ ⑺ቄᔕ↪‛ℂ
ቇળቇⴚ⻠Ṷળ㧘ᐔᚑ 15 ᐕ 9 ᦬ 1p-ZE-2(21) ਭ଻㓷๺㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrIn2VI4(VI=S,Se)ߩන⚿᥏૞⵾㧘╙ 64 ࿁ ⑺ቄᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ᐔᚑ 15 ᐕ 9 ᦬ 1p-ZE-3(22) ศᴛసೣ, ᷓ੗዆ผ, ᚑᧁ⚩਽㧘ဈ੗⋥㆏㧘᧛਄㓷ੱ㧘ᐔᨋᴰ㧘Ṛᴛᱞ↵㧘Flux motion and its
temperature dependence in the YBCO bulk superconductors during pulse field magnetization㧘11th
International workshop on critical currents in superconductors, Tokyo㧘June 31, 2003(23) ↰ਛᒄା㧘ဈ੗⋥㆏㧘᧛਄㓷ੱ㧘ᐔᨋᴰ㧘Ṛᴛᱞ↵㧘Fabrication and superconducting properties of
Ho-Ba-Cu-O bulk superconductors㧘11th International workshop on critical currents in superconductors,
Tokyo, 2003/6/30(24) A. Kato, M.Yamazaki, H.Najafov, K.Iwai, A.Bayramov, C.Hidaka, T.Takizawa㧘S.Iida㧘Radiative andnon-radiative processes of Ce related transitions in CaGa2S4

and SrGa2S4㧘The 13th International

Conference on Ternary and Multinary Compounds㧘ࡈ࡜ࡦࠬ ࡄ࡝㧘ᐔᚑ 14 ᐕ 10 ᦬(25) T.Takizawa, H.Ozawa㧘C.Hidaka㧘ESR study of Ce3+ ions doped in the CdIn2S4

lattice㧘The 13th

International Conference on Ternary and Multinary Compounds㧘ࡈ࡜ࡦࠬ ࡄ࡝㧘ᐔᚑ 14 ᐕ 10 ᦬(26) C.Hidaka,

N.Makabe, T.Takizawa㧘Dtermination of a pseudo-binary SrSe-Ga2Se3 phase diagram andsingle crystal growth of SrGa2Se4 compounds㧘The 13th International Conference on Ternary andMultinary Compounds  ࡈ࡜ࡦࠬ ࡄ࡝㧘ᐔᚑ 14 ᐕ 10 ᦬(27) ⌀ოિካ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrGa2Se4 න⚿᥏ߩ⦟⾰ൻ㧘╙ 63 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ᣂẟᄢቇ㧘ᐔᚑ 14 ᐕ 9 ᦬(28) ዊᴛᐢਯ㧘ች↰᦭␭㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Ce3+ ࠍ࠼࡯ࡊߒߚ CdIn2S4 න⚿᥏ߩ ESR ᷹ቯ㧘╙ 49 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᧲ᶏᄢቇ㧘ᐔᚑ 14 ᐕ 3 ᦬(29) ⌀ოિካ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrGa2Se4 න⚿᥏ߩ૞⵾㧘╙ 49 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᧲ᶏᄢቇ㧘ᐔᚑ 14 ᐕ 3 ᦬(30) ੑች␭৻㇢㧘ᣣ㜞ජ᥍㧘ᴉ↪⃿㧘࠽ࠫࡓ࡮ࡑࡔ࠼ࡈ㧘ጊᧄାⴕ㧘Ṛᴛᱞ↵㧘ᣓశᕈࠍ߽ߟ৻ゲᕈ⚿᥏ TeO2 ߩ Light Figure㧘╙ 49 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᧲ᶏᄢቇ㧘ᐔᚑ 14 ᐕ 3 ᦬(31) ዊᴛᐢਯ㧘ች↰᦭␭㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘CdIn2S4:Ce3+ ߩ ESR ᷹ቯ㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 13 ᐕ 11 ᦬(32) ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrGa2S4:Ce3+ න⚿᥏ߩశๆ෼ࠬࡍࠢ࠻࡞㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 13 ᐕ 11 ᦬(33) ⏷ᧄᓼਯ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrS-Ga2S3 ♽⁁ᘒ࿑ߣ Sr2Ga2S5 න⚿᥏૞⵾ߩ⹜ߺ㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 13 ᐕ 11 ᦬(34) ⌀ოિካ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘SrGa2Se4 ߩ⁁ᘒ࿑૞ᚑߣන⚿᥏ᚑ㐳㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 13 ᐕ 11 ᦬(35) ⌀ოિካ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘(Ca,Sr)-(Ga,In)2-(S,Se)4 ♽ൻว‛න⚿᥏૞⵾ߩߚ߼ߩᾲಽᨆ㧘╙ 62 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ᗲ⍮Ꮏᬺᄢቇ㧘ᐔᚑ 13 ᐕ 9 ᦬(36) ⏷ᧄᓼਯ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Sr2Ga2S5 ߩන⚿᥏૞⵾㧘╙ 62 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ᗲ⍮Ꮏᬺᄢቇ㧘ᐔᚑ 13 ᐕ 9 ᦬(37) ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘CaGa2S4 න⚿᥏ߩ⦟⾰ൻ㧘╙ 62 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ᗲ⍮Ꮏᬺᄢቇ㧘ᐔᚑ 13 ᐕ 9 ᦬(38) ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘CaGa2S4:Ce3+න⚿᥏૞⵾ߣశቇ⊛․ᕈ㧘╙ 48 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᣿ᴦᄢቇ㧘ᐔᚑ 13 ᐕ 3 ᦬(39) ዊᴛᐢਯ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘Ꮧ࿯㘃ర⚛ࠍ࠼࡯ࡊߒߚ CdIn2S4 න⚿᥏ߩ ESR ᷹ቯ㧘╙48 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᣿ᴦᄢቇ㧘ᐔᚑ 13 ᐕ 3 ᦬(40) ⏷ᧄᓼਯ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘᧻ਅ⵨੫㧘IIa,b-III2-VI4 ♽ൻว‛ߩ᭴ㅧᄌൻ㧘╙ 48 ࿁ᔕ↪
‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᣿ᴦᄢቇ㧘ᐔᚑ 13 ᐕ 3 ᦬(41) ᵻ㚅₺㓉㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘᧻ਅ⵨੫㧘CdS-In2S3-Ga2S3 ♽ߦ߅ߌࠆጀ⁁ൻว‛㧘╙ 48
࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᣿ᴦᄢቇ㧘ᐔᚑ 13 ᐕ 3 ᦬(42) ጊፒ㧘ጤ੗㧘࠽ࠫࡖࡎࡈ㧘ട⮮㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘㘵↰㧘CaGa2S4 ⚿᥏ਛߩ Ce ਇ⚐‛ਛᔃߩ⊒శ࡮㕖⊒శㆊ⒟㧘╙ 48 ࿁ᔕ↪‛ℂቇ㑐ㅪㅪว⻠Ṷળ㧘᣿ᴦᄢቇ㧘ᐔᚑ 13 ᐕ 3 ᦬(43) ጊፒ㧘ጤ੗㧘K.Nadjafov㧘ട⮮㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘㘵↰㧘CaGa2S4 ⚿᥏ਛߩ Ce ਇ⚐‛ਛ
ᔃߩశቇ․ᕈ II -- ๆ෼࡮ബ⿠ --㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 12 ᐕ 11 ᦬(44) ጤ੗㧘K.Nadjafov㧘ട⮮㧘ጊፒ㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘㘵↰㧘CaGa2S4 ⚿᥏ਛߩ Ce ਇ⚐‛ਛ
ᔃߩశቇ․ᕈ I -- ⊒శ --㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 12 ᐕ 11 ᦬(45) ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘CaGa2S4:Ce3+ න⚿᥏૞⵾ߣߘߩశๆ෼ࠬࡍࠢ࠻࡞㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 12 ᐕ 11 ᦬(46) ᵻ㚅₺㓉㧘ᣣ㜞ජ᥍㧘Ṛᴛᱞ↵㧘᧻ਅ⵨੫㧘CdS-In2S3-Ga2S3 ♽ߦ߅ߌࠆጀ⁁ൻว‛ߩ⚿᥏᭴ㅧߣశ‛ᕈ㧘ਃరᄙరᯏ⢻ᕈ᧚ᢱ⎇ⓥળ㧘ᐔᚑ 12 ᐕ 11 ᦬(47) H.Enomoto, K.Inoue, M.Muralidhar, M.Murakami㧘T.Takizawa㧘AC susceptibility of high-Tc
superconductor REBa2Cu3Oy㧘International Symposium on Superconductivity㧘ᐔᚑ 12 ᐕ 10 ᦬(48) Y.Akamatsu, K.Waki, K.Inoue, M.Murakami㧘T.Takizawa㧘AC susceptibility measurements for
Nd-Ba-Cu-O superconductor㧘International Symposium on Superconductivity㧘ᐔᚑ 12 ᐕ 10 ᦬(49) T.Matano, M.R.Koblischka, M.Muralidhar, M.Murakami㧘T.Takizawa㧘Superconducting transitions of
REBa2Cu3Ox superconductors in high fields㧘International Symposium on Superconductivity㧘ᐔᚑ 12
ᐕ 10 ᦬
(50) T.Kono, M.Tomita, M.Murakami㧘T.Takizawa㧘The viscous flux flow and flux creep induced by pulsed
magnetic fields in YBCO disk㧘International Symposium on Superconductivity㧘 ᐔᚑ 12 ᐕ 10 ᦬(51) ⿒᧻ఝ৻㧘⣁⠹৻㇢㧘᧛਄㓷ੱ㧘Ṛᴛᱞ↵㧘Nd-Ba-Cu-O ⿥વዉ૕ߦ߅ߌࠆ੤ᵹᏪ⏛₸᷹ቯ㧘╙ 61 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ർᶏ㆏ᄢቇ㧘ᐔᚑ 12 ᐕ 9 ᦬(52) ੦㊁ᥓብ㧘Michael R.Koblischka㧘᧛਄㓷ੱ㧘Ṛᴛᱞ↵㧘㜞⏛႐ਅߦ߅ߌࠆ㜞᷷⿥વዉ૕ߩ⿥વ
ዉォ⒖㧘╙ 61 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ർᶏ㆏ᄢቇ㧘ᐔᚑ 12 ᐕ 9 ᦬(53) ᴡ㊁⁴㧘ን↰ఝ㧘᧛਄㓷ੱ㧘Ṛᴛᱞ↵㧘ࡄ࡞ࠬ⏛႐ߦࠃࠅ⺃⿠ߐࠇߚ MTG-YBCO ਛߩ☼ᕈ⏛᧤ࡈࡠ࡯㧘╙ 61 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ർᶏ㆏ᄢቇ㧘ᐔᚑ 12 ᐕ 9 ᦬(54) Ṛᴛᱞ↵㧘ᄙరൻว‛⎇ⓥ㧦ᣂߒ޿ᯏ⢻᧚ᢱ߳ߩᦼᓙ㧘ࠪࡦࡐࠫ࠙ࡓ ✜⸒㧘╙ 61 ࿁ᔕ↪‛ℂ
ቇળቇⴚ⻠Ṷળ㧘ർᶏ㆏ᄢቇ㧘ᐔᚑ 12 ᐕ 9 ᦬(55) ᵻ㚅₺㓉㧘ᣣ㜞㧔ዊ᧻㧕ජ᥍㧘Ṛᴛᱞ↵㧘᧻ਅ⵨੫㧘CdS-Ga2S3-In2S3 ♽ߦ߅ߌࠆጀ⁁ൻว‛ߩ᭴ㅧᄙᒻ㧘╙ 61 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ർᶏ㆏ᄢቇ㧘ᐔᚑ 12 ᐕ 9 ᦬(56) ᣣ㜞㧔ዊ᧻㧕ජ᥍㧘Ṛᴛᱞ↵㧘CaGa2S4:Ce3+න⚿᥏ߩ⊒శ․ᕈߣ Ce3+Ớᐲଐሽᕈ㧘╙ 61 ࿁ᔕ↪‛ℂቇળቇⴚ⻠Ṷળ㧘ർᶏ㆏ᄢቇ㧘ᐔᚑ 12 ᐕ 9 ᦬(57) ᩉᎹ㇚㓶㧘㜞ᯅඳ᮸, ጊᧄ❥㧘⍹Ꮉᢥᵗ㧘ጊ↰⵨㧘ㄝ࿯ᱜੱ㧘਄ᐥ⟤਽㧘㉄ൻ‛⿥વዉ૕
Pr2Ba4Cu7O15-d ߩ࿶ജലᨐ㧘╙㧠㧡࿁㜞࿶⸛⺰ળ㧘⨲ᵤᏒ㧘ᐔᚑ 16 ᐕ 10 ᦬(58) ᩉᎹ㇚㓶㧘㜞ᯅඳ᮸, Ⴧ↰㓶৻㇢㧘ጊᧄ❥, ጊ↰⵨㧘ㄝ࿯ᱜੱ㧘਄ᐥ⟤਽㧘ᣂߒ޿⿥વዉ૕
Pr2Ba4Cu7O15-d ߩ⏛᳇⊛ᕈ⾰ߩ࿶ജലᨐΤ㧘ᣣᧄ‛ℂቇળ 2004 ⑺ቄᄢળ㧘㕍᫪Ꮢ㧘ᐔᚑ 16ᐕ9᦬(59) ᩉᎹ㇚㓶㧘㜞ᯅඳ᮸, ࿯㊄೑૫㧘Ⴧ↰㓶৻㇢㧘ጊᧄ❥, ጊ↰⵨㧘ᣂߒ޿⿥વዉ૕ Pr2Ba4Cu7O15-dߩ⏛᳇⊛ᕈ⾰ߩ࿶ജലᨐ㧘ᣣᧄ‛ℂቇળ╙㧡㧥࿁ᐕᰴᄢળ㧘⑔ጟᏒ㧘ᐔᚑ 16 ᐕ 3 ᦬(60) 㜞ᯅඳ᮸, ⨃ᧁ␭੺㧘㐳⼱Ꮉᱜ㧘㜞࿶ਅߦ߅ߌࠆ࠺࡜ࡈࠜࠨࠗ࠻ဳㆫ⒖㊄ዻ㉄ൻ CuFeO2 ߩ⏛᳇⊛ᕈ⾰㧘ᣣᧄ‛ℂቇળ╙㧡㧥࿁ᐕᰴᄢળ㧘⑔ጟᏒ㧘ᐔᚑ 16 ᐕ 3 ᦬(61) I.Yanagawa, T.Shimoda, and H. Takahashi㧘Pressure and Substitution Effect on Superconducting andMagnetic Transition

Temperature in

Oxide

Superconductors

Bi2201and La214㧘╙㧝㧥࿁㜞࿶ജߩ⑼ቇߣᛛⴚߦ㑐ߔࠆ࿖㓙ળ⼏(AIRAPT-19)㧘ࡈ࡜ࡦࠬ࿖ࡏ࡞࠼࡯㧘ᐔᚑ㧝㧡ᐕ㧣᦬(62) Y.Motegi, N.Kamata, H. Takahashi, R.Tsuchigane, and M. Hasegawa㧘Pressure effect on the magnetictransition in the delafossite-type oxides㧘╙㧝㧥࿁㜞࿶ജߩ⑼ቇߣᛛⴚߦ㑐ߔࠆ࿖㓙ળ⼏
(AIRAPT-19)㧘ࡈ࡜ࡦࠬ࿖ࡏ࡞࠼࡯㧘ᐔᚑ㧝㧡ᐕ㧣᦬(63) H. Takahashi, Y.Motegi, R.Tsuchigane, and M. Hasegawa㧘Pressure Effect on the Antiferromagnetic
Transition Temperature in CuFeO2㧘International Conference on Magnetism (ICM2003)㧘ࠗ࠲࡝ࠕ࿖

ࡠ࡯ࡑ㧘ᐔᚑ㧝㧡ᐕ㧣᦬(64) ᩉᎹ㇚㓶㧘ਅ↰ዏᐘ㧘㜞ᯅඳ᮸㧘㉄ൻ‛⿥વዉ૕ Bi2201 ߣ La214 ߦ߅ߌࠆ⿥વዉߣ⏛ᕈォ⒖᷷ᐲߩ࿶ജലᨐ㧘⟎឵ലᨐ㧘ᣣᧄ‛ℂቇળ 2003 ⑺ቄᄢળ㧘ᐔᚑ㧝㧡ᐕ㧥᦬(65) Ⴧ↰㓶৻㇢㧘ጊ↰⵨㧘ጊᧄ❥㧘㜞ᯅඳ᮸㧘᧻Ꮉ୶᣿㧘᧻ਅ᣿ⴕ㧘Pr2Ba4Cu7O15-d ㉄ൻ‛ߩᾲಣℂߦ઻߁࿶ജലᨐ㧘ᣣᧄ‛ℂቇળ 2003 ⑺ቄᄢળ㧘ᐔᚑ㧝㧡ᐕ㧥᦬(66) ⼱ญ⧐㓉㧘ዊဈ᣽ผ㧘Ძ೑ା↵㧘㜞ᯅඳ᮸㧘SQUID ⏛᧤⸘ߢ᷹ቯน⢻ߥ࠳ࠗࡗࡕࡦ࠼ࠕࡦࡆ
࡞࠮࡞ߩ㐿⊒㧘╙ 43 ࿁㜞࿶⸛⺰ળ㧘ᐔᚑ 14 ᐕ 11 ᦬(67) ⨃ᧁ૓੺㧘㜞ᯅඳ᮸㧘Co ㉄ൻ‛(La㧘Sr)2CoO4 ߩ㔚᳇ᛶ᛫ߩ࿶ജലᨐ㧘ᣣᧄ‛ℂቇળ 2002 ⑺ቄᄢળ㧘ᐔᚑ 14 ᐕ 9 ᦬(68) ਅ↰ዏᐘ㧘㜞ᯅඳ᮸㧘ㄝ࿯ᱜੱ㧘਄ᐥ⟤਽㧘TC ߩ࿶ജലᨐ߆ࠄ⷗ߚ㌃㉄ൻ‛⿥વዉ૕ߩ Cuࠨࠗ࠻⟎឵ലᨐ㧘ᣣᧄ‛ℂቇળ 2002 ⑺ቄᄢળ㧘ᐔᚑ 14 ᐕ 9 ᦬(69) ᩊ↰ᷕ㧘㜞ᯅඳ᮸㧘ጊ↰⵨㧘᧻ਅ᣿ⴕ㧘ฬཅ▵㧘RuSr2RECu2O8 (RE=Gd㧘Eu)ߩᒝ⏛ᕈ⁁ᘒߩ⏛႐࡮࿶ജലᨐ㧘ᣣᧄ‛ℂቇળ 2002 ⑺ቄᄢળ㧘ᐔᚑ 14 ᐕ 9 ᦬(70) ጊ↰⵨㧘ᩊ↰ᥓᐢ㧘ự↰ᵗᤘ㧘᧻ਅ᣿ⴕ㧘ฬཅ▵㧘㜞ᯅඳ᮸㧘ᩊ↰ᷕ㧘ᄢ⍹ᵏ↢㧘ਭ଻ⴐ઩㧘
RuSr2GdCu2O8 ㉄ൻ‛⿥વዉ૕ߩ㜞࿶ਅߢߩ‛ᕈߣ⚿᥏᭴ㅧ㧘ᣣᧄ‛ℂቇળ 2002 ⑺ቄᄢળ㧘ᐔᚑ 14 ᐕ 9 ᦬(71) ട⾐ጊ᦮ሶ㧘⊕⍹ੱ჻㧘ᴰ↰ቇ㧘㤥↰ⷙᢘ㧘Ⴧ↰㓶৻㇢㧘ጊ↰⵨㧘⪲㊄⧎㧘᧻ਅ᣿ⴕ㧘㜞ᯅඳ᮸㧘ᄢ⍹ᵏ↢㧘࠮࡝࠙ࡓ♽శ⸅ᇦ㉄ൻ‛ߩ㜞࿶ਅశๆ෼ II㧘ᣣᧄ‛ℂቇળ 2002 ⑺ቄᄢળ㧘ᐔ
ᚑ 14 ᐕ 9 ᦬(72) ᩊ↰ᷕ㧘ᓟ⮮ብ⚫㧘㜞ᯅඳ᮸㧘ጊ↰⵨㧘RuSr2GdCu2O8 ߩᒝ⏛ᕈォ⒖᷷ᐲߩ࿶ജലᨐ㧘ᣣᧄ‛ℂቇળ╙ 57 ࿁ᐕᰴᄢળ㧘ᐔᚑ 14 ᐕ 3 ᦬(73) ਅ↰ዏᐘ㧘ᩊ↰ᷕ㧘ⅶ↢ஜ຦㧘㜞ᯅඳ᮸㧘Ni ࠍ࠼࡯ࡊߒߚ㌃㉄ൻ‛⿥વዉ૕ߩߩ࿶ജലᨐ㧘
ᣣᧄ‛ℂቇળ╙ 57 ࿁ᐕᰴᄢળ㧘ᐔᚑ 14 ᐕ 3 ᦬(74) ᓟ⮮ብ⚫㧘ᩊ↰ᷕ㧘ਅ↰ዏᐘ㧘㜞ᯅඳ᮸㧘DAC ߦࠃࠆ㉄ൻ‛⿥વዉ૕ߩ࿶ജലᨐ㧘╙ 42 ࿁㜞࿶⸛⺰ળ㧘␹ᚭᏒ㧘ᐔᚑ 13 ᐕ 11 ᦬(75) ⅶ↢ஜ຦㧘ਅ↰ዏᐘ㧘㜞ᯅඳ᮸㧘Sr ࠼࡯ࡊߒߚ La2NiO4 ߩ㜞࠼࡯ࡊ㗔ၞߦ߅ߌࠆ࿶ജലᨐ㧘╙ 42 ࿁㜞࿶⸛⺰ળ㧘␹ᚭᏒ㧘ᐔᚑ 13 ᐕ 11 ᦬(76) 㜞ᯅඳ᮸㧘┻ਅ⋥㧘Ძ೑ା↵㧘ࠠࡘ࡯ࡆ࠶ࠢࠕࡦࡆ࡞ⵝ⟎ߢߩૐ᷷‛ᕈ᷹ቯ㧘╙ 41 ࿁㜞࿶⸛⺰ળ㧘ᨰᏒ㧘ᐔᚑ 12 ᐕ 11 ᦬(77) 㜞ᯅ⑲㓉㧘ਛ⷏೰ม㧘㜞ᯅඳ᮸㧘ዊᨋ㆐↢㧘ᷡ᳓స຦㧘Ძ೑ା↵㧘DAC ߦࠃࠆ㉄ൻ‛⿥વዉ૕ߩ࿶ജലᨐ╙ 41 ࿁㜞࿶⸛⺰ળ㧘ᨰᏒ㧘ᐔᚑ 12 ᐕ 11 ᦬(78) ਛ⷏೰ม㧘ᧄጊ⋥᮸㧘ਃ↰᧛⵨ᐘ㧘┻ਅ⋥㧘㜞ᯅඳ᮸㧘᳗ፒᵗ㧘ౝ↰ᘕ৻㧘Ძ೑ା↵㧘ࠬࡇࡦ࡜࠳࡯♽࿶ജ⺃⿠⿥વዉ‛⾰ Sr14-xCaxCu24O41 ߩ਄ㇱ⥃⇇⏛႐㧘╙ 41 ࿁㜞࿶⸛⺰ળ㧘ᨰᏒ㧘
ᐔᚑ 12 ᐕ 11 ᦬(79) T.Nakanishi, H.Takahashi, N.Takeshita, N.M?ri, N.Motoyama, H.Eisaki, S.Uchida, H.Fujino, T.Nagata,
J.Akimitsu, Resistive Upper Critical Field of Superconduction Spin-Ladder Sr14-xCaxCu24O41,
STRIPE 2000㧘Rome, Italy,ᐔᚑ 12 ᐕ 9 ᦬(80) H.Takahashi, H.Takahashi, T.Nakanishi, T.Arima, M.Noguchi, M.Oyanagi,N.Takeshita, N.Mori,
High-pressure effect on transport properties of spin-ladder compounds Na1-xCaxV2O5 andCa0.7Li0.3V2O5, International Conference on Magnetism 2000, Recife, Brazil, ᐔᚑ 12 ᐕ 8 ᦬

(81) T.Nakanishi, N.Motoyama, H.Mitamura, N.Takeshita, H.Takahashi, H.Eisaki, S.Uchida, T.Goto,
H.Ishimoto, N.M?ri, Pressure and field dependence of superconductivity in the spin-ladder
Sr14-xCaxCu24O41, International Conference on Magnetism 2000, Recife, Brazil, ᐔᚑ 12 ᐕ 8 ᦬ARTICLE IN PRESS

Journal of Crystal Growth 275 (2005) e433–e437
www.elsevier.com/locate/jcrysgro

Single crystal growth of SrIn2VI4 (VI ¼ S,Se) compounds
solidifying through supercooling
T. Takizawa, M. Kubo, C. Hidaka
Department of Physics, College of Humanities and Sciences, Nihon University, Sakura-josui 3-25-40, Setagaya-ku,
Tokyo 156-8550, Japan
Available online 8 December 2004

Abstract
The IIa–III2–VI4 (IIa ¼ Ca,Sr, III ¼ Ga,In, VI ¼ S,Se) compounds generally have high melting points more than
1100 1C, and some of them, e.g., SrIn2VI4 (VI ¼ S,Se) prefer freezing with supercooling, which makes their crystal
growth very difﬁcult. Here, we have adopted a carbon crucible sealed in a quartz ampoule to escape from both thesupercooling and the reactivity near the melting point. We have devised the shape of a crucible by preparing a small
capillary followed by a bigger hollow pipe for obtaining a large single crystal. A compound is ﬁlled in the hole of a
crucible by setting the thin part down. It is ﬁrst heated above the meting point to melt and then cooled down below thesupercooling point, where it is solidiﬁed. It is again heated to melt but this time keeping the temperature of the smallbottom part of a capillary a little below the melting point. Then the melt is slowly cooled down. The nucleation isstarted from the polycrystalline remainder near the bottom, resulting in a seed crystal in the rest of the thin part astemperature lowers. With the help of the seed, a single crystal continues to grow in a bigger hollow-pipe part of a
crucible. Single crystals of SrIn2S4 and SrIn2Se4 are grown by this method, and their optical absorption is measured.
r 2004 Elsevier B.V. All rights reserved.
PACS: 81.10.hKeywords: A1. Supercooling; A2. Horizontal Bridgman method; B1. SrIn2S4; B1. SrIn2Se4

1. Introduction
Recently rare earth element doped IIa–III2–VI4(IIa ¼ Ca,Sr, III ¼ Ga,In, VI ¼ S,Se) compounds
attract much attention as host materials forvisible-light emitting devices. In general, theCorresponding author. Tel./fax: +81 3 5317 9772.

E-mail address: takiz@chs.nihon-u.ac.jp (T. Takizawa).

constituent elements of these compounds are
chemically very reactive with each other, so that
explosion of the sealed container sometimes
happens during their synthesis. In addition, theresultant compounds have high melting points
more than 1100 1C, making their synthesis rather
difﬁcult. Further, some of them, e.g., SrIn2VI4(VI ¼ S,Se) prefer freezing with supercooling, also
making crystal growth difﬁcult. SrIn2VI40022-0248/$ - see front matter r 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jcrysgro.2004.11.015

ARTICLE IN PRESS
T. Takizawa et al. / Journal of Crystal Growth 275 (2005) e433–e437

e434(VI ¼ S,Se) compounds were ﬁrst studied by Klee
[1] in 1979, followed by Kipp [2], Donohue [3] andEisenmann [4]. However, the single crystals having
enough size for optical assessment were notobtained up to now mainly due to the reason
stated above.
Here, we have adopted a carbon crucible sealed
in a quartz ampoule to escape from both thesupercooling and the sticking between a melt andits container near the melting point, and succeededin growing their single crystals for the ﬁrst time.
The key point was how to make a seed for the
initial crystal growth and actually it was the shapeof the carbon crucible in our case. Single crystalsof SrIn2S4 and SrIn2Se4 are grown by this method,
and the results of their optical absorption arepresented.

2. Thermal properties
To begin with, the thermal properties of thecompounds composing SrIn2S4 and SrIn2Se4 were
examined by means of differential thermal analysis(DTA) [5]. In Fig. 1(a) and (b), exothermic andendothermic chemical reactions were seen as DTA
signals with peaks and dips, respectively. Srreacted with S and Se around 250 and 450 1C

accompanying abrupt emission of heat, respectively. This reaction sometimes gave strong thermal shock to cause quartz ampoules break. The
chemical reaction between In and (S and Se) also
occurred with abrupt heat emission around 650
and 250 1C, respectively, producing compounds of
In2S3 and In2Se3. The former often causes explosion of a quartz ampoule due to the high vapor
pressure of S, while the latter scatters In2Se3
droplets inside the whole ampoule due to theviolent chemical reaction. To escape from thosephenomena, compounds of In2S3 and In2Se3
prepared in advance were used instead of raw
elements (see the third and fourth DTA curves
from the top in Fig. 1). Finally, it should be notedthat a big supercooling occurred around 900 and
800 1C, respectively, far below each melting point
on cooling (see the dotted curves in Fig. 1).
Next, pseudo-phase diagrams of the SrS-In2S3
and -In2Se3 systems were constructed using DTA
and powder X-ray diffraction, as shown Fig. 2(a)and (b). Experimental details are described elsewhere [5–7]. As seen in Fig. 2, eutectic reactions
appear in both diagrams. In the case of SrIn2S4, it
forms a congruent melt, while SrIn2Se4 is anincongruent one having peritectic reaction. Thus
for the former compound, both melt and ﬂux(using In2S3 as a self ﬂux) growth methods can be

Sr+S
Sr+2In+4S
Sr+S+In2S3
1070°CSrIn2S4

2In+3Se
DTA signals[0.2mV/div]

DTA signals[0.5mV/div]

2In+3S

Sr+Se
Sr+2In+4Se
Sr+Se+In2Se3

SrIn2Se4 Cooling

Cooling SrIn2S4
0
(a)

200

400

600

0

800 1000

Temperature[°C]

1016°CSrIn2Se4

(b)

200

400

600

800

1000

Temperature[°C]Fig. 1. DTA signals of the composing compounds for (a) SrIn2S4 and (b) SrIn2Se4. The positive one shows the exothermic reaction,
while the negative one the endothermic one. The solid line expresses the heating process, and the dashed line the cooling process. The
numerals show the melting points of each compound.

ARTICLE IN PRESS
T. Takizawa et al. / Journal of Crystal Growth 275 (2005) e433–e437
1100

900

700

(a)

0
SrS

+In2S3950°C
SrIn2S4+In2S3

800

1100

Liq.

Liq.+SrSe
1016°C

Temperature [°C]

Temperature [°C]

1000

1200

1070°CLiq.
Liq.+
SrIn2S4

e435

1000
900

Liq.
Liq.
+In2Se3

Liq.
+SrIn2Se4

800

840°C

700

SrSe+
SrIn2Se4

SrIn2Se4+In2Se3

600
20

40
60
80
100
In2S3 [mol%]
In2S3

(b)

0
SrSe

20

40
60
80
In2Se3 [mol%]

100
In2Se3Fig. 2. The pseudo-binary phase diagrams of (a) SrS–In2S3 and (b) SrS–In2Se3. SrIn2S4 forms a congruent melt, while SrIn2Se4 does aperitectic one.

applied for preparing single crystals, while for thelatter one, the ﬂux growth (using In2Se3 as a self
ﬂux in this case) is preferred.
In conclusion of this section, we have to avoid
the supercooling when growing single crystals of
SrIn2S4 and SrIn2Se4 and also the peritectic
reaction in the case of SrIn2Se4. Based on theseresults, we have decided to grow single crystals
using seeds. If seeds exist, single crystals are
expected to grow without occurrence of supercooling even at the peritectic point [8].

3. Crystal growth
3.1. Preparation of precursors
The precursors of SrIn2S4 and SrIn2Se4 wereprepared by combining Sr, S, and Se elements with
In2S3 and In2Se3 compounds, respectively. The
metal and indium compounds were set in one endof a long quartz ampoule, while S and Se elements
were set in the other end. The metal part washeated and hold at 700 1C and the chalcogen partat 400 1C. After 1 day, all chalcogen was absorbedby the metal. Then the metal part was heated up to
about 5 1C below the melting point, while keeping
the chalcogen part at 600 1C. Thus the precursors
were ﬁnally prepared by the solid-state reaction,
which was important to prevent the products fromsticking to the ampoule wall. These products were
supplied for the crystal growth described below.
3.2. A specially devised crucible and the crystal
growthHow to make a seed just before the single crystal
growth starts is the key problem to be solved forthe successful crystal growing [8]. For thispurpose, the form of a crucible was speciallydevised. Carbon was adopted as a constructing
material. A small (3 mm in diameter) hole wasdrilled in a carbon rod of 12 mmø  100 mm for
40 mm in depth, and a bigger hollow cylinder of
8 mm in diameter and 60 mm in length was madecoaxially following it. A photo of the crucible isshown in Fig. 3(a). For easily taking out a grown
crystal, a crucible was cut into two parts along thecentral axis, and two caps were prepared for bothends for preventing the melt from ﬂowing out. A
compound is ﬁlled in the hole of a crucible bysetting the thin part down, that is, in the left-handside in Fig. 3. The crucible was then set in ahorizontal Bridgman furnace and heated above themeting point and then cooled down below thesupercooling point, where the compound is solidiﬁed. It is again heated to melt but this time keeping
the bottom part of the crucible a little below themelting point, that is, a temperature gradient was
intentionally made for it. Then it is slowly cooled

ARTICLE IN PRESS
T. Takizawa et al. / Journal of Crystal Growth 275 (2005) e433–e437

e436

down. The nucleation is started from the remaining polycrystals near the bottom, resulting in aseed crystal in the rest part of the thin hole astemperature lowers. With the help of the seed, asingle crystal continues to grow in a bigger hollow
part of a crucible as shown in Fig. 3(b). Cleaved
surfaces were clearly observed at both thin andthick parts of a grown SrIn2S4 crystal. A single
crystal was grown from about 10 mm after the
beginning of the thin part. Two kinds of single
crystals of SrIn2S4 and SrIn2Se4 were grown by
this method.

4. Optical absorption measurements
Absorption measurements were carried out
using single crystal plates with thickness of 20 mm
in the temperature range from 10 to 300 K as
shown in Fig. 4(a) and (b). The insets arephotographs of each sample plate used. SrIn2S4
is transparent and colorless, while SrIn2Se4 istransparent but dark-orange colored. The absorption edge energies, Eg of SrIn2S4 and SrIn2Se4 were
estimated as 3.6 and 2.8 eV at 0 K, respectively,
and their temperature variations were expressed asfollows:

Fig. 3. (a) A set of a specially devised crucible. Two type holes
are coaxially drilled in a carbon rod, which is then split into twoparts along the cylinder axis to remove a grown crystal easily
from the crucible. (b) A grown crystal in a crucible. A singlecrystal part was observed from after 10 mm from the left of thecrystalline rod.

(a)

300

80K
120K

200

100

200

10K
40K

160K
200K
240K
280K
300K

0
3.0 3.1 3.2 3.3 3.4 3.5 3.6
Photon energy [eV]

aT 2
;
T þb

where a are given as 8.8  104 and 7.8  104 eV/K, and b are 106 and 197 K, respectively. These
values are comparable with those of CaGa2S4(a ¼ 1:2  103 eV=K and b ¼ 235 K) and SrGa2S4

300K

Absorption coefficient [cm-1]

Absorption coefficient [cm-1]

400

E g ðTÞ ¼ E g ð0Þ 

240K
200K

100

160K
10K

50

0
2.3
(b)

280K

150

40K
80K
120K

2.4

2.5

2.6

2.7

2.8

2.9

Photon energy [eV]Fig. 4. Optical absorption spectra of (a) SrIn2S4 and (b) SrIn2Se4. The insets are photos of each crystal plate (the thickness is 20 mm).

ARTICLE IN PRESS
T. Takizawa et al. / Journal of Crystal Growth 275 (2005) e433–e437(a ¼ 1:7  103 eV=K and b ¼ 459 K) [7]. The
smaller values of b may indicate the weaker bondstrength in SrIn2S4 and SrIn2Se4 in comparison to
Ca and Sr thiogallates.
5. Summary
Single crystals of SrIn2S4 and SrIn2Se4 weresuccessfully grown using a specially devised carbon
crucible for escaping from the supercooling. It wasalso found that the carbon crucible was effective
for preventing the high-temperature melt fromsticking to the wall inside quartz ampoules.
Absorption measurements were carried out todetermine the energy gaps of both materials.

Acknowledgements
This work is partly supported by the grant
for the High-Technology Research Center Projecte437

for private universities from Ministry Of Education, Sports, Science, Culture and Technology,
Japan.

References[1] W. Klee, H. Schaefer, Rev. Chim. Miner. 16 (1979)465.
[2] D.O. Kipp, C.K. Lowe-Ma, T.A. Vanderah, Chem. Mater.
2 (1990) 506.
[3] P.C. Donohue, J.E. Hanlon, J. Electrochem. Soc. 121 (1974)
137.
[4] B. Eisenmann, A. Hofmann, Z. Kristallogr. 197 (1991)
167.
[5] H. Matsushita, T. Takizawa, Jpn. J. Appl. Phys. 34 (1995)
4699.
[6] C. Komatsu, T. Takizawa, J. Crystal Growth 210 (2000)
677.
[7] C. Hidaka, T. Takizawa, J. Crystal Growth 237 (2002) 2009.
[8] E. Niwa, K. Masumoto, Ternary and MultinaryCompounds in the 21st Century IPAP Books, vol. 1,
2001, p. 39.

Physica C 392–396 (2003) 391–395
www.elsevier.com/locate/physc

Eﬀect of pinning on the ﬂux motion of Gd–Ba–Cu–O
bulk superconductors
K. Yoshizawa a,b,*, S. Nariki b, M. Murakami b, T. Takizawa aaDepartment of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakura-Josui,
Setagaya-ku, Tokyo 156-8550, Japanb
Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-16-25 Shibaura,
Minato-ku, Tokyo 105-0023, Japan
Received 13 November 2002; accepted 17 February 2003

Abstract
We have observed the ﬂux motion using Hall probe sensors that are placed on the surface of high quality Y–Ba–Cu–O
and Gd–Ba–Cu–O disks 15 mm in diameter with 0.95 mm thickness with applying pulsed magnetic ﬁeld. The peak valueof the ﬁeld was varied from 0.1 to 0.8 T. The eﬀects of static bias ﬁelds was also studied in the ﬁeld range of 0–3 T at
77 K. Gd–Ba–Cu–O shows the clear secondary peak eﬀect on the Jc –B curve so that the pinning property was diﬀerent
from Y–Ba–Cu–O for which Jc monotonically decreases with ﬁeld. The ﬂux motion was enhanced in Y–Ba–Cu–O withincreasing static bias ﬁeld, while that was suppressed in Gd–Ba–Cu–O, reﬂecting the secondary peak eﬀect.
Ó 2003 Elsevier B.V. All rights reserved.
PACS: 74.72.)h; 74.60.Ge
Keywords: Pulsed-magnetic magnetization; Peak eﬀect; GdBa2 Cu3 Oy ; YBa2 Cu3 Oy

1. Introduction
Bulk Y–Ba–Cu–O exhibits the critical current
density (Jc ) exceeding 1  104 A/cm2 at 77 K and
has potential for various engineering applications.
Recently, LRE–Ba–Cu–O (LRE: Nd, Sm, Eu andGd) superconductors have been found to exhibit*

Corresponding author. Address: Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023,
Japan. Tel.: +81-3-3454-9284; fax: +81-3-3454-9287.
E-mail address: yoshizawa@istec.or.jp (K. Yoshizawa).

higher Jc values of 5–10  104 A/cm2 at 77 K
accompanied by the secondary peak eﬀect on the
Jc –B curve [1]. Hence LRE–Ba–Cu–O bulk superconductors are promising candidates for high ﬁeld
applications such as high trapped-ﬁeld magnets.
The secondary peak eﬀect of LRE–Ba–Cu–O
has been intensively studied in a static magnetic
ﬁeld [2–4]. It will be interesting to study how thepeak eﬀect aﬀects the dynamical motion of ﬂux
lines.
In this work, we therefore studied the responseof Y–Ba–Cu–O and Gd–Ba–Cu–O disk samples topulse magnetic ﬁelds with an emphasis placed on
the eﬀect of secondary peak on ﬂux pinning
properties.

0921-4534/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0921-4534(03)01047-5

392

K. Yoshizawa et al. / Physica C 392–396 (2003) 391–395

2. Experimental
Bulk Y–Ba–Cu–O (YBa2 Cu3 Oy :Y2 BaCuO5 ¼
10:4) and Gd–Ba–Cu–O (GdBa2 Cu3 Oy :Gd2 BaCuO5 ¼ 10:4) were prepared with the top-seeded
melt-growth (TSMG) process in air [5,6]. The disk
samples with dimensions of 15.03 mm in diameterand thickness of 0.95 mm were cut from TSMG
processed blocks with the c-axis perpendicular to
the wide surface.
Fig. 1 shows the distribution of the axial component of the trapped ﬂux density Bz at 77 K for
Y–Ba–Cu–O and Gd–Ba–Cu–O disk samples. A
single-peak proﬁle indicates that the both samples
are single-grain without weak-links. Fig. 2
shows the Jc –B curves for Y–Ba–Cu–O and Gd–
Ba–Cu–O specimens. The Jc values were estimatedbased on the extended Bean model [7]. The Gd–
Ba–Cu–O specimen exhibited the secondary peakeﬀect at about 2 T. Fig. 3 illustrates the geomet-

Fig. 2. Field dependence of the critical current density (Jc ) for
the Y–Ba–Cu–O and Gd–Ba–Cu–O samples. It should be notedthat Gd–Ba–Cu–O exhibits clear secondary peak eﬀect on the
Jc –B curve.

rical conﬁguration of the main part of our experimental apparatus [8]. The sample was set at thecenter of the inner normal conducting coil set in asuperconducting magnet. The peak value of theapplying pulsed ﬁeld was varied from 0.1 to 0.8 Twith static bias ﬁelds in the range of 0–3 T at 77 K.
Magnetic ﬂux distribution on the sample surface
was measured with ﬁve Hall probe sensors placedalong radial direction as shown in Fig. 3(b).

3. Results and discussion
3.1. Magnetic ﬂux density distribution

Fig. 1. Trapped ﬁeld distribution for (a) Y–Ba–Cu–O and (b)Gd–Ba–Cu–O samples about 15 mm in diameter measured byscanning a Hall sensor at 1 mm above the sample surface.

Fig. 4 shows the time-dependence of the ﬁeld
distribution on the surface of Gd–Ba–Cu–O and
Y–Ba–Cu–O samples when a single pulse of 0.6 T
was applied at 77 K in the presence of the static
magnetic ﬁeld of 0–2 T. The magnetic ﬂux penetrated from the edge of the sample, and its density
decreased from the edge toward the center. In thecase of Y–Ba–Cu–O, the amount of penetrated
ﬁeld was always greater in the presence of static
bias ﬁeld than that in the absence of the static ﬁeld.
In contrast, the resistance against ﬂux penetrationin case of Gd–Ba–Cu–O was enhanced with

K. Yoshizawa et al. / Physica C 392–396 (2003) 391–395

393

Fig. 4. Flux density distribution during the pulse ﬁeld magnetization process in Y–Ba–Cu–O and Gd–Ba–Cu–O samples at
77 K. The center of a sample is the origin. The data on the left
hand side is for the increasing ﬁeld process and those on theright hand side for the decreasing ﬁeld process.
Fig. 3. (a) Schematic diagram of an experimental setup. A
pulsed magnetic ﬁeld is generated by the main coil, and thestatic ﬁeld is generated by the superconducting magnet coil. The
sample was set at the center of the main coil. (b) The magnetic
ﬁeld of a sample surface was measured with ﬁve Hall sensors
placed on the sample surface.

increasing static bias ﬁeld, which reﬂects the secondary peak eﬀect.
3.2. Voltage–current characteristics
It is seen from Fig. 4 that the ﬂux gradient is
steeper near the edge in the ﬁeld increasing process. The radial ﬁeld gradient (oB=or) and the time
derivative (oB=ot) of magnetic ﬁeld correspond tothe current and voltage, respectively [8]. Based on
this, the static ﬁeld dependence of voltage–current(V –I) characteristics was deduced from Fig. 4, andthe results are shown in Fig. 5. In the case of Y–
Ba–Cu–O, the slope of V –I curve became steeper
and shifted toward the lower I region as the staticﬁeld increased. In the case of Gd–Ba–Cu–O,
however, at ﬁrst the inclination of V –I curve became steeper, and it became gradual by piecemeal
when the static ﬁeld topped 2 T. In addition, as thesuperimposed static magnetic ﬁeld increased, thevalue of I at V ¼ 0 (Jc ) was larger than the value
without static bias ﬁeld.
3.3. Flow resistivity
As is clearly seen from Fig. 5, V –I curves have
gradient like a normal conducting state, showingthat some resistance is created by ﬂux motion,

394

K. Yoshizawa et al. / Physica C 392–396 (2003) 391–395

the viscous coeﬃcient, respectively. For J > Jc , theelectric ﬁeld is E ¼ qf ðJ  Jc Þ. Consequently, g is
obtained from the following relation:
U0 B
g¼
:
ð5Þ
qf
Fig. 6 shows the viscosity coeﬃcients g evaluated. The eﬀect of the static magnetic ﬁeld on theviscosity coeﬃcient is much greater than that ofFig. 5. Static ﬁeld dependence of the voltage–current (V –I)
characteristics deduced from the pulse ﬁeld magnetization experiments. The time derivative (oB=ot) and the radial ﬁeld
gradient (oB=or) of the magnetic ﬁeld correspond to V and I,
respectively. The left hand side shows the characteristic of Gd–
Ba–Cu–O and the right side for Y–Ba–Cu–O.

which is called the ﬂow resistivity. Here the ﬂux
ﬂow resistivity qf is given by the following relation:
qf ¼

E
;
J

ð1Þ

where E is the electric ﬁeld and J the current
density.
The motion of quantized ﬂuxoids are governedby the balance of the pinning force FP the Lorentz
force FL and the viscosity force FV . These forces
are expressed by the following equation:
FP ¼ Jc  B;ð2Þ

FL ¼ J  B;j Bj
FV ¼ g
;
U0

ð3Þ
ð4Þ

where J , Jc , U0 and g is the current density,
the critical current density, the ﬂux quantum andFig. 6. Plots of the viscosity coeﬃcients g (a) as a function ofpulsed magnetic ﬁeld and (b) as a function of static magnetic
ﬁeld when the peak value of the pulsed magnet ﬁeld is ﬁxed at
0.6 T.

K. Yoshizawa et al. / Physica C 392–396 (2003) 391–395

the pulsed magnetic ﬁeld. And the value of viscosity coeﬃcient g of Y–Ba–Cu–O decreased withincreasing the static bias ﬁeld. In sharp contrast,
the static ﬁeld did not decrease the viscosity coefﬁcient g of Gd–Ba–Cu–O. It is also notable thatthe value of viscosity coeﬃcient g of Gd–Ba–Cu–O
reached minimum at 1 T, which also reﬂects thesecondary peak eﬀect.

395

Acknowledgements
This work was supported by the New Energy
and Industrial Technology Development Organization (NEDO) as Collaborative Research andDevelopment of Fundamental Technologies forSuperconductivity Applications.
References

4. Summary
In this work, we have measured the ﬂux motion
induced by pulsed magnetic ﬁeld in Y–Ba–Cu–O
and Gd–Ba–Cu–O disks. The eﬀect of static bias
ﬁeld on the ﬂux motion was also studied in therange of 0–3 T at 77 K. In the presence of the static
bias ﬁeld, the ﬂux motion of Gd–Ba–Cu–O was
diﬀerent from that of Y–Ba–Cu–O, reﬂecting thesecondary peak eﬀect. The ﬂux motion was enhanced with increasing static bias ﬁeld in Y–Ba–
Cu–O, while the ﬂux motion in Gd–Ba–Cu–O was
suppressed and the viscosity was enhanced withincreasing static ﬁeld.

[1] M. Muralidhar, M.R. Koblischka, M. Murakami, Adv.
Supercond. 12 (2000) 494.
[2] M.R. Koblischka, T.H. Johansen, M. Murakami, Supercond. Sci. Technol. 13 (2000) 745.
[3] T. Mochida, N. Chikumoto, M. Murakami, Phys. Rev. B 64
(2001) 64518.
[4] T. Matsushita, E.S. Otabe, Physica C 335 (2000) 153.
[5] A. Endo, H.S. Chauhan, T. Egi, Y. Shiohara, J. Mater. Res.
11 (1996) 795.
[6] H. Hinai, S. Nariki, S.-J. Seo, N. Sakai, M. Murakami, M.
Otsuka, Supercond. Sci. Technol. 13 (2000) 676.
[7] E.M. Gyorgy, R.B. van Dover, K.A. Jackson, L.F.
Schneemeyer, J.V. Waszcazk, Appl. Phys. Lett. 55 (1989)
283.
[8] T. Kono, M. Tomita, M. Murakami, T. Takizawa, Supercond. Sci. Technol. 13 (2000) 794.

Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517
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Radiative and non-radiative processes of Ce related transitions
in CaGa2S4 and SrGa2S4
A. Katoa,*, M. Yamazakib, H. Najafova, K. Iwaia, A. Bayramova, C. Hidakac,
T. Takizawac, S. Iidaaa

Nagaoka University of Technology, Nagaoka 940-2188, Japan
Nagaoka National College of Technology, Nagaoka 940-8532, Japanc
College of Humanities and Sciences, Nihon University, Tokyo 156-8550, Japanb

Abstract
The Ce emission appearing in the blue– green region was investigated for CaGa2S4 and SrGa2S4. The room
temperature quantum efﬁciency as high as 73% was observed for a 0.4 wt% Ce-doped CaGa2S4 single crystal grown by
the melt method. The quantum efﬁciency decreased for a 0.8 wt% Ce-doped CaGa2S4 crystal and clear photoacoustic
signal was detected in this sample, indicating an increase of non-radiative transition. For each of these compounds,
ultraviolet (UV) excitation produced a hitherto unreported new UV emission which is thought to originate from 5d(Eg)level of the Ce ion. Temperature dependent intensity changes observed in this UV emission and in the blue– green
emission suggest temperature dependent population transfer from the upper level of Eg to the lower level of T2g in the
excited state of 5d electrons.
q 2003 Elsevier Ltd. All rights reserved.

1. Introduction
Ce-doped alkaline earth thiogallates are regarded aspromising host materials for blue –green light emitting
devices including lasers [1,2]. Photoluminescence spectra of
CaGa2S4:Ce and SrGa2S4:Ce are known to exhibit thecharacteristic blue– green double bands [1]. In order torealize light emitting device applications, it is necessary to
fully understand radiative and non-radiative processes ofthis Ce impurity center. This study is concerned withphotoluminescence (PL) and photoluminescence excitation(PLE) spectra, absorption and photoacoustic (PA) spectra,
photoluminescence quantum efﬁciencies, and relations
among them, mainly with CaGa2S4 crystals of different Ceconcentrations.
In the ultraviolet region of the spectrum of eachcompound, a new emission which was not reported before
has been found in this study. Temperature dependent
intensity changes of the UV and blue –green emissions are* Corresponding author. Fax: þ 81-258-47-9500.
E-mail address: arikato@vos.nagaokaut.ac.jp (A. Kato).

discussed in terms of a conﬁguration coordinate model for
the Ce ion.
2. Experimental
Polycrystalline CaGa2S4:Ce and SrGa2S4:Ce samples
were synthesized from CaS/SrS and Ga2S3 powders mixed
in stoichiometric composition and annealed at 900 8C undera stream of H2S(10%) þ Ar for 15 h. The initially obtainedpolycrystalline samples were re-ground and then reannealed in the same atmosphere for 24 h. The dopant wasadded into the source powder in the form of Ce2S3. Generalemission characteristics are compared for polycrystalline
CaGa2S4:Ce and SrGa2S4:Ce. In order to know detailed
characteristics of the blue– green emission, single crystals of
CaGa2S4:Ce were grown by the melt method at an ampoulecooling speed of 0.5 cm/h from 1150 to 1100 8C [3]. The
sizes of crystals were about 2 £ 2 £ 1 mm3. For absorption
measurements, the crystals were polished to be about
0.1 mm thickness.
For PL measurements, the sample was excited bymonochromatic light obtained by combining a 150 W Xe

0022-3697/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0022-3697(03)00170-7

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A. Kato et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517

lamp (Hamamatsu, L2175) and a double monochromator(Ritsu, MC-30NW) or by the 3250 Å line of a He– Cd laser(Omnichrome, 3056-M-A01). Photoluminescence from thesample was dispersed through a monochromator (Nalumi,
RM-23) and detected by a photomultiplier (Hamamatsu,
R943-02) coupled to a photon counter (Hamamatsu, C767).
For PLE measurements, the sample was excited bymonochromatic light obtained by combining the 150 W
Xe lamp and the double monochromator. The sample wasmounted on the cold ﬁnger of an optical cryostat coupled toa closed cycle He-refrigerator (Iwatani, CryoMini D105) for
measurements of temperature dependence. For time decay
measurements, a dye laser (Lambda Physics, FL 3002E,
dye:stilbene 420) pumped by a Xe –Cl laser (Lambda
Physics, LEXTRA 200) or the Xe– Cl laser was used as theexcitation source. Emission from sample was dispersed
through a monochromator (Instruments SA, HR-320) andtemporal variation of the emission was monitored on adigital oscilloscope (Sony Tektronix, TDS380P) coupledwith a photomultiplier (Toshiba, PM55).
For absorption measurements, monochromatic lightobtained by combining the 150 W Xe lamp and the double
monochromator was transmitted through the sample. The
transmitted light was detected by the photomultiplier(Toshiba, PM55). The absorption coefﬁcient was derived
from the measured transmittance taking into account ofmultiple internal reﬂections. PA spectrum measurements
were done by gas-microphone method. The sample was
excited by monochromatic light obtained by combining a
500 W Xe lamp and a monochromator (Jobin Yvon, HR320). PA signal was detected by a microphone coupled to alock-in ampliﬁer (Stanford Research, SR-530).
Quantum efﬁciency measurements were performed atroom temperature with an integration glass semi-sphere
having a small hole at the top to introduce laser light for
exciting photoluminescence of the sample inside. The
diameter of this semi-sphere is 60 mm and the bottom of
the semi-sphere is covered by a glass plate. The innersurfaces of the semi-sphere and the glass plate were frosted
to diffuse light and the outer surface was coated by thick Al
evaporation to reﬂect and conﬁne light inside. The lightinside thus constructed semi-sphere is believed to becompletely diffused. The glass plate has a small non-Alcoated portion through which light inside the semi-spherecan be detected by a photomultiplier. Construction details
were given in Ref. [4]. A He– Cd laser (Omnichrome,4056-M-A01) emitting the 4416 Å line was used as a lightsource. The absorbed amount of excitation light and theemitted amount of photoluminescence were determined bymeasuring photomultiplier outputs with the help of a band
pass ﬁlter (Hoya, B390) or a cut-off ﬁlter (Toshiba, Y46)
by placing the sample inside in comparison with the output
for a small piece of non-absorbing opaque quartz. In
calculating the quantum efﬁciency values these outputs
were corrected by taking into account of measured
transmittances of the ﬁlters and the spectral sensitivityof the photomultiplier given by the manufacturer(Hamamatsu). For these obtained quantum efﬁciency
values, the error corresponding to the experimental
accuracy was checked to be less than 5% by measuring
the output corresponding to incident laser light whose
power was known.

3. Results
3.1. Blue –green emission
Fig. 1 shows PL and PLE spectra of 2 wt% Ce-doped
polycrystalline CaGa2S4:Ce (a) and SrGa2S4:Ce (b) atroom temperature. The PL and PLE spectra of bothcompounds are quite similar. The PL spectra consist of
two overlapping bands in the blue– green region. The PLE
spectra consist of a main blue band and an UV band. The
mirror image relation looks to hold between the higher
energy band of the PL spectra and the main band of the
PLE spectra for both compounds, showing the phonon
terminated transition character. The difference of theseemissions between CaGa2S4:Ce and SrGa2S4:Ce is only
the peak position. For PL spectrum of CaGa2S4:Ce, thepeaks are at 2.65 eV (4680 Å) and at 2.40 eV (5170 Å).
The main band of the PLE spectrum of CaGa2S4:Ce isseen at 2.8 eV. An almost parallel shift to higher energy
by about 0.1 eV is seen for all corresponding peaks in thecase of SrGa2S4:Ce.
Fig. 2 shows PL and PLE spectra of CaGa2S4:Ce single
crystals for various Ce concentrations at room temperature.
The excitation photon energy of the PL spectra was 2.89 eV
and the monitoring photon energy of the PLE spectra was
2.65 eV. The width of the main PLE band becomes broader
and the peak position shifts towards lower energy withincreasing Ce concentration. The shape of the band showssome changes at higher energy side. On the other hand,Fig. 1. PL and PLE spectra of (a) CaGa2S4:Ce (2 at%) and (b)SrGa2S4:Ce (2 at%).

A. Kato et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517

1513

Fig. 3. (a) Absorption spectrum of the CaGa2S4:Ce single crystal(0.8 wt%), (b) peak absorption coefﬁcient as a function of Ce
concentration.

Fig. 4(a) shows the PA spectrum of the 0.8 wt% Cedoped single crystal. For comparison, the absorption
spectrum is shown again in Fig. 4(b), and the PL and PLE
spectra in Fig. 4(c). From samples where the Ce concentrations are 0.1, 0.2 and 0.4 wt%, detectable PA signal was
not observed. The peak of the PA band corresponds to thatof the absorption band. The half width of the PA band isabout 220 meV, being broader than that of the absorption
band of 180 meV. The PA band broadens to higher energy
region compared to the absorption band.
3.2. UV emission

Fig. 2. PL spectra excited by 2.89 eV and PLE spectra monitored at
2.65 eV for different Ce concentrations of CaGa2S4: Ce single
crystals (0.1 –0.8 wt%).

the PL spectra do not show changes corresponding to the
PLE spectra except a slight peak shift to lower energy withincreasing Ce concentration. For the PLE spectrum ofpolycrystalline CaGa2S4:Ce (2 wt%) shown in Fig. 1(a), thepeak energy of the main PLE band is close to that of thesingle crystal CaGa2S4:Ce (0.8 wt%). However, the peakenergy of the PL spectrum is slightly lower than that of thesingle crystal.
The quantum efﬁciency as high as 73% was observed forthe 0.4 wt% Ce-doped single crystal, however the lower
value of 32% was observed for the 0.8 wt% Ce-doped single
crystal.
Fig. 3(a) shows absorption spectrum of the 0.8 wt% Cedoped CaGa2S4:Ce single crystal at room temperature. The
peak of the Ce absorption band is seen at 2.92 eV and thehalf width is about 180 meV. The shape of this observed
band does not change with Ce concentration. Fig. 3(b)shows peak absorption coefﬁcient as a function of Ce
concentration.

The solid line of Fig. 5 shows the PL spectrum of
0.1 wt% Ce-doped polycrystalline CaGa2S4 at 10 K excitedby the 3250 Å line of the He– Cd laser. UV excitation was
found to produce an emission in the region of 3500– 4250 Å
in addition to the blue– green emission. To the best of ourknowledge, there is no report on this UV emission of
CaGa2S4:Ce. The spectral shape of the UV emission is notsimilar to that of the blue– green emission which consists of
two overlapping bands. The PL spectrum of this UV
emission can be well reproduced by superposition of threeGaussian components (the ﬁrst component peaked at
3.39 eV (3650 Å), the second at 3.30 eV (3750 Å), thethird at 3.10 eV (3995 Å)) as shown in the inset of Fig. 5.
The energy difference of the peaks between the ﬁrst and thethird components is 0.29 eV. The difference between thesecond and the third components is 0.20 eV. The intensity of
the UV emission decreased with increasing Ce concentrations. The UV emission was not observed in undoped
samples, indicating a relation with Ce doping. The dottedline of Fig. 5 shows the PLE spectrum of the UV emission
monitored at 3995 Å. The PLE spectrum consists of a single
band peaked at 3285 Å (3.77 eV). The shape and the peak
position of this band were found to be independent of themonitoring wavelength. For SrGa2S4:Ce, the situation
was similar. Under UV excitation, the UV emission of

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A. Kato et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517

Fig. 4. Comparison among PA, absorption, PL and PLE spectra of the 0.8 wt% Ce-doped single crystal. (a) PA spectrum, (b) absorption
spectrum, (c) PL and PLE spectra.

SrGa2S4:Ce which was not reported before, similarly as in
CaGa2S4:Ce, was found to appear in the region of 3300–
4000 Å.
The intensity of the UV emission of CaGa2S4:Ce
gradually decreases with increasing temperature. The
emission disappears totally at temperatures higher than
220 K. In exchange of this quenching, an increase of theblue – green emission intensity is seen with increasing
temperature under UV excitation. Fig. 6(a) shows PLE
spectra of the UV emission at various temperatures
monitored at 3995 Å. The intensity gradually decreases
with increasing temperature and the peak position shifts
towards longer wavelengths. The activation energy of thisdecrease is obtained to be 0.08 eV. Fig. 6(b) shows the UVpart of the PLE spectra of the blue – green emission
monitored at 4620 Å at various temperatures. The PLE
spectrum at 25 K consists of a band peaked at 3080 Å and ashoulder at 3320 Å. The shoulder at 3320 Å gradually grows
with increasing temperature and becomes a well-resolved
band at temperatures higher than 77 K. The peak of the band
appearing above 77 K shifts towards longer wavelengths
with increasing temperature. A comparison between
Figs. 6(a) and (b) shows that the peak position of the PLEband of the blue – green emission appearing above 77 K
coincides with that of the UV emission at each temperature.
The corrected shape of the PLE band of the UV emission
by removing the contribution of the lower energy band
tail, and that of the blue– green emission by removing

A. Kato et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517

1515

Fig. 5. PL spectrum excited by 3250 Å (solid line) and PLE spectrum monitored at 3995 Å (dotted line) of CaGa2S4:Ce (0.1 wt%). The inset
shows three Gaussian curves (dotted lines) reproducing the ultraviolet part of the PL spectrum (solid line).

the contribution of the higher energy band tail are quite
similar for each corresponding temperature above 77 K. The
decay time constant of the UV emission was found to beabout 15 ns, independent of the monitoring wavelength.
This value is smaller than the reported value of the blue–
green emission of 24 ns [5].

4. Discussion
The PL and PLE spectra of the blue –green emission of
CaGa2S4:Ce and SrGa2S4:Ce are similar. For the UVemission, the PL spectra of both compounds are alsosimilar. Discussions are given mainly using the results of
CaGa2S4:Ce.
4.1. Radiative and non-radiative processes relatedwith the blue– green emission
The two overlapping bands seen in the PL spectra(Fig. 1) of CaGa2S4:Ce and SrGa2S4:Ce are known tooriginate from radiative transition from the 5d(T2g) levelof the excited state to levels of 4f(2F7/2) and 4f(2F5/2) ofthe ground state of the Ce ion split by spin – orbit
interaction [6].
The shape difference between the absorption and PLE
spectra may be related with the difference of the thickness
among the samples, since the PLE spectra were obtained
from thicker samples. Since the depths where the Ce ions are

excited in the PLE measurements are much larger than in theabsorption measurements, the shape of the PLE spectrum is
apt to be affected by inhomogeneous broadening. In thissystem of trivalent Ce ions substituting divalent Ca sites,
inhomogeneous broadening is expected to increase withincreasing Ce concentration. Data suggesting the presenceof the inhomogeneous broadening are given in Ref. [7]. The
slight shift of the PL band may be related with an effectassociated with the selective excitation at 2.89 eV in theinhomogeneous PLE band.
The appearance of PA signal and the reduction of thequantum efﬁciency under 4416 Å excitation which cannot
excite the UV emission in the 0.8 wt% Ce-doped sample
indicate an increase of non-radiative transition from theexcited state of the blue –green emission. The PA bandbroadens to higher energy region compared to the absorption band as shown in Fig. 4. This indicates that the quantum
efﬁciency has excitation photon energy dependence. These
quantum efﬁciency changes with Ce concentration andexcitation photon energy may also have some relation with
the inhomogeneous broadening. To clarify the details, PLE
measurements using samples having the same thickness andquantum efﬁciency measurements under different excitation
photon energies are necessary.
4.2. UV emission and its relation with the blue– green
emission
The UV and the blue –green parts of the PL spectra
exhibit opposite temperature dependences. As the intensity

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A. Kato et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517

Fig. 6. (a) PLE spectra of the UV emission at various temperatures monitored at 3995 Å. (b) PLE spectra of the blue Ce emission at various
temperatures (UV region) monitored at 4620 Å for CaGa2S4:Ce (0.1 wt%).

of the UV emission decreases with increasing temperature,
the intensity of the blue– green emission increases. Fig. 6(b)shows the saturation of this new band intensity at 300–
320 K. The difference between the observed intensity at eachtemperature and the saturated intensity was plotted as afunction of temperature. An activation energy value for theblue– green emission was calculated from this plot to be
0.09 eV. This value is practically the same as that of thetemperature quenching of the UV emission (0.08 eV). The
coincidence of the two activation energies strongly suggests
the occurrence of temperature-dependent population transfer
between the excited states of these transitions. This view is
supported by the fact that the peak positions and shapes ofboth PLE spectra are practically the same as explained in
Section 3.2.

The excited state 5d of the Ce ion in cubic crystal
symmetry is known to split into two levels Eg and T2g [6].
Fig. 7(a) shows the energy level diagram of the Ce ion
with cubic symmetry and spin – orbit splitting (2F7/2 and2
F5/2) of the 4f ground state. As the ﬁrst approximation,
this diagram is applicable to the Ce ion in CaGa2S4 having
symmetry close to cubic. Two bands of the blue– green
emission peaked at 2.68 and 2.41 eV in Fig. 5 are known
to be originated from radiative transitions from 5d(T2g) to
4f(2F5/2) and from 5d(T2g) to 4f(2F7/2), respectively, as
mentioned in Section 4.1. The energy difference (0.27 eV)
between the peak positions of the two bands is close tothat between the ﬁrst and the third components peaked at
3.39 and 3.10 eV in the UV emission spectrum (0.29 eV).
This suggests that the terminal states are the same both for

A. Kato et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1511–1517

1517

Fig. 7. (a) Energy level diagram of 4f5d conﬁguration of the Ce ion in CaGa2S4. (b) Qualitative conﬁguration coordinate description of the
Ce ion.

this UV emission pair and the blue – green bands. On theother hand, the different decay time constants of the UV
and the blue – green emission (15 and 24 ns [5],respectively) suggest that these two emissions originate
from different excited states. For the case of Ce-doped
SrGa2S4, the separation between levels 4f(2F5/2) and5d(Eg) was reported to be about 3.71 eV [8]. The peakenergy of the PLE spectrum of the UV emission(3.77 eV) is close to the above reported value. The
similarity of PL and PLE spectra between CaGa2S4 and
SrGa2S4 mentioned in Sections 3.1 and 3.2 suggest thatthe reported value approximately holds true also for thepresent case of CaGa2S4. Taking this situation into
account, the excited state of the UV emission is assigned
to the level 5d(Eg). Therefore, the ﬁrst and the third
components peaked at 3.39 and 3.10 eV are considered tooriginate from the transitions from 5d(Eg) to 4f(2F5/2) andfrom 5d(Eg) to 4f(2F7/2), respectively. To the best of ourknowledge, the observation of this UV emission from the5d(Eg) level is the ﬁrst one in thiogallate compounds.
The UV emission observed from Ce-doped elpasolite
compounds Cs2LiLaCl6 was interpreted as to be due tocore-valence processes [9], but not to the transition fromthe 5d(Eg) level.
Fig. 7(b) shows the conﬁguration coordinate descriptionof the Ce ion based on the energy level diagram discussed
above. The temperature-dependent population transfer
discussed above is thought to occur through the crosspoint between the parabolas 5d(Eg) and 5d(T2g) located at
0.08 eV above the minimum of the parabola 5d(Eg). The
origin of the second component peaked at 3.30 eV is still

uncertain. The origin may be related to the symmetry of the
Ce ion in this thiogallate, which is lower than the cubic
symmetry.
For the case of SrGa2S4:Ce, the UV emission as wellas the blue– green emission are seen and the PLE
spectrum of the latter is similar to that of CaGa2S4:Ce.
These facts suggest that the processes in SrGa2S4:Ce arealso explainable by the same scheme, since the energy
level diagrams of the Ce ion in these compounds are
the same.

References[1] A.N. Georgobiani, B.G. Tagiev, O.B. Tagiev, B.M. Izzatov,
R.B. Jabbarov, Cryst. Res. Technol. 31 (S-2) (1996) 849.
[2] S. Iida, T. Matsumoto-Aoki, T. Morita, N. Mamedov, B.G.
Tagiev, F.M. Gashimzade, K. Sato, Jpn. J. Appl. Phys. 39(Suppl. 39-1) (2000) 429.
[3] C. Komatsu, T. Takizawa, J. Cryst. Growth 222 (2001) 574.
[4] K. Maeda, Oyo Butsuri 40 (1971) 289 (in Japanese).
[5] H. Najafov, A. Kato, H. Toyota, K. Iwai, A. Bayramov, S. Iida,
Jpn. J. Appl. Phys. 41 (2002) 1424.
[6] T.E. Peters, J.A. Baglio, J. Electrochem. Soc. 119 (1972) 230.
[7] K. Iwai, Kh. Nadjafov, A. Kato, M. Yamazaki, C. Hidaka, T.
Takizawa, S. Iida, Ann. Rep. Professional Group Ternary
Multinary Compound (2001) 62 (in Japanese).
[8] L. Eichenauer, B. Jarofke, H.-C. Mertins, J. Dreyhsig, W.
Busse, H.-E. Gumlich, P. Bénalloul, C. Barthou, J. Benoit, C.
Fouassier, A. Garcia, Phys. Status Sol. (a) 153 (1996) 515.
[9] P.A. Rodyni, V.B. Mikhailik, G.B. Stryganyuk, A.S. Voloshinovskii, C.W.E. van Eijk, G.F. Zimmerer, J. Lumin. 86 (2000)
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Journal of Physics and Chemistry of Solids 64 (2003) 1797–1800
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Determination of a pseudo-binary SrSe – Ga2Se3 phase diagramand single crystal growth of SrGa2Se4 compounds
Chiharu Hidaka*, Nobuyasu Makabe, Takeo Takizawa
Department of Physics, College of Humanities and Sciences, Nihon University,
3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan

Abstract
We have investigated chemical reaction processes and thermal characteristics of IIa – III2 – VI4 compounds in order to growtheir single bulk crystals. Up to now, single crystals of Ca and Sr thiogallates have been successfully grown by the melt growthmethod based on their pseudo-binary phase diagrams. Here, a similar diagram of the SrSe – Ga2Se3 system has been constructed
for the ﬁrst time, where a eutectic reaction is found in the range of excess Ga2Se3 concentration, and it is shown that the
SrGa2Se4 compound has a congruent melting point (1110 8C) suitable for the melt growth. A single crystal is grown from themelt by the horizontal Bridgman method. A trial is also made to grow a high-quality single crystal of CaGa2S4 already known as
being grown easily.
q 2003 Elsevier Ltd. All rights reserved.

1. Introduction
The compounds of alkaline earth thio- and selenogallates (Ca,Sr,Ba)(Ga,In)2(S,Se)4 doped with rare earth
elements such as Ce3þ are expected as blue-light emitting
materials for full color displays [1]. Many studies concerning the brightness and efﬁciency of the devices have beenreported [2– 5], since they were regarded as promising for
EL devices [1].
On the other hand, few basic properties of thesecompounds have been reported. These properties haveever been studied by using single crystals preparedexclusively by the solid state reaction [6,7] and vaporization
reaction [8], where a single crystalline domain is inevitably
limited to a smaller size than that by the melt growthmethod. To obtain more detailed information on thesematerials, larger single crystals of good quality are
indispensable.
We have already constructed the pseudo-binary phase
diagrams of the CaS – Ga2S3 and SrS – Ga2S3 systems,
and grown crystals of CaGa2S4 and SrGa2S4 with asingle domain as large as 7 mm £ 5 mm by the melt
method [9,10].
* Corresponding author.

The purpose of the present study is to investigate thesuitability of the other compounds in the same group for themelt growth of single crystals. A trial to grow a high-quality
single crystal of CaGa2S4 is also made. The latter compoundis already known to be grown easily but the crystals stillcontain cracks and voids.

2. Differential thermal analysis of the IIa-III2 – VI4compounds
Differential thermal analysis (DTA) was carried out
using mixtures of three elements (IIa ¼ Ca or Sr, III ¼ Ga
or In, VI ¼ S or Se). The elements (three nine or better
purity) were weighted to about 0.3 g in total in a
stoichiometric composition and sealed in a quartz ampouleof 7 mmf (inner dia.) £ 40 mm under vacuum. DTA
measurements [11] were run twice at a speed of 2 8/min.
The chemical reaction process was investigated in the ﬁrst
run, and the melting and transition point were determined in
the second one.
Figs. 1 and 2 show DTA signals of a series of IIa – III2 –VI4 compounds (IIa ¼ Ca, Sr, III ¼ Ga, In, VI ¼ S, Se) in
the second run. Four compounds (CaIn2Se4, CaGa2S4,
SrGa2Se4 and SrGa2S4) were found to melt congruently,

0022-3697/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0022-3697(03)00096-9

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C. Hidaka et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1797–1800

3. Pseudo-binary phase diagram of the SrSe – Ga2Se3
systemFig. 1. DTA signals of Ca-III2 –VI4 compounds in the coolingprocess (2 8/min).

i.e. the melting and solidifying temperatures were exactly
the same.
After DTA measurements, powder X-ray diffraction
patterns (Cu Ka, 40 keV, 30 mA, step of 0.028) of the
products were measured to check if they were of a single
phase or not. Three compounds (CaGa2S4, SrGa2S4 and
SrGa2Se4) were conﬁrmed comparing to JCPDS’s data asa single phase within an experimental error of 2 mol%.
Since CaGa2S4 and SrGa2S4 were already known to begrown [9,10], only the procedure of single crystal growthof SrGa2Se4 will be presented later in Section 5.

Fig. 2. DTA signals of Sr-III2 –VI4 compounds in the coolingprocess (2 8/min).

Pseudo-binary phase diagram of the SrSe – Ga2Se3
system was constructed by DTA and XRD following theprocedure shown in Refs. [9,10]. Fig. 3 shows a part ofthe diagram. The SrGa2Se4 compound is formed just at theconcentration of 50 mol% Ga2Se3. The two-phase region of
SrGa2Se4 and Ga2Se3 was identiﬁed by XRD patterns in theconcentration range from 50 to 100 mol% Ga2Se3.
The melting point of SrGa2Se4 was determined as1110 ^ 2 8C. A eutectic reaction was found in the excess
Ga2Se3 concentration in this ﬁgure. Fig. 3 is very similar to
those of the CaS– Ga2S3 and SrS– Ga2S3 systems [9,10], andshows that single crystal growth is also possible for
SrGa2Se4 compound by the melt method at 50 mol%
Ga2Se3 and by the self ﬂux method using Ga2Se3 as a ﬂux
in the 50 – 75 mol% Ga2Se3 range. It should be mentionedthat quartz can be used as an ampoule material for the
crystal growth.

4. The chemical reaction processes of the SrGa2Se4
compound
Before growing single crystals, the chemical reaction
processes between elements should be investigated. The ﬁrst
scan of DTA measurements for binary (Ga – Se, Sr – Se) andternary (Sr– Ga– Se) mixtures gave us the information. The
results in the heating process are shown in Fig. 4, where
the exothermic reaction appeared as positive peaks and theendothermic one as negative dips. It is seen in Fig. 4 that
SrSe compounds were synthesized between 270 and 400 8C,
where exothermic chemical reaction occurred. This is very
similar to the formation of SrS compounds [9]. Then Ga2Se3
compounds were synthesized around 800 8C, where
exothermic reaction also occurred. This sometimes broke
ampoules. Escaping this explosive reaction, we used Ga2Se3

Fig. 3. Pseudo-binary phase diagram of the SrSe–Ga2Se3 system.

C. Hidaka et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1797–1800

Fig. 4. DTA spectra of Sr–Se, Ga –Se and Sr þ Ga þ Ga2Se3 in theheating process. The down-arrows show the melting points.

compounds together with Sr and Se elements as starting
materials (see the bottom of Fig. 4). It is seen that SrGa2Se4
compounds were synthesized at the melting point (1014 8C,
shown by the up-arrow in Fig. 4) of Ga2Se3. It should be
noted that the exothermic reaction due to III2VI3 compounds
disappeared. This was also very similar to the cases of
CaGa2S4 and SrGa2S4 [9,10].

1799

Fig. 5. A photograph of a SrGa2Se4 single crystal grown by the melt
method. A sliced and polished surface is shown.

in a larger quartz ampoule as mentioned above. A single
crystal was grown from melt by the horizontal Bridgman
method by moving a temperature proﬁle (temperature
gradient , 8 8C/cm, speed of growth 0.25 cm/h, withoutseed) [11]. Fig. 5 shows a photograph of a grown SrGa2Se4
single crystal with a grain as large as 2 mm £ 2 mm £ 0.1
mm (a sliced and polished surface).

6. Crystal growth of CaGa2S4 of high quality
5. Crystal growth of the SrGa2Se4 compound
Following the procedure as used in the single crystal
growth of Ca and Sr thiogallates [9,10], a single crystal of
SrGa2Se4 was prepared. The only difference is the selenization of the Sr element. Since the Sr element easily sublimates
above 700 8C, and the boiling point of Se is 685 8C very close
to the sublimation temperature of Sr, a special care should betaken for the selenization of Sr. We set both the Sr element
and Ga2Se3 compound into a carbon-coated quartz ampoule(7 mmf (inner dia.) £ 100 mm) with a hole for gas to ﬂow inand out. The ampoule was sealed in another larger ampoule(13 mmf (inner dia.) £ 150 mm) under vacuum together
with the Se element of the stoichiometric amount separately
set outside the inner ampoule. For the selenization of Sr, thewhole ampoule was kept at 650 8C for 24 h, where Se
evaporated and reacted with solid Sr. Then the temperature
was elevated to a value 60 8C above the melting point(1014 8C) of Ga2Se3. This temperature should be kept lower
than the melting point (1110 8C) of SrGa2Se4 to prevent thereaction between the melt and the wall of the quartz ampoule.
That is, the precursor is prepared by the so-called solid state
reaction. At this stage, the precursor of SrGa2Se4 was
prepared. The single phase was assured by XRD. The
precursor was taken out to be powdered and put in a carbon
boat (8 mmf (inner dia.) £ 100 mm) which was again sealed

The single crystals of the thiogallates, CaGa2S4 and
SrGa2S4 were already successfully grown [9,10]. Especially
CaGa2S4 can be stably grown. However, many cracks andvoids were still found in these crystals. The crystallinity
prepared from the melts could not be controlled even underFig. 6. The variation of the melting point against the sulfur content£ of the starting composition of CaGa2Sx

1800

C. Hidaka et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1797–1800

7. Summary
DTA measurements of various IIa – III2 – VI4 compounds
were executed. Apart from CaGa2S4 and SrGa2S4 alreadygrown as single crystals, SrGa2Se4 was found suitable forthe melt growth. Then, a pseudo-binary phase diagram of
the SrSe –Ga2Se3 system was constructed, and the SrGa2Se4
single crystal was successfully melt-grown on the bases ofthe diagram.
It was also found that to keep the vapor pressure of the VI
element to an appropriate value during the crystal growth
was very important to get a high quality single crystal.

Fig. 7. A photograph of a CaGa2S4 single crystal grown underexcess sulfur. A cleaved surface is shown.

the same growth condition. It was thought that the sulfur was
deﬁcient in a grown crystal because of the repeatedpulverization followed by vacuum seals in quartz ampoules.
We have investigated the variation of the melting temperatureof CaGa2Sx with sulfur content by means of DTA used in
Section 2. As shown in Fig. 6, the melting point decreased
with decreasing sulfur content from the stoichiometry, while
no phase other than CaGa2S4 was detected by XRD in thissulfur range. As increases sulfur content, the melting point
seems to reach a constant value. Similarly the lattice constants
slightly increased with sulfur content and kept the maximum
value above the stoichiometric composition. In addition,
when the sulfur content increased above x ¼ 4:05; excess
sulfur was clearly deposited on the wall of DTA ampoules.
Thus, it is considered that the compounds were stable above
the stoichiometric composition and no excess sulfur could be
introduced in the compound if sulfur content was increased
more than the stoichiometric amount. Preliminary measurements for the SrGa2Se4 compound showed that the same
behavior was also observed in the selenide. It is thought thatthe decrease of sulfur or selenium in the compounds worsened
the quality of the crystals, mainly due to the change in themelting temperature caused by the slight loss of the volatile VI
elements. Then the crystal growth was performed under thecondition with excess VI group element. Fig. 7 shows aphotograph of a grown CaGa2S4 crystal at an excess sulfur
content ðx ¼ 4:05Þ: The crystallinity of the compounds wasmuch improved in this case.

Acknowledgements
This work was partly supported by the Research Grant
from Nihon University.

References[1] W.A. Barrow, R.C. Coovert, E. Dickey, C.N. King, C. Laakso,
S.S. Sun, R.T. Tuenge, R. Wetross, J. Kane, SID Int. Symp.
Dig. (1993) 761.
[2] S.S. Sun, R.T. Tuenge, J. Kane, M. Ling, J. Electrochem. Soc.
141 (1994) 2877.
[3] K. Tanaka, Y. Inoue, S. Okamoto, K. Kobayashi, J. Cryst.
Growth 150 (1995) 1211.
[4] T. Yang, K. Wagner, M. Chaichimansour, W. Park, Z.L.
Wang, C.J. Summers, J. Vac. Sci. Technol. B 14 (1996) 2263.
[5] K. Tanaka, Y. Inoue, S. Okamoto, K. Kobayashi, K. Takizawa,
Jpn. J. Appl. Phys. 36 (1997) 3517.
[6] T.E. Peter, J.A. Baglio, J. Electrochem. Soc. 119 (2) (1972)230.
[7] B. Eisenmann, M. Jakowski, W. Klee, H. Shäfer, Rev. Chim.
Miner. 20 (1983) 225.
[8] K. Tanaka, T. Ohgoh, K. Kimura, H. Yamamoto, K.
Shinagawa, K. Sato, Jpn. J. Appl. Phys. 34 (1995) L1651.
[9] C. Komatsu, T. Takizawa, J. Cryst. Growth 210 (2000)
677 –682.
[10] C. Komatsu-Hidaka, T. Takizawa, J. Cryst. Growth 222 (2001)
574 –578.
[11] H. Matsushita, T. Takizawa, J. Cryst. Growth 160 (1996)
71– 77.

Journal of Physics and Chemistry of Solids 64 (2003) 1807–1810
www.elsevier.com/locate/jpcs

ESR study of Ce3þ ions doped in the CdIn2S4 lattice
Takeo Takizawa*, Hiroyuki Ozawa, Chiharu Hidaka
Department of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan

Abstract
Rare earth elements doped IIa –III2 – VI4 compounds are expected as host materials for ﬂuorescent devices. In particular,
since blue emission was observed in alkaline earth thiogallates doped with Ce3þ ions, much attention has been paid to develop
full color displays made of thin ﬁlms of the compounds above. Especially Ce3þ ions are thought as promising candidates for
dopants realizing blue light emission. Normally doped Ce3þ ions are considered to substitute the sites which are occupied withdivalent elements such as Ca or Cd. However, the substituting mechanism is not fully understood, since in view of the numberof valence, it is natural for a Ce atom to substitute a trivalent one.
In this report, we have grown single crystals of CdIn2S4 as host materials for Ce doping and investigated the site substitutionof the Ce atom in this crystal lattice by means of ESR. Two types of ESR centers are found. One consists of a Ce3þ ion
substituting a Cd site and a sulfur vacancy, and the other consists of a similar Ce3þ ion with 4 tetrahedrally surrounding sulfur
atoms.
q 2003 Elsevier Ltd. All rights reserved.

1. Introduction
Rare earth elements doped (Ca,Sr,Ba) – (Al,Ga,In)2 –(S,Se)4 compounds emit light with various color when
excited by UV light, high electric ﬁeld or high energy
electron beam [1,2]. In particular, since blue emission isobserved in alkaline earth thiogallates doped with Ce3þ
ions, practical researches are energetically developed toapply them to AC thin-ﬁlm electroluminescent (ACTFEL)
full-color displays [2,3].
In the emission above, Ce3þ ions play an important role, since the inner core states of the isolated
Ce3þ ion, i.e. 4f –5d electronic transitions mainly cause
the blue light emission. These electronic states arestrongly affected by host crystals, and the color of theemission changes according to the surrounding atomic
conﬁguration. The changes in the electronic states canbe studied by luminescence measurements which include
the complex variation in both ground and excited states.
On the other hand, ESR studies can reveal exclusively
the ground states of the doped ions which may serve to* Corresponding author. Tel.: þ81-3-5317-9772; fax: þ 81-35317-9772.
E-mail address: takiz@chs.nihon-u.ac.jp (T. Takizawa).

the full understanding of the ion substitution and the hostaffection to it.
Normally the doped Ce3þ ion is considered to substitutethe site which is occupied with a divalent element such as Ca
or Cd. However its mechanism is not fully understood, sincein view of the number of valence, it is natural for a Ce atom
to substitute a trivalent one.
In this report, we have adopted single crystals of CdIn2S4
as host materials for Ce doping and investigated the site
substitution of the Ce atom in this crystal lattice using ESR
measurement. The above crystal is chosen because it iseasily grown and in addition, has a rather simple lattice
structure with both di- and tri-valent cation sites.

2. Experimental procedure
Single crystals of CdIn2S4 were grown from a melt using
the three constituent elements. The details of this procedure
were described elsewhere [4,5] Ce doping was carried out
by mixing appropriate amount (0.1 –0.5 wt%) of Ce2S3
powder into a ground CdIn2S4 having been grown beforehand. No codoping was tried. The mixture was again melted,
and a Ce doped crystal was grown by the Horizontal

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doi:10.1016/S0022-3697(03)00166-5

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T. Takizawa et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1807–1810

Bridgman method (hereafter abbreviated as an ‘as-grownsample’). The grown crystal was cut into blocks of2 £ 2 £ 5 mm3 in size, the longest edge of which were
determined so as to be the [110] direction by the reﬂection
Laue method.
Alternative Ce doping was also made by annealing
CdIn2S4 single crystals in Ce2S3 powder at 950 8C for
several hours (hereafter abbreviated as ‘annealed samples’).
These crystals were oriented to the [110] direction inadvance. The difference in the ESR results of both samples
with different dopings will be described later.
ESR spectra were measured using an X band microwave
and a TE110 cavity by applying the magnetic ﬁeld
perpendicular to the [110] direction, the axis of rotation ofsamples.

3. Results and discussions
The observed ESR spectra of as-grown samples at 77 K
are summarized and shown in Fig. 1, where every curve
was normalized to each sample weight and the integrated
ESR line of DPPH used as a standard. Two types ESR
signals are seen in the ﬁgure. One is designated as S1, S2,S3 and S4 (hereafter called as Type 1), and the other as S5and S6 (hereafter called as Type 2). ESR curves arearranged in Fig. 1 according to the integrated strength of
the S4 signal, which is thought to indicate the true
concentration of Ce3þ ions. The order is not proportional tothe as-doped values of Ce3þ, showing that the true Ce3þconcentration is determined by the growing process and notby the starting amount of Ce3þ. The temperature variationof the intensities of each line was measured by varying
temperature down to 4.2 K. The results showed that every
ESR line obeyed the so-called Curie law.

Fig. 2. Resonant magnetic ﬁeld vs. angle of rotation of ESR signals(at 77 K) of a Ce3þ 0.075 wt% sample. These ESR signals areclassiﬁed as Type 1. Curves (a), (b) and (c) correspond to the Eqs.
(2)–(4) in the text, respectively. The splitting of each line is due tothe misalignment of the [110] direction from the axis of rotation(estimated as about 28). The (a) and (b) lines split into two, and the(c) line into 4, though only two of them are shown for simplicity.

The resonant magnetic ﬁeld vs. the angle of rotation for
the ESR curve of the 0.075 wt% sample is shown in Fig. 2,
where only the signals of Type 1 are seen. The curves ofFig. 2 is describable if we assume a simple spin-Hamiltonian
HS ¼ b H·g·S

where b is the Bohr magneton, H the magnetic ﬁeld, g theso-called g-tensor and S the effective spin. Here we havechecked possibilities of several symmetry sites such as
tetragonal, tetrahedral and octahedral ones. However, nogood results were obtained except for the tetrahedral site,
i.e. Ce3þ substituting Cd2þ in a tetrahedron. More precisely,
we should take tetrahedral sites occupied by Ce3þ ions in the
CdIn2S4 lattice with S ¼ 1=2 to reproduce the observed
angle dependence of ESR curves.
There are eight equivalent directions from the center of atetrahedron to its tetrahedral corners in the spinel lattice. If
the translational symmetry is taken into account, these areclassiﬁed into three independent ones ([1̄11̄], [1̄11], [111]),
where the [110] direction is taken as the rotation axis. The
magnetic ﬁeld is applied perpendicular to this axis.
Diagonalization of the spin-Hamiltonian leads to thefollowing resonant magnetic ﬁelds for the respective
direction [6]H1 ¼

Fig. 1. ESR curves of CdIn2S4 with different Ce3þ concentration. S1
to S4 signals are classiﬁed as the ESR centers of Type 1, and S5 andS6 as those of Type 2. Curves are arranged according to theintegrated intensities of the S4 signal, which indicate the true
concentration of Ce3þ doped. Type 2 signals appear only above acertain value of Ce3þ concentration.

ð1Þ

hv
 1
 manifolds
qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ for ½112
2
b g’ sin u þ g2k cos2 u

ð2Þ

hv

H2 ¼ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ for ½111
b g2’ sin2 ð70:53 2 uÞ þ g2k cos2 ð70:53 2 uÞ
manifolds

ð3Þ

T. Takizawa et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1807–1810

1809

If we used the values, gk ¼ 2:3 and g’ ¼ 0:8; the best ﬁtting
was obtained as shown in Fig. 2 by the solid lines, where themisalignment of the [110] direction from the axis of rotation
was taken into account. The misalignment caused thesplitting of each curve so that curves (1) and (2) in Fig. 2
split into two, and curve (3) into 4, that is, the eight
manifolds separately appeared as ESR signals. In the ﬁtting,the misalignment was set to 28. These splittings were moreclearly observed at 4.2 K.
Fig. 3 shows ESR curves of a CdIn2S4 sample dopedwith 0.375 wt% Ce3þ ions. As mentioned previously, twotypes of ESR signals were observed. Type 1 was speciﬁedby the g-values of gk ¼ 2:3 and g’ ¼ 0:8; the same values
as obtained in Fig. 2. It is interesting to note that Type 2
could be also reproduced by the same model used forType 1 but using the g-values of gk ¼ 1:13 and g’ ¼
1:37: Thus the g-value’s anisotropy of Type 2 is verysmall compared with that of Type 1. The eight manifolds
due to the misalignment of the rotation axis were also
clearly observed at 4.2 K (though difﬁcult at 77 K) in thiscase. This strongly indicates that Type 2 is also ascribedto an ESR center at the tetrahedral site. However, theorder of the magnitude of gk and g’ were reversed in
Type 1 and 2. This ﬁnding and the small anisotropy
suggest that the wave-function of the unpaired electron
around the ESR center of Type 2 spread out by escaping
the bonding direction to the surrounding sulfur atoms,
while that of Type 1 is conﬁned mainly to the direction
toward a sulfur vacancy. That is, Type 1 consists of a
substituted Ce3þ ion and a sulfur vacancy, and Type 2

consists of a similar Ce3þ ion centered at tetrahedrally
arranged four sulfur atoms.
From Fig. 1, it is seen that Type 2 emerges according to
the doped amount of Ce3þ ions. To clarify the origin of boththe ESR centers, the Ce3þ doping was carried out by
annealing undoped samples in Ce2S3 powder at hightemperature below the melting point of CdIn2S4. The
annealing temperature was determined so as to get mosteffective doping after several trials by varying thetemperature systematically. Fig. 4 shows ESR resonancecurves using a sample annealed at 950 8C for 2 h. Here only
ESR signals of Type 2 were observed. The annealing time
was extended to 50 h at the same temperature. Then small
signals due to Type 1 centers emerged in addition to Type 2
signals. These were so small as to be detected only at 4.2 K
Annealing was also conducted for the 0.225 wt% Ce3 þ
doped sample, having been shown at the top in Fig. 1. In thiscase, Type 1 signals were decreased as annealing time was
elongated, and Type 2 signal emerged in the same way
stated above.
From the results of annealing, it can be said that theformation energy of Type 1 ESR centers is greater than thatof Type 2, since the ESR center of Type 1 was createdexclusively at high temperature as a pair of a Ce3þ centerand a sulfur vacancy. In the melt grown process, the ESR
center of Type 2 was formed only after the concentration
was increased up to a certain appropriate value. This centeris considered to consist of a Ce3þ ion placed in the center ofa sulfur tetrahedron, where a sulfur vacancy may exist
somewhere apart from the center to keep the charge
neutrality.
The center of Type 1 is difﬁcult to be formed byannealing in Ce2S3 powder below the melting temperatureof CdIn2S4, where Type 2 centers are easily formed.
However, it seems that there is ﬁnite probability to create
Type 1 centers when the annealing time is kept longer thanFig. 3. Resonant magnetic ﬁeld vs. angle of rotation of ESR signals(at 77 K) of a Ce3þ 0.375 wt% doped sample. Both Type 1 and 2
signals appeared. In the ﬁtting, gk ¼ 2:3 and g’ ¼ 0:8 for Type 1,
and gk ¼ 1:13 and g’ ¼ 1:37 for Type 2 were used in the Eqs.
(2) –(4) in the text.

Fig. 4. Resonant magnetic ﬁeld vs. angle of rotation of ESR signals
at 77 K of an undoped sample which was annealed in Ce2S3 powder
at 950 8C for 2 h. Here the ﬁtting was made using gk ¼ 1:13 andg’ ¼ 1:37 in the Eqs. (2) –(4) in the text.

hv
H3 ¼ sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
for ½111


1
1 2 2
2
2
b g’ 1 2 cos u þ gk cos u
3
3
manifolds:

ð4Þ

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T. Takizawa et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1807–1810

50 h. Thus it is considered that Type 1 needs a larger
creation energy than Type 2.

Acknowledgements
This work was partly supported by the Research Grant
from Nihon University.

4. Conclusion
References
To investigate the substitution mechanism of RE atoms
doped in a crystal lattice of the IIa – III2 – IV4 system,
dopings of Ce3þ into CdIn2S4 by melt and by annealing
were carried out. ESR measurement revealed two types ofcenters. One (Type 1) consists of a Ce3þ ion accompanied
by a sulfur vacancy at its nearest neighbor site. The ion
substitutes a divalent Cd site and not a trivalent In one.
The other (Type 2) consists of a similar Ce3þ ion placedin a sulfur tetrahedron, where a charge compensating
sulfur vacancy is expected to exist at an appropriate sulfursite apart from the Ce3þ ion. The formation energy of a
Type 1 center is considered to be larger than that ofType 2.

[1] T.E. Peter, J.A. Baglio, J. Electrochem. Soc. 119 (230) (1972)
1720.
[2] W.A. Barrow, R.C. Coovert, E. Dickey, C.N. King, C. Laakso,
S.S. Sun, R.T. Tuenge, R. Wetross, J. Kane, SID Int. Symp. Dig.
(1993) 761.
[3] K. Tanaka, S. Okamoto, Y. Izumi, Y. Inoue, K. Kobayashi, Jpn
J. Appl. Phys. 38 (1999) L1419.
[4] T. Takizawa, E. Christoffel, A. Goltzené, C. Schwab, Jpn
J. Appl. Phys. 33 (1994) 1951.
[5] T. Takizawa, C. Komatsu, H. Matsushita, A. Goltzené,C. Schwab, Cryst. Res. Technol. 31 (1996) 173.
[6] A. Yariv, in: W. Low (Ed.), Proceedings of ﬁrst International
Conference on Paramagnetic Resonance, Jerusalem, July, 1962,
p. 189.

Journal of Physics and Chemistry of Solids 64 (2003) 1959–1962
www.elsevier.com/locate/jpcs

Light ﬁgure spectroscopy of optically active anisotropic materials
Nobuyuki Yamamotoa,*, Nazim Mamedova, Yonggu Shima, Chiharu Hidakab,
Takeo Takizawab, Eiji Niwac, Katashi Masumotoca

Department of Physics and Electronics, Graduate School of Engineering, Osaka Prefecture University,
Gakuen-cho 1-1, Sakai, Osaka 599-8531, Japanb
Department of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui,
Setagaya-ku, Tokyo 156-8550, Japanc
Research Institute for Electric and Magnetic Materials, 2-1-1 Yagiyama-minami, Taihoku-ku, Sendai 982-0807, Japan

Abstract
Low order interference curves in optic-axis light ﬁgures of the optically active AgGaS2 and TeO2 are investigated in thevisible spectral range at room temperature. Light ﬁgure patterns of AgGaS2 are found not to be affected by optical activity
within the incidence angles of 108 for which, according to our symmetry considerations, the normal component of gyration
tensor is small and evolution of light ﬁgures with wavelength is overwhelmingly determined by optical anisotropy. The absolutevalue of this anisotropy is falling down to null when passing through the isotropic point, with the result of a remarkable changeof the parameters of light ﬁgure patterns. Unlike the case of AgGaS2 and consistently with our symmetry considerations, lightﬁgures of TeO2 are inﬂuenced by optical activity especially strongly in low orders of interference. The obtained results arecompared with similar results for optically inactive CaCO3 and discussed in the frameworks of our recent analyses.
q 2003 Elsevier Ltd. All rights reserved.
Keywords: A. Inorganic compounds; A. Optical materials; D. Crystal structure; D. Dielectric properties; D. Optical properties

materials, AgGaS2 (D2d ) [5] and TeO2 (D4 ) [6], withespecially large optical rotatory power.

1. Introduction
Light ﬁgure spectroscopy is a very informative andvaluable tool for optical characterization of the anisotropic
materials and phase transitions [1 – 2]. Using a newly
designed experimental set-up for determination of lightﬁgure parameters with high accuracy [1], and a new methodfor determination of the relative dispersion of the refractive
indices [3], we have already managed to extend theapplication of light ﬁgure method beyond the usual
standards. An excellent agreement has then been achieved
between experimental and numerical results for the opticallyinactive uniaxial material, CaCO3 (point group of crystal
symmetry-D3d ) [4].
In this work we extend the application of light-ﬁgure
method further by addressing optically active uniaxial* Corresponding author. Fax: þ 81-722-54-9908.
E-mail address: yamamoto@pe.osakafu-u.ac.jp
Yamamoto).

(N.

2. Light ﬁgures of CaCO3, AgGaS2 and TeO2
The samples of CaCO3, AgGaS2 and TeO2 used in thiswork were all (001)-cut plane-parallel plates with athickness of 1.225, 8.20, and 1.42 mm, respectively. The
details of the experimental setup for light ﬁgure acquisition
were already reported earlier [1].
Like all uniaxial materials, above crystals are characterized by a single birefringence. As seen from Fig. 1, thebirefringence in these crystals assumes negative, positiveto-negative, and positive values depending on material. In
principle, isochromatic curves in optic-axis light ﬁgures ofthese materials are supposed to be circles with radiusvﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
u


ml u
2dDn 2t
Rm < M
;
ð1Þ
1þ 1þ
ml
2Dn

0022-3697/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0022-3697(03)00203-8

1960

N. Yamamoto et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1959–1962

falls down and observation of the well-deﬁned light ﬁgure
patterns becomes practically impossible.
As estimations show, for a 1.225 mm-thick plate of
CaCO3 condition 2dDn=ml q 1 is fulﬁlled up to 100th orderof interference in all the accessed spectral range and relation(1), as well as expression for ratio Rmþ1 =Rm ; can be
simpliﬁed down to
Rm < Mrﬃﬃﬃﬃﬃﬃﬃ
mdl
2Dn

ð2Þ

rﬃﬃﬃﬃﬃﬃﬃﬃﬃ
mþ1
;
m

ð3Þ

and
Rmþ1
<
Rm
Fig. 1. Wavelength dependences of optical anisotropy of TeO2,
AgGaS2 and CaCO3. The cross-point of vertical and horizontal
dashed lines is the isotropic point ðli Þ of AgGaS2.

where M is the magniﬁcation factor for the employed opticalsystem, Dn-birefringence, d-sample thickness, and m-theorder of interference curve [1].
2.1. Optically inactive caseFig. 2 displays most important features of the change oflight ﬁgure patterns of CaCO3 [4] and AgGaS2 withwavelength.
As for CaCO3, we can see more than four isochromate
circles whose radiuses increase monotonically with increasing wavelength in the visible spectral range. For AgGaS2 theradiuses of the observed isochromates ﬁrst increase withincreasing wavelength from 476 to 484 nm, then decrease
with further increasing wavelength beginning from 510 nm.
In the range between 488 and 504 nm, including theaccidental isotropic point (497.3 nm) with null value ofbirefringence [5], birefringence-dependent contrast function
determining visibility of interference pattern dramaticallyrespectively. For 8.20 mm-thick plate of AgGaS2 relations(2) and (3) should be fully justiﬁed at least for interference
curves with m ¼ 1 and m ¼ 2; and for all wavelengths
longer than 540 nm. Experimental R2 =R1 ratios obtained forthe plane-parallel plates of all investigated materials,
including TeO2, are given in Fig. 3.
Indeed, for CaCO3 this ratio is everywhere the same aspthe ‘thick-sample’ limit given by Eq. (3) as 2. For AgGaS2,
this ratio is 2 for all wavelengths above 540 nm. For smaller
wavelengths, such as 476 and 450 nm that are below
isotropic point, this ratio is respectively 1.47 and 1.50 in fullagreement with relation (1). The relations (1)– (3) are
written for the opticaly inactive case and the fact thatexperimental data for AgGaS2 follow this case means thatno inﬂuence of optical activity is observed for low orderinterference curves, which is consistent with results of ourrecent symmetry analysis [7].
For the measured thick TeO2 plate, the ratio R2 =R1 only
approaches 2 with wavelength increase, remaining larger
than 2 and signiﬁcantly exceeding this value in theneighborhood of some short-wavelength limit, denoted as
l1 in Fig. 2. Such behavior of R2 =R1 can be explained onlywith allowance for optical activity of TeO2.

Fig. 2. Light ﬁgure patterns of CaCO3 and AgGaS2 for different wavelengths.

N. Yamamoto et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1959–1962

Fig. 3. Wavelength dependences of the ratio of the radii of thesecond and ﬁrst isochromatic curves of TeO2, AgGaS2 and CaCO
pﬃﬃ3.
Horizontal dashed line shows the ‘thick-sample’ limit equal to 2:
Vertical dashed lines outline isotropic point ðli Þ of AgGaS2 andshort-wavelength limit ðl1 Þ for observation of the ﬁrst-order ðm ¼
1Þ isochromatic curve of TeO2. Dashed curve (TeO2) is drawn
speculatively to show that experimental curve approaches ‘thicksample’ limit with increasing wavelength.

2.2. Optically active caseIn the presence of optical activity the radius of an mthorder isochromatic curve differs from that in the absence of
optical activity and the difference DRm is given approximately as [7]rﬃﬃﬃﬃﬃﬃﬃ
mld 3
ð4Þ
n rG;
lDRm l < M
2Dn

1961

where refractive index, n; of the ordinary ray and opticalanisotropy Dn are taken with their optically inactive values.
As follows from Eq. (4), the change DRm brought in by
optical activity is greatly dependent on the always positive
product rG; where r is ellipticity and G is normalcomponent of gyration tensor, and r and G; both areincident angle dependent functions. This product strongly
depends upon incident angle, um ; at which mth orderishochromate is observed.
For TeO2 the value of rG strongly decreases withincreasing um [7] and higher interference orders are lessinﬂuenced by optical activity than lower ones. Accordingly,
for a thick TeO2 plate the ratio R2 =R1 will be larger than 2and deviation from this value will increase with decreasing
interference angle or when approaching short-wavelength
limit l1 in the neighborhood of which R1 ! 0 much fasterthan R2 :Total picture with wavelength dependencies of interference curves up to ﬁfth interference order is given in Fig. 4
including light ﬁgure patterns (inset) that reﬂect key
elements of evolution of light ﬁgures of TeO2 withwavelength. Every mth order isochromatic curve has its
own wavelength limit and tends to shrink into zero-size
isochromate when approaching this limit given by

lm ¼

1 3
n ðlm ÞGk ðlm Þd;mð5Þ

where Gk is the absolute value of G33 component of gyration
tensor of TeO2 [7]. Condition (5) corresponds to multiples
of p=d for rotatory power [7] and each lm in Fig. 4 is given
together with the corresponding p=d value in the brackets.

Fig. 4. Wavelength dependences of the radiuses of isochromatic curves with different interference orders ðmÞ for TeO2. Vertical dashed lines
indicate the short-wavelength limits for each interference order. Inset: light ﬁgure patterns, for m ¼ 1; of TeO2.

1962

N. Yamamoto et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1959–1962

For AgGaS2 only two major components, G11 andG22 ðG11 ¼ 2G22 Þ; of gyration tensor are different from null.
Component G33 is null and the situation is just the oppositeof that for TeO2. The value of rG strongly decreases withdecreasing interference angle and most favorable conditions
for observation of the optical activity effect are realized atinterference angles close to 908. The use of large numericalapertures of ,608 may provide necessary conditions forobservation of this effect, as well as determination of
gyration parameter in the visible spectral range. Presently
this parameter is known only for one wavelength from thedata on rotatory power for isotropic point [5]. It is alsointeresting to investigate whether the shape of interference
curves does really deviate from circular, as predicted by ourrecent analysis [7].

3. Conclusion
By this work we have shown that light ﬁgure
spectroscopy is a valuable tool for visualization of opticalactivity effect on optical constants of anisotropic materials.

References[1] N. Yamamoto, N. Mamedov, T. Shinohara, T. Kunie,
Visualization of light dispersion and structural phase transitions
with light ﬁgures, J. Cryst. Growth 237 – 239 (2002)
2023–2027.
[2] N. Mamedov, Y. Shim, N. Yamamoto, Polarized transmission
intensity studies of off-zone-center incommensurate semiconductors-ferroelectrics TlMeX2, Jpn. J. Appl. Phys. 41 (2002)
7254–7259.
[3] N. Mamedov, N. Yamamoto, T. Kunie, Light ﬁgures and groupto-phase velocity ratio in anisotropic media, Jpn. J. Appl. Phys.
40 (2001) 4938–4942.
[4] Y. Shim, N. Mamedov, N. Yamamoto, Numerical andexperimental approbation of extended application of lightﬁgures, J. Appl. Phys. 91 (2002) 4110–4113.
[5] M. Susaki, N. Yamamoto, H. Horinaka, W.Z. Huang, Y. Cho,
Performance of AgGaS2 crystal ﬁlter for Raman spectroscopy,
Jpn. J. Appl. Phys. 33 (1994) 1561–1565.
[6] T. Takizawa, Optical absorption and reﬂection spectra ofparatellurite, TeO2, J. Phys. Soc. Jpn 48 (1980) 505– 510.
[7] N. Mamedov, N. Yamamoto, Y. Shim, Y. Ninomiya, T.
Takizawa, Extended application of light ﬁgures to optically
active materials with transversally isotropic dielectric function,
Jpn. J. Appl. Phys. (2003) in press.

Journal of Physics and Chemistry of Solids 64 (2003) 1825–1829
www.elsevier.com/locate/jpcs

Schottky properties of CuInSe2 single crystals grownby the horizontal Bridgman method with controlling
Se vapor pressure
Hiroaki Matsushitaa,*, Yukio Tojob, Takeo TakizawabaDepartment of Material Science and Technology, School of High-Technology for Human Welfare,
Tokai University, 317 Nishino, Numazu-city, Shizuoka 410-0395, Japanb
Department of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui,
Setagaya-ku, Tokyo 156-8550, Japan

Abstract
The electrical properties of the Schottky barriers fabricated by using good quality single crystals of CuInSe2 grown by thehorizontal Bridgman method with controlling Se vapor pressure have been investigated, since the Schottky effect gives ususeful information concerning defect physics. The electrical resistivities, Hall coefﬁcients and mobilities are measured as afunction of temperature down to 20 K, and the activation energy EA and the density NA of acceptors are estimated. Schottky
junctions are prepared by vacuum evaporation of Al or In on chemically etched surfaces of the samples. From the currentvoltage characteristics of these junctions, the ideality factor and barrier height are estimated as 3.6 – 4.8 and 0.60 – 0.61 eV forjunctions using Al, and as 1.9– 3.0 and about 0.54 – 0.59 eV for those using In. The capacitance-voltage characteristics are alsomeasured. Based on these results, it is expected that the prepared junctions do not follow the Schottky model, but rather obey the
MIS one.
q 2003 Elsevier Ltd. All rights reserved.

1. Introduction
Many trials fabricating photovoltaic cells using
CuInSe2 solid solutions, e.g. n-CdS/p-Cu(Ga,In)Se2 hetrojunctions have been carried out, and recently some ofthem are practically utilized. On the other hands, rather
few studies of the Schottky junctions using p-CuInSe2
crystals were reported [1 – 3], though the Schottky effectgives us useful information concerning defect physics aswell as electric transport through metal-semiconductor
junctions. In addition, the electrical properties of CuInSe2
bulk crystals have scarcely been taken into account in theanalysis of the Schottky junctions. This is because thehigh-quality single crystals such that electrical properties
could be measured down to liq. N2 temperature were notavailable before.
* Corresponding author. Tel.: þ81-559-68-1211-4407; fax: þ 81559-68-1155.
E-mail address: matusita@wing.ncc.u-tokai.ac.jp (H.
Matsushita).

In this study, we report the results on the electricalproperties of the Schottky barriers fabricated by using
good quality single crystals of CuInSe2 grown by thehorizontal Bridgman method with controlling Se vapor
pressure [4,5].

2. Experimental procedure
CuInSe2 bulk single crystals were grown undercontrolling Se vapor pressure from 5 to 25 Torr [4,5].
Here, the proﬁle of temperature gradient of 3 K/cm waselectrically moved at a speed of about 1 cm/h after
selenizing the CuIn alloy. Grown crystals were cut into
three parts along the growth direction, i.e. ‘Top (T)’,‘Middle (M)’ and ‘End (E)’. ‘T” denotes the initial part ofsolidifying. The preﬁxed number such as ‘10T” denotes Se
vapor pressure in Torr during the crystal growth. The
composition was determined using an electron probe
microanalyzer (EPMA). The Hall coefﬁcient and mobility

0022-3697/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0022-3697(03)00247-6

1826

H. Matsushita et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1825–1829

Table 1
Composition and electrical properties of CuInSe2 bulk crystals atroom temperature
Sample

Cu/
In

Se/
metal

Res.
(ohm-cm)mob.
(cm2/Vs)

EA
(meV)

NA
(cm23)

10E
20M
25T

0.95
1.00
0.93

1.05
1.03
1.06

0.5
11.6
0.7

30
38
20

10
60
5

2 £ 1018
3 £ 1017
2 £ 1018

were estimated, whereby the electron effective mass in pCuInSe2, mh * ¼ 0:73m0 ;[9] was used, where m0 is the rest
mass of an electron. The capacitance-voltage (C – V)characteristics were also measured in the dark at 10 –100 kHz frequencies, using ANDO AG-4311 LCR meter.
The carrier concentrations were estimated from the slope of
C22-V plots, where the speciﬁc dielectric constant of 8.5
was adopted.

3. Results and discussion
were measured using the six-electrode method as afunction of temperature down to about 20 K, and theactivation energy EA and the density NA of acceptors were
estimated from the change in Hall coefﬁcients with respect
to temperature.
CuInSe2 plates were mechanically polished by using
Al2O3 powder, and then rinsed by supersonic syringe in
acetone, and after it in distilled water. Generally, K2Cr2O7
saturation water solution (i.e. K2Cr2O7 aq.) þ H2SO4 [1,2,6]
and Br2þCH3OH solution [2,3,7,8] were used as an etchantfor those metal-semiconductor junctions. In this study,
sample plates were etched in K2Cr2O7 aq. þ H2SO4 for one
minute, followed by the same procedure in Br2þCH3OH for
one minute. Schottky junction was formed by vacuum
evaporation of Al or In on one chemically etched (112)
surface, while the other surface was DC sputtered by Au to
make ohmic contact.
Both of the forward and reverse current-voltage (I –V)
characteristics were measured for these junctions in the dark
at room temperature. From the results of the I – V
characteristics, the ideality factor n and barrier height VB

3.1. Hall effects
Table 1 shows the atomic compositions and electricalproperties of several p-type CuInSe2 samples. Fig. 1 shows
the temperature dependence of electrical resistivity, Hall
coefﬁcient and Hall mobility of these samples. Among thesamples, the 20 M has a higher Hall mobility of p-typeconduction within the Se pressure range of crystal growth.
On the other hands, the other samples are like degenerate
semiconductors.
There were varieties in the Hall coefﬁcient vs.
temperature curves of p-type samples, and the Hall
coefﬁcient overshoots, which are typical in two carrier
conduction of binary and ternary compensated semiconductors, were often observed [4,5]. All of samples asshown in Fig. 1 do not show the Hall coefﬁcient
overshoots, and thus these samples have lower donor
density as compared with the acceptor density. We haveclassiﬁed the p-type samples into the deep (D), shallow(S) or a combination of both (B) types, on the basis ofFig. 1. Temperature dependence of (a) electrical resistivity, (b) Hall coefﬁcient and (c) Hall mobility of p-type samples grown by the horizontal
Bridgman method with controlling Se vapor pressure.

H. Matsushita et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1825–1829

1827

Fig. 2. I –V characteristics of Schottky junctions of Al/p-CuInSe2 and In/p-CuInSe2 in the dark at room temperature; (a) 10 E, (b) 20 M and (c)25 T.

the density ratio between the shallow and deep acceptors[4,10]. Two kinds of acceptors are revealed, one with anactivation energy of about 10 meV such as 10E and 25T
and the other with an activation energy of about 60 meVsuch as 20 M. The shallow acceptors exist in the S-typesamples with Cu-poor composition, where the origin of
the acceptors was ascribed to Cu vacancies. On the other
hand, the origin of the deep acceptors in the D- andB-type samples (Cu/In ¼ 1 and Cu/In . 1, respectively)
was ascribed to In vacancies.
3.2. Etching effects
In order to understand the effect of etching on
CuInSe2 crystals, the surface SEM images and thecomposition variations before and after chemical etchingwere investigated. As the result of the SEM observation
by varying the concentration of K2Cr2O7 aq. from 0 to
15%, the K2Cr2O7 aq. (5%) þ H2SO4, where the effect of
etching seemed remarkable, was adopted as the ﬁrst
etchant. However, during the measurement of I – V
characteristic, the current values in the voltage elevatingprocess did not coincide with that in the voltage lowering
one. In addition, the electrical condition was not stableon the measurement. Then, Br2þCH3OH solution was
adopted to test as the second etchant. In this case, theproblems above were improved remarkably. From theSEM observation of the sample surface treated in the
Br2þCH3OH solution with Br2 concentration of 0.5, 1, 3
and 5%, it was found the crystallization surface etchedby the Br2 þ CH3OH solution (3%) was uniformly
shaved.

The Cu/In ratio increased a little after etching with
K2Cr2O7 aq. þ H2SO4 solution, and the Se content seemed
to decrease by etching with Br2 þ CH3OH solution.
3.3. Schottky barriersFig. 2 shows I– V characteristics of Al/p-CuInSe2 andIn/p-CuInSe2 Schottky junctions. It is seen that therectiﬁcation ratio of all samples is more than two ordersof magnitude at the bias of about 1 V. The ideality factor
n and barrier height VB estimated from the I – V
characteristics are shown in Table 2. Here, the ideality
factor was determined from the exponential curves of thecurrent density vs. forward voltages at a voltage less than
1 V as shown in Fig. 2. In the case of the forward bias,
the cut-in voltages of Al/p-CuInSe2 junctions are somewhat larger than those of In/p-CuInSe2, and thus it isexpected that the diffusion potentials of Al/p-CuInSe2
Table 2
Schottky properties of junctions using p-CuInSe2 bulk crystals
Sample Metal n

Carrier
VB(eV) concentrationfrom C –V
characteristic (cm23)

10E

0.60
0.54
0.61
0.59
0.62
0.57

20M
25T

Al
In
Al
In
Al
In

3.6
3.0
3.5
1.9
4.8
2.2

5.9 £ 1015
4.2 £ 1016–
1.7 £ 1015
2.2 £ 1015
5.9 £ 1016

Carrier
concentrationfrom Hall
effect (cm23)
4.2 £ 1017
1.4 £ 1016
4.6 £ 1017

1828

H. Matsushita et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1825–1829

Fig. 3. C– V characteristics of Schottky junctions of Al/p-CuInSe2 and In/p-CuInSe2 at 50 kHz frequency in the dark at room temperature; (a)10 E, (b) 20 M and (c) 25 T.

junctions become larger. In addition, it is found that theideality factors of In/p-CuInSe2 junctions are closer to 1
than that of Al/p-CuInSe2. In the case of the reverse bias,
the leak current was very low in the Al/p-CuInSe2
junctions, and no breakdown current was observed in
the voltage range down to 2 10 V. Judging from thefounding that the ideality factors was far from unity, it issuggested that insulation layers (for instance, oxidation
layers) and/or carrier trap levels for surface states wereformed between metals and semiconductors.
Fig. 3 shows the plots of C22-V characteristics at
50 kHz frequency of Al/p-CuInSe2 and In/p-CuInSe2
Schottky junctions. In the case of Al/p-CuInSe2 junctions,the frequency dependence of C22 – V characteristics wasobserved. This may be due to the existence of insulation
layers in the junction interface. The junction capacitancedecreased as the frequency increased from 10 to
100 kHz. In the case of In/p-CuInSe2 junctions, thecapacitance was almost independent of frequency. The
measured capacitances of In/p-CuInSe2 junctions are seen
to be generally larger than those of Al/p-CuInSe2
junctions. Furthermore, two straight-line regions of
C22 – V plots exist in the low and high bias regions,
respectively. It was reported by Fonash that the slope of
C22 – V plots at a low bias in the MIS type metalsemiconductor junctions is sometimes different from thatin the perfect metal-semiconductor junctions [11]. The
carrier concentrations determined from the slope of C22 –V plots at a high bias were shown in Table 2, where thecarrier concentrations obtained by Hall effect were also
shown for comparison. It is shown that the carrier
concentrations of all samples estimated from C22 – Vcharacteristics are one to two orders of magnitude lower
than those from Hall effect. It is because Se vacancies
increased in the depletion layer, which were formed at
the surface of CuInSe2 crystals by the decrease of Se
contents after etching with Br2 þ CH3OH solution. In
other wards, the carriers in the depletion layer arecompensated by donors for Se vacancies. Thus, the C22 –V characteristics may not reﬂect the bulk properties,
since the composition of bulk crystal is different fromthat of the crystal surface. In addition, the inﬂuence of
insulation layers to the capacitance seem to lower the
carrier concentrations estimated from C22 – Vcharacteristics.

4. Summary
Schottky barriers were fabricated by using good quality
single crystals of CuInSe2 grown by the horizontal Bridgman method with controlling Se vapor pressure. The defectphysics of the metal/p-CuInSe2 junctions was investigatedfor samples having shallow or deep acceptors.
Judging from the results of the investigations by SEM
and EPMA before and after etching, the etching condition
was determined to use Br2þCH3OH (3%) for one minuteafter etching in K2Cr2O7 aq. (5%) þ H2SO4 for 1 min.
From the I– V characteristics of the metal/p-CuInSe2
junctions, the ideality factor and barrier height are
estimated as 3.6– 4.8 and 0.60– 0.61 eV for Al/p-CuInSe2,
and as 1.9– 3.0 and about 0.54– 0.59 eV for In/p-CuInSe2.
The C– V characteristics are also measured and analyzed
in the 10 – 100 kHz frequency range, and it is expectedH. Matsushita et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1825–1829

that the prepared junctions do not follow the Schottky
model, but rather obey the MIS one.

References[1] C.L. Chan, I. Shih, J. Appl. Phys. 68 (1990) 156.
[2] B. Koscielniak-Mucha, A. Opanowicz, Phys. Stat. Sol. A 141(1994) K67.
[3] M.A. Magomedov, V.D. Prochukhan, Yu. V. Rud, Sov. Phys.
Semicond. 26 (1992) 1123.

1829[4] H. Matsushita, T. Takizawa, J. Cryst. Growth 160 (1996) 71.
[5] H. Matsushita, A. Iwabuchi, T. Takizawa, S. Endo, Cryst. Res.
and Technol. 31 (1996) 77.
[6] A.L. Li, I. Shih, J. Elec. Mater. 22 (1993) 195.
[7] F.A. Abou-Elfotouh, L.L. Kazmerski, R.J. Matson, D.J.
Dunlavy, T.J. Coutts, J. Vac. Sci. Technol. A 8 (1990)
3251.
[8] E. Moon, J. Elec. Mater. 22 (1993) 275.
[9] S. Endo, T. Irie, Solar Cells 16 (1986) 1.
[10] H. Matsushita, T. Takizawa, Jpn. J. Appl. Phys. 37 (1998)4258.
[11] S.J. Fonash, J. Appl. Phys. 54 (1983) 1966.

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. 5145–5152
Part 1, No. 8, August 2003
#2003 The Japan Society of Applied Physics

Extended Application of Light Figures to Optically Active Materials
with Transversally Isotropic Dielectric Function
Nazim M AMEDOV, Nobuyuki Y AMAMOTO, Yonggu SHIM, Yuichiro NINOMIYA and Takeo T AKIZAWA1
Department of Physics and Electronics, Osaka Prefecture University, Gakuen-cho 1-1, Sakai, Osaka 599-8531, Japan1
Department of Physics, Nihon University, 3-25-40 Sakura-josui, Setagaya-ku, 156-8550 Tokyo, Japan(Received August 23, 2002; accepted for publication April 2, 2003)

An analytical approach to optic-axis light ﬁgures of optically active transparent materials with transversally isotropic linear
dielectric function is developed. The ratio of the gyration constant to the parameter of anisotropy of this function is shown tobe essential for the scale of the gyration eﬀect on light ﬁgures. An algorithm for determination of all material-related opticalparameters is proposed in the form covering both symmetries possible for optical activity in uniaxial materials, such as
AgGaS2 and TeO2 . For AgGaS2 , a deviation of the shape of the interference curves from circular is expected at enough large
angles of interference. In full agreement with the performed theoretical analysis, the shrinking of interference curves into zerosize isochromates is observed at multiples of  for rotation angle of a thick 1420 mm-plate of TeO2 . Transversal component ofgyration pseudo-tensor of TeO2 is determined for the ﬁrst time. The recently proposed relative light-ﬁgure method is reformulated and brieﬂy discussed with allowance for optical activity. [DOI: 10.1143/JJAP.42.5145]
KEYWORDS: light ﬁgures, optical activity, gyration pseudo-tensor, rotatory power, isogyros, isochromus

1.

Introduction

2.
1–4)

Recent developments
in light ﬁgure (LF) spectroscopy,
which is used for optical characterization of anisotropic
materials since long time ago,5,6) give a hope that applicationof LF can be extended to investigation of optical eﬀects insubstances with nanosize structures. Most promising for thispurpose is thought to be relative LF method1) that has
already received comprehensive experimental approval.2) At
the same time absolute LF method may also be useful. Thismethod was sensitive to the formation of an incommensurate
superstructure with correlation length of the order of10 nm and spatial dispersion of the order parameter wasthen found to give a signiﬁcant optical anisotropy of theorder of 103 with the background value of 104 forbasic lattice.3,4) For comparison, spatial dispersion in
optically non-active materials with usual interatomic distances can give only a very small correction of the order of
106 to the refraction index.7)
Optical activity is a ﬁrst order spatial dispersion eﬀect thatusually inﬂuences refraction index in the order of 104 or
less. Conventional methods face diﬃculties in measuring
such small variations of refraction indices and full characterization of many anisotropic optically-active substances has
not been done yet.8) LF, which, in our opinion, is basically
free of the deﬁciencies inherent to the other methods, canassist in solving the problem. However a relevant analytical
approach is currently in lack.5,6)
Here we are considering optic-axis LFs of optically active
materials with transversally isotropic linear dielectric function in trial to ﬁnd analytical approximations qualifying forpractical use in the frames of both absolute and relative LF
methods. Basing on the obtained results, we accomplish
numerical and experimental application to the TeO2 having
one of the two symmetries possible for optical activity inuniaxial materials, and give general analysis to a representative of the other symmetry, AgGaS2 . As far as gyrationinduced variations of refraction indices are concerned, we
demonstrate that LFs are able to expose such variations
down to at least 105 , which is still above the level ofvariations (106 ) caused by thermal ﬂuctuations (0:1 K).

Inﬂuence of Optical Activity on Refraction Indices

Maxwell equations for transparent materials with gyration
permit solution in the form of the two elliptically polarizedwaves.7) If we select a coordinate system with Z-axis
parallel to the optic axis, we can write refraction indices ofthese waves in the forms
ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1ﬃ
1
ð1Þ
noG ¼
 o Go
"?
andsﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1"k cos2 e þ "? sin2 e
neG ¼ e Ge"k "?

ð2ÞHere subscripts o and e are related to the ordinary andextraordinary waves, respectively. Parameter , or ellipticity, is determined asqﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1 2 sin4 e þ 4G2o,e   sin2 o,e
o,e ¼ð3Þ
2Go,e
It has always the same sign as Go,e . Parameter , orparameter of anisotropy of dielectric function, introduced
into eq. (3) equals "?  "k 
 ¼ 
ð4Þ
" " 
? k

Angle o,e is the angle between ko,e and optic axis, ? and k
are transversal and parallel components of the dielectric
function tensor , respectively. The upper and lower signs in(1) and (2), as well as all the other expressions given
hereafter are taken for "? > "k and "? < "k cases, respectively. Analytical form of the parameter Go,e that is nothingelse but a normal component of gyration pseudo-tensor G in
k direction can be found as
Go,e ¼ ko,e Gko,eð5ÞThis form depends on the class of symmetry of opticalactivity. In materials under consideration tensor G has either/2 or 4 2m symmetry. Note that this symmetry is notnecessarily the same as crystal point symmetry.

5145

5146

Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

N. MAMEDOV et al.

For /2 symmetry (/-axis parallels Z), tensor G has eigen
value Gk for eigen vector that parallels Z and G? for all
eigen vectors in XY plane. Therefore this tensor is transversally isotropic and normal component can be written as
Go,e ¼ Gk þ ðG?  Gk Þ sin2 o,eð6ÞFor 4 2m-symmetry (4 -axis parallels Z, 2-axes coincidewith X and Y) tensor G is not transversally isotropic because
it has three diﬀerent principal components G11 ¼ Go , G22 ¼
Go and G33 ¼ 0. At the same time, only one of thesecomponents is unknown and normal component can be
written as
Go,e ¼ G0 cos 2’ sin2 o,e

ð7Þwhere ’ is an angle counted from X or Y. Note that for somecrystal symmetries with above symmetry of optical activity
X and Y axes do not coincide with crystal axes a and b. But
this has no inﬂuence on LFs for which only the symmetry of
optical activity is essential.
3.

Inﬂuence of Optical Activity on Optic-Axis Light
Figures

The general condition of interference5) for a uniaxial
optically non-active plate with thickness d can be re-written
to the form
qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ n2  sin2 m  n2  sin2 m  ¼ m
ð8Þ
o
 e

where
m ¼

m
d

ð9Þ

For optically active materials the general condition ofinterference remains valid in the form eq. (8) after making
transformationrﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ"
ð10Þ
no ! noG ¼
1  "o Go
sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ"ð1   sin2 mG Þ
ne ! neG ¼
ð11Þ
1  "e Ge
Here, " is transversal component "? , m and mG are theincident angles at which the m-th order isochromatic curve isobserved in optically non-active and active cases, respectively. Parameter sin m or sin mG can be determined
experimentally and separately for each interference curveby using an objective (or condensing) lens with variable
numerical aperture.
The eﬀect of optical activity on LF will obviously dependon how much the interference condition (8) written for
optically non-active case will be aﬀected after allowance forgyration. Examination of eqs. (10) and (11) immediately
shows that inﬂuence of optical activity on LF will be
determined by the "G-terms related to ordinary andextraordinary waves, respectively.
In contrast with the optically non-active case, now theinterference eﬀect is possible even at mG ¼ 0 for which
condition (8) transforms into
rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ


"
"


ð12Þ
 1  " G  1  " G  ¼ m
o

o

o

o

It is clear that optical activity will modify not only theinterference angles (m ! mG ) but also the radiuses(rm ! rmG ) of interference curves.
The eﬀect of optical activity on light ﬁgures can beobserved if diﬀerence jrmG  rm j is larger than diﬀraction
limited resolving power of the objective lens with numericalaperture sin , orjrmG  rm j > 0:61= sin ð13Þ

According to condition (13), the use of variable numericalaperture with sin  ¼ sin mG is justiﬁed only for enoughlarge interference angles. For small interference angles
variable numerical aperture is less useful and information we
can obtain is restricted to the values of the radiuses of theisochromatic curves.
It can be shown that the eﬀect of optical activity on theradius of an m-th order interference curve can be roughly
evaluated asrﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
md 3
ð14Þ
n m Gm
jrmG  rm j 2nwhere optical anisotropy n is the diﬀerence between
refraction indices of extraordinary and ordinary rays, nrefraction index of ordinary ray. Here m Gm is taken for the
direction of mean path ray having refraction index nm (seeAppendix).
4.

Optical Activity and Optic-Axis Light Figures ofSilver Thiogallate and Paratellurite

4.1 State of art
Silver thiogallate, AgGaS2 , and paratellurite, TeO2 , arerepresentatives of two diﬀerent symmetries (4 2m and /2,
respectively) possible for optical activity in non-centersymmetrical materials with transversally isotropic tensor of
linear dielectric function. To the best of our knowledge,
there are no reports on LFs of the above materials.
AgGaS2 with 4 2m (D2d )-point group of crystal symmetry
has only one independent component (Go ) of gyration
pseudo-tensor. This component is known only for theisotropic point ( ¼ 497:3 nm),9) and ﬁnding Go in a wide
spectral range is yet to be done, in particular, by using opticaxis (or perpendicular-to-optic-axis) LFs.
As follows from (3) and (7), for AgGaS2 a "m Gm -term
can be written as
0sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1
 2
" sin2 mG @G0"m Gm ¼
cos2 2’  1A ð15Þ
1þ4
2n2m

For most cases the second term under the square root ismuch smaller than the ﬁrst one. Therefore, expression (15)can be evaluated by
G20
ð16Þ
cos2 2’ sin2 mG

pﬃﬃﬃ
where we have taken nm ¼  for simplicity.
As follows from (15) and (16), LF patterns will not be
inﬂuenced by optical activity at mG ¼ 0 and ’ ¼ =4  l,
where l is an integer. In all the other cases this inﬂuence
depends upon values of mG and ’, being largest when ’ ¼
l and mG ¼ =2. Strictly speaking, cos 2’-modulation in"m Gm 

Parameter γ

0.02550.0250

−no
−ne
−Δn

2.6
2.5
2.4
2.3
2.2

400 500 600 700 800 900 1000

0.0245

0.20
0.19
0.18
0.17
0.16
0.15
0.14
0.13

0.00300.00250.0020

Wavelength (nm)0.00150.0240⏐G||/γ⏐0.02355147

Parameter ⏐G||/γ⏐

Refraction Index

0.0260N. MAMEDOV et al.

Optical Anisotropy

Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

0.0010γ
0.00050.0230
400

500

600

700

800

900

1000

Wavelength (nm)Fig. 1. Parameter  and parameter jGk =j for TeO2 , as restored from the previous data.11,12) Inset: optical constants and opticalanisotropy of TeO2 according to the work.11)

eq. (15) or (16) will lead to the similar modulation ofinterference angles and radiuses of interference curves sothat one can expect deviation of the shape of interference
curves from circular at least at enough large angles ofinterference. More details related to this deviation, as well as
numerical estimates and experimental data for AgGaS2 will
be given in another work.10)
Here we focus on the representative of the other symmetryof optical activity, paratellurite (crystal symmetry 422 (D4 )),which is optically well studied.11,12) As follows from eqs. (3)and (6), a "m Gm -term of paratellurite can be written as
" sin2 mG
2n2m
9
8"

2 # 12 =
<

jG
j
jG

G
j
k
?
k

1 þ 4 n2m
þ
1
;
:

 sin2 mG"m Gm ¼

ð17Þ
Here the superscript  indicates that jG?  Gk j should betaken with sign + if gyration constants have the same sign,
and with sign  if they have opposite signs. The estimations
based on the available data11,12) show that the second term
under the square root of (17) is much larger than the ﬁrst one
for all incident angles less than 7 , which is slightly larger
than our experimental angular aperture (6 ). Therefore, formG < 7 we have

jG?  Gk j 1
ð18Þ sin2 mG"m Gm  "jGk j þ4
Unlike the case of AgGaS2 , now we can expect strong
inﬂuence of optical activity on LF at small angles ofinterference, too. For suﬃciently large interference angles,
such as mG > 7 in the case of TeO2 , the second term under
the square root of relation (17) becomes smaller than 1 andwe have"m Gm jGk j "2 jGk jþ 2" jG?  Gk jsin2 mG

jG?  Gk j2 2sin mG Þ
þ
jGk j

!
ð19Þ

Wavelength dependence of parameter , as well as theratio jGk j= essential for both the scale of the gyration eﬀect
on LF of TeO2 and the best conditions for observation of theeﬀect from transversal component of gyration (see Appendix) is shown in Fig. 1. We used the reported values11) of
optical constants (inset) to obtain data on Fig. 1. Component
Gk was calculated using the well-known expression for
rotatory power, ,ð20Þ
Gk ¼ 3npﬃﬃﬃ
where n ¼ ", and values of n and from the works.11,12)
Note that optical anisotropy of TeO2 (inset) and  depend
upon wavelength just in an opposite way. In the next section
we will give an extended analysis of our experimental resultson TeO2 for which transversal component (G? ) of pseudotensor of gyration is unknown and will be determined in thiswork for the ﬁrst time.
4.2 Experimental results and analyses for paratellurite
Experimental results were obtained in the range 400–
700 nm at room temperature for a 1420 mm-thick TeO2 -plate
cut perpendicular to the optic axes. The details concerningwith experimental set-up and digital processing of the data
were described earlier.2,3)
A typical transformation of LFs with wavelength is shownin Fig. 2 including radial distribution of light intensity in LF
patterns (inset) obtained at wavelengths of 510 nm, 480 nm
and 450 nm. The radius Rs of the smallest interference ring isdecreasing with decreasing wavelength and the ring, itself,
becomes unobservable around a wavelength of 450 nm forwhich full extinction in the central part of LF pattern isobserved.
The key elements of the above transformation arepreserved over all visible spectral range and can beunderstood from Fig. 3.

N. MAMEDOV et al.

Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

1000

Radius (point)

Rotatory Power (deg/mm)

5148

800
600
400

TeO2

5π/d

d=1.42mm

4π/d
3π/d
2π/d

π/d

200
0
100
80
60
40
20
0

m=4

m=5

m=3

m=2
m=1

400

500

600

700

Wavelength (nm)Fig. 3. Rotatory power of TeO2 from the works11,12) and experimental
radiuses of interference curves of a thick plate of TeO2 as functions ofwavelength. Open circles-experimental data; solid curves-results ofpolynomial ﬁtting; dashed continuations of the solid curves-speculative
behavior.

011
sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ

2ﬃ 2
Rmþ1 m þ 1 @
2nd
A

1þ 1þ
Rm
m
ðm þ 1Þ0

1 1
sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ2ﬃ  2
2nd A @1 þ 1 þmFig. 2. Experimental radial distribution of light intensity in light ﬁgure
patterns (upper part) of a thick plate of TeO2 at diﬀerent wavelengths.

Every interference curve with the lowest interference
order tends to shrink into zero-size isochromate at multiplesof =d for rotatory power. After shrinking, the interference
curve disappears from the LF pattern in full agreement withthe fact that interference order m in optically active material
can not exist below a wavelength, m , given, according tocondition (12), byn3 ðm ÞGk ðm Þd  mm

ð21Þ

Condition (21) immediately leads to the corresponding
condition for rotatory powerðm Þ  m
ð22ÞdNumbering of interference orders m in Fig. 3 is therefore
done according to the last relationship that can be reformulated as a condition of multiples of  for rotation angle(’ ¼ d).
In Fig. 4 we show the results of comparison of theexperimental modiﬁed-by-gyration ratio Rmþ1 =Rm for neighboring interference orders m and m þ 1 with that calculated
for optically non-active case according to the approximate
expression

ð23Þ

that can be easily derived from our previous results.1,3) Here,
we use large R instead of small r for radius of interference
curve since experimental radius R is enlarged in comparison
with real (small) radius r.
Note that ratio (23) is always within the following limits
rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
m þ 1 Rmþ1 m þ 1
ð24Þ
Rm
m
m
For thick samples, such as in our case, when condition
m
ð25Þ
d
2n
is fulﬁlled, this ratio is supposed to be close to the values
given by the left-hand limit of relation (24).
Onﬃﬃﬃﬃﬃﬃﬃ
thepﬃﬃﬃ pﬃ pright
ﬃﬃﬃﬃﬃﬃﬃﬃ
scalepof
Fig.
4
these
values
are
given
as
2
,
3=2
, 4=3
ﬃﬃﬃﬃﬃﬃﬃﬃ
and 5=4. The calculated ratios are practically independentof wavelength since interference angles for the involved
interference orders are very small. Experimental ratios,
however, behave very diﬀerently from and approach thecalculated values only in the long-wavelength regions whererotatory power is decreased. As seen from Fig. 4, every
Rmþ1 =Rm p
ratio
has
own
limit given by
ﬃﬃﬃ ppﬃﬃﬃﬃﬃﬃﬃﬃ
ﬃﬃﬃﬃﬃﬃﬃits
ﬃ p
ﬃﬃﬃﬃﬃﬃﬃﬃ long-wavelength
numbers 2, 3=2, 4=3 and 5=4. Therefore one candetermine the interference orders of any two neighboring
interference curves.
Above we have described two independent methods forcorrect determination of the interference order m in the caseof optically active material. Note that this case is diﬀerent
from the case of optically non-active material for which thesmallest interference ring always has m ¼ 1 and numberingof interference orders presents no diﬃculty.

Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

5.

2

R3/R2

R4/R3

3
2

1.2 R /R
5

1.0

4
3
5
4

4

400

500

600

700

Wavelength (nm)Fig. 4. Experimental (open circles—experimental data; solid curves—
results of polynomial ﬁtting) and calculated (horizontal dashed curves)
ratios of the radiuses of the two neighboring interference curves asfunctions of wavelength for a thick plate of TeO2 .

At least to an observable extent given by Fig. 4 we can seethat the lower m is the stronger the experimental values ofRmþ1 =Rm deviate from their long-wavelength limits for any
chosen wavelength. This can be understood if normalcomponent of gyration pseudo-tensor is decreasing withincreasing interference angle. The traces of black isogyros
curve in the distant from central parts of LF patterns (Fig. 2,
inset) are also witnessing that higher interference orders areless inﬂuenced by optical activity than lower interference
orders.
Since we used a thick plate and low interference orders,and did not determine interference angles, we employed ourexperimental data together with available data on opticalconstants11) to obtain transversal component G? of the
gyration pseudo-tensor of TeO2 . The sign of this component
turned out to be opposite with that of Gk .
Both components are shown in Fig. 5. As far as Gk is
negative (left-hand rotation),11,12) positive sign (right-handrotation) is appropriate for G? . A relative mistake of 70%
should be assigned to the obtained values of G? because of-0.00007

TeO2-0.00006

G||

0 m=5

0.00006-50.00004G⊥G||-0.00004

0.00003-0.00003

G⊥-0.00002

0.00002-0.00001

0.00001

0.00000

0.00000

400

500

600

700

For TeO2 , the lower sign must be selected. The ﬁrst term in
the right-hand part of relation (27) behaves as shown in
Fig. 6. It assumes quite large negative values ( 2) even at
wavelengths distant from m [see relation (21)] for which
gyration-related correction to the refraction index n is
maximal (104 ) and this term is already of the order of 10. For comparison, thick plates [see condition (25)] of
optically non-active materials typically display smaller
values of this term, such as hardly above  11,2) As seenfrom Fig. 6, this term is nearly constant in the regions far
from m . For these regions the gyration-related correction isalready of the order of 106 , as indicated by "m Gm
increasing downward on the right-hand scale of Fig. 6. Since"m Gm ¼ jGk j at mG ¼ 0 , we can ﬁgure out that we

0.000070.00005-0.00005

Note that in regions with normal dispersion (or below energygap) the relative dispersion of the refraction index always
assumes negative values. The ﬁrst term in the right-hand partof eq. (26) can be negative or positive depending on whether
optical anisotropy (n) decreases or increases with increasing wavelength. The sign of the second term in the righthand part of eq. (26) is always opposite with that of the ﬁrst
term.
In the presence of optical activity eq. (26) transforms into


 dn
n2 G
 dn 1  dGþn d 1  n2 G n d 2 G d
ð27Þ
 dRmGdmG ðÞþ  cot mG ðÞ¼
RmG d
d

Wavelength (nm)Fig. 5. Parallel component (Gk ) of gyration pseudo-tensor, as restoredfrom the previous data,11,12) and transversal component (G? ) of thistensor, as ﬁrstly obtained in this work by using optic-axis light ﬁgures andthe data on  and " restored from the work.11)

-10

10-6
Rm=const

m=4

m=3

m=2

m=1

-15
-20
-25

400

500

ε ρ mGm

1.4

The relative optic-axis LF method is based on thefollowing relation justiﬁed for small angles of interference1)
 dn
 dRm
dm ðÞð26Þ
¼
þ  cot m ðÞ
n d
Rm d
d

λ(R1)

R2/R1

Optical Activity and Relative Light-Figure Methodλ(π/d)

1.6

λ(2π/d)λ(π/d)-λ/RmdRm/dλRatio Rm+1/Rmλ(3π/d) λ(2π/d)λ(R2=R1)

TeO2

1.8

5149

the insuﬃcient accuracy of the experimental values11) of the
optical anisotropy that inﬂuenced parameter  and the ﬁnal
solution obtained according to the proposed algorithm (seeAppendix).

λ(R3=R2=R1)

experimental
calculatedλ(3π/d)2.0

N. MAMEDOV et al.

600

700

Wavelength (nm)Fig. 6. Relative wavelength dispersion of the radiuses of interference
curves of a thick plate of TeO2 . Gyration-induced correction to therefraction index is shown on the right-hand scale. Dashed curve connects
the points with equal radiuses on diﬀerent interference curves.

5150

Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

reliably detect every gyration-induced variation from 2 105 down to 106 . According to Fig. 6, and as expected,
inﬂuence of optical activity on LFs increases with decreasing wavelength, as shown by dashed curve connecting thepoints with equal radiuses on diﬀerent interference curves.
Simple estimations show that the absolute value of therelative dispersion of the refraction index of TeO2 , as well as
most materials, is less than 0:1. On the other hand, we have
giant values of the relative dispersion of the radiuses ofinterference curves (Fig. 6). As calculations show, for TeO2
the second term in the right-hand part of eq. (27) behavesnearly in the same manner and has nearly the same (butpositive) amplitude as the ﬁrst term. Both terms together
give very small total dispersion that equals the value givenby the left-hand part of eq. (27). Separately, however, eachterm reﬂects very strong dependence of interference angles
in eq. (8) upon gyration. This is in the heart of highsensitivity of both absolute and relative light-ﬁgure methods
to the optical activity.
6.

N. MAMEDOV et al.

to 2 provided that interference angle and radius ofinterference curve, both are known for any chosen wavelength.
Let us leave equation for radius of interference curve inthe previous form2)
d sin mGd sin3 mG
rmG ¼ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ þ2n2mG  sin2 mG






1
1


  qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ  qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ 

 2
2
2
2
nemG  sin mG  nomG  sin mG

and re-write auxiliary equations for mean path ray refraction
index, nmG , and mean path length, dm , as one equation
Am
ðA:2Þ
nmG ¼
2Bm
n2omG
n2emG
ﬃ
þ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
Am ¼ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
n2omG  sin2 mG
n2emG  sin2 mG
8
0
>
<
2
sin mG B1
Bm ¼ 1 þ@ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ>
4:n2omG  sin2 mG
12 9
>
=
1
C
þ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ A>
n2  sin2 mG ;Conclusions

An analytical approach to LF of optically active materials
with transversaly isotropic linear dielectric function wasdeveloped and an algorithm for ﬁnding all material-related
optical parameters from experiment was proposed. The
recently introduced relative LF method was re-formulatedwith allowance for optical activity. The developed approach
was successfully applied to TeO2 . The transversal component of gyration pseudo-tensor of TeO2 was determined forthe ﬁrst time. For AgGaS2 , a deviation of the shape ofinterference curves from circular might be expected atenough large angles of interference.
Acknowledgement
One of the authors (N. M.) would like to cordially thankProf. H. Horinaka and Professor Y. Kayanuma for the
fruitful comments after reading the manuscript. Also, thesame author is very grateful to Professor H. Naito, Professor
Y. Nakayama, Professor K. Wakita, Professor K. Wada, andProfessor T. Ishida for the constant interest and support.
Thanks are also due to the reviewer for the suggestions that
led to the improvement of the manuscript. The authors arethankful to Mr. N. Uneme for preparation of LaTEX versionof the paper.
Appendix: Determination of All Optical Parameters ofa Uniaxial Optically-Active Material from
Optic-Axis Light Figures
If interference angles or radiuses of interference curves
are known for three interference orders, we can in principle
determine three unknown parameters (," and G? or G0 ;jGk j is not an additional unknown parameter since, using eq.
(20), it can be expressed, through " and that can always be
restored from the data for central part of LF) by solving
numerically a set of eq. (8) for optically active case.
However, in practice it is preferable to reduce the number ofthe used interference orders for the accuracy-related problems (see below). Here we are considering an additional
equation that relates the radius of interference curve and themean path ray refraction index. This equation can be used toreduce the number of the necessary interference orders down

ðA:1Þ

ðA:3Þ

ðA:4Þ

emG

For all mG less than =4, the ratio between the second andﬁrst terms of relation (A·1) is very small
pﬃﬃﬃ
0:25 sin4 mG ð "  0:5 sin2 mG Þð2 þ Þ
pﬃﬃﬃ
"  0:5 "ð2 þ Þ sin2 mG þ 0:25ð1 þ Þ sin4 mG
ðA:5Þ

103

Therefore, for all practical purposes one can take only theﬁrst term into account.
If we use variable numerical aperture, the following
parameters of LF will be known
qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
rmGm
1  a2m ;; sin mG ¼ m ; nmG ¼
am ¼
Md
m
mm
and
¼ m
ðA:6Þ
d
where M is a calibration constant determined according to
the reported procedure.2)
After making transformations (10) and (11) in interference
condition (8), and by combining (A·2) and (A·6), we have
two independent equations for any interference order m todetermine nomG and nemG
qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
 2

2
2
2
 n
ðA:7Þ
 emG  m  nomG  m  ¼ m
andqﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
Am
1  a2m ¼¼ fm ðnomG ; nemG ;
m
2Bm
m

mÞ

ðA:8Þ

On the other hand, we can obtain expressions for G? or G0
in analytical form by using eqs. (3), (6) and (7) andJpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

N. MAMEDOV et al.

remembering that according to eqs. (1) and (2)"  n2omG"om Gom ¼ 
n2omG

ðA:9Þ

and
"em Gem ¼ "ð1   2m Þ  n2emG
n2emG

ðA:10Þ

After exclusion of G? or G0 , we can ﬁnally get an
equation that relates only two unknown parameters,  and ",for any order of interference. Note that the just-describedalgorithm requires data only for two interference orders to
obtain  and ". After  and  are obtained G? or G0 are
found from eq. (3). In some cases this algorithm can be
simpliﬁed by replacing both om Gom and em Gem with m Gm ,which is taken for the direction of the mean path ray withrefraction index, nmG .
To understand the consequences of such replacement, let
us analyze the relationship between nomG and nemG before
and after replacement is done. Respectively, we haven2omG
11  "em Gem¼
n2emG
1   sin2 mG 1  "om Gomfor optically non-active case and optimizing the obtained
values afterwards. Indeed, as follows from eqs. (16) and(18), the inﬂuence of optical activity will be negligible forsome angles of interference. In optically non-active case, we
need, in principal, to know only the radiuses of interference
curves (or interference angles) for two orders of interference
to obtain  and ". After getting  and " we can determine
gyration constants, using the interference condition (A·7) in
the form
sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
 "ð1   sin2  ÞmG sin2 mGm ¼ 
1  "em Gem
ðA:14Þ
rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ" sin2 mG 
1  "om Gom
where"om Gom ¼

ðA:11Þ

and

5151


1  2 4
 sin mG þ 4ð"jGk j2
1
þ jG?  Gk j sin2 mG Þ2 2   sin2 mG
ðA:15Þ

and

n2omG
1
n2m  "m Gm ðn2m  sin2 mG Þ
¼

n2emG
1  "m Gm
n2m   sin2 mG
ðA:12Þ
Both (A·11) and (A·12) follow from eqs. (1) and (2). In
particular, (A·12) was obtained by considering that refraction indices of the waves propagating along the same
direction m (direction of the mean path ray) in an optically
active material should obey the following relationships
2
2
ðA:13Þn2
n2
omG ¼ nom  m Gm
emG ¼ nem  m Gm
The diﬀerence between (A·11) and (A·12) approximately
equals  sin2 mG which should be less than desirable
accuracy (or "m Gm ) in order to apply this approach. As
estimations show, the last condition is fulﬁlled for TeO2 onlyat mG < 1 and application of this approximation is notjustiﬁed for most incident angles at which experimental data
were obtained.
Obviously enough, the above described procedure could
be also applied to optically non-active case and only one
interference order would be necessary to determine  and ".
If interference angles are unknown like in our case, theinformation we obtain from LFs is restricted to the radiuses(am ) of the interference curves. In such case, determinationof all optical parameters requires, in principle, threeinterference orders. But, as we found after the examinationof our experimental data (see Fig. 3), the accuracy ofdetermination of G? may become insuﬃcient in this case. At
least for TeO2 and rather small interference angles(mG < 7 ) we could not get a reliable value of G? by using
simultaneously three interference orders for the same wavelength. Therefore we could not determine transversal
component unless we used the data for  and ". In our case
 and " were restored from the data on optical constants inthe work.11) Generally, however, we could obtain  and "from LF of optically active material by solving the problem"em Gem ¼1
2ð1   sin2 mG Þ

 2 sin4 mG
1

þ 4½"jGk j þ ð   jG?  Gk jÞ sin2 mG 2 2  sin2 mG

ðA:16Þ

On the other hand, it follows from (A·1) and (A·6) thatsﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1 þ a2m
ðA:17Þ
nm ¼
sin mGa2mEquation (A·2) with left-hand part given by (A·17) andright-hand part given by (A·3), and (A·4) with refraction
indicessﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ""ð1   sin mG Þ; nemG ¼
nomG ¼
1  "om Gom
1  "em Gem
ðA:18Þ
where "om Gom and "em Gem are given respectively by eqs.
(A·15) and (A·16), and eq. (A·14) are two equations fromwhich interference angle and transversal component ofgyration are determined by using only one interference
order. In practice, however, we have to analyze a number ofinterference orders to ﬁnd the one(s) that provides best
conditions for determination of the transversal component.
Following the just-described procedure, we performed
calculations for all interference curves in Fig. 3. We ﬁrst
determined the angle of interference by living in eqs. (A·15)and (A·16) only the known parallel component of gyrationand then included both components (jGk j and jG?  Gk j) to
see how much was the diﬀerence between the interference
angles. This diﬀerence was maximal (0:3 ) only at someangles from 2 to 5 depending on the wavelength. And,
these angles were found to be very close to the angles for
which

5152

Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 1, No. 8

sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
jGk jsin mG  2
N. MAMEDOV et al.

ðA:19Þ

The G? was determined exactly within a range of theseangles of interference. Below and above this range determination of G? was exceedingly diﬃcult because the inﬂuenceof jG?  Gk j was down to a negligible value of 0:01 . For
this reason, we used only some section of any interference
curve in Fig. 3 to obtain G? . Therefore, G? -curve in Fig. 5 isa resultant curve composed from experimental results fordiﬀerent interference orders.
1) N. Mamedov, N. Yamamoto and A. Kunie: Jpn. J. Appl. Phys. 40(2001) 4938.
2) Y. Shim, N. Mamedov and N. Yamamoto: J. Appl. Phys. 91 (2002)
4110.

3) N. Yamamoto, N. Mamedov, T. Shinohara and A. Kunie: J. Cryst.
Growth 237–239 (2002) 2023.
4) N. Mamedov, Y. Shim and N. Yamamoto: Jpn. J. Appl. Phys. 41(2002) 7254.
5) M. Born and E. Wolf: Principles of Optics (Pergamon, London, 1970).
6) E. E. Wahlstrom: Optical Crystallography (Wiley, New York, 1979).
7) V. M. Agranovich and V. L. Ginzburg: Crystal Optics with Spatial
Dispersion and Excitons (Springer, Tokyo, 1984).
8) H. Horinaka, K. Tomii, H. Sonomura and T. Miyachi: Jpn. J. Appl.
Phys. 24 (1985) 755.
9) M. Susaki, N. Yamamoto, H. Horinaka, W. Z. Huang and Y. Cho: Jpn.
J. Appl. Phys. 33 (1994) 1561.
10) N. Yamamoto, N. Mamedov, Y. Shim, C. Hidaka, T. Takizawa, E.
Niwa and K. Masumoto: submitted to Proc. of 13th International
Conference on Ternary and Multinary Compounds, Paris, 2002.
11) N. Uchida: Phys. Rev. B 4 (1971) 3736.
12) T. Takizawa: J. Phys. Soc. Jpn. 50 (1981) 3054.

Physica C 378–381 (2002) 513–516
www.elsevier.com/locate/physc

Flux creep properties in Dy–Ba–Cu–O bulk superconductors
H. Enomoto a,b,*, K. Inoue b, S. Nariki b, M. Murakami b, T. Takizawa aaGraduate School of Integrated Basic Science, Nihon University, 3-25-40 Sakura-Josui, Setagaya-ku, Tokyo 156-8550, Japanb
Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan
Received 27 September 2001; accepted 7 January 2002

Abstract
We have investigated how the oxygen-annealing temperature and RE211 addition inﬂuence the ﬂux creep at 77 K in
melt-processed DyBa2 Cu3 O7d (Dy123). By making conventional ﬂux creep experiments, we found that Dy211 contents
suppress the ﬂux creep. It was also found that the ﬂux creep is more suppressed by the annealing treatment in the lower
temperature. A suppression in the ﬂux creep was observed for samples with the secondary peak eﬀect.
Ó 2002 Published by Elsevier Science B.V.
PACS: 74.60.Ge; 74.60.Jg
Keywords: Magnetic relaxation; Secondary peak; Flux creep; DyBa2 Cu3 O7d

1. Introduction
In the ﬁeld of power applications it is necessary
to fabricate superconducting materials with highcritical current densities Jc . An enhancement of Jc
value is in general achieved by increasing thenumber of eﬀective pinning centers in superconductors. The melt-processed REBa2 Cu3 Oy (RE:Nd, Sm, Eu and Gd) exhibits the secondary peakeﬀect on the magnetization hysteresis curve, whichis ascribed to RE rich RE123 clusters with depressed Tc in the matrix [1]. Jc values are largely
enhanced by the secondary peak eﬀect. Recently,
Nariki and Murakami [2] has reported that the*Corresponding author. Address: Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku,
Tokyo 105-0023, Japan. Tel.: +81-3-3454-9284; fax: +81-33454-9287.
E-mail address: h-enomoto@istec.or.jp (H. Enomoto).

superconducting properties of the DyBa2 Cu3 O7d
(Dy123) bulk samples were strongly aﬀected by the
Dy211 contents and the oxygen-annealing temperature. Although there is no Dy–Ba solid solution and thus no Dy rich clusters, Dy123 exhibits
relatively large secondary peak eﬀect, which is ascribed to the presence of oxygen deﬁcient clusters.
It is well known that the amount of oxygen vacancies in RE123 phase increases with increasing
oxygenation temperature. A large variation in the
superconducting properties of the present Dy123
with the oxygen-annealing temperature is thus
caused by the variation in the size and distribution of oxygen deﬁcient regions. Oxygen deﬁcient
clusters with depressed Tc act as the ﬁeld-induced
pinning centers, which is the source of the peakeﬀect [3]. In the Dy123/Dy211 composite system
containing the low-Tc phase and Dy211 phase, theﬂux creep behavior is expected to be diﬀerent fromthat of a single phase system.

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514

H. Enomoto et al. / Physica C 378–381 (2002) 513–516

In the present work, we investigated the eﬀect of
Dy211 addition and oxygen-annealing temperature on the ﬂux creep properties of Dy123/Dy211
composite bulk superconductors by measuring themagnetic hysteresis and magnetic relaxation.

2. Experimental
The Dy123/Dy211 composite samples used in
the present study were fabricated by the top-seeded melt-growth process, the details of whichwere described elsewhere [2]. For the measurements of the superconducting properties, rectangular pieces with dimensions of about 2  2  1
mm3 were cut from as-grown bulk samples. To
investigate the eﬀect of oxygen-annealing temperature on the ﬂux creep properties, we used
Dy123 containing 5 mol% Dy211, which wasannealed in ﬂowing oxygen gas at 400, 450, 500,
and 550 °C for 100 h. The eﬀects of Dy211 addition on the ﬂux creep properties were alsostudied with Dy123 containing 5, 10, 20, and 40
mol% Dy211, which were annealed in ﬂowing
oxygen gas at 450 °C for 100 h. The hysteresis
loop and magnetic relaxation measurements were
performed using a commercial SQUID magnetometer (Quantum Design, MPMS) with magnetic ﬁeld applied parallel to the c-axis.
We conﬁrmed that the samples with various
Dy211 contents exhibited almost the same Tc valueof 91.5 K. We also conﬁrmed that no appreciable
diﬀerence in Tc values was observed for the samples with diﬀerent annealing temperatures and the
Tc was also around 91.5 K except the sample annealed at 550 °C, which showed a Tc value of 89 K
and a broad transition.
For the magnetic relaxation measurements, it isessential for the external ﬁeld penetrating to thecenter of the sample. To establish this condition,
the magnetic ﬁeld of 7 T was ﬁrst applied to thesample and then swept to the desired value. The
time decay of magnetization MðtÞ was measured
for 4200 s at various ﬁelds ranging from 0.25 to 3
T at 77 K. The starting time of decay measurements was deﬁned to be tinit ¼ 70 s. This value oftinit was certiﬁed to be suﬃciently long with the two
diﬀerent determination methods of l [4].

3. Results and discussion
Fig. 1(a) and (b) shows the magnetic ﬁeld dependence of Jc at 77 K, which were calculated fromthe hysteresis loop using the extended Bean model[5]. As shown in Fig. 1(a) the Jc in a low ﬁeld region increases with increasing Dy211 contents. In
contrast the secondary peak height decreases withincreasing Dy211 contents. Due to the largest peakeﬀect, Dy123 containing 5 mol% Dy211 exhibits

Fig. 1. Jc –B curves for the bulk Dy123/Dy211 composite
samples with (a) the diﬀerent Dy211 contents annealed in O2 at
450 °C and (b) 5 mol% Dy211 annealed in O2 at temperaturesof 400–550 °C.

H. Enomoto et al. / Physica C 378–381 (2002) 513–516

the highest Jc values even at the higher ﬁelds above
the secondary peak. Furthermore, in Fig. 1(b) one
can see that the secondary peak position gradually shifts to lower ﬁelds with increasing oxygenannealing temperature. The Jc value was drasticallydepressed over a wide ﬁeld range in the sample
annealed at 550 °C primarily due to low Tc . Although no appreciable diﬀerence was observed in
Tc , one can see a systematic increase in Jc and thepeak ﬁeld with lowering annealing temperature. In
general the number of oxygen vacancy is increased
at lower temperatures. However, for the enhancement of the secondary eﬀect, one needs to have awell annealed matrix wherein the small oxygendeﬁcient clusters are uniformly distributed. We
believe that such microstructure is produced by
low temperature annealing.
Fig. 2(a) and (b) shows the magnetic ﬁeld dependence of normalized relaxation rate S at 77 K,
which was obtained from the slope of ln M versus
ln t using the least-square method. For the samples
containing 10, 20, 40 mol% Dy211, S was loweredwith increasing the Dy211 contents accompanied
by an increase in the Jc values (see Fig. 1(a)). For
the sample containing 5 mol% Dy211, which exhibits the large secondary peak, shows the lowest
normalized relaxation rate. These results suggestthat both the Dy123/Dy211 interfacial pinning andthe ﬁeld-induced pinning caused by the oxygendeﬁcient clusters are eﬀective in reducing the ﬂux
creep. Mochida et al. [6] reported that such a
combined eﬀect of two diﬀerent pinning mechanisms led to the suppression in S for the Nd123
system, which is consistent with the present Dy123
system. In Fig. 2(b) one can also see that normalized relaxation rate S is lowered with decreasing oxygen-annealing temperature. This result isalso consistent with Jc –B data for the sample with
diﬀerent oxygen annealing temperatures.
Next, we analyzed the present relaxation data
based on the collective pinning theory [7,8]. According to this theory, the exponent l in the plotof M l versus lnðtÞ is an important parameterto characterize both the relaxation and vortex
dynamics. Phenomenologically, l ¼ 1 gives astraight line, while l < 1 and l > 1 gives
respective convex and concave curves. In the collective-pinning theory, three diﬀerent pinning re-515

Fig. 2. Field dependence of S at 77 K for the Dy123/Dy211
bulk samples with (a) the diﬀerent Dy211 contents annealed in
O2 at 450 °C and (b) 5 mol% Dy211 annealed in O2 at temperatures of 400–550 °C.

gimes of single-vortex pinning, small and largeﬂux bundles are characterized by l ¼ 1=7, 3=2,
and 7=9, respectively. Fig. 3(a) and (b) shows themagnetic ﬁeld dependence of the l at 77 K for the
samples with various Dy211 contents and annealing temperatures. The l are estimated by selecting
a trial value of l and plotting M l versus lnðtÞ. For
the determination of the l value, a linear regressions was repeated until the quantity (1  R2 )reached the minimum value, where R2 is a statistical correlation constant and ideally unity for a
perfect ﬁtting. The l exhibits the peak for the
sample with 5 mol% Dy211 which has the remarkable secondary peak. The samples with

516

H. Enomoto et al. / Physica C 378–381 (2002) 513–516

seems to be strongly correlated with ﬁeld-induced
pinning.

4. Summary
We measured the magnetic relaxation in Dy123/
Dy211 composite bulk superconductors. An increase in the Dy211 contents was eﬀective in suppressing the ﬂux creep. The oxygen-annealing at
lower temperature could enhance the secondary
peak eﬀect and was also eﬀective in reducing therelaxation. A reduction in S was observed for the
sample with the large secondary peak. The positive
peak value of l is the higher for the sample withthe larger secondary peak. This implies that the lis correlated with the ﬁeld induced pinning.

Acknowledgements
This work was supported by the New Energy
and Industrial Technology Development Organization (NEDO) as Collaborative Research andDevelopment of Fundamental Technologies forSuperconductivity Applications.

References
Fig. 3. Field dependence of l at 77 K for the Dy123/Dy211
bulk samples with (a) the diﬀerent Dy211 contents annealed in
O2 at 450 °C and (b) 5 mol% Dy211 annealed annealed in O2 attemperatures of 400–550 °C.

higher Jc which includes 10 and 20 mol% Dy211,
have the higher l in the low ﬁeld. In Fig. 3(b) one
can see that the maximum position of l shift tolower ﬁeld with increasing oxygen-annealing temperature for samples with the clear secondary peakwhich were annealed at 400, 450 and 500 °C. The
positive peak value of l increases with decreasing
oxygen-annealing temperature, that shows the lvalue is the higher for the sample with the larger
secondary peak (see Fig. 1(b)). Hence the l value[1] M. Murakami, S.I. Yoo, T. Higuchi, N. Sakai, J. Weltz,
N. Koshizuka, S. Tanaka, Jpn. J. Appl. Phys. 33 (1994)
L715.
[2] S. Nariki, M. Murakami, Supercond. Sci. Technol. 15(2002) 786.
[3] M. Daeumling, J.M. Seuntiens, D.C. Larbalestier, Nature
346 (1990) 332.
[4] L. Civale, L. Krusin-Elbaum, J.R. Thompson, F. Holtzberg,
Phys. Rev. B 50 (1994) 7188.
[5] E.M. Gyorgy, R.B. van Dover, K.A. Jackson, L.F.
Schneemeyer, J.V. Waszczak, Appl. Phys. Lett. 55 (1989)
283.
[6] T. Mochida, N. Chikumoto, M. Murakami, Phys. Rev. B 64
(2001) 64518.
[7] M.V. Feigel’man, V.B. Geshkenbein, A.I. Larkin, V.M.
Vinokur, Phys. Rev. Lett. 63. (1989) 2303.
[8] M.V. Feigel’man, V.M. Vinokur, Phys. Rev. B 41 (1990)
8986.

Journal of Crystal Growth 237–239 (2002) 1986–1992

Cu-based multinary compounds and their crystal growth:
synthesis processes, phase diagrams and control ofvapor pressures
Hiroaki Matsushitaa,*, Akinori Katsuia, Takeo TakizawabaDepartment of Material Science and Technology, School of High-Technology for Human Welfare, Tokai University, 317 Nishino,
Numazu, Shizuoka 410-0395, Japanb
Department of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku,
Tokyo 156-8550, Japan

Abstract
In order to overcome the difﬁculties in getting bulk single crystals of Cu-based multinary compounds of high quality,
we have investigated the chemical reaction involving single phase formation, the phase diagrams for bypassing theperitectic reaction, and the solid-state phase transition and the effect of VI vapor pressure on the crystal growth. The
selenization or sulfurization method of a CuIn alloy is devised to grow single crystals of CuInSe2 or CuInS2. To bypass
the peritectic reaction of CuGaSe2, solution growth has been performed by using a self-ﬂux, and it is shown that large
single crystals can be grown better from a CuSe solvent than from a Cu2Se solvent. In addition, a solvent of Sb2Se3 isused to grow CuInSe2 single crystals at temperatures below the solid-state phase transition. Furthermore, the melt
growth under controlled VI vapor pressure is adopted to grow high-quality crystals of CuInSe2 and CuInS2. r 2002
Elsevier Science B.V. All rights reserved.
PACS: 81.30.Dz; 81.10.hKeywords: A1. Phase diagrams; A2. Single crystal growth; B2. Semiconducting ternary compounds

1. Introduction
There are few practical opto-electronic devices
composed of multinary compounds with tetrahedral coordinations, in spite of their enormous
potential for various applications. One of the
difﬁculties is caused by the uncontrollability of thephysical properties of these compounds, arising*Corresponding author. Tel.: +81-559-68-1211-4407; fax:
+81-559-68-1155.
E-mail address: matusita@wing.ncc.u-tokai.ac.jp(H. Matsushita).

from the fact that they essentially consist of morethan three elements. Actually, each compositional
atom has the possibility of occupying various
lattice sites and even generating a vacancy and/or
an interstitial during growth, inevitably leading to
difﬁculties in getting a bulk single crystal of highquality. In addition, there are always several paths
to obtain precursors of multinary compounds. In
other words, they can be synthesized throughdifferent chemical reaction processes.
In order to overcome the difﬁculties abovementioned, we have investigated (1) all thechemical reactions until a single phase is formed,

0022-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved.
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H. Matsushita et al. / Journal of Crystal Growth 237–239 (2002) 1986–1992(4) InSe, In6Se7: solid-liquid at B6001C.
(5) In2Se3: solid-liquid at about 9001C.
(6) Cu7Se4, InSe, In2Se3-CuInSe2 above 9501C.
(7) CuInSe2(sphalerite): solid-liquid at 9961C.

while at the same time, the intermediate binary
products synthesized during the formation process, (2) the pseudo-binary phase diagrams which
are necessary for the strategy to grow a single
crystal bypassing the peritectic reaction and thesolid-state phase transition if they exist, and (3)the effect of vapor pressure of VI group elementson the growth of single crystals.

It was found that a few exothermic reactions
just below the melting point of CuInSe2 did notnecessarily occur, and the solid phases of Cu2xSe
and/or copper sometimes remained even at 10401C
in the liquid of the mixture [1].
For CuIn+2Se mixture, the chemical reactions
and phase transitions are summarized as follows.

2. Chemical reactions synthesizing a single phase
Prior to the growth of single crystals of better
quality, we should know the formation mechanisms, i.e., the chemical reaction process forming asingle phase. We present here the results of
CuInSe2, CuInS2 and CuGaSe2 [1–3]. Differential
thermal analysis (DTA) and X-ray diffraction(XRD) are used throughout this report. Figs. 1(a)and (b) show DTA curves of Cu+In+2Se,
CuIn+2Se mixtures and Cu+Ga+2Se, CuGa+2Se mixtures in the heating process, respectively, where DTA curves of elements andcompounds are also shown for comparison.
For Cu+In+2Se mixture, the chemical reactions and phase transitions are summarized asfollows.

(1) Cu1xInx (x > 0:5), Se-CuInSe2, InSe at
5201C.
(2) Cu1xInx (xo0:5), Se, InSe-CuInSe2 at
5751C.
(3) InSe: solid-liquid at about 6501C.
(4) CuInSe2: chalcopyrite-sphalerite at about
8101C.
(5) CuSe, InSe-CuInSe2 above 9501C.
(6) CuInSe2 (sphalerite): solid-liquid at 9961C.
According to the phase diagram of the Cu–In
system [4], it is known that CuIn alloy decomposes
into Cu-rich Cu–In phase and In-rich Cu–In phasewith increasing temperature.
In the selenization reaction of In-rich Cu–In
phase at 5201C, CuInSe2 and InSe compounds
were formed, and then most of the CuInSe2
compound was produced at 5751C.

(1) In, Se-In2Se, In6Se7 at 2501C.
(2) Cu, Se-Cu3Se2, Cu7Se4 at 280–4201C.
(3) In2Se: solid-liquid at B5001C.

In

Se
CuGa

CuIn
2Cu+Se2In+3Se
Cu+In+2Se
CuIn+2Se
Cu2Se+In2Se3

DTA signal (0.2mV/div.)

DTA signal (0.2mV/div.)Se

CuInSe2
0

(a)

200

1987

400 600 800 1000 12000Temperature ( oC)
(b)

Cu+Se
2Ga+3Se
CuSe2+Ga
Cu+Ga+2Se
CuGa+2Se
Cu2Se+Ga2Se3
CuGaSe2
200 400 600 800 1000 1200 1400
Temperature ( oC)

Fig. 1. (a) DTA curves of Cu+In+2Se, CuIn+2Se mixtures, and (b) Cu+Ga+2Se, CuGa+2Se mixtures in the heating process,where DTA curves of elements and compounds are also shown for comparison.

1988

H. Matsushita et al. / Journal of Crystal Growth 237–239 (2002) 1986–1992

Similar to CuInSe2, most of the CuInS2
compound was also formed from a Cu+In+2S
mixture below the melting point of CuInS2
through the chemical reaction between Cu2xS
and In2S3x [3]. Considerable amounts of heterogeneous phases, for instance, Cu sulﬁdes having
melting points higher than that of CuInS2, areconsidered to coexist with the CuInS2 phase atabout 11001C. On the other hand, the explosive
exothermic reactions from a CuIn+2S mixture at
4801C and 7001C were ascribed to the sulfurizationof the Cu–In phase, where most of the CuInS2
compound is formed [3]. In conclusion, theselenization or sulfurization method of a CuIn
alloy at temperatures other than 575 or 7001C is
one of the best methods to grow single crystals of
CuInSe2 or CuInS2.
In contrast to the cases mentioned above, thechemical reactions and phase transitions of CuGa+2Se are summarized as follows.
(1) CuSe: solid-liquid at B5501C.
(2) Cu-Ga alloy, Se-GaSe, Ga2Se3, CuSe at 550–
7501C.
(3) Ga and Cu selenides: decomposition and/or
selenization at B8001C and B9001C.
(4) CuGaSe2 (chalcopyrite)-CuGaSe2 (sphalerite)+liquid at 10601C.
(5) Cu7Se4, GaSe, Ga2Se3-CuGaSe2 (sphalerite)
above 10801C.
(6) CuGaSe2 (sphalerite): solid-liquid at 11051C.
The CuGa alloy decomposes into Cu-rich Cu–
Ga phase and Ga-rich Cu–Ga phase with increasing temperature, in accordance with the phase
diagram of the Cu–Ga system [5]. The CuGaSe2
phase has already been derived below 9501C
through the liquid phase reaction between the
Cu–Ga phase, mentioned above, and selenium [2].
About a half of the CuGaSe2 phase was conﬁrmed
to be formed, judging from the following two
results.
(1) XRD intensities of the CuGaSe2 phasereduced to about half after heating up
to 9501C in comparison to those up to11501C [2].
(2) The heat of transition from the chalcopyrite
phase to the (sphalerite+liquid) phase at

10601C of CuGa+2Se was smaller than thatof CuGaSe2 as shown in Fig. 1(b).
In addition, CuGaSe2 compound was not
perfectly formed at about 11001C since the heatof fusion at about 11001C of CuGa+2Se waslesser than that of CuGaSe2 as seen in Fig. 1(b).
Thus, the selenization of the CuGa alloy is notnecessarily needed for the CuGaSe2 single phase incontrast to the cases of CuInSe2 and CuInS2.
To ﬁnd another preparation method except forthe selenization of the CuGa alloy, we investigatedthe chemical reaction process of Cu+Ga+2Se
mixture as follows.
(1) Cu, Se-CuSe2, CuSe, Cu3Se2 at 280–3801C.
(2) CuSe2, CuSe: solid-phase transition at about
3801C.
(3) CuSe2, CuSe: solid-liquid at about 5301C.
(4) Ga, Se-GaSe at 700–8001C.
(5) Ga, CuSe2, CuSe, GaSe-CuGaSe2 at about
9001C.
(6) CuGaSe2 (chalcopyrite)-CuGaSe2 (sphalerite)+liquid at 10601C.
(7) CuGaSe2 (sphalerite): solid-liquid at 11051C.
The heat of transition at 10601C of Cu+Ga+2Se is in good agreement with that of
CuGaSe2 as seen in Fig. 1(b). Hence, the CuGaSe2
phase is formed by the exothermic reaction atabout 9001C. Thus, it is considered that the
CuGaSe2 phase is completely formed from a
Cu+Ga+2Se mixture below 10601C. In addition,
the heats of transition and fusion at about 10601C
and 11001C of a CuSe2+Ga mixture are also inagreement with those of CuGaSe2. Therefore, it isexpected that the chemical reaction between Cu
selenides and gallium is one of the best preparation
methods for CuGaSe2.

3. Phase diagrams and solution growth
On the basis of the pseudo-binary phase
diagram of Cu2Se–Ga2Se3 system, it is shown that
the CuGaSe2 chalcopyrite phase is formed througha peritectic reaction from the (sphalerite+liquid)phase to the chalcopyrite phase [6,7]. Therefore, aH. Matsushita et al. / Journal of Crystal Growth 237–239 (2002) 1986–1992

large single crystal is difﬁcult to be grown from thestoichiometric melt, and hence the solution method using a self-ﬂux is recommended to obtain asingle crystal of higher quality. Actually, thecrystal growth of CuGaSe2 has been performedby the self-ﬂux method, using Cu2Se and CuSe
solvents [8,9].
The Cu2Se–CuGaSe2 phase diagram shows thatthe transition line from sphalerite to chalcopyrite
phase exists at 10541C in 55–100 mol% CuGaSe2.
In addition, a eutectic line was deduced at 9961C in
25–100 mol% CuGaSe2, and the eutectic point
exists at 9961C for 34 mol%. In this case, single
crystals of CuGaSe2 could be grown using theliquidus line in the composition ranging from 35 to
50 mol% CuGaSe2, resulting in a short (20 mm atmost) single crystal [8].
In contrast to the Cu2Se solvent, the phase
diagram of the CuSe–CuGaSe2 system was deduced as shown in Fig. 2(a). The transition linefrom sphalerite to chalcopyrite phase is considered
to be between 58 and 100 mol% CuGaSe2. The

1989(chalcopyrite+liquid) phase exists under theliquidus line in the composition ranging from 0
to 58 mol% CuGaSe2, which can be used to grow
the CuGaSe2 crystals. Here, the crystal growth wasachieved using the 10–55 mol% CuGaSe2 range.
As the liquidus line for the chalcopyrite phase to
be precipitated is wide in comparison to the Cu2Se
case, a long single crystal of 50 mm in length was
obtained as shown in Fig. 2(b). The XRD patternsof the grown ingot are shown in Fig. 2(c). The top
50 mm of it (‘‘15 mm’’ and ‘‘45 mm’’ in this ﬁgure)had the single chalcopyrite phase of CuGaSe2. The
XRD intensity of the CuSe phase shown by open
circles increases as it moves from ‘‘65 mm’’ to theend of the ingot. It was found that the compositionof the top (‘‘15 mm’’ and ‘‘45 mm’’) was nearlystoichiometric (Cu=26%, Ga=24%, Se=50%).
It was also shown that larger single crystals weregrown from a CuSe solvent than a Cu2Se solvent.
On the other hand, we have attempted to
grow CuInSe2 single crystals at temperatures
below the solid-state phase transition using Sb2Se3

Fig. 2. (a) Pseudo-binary phase diagram of the CuSe–CuGaSe2 system, (b) a photograph of an as-grown ingot and (c) XRD patternsof ingots grown using a CuSe solvent. The CuSe phase is indicated by open circles. Each spectrum is normalized to the (1 1 2) line of‘‘15 mm’’.

1990

H. Matsushita et al. / Journal of Crystal Growth 237–239 (2002) 1986–1992

as a solvent [10]. It is expected that Sb2Se3 is notincorporated in CuInSe2 crystals, which is considered from the results of the liquid phase
epitaxial growth of AgGaS2 using an Sb2S3 solvent[11]. The phase diagram of the Sb2Se3–CuInSe2
system determined from the XRD and DTA
results is shown in Fig. 3(a). The eutectic temperature is deduced as 5201C between 5 and 90 mol%CuInSe2. The eutectic composition is evaluated tobe 10 mol% CuInSe2. The transition point fromsphalerite to chalcopyrite phase exists at about
8001C in 50–100 mol% CuInSe2. Hence, it isexpected that a CuInSe2 chalcopyrite phase rises
much lower than the transition point in 10–
50 mol% CuInSe2 at 520–8001C.
Based on the phase diagram of Fig. 3(a), thebulk single crystals were grown from a solution of
50 mol% CuInSe2. A photograph of a typicalgrown boule is shown in Fig. 3(b). A single crystalof about 11 mm in length was grown from thebottom of the boule along the growth direction.
From XRD patterns of three parts labeled ‘‘a’’,‘‘b’’ and ‘‘c’’ of the boule, only the ‘‘a’’ partshowed the pure CuInSe2 chalcopyrite phase. In
the ‘‘b’’ and ‘‘c’’ parts, the Sb2Se3 phase wasincluded. Fig. 3(c) shows the composition variation along the growth direction of the boulemeasured by EPMA. The Cu:In:Se ratio is shown
to be about 1:1:2 and is uniform throughout theregion ‘‘a’’ of the single crystal, while antimony isdetected in the boule above 12 mm. The impurity
analysis of the ‘‘a’’ part was performed by meansof inductively coupled plasma (ICP) spectrometry.
The result indicated that the region ‘‘a’’ contained
antimony at a level o0.1 mol%.

4. Crystal growth under controlling VI vapor
pressure
It is sometimes effective to grow bulk single
crystals of multinary selenides and sulﬁdes byapplying vapor pressure of VI group element,
because the VI vapor pressure is normally very

Fig. 3. (a) Pseudo-binary phase diagram of the Sb2Se3–CuInSe2 system, (b) a photograph of a grown boule, region ‘‘a’’ corresponds to
the CuInSe2 single crystal in the bottom, and (c) variations of Cu, In, Se and Sb compositions of a grown boule along the growth
direction.

H. Matsushita et al. / Journal of Crystal Growth 237–239 (2002) 1986–1992

high in comparison to that of the other compositional elements so that the VI elements are easily
evaporated from the products even after ﬁnal
compounds are synthesized. In addition, thesolidifying points were found to be sensitive tothe vapor pressure of VI group elements as well as
the compositional deviation from stoichiometry[12]. Fig. 4(a) shows the VI vapor pressure
dependence of the solidifying points of CuInSe2,
CuGaSe2, AgGaSe2, AgInSe2 and CuInS2 compounds. For example, the solidifying point of
CuInSe2 decreased by about 1301C with increasing
Se vapor pressure up to 760 Torr. The phasetransition point from chalcopyrite to sphalerite
structure decreased down to about 8001C as Se
composition increased at the (CuIn)–2Se system[13], while the transition point was found to bealmost ﬁxed at B8201C with varying Se vapor
pressure [14]. It is expected that the heterogeneousFig. 4. (a) VI vapor pressure dependence on solidifying pointsof several ternary compounds and (b) a photograph of the asgrown crystal by horizontal Bridgman method controlling Se
vapor pressure.

1991

phases in the CuInSe2 phase are not produced in
the region under 760 Torr of Se vapor pressure.
The solidifying point without applying Se vapor
pressure was 9961C in good agreement with that of
5 Torr. It is suggested that CuInSe2 crystals grownunder the applied Se vapor pressure of >5 Torrhave Se-rich compositions, while the crystals
grown under o5 Torr have the (CuIn)-rich compositions. This can be explained by the facts that
the Se-poor crystals grown under lower Se vapor
pressures (2–7 Torr) showed the n-type conduction, and the others (Se-rich crystals) showed thep-type conduction [15,16].
Fig. 4(b) shows a photograph of the as-grown
crystal by horizontal Bridgman method controlling Se vapor pressure. The part of a Cu+In
mixture was ﬁrst heated to 7001C and thensolidiﬁed to make a CuIn alloy. Next, the CuIn
alloy in the high-temperature zone was heated up
to 10201C, while the low-temperature zone washeated to a temperature corresponding to thedesired Se vapor pressure. At the high-temperaturezone, the CuIn phase was selenized to form the
CuInSe2 phase. Then, the temperature gradient of
31C/cm was moved electrically at a speed of about
1 cm/h. All portions of bulk crystal grown from‘‘T’’ to ‘‘E’’ in Fig. 4(b) had a single phase of thechalcopyrite structure and no extra XRD lines
were observed. It is seen that the single crystals of
p-type conduction with large Hall coefﬁcients andmobilities were prepared at Se vapor pressuresfrom 10 to 25 Torr [16]. Here, it was shown in viewof the phase diagram of CuIn–2Se system [13] thatsingle crystals of high quality could be grown bycontrolling the Se vapor pressure. The crystals
contained no cracks and twins so that the Hall
effect could be successfully measured down toabout 20 K [16,17].
In addition, we attempted the growth of CuInS2
bulk single crystals by the same preparation
method as that of CuInSe2 [3]. On visual inspection, the crystallinity of the bulk crystals became
better with decreasing S vapor pressure down to
200 Torr. In other words, the samples prepared
under higher S vapor pressures contained many
voids and cracks, and single crystals of better
crystalline quality were grown under S vapor
pressure around 200 Torr.

1992

H. Matsushita et al. / Journal of Crystal Growth 237–239 (2002) 1986–1992

5. Summary(1) Prior to the growth of better quality single
crystals of multinary compounds, we haveinvestigated the formation mechanisms, i.e.,the chemical reaction process forming thesingle phase. For the most suitable preparation
method, the selenization or sulfurization
method of a CuIn alloy was devised to growsingle crystals of CuInSe2 or CuInS2, respectively, but at the same time it was shown that
this was not the case for CuGaSe2.
(2) To obtain a CuGaSe2 single crystal of higher
quality, where the chalcopyrite phase isformed through a peritectic reaction from the(sphalerite+liquid) phase to the chalcopyrite
phase, the solution growth of CuGaSe2 hasbeen performed based on the phase diagramsof the Cu2Se–CuGaSe2 and CuSe–CuGaSe2
systems. The results showed that large single
crystals could be grown better from a CuSe
solvent than from a Cu2Se solvent. On theother hand, we attempted to grow CuInSe2
single crystals using Sb2Se3 as a solvent at
temperatures below the solid-state phase transition. The phase diagram of the Sb2Se3–
CuInSe2 system showed that an Sb2Se3 solvent
was suitable for the growth of CuInSe2
crystals, which was also proved to be correct
for the actual crystal growth.
(3) It is sometimes effective to grow bulk single
crystals of multinary selenides and sulﬁdes byapplying VI vapor pressure, since the solidifying points are found to be sensitive to the VI
vapor pressure. For example, in the case of
CuInSe2, it was shown that the single crystalsof high quality without cracks and twins could
be grown by controlling Se vapor pressure. In
addition, the crystal growth of CuInS2 was
performed by the same preparation method asthat of CuInSe2.
Finally, we also described the synthesis solute
diffusion method by controlling the growth rate
for the single crystal growth of CuInSe2 [18]. The
CuInSe2 phase precipitated from CuIn and Se
solutions at temperatures below the melting pointof CuInSe2 as was predicted by the phase diagramsof the CuIn–2Se system.
Recently, we have been applying the investigations mentioned above to grow bulk single crystalsof Cu-based chalcopyrite-like quaternary compounds [19,20].

References[1] H. Matsushita, T. Takizawa, Jpn. J. Appl. Phys. 34 (1995)
4699.
[2] H. Matsushita, H. Jitsukawa, T. Takizawa, Jpn. J. Appl.
Phys. 35 (1996) 3830.
[3] H. Matsushita, T. Mihira, T. Takizawa, J. Crystal Growth
197 (1999) 169.
[4] F.A. Shunk, Second Supplement to the Constitution of
Binary Alloys, McGraw-Hill, New York, 1969.
[5] M. Hansen, Constitution of Binary Alloys, McGraw-Hill,
New York, 1958.
[6] J.C. Mikkelsen Jr., J. Electron. Mater. 10 (1981) 541.
[7] L.S. Palatnik, E.K. Belova, Izu. Acad. Nauk. SSSR.,
Neorgan Mater. 3 (1967) 2194.
[8] H. Jitsukawa, H. Matsushita, T. Takizawa, J. Crystal
Growth 186 (1998) 587.
[9] H. Matsushita, H. Jitsukawa, H. Sugano, T. Takizawa, S.
Endo, Institutional Physics Conference Series No 152:
Proceedings of the 11th International Conference on
Ternary and Multinary Compounds, Salford, 1997, p. 535.
[10] S. Ai, H. Matsushita, A. Katsui, J. Mater. Sci. 35 (2000)
2553.
[11] S.R. Sashital, A.L. Gentile, J. Crystal Growth 69 (1984)379.
[12] M.L. Fearheiley, Sol. Cell 16 (1986) 91.
[13] H. Matsushita, T. Takizawa, J. Crystal Growth 179 (1997)
503.
[14] H. Matsushita, H. Jitsukawa, T. Takizawa, Transac.
Mater. Res. Soc. Japan 20 (1996) 715.
[15] H. Matsushita, T. Suzuki, S. Endo, T. Irie, Jpn. J. Appl.
Phys. 34 (1995) 3774.
[16] H. Matsushita, T. Takizawa, J. Crystal Growth 160 (1996)
71.
[17] H. Matsushita, T. Takizawa, Jpn. J. Appl. Phys. 37 (1998)4258.
[18] H. Matsushita, S. Ai, A. Katsui, J. Crystal Growth 224(2001) 95.
[19] H. Matsushita, T. Maeda, A. Katsui, T. Takizawa, J.
Crystal Growth 208 (2000) 416.
[20] H. Matsushita, T. Maeda, A. Katsui, T. Takizawa, Jpn.
J. Appl. Phys. 39; Proceedings of the 12th International
Conference on Ternary and Multinary Compounds,
Hsinchu, 2000, p. 62.

Journal of Crystal Growth 237–239 (2002) 2009–2013

Single-crystal growth and optical properties of undoped andCe3þ doped CaGa2 S4
C. Hidaka, T. Takizawa*
Department of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan

Abstract
To improve the crystallinity of CaGa2 S4 single crystals, we have grown the crystals under various conditions by thehorizontal Bridgman method using a travelling temperature gradient. If we lower the growth speed to o0:5 cm=h while
keeping the growth temperature close to but a little higher than the melting point, cracks and voids in the crystals aresubstantially reduced. A carbon boat is adopted in order to avoid the reaction of an ampoule with the material solution,
which is found effective to improve the quality of a grown crystal. However, an absorption band with a peak at 3.2 eV
newly emerges to turn a grown crystal yellowish.
Absorption spectra of Ce3þ -doped crystals are also measured. As a result, the energy separation between the 5dsublevels of Ce3þ ion, i.e., T2g and Eg is ﬁrst estimated as 0.8 eV. r 2002 Elsevier Science B.V. All rights reserved.
PACS: 81.10.hKeywords: A1. Doping; A2. Bridgman technique; A2. Growth from melt; A2. Single crystal growth; B1. Calcium compounds;
B1. Sulﬁdes1. Introduction
alkalineearth
thiogallates
Ce3þ -doped(MGa2 S4 ; M=Ca, Sr, Ba) have been regarded as
host materials for blue electro-luminescent devices.
So far, thin ﬁlms of these thiogallates have been
exclusively investigated, because they were thecandidates closest to practical applications, since
the ﬁrst EL device using CaGa2 S4 :Ce3þ thin ﬁlms
was fabricated by Barrow et al. in 1993 [1].

*Corresponding author. Tel.: +81-3-5317-9733; fax: +81-35317-9432.
E-mail address: takiz@chs.nihon-u.ac.jp (T. Takizawa).

Another interesting property found in thesematerials is a laser oscillation which has been ﬁrst
recognized in a Eu2þ -doped CaGa2 S4 single crystal[2]. In the case of Ce3þ doping, a similar
phenomenon is also expected in the same orsimilar thiogallates. However, to check the usefulness of the material for laser devices, a large hostsingle crystal which is free from strain, voids andcracks is needed. It should also be homogeneouswith respect to the distribution of the rare earth
element doped. Thus, growing high-quality single
crystals is highly desired from both practical andbasic research points of view.
Driven by the motivations above, we haveconstructed the pseudo-binary phase diagrams of0022-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 0 2 4 8 ( 0 1 ) 0 2 2 4 2 - 4

2010

C. Hidaka, T. Takizawa / Journal of Crystal Growth 237–239 (2002) 2009–2013

the CaS–Ga2 S3 and SrS–Ga2 S3 systems using thedifferential thermal analysis (DTA) and powder
X-ray diffraction [3,4]. It is found that bothmaterials have congruent melting points witheutectic reactions between SrGa2 S4 or CaGa2 S4(50 mol% Ga2 S3 ) and Ga2 S3 (100 mol% Ga2 S3 ). It
has already been reported that alkaline earth
thiogallates have high melting points of > 11501C
which is too high to utilize quartz ampoules for the
crystal growth. One of the methods to overcome
this difﬁculty is the single-crystal growth using aself-ﬂux, whereby single crystals can be grown attemperatures lower than a melting point.
In the processes of constructing the phase
diagrams, the melting points of CaGa2 S4and SrGa2 S4 have been exactly determined as11321C and 12301C, respectively. The former
value is low enough to use a quartz ampoule forthe crystal growth. Thus, we try to growsingle crystals of CaGa2 S4 by the melt method
using a vacuum-sealed quartz ampoule. However,in the case of SrGa2 S4 ; the melting point is toohigh to use quartz, and the ﬂux method (Ga2 S3 isused as a ﬂux) should be adopted instead. In thiscase, even if a conventional furnace with anappropriate temperature gradient is used, compositional deviation may take place along thegrowing direction, and special care should betaken to keep the homogeneity of the Ce3þconcentration in the growing process. Here, forsimplicity, we conﬁne ourselves only to CaGa2 S4
and describe its crystal growth in detail together with its optical absorption and photoluminescence (PL).
A single, transparent and colorless crystal of
CaGa2 S4 has been successfully grown, and Ce3þ
doping has also been carried out [4]. However, theresultant crystals contained many voids andcracks. In addition, as the amount of Ce3þ content
was increased, the crystallinity became worse andif the content was increased more than 1.0 wt%,
crystals were colored too blackish to be used for
optical measurement.
In order to improve the crystallinity of undoped
CaGa2 S4 ; we searched for the proper temperatureand the growth speed for single-crystal growth of
CaGa2 S4 : In what follows, we report the results
ever obtained and also the relation between doping

content and crystallinity as well as the opticalabsorption and PL of the resultant crystals.

2. Crystal growth of CaGa2 S4 in a horizontal
furnace
Two elements of Ca, S and a compound of
Ga2 S3 were weighed approximately to 7 g. The
mixtures of Ca þ Ga2 S3 and sulfur element wereseparately set in both sides of a quartz ampoule of
13 mm f  300 mm: The Ca þ Ga2 S3 side wascontrolled at 4001C and the sulfur side at 3001C
for 24 h. After this treatment, the precursor was
synthesized by heating the whole ampoule up to11201C. The details were described in a previous
paper [4]. The precursor thus prepared was divided
into two or three parts. Each part was poured intoa respective carbon boat and sealed in anotherampoule and was grown under various conditions
described below. A carbon boat was used forpreventing reaction between an ampoule and theprecursor at high temperature. Growth speeds
were chosen at 0:5 cm=h and 0:25 cm=h: Threesolidifying temperatures, 11301C, 11321C (melting
point) and 11351C were adopted to grow single
crystals. The melts were kept for 1 h at thesetemperatures, respectively, and cooled down ateach speed in a horizontal Bridgman furnace. Thus
six different types of samples were grown. The
solidifying temperature 11351C, a little higher thanthe melting point (11321C) together with theslower growth speed gave the best result of all.
Temperature much higher than the melting point
resulted in many cracks in the grown crystals.
Fig. 1(a) shows a photograph of a product grown
at a speed of 0:25 cm=h at 11321C. It wasapproximately 2 cm in length and yellow in color.
As shown in this ﬁgure, it was like a sinteredpolycrystal composed of small grains. Fig. 1(b)shows a photograph of a crystal prepared at
0.25 cm/h at 11351C. In this case, the crystal wastransparent for the whole length. The grain size ofthe resultant crystals was plotted against solidifying temperatures at two growing speeds (Fig. 2). It
was estimated by measuring the maximum diameter of single grains in a crystal under an optical
microscope. As the maximum temperature of the

C. Hidaka, T. Takizawa / Journal of Crystal Growth 237–239 (2002) 2009–2013
12

2011

melting point

Length [mm]1080.25cm/h
0.50cm/h

6
4
1130

1131

1132

1133

1134

1135

Temperature [°C]Fig. 3. Variation of the length of a single domain in a grown
crystal along the growth direction vs. the maximum temperature of each melt.

Fig. 1. Photographs of single crystals grown at a speed of
0.25 cm/h from: (a) 11321C and (b) 11351C.
5.0

Grain size [mm]4.5

melting point

4.0
0.25cm/h
0.50cm/h

3.5
3.0

0.25 cm/h, the size of a single domain became
larger with increasing temperature. On the other
hand, those of the single crystals grown at
0.50 cm/h did not show remarkable variations
with solidifying temperature. In conclusion, thesize of a single domain in a grown crystal along the
growth direction was determined mainly by thegrowth speed. The crystals prepared by thismethod were a little opaque and yellowish, while
the crystals grown without a carbon boat wastransparent and colorless as reported in a previous
paper [4]. To investigate the origin of the yellowish
color of the crystals grown in a carbon boat,
optical absorption spectra were measured and theresults are discussed in the next section.

2.5
2.0
1130

1132

1134

1136

1138

Temperature [°C]Fig. 2. Maximum grain sizes in crystals grown from different
temperature vs. the maximum temperature of each melt.

melt was increased and the growth speed was
slowed, a grain with larger size was obtained.
Fig. 3 shows the relationship between the lengthsof single-crystal domains along the growth direction and solidifying temperatures. At a speed of

3. Absorption spectra of a crystal grown in a carbon
or a quartz boat
Absorption spectra were measured using adeuterium lamp as a light source. Light from amonochromator (NALUMI RM-23-I) was transmitted through a sample attached to a cold head ofa cryostat and detected by a photomultiplier(HAMAMATSU R562). Temperature was varied
between 10 and 300 K. Fig. 4 shows light absorption spectra of two respective single crystals at a
speed of 0.50 cm/h at 11351C. One is grown in a
carbon boat and the other in a quartz boat coatedC. Hidaka, T. Takizawa / Journal of Crystal Growth 237–239 (2002) 2009–2013

200

4.40

Optical band gap [eV]-1

Absorption coefficient [cm ]

2012

300K
150
quartz boat with carbon film

100
50
0

carbon boat

4.35
4.30
4.25
4.20
4.15

2.0

2.5

3.0

3.5

4.0

0

4.5

50

100

Photon energy [eV]Fig. 4. Absorption spectra of crystals grown in a carbon boat
and a quartz boat coated with carbon ﬁlm.

4. Absorption spectra of Ce3þ -doped crystals
In crystals doped with Ce3þ ; absorption spectra
were also observed. The crystals used in thismeasurement were grown in quartz boats. The
concentration of Ce3þ was varied from 0.1 to
1.5 wt%: Absorption spectra of the crystals with

200

250

300

Fig. 5. Temperature variation of the band edge of an undoped
crystal.

-1

Absorption coefficient [cm ]140with carbon ﬁlm. The crystal grown in a quartz
boat shows only the fundamental absorption. In
contrast, an absorption band with a peak at 3.2 eV
was observed in the crystal grown in a carbon
boat. By measuring temperature variation of theabsorption at 3.2 eV, it was found that the peak
position, shape of the absorption spectrum showedalmost no change with temperature. The origin of
this absorption was not made clear at this stage,
but was considered to be related with the
impurities incorporated from a carbon boat.
Fig. 5 shows temperature variation of the bandedge of an undoped crystal with temperature. Theband edge was estimated by extrapolating theslope of the square of absorption coefﬁcientagainst photon energy to zero absorption. From
the temperature gradient > 100 K; the temperature
coefﬁcient of the absorption band edge wasestimated as 1:2  103 eV=K: The coefﬁcient isalmost the same as that of the ionic crystals suchas AgCl, suggesting that the CaGa2 S4 crystal has astrong ionic character.

150

Temperature [K]

120
100

0.1wt%
0.2wt%
0.4wt%
0.5wt%
0.8wt%
1.5wt%

80
60
40
20
0

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

Photon energy [eV]Fig. 6. Absorption spectra of crystals with various Ce3þconcentrations.

various Ce3þ concentration at room temperatureare shown in Fig. 6. Two absorption bands wereobserved. One has a peak at 2.9 eV and the otherappears as a shoulder near the band edge. The
intensities of the absorption of the two bands
increased with increasing Ce3þ concentration. The
absorption band around 2.9 eV was already known
to arise from Ce3þ and was attributed to theoptical transition between 4f and 5d states. The 4f
states of Ce3þ ions split into the spin–orbit pairconsisting of 2 F7=2 and 2 F5=2 ; while the upper 5dstates split into an upper Eg and a lower T2g due tothe crystal ﬁeld. The absorption around 2.9 eV is
assigned to the transition from 2 F7=2 to T2g : The

C. Hidaka, T. Takizawa / Journal of Crystal Growth 237–239 (2002) 2009–2013

absorption band appearing as a shoulder near thefundamental absorption edge was observed for theﬁrst time, thanks to the high quality of the crystal
used in this experiment. The new band isconsidered to be the transition from 2 F7=2 to Eg :Now, the difference between Eg and T2g can be
estimated as 0.8 eV.

2013

Absorption spectra were measured for Ce3þ doped crystals grown in quartz boats and two
absorptions were found at 2.9 eV and near theband edge. As a result, the energy separation
between T2g and Eg of the 5d multiplets of Ce3þwas estimated as 0.8 eV for the ﬁrst time.

Acknowledgements
5. Conclusion
We have grown single crystals of CaGa2 S4under various conditions. A slower growth speed
and higher temperature of the melt were found tobe effective in growing a large single crystal. The
growth speed was also a key factor to make a large
single domain along the growth direction.
Although a carbon boat was used to avoid
reaction of a quartz ampoule with the crystal,
the resultant crystal became a little opaque andyellowish, giving rise to a new absorption bandaround 3.2 eV. The origin of the absorption isbelieved to be due to the contaminations from a
carbon boat.

This work was partially supported by the
Research Grant from Nihon University.

References[1] W.A. Barrow, R.C. Coovert, E. Dickey, C.N. King, C.
Laakso, S.S. Sun, R.T. Tuenge, R. Wetross, J. Kane, SID
Int. Symp. Dig. (1993) 761.
[2] S. Iida, T. Matsumoto, N.T. Mamedov, Y. Maruyama, A.I.
Bairamov, B.G. Tagiev, O.B. Tagiev, R.B. Dzhabbarov,
Jpn. J. Appl. Phys. 36 (1997) L857.
[3] C. Komatsu, T. Takizawa, J. Crystal Growth 210 (2000)
677.
[4] C. Komatsu-Hidaka, T. Takizawa, J. Crystal Growth
222–223 (2001) 574.

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<  _   =   _  }       }                    }           } Z"Z O    Z [ >   < \]$ ^#_ \]

'  }      
' } !
 
> '!    # '!   # _! _ #   !
 !   !  >? >~>!
X ! "  # '!  # '! '  # !  <#  !  !   ! >^ XZZZ ~!

^ ! "  # '!  # '! '  # !  <#  
}      }                #    ^>~^ XZZZ X^~X^!
 !  <# '! < # '! '  #     X~X XZZZ ~?!
 ! # '!! #  ! =! >Z >?>>!
? '!  #         # "#   # >Z!

    ^~^?Z XZZ> >~! !  

   } 
~~ ~    
!  



# "! `  # # "!  # '! '   #&# !  <          !    "  #$ !&&   ' *+   ##$ + =   "  # !&' Q "   '  `   O +j "  #%% !&=  >?    XZZZ\   X^ _  XZZZ
~~ ~  }                           | !      #  ~~ ~    <       { #               }  !    
      {         | !   #           _#       |          ! Ó XZZ>         !!
>?< @ !?Z!\ !?Z!
OQ @ \    \  |        =~~ ~ = #
 # #      }       '  
>            #             X!  #             =~~ ~
    !        }    }                #                 &      !  >^^X!
;W @     ! ! '! '  !

  }  !                          
! `          ~~ ~     !               {           _    _ <    !

            X  ^   XZ    X  X >Z}    '  #   }       >!   ZX>^Z>   }   Ó XZZ>          !!
  Z  X >    ^   Z >  Z Z     ZX

qZ ? W   Z [ >   < \]$ ^#_ #]

  
} X>  >  >Z? ^ }     !     #
 #  ! "       > "        ¡¢_ !             #          ^!  _        !     ! `   }{    >X <       X!^ !   
    _ <       } <   }    ¡¢_   ¡   _ !

    
! >      }      }       } >!>       } _  }  ~~ ~    !            }      }      !               }  Z  X!^ !  <  #  
#         |!
! X       }     #         

! >!      }  } '   ~~ ~       }    !

! X!      }              }       !

       }            !                  !      
             #        }   !     } _                }   #  
{          }  
!
`         
 #         !
       }  
|  }    }  
#                 }  !        
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  
Z  Z # #       }  
#  
 {       }  #    !
! ^         "   ! `       # 

qZ ? W   Z [ >   < \]$ ^#_ #]

! ^!       }    }     
 !

      !
  }   }              !
 #       #        #                !    #  
    }      }     !      #   }                           }  
  ! !        } 
   <     "!         |    ^ !    _    #
         _  !  
         
|     "#      } <           |    "! !        }     !      >     !        }             }  #     ~~ ~        } >! !      #   }    }   >!#~~ ~     }   
'        }  ! `      }   } ^! !     }          <        "!

! !      }       !      } >    !         >!     !

 !        }    #      
    } >ZZ  X !       } ># ^  ?   >!?# ?!?
 X! "#   !            !       #                      }_   !   { #          _       }      !



 

qZ ? W   Z [ >   < \]$ ^#_ #]

`        } }  '   ~~
 ~         _!      _      }
}           ! `      {  !                
|     "!   #          _   ! `        |             !
                _  

<  _   =   _  }       }                    }           } '  }      
' } !

 
> !!  # !  # !   # '! '  # !  !
! ? > ?^^!
X '! '  # !!  # !  # !  # ! `<#! " < # !  # ! ! !  ! ^^ >
>!
^ !'! # !  ! X >? >X!
 ! " # !   # "! '#   !  !
  !  > Z?!
 ! ' # ! # ! # "! " # '! ' # !
! !  ! ^Z >> ^X!

    ^~^?Z XZZ> ~>! !        } Z^^ Z^^Z^^X ^      ! '
#&# '!=! "    # '! '  # '! '   # !  <          !    "  #$ !&  &    "   ?[  > &  $% {O$ |+ {W&   ' *+     &   "   < ##$ + =  
"  # !&=  >?    XZZZ\   >^   XZZ>           
       
    Z!>     =X  ^     =       
| !                 !               <         | ! Ó XZZ>          !!
>?< @ !X!{\ !X!\ !?X!_OQ @     \ =X  ^    \  |         }              !  #           <   
 D    #    
££ | ¤¤  ££ ¤¤ >#X!   |                   !
= # X  ^  ~~ ~  }           &      !  >^^^X!
;W @    ! ! ! ' !

<           
}   >#^#        
| ! } #      
~~ ~       
|  #!      }      !       
|          #              !         <          | !                     #       }       }     |   ~~ ~ ?!
  #      } 
=~~ ~         | #    =     #  #  !

ZX>^Z>   }   Ó XZZ>          !!
  Z  X >    ^   Z >  Z Z ^    >"Z =   Z [ >   < \]$ ^#_ %]#    `  >X^            '   !
>X^            >!       X>> >Z~
Z      Z!   #      >Z } X>>#      } #  #  !
      }           
    `       }     ¡¢_   ¡  _ #   ¥!                           ^ " >      \         } Z "!            }         ¡¢_  #  }     !   }   } #       > !

    
! >    ± }     }>X^  X>>  !        |        
 !          
 >Z# ^Z  Z  }  X>>    X>>
    #         }!  } XZ  Z           X>>   ! '  #   X>>      }            |    }  XZ  }  X>>!  

! >!    }        } 
>X^  X>>    }          "!

  |   }          #         }   }                  | !   #   Z    X>># }           !
! X       }    }  >X^ X>>    
!            }             X>> !        }              =  !   #        <              >X^ #       
 >X^      |  ?!      >X^      X        #    |   >X^         }       _   ! !     }      } >X^     }        }      |   >
     '  
>X^
>X^

 X>> X>> 

X>>        

#  #    X>>

>Z~Z
>Z

Z!
Z!

~
XX?# XZ"Z =   Z [ >   < \]$ ^#_ %]#! X!    }       >X^  X>>>Z±Z         
!             \  `   }       |   !

  !        =         }    | 
 =>X^  =~     >Z!
                       #             Z   X>>!                     | !

! !    }       >X^ >Z  } X>>   }    !

 }     }! ^    ±>X^ >Z   X>>!       =  } X>>     XX?  X!            | !     ! #              
 !     }      >X^#                      |  ?#             
|       }       #        "     ! >!
 #    ! >>                    !                !

 

! ^!  ~  }  >X^ >Z     }      } X>>   "!





`       } <       } _   } >X^      
| !          #

"Z =   Z [ >   < \]$ ^#_ %]#                | !   #   }    }          |       !     #        #      |      }          
 !



                _  
<  _     =   _  }       }                   }            }'  }      
' } !

> 
> '!=! "   # '! ' # !  # "! ` #
!    # '! '  #   !  !   !
>X > X!
X ! "# !=!  # !    # ! # ! '
 # ! # ! `#  ! =!   > Z^!
^ ! ` }# !!  # ! "}# =! '# !
 #  ! =!  ? > ?^Z!
 '! '  # !  # !  # !!  #   !
 !   !  >? >Z>!
 ¥!! # !!   # !`! #     XX~X
> X>>!
? ! ' # '!=! "   # !`! # '! '  #!  <#   !  !   ! >^ XZZZ Z!
 '! ' # '!=! "   # !  # '! ' #   !  !   ! >> > >^!
 !  # !!  # "! # !  # '! '  #    X?^ >? ^?!
 '! _ # !'!   # _!!  #  ^? >Z ^^X!
>Z '! '  # !  # !    # ! "  # !
 # !!  #     XXX > ^>!
>> "!  # '! ' # "! ` # '! '  #  !  !   ! >^ XZZZ ??!

    ^~^?Z XZZ> ~! !  

 } 

!   #&    =X ^

 # '! '  # '! '   # !  < # "!   &   '       !    "  #$% !&*+    ";< ##$ + =   "  # !&=  >?    XZZZ\   >^   XZZ> 
     }    |      Z^^  Z^^ Z^^ X  ^        # X  ^          X  ^      ! ` }            }          
 !     |  }        }        
 ! Ó XZZ>      !!    !
>?< @ !?Z!\ !?Z!
OQ @ \    \   \ =X  ^       =X  ^  = #
#         |   <     >!     =X  ^    => X  ^ =>X^      ! ` =~~ ~            # =  =>X^            =X  ^                  #      }     |  >!           #          | }   }    !   &      ! ! >^^X\ } >^^X!
;W @      ! ! !    !

         }   X!                 }   |  }       ^!
     #      }      
                       }  !

          Z^^  Z^^ Z^^ X  ^ >X^  >Z   X>>    X?
"# X   >X^  XZ   XX   > "#  X  ^  >X^ Z   X>>    > "!  
    >  >?  Z ^  XX  XZ >Z ^ #  XZ  >?  Z^ ^ #   !

ZX>^Z>   }   Ó XZZ>      !!    !
  Z  X >    ^   Z >  Z Z ^  ?  ¥?

`Z ; W    Z [ >   < \]$ ^#_ ]\        }         ¡   _ '' ¡¢_  !    }       
XX  !     
 >    }{    >X <!  _     ! !         +          !

    
! >        }  Z "#      }             !    >X^     
 # >X^        >X^     !
! X      }           }  Z " }    !   <          > }       _ #   <  
       Z "!           }           X!  

! >! '    !

}   Z " }  

! X!   }    Z " }    !               !

        !
>X^          #  >X^               !
! ^        }       }  }    !
`      <       }  }    #    
! ^!               !    } >X^                !       |  }        #              }      ^! } #                    |     !
"  !              }     }  >X^   !   #                     !            #              ! `         #       }`Z ; W    Z [ >   < \]$ ^#_ ]\ !                 }          !

!

`     }      >X^       #>X^        
>X^      !   }        }           !                }         !

! ^!         <        }  }    !                !

     } #            !     #      |       =  =>X^     !                   }      #        }         }     `  _! !   }     >X^!                _ 
<  _     =  
 _  }      }                      }           } '  }      
' } !

 
> '! '  # !!  # !  # !  # ! `<# !
" < # !  # ! ! !  ! ^^ > >!
X ! #   !  !   ! >Z > X^!
^ !! #  ! =!   > ?X^!
 !'!  # =!!  _ # "!! # !!  
# !! ` < < # !  ! !  > X^!
 ! "# !=!  # !    # ! # ! ' 
 # ! # ! `#  ! =!   > Z^!

J f

Ph dgm f h G h 222 (2001) 574–578

S–G2S3  m d m  g h f
G2S4 g 

. Km-Hdk, . kz *
Department of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, JapanR  v d 6 J 2000;   d 2 Nv m  2000
mm d  . H

Abstract
W hv  d h  d- h dgm f h S–G2 S3  m  d     g  f
G2 S4 . B d  h dgm, g  d d h 0.1, 0.2, 0.4, 0.8 d 1.5 % 3þ  g  fm m  h hz Bdgm m hd. Phm     f h    m  d  m  m  . hv  f     gd g m  h h   d d f h ﬁm. H v , h m   d  3þh      h h d d   m h 0.4 %,  m   f h   g fm h v dg. # 2001 E v  S  B..  gh   v d.
PACS: 81.10.hKeywords:

S; G2 S3 ;G2 S4 ; Ph dgm; M  g h; Hz Bdgm m hd

1. Introduction
F g   v k  h    h   mg h f SG2 S4 [1], k ,  m  f G2 S4 .  m
 m  d d G2 S4 h  d  m f v  gh, d 
 gd d   mg dd f   m  f h f  d [2].
h   f     h   
h   v d  G2 S4 : E2þ g    d  h d  m hd [3].
  m d   g RE-d d*  dg h.  .: +81-3-3329-1151; f : +81-35317-9432.
E-mail address: kz@h.h-..j (. kz ).
0022-0248/01/$ -  f m  # 2001 E v  S  B..
PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 9 5 7 - X

G2 S4   gg  d  Id  . [4], hhh  gd dvg f  v  gh      g  d   v   g.
H  ,  hd    d h h    z d  f  g  f hgh q g .
H v ,   h  f SG2 S4 , g f hgh q hv    g   ,d h   k   h  
   f G2 S4 . N ,    hdgm f h  d-  m f S–
G2 S3  g  q d f h m  g h f
h .
I h  , ﬁ,   h hdgm f h
S–G2 S3  m  dhgh D v  d  d  X- dﬀ
  f d     f h  g h gh   v d.

C. Komatsu-Hidaka, T. Takizawa / Journal of Crystal Growth 222 (2001) 574–578

f G2 S4 : 3þ  h hz Bdgmm hd. D   md  h m
 m  hm   f h g3þ
f   
 d d hgg fm 0.1  1.5 %.

2. Phase diagram of the CaS–Ga2S3 systemh D m   h m    v   [5]. h   d f h D
m  m   ﬁ d  28 /m.    m f m d f d  md f G2 S3
gh d     h d d m
   g  ﬁ d h g g d   d  qz m f 7 mm1  40 mm d vm f 103 . h m hd f  
f G2 S3  h m    d    v  [1]. h   f f  qz m  d h  ﬁm  ﬁg   
. h  m  d  v  h m  f hm  fm kg  h d m . h d f  D m  m  z d   d  X- dﬀ m  m  g h -Ka  .
Fg. 1() h  D v   h g    50 d 75 m% G2 S3 . hm g  f h md   h575 g G2 S3  . h  k 9758
 fd  v  D v f hmd v 50 m% G2 S3 . Fg. 1()h   d  X- dﬀ   fh d f  D m  m , h h dﬀ    mz d  hm mm. h dﬀ   fm  mh 50 m% G2 S3   g m  h h  d X-   f G2 S4 [6]. F , mk d h d h   f G2 S3
Fg. 1(). I    h h dﬀ   fh md  h   v
50 m% G2 S3
 m d   f G2 S4
d G2 S3 .
Fg. 2() h  D v  f h md  75 d 100 m% G2 S3 . E   f
100 m% G2 S3 , h    d h g 
975, 9958 d  h m g .  Fg. 1(), h m g    h  g
G2 S3  ,  d d  h   Fg. 2(). Fg. 2() h   d  X- dﬀ
  f h d f  D m  m .
h dﬀ   f G2 S4  d d h g . I      h h md f h m   f G2 S3 d G2 S4 .
B d  h   , h  d- hdgm f h S–G2 S3  m  d d d h   Fg. 3 v  m  h f SG2 S4 .

Fg. 1. () D v  f 50–75 m% G2 S3  h g    h S–G2 S3  m. h h g d g    ﬁ d
 28 /m. () h  dg X-  d  dﬀ   mz d  h   v hgh   . h d d hG2 S3 h .

576

C. Komatsu-Hidaka, T. Takizawa / Journal of Crystal Growth 222 (2001) 574–578

Fg. 2. () D v  f 75.0–100 m% G2 S3  h g    h S–G2 S3  m. h h g d g   
ﬁ d  28 /m d () h  dg X-  d  dﬀ   mz d  h   v hgh   . h dg  d h G2 S4 h .

dg,   h d v f m d  m  v      d h m  g h  m  h ( ) g h m hd. B d  h d ,h  g h   fm d  h m 
m hd  h     , d h d  d  d  h    .

3. Crystal growth of CaGa2S4
Fg. 3. P d- h m.

dgm f h

S–G2 S3     fd  h  g fm
50  100 m% G2 S3 h h    
9758  75.0 m% G2 S3 . Sm  h  f
SG2 S4 , h  f- m hd  g G2 S3      mm d d f h g  g h f G2 S4 . H v , h m g f G2 S4 (11328 )   1008  h h f SG2 S4 (12308 ), d   
f h m  g h g  qz m . Idd, f RE  dg   q d, h m g h       h v h hmg    h  f SG2 S4 , II  m  g   d 3008
h h S  m ,m m  g h d  f qz   h h  f hh m  .
B kg      h  ,  d h   f G2 S4  h f g  d . F,    m  f (3N),
S(6N) d   -  d md f G2 S3 gh d  h hm  m  7 g    g g mh  . h   d   qzh+G2 S3 m  (8 mm1100 mm)  d h  ﬁmd . h        d f h qz m (13 mm1300 mm). h S  d        h h  d f h

577

C. Komatsu-Hidaka, T. Takizawa / Journal of Crystal Growth 222 (2001) 574–578

m hh  ﬁ   d d  vm f
106 .
h v d m      -zf , d h
+G2 S3   h  d 
4008 , h h f   k   3008 f
24 h. h  d   m      d S, . , S  m    d  h
+G2 S3 m   h qz . h , hh m h  d   11208 jv h m g  f G2 S3 d k  f 1 h.
h  h   f G2 S4  h z d. h    k   fm hm d gd, d  ﬁ d  h   d qz . h   gd   d  h  qz m
(13 mm1120 mm)  h m m   d  d  v. h  g h   fm d   vg h  m  f hm  11508 d  mkg   m  gd  f 78 /m d mvg h  m  ﬁ   [5]. h g h  d  0.5 m/h.
3þdg  md  m g  d  dqh h2 S3 f   . h, dg f 0.1, 0.2, 0.4, 0.8 d3þ  fm d.  d d
1.5 %h   h 0.5 % 3þ   ,    h d  ,  h v
0.5 %  m  d k hgh 
 . h   m h   f  d. I h    , f h   md g   h
1.5 %, h     m k d m  . I dd, h  hd mk d vd d .
I Fg. 4  h   hgh f  0.8 %3þd d . h    7 mm dm   d 5 mm   gh. I    v d
g h g h d , . ., h [1 0 0] d ,         vg f Fg. 4.

15M) h     f 23 mW, h  f hh   d d  1/10 g   ﬁ . h m  d  d  mhm(N LUMI RM-23-I) d d   d   hm (H M M SU
R562).
Fg. 5 h  m   f g 
f
G2 S4
h v
 .

Fg. 4. Phgh f   f  G2 S4 g d d h3þ
0.8 %g  fm m   h hz Bdgmm hd. h m h z  h ﬁg  1 mm  1 mm. hhk    5 mm. h   d  f md   vg h  g h g h d .

4. Emission spectra of CaGa2S4 : Ce3+h m   f G2 S4 : 3þm  d  m  m  . Sm   d   325 m H – d  (Omhm 3056-

Fg. 5. Em   f .

G2 S4 d d

h v

3þ

578

C. Komatsu-Hidaka, T. Takizawa / Journal of Crystal Growth 222 (2001) 574–578

Em    m  d  g  d  d m  ﬁ d    hvg 
m z . h m hd  d v d  hmg zhm fm h   d f  fg  d  m h ﬀ  f hm z f h .
I    fm Fg. 5 h h m  
    h   f  , d3þh    v 0.4 %. I v f    gd g m  h h   dd f h ﬁm [7]. O h , h v ,h h m fm h ﬁm       6.0 % f 3þ d h   v  [7].
I h    g h m hd,   m 3þmk     h dgh 1.5 %   d m  d  h  v . h h dg m hm  hgh 
 v  dﬀ     h m  g h d hh ﬁm  . I v
f h fmhg,    d h h k   hgh d d   f     d v    g d  d. S h3þ
hg m    h d f 
2þ   h f G2 S4 , v  h k hd  d d     h  k  h hg  .
H v , f h   f  hgh  m  d  h v , hm    d   , gvg dk   g    f h   m g , h m fm k  vd d h . h m f   m  dﬀ    h  . I    h h mqm  h m  g h  h d  m  mh hgh  h h  h h ﬁm.
   m  , h m v  m fmg       v   hgh  m  . h  f h  v   h ﬁm,  d  d  md v  hgh  m  h   m g  .
F m g d f h ﬀ  f3þ
dg  h m, h   k  dg  h dg   hd   q d.

H v ,   d ESR m  m     h m   hg f h f      d  , h hd  d d   d h      g h 
h  f h m   m  d.

5. Conclusion
W hv  d h  d- hdgm f h
S–G2 S3  m.
    fd  h m gfm 50–100 m% G2 S3 . h
G2 S4 md  fd   g  h h m g3þ-d d f 11328 . W hv g 
G2 S4 g  fm m   h hz Bdgm m hd.   d   h g   d. Fm h f h m    h  v 0.4 %,   d d hh  m f h   h   m  h h ﬁm  .

Acknowledgementsh k    d  h R  hG fm Nh Uv .

References[1]. Km, . kz , J.  G h 210 (2000)
677.
[2] W. . B , R. . v , E. Dk , .N. Kg, .
Lk, S.S. S, R..  g , R. W , J. K , 1993
SID I  Smm Dg , 1993, . 761.
[3] S. Id, . Mm, N.. Mm dv, Y. Mm, .I.
Bmv, B.G. g v, O.B. g v, R.B. Dzhv,
J. J. . Ph. 36 (1997) L857.
[4] S. Id: v mm.
[5] H. Mh, . kz , J. J. . Ph. 34 (1995)
4699.
[6] .E. P  , J. . Bg, J. E h m. S. 119 (1972) 230.
[7] S.S. S, R..  g , J. K , M. Lg, J. E h m.
S. 141 (1994) 2877.

ARTICLE IN PRESS

Journal of Magnetism and Magnetic Materials 272–276 (2004) 216–217

Pressure effect on the antiferromagnetic transition temperature
in CuFeO2
H. Takahashia,*, Y. Motegia, R. Tsuchiganea, M. HasegawabaCollege of Humanities and Sciences, Nihon University, Sakurajousui, Setagaya-ku, Tokyo 156-8550, Japanb
Institute for Material Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan

Abstract
Effect of pressure on the magnetic transition temperature of CuFeO2 with a delafossite-type structure has been
investigated using a piston-cylinder-type high-pressure apparatus designed for SQUID magnetometer. CuFeO2 having
triangular layer of magnetic Fe3+ shows the successive antiferromagnetic transition at 13 K (TN1) and at 9 K (TN2). It isfound that both transition temperatures decrease with applying pressure up to 0.7 GPa at a rate of 1 K/GPa.
r 2003 Elsevier B.V. All rights reserved.
PACS: 74.62.Fj; 75.30.Kz; 75.50.Ee
Keywords: Delafossite; CuFeO2; High pressure; Spin frustration

Since the high-TC superconductor was discovered,great attention has been paid to low-dimensionaltransition metal oxides, from the view of strongly
correlated electron systems. CuFeO2 with a delafossitetype structure has been attractive because of its lowdimensional triangular structure. The delafossite structure with space group R3m consists of respective
hexagonal layers. CuFeO2 has magnetic Fe3+ layers,which form a layered triangular lattice frustrated
antiferromagnet, separated by nonmagnetic Cu+ andO2 layers. In a frustrated system, the magnetic phasetransitions take place under a subtle balance of magnetic
interactions. CuFeO2 exhibits two successive antiferromagnetic transitions at 13 K (TN1) and 9 K (TN2) [1].
Mitsuda et al. [2] determined the magnetic structure of
CuFeO2 by neutron diffraction studies. They reported
that the magnetic ground state has a four-sublattice
antiferromanetic structure in which spins are collinear
and parallel to the c-axis, and the high-temperature
antiferromagnetic phase is partially distorted. Moreover, they indicated that the Ising character of Fe3+ inthe antiferromagnetic phases is unusual. Thus the origin*Corresponding author. Tel.: +81-3-3329-1151; fax: +81-35317-9432.
E-mail address: hiroki@chs.nihon-u.ac.jp (H. Takahashi).

of the magnetic orderings is considered to be very
complicated.
Ajiro et al. [3] and Kasahara et al. [4] studied impurity
effect on the stability of the ground-state spin conﬁguration in CuFeO2. They substituted magnetic Cr3+ andnonmagnetic Al3+ to Fe, and reported that a small
impurity affects the magnetic states strongly. Hasegawa
et al. [5] reported that the oxygen nonstoichiometry
largely affects the antiferromagnetism of CuFeO2 single
crystals. Oxygen nonstoichiometry accompanies changesof cation valences and lattice parameters. In this way,
the slight disturbance of the triangular spin latticestrongly affects the magnetic interactions.
The pressure effect is also expected to affect themagnetic state. Zhao et al. [6] carried out X-ray
diffraction study of CuFeO2 under high pressure up to
10 GPa. From the X-ray experiments, they reported nostructural transition and indicated that the a-axis isabout 3.9 times more compressible than c-axis. However, this situation seems strange if this anisotropic
compression is compared to cuprate superconductors, inwhich c-axis is usually more compressible than a-axis,
except for (La, Sr)2CuO4 which accompanies a tilting of
CuO6 octahedron with applying pressure [7].
In this study, we report the effect of pressure on theantiferromagnetic transition temperature of CuFeO2.

0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2003.11.084

ARTICLE IN PRESS
H. Takahashi et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 216–217

217

Fig. 1. DC susceptibility of CuFeO2. TN1 and TN2 are indicatedby arrows.
Fig. 2. Pressure dependence of TN1 and TN2.

Single crystal of CuFeO2 was grown by the ﬂoating-zone
method described elsewhere [8]. Magnetic susceptibility
was measured with a SQUID magnetometer (Quantum
Design MPMS-XL). A piston-cylinder-type high-pressure apparatus made by Cu–Be alloy designed for
SQUID magnetometer was used.
Fig. 1 shows the magnetic susceptibility of CuFeO2, in
which TN1 and TN2 are observed. The TN1 and TN2
decrease with pressure up to 0.7 GPa at a rate of 1 K/
GPa, as shown in Figs. 1 and 2. During the highpressure measurements, the shape of anomalies accompanied with transitions in w(T) curve does not change.
Suppression of TN1 and TN2 was also observed when
excess oxygen is introduced to CuFeO2 [5]. Since c/a
decreases with introduction of excess oxygen while c/a
increases with pressure, the present results cannot be
explained by a single source about crystal structure.
However, large change of intra-layer magnetic interactions is suggested from the high-pressure X-ray results,
in which the a-axis is about 3.9 times more compressible
than c-axis. If the TN1 and TN2 decrease linearly at a rateof 1 K/GPa, it disappears at 10 GPa. Then it is very
interesting to perform high-pressure studies at morethan 10 GPa, since a new magnetic phase can be
expected at the pressure where the magnetic ordering
state disappears, as observed in UGe2 [9]. From thepreliminary electrical resistivity measurements underhigh pressure, the resistivity decreases to 0.1 times value
at 10 GPa. The susceptibility and electrical resistivity
measurements are in progress at higher pressures.

References[1] M. Mekata, N. Yaguchi, T. Takagi, S. Mitsuda,
H. Yoshizawa, J. Magn. Magn. Mater. 104–107 (1992) 823.
[2] S. Mitsuda, H. Yoshizaki, N. Yaguchi, M. Mekata, J. Phys.
Soc. Japan 60 (1991) 1885.
[3] Y. Ajiro, K. Hanasaki, T. Asano, T. Takagi, M. Mekata,
H. Aruga-Katori, J. Phys. Soc. Japan 64 (1995) 3643.
[4] N. Kasahara, Y. Matsumoto, K. Tanaka, S. Mitsuda,
H. Yoshizawa, M. Mekata, unpublished.
[5] M. Hasegawa, M.I. Batrashevich, T.R. Zhao, H. Takei,
T. Goto, Phys. Rev. B 63 (2001) 184437.
[6] T.R. Zhao, M. Hasegawa, T. Kondo, T. Yagi, H. Takei,
Mater. Res. Bull. 32 (1997) 151.
[7] H. Takahashi, N. Mori, in: A.V. Narlikar (Eds.), Studies ofHigh Temperature Superconductors, Vol. 16, Nova Science
Publishers, Inc., New York, 1996.
[8] T.R. Zhou, M. Hasegawa, H. Takei, J. Crystal Growth 154(1995) 322.
[9] S.S. Saxena, et al., Nature 406 (2000) 587.

INSTITUTE OF PHYSICS PUBLISHING

JOURNAL OF PHYSICS: CONDENSED MATTER

J. Phys.: Condens. Matter 16 (2004) 3385–3400

PII: S0953-8984(04)75894-4

High pressure studies of anomalous electronic states ofY1−x Ux Pd3
Gendo Oomi1 , Tomoko Kagayama2, Yuji Aoki3 , Hideyuki Sato3 ,Yoshichika Ōnuki4 , Hiroki Takahashi5 and Nobuo Môri6
1 Department of Physics, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan
2 Research Centre for Materials Science at Extreme Conditions, Osaka University, Toyonaka,
Osaka 560-8531, Japan
3 Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
4 Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
5 Department of Physics, CHS, Nihon University, Setagaya-ku, Tokyo 156-8550, Japan
6 Department of Physics, Saitama University, Saitama 338-8570, Japan

Received 12 January 2004
Published 7 May 2004
Online at stacks.iop.org/JPhysCM/16/3385
DOI: 10.1088/0953-8984/16/20/010

Abstract
The electrical resistivity ρ(T ) of Y1−x Ux Pd3 (x = 0, 0.05 and 0.2) and thelattice constants for x = 0 have been measured at high pressure. It is foundthat the cubic Cu3 Au structure is stable up to 12 GPa at room temperature.
The Kondo temperature TK was extracted from the ρ(T ) curve and it was
found that it increases with pressure. A logarithmic temperature dependence
characteristic of the Kondo effect was found for x = 0.2 in the temperature
range above about 0.5TK . Fermi liquid behaviour in ρ(T ) for x = 0.05,
i.e., ρ(T ) ∝ T 2 , is observed and its stability at high pressure is discussed.
The pressure dependence of the Kondo temperature TK is discussed using theGrüneisen parameters at TK , K . It appears that the values of K are the samefor these two compounds (x = 0.05 and 0.2): K = 12. The T -linear behaviourin ρ(T ) for x = 0.2, which is characteristic behaviour for non-Fermi liquids,
is collapsed by an application of pressure and typical Fermi liquid quadratic
temperature dependence recovers at high pressure. From the result for x = 0.2,
the power n of the temperature in ρ(T ) ∝ T n is determined as 1.0 at ambientpressure and 1.9 at 5.8 GPa. It is pointed out that the hybridization effect due
to the application of pressure gives rise to a crossover from a non-Fermi liquidstate to Fermi liquid state. But the crossover temperature Tcr shows a pressure
dependence different from that predicted by the two-channel Kondo model.

1. Introduction
It has been reported that some intermetallic compounds including U or Ce show a lotof interesting electronic properties such as heavy fermions (HF), the Kondo effect and0953-8984/04/203385+16$30.00© 2004 IOP Publishing Ltd

Printed in the UK

3385

3386

G Oomi et al

superconductivity [1]. Among them, the compounds showing behaviour substantially different
from the normal Landau Fermi liquid (FL) type have been extensively studied [2–4]. The
electronic state displaying these behaviours has been called the ‘non-Fermi liquid’ (NFL)state. As for the electrical resistivity, ρ(T ) for these compounds shows a weak power law at
low temperatures, such as T n (n = 1–1.5) [5, 6], which is in sharp contrast to that for normal
FL behaviour: T 2 at low temperature. Anomalous behaviours have been observed for otherphysical quantities such as magnetic susceptibility and speciﬁc heat [3–5]. Several theoreticalmodels from different points of view for interpreting these anomalous properties have beenpresented [4]. But the origin of the NFL state has not been completely understood yet.
The instability of the NFL state under the inﬂuence of perturbation or changing the control
parameters has been studied extensively by many investigators [5–7]. In this area, high pressure
study of NFL gives us a lot of important information because high pressure is considered asa ‘uniform perturbation’ and it gives rise to an electronic and structural phase transition or
crossover in the materials having highly correlated marginal electronic states, which supplies
a lot of crucial information for clarifying the electronic and magnetic structures of thesematerials [8]. Furthermore, since the disorder in the doped sample has been pointed out toplay an important role in these systems [9, 10], high pressure study of undoped materials
showing NFL behaviours is highly desired.
Until now, we have reported mainly, for several Ce compounds, on the pressure-induced
crossover from the concentrated Kondo (CK) state or the HF state to the intermediate valence(IV) state in which the valence of the rare earth elements is not integer [11]. Since HF
compounds generally have low Kondo temperature TK but IV compounds have high TK , thecrossover is usually accompanied by a large increase of the Kondo temperature and a large
decrease of the Grüneisen parameter for TK at high pressure [12]. On the basis of high pressure
work on the NFL, it has been reported that the NFL state becomes unstable at high pressure,showing a crossover to the normal FL [7, 13–16]. The results have been discussed on the basis ofseveral different viewpoints. This also emphasizes the importance of pressure as a perturbationin tuning the electronic state of NFL compounds. However, in most work on pressure-induced
crossover in NFL compounds (mostly for Ce compounds), almost all experimental researchhas been focused mainly on the ground state properties around 1 K or below, i.e., on the lowtemperature properties. But for Ce based compounds, we have pointed out the importance ofthe high temperature properties in connection with the Kondo effect [17].
Y1−x Ux Pd3 exhibits a variety of interesting magnetic behaviours such as spin glasses, theKondo effect and magnetic ordering, depending on x [3, 5, 18, 19]. Among these properties,
the most interesting aspect of this pseudobinary compound is the NFL behaviours observed
near x = 0.2: the approximately T -linear dependence (n = 1.0–1.1) in the electrical resistivity
and a T log T dependence in the speciﬁc heat have been observed. In the high temperature
range above about 80 K, a logarithmic temperature dependence in ρ(T ) was also observed,
but there is no antiferromagnetic ordering at least down to 0.2 K [20]. This compound isa prototypical material showing NFL behaviour. With decreasing x, TK increases, the NFLstate quickly becomes unstable and then ﬁnally FL is stabilized at a low concentration of U(x  0.1). As was mentioned in the foregoing section, TK for CK and HF systems changes
drastically on applying pressure. We expect also a lot of variety in the electronic states ofY1−x Ux Pd3 compounds on tuning TK by applying pressure. However, the crossovers from
NFL to FL reported until now were mainly for doped samples at ambient pressure or limited
to a relatively low pressure range below 2 GPa, which may not be enough to induce thecrossover in the sample with x = 0.2. It is interesting to observe an electronic crossover ofthis prototypical NFL compound at high pressure above 2 GPa and to compare the electronic
state with those of other materials showing NFL and/or FL behaviour.

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

3387

In the present work we measured the temperature dependent electrical resistivity ρ(T )for Y1−x Ux Pd3 compounds having x = 0.05 and 0.2 at high pressure in order to examine theelectronic crossover from the NFL to the FL state (and vice versa) induced by high pressure andfurthermore the stability of the Kondo state under pressure. The lattice constants for x = 0(YPd3 ) are observed to obtain the bulk modulus and to check the pressure-induced crystal
structure change. The present results are explained in connection with the x–T phase diagram
and the Grüneisen parameters for the Kondo temperature TK . The electronic state for x = 0.2
at low temperature will be discussed, taking into account critical ﬂuctuation near the phaseboundary, and then compared with several theoretical models.
2. Experimental procedures
2.1. Sample preparation
The polycrystalline samples of Y1−x Ux Pd3 with x = 0, 0.05 and 0.2 were prepared by arc
melting the constituent elements under an argon atmosphere [18]. All the samples wereremelted several times to ensure homogeneity and annealed in evacuated quartz tubes for
100 h at 900 ◦ C. X-ray diffraction analysis shows that all the samples are single phase with the
cubic Cu3 Au type crystal structure. The lattice parameter a (Å) changes linearly as a functionof U concentration x as a = 4.0701 + 0.0193x (Å).
2.2. X-ray diffraction study under high pressure
Crystal structure and lattice constants under high pressure were investigated by means of x-ray
diffraction. Hydrostatic pressure was generated by using WC Bridgman anvils having a faceof 3 mm diameter [21]. A 4:1 methanol/ethanol mixture was used as a pressure transmitting
medium. The powdered sample and NaCl were placed in a 0.3 mm hole at the centre of aberyllium disc gasket having 0.5 mm thickness. In order to obtain diffraction patterns withsharp lines and low background, we used a Guinier type focusing camera with a bent quartz
monochromator. The diffraction lines were recorded on highly sensitive curved ﬁlm. The
pressure was determined by using Decker’s equation of states for NaCl [22]. The P–V relation
was observed only for YPd3 (x = 0) at room temperature.
2.3. Electrical resistance measurements under high pressure
Electrical resistance was measured in the temperature range between 4.2 and 300 K by using
a standard dc four-probe method. Hydrostatic pressure below 2 GPa was generated by usinga WC piston and a Cu–Be cylinder device. A 1:1 mixture of Fluorinert, FC70 and FC77,
was used as a pressure transmitting medium. Above 2 GPa, we used a cubic anvil type highpressure apparatus. The pressure was changed only at room temperature in order to minimize
the internal strain in the sample and kept constant within ±1% throughout each measurement.
The details of the high pressure systems were reported previously [23, 24].
3. Results
3.1. Pressure dependence of the volume and electrical resistance at room temperature
Figure 1 shows the lattice constants of YPd3 as a function of pressure below 12 GPa at room
temperature. The cubic Cu3 Au crystal structure is stable up to 12 GPa since no new diffractionlines were observed at high pressure. It was found that the compression curve could be3388

G Oomi et al

Figure 1. The pressure dependences of the lattice constants of YPd3 at room temperature.

Figure 2. The relative change of the electrical resistivity, ρ(P)/ρ(0), for x = 0.05 and 0.2 at room
temperature.

approximated by a straight line, as shown in the ﬁgure. The bulk modulus B (=−V ∂ P/∂ V )is estimated to be 148 GPa, which is smaller than that of URu2 Si2 (B = 215 GPa) [25] but
larger than that of UGe2 (B = 69 GPa) [26]. Considering the fact that the lattice constant for
x = 0.2 is almost the same as that for x = 0 [5], the bulk moduli for x = 0, 0.05 and 0.2 may
be nearly the same. This result will be used in the following section when we calculate theGrüneisen parameters.
The normalized electrical resistivity ρ(P)/ρ(0) for x = 0.05 and 0.2 at room temperature
is shown in ﬁgure 2 as a function of pressure up to 2 GPa, where ρ(0) is the resistivity at ambientpressure. ρ for the two samples increases with increasing pressure, approximately in a linear
fashion. The pressure coefﬁcient of ρ is estimated to be (1/ρ)(∂ρ/∂ P) = 30 × 10−3 GPa−1
for x = 0.05. The pressure coefﬁcient of ρ for x = 0.2 is 46 × 10−3 GPa−1 , which is 1.5
times larger than that for x = 0.05, suggesting that the conduction electrons are scattered in acomplex way on the border of the instability of the electronic state near x = 0.2, which may
give rise to an increase in the pressure coefﬁcient of ρ. The electrical resistivity for x = 0.2

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

3389

Figure 3. The electrical resistivity for x = 0.05 as afunction of temperature at various pressures.

Figure 4. The electrical resistivity for x = 0.05 with alogarithmic scale for temperature at various pressures.

Figure 5. The Kondo temperature TK for x = 0.05 as afunction of pressure.

Figure 6. ρ(T ) as a function of T 2 for x = 0.05 at highpressure.

is found to increase with pressure up to 6 GPa at room temperature, having almost the samepressure coefﬁcient as mentioned above.
3.2. Temperature dependent electrical resistivity for x = 0.05 under high pressure
Figure 3 shows the ρ(T ) curve at various pressures up to 2.1 GPa. ρ(T ) shows a smooth
decrease with increasing temperature even at high pressure; all ρ(T ) curves seem to be almost
parallel without any crossing but the values of ρ increase with pressure as was mentioned inrelation to ﬁgure 2. The magnetic part of the resistivity ρmag was estimated by the equation
ρmag (T ) = ρ(T, x = 0.05) − ρ(T, x = 0 (YPd3 )), assuming that the ρ(T ) of YPd3 (seeﬁgure 8 in the following section) is mainly dominated by phonon scattering. Figure 4 shows
the results; ρmag (T ) is shown with a logarithmic scale for T at various pressures.
In the present work, we deﬁne the value of the Kondo temperature TK as the temperature
where the value of ρmag (T )/ρmag (T = 4.2 K) is 0.5 [27]. TK for x = 0.05 was obtained by
an extrapolation of the present ρmag (T ) curve to high temperature. Figure 5 shows TK as afunction of pressure. TK increases almost linearly with pressure up to 2 GPa having a rate of3390

G Oomi et al

Figure 7. The coefﬁcients of the T 2 term in ρ(T ) for x = 0.05, A , as a function of pressure.

Figure 8. ρ(T ) as a function of T for x = 0.2 at high pressure including ρ(T ) for x = 0 as areference.

∂ TK /∂ P = 50 K GPa−1 . Usually ρ(T ) for Kondo compounds shows normal Fermi liquid
properties such as a T 2 dependence at low temperature. In order to examine this temperaturedependence, we plotted the values of ρmag (T ) as a function of T 2 , in ﬁgure 6. A T 2 dependence
in the ρmag (T ) curve, ρmag (T ) = ρ0 − A T 2 (ρ0 : residual resistivity), is found over the wide
range of temperature below 50 K, which indicates that the ground state for x = 0.05 is welldescribed as a Fermi liquid. The values of A are plotted in ﬁgure 7 as a function of pressure.
It is found that A decreases with pressure: A is decreased by about 30% on applying 2 GPa.
Considering that A is proportional to TK−2 [28], this implies that TK increases with pressure,which is consistent with the result in ﬁgure 5. We will discuss this point in detail later.

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

3391

Figure 9. ρ(T ) for x = 0.2 below 60 K at various pressures. A small deviation from the linear
temperature dependence is observed below 12 K at 2.1 GPa, which is shown by an arrow.

3.3. Temperature dependent electrical resistivity for x = 0.2 at high pressure
ρ(T ) for x = 0.2 is shown in ﬁgure 8 at various pressures together with that for x = 0 (YPd3 ).
It is evident that the ρ(T ) curve at 5.8 GPa is very different from those below 2 GPa, particularly
below 100 K. Figure 9 shows the electrical resistivity below 60 K as a function of T at 0, 0.6
and 2.1 GPa. It is found that the linear temperature dependence in ρ, which is evidence ofNFL behaviour, is well observed below 50 K; i.e., ρ(T ) below 50 K is approximated by theequation ρ(T ) = ρ0 (1 − T /T1 ), where ρ0 is the residual resistivity and T1 is the characteristic
temperature which may be related to the Kondo or spin ﬂuctuation temperature. But at 2.1 GPa,a small deviation from the linear temperature dependence is found below about 12 K, which
may be a precursor of the collapse of the NFL state. We will discuss later the origin of thisdeviation. Figure 10 shows the coefﬁcients A of the T -linear term, A = ρ0 /T1 , and T1 as afunction of pressure. The magnitude of A at ambient pressure (0.72 μ cm K−1 ) is nearly
the same as those reported previously [4]. The value of A is found to decrease with increasingpressure, having a rate (1/A)(∂ A/∂ P) = −5.7 × 10−2 GPa−1 . From the linear extrapolationof A(P), A is 0 around 18 GPa, where the NFL state is expected to disappear.
Figure 11 shows the magnetic part of the electrical resistivity ρmag (T ) at various pressureswith a logarithmic scale for T , which was estimated by means of the same method as mentioned
in section 3.2. The Kondo temperature TK was also deﬁned in the same way as that for
x = 0.05. The results are shown in ﬁgure 12. TK increases almost linearly with increasingpressure below 2 GPa, but the point at 5.8 GPa deviates upwards slightly from that extrapolated
from low pressure below 2 GPa. It should be noted that the effect of pressure on TK is opposite
to the effect of the U concentration x [5, 18]: TK decreases with x but increases with pressure.

3392

G Oomi et al

Figure 10. The coefﬁcients of the linear term A and the characteristic temperature T1 as a functionof pressure for x = 0.2.

Figure 11. The magnetic part of the electrical resistivity ρmag (T ) for x = 0.2 on a logarithmic
scale at high pressure.

4. Discussion
In this section we discuss the experimental results obtained in the present work in connection
with the Kondo effect and the crossover from a NFL state to a FL one. We divide the discussion
into four parts.

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

3393

Figure 12. The Kondo temperature TK for x = 0.2 as a function of pressure.

4.1. Stability of the Kondo state under high pressure—high temperature electronic properties
above 100 K
We discuss the high temperature behaviour of ρ(T ), in which Kondo scattering dominates
ρ(T ). In the foregoing section, we obtained the Kondo temperature TK as a function ofpressure, where we found an approximately linear dependence against pressure. TK may bedescribed by the following equation in the single-impurity regime:


1
,
(1)
TK ∝ exp −|J N(0)|where J is the s–f exchange interaction and N(0) is the density of states at the Fermi level. J
is written asJ∼Vsf2 ,
5f

(2)

where Vsf is the strength of hybridization and 5f is the energy difference between the 5f level
and the Fermi level. 5f may be expressed as 5f ∼ 0 + 1 x − ω P, where 0 , 1 and ω areconstants [5, 29]. This indicates that the effect of x on J or TK is opposite to that of pressure,which is the same as the case for CeR alloys (R: rare earth element) [29].
Since Vsf increases and 5f decreases with increasing pressure, J shows an increase on
applying pressure. This indicates that TK is enhanced by applying pressure. The pressure
dependence of TK is derived from equations (1) and (2) as TK ∼ (TK )0 eγ P , where (TK )0 is
TK at P = 0 and γ is a positive constant. In this derivation, we assumed that Vsf2  and N(0)are constant and pressure is not too high. The solid line in ﬁgure 12 was plotted by assuming
γ = 7.3 × 10−2 GPa−1 and TK (0) = 215 K; the experimental results are well reproducedby this equation. On the same assumptions, when pressure is constant, we can derive thefollowing relation for the concentration (x) dependence of TK : TK = TK (0) exp(−θ x), whereθ is a positive constant. This means that TK (x) decreases with increasing U concentration.
On the other hand, the value of γ is obtained as 8.0 × 10−2 GPa−1 for x = 0.05 by using
the data for TK shown in ﬁgure 5. These two values are approximately the same. This meansthat as far as the effect of pressure on the Kondo state is concerned, there is no signiﬁcantdifference between x = 0.05 and 0.2. In other words, the high temperature behaviour of ρ(T )can be treated in the framework of the Kondo single-impurity model.

3394

G Oomi et al

Figure 13. ln[TK (P)/ TK (0)] as a function of pressure for x = 0.2.

4.2. Estimation of Grüneisen parameters for Y1−x Ux Pd3
The Grüneisen parameter is often used to evaluate the electronic state of highly correlated
electron systems [8, 11, 12, 17, 25]. So we attempt to estimate this parameter for TK . The
Grüneisen parameter of TK is deﬁned as∂ ln TK∂ ln TK=B,(3)
K ≡ −∂ ln V∂P
where B is the isothermal bulk modulus. The pressure dependences of TK were shownin ﬁgures 5 and 12 for x = 0.05 and 0.2, respectively. Equation (3) is rewritten as
K = B∂ ln(TK (P)/TK (0))/∂ P, where TK (0) is TK at ambient pressure. Figure 13 shows
the pressure dependence of the value of ln[TK (P)/TK (0)] for x = 0.2. The slope of the plotcorresponds to K /B [12]. The value of K /B is estimated to be 0.08 GPa−1 . K for x = 0.2
is 12 at ambient pressure, assuming the value of B to be the same as that of YPd3 (=148 GPa),
which is smaller than those of UAl2 ( ∼ 20) [8] and URu2 Si2 ( ∼ 30) [25]. It is interesting
to note that the magnitude of K for x = 0.2 is comparable with that for the intermediate
valence compounds CePd3 ( ∼ 6) [30] and CeNi ( ∼ 9) [31]. K for x = 0.05 is calculated
in the same way, using the data in ﬁgure 5, to be 12, which is the same as that for x = 0.2.
This result indicates that there is no signiﬁcant difference in pressure effect on the Kondo
state above 100 K between the x = 0.05 and 0.2 cases, as was pointed out in the foregoing
section.
Here we apply the compressible Kondo model [32] to equation (1). The volume change
of |J N(0)| is assumed asV − V0,(4)|J N(0)| = |J N(0)|0 exp −q
V0
where q is a constant between 6 and 8 and |J N(0)|0 is |J N(0)| at ambient pressure. By using
equations (1) and (4) we obtainq.
(5)|J N(0)|0 =KWhen we derived equation (5), we used the following approximation: exp(q(V − V0 )/V0 ) =1+q(V −V0 )/V0 , which is valid at low pressure because the volume change is small. Assumingq = 6 [32], we obtain 0.5 for both x = 0.2 and 0.05. This is larger than those for URu2 Si2 (0.2)
and UAl2 (0.3), but the same as that for α-Ce(∼0.5) [33]. The results indicate that the 5f
electrons for x = 0.2 and 0.05 are more itinerant than those in URu2 Si2 and UAl2 .

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

3395

Figure 14. The coefﬁcients of the log T term m for x = 0.2 as a function of pressure.

It is well known that the Kondo effect is manifested in the existence of a log T term in theelectrical resistivity. The electrical resistivity of dilute Kondo alloys may be described as
ρ(T ) = ρB − C|J N(0)|3 log T,(6)where C is the constant and ρB is the temperature independent resistivity calculated from Bornﬁrst-order perturbation of J . From the above equation (6), the slope m in the ρ versus log T
curve is derived to be
m = C|J N(0)|3 .

(7)

The values of m for x = 0.2 are plotted in ﬁgure 14 as a function of pressure. In thiscalculation of m, we used the data in the range 0.5TK < T < 1.1TK (TK = 215 K at ambientpressure for x = 0.2). For this reason, we did not calculate the values of m for x = 0.05
because TK for x = 0.05 is 620 K at ambient pressure and then 0.5TK is 310 K, which is outside
the temperature range in the present experiment. So in this section we limited our discussion
to the x = 0.2 case. It is found that the value of m increases substantially with pressure for
x = 0.2, as has been observed in many Ce based HF systems [12].
On the basis of the compressible Kondo model, we can explain the results in ﬁgure 14 as
follows. |J N(0)|3 is described from equation (4) as
V0 − V|J N(0)|3 ≈ |J N(0)|30 1 + 3q.
(8)
V0
From equations (7) and (8), we get the magnitude of m as proportional to 1 + 3q(V0 − V )/V0 ≈1 + 3qκ P, where κ is the compressibility. This implies that m increases with pressure, which
explains qualitatively the results in ﬁgure 14.
4.3. Pressure-induced crossover from the NFL to the FL—low temperature electronic
properties
Here we discuss ﬁrst the relation between the values of TK and the coefﬁcients of the T 2 term
for x = 0.05. In the Kondo compounds, the electrical resistivity at low temperature (TTK )is approximated by the following temperature dependence: 2 
T,(9)
ρ(T ) = ρ0 1 −
TK

3396

G Oomi et al√
Figure 15. TK as a function of 1/ A for x = 0.05.


where ρ0 is the residual resistivity. In this approximation, the value√ of A is roughly proportional2for
to 1/TK . Figure 15 shows the relation between TK and 1/ A at different pressures√x = 0.05. It is found that there is a good linear relationship between TK and 1/ A . Using
equation (9), we obtain the value of K as 13, which is in good agreement with the value
obtained in section 4.2: 12. This suggests that the behaviour for x = 0.05 is well describedby the single-impurity Kondo model over a wide range of temperature.
Next we consider the ground state for x = 0.2 at high pressure. The NFL behaviour
below 2.1 GPa is evidenced by the existence of T -linear behaviour in ρ(T ), which was also
observed below about 50 K at ambient pressure in the present work, as shown in ﬁgure 9.
The coefﬁcient A of the T -linear term decreases with increasing pressure, which may be
explained by the increase of T1 at high pressure. T1 is related to some kind of ﬂuctuation suchas a spin or spatial one. Critical ﬂuctuations associated with antiferromagnetic ordering wereobserved for x = 0.2 at low temperature down to 0.2 K using neutron scattering [20]. In thissense, the decrease of A (or the increase in T1 ) suggests that the critical ﬂuctuations near thephase boundary (x ∼ 0.2) between the NFL state and spin glass state [5] are suppressed byapplication of pressure. If antiferromagnetic ordering took place, T1 would become 0 and A
would diverge near a critical value of a control parameter.
To allow comparison of the electronic state at 5.8 GPa and that at ambient pressure, theρmag (T ) curves are shown in ﬁgure 16 along with that for x = 0.05, which shows the typicalFL behaviour. It is easily seen that the overall behaviour of ρmag (T ) at 5.8 GPa is similar tothat for x = 0.05 at ambient pressure. This implies that the electronic state for x = 0.2 at
5.8 GPa can be considered as a normal FL one.
Figure 17 shows the normalized resistivity ρmag (T )/ρmag (4.2 K) as a function of the
reduced temperature T /TK at various pressures. The data below 2.1 GPa are found to fall ona universal curve. This indicates that the electronic state or NFL state is almost independentof pressure up to 2.1 GPa. But the curve at 5.8 GPa substantially deviates from the universal
curve below 2.1 GPa. The large change in the temperature dependence suggests a crossoverin the electronic state from the NFL to another state on applying pressure.
In order to see the result more clearly and examine the power law in T , we plot the valuesof 1 − ρmag (T )/ρmag (0) below 30 K in ﬁgure 18 both at ambient pressure and at 5.8 GPa asa function of T on a logarithmic scale. It is found that ρmag (T ) at low temperature below
30 K changes from a T -linear dependence (n = 1.0) at ambient pressure to a T n (n = 1.9)

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

Figure 16. The temperature dependence of ρmag (T ) for
x = 0.2 at 0 and 5.8 GPa and that for x = 0.05 forcomparison.

3397

Figure 17.
The normalized electrical resistivity,ρmag (T )/ρmag (4.2 K), as a function of the reduced
temperature, T / TK , for x = 0.2.

Figure 18. The magnetic part of the electrical resistivity for x = 0.2, ρmag (T ), as a function oflog T . The data for x = 0.05 are also shown for comparison.

dependence below about 17 K and the line for x = 0.05, which shows FL behaviour, is almost
parallel to that at 5.8 GPa.
The change in the power from 1 to 1.9 suggests a collapse of the NFL state followed by
the recovery of the FL state at high pressure. This result indicates that the crossover from NFL
to FL states takes place at a pressure between 2.1 and 5.8 GPa, which is smaller than 18 GPa,
where the value of A may vanish as was mentioned before. This is the ﬁrst report of such acrossover induced by pressure for the prototype NFL compound x = 0.2.
Several theoretical models based on different viewpoints, for example the two-channel
Kondo effect [34, 35], proximity to a quantum critical point [3, 36] and distribution of Kondo
temperatures [37], have been proposed to explain the transport and thermodynamic properties
of NFL compounds. However, there have been no theories succeeding in explaining all aspects
of NFL behaviours [4]. Furthermore, it is not clear at present which model should be applied
to explain the high pressure behaviour of NFL compounds. It is well known that the strength

3398

G Oomi et alof hybridization is increased by application of pressure and the electronic properties of the
Kondo compounds have been interpreted in terms of a change in the hybridization caused bydoping or pressure.
The effect of hybridization on the stability of FL and/or NFL compounds has been
investigated by Koga and Shiba [38, 39] on the basis of the two-channel Kondo model. They
calculated the phase diagram of the stability region of the FL and NFL as a function of Coulomb
U and Hund couplings JH .
According to their calculation, the enhancement of the strength of hybridization is found tostabilize the FL state compared with the NFL state. In other words, the application of pressure,which implies an increase of hybridization, gives rise to a crossover from NFL to FL behaviour.
The present result seems to be explained qualitatively by taking their result into account as far
as the crossover from the NFL to the FL state is concerned. Furthermore, the theory predicts
that the temperature of crossover from NFL to FL behaviour, Tcr , decreases as the electronic
state of the system approaches the NFL/FL boundary. Tcr may be described approximately
as Tcr ∝ |JH − JH,b |α , where JH,b is the value of JH at the boundary and α is a constant,in the range 8–9 [40]. If we assume Tcr = T1 , the present result indicates that Tcr increases
with increasing pressure as shown in ﬁgure 10, i.e., Tcr increases as the system approaches the
FL/NFL boundary, which is in sharp contrast to the theoretical prediction. In other words, thepresent result suggests that there is no such boundary in the pressure change of the electronic
state for x = 0.2 and the two-channel Kondo model may not be applicable in explaining thepressure change of characteristic temperatures or the pressure-induced crossover for x = 0.2.
The electrical resistivity ρ(T ) for NFL compounds has been calculated by Moriya
and Takimoto on the basis of the self-consistent renormalization (SCR) theory of spin
ﬂuctuations [41]. Around the critical boundary, ρ(T ) shows a T 3/2 dependence followed by a
T -linear dependence as T increases. Off the critical boundary region, ρ(T ) is proportional toT 2 , indicating the recovery of FL behaviour. As was shown in ﬁgure 18, ρ(T ) for x = 0.2 at
5.8 GPa is similar to that for x = 0.05, the Fermi liquid compound, which is also proved by theexistence of a T 2 dependence at low temperature. The facts suggest that the spin ﬂuctuation for
x = 0.2 is expected to be suppressed by the application of pressure, which indicates an increaseof T1 , and then the NFL behaviour is collapsed to give rise to the recovery of the FL behaviour.
Recently, a phase diagram of heavy fermions including the quantum critical point has
been presented by Continentino [42]; the Fermi liquid behaviour is expected to be stable
off the critical region and the coherence temperature Tcoh increases as the value of |J N(0)|(or pressure) increases. If we assume Tcoh as T1 or TK , the low temperature properties ofY1−x Ux Pd3 (x = 0.2) may be qualitatively explained according to this diagram. In otherwords, since the sample for x = 0.2 is basically just on the quantum critical point, we expect
the non-Fermi liquid behaviour and the pressure to have the effect of moving this sample off
the critical point, which also gives rise to an increase in T1 or TK .
Roughly speaking, the common feature of these theories is that the NFL behaviours may
collapse at high pressure showing a recovery of FL behaviour, but there is a difference between
the semiquantitative explanations of the characteristic temperatures such as T1 or TK . Judging
from the present results and the above-mentioned discussion, it is plausible to consider thatthe sample with x = 0.2 exists near or just on the quantum critical point [3, 36, 42] with alarge magnetic ﬂuctuation showing NFL behaviour, but with increasing pressure the quantum
ﬂuctuation is suppressed resulting in a crossover from the NFL to the FL state. In order todiscuss which model is suitable for the pressure dependence of the NFL behaviour in thepresent work, more quantitative analysis of the experimental results is needed, not only for the
resistance but also for the susceptibility or speciﬁc heat at high pressure. It seems difﬁcult to
explain all aspects of NFL behaviours by applying one theoretical model.

High pressure studies of anomalous electronic states of Y1−x Ux Pd3

3399

4.4. The relation between the U concentration x and the effect of pressure
In the compounds Y1−x Ux Pd3 , the lattice constants increase slightly with x, i.e., the lattice
expands with x, which is opposite to the pressure effect. Here we derive the quantitative relation
between the pressure P (GPa) and x by using the Kondo temperature TK and lattice constanta as implicit variables. The fractional increase a (Å) in the lattice constant is obtained fromthe result in section 2.1 as a function of the U concentration x: a = 19.3 × 10−3 x. On
the other hand, the relation between the lattice constant and the pressure is obtained from thebulk modulus. From the bulk modulus in section 3.1, we obtain a(P) = −9.2 × 10−3 P,
where P is in GPa. Using these two relations, we get the following equation:
P = −2.1 x.

(10)Since the difference in x between x = 0.05 and 0.2 is −0.15, the value of P is estimatedto be 0.3 GPa from the above equation (10). This result implies that the electronic state for
x = 0.2 becomes similar to that for x = 0.05 on applying 0.3 GPa. But in section 4.3,
we observed that the electronic state for x = 0.2 becomes the same as that for x = 0.05
above 4–5 GPa, which is extremely large compared to the estimated value—by an order ofmagnitude. This indicates that scaling using the lattice constants or the volume is impossible
for this compound and the pressure-induced crossover from NFL to FL behaviour for x = 0.2
cannot be explained by just considering the lattice compression.
The Kondo temperature TK of this material decreases with increasing x [5, 18]. Next
we consider this using TK as an implicit parameter. In section 4.1, we showed that TK
can be described as TK (P) = (TK )0 exp(γ P). The fractional change in TK is derived as
TK /TK = γ P. On the other hand, ln TK at ambient pressure is well known to be a
linear function of x because of the relation TK (x) = TK (x = 0) exp(−θ x) [5]. We get
TK /TK = −θ x. Thus we get the relation P = −θ/γ x. By using the pressure
dependence of TK and θ = 7.1, we obtain
P = −88 x.

(11)

If we put x = −0.15, we get P = 13 GPa. This means that about 13 GPa is needed for
x = 0.2 to get the same electronic state as for x = 0.05. It is interesting to note that a pressureof several GPa is needed to destroy the NFL state for x = 0.2, which is comparable with thepressure mentioned above. This indicates that the change in the ‘effective pressure’, P, is
not due to just a change in the lattice constant but also a change in the electronic state followed
by a small change in the lattice constant. Taking these results into account, the electronic state
for Y1−x Ux Pd3 compounds, particularly for x = 0.2, can be considered to be a marginal stateon the border of magnetic instability.
5. Conclusion
In the present study, we have measured the electrical resistivity of Y1−x Ux Pd3 (x = 0, 0.05
and 0.2) and lattice constant of YPd3 at high pressure. The main conclusions are summarized
as follows:(1) The Cu3 Au structure of YPd3 is stable up to 12 GPa at room temperature.
(2) As far as the pressure effect on the Kondo state above 100 K is concerned, there is no
great difference between x = 0.05 and 0.2 because the Grüneisen parameter for TK for
x = 0.2 is the same as that for x = 0.05.
(3) The non-Fermi liquid behaviour at ambient pressure for x = 0.2 shows a crossover athigh pressure above 4–5 GPa, followed by a recovery of Fermi liquid behaviour.

3400

G Oomi et al(4) The quantitative relation between pressure and U concentration has been discussed and thechange in the internal (or effective) pressure is mainly dominated by the contribution froma change in the electronic state induced by a small compression in the lattice constant.
References[1] Grewe N and Steglich F 1991 Handbook on the Physics and Chemistry of Rare Earths vol 14,
ed K A Gschneidner and L Eyring Jr (Amsterdam: Elsevier) p 343[2] Seaman C L, Maple M B, Lee B W, Ghamaty S, Torikachvili M S, Kang J S, Liu L Z, Allen J W and Cox D L 1991
Phys. Rev. Lett. 67 2882
[3] Andraka B and Tsvelik A M 1991 Phys. Rev. Lett. 67 2886
[4] Stewart G R 2001 Rev. Mod. Phys. 73 797[5] Maple M B, Dickey R P, Herrmann J, de Andrade M C, Freeman E J, Gajewski D A and Chau R 1996 J. Phys.:
Condens. Matter 8 9773 and see the references therein[6] Knebel G, Eggert C, Schmid T, Krimmel A, Dressel M and Loidl A 1997 Physica B 230–232 593[7] von Löhneysen H 1996 J. Phys.: Condens. Matter 8 9689 and see the references therein[8] Thompson J D and Lawrence J M 1994 Handbook on the Physics and Chemistry of Rare Earths vol 19,
ed K A Gschneidner Jr et al (Amsterdam: Elsevier) p 383[9] Steglich F, Buschinger B, Gegenwart P, Lohmann M, Helfrich R, Langhammer C, Hellmann P, Donnevert L,
Thomas S, Link A, Geibel C, Lang M, Sparn G and Assmus W 1996 J. Phys.: Condens. Matter 8 9909
[10] Castro Neto A H, Castilla G and Jones B A 1998 Phys. Rev. Lett. 81 3531
[11] Kagayama T, Oomi G, Takahashi H, Môri N, Ōnuki Y and Komatsubara T 1991 Phys. Rev. B 44 7690
[12] Kagayama T and Oomi G 1996 J. Phys. Soc. Japan 65 42[13] Bogenberger B and Löhneysen H v 1995 Phys. Rev. Lett. 74 1016
[14] Chau R, Han S H, Maple M B, Löhneysen H v and Aronson M C 1997 Physica B 230–232 600[15] Umeo K, Kadomatsu H and Takabatake T 1996 Phys. Rev. B 54 1194[16] Gabani S, Bauer E, Berger S, Flachbart K, Padeno Y, Paul C, Pavlik V and Shitsevalova N 2003 Phys. Rev. B
67 172406[17] Kagayama T, Oomi G, Ito E, Ōnuki Y and Komatsubara T 1994 J. Phys. Soc. Japan 63 3927
[18] Aoki Y, Terayama K, Sato H, Maeda K and Ōnuki Y 1995 Physica B 206/207 451[19] Zochowski S W, de Podesta M, Lester C and McEwen K A 1995 Physica B 206/207 489[20] Dai P, Mook H A, Seaman C L, Maple M B and Koster J P 1995 Phys. Rev. Lett. 75 1202
[21] Kagayama T and Oomi G 1995 J. Magn. Magn. Mater. 140–144 1227
[22] Decker D L 1971 J. Appl. Phys. 42 3239
[23] Môri N and Takahashi H 1990 Atsuryoku Gijutsu (Pressure Engineering) J. High Pressure Inst. Japan 28 124(in Japanese)[24] Oomi G and Kagayama T 1997 Physica B 239 191[25] Kagayama T, Oomi G, Iki K, Môri N, Ōnuki Y and Komatsubara T 1994 J. Alloys Compounds 213/214 387[26] Oomi G, Ohashi M, Honda F, Haga Y and Onuki Y 2003 J. Phys.: Condens. Matter 15 S2039[27] Hamann D R 1967 Phys. Rev. 158 570[28] Yoshimori A and Kasai H 1983 J. Magn. Magn. Mater. 30–34 475[29] Alascio B, López A and Olmedo C F E 1973 Phys. Rev. B 7 1274
[30] Sawamura T, Kagayama T and Oomi G 1997 Physica B 239 106[31] Oomi G and Môri N 1994 J. Alloys Compounds 207/208 275[32] Lavagna M, Lacroix C and Cyrot M 1983 J. Phys. F: Met. Phys. 13 1007
[33] Allen J W and Martin R M 1982 Phys. Rev. Lett. 49 1105
[34] Cox D L 1987 Phys. Rev. Lett. 59 1240
[35] Cox D L and Zawadowski A 1998 Adv. Phys. 47 599 and see the references therein[36] Continentino M A 1994 Phys. Rep. 239 179[37] Miranda E, Dobrosavljevic V and Kotliar G 1996 J. Phys.: Condens. Matter 8 9871
Miranda E, Dobrosavljevic V and Kotliar G 1997 Phys. Rev. Lett. 78 290[38] Koga M and Shiba H 1995 J. Phys. Soc. Japan 64 4345
[39] Koga M and Shiba H 1997 J. Phys. Soc. Japan 66 1485
[40] Koga M 1995 Thesis Tokyo Institute of Technology[41] Moriya T and Takimoto T 1995 J. Phys. Soc. Japan 64 960[42] Continentino M A 2000 Eur. Phys. J. B 13 31

Physica C 388–389 (2003) 235–236
www.elsevier.com/locate/physc

Pressure eﬀect on a ferromagnetic transition
temperature of RuSr2GdCu2O8
Jun Shibata a,*, Hirotsugu Goto a, Hiroki Takahashi a,
Yuh Yamada b, Akiyuki Matsushita caCollege of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya 156-8550, Japanb
Shimane University, 1060 Matsue-shi, Nishikawazu-cyo 690-0823, Japanc
NIMS, 1-2-1 Sengen, Tsukuba-shi 305-0047, Japan

Abstract
A number of attention has been paid for RuSr2 GdCu2 O8 because of the coexistance of ferromagnetic state andsuperconducting state below about 30 K. In order to investigate the character of the superconducting state which
coexists with ferromagnetism, the pressure experiments on a ferromagnetic transition temperature have been performed. The enhancement of ferromagnetic transition temperature was observed with increasing pressure. Highpressure X-ray experiments on this material are in progress.
Ó 2003 Elsevier Science B.V. All rights reserved.
Keywords: Ferromagnetism; Superconductivity; Pressure eﬀect; Ru1212

1. Introduction
RuSr2 GdCu2 O8 (Ru1212) discovered in recent years
is an interesting material in which ferromagnetic stateand superconducting state coexist. The lattice structureof Ru1212 is similar to that of YBa2 Cu3 O7d (YBCO).
Ru1212 is derived from the YBCO structure by replacing Y with Gd, Ba with Sr, and the CuO chains with a
RuO2 plane, respectively. This system was ﬁrst reported
by Bauernfeind et al. [1] as superconducting but notmagnetic material. However, Ru1212 have a Curie
temperature ðTCurie Þ  135 K and bulk superconducting
transition temperature ðTC Þ  0–46 K, depending on theheat treatment. Although there is a judgment that ferromagnetic impurities SrRuO3 with TCurie  160 K is
contained [2], ﬁeld-induced ferromagnetism was observed by neutron diﬀraction measurements [3]. It isreported that Ru moments with parallel to c-axis incline
gradually to ab-plane with applying ﬁeld. Yamada et al.

[4] reported pressure eﬀect on the TC up to 8 GPa byelectrical resistivity measurements. They observed theonset temperature increase and the oﬀset temperature
decreases with applying pressure. However, since theaverage of onset and oﬀset temperature does not change
so much, they indicated that the pressure eﬀect on TC is
small and transition width broadened with pressure.
Yamada et al. synthesized another superconductor
FeSr2 GdCu2 O8 (Fe1212) with the same crystal structure
as Ru1212 in which ferromagnetism does not exist. Theyobserved both onset and oﬀset TC of Fe1212 increase
with applying pressure, in contrast to Ru1212. In thiswork the pressure eﬀect of a ferromagnetic transition
temperature has been measured by AC susceptibility
method, in order to study the ferromagnetic state andthe relation between ferromagnetic and superconducting
state.

2. Experimental*

Corresponding author.
E-mail address: happyjun@sol.dti.ne.jp (J. Shibata).

Ru1212 was synthesized by solid-state reaction of
stoichiometric powders of RuO2 , SrCO3 , and CuO.

0921-4534/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0921-4534(02)02397-3

236

J. Shibata et al. / Physica C 388–389 (2003) 235–236

The mixture was ﬁrst decomposed in air at 950 °C andheated for 24 h. It was pressed into pellets and heated at
960 °C for 24 h in air. Next sintering step took place inﬂowing nitrogen at 960 °C for 24 h, and heated at 1060
°C for 44 h in ﬂowing oxygen. Last sintering step took
place in ﬂowing oxygen at 300 °C under 100 atm for 36
h. This Ru1212 shows superconducting transition temperature TC ¼ 31 K and ferromagnetic transition temperature TCurie ¼ 135 K. Pressure generating equipment
is a cubic-anvil apparatus that was used to generatehydrostatic pressures up to 8 GPa at temperatures down
to 15 K in NIMS. The mixture of Fluorinert FC70 and
FC77(1:1) was used for the pressure transmitting medium.

Fig. 2. Pressure dependence of the ferromagnetic transition
temperature of Ru1212.

3. Results and discussion
Fig. 1 shows the output signal of AC susceptibility
measurements as a function of temperature at eachpressures. The sudden change at around 30 K and thecusp at around 140 K correspond to TC and TCurie , respectively. The pressure dependence of TC and TCurie areshown in Figs. 2 and 3. From Fig. 2 TCurie increases withpressure at a rate of 6 K/GPa. However, this pressure
eﬀect is larger than the previous results measured at themagnetic ﬁeld of 2 T [4]. It seems that the ferromagnetic
state is strongly aﬀected by the external ﬁeld. On theother hand, the cusp-shape anomaly accompanied byferromagnetic transition becomes sluggish at higher
pressure. This behavior is considered that the ferromagnetic moment in Ru is suppressed by pressure.
Concerning superconductivity, TC does not change somuch with applying pressure as shown in Fig. 3, which isconsistent with the electrical resistivity measurements[4]. Thus this pressure dependence is considered to depend on whether the system has ferromagnetic state or

240

Magnitude (10-6 V)

220
1atm
200
6GPa
5GPa
3GPa

180

Fig. 3. Pressure dependence of the superconducting transition
temperature of Ru1212.

not. High-pressure experiments with changing magnetic
ﬁeld are in progress. High-pressure X-ray measurements
for Ru1212 and Fe1212 have been carried out. Precise
reﬁnements are now in progress in order to clarify the
relation between crystal structure and magnetic properties.

160
1GPa

References

140
120
100
0

50

100
Temperature(K)

150

200

Fig. 1. Temperature dependence of the susceptibility of Ru1212
under various applied pressures.

[1] L. Bauernfeind, W. Widder, H.F. Braun, Physica C 254(1995) 151.
[2] I. Felner, U. Asaf, S. Reich, Y. Tsabba, Physica C 311(1999) 163.
[3] H. Takagiwa, J. Akimitsu, H. Kawano-Furukawa, H.
Yoshizawa, J. Phys. Soc. Jpn. 70 (2001) 333.
[4] Y. Yamada et al., in: Proceedings of AIRAPT in Beijing,
2001.

EUROPHYSICS LETTERS

1 June 2002

Europhys. Lett., 58 (5), pp. 758–763 (2002)

Electronic phase diagram of a hole-doped two-leg
ladder system, Sr14−x Cax Cu24 O41
N. Motoyama 1 , H. Eisaki 1 (∗ ), S. Uchida 1 , N. Takeshita 2 (∗∗ ),N. Môri 2 (∗∗∗ ), T. Nakanishi 3 and H. Takahashi 3
1
Department of Superconductivity, The University of Tokyo
2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan
2
Institute for Solid State Physics, University of Tokyo
Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan
3
College of Humanities and Sciences, Nihon University
3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan(received 13 September 2001; accepted in ﬁnal form 6 March 2002)
PACS. 72.15.Nj – Collective modes (e.g., in one-dimensional conductors).
PACS. 74.25.Fy – Transport properties (electric and thermal conductivity, thermoelectric effects, etc.).
PACS. 74.72.Jt – Other cuprates.
Abstract. – We have investigated the evolution of the electronic state of hole-doped two-leg
ladder compounds, Sr14−x Cax Cu24 O41 with Ca content x (x = 0–12) and hydrostatic pressure
P (P ≤ 8 GPa) by measuring anisotropic resistivity on single crystals. An insulator-to-metaltransition occurs by applying P ∼ 6.5 GPa for Sr14 Cu24 O41 which is activation-type insulating
at low P . The compounds with x ≤ 8 show an insulating behavior at all P , though the doped
hole density is fairly high (0.07–0.17 holes/Cu). On the other hand, the compounds withx ≥ 10 become a superconductor by applying pressure P = 3–5 GPa. From these results, weconstructed an x-P phase diagram.

Ladder materials show many novel and interesting properties, such as spin gap, hole pairing, and superconductivity, which are characteristics in common with high-Tc cuprates. The
most intensively studied material is Sr14 Cu24 O41 , since this is the only known system capableat the moment of carrier doping into a two-leg ladder system. A spin gap with ∼ 500 K [1]is observed. Carrier density (n) can be controlled by substituting Sr by Ca [2]. The mostintriguing fact is an occurrence of superconductivity in heavily Ca-substituted material underpressure [3], which is theoretically predicted for a ladder system [4].
However, superconductivity in this system has been explored for only heavily Ca-substituted
compounds [3, 5]. Although Sr14 Cu24 O41 compound has fairly high hole density n ∼ 0.07 per
ladder Cu [2], which is a suﬃcient amount in order to realize high-Tc superconductivity for
two-dimensional (2D) cuprates, it is an insulator at ambient pressure [6]. The reason for the(∗ ) Present address: Geballe Laboratory for Advanced Materials, Stanford University, McCullough Building,Room 346, Stanford University - Stanford, CA94305, USA.
(∗∗ ) Present address: Joint Research Center for Atom Technology (JRCAT) - 1-1-4 Higashi, Tsukuba-shi,
Ibaraki 304-0046, Japan.
(∗∗∗ ) Present address: Saitama University - 255 Shimookubo, Saitama-shi, Saitama 338-8570, Japan.
c EDP SciencesN. Motoyama et al.: Electronic phase diagram of a hole-doped etc.

759

insulating nature of Sr14 Cu24 O41 is not well understood. Several measurements, such as resistivity (ρ) [7], NQR [8], and microwave conductivity [9], suggest that a charge-ordered statemight be realized in this compound. Theories also predicted that a charge-ordered state is apossible phase competing with superconducting phase in the ladder system [10]. This chargeordered state at Sr14 Cu24 O41 might make this system insulating in spite of its considerable
high hole density.
We can make the compound conductive by substituting Ca for Sr, and even realize ametallic behavior (dρ/dT > 0) at moderate temperatures T above ∼ 100 K for x ≥ 10 [6].
However, even in this case the compound is an insulator with the resistivity increasing divergently as T → 0, which was also ascribed to the charge ordering of the hole pairs formed on
ladders [11, 12].
To get better understanding of the competition between charge order and superconductivity and make the roles of pressure and Ca substitution clear, we measured resistivity as afunction of T for Sr14−x Cax Cu24 O41 with various x’s (x = 0–12) under hydrostatic pressure
P (P ≤ 8 GPa). Due to the restriction of measurements under very high P (P ≥ 3 GPa),
the resistivity is only an available and reliable probe to explore the electronic state undersuch high P . It is found that the compound with x ≤ 8 continues to be an insulator with
its resistivity increasing divergently as T → 0 up to the highest P , except for x = 0 which
undergoes an insulator-to-metal transition at P ∼ 6.5 GPa. On the other hand, for x ≥ 10, we
observed a superconducting transition at P ≥ 3–5 GPa. From these results, we can construct
an x-P phase diagram of this system.
We prepared single crystals of Sr14−x Cax Cu24 O41 (x = 0, 3, 6, 8, 10, 11, and 12) grown by
the traveling-solvent-ﬂoating-zone (TSFZ) method [6]. The growth was done using an infrared
furnace under oxygen gas at 1 MPa. The single crystals have typically about 4 mm diameterand 50 mm length. These single crystals were characterized using a Laue diﬀractometer andfound to be composed of a single domain. The resistivity measurements were performed by
the 4-probe method in the T -range between 2 K and 300 K. Dots of silver paste were heatedas electrodes on the samples at 300 ◦ C in oxygen. To generate hydrostatic pressure up to
8 GPa, a cubic-anvil–type apparatus was used [13].
In ﬁg. 1, we show the P -dependence of the resistivity for Sr14 Cu24 O41 parallel to the c-axis(along the ladder legs, ρc ), and a-axis (along the ladder rungs, ρa ) [14]. ρc and ρa show anactivation-type (activation energy ∼ 0.21 eV) insulating behavior at ambient pressure. Upon
applying P , the resistivity in both directions decreases drastically (note the logarithmic scales
for resistivities in ﬁg. 1). With increasing P a step-like increase of the resistivity becomesapparent, indicative of some underlying transition to the insulating state. The resistivity
step shifts toward low temperatures with P . Above 6 GPa, both ρc and ρa show metallic
T -dependences over the whole T -range, although a bump remains in ρa due possibly to an
incomplete transition to the metallic state by inhomogeneity in P . For P = 8 GPa the value ofρc is ∼ 2 mΩ cm at room temperature and decreases to ∼ 300 μΩ cm at ∼ 10 K. These values
are comparable to those of the in-plane resistivity for two-dimensional (2D) La2−x Srx CuO4
with hole density x ∼ 0.07 and Tc ∼ 22 K. However, no superconductivity is observed in thismetallic state down to 2 K.
In ﬁg. 2(a), ρc (T ) for x = 3, 6, 8, and Sr13 Y1 Cu24 O41 compound are shown at various P ’s.
The Sr13 Y1 Cu24 O41 has slightly lower hole density in the ladders (n ∼ 0.05) than Sr14 Cu24 O41 .
The magnitude of ρc continuously decreases with increasing P for all compounds investigated.
Although there appears a T -range in which dρ/dT > 0 for x = 6, all three compounds are
insulators with the resistivity increasing divergently as T → 0 at any P ’s, up to 8 GPa. It
never becomes metallic even at very high P . The high-P metallic phase has so far been
observed only for x = 0 (Sr14 Cu24 O41 ).

760

EUROPHYSICS LETTERS

ρc (Ω cm)

10
10
10
10
10

10

Sr 14 Cu 24 O41 0GPa

1

2GPa
3GPa
4GPa
5GPa
6.5GPa
8GPa

0
-1

10

-2
-3

10
10
10
10

-4

0

100

T (K)

-3

ρ av (10 Ω cm)

102

ρ a (Ω cm)

10

200

10

300

3

Sr 14 Cu 24 O41 0GPa

2

2GPa
3GPa
4GPa
5GPa
6.5GPa
8GPa

1
0
-1
-2
-3

0

100

8

200

300

5GPa

6

6.5GPa

4
2

T (K)

8GPa

Mott Limith/4e 2

0
0

100

T (K)

200

300

Fig. 1 – The temperature-dependences of ρc and ρa for Sr14 Cu24 O41 at various P ’s between 0 and√
8 GPa (from top to bottom curves in each panel). The geometrically averaged resistivity ρav = ρc ρaat three P ’s near the metal-insulator transition is plotted in the bottom panel.

The x = 10 compound shows a diﬀerent behavior from those for x ≤ 8 compounds(ﬁg. 2(b)). Even at P ∼ 0, ρc shows a metallic T -dependence (dρ/dT > 0) at moderatetemperatures. With the increase of P , the metallic T -range widens, though the resistivity
eventually goes up at low T . Finally, an onset of superconductivity is observed at 5 GPa (seethe right panel of ﬁg. 2(b)). The critical pressure Pc of the superconducting (SC) onset decreases with the increase of x. In the present experiment Pc ∼ 4 GPa and 3.5 GPa for x = 11
and 12 [15], respectively (the value of Pc is indicated by the cross mark in ﬁg. 3 together withthe results of the previous work for x = 11.5 [5] and 13.6 [3]). After an abrupt onset of superconductivity Tc gradually decreases with increasing P , and the onset is no longer seen above
2 K for P = 8 GPa. From this, we infer that the SC region might have an upper bound for
P . An indication that SC tends to degrade at higher P was seen in the previous experimenton x = 11.5 [5] and 13.6 [3]. The nature of the “over-pressure” state is not clear. After the
onset of SC at Pc , Tc gradually decreases with increasing P . The x = 11 and 12 compounds
show essentially the same behavior as that for x = 11.5. However, the disappearance of SC at“over”-pressures is not seen below 8 GPa. These data suggest that the superconducting phasehas an upper bound in P and beyond this bound the compound would become a “non-SC”
metal [5]. In order to clarify the nature of the high-P non-SC phase, the experiment above
8 GPa is necessary. The x = 10 compound appears to show a re-entrance to the insulatingstate at 8 GPa. Probably, x = 10 is marginal because the insulating phase of the lower x
would be mixed up with the P -induced superconducting phase due to the ﬂuctuation of x in
the sample. Based on these results and the extrapolated behaviors to T = 0 K, we illustrate
the x-P phase diagram in the ground state as shown in ﬁg. 3.
Coming back to the insulator-to-metal transition in Sr14 Cu24 O41 , Carter et al. [7] reported
that the resistivity for x = 0 shows a crossover by cooling at T ∼ 150 K at ambient pres-

761

N. Motoyama et al.: Electronic phase diagram of a hole-doped etc.

1

10

0

(b)

Sr13Y1Cu24O41

ρc (10-3Ωcm)

ρc (Ωcm)

3

10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
60

x=3

0.5

x=6

40
20

5GPa

2GPa
3.5GPa
5GPa
8GPa

8GPa

0.5
0.4
0.3

6GPa

0
0

0GPa
2GPa
3.5GPa
5GPa
8GPa

100

T (K)

x=8

10
5
0

100

T (K) 200

0

200

0.2

2

4

6

T (K)

0
8 10

(c)
0.5

x=12

1.0

0

3.5GPa

0GPa

0.1

0
15

ρc (10-3Ωcm)

1.0

0GPa
2GPa
3.5GPa5GPa
6.5GPa
8GPa

0.6

x=10

ρc (10-3Ωcm)

10

0GPa
2GPa
3.5GPa5GPa
6.5GPa
8GPa

0GPa
2GPa
3.5GPa
5GPa
8GPa

0.5

3GPa
3.5GPa4.5GPa5.7GPa

x=12

3GPa

0.4

0GPa
3.5GPa005.7GPa

100

T (K)

0.3
0.2

4.5GPa300ρc (10-3Ωcm)

2

ρc (10-3Ωcm)

10

ρc (10-3Ωcm)

ρc (Ωcm)(a) 10 3

200

0

2

4

6

T (K)

0.1

0

8 10

Fig. 2 – (a) The results for Sr14−x Cax Cu24 O41 (x = 3, 6, and 8) and Sr13 Y1 Cu24 O41 at various P ’s.
(b) ρc (T ) for Sr4 Ca10 Cu24 O41 at various P ’s. The data near the onset of the superconductivity are
shown in the right panel. (c) The same set of ρc (T ) data for Sr2 Ca12 Cu24 O41 .

sure. We observed in our resistivity measurements under P that this crossover transforms
into a sharp transition probably due to an increase in the interladder coupling strength withincreasing P . Such a sharp resistivity jump is reminiscent of a charge-density-wave (CDW)
transition in quasi–one- and two-dimensional systems [16]. As mentioned earlier, several measurements [7–9] suggest that a charge ordering may occur in this system. Hence, the insulatingstate of the x = 0 compound at moderate P is understood as a charge localization associatedwith the charge ordering. At higher P , the charge-ordered state is destroyed and gives way toa metallic state. In this metallic state, the anisotropic ratio ρa /ρc is 3–5, nearly independentof T , and the magnitude of anisotropy is comparable to the result of the band calculation [17].
This fact indicates that this metallic state is at least 2D, or even 3D. In fact the insulator√
metal transition takes place at the geometrically averaged resistivity ρav = ρc ρa ∼ 1.6 mΩcm
which is near the Mott-Ioﬀe-Regel critical resistivity for 3D localization (inset of ﬁg. 1).
An alternative scenario to explain this P -induced insulator-to-metal transition in the x = 0
compound is that more holes may be transferred from chains into ladders by P like the caseof Ca-substitution [2]. At the moment we have no way to estimate how many holes increase
under high P . However, considering that the magnitude of the resistivity in the metallic state
at 8 GPa (ﬁg. 1) is comparable to that of La2−x Srx CuO4 with x ∼ 0.07, the estimated holedensity n = 0.07 at P ∼ 0 may not increase appreciably at high P .
In ﬁg. 3 we see that the insulating phase occupies most part of the x-P phase diagram

762

EUROPHYSICS LETTERS

Fig. 3 – The x-P phase diagram for Sr14−x Cax Cu24 O41 . The “minus” x-axis is for Sr14−x Yx Cu24 O41
and La6 Ca8 Cu24 O41 . The ladder hole density (nh (ladder)) estimated by the optical spectrum is also
indicated in the transverse axis (nh is not necessarily linear with x). The crossover in the nature of
the insulating state is indicated by the thick-dashed vertical line. The SC phase is restricted at highP and for x ≥ 10 and the experimentally determined critical pressure Pc is plotted as cross marks.

(T = 0 K). For compounds with x ≥ 10, there is a T -region where dρc /dT > 0 and dρa /dT < 0even at low pressures [5, 6]. At P = 0, the minimum (Tm ) in ρc (T ) gradually shifts tohigher temperatures with decreasing x from 12 (nh ∼ 0.21, Tm ∼ 60 K) to 10 (nh ∼ 0.19,
Tm ∼ 140 K). However, upon reducing x from 10, Tm accelerates its increase, and for x = 8(nh ∼ 0.17) the resistivity minimum, i.e. the high-T metallic behavior, is not seen (below
400 K) even at P = 8 GPa. In addition, the optical conductivity spectrum of x = 11 for lightpolarized parallel to the rungs (σa (ω)) [12] gave evidence for the development of a pseudogapwith lowering T which would be associated with a formation of hole pairs. The hole pairs
tend to be localized at low T by quantum interference eﬀects in the presence of disorder [18]or by forming a charge-ordered array which is pinned by defects or impurities on the ladders.
The pseudogap width rapidly increases, from ∼ 700 cm−1 for x = 11 to ∼ 1100 cm−1 for
x = 8 [12], and for x = 6 σa (ω) no longer shows a well-deﬁned pseudogap [19].
From these results we speculate that the nature of the insulating state would rapidly change
upon reducing x from 10. At high hole densities (Insulator 2) the insulating state is likely
a charge-ordered state of hole pairs which would be weakly pinned. At low hole densities(Insulator 1) the doped holes could no longer form pairs, and single holes form a chargeordered state in x = 0. Randomness introduced by Ca-substitution and/or oxygen excess
or oxygen deﬁciency may also play a role in the robustness of a localized state in the low-x
compounds. Probably, the diﬀerent nature of the two insulating states might be connectedwith the occurrence or non-occurrence of superconductivity.
The fact that the superconducting state is observed only in high-P and large-x regions sug-

N. Motoyama et al.: Electronic phase diagram of a hole-doped etc.

763

gests that superconductivity in this system requires the following two eﬀects simultaneously:i) promotion of hole-pair formation by increasing the hole density in the ladders via heavy
Ca-substitution, and ii) increase of interladder coupling (dimensionality) by applying high P .
The anisotropic resistivity measurement for x = 11.5 [5] demonstrated that the superconducting transition occurs when ρav per ladder plane comes near h/4e2 , the universal 2D resistivity
suggestive of an increase in electronic dimensionality from one to two. We conclude that the
primary eﬀect of P is to increase the dimensionality of the electronic state by way of increasing interladder coupling and hence dissociating hole pairs. A collapse of the spin gap at highP [20] is a direct evidence for the pair dissociation. We speculate that the pairing correlation
remains in the ladder planes at high P , which would trigger the formation of Cooper pairs in
the 2D ladder planes. More systematic NMR measurements under P are necessary in order
to conﬁrm this scenario and to fully understand the phase diagram presented in this work.
∗∗∗
We are grateful to J. Akimitsu and T. Nagata for the collaboration in the early stageof this study. This work is supported by a Grant-in-Aid for Scientiﬁc Research and a COE
Grant from the Ministry of Education, Culture, Sports, Science and Technology.
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[9]
[10]

[11]
[12]
[13]
[14]
[15]
[16]

[17]
[18]
[19]
[20]

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Gopalan S. and Sigrist M., Europhys. Lett., 23 (1993) 445.
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Troyer M. and Rice T. M., Phys. Rev. B, 51 (1995) 16456; Hayward C. A. and PoilblancD., Phys. Rev. B, 53 (1996) 11721.
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A preliminary result was published by Eisaki H. et al., Physica C, 341-348 (2000) 363.
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957.
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Physica B 322 (2002) 408–412

Metal to insulator transition of ﬁlled skutterudite PrRu4P12
at low temperatures and high pressures
Ichimin Shirotania,*, Junichi Hayashia, Takafumi Adachia, Chihiro Sekinea,
Takateru Kawakamib, Takeshi Nakanishic, Hiroki Takahashic, Jie Tangd,
Akiyuki Matsushitad, Takehiko MatsumotodaFaculty of Engineering, Muroran Institute of Technology, 27-1, Mizumoto, Muroran-shi, 050-8585, Japanb
Faculty of Engineering Science, Osaka University, Toyonaka-shi 560-8531, Japanc
College of Humanities & Science, Nihon University, Tokyo 156-8550, Japand
National Institute for Materials Science, Tsukuba-shi 305-0047, Japan
Received 31 August 2001; received in revised form 19 March 2002; accepted 21 May 2002

Abstract
X-ray diffraction of a single crystal of PrRu4P12 has been studied at ambient pressure. PrRu4P12 has a ﬁlled( Z ¼ 2; Dcalc ¼ 5:826 g/cm3. Positionalskutterudite-type structure; space group: Im3, lattice constant: a ¼ 8:055ð4Þ A,
parameters and interatomic distances in the phosphide were determined. By use of synchrotron radiation, powder X-ray
diffraction patterns of PrRu4P12 were measured up to 50 GPa at room temperature. The lattice constant monotonicallydecreases with increasing pressure. The cell volume vs. pressure curve for PrRu4P12 is ﬁtted with the Birch equation ofstate. The bulk modulus of the phosphide is 207712 GPa. The resistivity of PrRu4P12 was measured as a function oftemperature at high pressures. The metal to insulator transition is found at around 62 K under ambient pressure. The
transition temperature (TMI ) rapidly increases with pressure at the rate of about 0.9 K/GPa up to 4.5 GPa. Above
6 GPa, TMI abruptly decreases with increasing pressure. The semiconductor-like behavior below TMI for PrRu4P12 ismarkedly suppressed at around 8 GPa. The metal to insulator transitions at low temperatures and high pressures are
discussed. r 2002 Elsevier Science B.V. All rights reserved.
Keywords: Metal–insulator transition; Resistivity; Skutterudite compound; High pressure; X-ray diffraction

1. Introduction
Ternary metal pnictides with a general formula
LnT4X12 (Ln=lanthanide; T=transition metal;
X=pnicogen) crystallize with a ﬁlled skutteru*Corresponding author. Tel.: +81-143-46-5544; fax: +81143-46-5501.
E-mail address: sirotani@eee.elec.muroran-it.ac.jp(I. Shirotani).

dite-type structure [1,2]. This structure is cubic,
space group Im-3, Z ¼ 2: Ln atoms locate at (0 0 0)
and ð12 12 12Þ of a cubic structure like BCC. The
transition metal atoms (T) are in the center of a
distorted octahedral environment of six pnicogenatoms. The skutterudite-type structure is characterized by formation of well-deﬁned X4
4 groups.
The skutterudite compounds show interesting
electrical and magnetic properties at low temperatures [3,4].

0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 5 2 6 ( 0 2 ) 0 1 2 9 3 - 0

I. Shirotani et al. / Physica B 322 (2002) 408–412

We have found an interesting metal to insulator(MI) transition for PrRu4P12 at around 60 K underambient pressure [5]. Anomalous behavior in themagnetic susceptibility is not observed at around
60 K. This suggests that the MI transition in
PrRu4P12 is not caused by magnetic ordering [5].
PrL2-edge XANES measurements indicate thatthe valence state in the Pr atoms is trivalent down
to 20 K [6]. Below the transition temperature (TMI )an energy gap of PrRu4P12 is estimated to be about
100 cm1 from the optical reﬂection spectrum [7].
The Raman spectra of the phosphide are measured
between 6 and 300 K; the 380 cm1 mode assigned
to the vibration involving P atoms shows softening
and broadening below the TMI [8]. A slight jump in
the thermal expansion coefﬁcient is found at the
TMI [9]. The small anomaly in the speciﬁc heatappears at the TMI [10]. Recently, using theelectron diffraction technique, superlattice spots
in the single crystal of PrRu4P12 are observed
below the TMI [11].
We have studied X-ray diffraction of a single
crystal at ambient pressure and powder X-ray
diffraction of PrRu4P12 up to 50 GPa at room
temperature. The resistivity of PrRu4P12 hasbeen measured at low temperatures and highpressures. In this report, the metal to insulatortransition of PrRu4P12 at high pressure is discussed.

409

By use of synchrotron radiation, powder X-ray
diffraction patterns of PrRu4P12 were measured
with a diamond-anvil cell and an imaging plate up
to 50 GPa at room temperature [12]. The incident
beam was monochromatized with Si (1 1 1) double( The pressure
crystals to a wavelength of 0.6888 A.
in the diamond-cell was determined from apressure shift in the sharp R-line ﬂuorescence
spectrum of ruby. A 4:1 methanol–ethanol solution was used as the pressure-transmitting ﬂuid.
A high-pressure apparatus with a cubic-anvil
device was used for the resistivity measurement of
PrRu4P12 under hydrostatic conditions up to
8 GPa at low temperatures down to 4.2 K [13].
Polycrystals of PrRu4P12 were used for measurements of the resistivity and the powder X-ray
diffraction. These samples were prepared at hightemperatures and high pressures [5].

3. Results and discussion
Fig. 1 shows the crystal structure of PrRu4P12
determined from X-ray data of the single crystal.
The resulting positional and thermal parameters
are given in Table 1. The interatomic distances andangles are listed in Table 2. This structure issimilar to that of LaFe4P12 that has already been
determined from single crystal counter data by

2. Experimental details
X-ray diffraction of a single crystal of PrRu4P12
was studied at room temperature (295 K). Intensity data were collected on a Rigaku automatic
four-circle diffractometer using graphite-monochromated MoKa radiation. The structure
was reﬁned with a full-matrix least-squares
program; space group: Im-3, lattice constant:( Z ¼ 2; Dcalc ¼ 5:826 g/cm3, F000 ¼a ¼ 8:055ð4Þ A,
830:00; mðMoKaÞ ¼ 119:96: The conventional residual (R) and the weighted residual (Rw ) are 0.032
and 0.034, respectively. Single crystals of PrRu4P12
were grown by a Sn ﬂux method. The mixtureswith atomic ratio Pr:Ru:P:Sn=1:4:20:50 were
heated at 10001C for a week and then cooled
down slowly to 6001C at 21C/h [11].

Fig. 1. Crystal structure of PrRu4P12. The Ru atom is taken as
the origin (0 0 0).

I. Shirotani et al. / Physica B 322 (2002) 408–412

410

Table 1
Positional and thermal parameters in PrRu4P12 at ambientpressure
Im3%

Pr
2(a)

Ru
8(c)

P
24(g)

x
y
z
U11
U22
U33
Beq

0
0
0
0.0074 (3)U11U110.582 (4)0.25000.25000.25000.0019 (3)U11U110.151 (4)00.35790.14370.0051 (4)0.0033 (4)0.0035 (4)0.31 (2)Table 2
Interatomic distances and angles in PrRu4P12 at ambientpressure(Interatomic distances (A)
Pr–P
Pr–Ru
Ru–P
P–P0
P–P00

3.107 (1) (12  )3.488 (1) (8  )2.355 (1) (6  )2.314 (2) (1  )2.289 (2) (1  )Interatomic angle (deg)Pr–P–Ru
Pr–P–P0
Pr–P–P00
Ru–P–P0
Ru–P–P00
Ru–P–Ru
P0 –P–P00

78.04 (3)158.13 (2)68.13 (2)111.67 (2)111.33 (2)117.56 (5)90Patterson and Fourier methods [1]. The skutterudite-type structure is characterized by formationof rectangular P4
4 clusters. The P–P distances in( along the shorter edge andPrRu4P12 are 2.289 A( along the longer edge. These are rather
2.314 A(
shorter than the P–P distances (2.289 and 2.356 A)
in LaFe4P12 although the cell volume of PrRu4P12
is considerably larger than that of the ironcompound. The Ru–P distance is shorter than( of Ru atom andthe sum of atomic radius (1.34 A)( of P atom. The Pr–P
the covalent radius (1.06 A)
distance almost agrees with the sum of the atomic( of the Pr atom and the atomic
radius (1.82 A)( of the P atom. These distances
radius (1.28 A)
in PrRu4P12 suggest metallic bond character. The
X-ray diffraction of PrRu4P12 has been studied at
low temperatures. The positional parameter of thephosphorus atom is insensitive to temperature.
The ratio of lattice constant (a0  aT =a0 ; a0 —room temperature, aT —low temperatures) of
PrRu4P12 decreases with decreasing temperature

Fig. 2. Powder X-ray diffraction patterns of PrRu4P12 at highpressures.

at the rate of 8.7  104/K. This value is slightly
smaller than the result of the linear thermal
expansion measured by the three terminal capacitance method [9].
Fig. 2 shows powder X-ray diffraction patternsof PrRu4P12 with synchrotron radiation at highpressures and room temperature. The diffractionlines shift to the high angle region with increasingpressure. The width of the diffraction lines
becomes broad at higher pressures. Fig. 3 shows
the lattice constant vs. pressure curve for PrRu4P12
up to 50 GPa at room temperature. The structuralanomaly in PrRu4P12 is not observed up to 50 GPa
at room temperature. The ratio of the lattice
constant (a0 2aP =a0 ; a0 —ambient pressure, aP —high pressures) decreases at the rate of2.1  102/GPa up to 4.5 GPa. Thus, the pressure dependence of the lattice constant is muchlarger than its temperature dependence. The
pressure vs. volume curve for PrRu4P12 can beﬁtted by a Birch equation of state [14]. The bulk

I. Shirotani et al. / Physica B 322 (2002) 408–412

Fig. 3. Lattice constant vs. pressure curve for PrRu4P12.

modulus obtained by a least-squares ﬁt is
207712 GPa for PrRu4P12. This value is about
2.8 times that of PrP with a NaCl-type structure[12]. PrRu4P12 is a very hard material.
Fig. 4 shows the electrical resistivity vs. temperature curves for PrRu4P12 at high pressures.
The resistivity decreases with increasing pressure
up to 8 GPa under hydrostatic conditions. Whenthe temperature dependence of the resistivity ofthe phosphide is measured at constant pressures,the MI transitions are observed at low temperatures and high pressures. The semiconductor-likebehavior below the TMI in PrRu4P12 is markedly
suppressed at around 8 GPa. Fig. 5 shows theeffect of pressure on TMI for PrRu4P12. TMI
rapidly increases with pressure at the rate of about
0.9 K/GPa up to 4.5 GPa. Above 6 GPa, TMI
abruptly decreases with increasing pressure.
PrRu4P12 shows the MI transition at around
62 K under ambient pressure. This anomalous
behavior does not arise from magnetic orderingand valence ﬂuctuations based on the f electrons inPr [5,6]. A l-like second order-type anomaly in thespeciﬁc heat appears at TMI ; this does not dependon the magnetic ﬁeld at least up to 12 T [10].
Superlattice spots in the single crystal of PrRu4P12
are observed below the TMI ; this may arise from

411

Fig. 4. Resistivity vs. temperature curves for PrRu4P12 at highpressures.

Fig. 5. TMI plotted as a function of pressure for PrRu4P12.

the opening of a band gap due to a nesting of the
Fermi surface [11]. The appearance of the superlattice structure provides two possible origins of
the MI transition, a charge density wave (CDW)
transition or antiferro-quadrupolar (AFQ) ordering. Matsuhira et al. suggest that the MI transitionin PrRu4P12 is due to the CDW transition rather

412

I. Shirotani et al. / Physica B 322 (2002) 408–412

than the AFQ transition from the detailed study ofthe electronic speciﬁc heat [15].
We have studied the magnetic susceptibility andelectrical resistivity of the alloys La1xPrxRu4P12
diluted by La atom [16]. As the lattice constant in
the alloys increases with increasing La concentration, the average Pr–Pr distances increase. TMI of
the alloys shifts to lower temperatures withincreasing La concentration.
The lattice constant of PrRu4P12 decreases from( at ambient pressure to 7.887 A( at 4.5 GPa.
8.057 AThus, the distance between the nearest Pr atoms( at ambient pressure to
decreases from 6.98 A(
6.82 A at 4.5 GPa. The increase of inter-site
interactions between Pr atoms drives up TMI : Thistendency is consistent with the result of the alloys
La1xPrxRu4P12. However, TMI surprisingly decreases with increasing pressure above 4.5 GPa
although the Pr–Pr distances shorten successively
with pressure. The resistivity of PrRu4P12 below
TMI is remarkably suppressed at around 8 GPa.
The f-electrons in PrRu4P12 may easily be itinerant
in the crystal at higher pressures. Thus, theseresults suggest that the MI transition in PrRu4P12
may disappear at very high pressures. As
PrRu4As12 shows superconductivity at around
2.4 K [17], PrRu4P12 may behave as a superconductor at very high pressures.

Acknowledgements
This work was partly supported by a Grant-inAid for Scientiﬁc Research from the Ministryof Education, Science and Culture of Japan: No.
13874040(IS) and No. 14204032(IS).

References[1] W. Jeitschko, D. Braun, Acta Crystallogr. B 33 (1977)
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[2] D.J. Braun, W. Jeitschko, J. Less-Common Met. 72 (1980)
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G.P. Meisner, Phys. Rev. B 36 (1987) 8660.
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Lett. 79 (1997) 3218.
[6] C.H. Lee, H. Oyanagi, C. Sekine, I. Shirotani, M. Ishii,
Phys. Rev. B 60 (1999) 13253.
[7] T. Nanba, M. Hayashi, I. Shirotani, C. Sekine, Physica B
259–261 (1999) 853.
[8] C. Sekine, H. Saito, A. Sakai, I. Shirotani, Solid State
Commun. 109 (1999) 449.
[9] K. Matsuhira, T. Takikawa, T. Sakakibara, C. Sekine,
I. Shirotani, Physica B 281&282 (2000) 298.
[10] C. Sekine, T. Inaba, I. Shirotani, M. Yokoyama,
H. Amitsuka, T. Sakakibara, Physica B 281&282 (2000)
303.
[11] C.H. Lee, H. Matsuhata, A. Yamamoto, T. Ohta, H.
Takazawa, K. Ueno, C. Sekine, I. Shirotani, T. Hirayama,
J. Phys. Condens. Matter 13 (2001) L45.
[12] J. Hayashi, I. Shirotani, K. Takeda, T. Uchiumi, S.
Kimura, T. Adachi, T. Kikegawa, Science and technologyof high pressure, in: M.H. Manghani, W.J. Nellis, M.F.
Nicol (Eds.), Proceedings of AIRAPT-17, Universities
Press, Hyderabad, India, 2000, p. 722.
[13] H. Takahashi, A.T. Yamamoto, N. Mori, S. Adachi, H.
Yamauchi, S. Tanaka, Physica C 218 (1993) 1.
[14] F. Birch, Phys. Rev. 71 (1947) 809.
[15] K. Matsuhira, Y. Hinatsu, C. Sekine, I. Shirotani, Physica
B 312&313 (2002) 829.
[16] C. Sekine, T. Inaba, K. Kihou, I. Shirotani, Physica B
281&282 (2000) 300.
[17] I. Shirotani, T. Uchiumi, K. Ohno, C. Sekine, Y.
Nakazawa, K. Kanoda, S. Todo, T. Yagi, Phys. Rev. B
56 (1997) 7866.

Journal of Magnetism and Magnetic Materials 226}230 (2001) 246}248

High-pressure e!ect on transport properties of spin-laddercompounds Na
Ca V O and Ca Li V O
\V V     
H. Takahashi *, T. Nakanishi , T. Arima, M. Noguchi, M. Oyanagi,N. Takeshita, N. Mo( ri
Department of Physics, College of Humanities and Sciences, Nihon University, 2-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550, Japan
Institute of Materials Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-0006, Japan
Institute for Solid State of Physics, The University of Tokyo, 5-1-5 Kahiwanoha, Kashiwa, Chiba 277-8581, Japan

Abstract
Electrical resistivity of layered vanadium oxides Na
Ca V O and Ca Li V O has been measured under high\V V     pressures of up to 10 GPa. These compounds have V}O networks forming a two-leg spin-ladder layer in somecomposition range. In the spin-ladder compound Na
Ca V O , electrical resistivity measurements show semicon\V V  ducting behavior. However, the electrical resistivity has been signi"cantly reduced under high pressure, although it
remains semiconducting up to 8 GPa. On the other hand, the electrical resistivity of Ca Li V O which also has   a two-leg spin-ladder layer is lower than Na
Ca V O by several orders of magnitude. The electrical resistivity of
\V V  
Ca Li V O was greatly reduced even at low-temperature range by applying pressure.  2001 Elsevier Science B.V.
   
All rights reserved.
Keywords: Spin ladder; Metal}insulator transition; Pressure

1. Introduction
Great attention has been paid to the so-called spinladder materials. While several cuprate high-¹ super!
conductors have been found out, discovery of new superconducting materials is strongly desired to elucidate thehigh-¹ mechanism and "nd out new superconductors!
having higher ¹ . In such an investigation spin-ladder!
materials were thought to be good candidates as new
superconducting systems. Spin-gap behavior which isone of the characteristic properties of cuprate superconductors was theoretically predicted [1,2] and later observed in even-leg spin-ladder materials such as
SrCu O [3,4]. Sr
Ca Cu O
has also been \V V  
studied as a spin-ladder material; its electrical resistivity
is greatly reduced by substituting Ca for Sr showing
semiconducting behavior over the entire composition* Corresponding author. Fax: #81-3-5317-9432.
E-mail address: hiroki@chs.nihon-u.ac.jp (H. Takahashi).

ranges. However, insulator}metal transition occurs under high pressure. In addition to the insulator}metaltransition, superconductivity was discovered at pressurelarger than 4 GPa [5] with ¹ increasing up to 12 K at!
6 GPa. The e!ect of high pressure seems to play animportant role for the delocalization of carriers in theladder layer. Although the characterization of this superconductivity is di$cult due to the necessity of a highpressure technique, a recent advanced high-pressuretechnique revealed the magnetic properties of this superconducting material [6].
Recently, doping e!ects on vanadate spin-ladder materials have been intensively investigated in relation to
low-dimensional magnetic and electrionic properties[7,8]: spin-gap behavior has been reported in CaV O [9], and substitution of Na for Ca has been achieved,
leading to a greatly reduced electrical resistivity in theNa
Ca V O system [10,11]. However, they show
\V V  
semiconducting behavior over the entire substitution
range. Hence, high-pressure techniques are expected to
be a powerful tool to study metallization in this system.
Here we report the pressure e!ects on the electrical0304-8853/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 2 9 1 - 9

H. Takahashi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 246}248

Fig. 1. Pressure dependence of the electrical resistivity for
Na Ca V O , Na Ca V O , and Ca Li V O .
         

resistivity of this system and lately synthesized
Ca Li V O .
Theelectricalresistivityof   
Ca Li V O is much smaller than that for the   Ca
Na V O system.
\V V  
Polycrystalline samples of Na
Ca V O and\V V  
Ca Li V O have been synthesized under high-pres   sure conditions. The lattice constants along the a andb-axis remain almost constant with changing x, while theone along the c-axis decreases with decreasing x. Detailsof sample preparations are described elsewhere [10,11].
Electrical resistivity measurements were carried out under high pressures at low temperature by means of a DC
four-probe technique. A cubic-anvil apparatus was used
to generate hydrostatic pressures up to 10 GPa at temperatures down to 4 K. During these measurements the247pressure was controlled to be kept constant on bothcooling and heating processes.
Fig. 1 shows the pressure dependence of the electricalresistivity at room temperature for Na Ca V O ,   
Na Ca V O , and Ca Li V O . The electrical      
resistivity is greatly reduced under high pressure for eachmaterial, as shown in Fig. 1. While the electrical resistivities of Na Ca V O and Na Ca V O decrease      
to  the value at 8 GPa compared with the one at 1 atm,the electrical resistivity of Ca Li V O decreases to    the value at 10 GPa. Figs. 2(a) and (b) show the temperature dependence of the electrical resistivity at several
constant
pressuresfor
Na Ca V O
and   
Ca Li V O , respectively. From Fig. 2(a) the electri   
cal resistivity of Na Ca V O decreases with pres   sure and the shape of the (¹) curve does not change
signi"cantly up to the maximum pressure. On the other
hand, it is observed from Fig. 2(b) that the electricalresistivity of Ca Li V O decreases with pressure   
especially in the low-temperature range. However, theelectrical resistivity still displays semiconducting behavior even at the maximum pressure of 10 GPa.
In spin-ladder materials it is thought that the conduction of carriers occurs through the ladder layer. All theseexperiments make it clear that the pressure plays animportant role in delocalizing carriers in the ladder layer,
which is similar to the pressure e!ect observed in theSr
Ca Cu O system. From Fig. 1 the lowest resis\V V  
tivity for Ca Li V O is 4;10\  cm at 300 K and   
10 GPa. In the superconducting Sr Ca
Cu O     
spin-ladder system, the electrical resistivity is about
4;10\  cm at 300 K and 3 GPa [12]. The electricalresistivity in usual high-¹ superconductors is less than!
1;10\  cm at 300 K. Thus, further carrier doping
and/or applying higher pressure are thought to be necessary to give rise to the insulator}metal transition in thisFig. 2. Temperature dependence of the electrical resistivity for (a) Na Ca V O and (b) Ca Li V O measured at constant      pressures, respectively.

248

H. Takahashi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 246}248

system. Superconductivity is also expected in such a metallic phase.
This work was partly supported by Grant-in-Aid Nos.
10440114 and 11554015 from the Ministry of Education,
Science and Culture of Japan.

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N. Mo( ri, Phys. Rev. Lett. 81 (1998) 1090.

PHYSICAL REVIEW B, VOLUME 63, 115203

Pressure-induced semiconductor-metal-semiconductor transitions in FeS
Hisao Kobayashi*
Department of Physics, Tohoku University, Sendai 980-8578, Japan

Nao Takeshita and Nobuo Môri
Institute for Solid State Physics, The University of Tokyo, Chiba 277-8581, Japan

Hiroki Takahashi
College of Humanities and Sciences, Nihon University, Tokyo 156-8550, Japan

Takashi Kamimura
Department of Physics, Tohoku University, Sendai 980-8578, Japan
共Received 11 July 2000; published 1 March 2001兲
The semiconductor-metal-semiconductor transitions in stoichiometric FeS compounds were observed undernearly hydrostatic pressure condition up to 8 GPa and a temperature down to 4 K. In the low-pressure
semiconductor state, the energy gap caused by the electron correlation decreases with a volume reduction. On
the other hand, FeS in a high-pressure semiconductor state is a band insulator and the energy gap increases
with pressure when the gap is formed between the occupied nonbonding and unoccupied antibonding bands. In
the metallic phase at intermediate pressure range FeS can be regarded as a strongly correlated metal because of
the large quadratic temperature dependence of resistivity at low temperature.
DOI: 10.1103/PhysRevB.63.115203

PACS number共s兲: 71.30.⫹h, 62.50.⫹p

I. INTRODUCTION⌬, U and W can be varied much larger by pressure than bytemperature and magnetic field. Thus there is great interest to
study pressure-induced phase transitions in these compounds.
In 3d transition-metal chalcogenides the ligand-to-metal
hybridization interaction generally becomes stronger thanthat in oxides because of the large covalency between thetransition-metal d orbitals and the anion p orbitals. At theambient conditions, stoichiometric FeS has the troilite crystal
structure that is closely related to a NiAs type and is an
antiferromagnetic semiconductor with T N ⫽589 K. The
phase transition from the troilite to NiAs type structures
occurs at about 420 K.2,3 FeS is believed to belong to
the intermediate regime, where ⌬⭐U and U is not solarge.4,5 As indicated by high-pressure x-ray diffraction
measurements,6–9 it undergoes two successive first-orderphase transitions with increasing pressure at room temperature. The first transition occurs at 3.5 GPa and the structuretransforms to a MnP type. The second transition takes place
at 6.5 GPa with about 7% volume reduction. The structure
above 6.5 GPa was determined to have a monoclinic unit cellwith space group P2 1 /a. 10
The previous high-pressure resistance measurement11 indicated that FeS shows a slight increase in resistance withtemperature above 8 GPa. On the other hand, recently nonmetallic behaviors in resistance were observed at 6 and 10
GPa down to about 80 K.12 The measurement of 57Fe Mössbauer spectra was carried out under pressure up to about 15
GPa.13 It was found that the significant change in volume
dependence of the center shift occurs around 6.5 GPa. This
result indicates a distinct change of the 3d electron configuration on Fe ion at the second phase transition. Recently, theMössbauer study showed the nonmagnetic quadrupole spectrum down to 5 K at 12 GPa and the x-ray emission experi-

It is well known that the electron correlation plays animportant role in 3d transition-metal compounds since conventional one-electron band-structure calculations do not explain some of the experimental results in many of these compounds. Accordingly, there is a tendency for 3d electrons to
be localized in these compounds and then systems become
antiferromagnetic insulators. The electronic properties ofthese compounds have been renewed as interesting subjects
since the discovery of high-T c superconductors because theparent compounds are antiferromagnetic insulators. One of
the interesting properties in these compounds is an insulatormetal transition. Recently Zaanen, Sawatzky, and Allen
共ZSA兲 have developed a general framework for these compounds using the three-band Hubbard model.1 The ligand-tometal charge-transfer energy ⌬ and the ligand-to-metal hybridization interaction t pd , as well as the d-d Coulombinteraction U are explicitly included as parameters in theirmodel Hamiltonian.
The possible ground states of transition-metal compounds
can be classified into four regimes based on the relative magnitudes of ⌬, U, and the bandwidth W according to the ZSA
scheme. In the Mott-Hubbard regime for U⬍⌬, there are an
insulating state with a gap due to U for U⬎W and a d-type
metallic state for U⬍W where both holes and electrons arein the d bands. On the other hand, for U⬎⌬, compounds
become the charge-transfer insulators if ⌬⬎W and p-type
metals if ⌬⬍W where holes are in the anion valence band.
Although the character of elements in these compounds isdominant in these high-energy-scale charge fluctuations, thisZSA scheme has been successful to describe the ground-state
properties of these compounds. Since pressure can change abond length as well as a bond angle, these parameters such as0163-1829/2001/63共11兲/115203共6兲/$15.00

63 115203-1©2001 The American Physical Society

HISAO KOBAYASHI et al.

PHYSICAL REVIEW B 63 115203

ments under pressure observed the pressure-induced reduction of the satellite amplitude in these spectra around 6.3
GPa.12,14 These results strongly suggest that this second
phase transition is the high-spin to low-spin transition in the
Fe2⫹ ion.
It was indicated that FeS belongs to the boundary between
the charge-transfer and Mott-Hubbard insulators in the ZSA
scheme.1,4 Its pressure-induced phase transitions have beenvery controversial since the two successive structural phasetransitions were observed. The electrical resistivity ofstoichiometric FeS compound was measured under hydrostatic pressure up to 8 GPa in the temperature range from 4 K
to room temperature. We report evidence of pressureinduced semiconductor-metal-semiconductor transitions in
FeS and discuss the electronic properties in each phase fromthe temperature dependence of resistivity.
II. EXPERIMENT

Polycrystalline samples were prepared using the following procedure. Appropriate amounts of starting materials Fe
共99.998% purity兲 and S 共99.9999% purity兲 were sealed in an
evacuated silica tube and then were heated to 900 °C for
several days; the product was ground in an Ar atmosphereand kept at 900 °C for further several days. Sulfur vapor
reacted to the iron block completely during these processes.
The almost stoichiometric FeS compound was produced byslow cool from 800 °C. The obtained sample was analyzed
by the x-ray diffraction using Cu K ␣ radiation and was confirmed to be in single phase with the troilite structure. The
estimated lattice parameters, a and c, are (5.965⫾0.001) and(11.757⫾0.002) Å, respectively. Iron sulfide, Fe1⫺x S, has asubstantial deficiency at the iron sites in the range 0⭐x⭐0.15. The obtained sample has a purely stoichiometriccomposition with experimental accuracy as determined using
the empirical relation for the concentration of Fe in Fe1⫺x S
vs the 共102兲 interplanar spacing with the NiAs-type
structure,15 which corresponds to the 共114兲 interplanar spacing with the troilite structure.
A cubic-anvil type apparatus was used to measure theelectrical resistance under pressure up to 8 GPa at temperature down to 4 K.16 The force applied to the apparatus wascontrolled to keep constant during measurements; these measurements were always performed at constant pressure. Pressure was retained nearly hydrostatic in a Teflon cell filledwith Fluorinert as a pressure-transmitting medium. Pressure
was calibrated by a measurement of resistance of Bi metal
under applied force at room temperature. The electrical resistance under high pressure was measured by a standard dc
four-probe technique. Gold wires of 20 ␮m in diameter wereused as electrical leads with silver paint contact on the surface of sample. The typical size of sample under pressure isabout 0.7⫻0.3⫻0.3 mm3. The temperature dependence ofresistance was measured with increasing temperature at various pressures and the pressure was always increased at room
temperature. All resistance data were obtained in the Ohmic
relation between applied current and observed voltage. The
absolute accuracy of resistivity under pressure is limited because of the uncertainties in determinations of length be-

FIG. 1. Pressure dependence of resistivity ␳ in stoichiometric
FeS compound at room temperature.

tween the electrical leads and area perpendicular to the current. Then the obtained resistance data under pressure werenormalized to the absolute resistivity determined at the ambient conditions although the estimated resistivity in the
cubic-anvil type apparatus at the ambient conditions isroughly consistent with the absolute one.

III. EXPERIMENTAL RESULTS

Figure 1 shows the room temperature electrical resistivity,
␳, of FeS as a function of pressure. Initially the ␳ value
decreases exponentially with increasing pressure up to 2.5
GPa and abruptly decreases around 3.5 GPa. Furthermore, ␳decreases up to 6.6 GPa and then increases with increasingpressure. These two anomalies in pressure dependence of ␳
indicate the occurrence of two successive phase transitions
and these transition pressures are consistent with those of thestructural phase transitions.6,10 Although the phase transition
at 6.6 GPa is a first order one with about 7% volume reduction, the pressure dependence of ␳ varies with no discontinuity around 6.6 GPa and there is no observable hysteresis withpressure. The about two orders decrease of magnitude in ␳
around 3.5 GPa suggests that a activation energy in ␳ should
go to zero. From now on, we call the phases below 3.5 GPa,
between 3.5 and 6.6 GPa, and above 6.6 GPa as phases I, II,
and III, respectively.

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PRESSURE-INDUCED SEMICONDUCTOR-METAL . . .

PHYSICAL REVIEW B 63 115203

FIG. 2. Typical temperature dependencies of resistivity ␳ in stoichiometric FeS compound at various pressure 共a兲 and a plot of( ␳ ⫺ ␳ 0 ) vs T at 4.4 GPa as logarithmic scales, 共b兲 where ␳ 0 is theresidual resistivity. The solid line represents the result of fitting.

Figure 2共a兲 shows the typical temperature dependenciesof ␳ at various pressure. As seen in this figure, the resistivity
exhibits nonmetallic behavior below 3 GPa, where a temperature coefficient of ␳ is negative in the whole observed
temperature range. Although there are some tendencies for ␳
to saturate at low temperature, the resistivity exhibits activated behavior above 150 K, which is referred to as theintrinsic property. Since the electronic contribution in lowtemperature specific heat of FeS is almost zero at ambientpressure,17 the ground state has an insulating character. Thus
the value of activation energy E a is estimated from the resistivity curves in the intrinsic temperature region by theequation␳ ⫽ ␳ ⬁ exp共 E a /2k B T 兲 ,共1兲

where ␳ ⬁ is the high-temperature resistivity and k B is theBoltzmann’s constant.
The E a values estimated by this way are shown in Fig. 3
as a function of pressure. The E a value at ambient pressure(38.9⫾0.1) meV, is in good agreement with the value 40
meV determined previously by measurements of resistivity

FIG. 3. Pressure dependence of the activation energy E a in thesemiconductor states of FeS. The solid lines represent the results offitting.

on a single crystal Fe0.996S. 3 Since the E a value decreases
with pressure, we obtained a linear fit of the form
E a ⫽ 共 39.0⫾0.3兲 ⫺ 共 4.5⫾0.2兲 P 共 GPa兲 meV

共2兲

within the accuracy of the data. The critical pressure isevaluated to be (8.7⫾0.1) GPa by extrapolating E a to zero, avalue that is much higher than the critical pressure, 3.5 GPa,at room temperature.
As seen in Fig. 2共a兲, the temperature dependence of ␳ at
4.4 GPa clearly shows a metallic behavior down to 4 K.
Accordingly the anomaly in pressure dependence of ␳
around 3.5 GPa at room temperature corresponds to apressure-induced semiconductor-metal transition in FeS. The
residual resistivity ␳ 0 is 11.90 ␮⍀ cm and the residual resistivity ratio is 32 at 4.4 GPa. These values are comparablewith those of pressure induced metallic state of V2O3. 18 The
␳ 0 value is much smaller than those of metallic states incarrier-doped systems.19 The temperature dependence of ␳ ismarkedly different from a usual metal. Figure 2共b兲 shows aplot of ( ␳ ⫺ ␳ 0 ) vs T at 4.4 GPa as logarithmic scales. Experimental results indicate a relation ( ␳ ⫺ ␳ 0 )⬀T ␯ , and the ␯value is estimated to be (2.09⫾0.05) at 4.4 GPa. This nearlyquadratic temperature dependence of ␳ implies that theelectron-electron collision is an important effect in lowtemperature resistivity in phase II. It was found that ␳ is115203-3

HISAO KOBAYASHI et al.

PHYSICAL REVIEW B 63 115203

almost independent of temperature above 270 K. The similartendency for resistivity to saturate was observed above 300
K in the metallic state of V2O3. 18
Further increasing pressure above 6.6 GPa, the temperature dependence of ␳ shows nonmetallic behavior again as
seen in Fig. 2共a兲. This result is consistent with that of therecent resistance measurement at 10 GPa down to about 80
K.12 In our previous paper,13 we proposed the nonmagnetically metallic state of FeS in this phase. However, our proposed electronic state is inconsistent with the present resultof ␳. The anomaly in pressure dependence of ␳ around 6.6
GPa at room temperature, thus, indicate a re-entrant metalsemiconductor transition. As observed in phase I, there aresimilar tendencies for ␳ to saturate at low temperature. However, ␳ exhibits activated behavior above 200 K. Thus the E avalue is estimated from the resistivity curves in the intrinsic
temperature region using Eq. 共1兲. As shown in Fig. 2共a兲,significant anomaly is found at 55 K in the temperature dependence of ␳ at 6.2 GPa. At higher temperature ␳ behaves
like metallic and at lower temperature ␳ nonmetallic. Accordingly the E a value at 6.2 GPa is estimated in the temperature between 30 and 50 K. The obtained E a values arealso shown in Fig. 3 as a function of pressure. In contrast
with the pressure dependence of E a in phase I, it is foundthat E a increases with pressure in phase III. Within the accuracy of the data, we also obtained linear fit of the form
E a ⫽ 共 ⫺125⫾6 兲 ⫹ 共 21.8⫾0.5兲 P 共 GPa兲 meV.

共3兲

If ␳ ⬁ in Eq. 共1兲 is assumed to be independent of pressure andE a ⫽ ␣ ( P⫺ P c ), the resistivity would increase exponentiallywith pressure. It is noted that ␣ as determined from the slopeof ␳ at room temperature for P⭓6.8 GPa is 20.4 meV/GPa ingood agreement with dE a /d P determined from Eq. 共3兲.
IV. DISCUSSIONAs shown in Fig. 3, it seems that E a depends linearly onpressure in phase I. However, the critical pressure 8.7 GPa,determined from Eq. 共2兲, is much higher than 3.5 GPa wherepressure dependence of ␳ shows anomaly at room temperature. According to the ZSA scheme, the pressure dependenceof gap in electronic structure is related to the pressure dependence of U or ⌬, W, and the hybridization of the electron
configurations. These values do not depend directly on pressure but on a bond length as well as bond angle. From thepressure dependence of volume6,7 and Eq. 共2兲, we approximately obtained a linear dependence of E a on the volume
with the form
E a ⫽ 共 38.8⫾0.1兲 ⫺ 共 335⫾4 兲 ⌬V/V 0 meV,

共4兲

where ⌬V/V 0 ⫽ 关 V(0)⫺V( P) 兴 /V(0). The critical value of⌬V/V 0 is estimated to be (0.11⫾0.01), which corresponds
to be the volume of phase II with MnP-type structure. Thus itis suggested that the volume reduction induced by pressurein phase II is sufficient to close the gap caused by the electronic correlation in phase I.
It is confirmed that the semiconductor-metal transition
takes place at around 3.5 GPa in FeS. At least, the structureof FeS transforms from the troilite to the MnP-type with thistransition at room temperature. Thus, this transition is possibly caused by the electronic correlation and/or electronphonon coupling. First we will discuss a distortion in the
FeS6 octahedra with this structural transition. The FeS6 octahedra in the troilite structure with hexagonal symmetry havemore complex distortion than the trigonal one from O h symmetry. A quantitative measure of distortion in octahedra isgiven by a quadratic elongation, ␭, and an octahedral angle,
␴ 2␪ , which are linearly correlated.20 The mean values of ␭and ␴ ␪2 are defined as
6

¯
␭⫽

兺

i⫽1

冉 冊冒
li 2
l0

6

共5兲

and
12

␴ 2␪ ⫽

兺 共 ␪ i ⫺90° 兲 2 /11,

i⫽1

共6兲

respectively, where l 0 is the center-to-vertex distance for anoctahedron with O h symmetry whose volume is equal that ofthe distorted octahedron with bond lengths l i , and ␪ i arebond angles. At the ambient conditions, ¯␭ ⫽1.019 and ␴ ␪2
⫽59.92 of the FeS6 octrahedra with the troilite structure.6
Although the MnP-type structure has an orthorhombic symmetry, the value of ␦ (⫽c/)b⫺1), which is a measure oforthorhonbic distortion from the hexagonal symmetry, isevaluated to be just 0.7% in phase II. In 3d-monopnictides
with the MnP-type structure,21 these ␦ values are about 7%,
which are 10 times larger than that in phase II. Thus the b-cplane has the pseudohexagonal cell matrix in phase II. At 6.3
GPa and room temperature,6 ¯␭ ⫽1.018 and ␴ 2␪ ⫽63.04, which
are comparable to those in phase I. Consequently, the distortion of the Fe atom’s coordination polyhedra does not essentially change at this structural phase transition.
Next we will discuss the electronic states of Fe ion inphases I and II. It was found by Mössbauer spectroscopy
under pressure12,13 that the Fe state in FeS has divalent withhigh-spin configuration up to 6.3 GPa. Recently this result is
confirmed by x-ray emission spectroscopy under pressure
where well-defined satellite below 13 eV from the main peak
was observed in the emission spectra up to 6.3 GPa.14 Since
the center shift of Fe in FeS decreases linearly with decreasing volume up to 6.3 GPa, there is no discontinuous chargetransfer between Fe and S ions at the semiconductor-metaltransition. Therefore the electronic correlation plays an important role in this pressure-induced collapse of energy gap
in spite of the structural transformation. It is noticed that
there is antiferromagnetic order in FeS up to 6.6 GPa at room
temperature.12,13,22
The temperature dependence of ␳ in phase II is well characterized with the relation, ␳ ⫽ ␳ 0 ⫹AT 2 , at least up to 30 K.
The coefficient A was obtained to be (7.52⫾0.02)⫻10⫺3
and (5.4⫾0.3)⫻10⫺3 ␮ ⍀ cm/K2 at 4.4 and 5.5 GPa, respectively, by the least-squares fitting in the temperature range
between 4 and 25 K. These values are about 500 times larger
than the typical values of transition metals23 and comparable

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PRESSURE-INDUCED SEMICONDUCTOR-METAL . . .

PHYSICAL REVIEW B 63 115203

with those of the highly correlated electron systems.18,19 Thislarge A value suggests that the electronic state in phase II isa highly correlated metal. The pressure-induced decrease in
A is attributed to the decrease of the electron correlation
because W increases with pressure and U decreases because
of increasing a screening effect.
At higher temperature in phase II, ␳ linearly increases
from 80 K and is almost independent of temperature above
270 K. It seems that the tendencies for ␳ to saturate in themetallic V2O3 above 300 K are caused by the strongly
electron-electron scattering effect because the large A value
was observed. In normal metals, the characteristic temperature of flattening in resistivity is an order of the Fermi energy. However, the large enhancement of effective mass dueto the correlation in metal decreases this characteristic temperature. If we regard the flattening in ␳ of FeS as the effectof large mass enhancement, the characteristic temperature isevaluated to be an order of room temperature. This evaluatedcharacteristic temperature is probably too low because the A
values in FeS are five times smaller than those in the metallic
V2O3. Thus, whether the observed anomaly in ␳ of metallic
FeS at high temperature is coupled with the highly correlated
metal state is still an open question for experiment.
It was found by the present electronic measurements thatthe phase III shows nonmetallic behavior down to 4 K. The
estimated E a value increases with pressure at the rate of 21.8
meV/GPa in phase III, while E a decreases with pressure inphase I. This increment of E a with pressure cannot be expected for the insulators where the electronic correlation
causes to open up a gap in electronic structure. Accordingly,
phase III is most likely to be a band insulator rather than the
Mott-Hubbard or charge-transfer insulator.
This nonmetallic behavior is consistent with the results ofprevious and recent Mössbauer and x-ray emission measurements where the Fe state in this phase is suggested to havethe low-spin Fe共II兲 state.12,14 Even though the lower local
symmetry and the probability of covalent bonding complicate the situation in FeS, the large volume reduction at thisphase transition suggests that not only the bandwidth but also
the hybridization of the electron configurations is increased.

These increments with the compression would induce thehigh-spin to low-spin transition in the Fe2⫹ ion as observedin the system FeS2-MnS2. 24,25
Although the local symmetries at Fe sites in this phase are
more distorted from O h symmetry than those in phases I andII, the orbitals of Fe 3d with an e g doublet character would
have a large overlap with the S 3p orbitals. This ␴-type overlap forms the antibonding state with highest energy and thebonding state with lowest energy around the Fermi level
where the former is predominantly of Fe 3d character andthe later predominantly of S 3p character. Therefore, thelow-spin Fe共II兲 state in FeS consists of the occupied nonbonding band with a mainly t 2g triplet character where degeneracy is lifted by the distortion and the unoccupied antibonding band. Since the increment of E a with pressure wasobserved in this phase, the gap between the nonbonding andantibonding bands increases more rapidly with the pressureinduced overlap than the bandwidth.

*Email: kobayash@nuclear.phys.tohoku.ac.jp

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V. CONCLUSION

We have measured the electrical resistivity of stoichiometric FeS compound under pressure. It was found that thesemiconductor-metal and metal-semiconductor transitions
occur at 3.5 and 6.6 GPa, respectively. In phase I, E a decreases linearly with ⌬V/V 0 and the estimated critical⌬V/V 0 value corresponds to be the volume of phase II with
the MnP-type structure. The volume reduction induced bypressure in phase II is sufficient to close the gap caused by
the electronic correlation in phase I. On the other hand, E a
increases with pressure and then phase III is most likely to bea band insulator. As result of the large volume reduction inphase III, the Fe state changes from the high-spin to low-spin
Fe共II兲 state and the electronic structure consists of the occupied nonbonding and unoccupied antibonding bands aroundthe Fermi level. In phase II, the resistivity rises quadraticallywith temperature at low temperature. It was found that the A
values are much larger than the typical values of transition
metals. This large A value suggests that the electronic state inphase II is a highly correlated metal.

9115203-5

HISAO KOBAYASHI et al.
17

PHYSICAL REVIEW B 63 115203

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115203-6

Journal of Magnetism and Magnetic Materials 226}230 (2001) 449}451

Anisotropy of the upper critical "eld of the spin-ladderSr
Ca Cu O
\V V  

T. Nakanishi  *, N. Motoyama, H. Mitamura , N. Takeshita , H. Takahashi,H. Eisaki, S. Uchida, T. Goto , H. Ishimoto , N. Mo( riInstitute for Solid State Physics, University of Tokyo, Kashiwa-shi, Chiba 277-8581, JapanDepartment of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, JapanDepartment of Superconductivity, University of Tokyo, Tokyo 113-8656, Japan

Abstract
We report on the resistive upper critical "eld, H (¹) for the hole-doped two-leg ladder Sr
Ca Cu O (x"12)\V V  
single crystal, which becomes superconducting with ¹ &5 K in a pressure above &3.0 GPa. From the results ofmagneto-transport measurements on a single sample at a pressure of 3.5 GPa, H (¹) has been determined up to 20 Talong the a-axis (N ladder) and up to 7 T both along the b-axis (N ladder-plane) and along the c-axis ( ladder). A clear
di!erence in H (¹) is observed among these three directions, indicating that this system has an anisotropic supercon
ducting ground state. Also, it is found that H@ (¹) shows non-linearity near ¹ at zero "eld and no saturation down to
¹/¹ &0.03, exhibiting an upward curvature. Furthermore, H? is found to exceed the Pauli limit by a factor of morethan 2. This fact suggests a possibility of triplet superconductivity.  2001 Elsevier Science B.V. All rights reserved.
Keywords: Spin ladders; Superconductors; Low-dimensional system; High pressure

Since the discovery of superconductivity in the holedoped two-leg ladder compound Sr
Ca Cu O
\V V  [1,2], the study of ladder materials has been one of themost attractive and active ones in the "eld of low-dimensional systems [3]. This spin-ladder system becomessuperconducting with ¹ &5 K in a pressure above&3.0 GPa, and, at present, is the only known superconducting ladder material, although its superconducting
properties have been reported only in a previous paper[4], describing preliminary results for the upper critical"eld of the Sr Ca Cu O single crystal. Those results   
suggest that superconducting correlations along theinterladder direction are stronger than along the ladderdirection, although the normal state conductivity is* Correspondence address: Department of Physics, College of
Humanities and Sciences, Nihon University, 3-25-40, Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan. Tel.: #81-3-33291151, ext. 5514; fax: #81-3-5317-9432.
E-mail address: tn@chs.nihon-u.ac.jp (T. Nakanishi).

higher along the c-axis ( ladder) than along the a-axis( interladder) [2]. However, in those experiments three
di!erent batches of the single crystal were used for eachAC susceptibility measurement in the "eld along di!erent
axis. Therefore, a possibility still remains that the results
depend on the measured batches because the superconductivity begins to appear at a certain critical pressure,the value of which may depend on the batch. In otherwords, it is di$cult to reproduce the same high-pressure
condition, which induces the superconductivity, in eachmeasurement. In order to eliminate the above possibility,
here we perform magneto-transport measurements ona single sample to clarify the anisotropy of the upper
critical "eld of Sr Ca Cu O .
   
Single crystals of Sr Ca Cu O were grown by the   travelling-solvent #oating zone method using an infrared
furnace under oxygen gas. Using a newly developed selfclamped high-pressure cell [5,6] which employs Bridgman anvils with a Te#on capsule "lled with a pressuretransmitting medium (a 1:1 mixture of Fluorinert FC 70
and FC 77), we can pressurize a delicate sample such asoxide or organic crystals under hydrostatic conditions up

0304-8853/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 3 4 2 - 1

450

T. Nakanishi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 449}451

Fig. 1. Temperature dependence of resistivity along the c-axis,
 , of Sr Ca Cu O at 3.5 GPa in various magnetic "elds   
applied along the a-axis.

to &6 GPa and measure the absolute values of electricalresistivity by four-probe technique. Because of its compact body, we can attach the high-pressure cell to a dilution refrigerator which can be set in a superconducting
magnet of cylindrical 20 T or horizontally rotatable
split-type 7 T. By using these apparatuses, the temperature dependence of resistivity along the c-axis was measured on a single sample in "elds up to 20 T along thea-axis (N ladder) and up to 7 T along the b-axis (N ladder-plane) and the c-axis ( ladder) at temperatures down
to &140 mK.
As a typical result, the temperature dependence of theresistivity along the c-axis,  , of Sr Ca Cu O atA   a pressure of 3.5 GPa in various magnetic "elds appliedalong the a-axis up to 20 T is shown in Fig. 1. As seen in
the "gure, the transition shifts to lower temperatures as
the magnetic "eld is increased although a resistive hump,the origin of which is unknown at present, is observed in
the transition. Fig. 2 shows the resistive upper critical"eld, H for Ha, de"ned by several ways as illustrated
in the inset. This "gure indicates that essential feature of
the behavior of H is independent of the way determining ¹ . From the result, H , de"ned as a midpoint of thetransition, is summarized in Fig. 3, together with theresults for Hb and Hc, where the measuring current isalways parallel to the c-axis. As seen in Fig. 3, the temperature dependence of H is di!erent for these three direc
tions such as HA 'H? 'H@ within this measured
temperature and magnetic "eld range, which are in linewith the normal state conductivity anisotropy [2,7] andin contrast to the previous result [4]. One of the possible
reasons of this discrepancy may be due to the sample
dependence in the previous measurements. Fig. 3 clearlyFig. 2. Temperature dependence of the resistive upper critical"eld, H (¹), of Sr Ca Cu O
at 3.5 GPa for Ha-axis,   
where several ways determining ¹ are used as illustrated in theinset.

Fig. 3. Temperature dependence of the resistive upper critical"eld, H (¹), of Sr Ca Cu O
at 3.5 GPa for Ha-axis   (closed circles), Hb-axis (open squares) and Hc-axis (opencircles). A broken line indicates the Pauli limit, H .
.

indicates that the superconducting phase in the present
ladder system is an anisotropic one in the three directions. If we use the Werthamer}Helfand}Hohenberg
formula [8] as H (0)"!0.7¹ (0)(dH /d¹ ) 
by



 2 
using the slope near ¹ (0), we obtain the following esti
mated values: H? (0)&8 T, H@ (0)&0.7 T, HA (0)&27 TAwhich corresponds to the Ginzburg}Landau coherence
length as  &120 As ,  &10 As , &400 As . As easily?
@A

T. Nakanishi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 449}451

seen in Fig. 3, these estimated values of H (0) are well
below the obtained experimental values, indicating thatthe behavior of H in this ladder material is not de
scribed by the conventional picture. In particular, it isfound that H@ shows non-linearity near ¹ (0) and no
saturation down to ¹/¹ &0.03, exhibiting an upwardcurvature. These behaviors are quite di!erent from thoseof conventional BCS superconductors in which Hexhibits negative curvature with saturation at low
temperatures. Such anomalous temperature dependencesof H are similar to that of some high-¹ super
conductors (HTSC) in the case of applying magnetic"elds perpendicular to the CuO planes, which have been

recently observed in Tl Ba CuO [9], Bi Sr CuO [10]
 

 
W
and LaSr CuO [11]. Thus, this anomalous behav\V V
ior of H is found to be a similarity between the ladders
and HTSC in the superconducting properties in themagnetic "eld while some similarities in the normal
state properties have been pointed out so far [3]. The
other important fact seen in Fig. 3 is that H? exceeds thevalue of the Pauli limit (in this case &9.0 T as indicatedby a broken line in Fig. 3) by a factor of more than 2,
which is given by H (¹"0) " 1.84 ¹ (0) for isotropic
s-wave pairing without spin}orbit scattering [12,13] (orbeing reduced by a factor of 0.86 for anisotropic singlet
pairing [14]). Such a large evolution of H at lowtemperatures has been observed in the quasi-one-dimensional molecular superconductor (TMTSF) PF [15] in which the spin-triplet pairing may be realized [16].

451

Therefore, the behavior of H exceeding the Pauli limitsuggests a possibility of triplet superconductivity inSr
Ca Cu O .
\V V  This work was supported by a Grant in Aid for Scienti"c Research from the Japanese Ministry of Education,
Science and Culture.

References[1] M. Uehara et al., J. Phys. Soc. Jpn. 65 (1996) 2764.
[2] T. Nagata et al., Phys. Rev. Lett. 81 (1998) 1090.
[3] E. Dagotto, Rep. Prog. Phys. 62 (1999) 1525.
[4] T. Nakanishi et al., Physica B 281 & 282 (2000) 957.
[5] T. Nakanishi, Ph.D. Thesis, University of Tokyo, 2000
(Chapter 2) (in Japanese).
[6] T. Nakanishi et al., to be published.
[7] N. Motoyama et al., Phys. Rev. 55 (1997) R3386.
[8] N.R. Werthamer, E. Helfand, P.C. Hohenberg, Phys. Rev.
147 (1966) 295.
[9] A.P. Mackenzie et al., Phys. Rev. Lett. 71 (1993) 1238.
[10] M.S. Osofsky et al., Phys. Rev. Lett. 71 (1993) 2315.
[11] Y. Ando et al., Phys. Rev. 60 (1999) 12475.
[12] A.M. Clogston, Phys. Rev. Lett. 9 (1962) 266.
[13] B.S. Chandrasekar, Appl. Phys. Lett. 1 (1962) 7.
[14] Y. Hasegawa, H. Fukuyama, J. Phys. Soc. Jpn. 56 (1987)877.
[15] I.J. Lee et al., Phys. Rev. Lett. 78 (1997) 3555.
[16] I.J. Lee et al., cond-mat/0001332.

Journal of Magnetism and Magnetic Materials 226}230 (2001) 246}248

High-pressure e!ect on transport properties of spin-laddercompounds Na
Ca V O and Ca Li V O
\V V     
H. Takahashi *, T. Nakanishi , T. Arima, M. Noguchi, M. Oyanagi,N. Takeshita, N. Mo( ri
Department of Physics, College of Humanities and Sciences, Nihon University, 2-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550, Japan
Institute of Materials Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-0006, Japan
Institute for Solid State of Physics, The University of Tokyo, 5-1-5 Kahiwanoha, Kashiwa, Chiba 277-8581, Japan

Abstract
Electrical resistivity of layered vanadium oxides Na
Ca V O and Ca Li V O has been measured under high\V V     pressures of up to 10 GPa. These compounds have V}O networks forming a two-leg spin-ladder layer in somecomposition range. In the spin-ladder compound Na
Ca V O , electrical resistivity measurements show semicon\V V  ducting behavior. However, the electrical resistivity has been signi"cantly reduced under high pressure, although it
remains semiconducting up to 8 GPa. On the other hand, the electrical resistivity of Ca Li V O which also has   a two-leg spin-ladder layer is lower than Na
Ca V O by several orders of magnitude. The electrical resistivity of
\V V  
Ca Li V O was greatly reduced even at low-temperature range by applying pressure.  2001 Elsevier Science B.V.
   
All rights reserved.
Keywords: Spin ladder; Metal}insulator transition; Pressure

1. Introduction
Great attention has been paid to the so-called spinladder materials. While several cuprate high-¹ super!
conductors have been found out, discovery of new superconducting materials is strongly desired to elucidate thehigh-¹ mechanism and "nd out new superconductors!
having higher ¹ . In such an investigation spin-ladder!
materials were thought to be good candidates as new
superconducting systems. Spin-gap behavior which isone of the characteristic properties of cuprate superconductors was theoretically predicted [1,2] and later observed in even-leg spin-ladder materials such as
SrCu O [3,4]. Sr
Ca Cu O
has also been \V V  
studied as a spin-ladder material; its electrical resistivity
is greatly reduced by substituting Ca for Sr showing
semiconducting behavior over the entire composition* Corresponding author. Fax: #81-3-5317-9432.
E-mail address: hiroki@chs.nihon-u.ac.jp (H. Takahashi).

ranges. However, insulator}metal transition occurs under high pressure. In addition to the insulator}metaltransition, superconductivity was discovered at pressurelarger than 4 GPa [5] with ¹ increasing up to 12 K at!
6 GPa. The e!ect of high pressure seems to play animportant role for the delocalization of carriers in theladder layer. Although the characterization of this superconductivity is di$cult due to the necessity of a highpressure technique, a recent advanced high-pressuretechnique revealed the magnetic properties of this superconducting material [6].
Recently, doping e!ects on vanadate spin-ladder materials have been intensively investigated in relation to
low-dimensional magnetic and electrionic properties[7,8]: spin-gap behavior has been reported in CaV O [9], and substitution of Na for Ca has been achieved,
leading to a greatly reduced electrical resistivity in theNa
Ca V O system [10,11]. However, they show
\V V  
semiconducting behavior over the entire substitution
range. Hence, high-pressure techniques are expected to
be a powerful tool to study metallization in this system.
Here we report the pressure e!ects on the electrical0304-8853/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 2 9 1 - 9

H. Takahashi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 246}248

Fig. 1. Pressure dependence of the electrical resistivity for
Na Ca V O , Na Ca V O , and Ca Li V O .
         

resistivity of this system and lately synthesized
Ca Li V O .
Theelectricalresistivityof   
Ca Li V O is much smaller than that for the   Ca
Na V O system.
\V V  
Polycrystalline samples of Na
Ca V O and\V V  
Ca Li V O have been synthesized under high-pres   sure conditions. The lattice constants along the a andb-axis remain almost constant with changing x, while theone along the c-axis decreases with decreasing x. Detailsof sample preparations are described elsewhere [10,11].
Electrical resistivity measurements were carried out under high pressures at low temperature by means of a DC
four-probe technique. A cubic-anvil apparatus was used
to generate hydrostatic pressures up to 10 GPa at temperatures down to 4 K. During these measurements the247pressure was controlled to be kept constant on bothcooling and heating processes.
Fig. 1 shows the pressure dependence of the electricalresistivity at room temperature for Na Ca V O ,   
Na Ca V O , and Ca Li V O . The electrical      
resistivity is greatly reduced under high pressure for eachmaterial, as shown in Fig. 1. While the electrical resistivities of Na Ca V O and Na Ca V O decrease      
to  the value at 8 GPa compared with the one at 1 atm,the electrical resistivity of Ca Li V O decreases to    the value at 10 GPa. Figs. 2(a) and (b) show the temperature dependence of the electrical resistivity at several
constant
pressuresfor
Na Ca V O
and   
Ca Li V O , respectively. From Fig. 2(a) the electri   
cal resistivity of Na Ca V O decreases with pres   sure and the shape of the (¹) curve does not change
signi"cantly up to the maximum pressure. On the other
hand, it is observed from Fig. 2(b) that the electricalresistivity of Ca Li V O decreases with pressure   
especially in the low-temperature range. However, theelectrical resistivity still displays semiconducting behavior even at the maximum pressure of 10 GPa.
In spin-ladder materials it is thought that the conduction of carriers occurs through the ladder layer. All theseexperiments make it clear that the pressure plays animportant role in delocalizing carriers in the ladder layer,
which is similar to the pressure e!ect observed in theSr
Ca Cu O system. From Fig. 1 the lowest resis\V V  
tivity for Ca Li V O is 4;10\  cm at 300 K and   
10 GPa. In the superconducting Sr Ca
Cu O     
spin-ladder system, the electrical resistivity is about
4;10\  cm at 300 K and 3 GPa [12]. The electricalresistivity in usual high-¹ superconductors is less than!
1;10\  cm at 300 K. Thus, further carrier doping
and/or applying higher pressure are thought to be necessary to give rise to the insulator}metal transition in thisFig. 2. Temperature dependence of the electrical resistivity for (a) Na Ca V O and (b) Ca Li V O measured at constant      pressures, respectively.

248

H. Takahashi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 246}248

system. Superconductivity is also expected in such a metallic phase.
This work was partly supported by Grant-in-Aid Nos.
10440114 and 11554015 from the Ministry of Education,
Science and Culture of Japan.

References[1] E. Dagotto, J. Riera, D. Scalapino, Phys. Rev. B 45 (1992)
5744.
[2] T.M. Rice, S. Gopalan, M. Sigrist, Europhys. Lett. 23(1993) 445.
[3] M. Azuma, Z. Hiroi, M. Takano, K. Ishida, Y. Kitaoka,
Phys. Rev. Lett. 73 (1994) 3463.
[4] K. Ishida, Y. Kitaoka, K. Asayama, M. Azuma, Z. Hiroi,
M. Takano, J. Phys. Soc. Japan 63 (1994) 3222.

[5] M. Uehara, T. Nagata, J. Akimitsu, H. Takahashi, N.
Mo( ri, K. Kinoshita, J. Phys. Soc. Japan 65 (1996)
3764.
[6] T. Nakanishi, N. Motoyama, H. Mitamura, N. Takeshita,
H. Takahashi, H. Eisaki, S. Uchida, T. Goto, H. Ishimoto
and N. Mo( ri, in this volume.
[7] H. Iwase, M. Isobe, Y. Ueda, H. Yasuoka, J. Phys. Soc.
Japan 65 (1996) 2397.
[8] M. Onoda, N. Nishiguchi, J. Solid State Chem. 127 (1996)
359.
[9] M. Isobe, Y. Ueda, J. Magn. Magn. Mat. 177}181 (1998)
671.
[10] P.N. Rogers, R.N. Shelton, Solid State Commun. 114(2000) 607.
[11] T. Arima and M. Noguchi, private communication.
[12] T. Nagata, M. Uehara, J. Goto, J. Akimitsu, N. Motoyama, H. Eisaki, S. Uchida, H. Takahashi, T. Nakanishi,
N. Mo( ri, Phys. Rev. Lett. 81 (1998) 1090.

Journal of Magnetism and Magnetic Materials 226}230 (2001) 449}451

Anisotropy of the upper critical "eld of the spin-ladderSr
Ca Cu O
\V V  

T. Nakanishi  *, N. Motoyama, H. Mitamura , N. Takeshita , H. Takahashi,H. Eisaki, S. Uchida, T. Goto , H. Ishimoto , N. Mo( riInstitute for Solid State Physics, University of Tokyo, Kashiwa-shi, Chiba 277-8581, JapanDepartment of Physics, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-8550, JapanDepartment of Superconductivity, University of Tokyo, Tokyo 113-8656, Japan

Abstract
We report on the resistive upper critical "eld, H (¹) for the hole-doped two-leg ladder Sr
Ca Cu O (x"12)\V V  
single crystal, which becomes superconducting with ¹ &5 K in a pressure above &3.0 GPa. From the results ofmagneto-transport measurements on a single sample at a pressure of 3.5 GPa, H (¹) has been determined up to 20 Talong the a-axis (N ladder) and up to 7 T both along the b-axis (N ladder-plane) and along the c-axis ( ladder). A clear
di!erence in H (¹) is observed among these three directions, indicating that this system has an anisotropic supercon
ducting ground state. Also, it is found that H@ (¹) shows non-linearity near ¹ at zero "eld and no saturation down to
¹/¹ &0.03, exhibiting an upward curvature. Furthermore, H? is found to exceed the Pauli limit by a factor of morethan 2. This fact suggests a possibility of triplet superconductivity.  2001 Elsevier Science B.V. All rights reserved.
Keywords: Spin ladders; Superconductors; Low-dimensional system; High pressure

Since the discovery of superconductivity in the holedoped two-leg ladder compound Sr
Ca Cu O
\V V  [1,2], the study of ladder materials has been one of themost attractive and active ones in the "eld of low-dimensional systems [3]. This spin-ladder system becomessuperconducting with ¹ &5 K in a pressure above&3.0 GPa, and, at present, is the only known superconducting ladder material, although its superconducting
properties have been reported only in a previous paper[4], describing preliminary results for the upper critical"eld of the Sr Ca Cu O single crystal. Those results   
suggest that superconducting correlations along theinterladder direction are stronger than along the ladderdirection, although the normal state conductivity is* Correspondence address: Department of Physics, College of
Humanities and Sciences, Nihon University, 3-25-40, Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan. Tel.: #81-3-33291151, ext. 5514; fax: #81-3-5317-9432.
E-mail address: tn@chs.nihon-u.ac.jp (T. Nakanishi).

higher along the c-axis ( ladder) than along the a-axis( interladder) [2]. However, in those experiments three
di!erent batches of the single crystal were used for eachAC susceptibility measurement in the "eld along di!erent
axis. Therefore, a possibility still remains that the results
depend on the measured batches because the superconductivity begins to appear at a certain critical pressure,the value of which may depend on the batch. In otherwords, it is di$cult to reproduce the same high-pressure
condition, which induces the superconductivity, in eachmeasurement. In order to eliminate the above possibility,
here we perform magneto-transport measurements ona single sample to clarify the anisotropy of the upper
critical "eld of Sr Ca Cu O .
   
Single crystals of Sr Ca Cu O were grown by the   travelling-solvent #oating zone method using an infrared
furnace under oxygen gas. Using a newly developed selfclamped high-pressure cell [5,6] which employs Bridgman anvils with a Te#on capsule "lled with a pressuretransmitting medium (a 1:1 mixture of Fluorinert FC 70
and FC 77), we can pressurize a delicate sample such asoxide or organic crystals under hydrostatic conditions up

0304-8853/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 3 4 2 - 1

450

T. Nakanishi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 449}451

Fig. 1. Temperature dependence of resistivity along the c-axis,
 , of Sr Ca Cu O at 3.5 GPa in various magnetic "elds   
applied along the a-axis.

to &6 GPa and measure the absolute values of electricalresistivity by four-probe technique. Because of its compact body, we can attach the high-pressure cell to a dilution refrigerator which can be set in a superconducting
magnet of cylindrical 20 T or horizontally rotatable
split-type 7 T. By using these apparatuses, the temperature dependence of resistivity along the c-axis was measured on a single sample in "elds up to 20 T along thea-axis (N ladder) and up to 7 T along the b-axis (N ladder-plane) and the c-axis ( ladder) at temperatures down
to &140 mK.
As a typical result, the temperature dependence of theresistivity along the c-axis,  , of Sr Ca Cu O atA   a pressure of 3.5 GPa in various magnetic "elds appliedalong the a-axis up to 20 T is shown in Fig. 1. As seen in
the "gure, the transition shifts to lower temperatures as
the magnetic "eld is increased although a resistive hump,the origin of which is unknown at present, is observed in
the transition. Fig. 2 shows the resistive upper critical"eld, H for Ha, de"ned by several ways as illustrated
in the inset. This "gure indicates that essential feature of
the behavior of H is independent of the way determining ¹ . From the result, H , de"ned as a midpoint of thetransition, is summarized in Fig. 3, together with theresults for Hb and Hc, where the measuring current isalways parallel to the c-axis. As seen in Fig. 3, the temperature dependence of H is di!erent for these three direc
tions such as HA 'H? 'H@ within this measured
temperature and magnetic "eld range, which are in linewith the normal state conductivity anisotropy [2,7] andin contrast to the previous result [4]. One of the possible
reasons of this discrepancy may be due to the sample
dependence in the previous measurements. Fig. 3 clearlyFig. 2. Temperature dependence of the resistive upper critical"eld, H (¹), of Sr Ca Cu O
at 3.5 GPa for Ha-axis,   
where several ways determining ¹ are used as illustrated in theinset.

Fig. 3. Temperature dependence of the resistive upper critical"eld, H (¹), of Sr Ca Cu O
at 3.5 GPa for Ha-axis   (closed circles), Hb-axis (open squares) and Hc-axis (opencircles). A broken line indicates the Pauli limit, H .
.

indicates that the superconducting phase in the present
ladder system is an anisotropic one in the three directions. If we use the Werthamer}Helfand}Hohenberg
formula [8] as H (0)"!0.7¹ (0)(dH /d¹ ) 
by



 2 
using the slope near ¹ (0), we obtain the following esti
mated values: H? (0)&8 T, H@ (0)&0.7 T, HA (0)&27 TAwhich corresponds to the Ginzburg}Landau coherence
length as  &120 As ,  &10 As , &400 As . As easily?
@A

T. Nakanishi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 449}451

seen in Fig. 3, these estimated values of H (0) are well
below the obtained experimental values, indicating thatthe behavior of H in this ladder material is not de
scribed by the conventional picture. In particular, it isfound that H@ shows non-linearity near ¹ (0) and no
saturation down to ¹/¹ &0.03, exhibiting an upwardcurvature. These behaviors are quite di!erent from thoseof conventional BCS superconductors in which Hexhibits negative curvature with saturation at low
temperatures. Such anomalous temperature dependencesof H are similar to that of some high-¹ super
conductors (HTSC) in the case of applying magnetic"elds perpendicular to the CuO planes, which have been

recently observed in Tl Ba CuO [9], Bi Sr CuO [10]
 

 
W
and LaSr CuO [11]. Thus, this anomalous behav\V V
ior of H is found to be a similarity between the ladders
and HTSC in the superconducting properties in themagnetic "eld while some similarities in the normal
state properties have been pointed out so far [3]. The
other important fact seen in Fig. 3 is that H? exceeds thevalue of the Pauli limit (in this case &9.0 T as indicatedby a broken line in Fig. 3) by a factor of more than 2,
which is given by H (¹"0) " 1.84 ¹ (0) for isotropic
s-wave pairing without spin}orbit scattering [12,13] (orbeing reduced by a factor of 0.86 for anisotropic singlet
pairing [14]). Such a large evolution of H at lowtemperatures has been observed in the quasi-one-dimensional molecular superconductor (TMTSF) PF [15] in which the spin-triplet pairing may be realized [16].

451

Therefore, the behavior of H exceeding the Pauli limitsuggests a possibility of triplet superconductivity inSr
Ca Cu O .
\V V  This work was supported by a Grant in Aid for Scienti"c Research from the Japanese Ministry of Education,
Science and Culture.

References[1] M. Uehara et al., J. Phys. Soc. Jpn. 65 (1996) 2764.
[2] T. Nagata et al., Phys. Rev. Lett. 81 (1998) 1090.
[3] E. Dagotto, Rep. Prog. Phys. 62 (1999) 1525.
[4] T. Nakanishi et al., Physica B 281 & 282 (2000) 957.
[5] T. Nakanishi, Ph.D. Thesis, University of Tokyo, 2000
(Chapter 2) (in Japanese).
[6] T. Nakanishi et al., to be published.
[7] N. Motoyama et al., Phys. Rev. 55 (1997) R3386.
[8] N.R. Werthamer, E. Helfand, P.C. Hohenberg, Phys. Rev.
147 (1966) 295.
[9] A.P. Mackenzie et al., Phys. Rev. Lett. 71 (1993) 1238.
[10] M.S. Osofsky et al., Phys. Rev. Lett. 71 (1993) 2315.
[11] Y. Ando et al., Phys. Rev. 60 (1999) 12475.
[12] A.M. Clogston, Phys. Rev. Lett. 9 (1962) 266.
[13] B.S. Chandrasekar, Appl. Phys. Lett. 1 (1962) 7.
[14] Y. Hasegawa, H. Fukuyama, J. Phys. Soc. Jpn. 56 (1987)877.
[15] I.J. Lee et al., Phys. Rev. Lett. 78 (1997) 3555.
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