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Fig. 2

Schematic illustration of a quasiperiodic lattice that contains
a charge degree of freedom. Each lattice point can assume
either a divalent form (light blue circles) or a trivalent one(dark blue circles), for example. Typically two kinds ofcharge motion are possible: an itinerant state and a localized
one. ``L'' and ``S'' respectively denote the long segment andshort one in the so­called Fibonacci chain that is a typical ex­
ample of a quasiperiodic lattice.

Fig. 3

Schematic illustration of a pressure eect on the Yb valence
state.

Fig. 4

Successive shells of the Tsai­type atomic cluster in a Cd_Yb
icosahedral quasicrystal: (a) 4Cd tetrahedron, (b) 20Cd
dodecahedron, (c) 12Yb icosahedron, and (d) 30Cd
icosidodecahedron. A Cd_Mg_
Yb quasicrystal is obtainedby Mg substitution at the Cd sites.

úËõ May 2012 Vol.25 No.3  177

Yb ³20ÊÌ^»iCd84Yb16jðÎÛÆµÄIñ¾B
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Fig. 5

Schematic illustration of the experimental setup for the x­rayabsorption and diraction measurements under high pres­sure at SPring­8 BL22XU.

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Fig. 6

Normalized Yb L3 XANES spectra of Cd_
Yb quasicrystal atselect pressures at room temperature (open circles). Eachspectrum is tted by the sum (solid line) of the divalent (dot­ted line) and trivalent (dashed line) components.

Fig. 2 É¦µ½óµÆÍÙÈÁÄ¨èC»ÝÌnÌêÍ
A_[\fÌüúÅÉ·énÆÈÁÄ¢éBæÁÄCFig. 2 ÅÍ¶ÝµÈ¢êl¿ÅÂÇÝIÈêCÂÜèCÇÝ¥C[gª`±dqÅêÕÁ³êÈªçàeTCgÉ¶Ý·éóµàN±è¦éB±±ÅCXANES ªèÌ^CEChEÉÂ¢ÄGêÄ¨­Bêl¿Ì¿h®óÔÆ¢¤_ÌêûÅC
XANES XyNgÍ 2 ¿¬ªÆ 3 ¿¬ªÌdËí¹ÅèCæÁÄC2 ¿ÌTCgÆ 3 ¿ÌTCgÆª»ê¼ê
¶Ý·éæ¤ÉàÝ¦éBµ©µCXANES É¨¯éõwJÚ Ìfßö Í¨æ»10|16 sec Æñí É¬¢àÌ ÅéB»Ì½ßC¿h®óÔÉÂ¢Äà»ÌXibvVbgðÆé±ÆÉÈèCâÍè 2 ¿¬ªÆ 3 ¿¬ªÌdËí¹Æ¢¤Êð^¦éBÂÜèCXANES ªèÍCÕðÉÇÝÉÖ·éîñÍ^¦È¢êûÅCóÔ@½ÉÖç¸¿Ì½Ïlð^¦Ä­êéè@ÅFig. 7

Pressure dependence of Yb valence in a Cd_
Yb quasicrystal(dark blue circles) and that in a Cd_Mg_Yb quasicrystal(light blue circles).

»ÉÍCOqÌæ¤É 2 íÞÌÇ\¢ÌÙÈéT
CgªèCXÉCÇ\¢ª¯êÅà»wIÉÍ·×ÄÌTCgªñ¿Åé½ßCãÒÌÂ\«àl¦çêéÆ]¦éB5. Ô¿ Yb üúnÉ¨¯é¿ÍÍÌg£ÉäXÍCÔ¿ Yb üúnÌ¿ÍÍð 3 ¿Éü©ÁÄæèg°é±ÆðÚwµ½Bêl¿óÔÌÔ¿ Yb n»¨ÌêC¿ÁÍdqÖÌÁÉÎ½Bµ©µCÇÌ Yb TCgà Cd ´qÉæÍÜêÄ¢é

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±ÆÉÍÏíèÍÈ­CÂC»Ì´qpbLOÍf§üúnðnë¤Æ¢¤Ìª_¢ÅÅé±Æ©çCÇÌTCgÌ Yb àêlÉCI¼aªéB

Fig. 8 ÍCã\IÈ Yb »¨ÉÂ¢Ä Yb ¿Ædq
é35,36)BdqäM¸­µÄCOÒÌÊð^¦½àÌÆl¦çêéB±ÌäMWÌÖWðvbgµ½àÌÅ_ÉéÚ×Í¶£34É÷éÆµÄCTvÍÌÊèÅWÌå«³ÍdqÖÌ­³ÉÎ·éÌÅCFig. 8 ÉéBCd_Yb »ÉÍÎ·éüúnÅ

éß»Ýçêé¿ÁÆÆàÉdqäMWªÁ·élq

Cd6Yb ª¶ÝµCFig. 4 Ì´qNX^[ª bcc zñµ½ÍC¿ÁÉ]ÁÄdqÖª­­ÈÁÄ¢é±Æð¦úËõ May 2012 Vol.25 No.3  179

Fig. 9Fig. 8Relationship between the electronic specic heat coecient(g) and the Yb valence in intermediate­valence Yb­based
compounds. Light blue line is to guide the eye. The open
circle denotes the contribution of the higher valence ions in
Yb2Pt3Sn5. Valence regions developed in the studies on a
Cd_Yb quasicrystal and on a Cd_Mg_Yb quasicrystal arealso shown. More detailed information regarding this plot isgiven in Ref. 35.

The pressure­volume relationship of a Cd_Mg_Yb
quasicrystal (closed circles). The solid line shows a t of the
Birch­Murnaghan equation of state. Compression curve of a
Cd_Yb quasicrystal is also shown (dotted line, Ref. 39).

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Pressure­Induced Formation ofIntermediate­Valence Quasicrystalline
Systems in Yb­based alloys
Tetsu WATANUKI

Condensed Matter Science Division, Japan Atomic Energy Agency
1_1_1 Kouto, Sayo, Hyogo 679_5148, Japan

Daichi KAWANA

Condensed Matter Science Division, Japan Atomic Energy Agency
present address: Institute of Materials Structure Science, KEK
1_1 Oho, Tsukuba, Ibaraki 305_0801, Japan

Akihiko MACHIDA

Condensed Matter Science Division, Japan Atomic Energy Agency
1_1_1 Kouto, Sayo, Hyogo 679_5148, Japan

AnPang TSAI

Institute of Multidisciplinary Research for Advanced Material, Tohoku University
Katahira 2_1_1, Aoba­ku, Sendai 980_
8577, Japan

Abstract

Quasiperiodic intermediate­valence systems were prepared by applying pressure to Yb­based
quasicrystals. In these systems, each quasiperiodic lattice point has a charge degree of freedom.
Synchrotron radiation x­ray absorption spectroscopy experiments near the Yb L3­edge demonstratethat the Yb valence in a Cd_Yb icosahedral quasicrystal increases continuously upon compression froma divalent state at ambient pressure and reaches 2.33 at 31.7 GPa, where the quasiperiodically arranged
Yb ions take a valence uctuation state. For the case of a Cd_Mg_Yb icosahedral quasicrystal, the Yb
valence reaches a value of 2.71 at 57.6 GPa. By following the trend of Yb­based intermediate­valence
crystalline compounds, this large valence increase suggests that the 4f electron system in this quasicrystal
varies from a valence uctuation regime to a strong correlated electron regime.

úËõ May 2012 Vol.25 No.3  183