Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

7C/2004G272

Analysis of rare-earth substitution for BaTiO3 by XAFS
Takanori ISHIKAWA1, Kenji OHNUMA1, Ken-ichi KAKIMOTO1, Hitoshi OHSATO1* andYouichi MIZUNO2
1
Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
2

Taiyo Yuden co., Ltd., 5607-2 Nakamuroda, Haruna-Machi, Gunma-Gun, Gunma 370-3347, Japan

Introduction
The thickness of a layer of multi layer ceramiccapacitor becomes thinner to obtain and higher capacity. Itis, therefore, important to enhance the reliability for themicrostructure of the thin dielectric layer sandwiched byelectrode layers. The microstructure and electric
properties of BaTiO3 have been improved by addition ofrare-earth oxides. To discuss the mechanism, it isimportant to examine the solid solution structure of
rare-earth doped BaTiO3 (ABO3).
In previous studies, preferential soluble sites of rareearth in BaTiO3 have been presumed by Rietveld
refinement analysis. As a result, the preferential solublesite has been clarified by their ionic radii.
In this study, rare-earth doped BaTiO3 solid solutions
were analyzed by XAFS to reveal the information of thefine structure of BaTiO3.
Experimental
Model samples of (Ba1-xRx)(Ti1-xRx)O3(R=Eu or Sm,
x=0.03, 0.05 and 0.10) were prepared by a conventional
solid reaction method. The L3-edge XAFS spectra of Eu(6.98keV) and Sm (6.72keV) were measured at BL-7C in
the Photon Factory, KEK, Tsukuba, Japan. The X-rays
were monochromatized with Si (111) crystal at the station,and the absorption spectra were observed in atransmission mode.
The EXAFS date were refined by REX2000 program(ver2.3). The k3-weighted EXAFS functions were used forthe calculation of the radial structure functions, in thek-region of 3.0-9.2 Å-1 for Eu L3-edge EXAFS spectraand 3.0-9.1 Å-1 for Sm L3-edge EXAFS spectra. The
backscattering amplitudes and phase shifts werecalculated. Furthermore, the spectra of [Ba(Ti,R)O3] weresimulated for comparison by FEFF7 software.
Results and Discussion
Figure 1 shows the Fourier transformed k3-weighted
EXAFS spectra for (Ba1-xEux)(Ti1-xEux)O3 (x=0.03, 0.05and 0.10) and (Ba1-xSmx)(Ti1-xSmx)O3 (x=0.03, 0.05 and0.10). The measured samples exhibited separated peaks,indicating the existence of different R-O distances. Thepeak located at around 1.8Å represents the nearest
neighbor shell around R in B site that is composed of 6
oxygen atoms. The peak located at around 2.5 Årepresents the nearest neighbor shell around R in A sitethat is composed of 12 oxygen atoms. The simulated
EXAFS spectra show a strong peak which locates atsmaller R than 2.0Å. On the other hand, the observed
peak at 2.5Å was assigned to the peak of R-O(12CN).
This result indicates that R is soluble in both A and B sitesof BaTiO3.
Table1 show the structural parameters derived fromEXAFS analysis of the R-L3 edge of (Ba1-xRx)(Ti1-xRx)O3.
The interatomic distances between R and oxygen for
B-site (6CN) were about 2.34Å(R=Eu) and 2.36Å(R=Sm)
in all compositions. These values are almost equal to thesum of the ionic radii[1] of R3+ and O2-:
0.947Å(Eu3+6CN), 0.958Å(Sm3+6CN) and 1.4Å(O2-6CN).
The interatomic distance between Ti4+ (0.605Å, 6CN) andO2- was about 2.0Å. It means that B-site expands by thesubstitution of R3+ to the B-site of BaTiO3, because ionicradii are in the order of Sm3+ (0.958 Å) > Eu3+ (0.947 Å)> Ti4+ (0.605Å). On the other hand, the interatomic
distances between R and oxygen for A-site (12CN) wereabout 2.66-2.77Å in all compositions. A-site of BaTiO3contract by R3+ incorporation, because the interatomicdistance (2.84Å) between Ba2+ and O2- are larger than that
(2.66-2.77 Å) between R3+ and O2-.

References[1]R.D.Shannon, Acta Cryst.A32, 751(1976)*ohsato.hitoshi@nitech.ac.jp

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