Ceramics-Silikáty 53 (2) 118-127 (2009)

Correlation between local structures and partial electronic band states in ferroelectric Bi_4–XLa_XTi₃O₁₂; 0.0≤x≤1.46

M. Hidaka, R. P. Wijesundera, R. Kumara, Y. Noguchi, M. Miyayama, S.-H. Choi, N. E. Sung, M. G. Kim

The local structures and the partial band states near a Fermi level (EF) have been studied at room temperature in the ferroelectric phase of Bi_4–XLa_XTi₃O₁₂ (BLT) with 0.00≤x≤1.46 by means of X–ray absorption spectra (XAS) including EXAFS and XANES. The EXAFS spectra suggest that, as increasing the substituted La ions, the local structures around Ti and Bi ions in perovskite-blocks of (Bi_2–XLa_XTi₃O₁₀)^-2 are gradually deformed till x=0.85, and are largely changed by a structural phase transition occurring between x=0.85 and 1.20. The XANES spectra suggest that there is a strong hybridization between Ti-3d(t_2g) and O-2p bands and between Bi-6s and O-2p bands in the valence band states, while between Ti-3d(eg) and O-2p bands and Bi-6p and O-3s bands in the conduction band states. All of the XAS show interesting dependency on the concentration of the substituted La ions in BLT. The results suggest that, in BLT, a reducing spontaneous polarization induced by the La-substitution results from the deformation of the local structures around Ti and Bi ions and from modulation of the hybridized band states near E_F.

Keywords: Ferroelectric thin film; Bi_4–XLa_XTi₃O₁₂; EXAFS; XANES