Evolution of the chemical bonding nature of ferroelectric bismuth titanate upon cation substitution

The effect of cation substitution on the crystal and electronic structures of ferroelectric bismuth titanate has been systematically investigated. According to the x-ray diffraction analyses on Bi_3.25A _0.75Ti₃O₁₂ (A = Bi, La, Gd, and Y), it was found that the cation substitution gives rise to the contraction of the volume of the unit cell and to the decrease of the structural distortion of the bismuth titanate, as well. The present x-ray absorption spectroscopic results reveal that the local structural change upon chemical reduction is remarkably depressed by the cation substitution through the enhancement of (Ti - O) bonds. Such a stabilization of TiO₆ octahedra can be understood by a competition between adjacent (Bi - O) and (Ti - O) bonds as well as the contraction of the unit cell.