Disordered off-center direction of Ti4+ in pseudo-cubic type BaTiO3 prepared by mixed hydroxide process

Abstract

Recently, perovskite-type BaTiO3 showing sharp X-ray diffraction peak comparable to that synthesized by a conventional solid-state reaction was obtained by mixing Ba(OH)2 and TiO2 hydrous gel and by leaving the mixture at 323 K or less. However, the obtained BaTiO3 was cubic crystal system, which was different from that synthesized by a conventional solid-state reaction. In this study, the structural analysis of cubic-BaTiO3 obtained by this technique was conducted, and the factors to form cubic structure were investigated. Since no second harmonic generation signal was observed, the structure of BaTiO3 was essentially different from that of traditional tetragonal-BaTiO3. Rietveld analysis with the initial structure model of ideal cubic perovskite structure exhibited that Ti4+ had exceptionally large isotropic atomic displacement parameter. A reasonable isotropic atomic displacement parameter was obtained by considering the static site disorder in the initial structural model, that is, Ti4+ locates at off-center position in TiO6 octahedron by displacing in a disordered direction, resulting in pseudo-cubic symmetry.