Influence of the Hydride Content on the Local Structure of a Perovskite Oxyhydride BaTiO3-xHx

Abstract

The local structure of BaTiO3 perovskite has been investigated for studying phase transitions by several groups. While it has been shown that H- doping into BaTiO3 changes its long-range average crystal symmetry from tetragonal to cubic, factors contributing to the structural change have not been fully understood. In this work, we investigated the dependence of the local structure of BaTiO3-xHx on the doped H- amount by means of Raman and X-ray absorption fine-structure (XAFS) spectroscopy measurements. The x value of BaTiO3-xHx could vary in the range of 0-0.5 by changing the amount of the CaH2 precursor in the topochemical synthesis of BaTiO3-xHx. Raman spectroscopy indicated that the cubic phase is induced in the initial tetragonal phase when the doped H- amount was relatively large (x ≥ 0.2). On the other hand, XAFS measurements revealed that the symmetry of the TiO6 octahedral in BaTiO3-xHx is strongly affected by the doped H- amount. The local distortion of the Ti [111] displacement is relaxed with an increase of H-, causing the tetragonal-to-cubic structural change.