Crystal Structures of SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9 Ferroelectric Materials

Abstract

AbstractStructural and ferroelectric properties of stoichiometric SrBi2Ta2O9 and Sr-deficient-and-Bi-excess Sr0.8Bi2.2Ta2O9 bulk ceramics materials are studied. The ferroelectric Curie temperatures for SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9 are 300 and 400°C, respectively. Structure analysis by neutron powder diffraction reveals that Bi2O2 layer and TaO6 octahedra are considerably distorted and that atomic displacement along the a-axis causes ferroelectric spontaneous polarization. In Sro8Bi22Ta2O9, both Bi-substitution and cation-vacancies exist at the Sr-site. The calculated polarization of Sr0.8Bi2.2Ta2O9 is higher than that of the stoichiometric sample, which is consistent with observations of remanent polarization in thin-film capacitors. The Bi-substitution and the cation-vacancies at the Sr site enhance structural distortion in the TaO6 octahedron and lead to the higher Curie temperature and the higher ferroelectric spontaneous polarization.