Inference of oxygen vacancies in hydrothermal Na0.5Bi0.5TiO3

A high-resolution x-ray powder diffraction study has been made of pseudo-rhombohedral and tetragonal phases in Na0.5Bi0.5TiO3 (NBT), produced via hydrothermal and conventional solid-state methods. Hydrothermal NBT exhibits significantly greater structural distortion at room temperature than solid-state NBT. Peak widths and superstructure peak intensities show a phase transition at similar to 305 degrees C, with trends suggesting that the structure tends towards cubic symmetry at this temperature. Structural refinements indicate that the transition occurs via a phase coexistence region with no clear intermediate phase. Piezoelectric data show evidence of polarisation pinning in hydrothermal NBT, interpreted as a high proportion of oxygen vacancies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4755882]