Phase relations in the system of (Na1/2Bi1/2)TiO3–PbTiO3. I. Structure

Abstract

The region of the (Na_1/2Bi_1/2)_1−xPb_xTiO₃ phase diagram from 0≤x≤0.2 was established through analysis of structure and thermal anomalies associated with changes in temperature and composition. The rhombohedral‐tetragonal morphotropic phase boundary (MPB) was investigated considering the dependence of the rhombohedral lattice distortion of (Na_1/2Bi_1/2)TiO₃ (NBT) on chemical stoichiometry and fabrication processes. It was found that the MPB would lie in the composition range 0.13<x1/2Bi_1/2)TiO₃ are 3.886 Å and 89.6°, respectively. The phase transition sequence of (Na_1/2Bi_1/2)_1−xPb_xTiO₃ was rhombohedral↔tetragonal↔cubic as that of pure NBT when x was less than MPB composition. However, the intermediate tetragonal phase has either low tetragonal distortion for compositions with x<x_rc (composition where rhombohedral↔cubic transition exists) or high tetragonal distortion for compositions with x≳x_rc. The changes in structure and phase transition behavior of this solid solution system with temperature and composition are discussed.