Phase relations in the system of (Na1/2Bi1/2)TiO3-PbTiO3 .1. Structure

The region of the (Na1/2Bi1/21)(1-x)PbxTiO3 phase diagram from 0 less than or equal to x less than or equal to 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 (Na1/2Bi1/2)TiO3 (NET) on chemical stoichiometry and fabrication processes. It was found that the MPB would lie in the composition range 0.13 < x < 0.15 when the lattice constant and lattice distortion of (Na1/2Bi1/2)TiO3 are 3.886 Angstrom and 89.6 degrees, respectively. The phase transition sequence of (Na1/2Bi1/2)(1-x)PbxTiO3 was rhombohedral <----> tetragonal <----> cubic as that of pure NET 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. (C) 1996 American Institute of Physics.