'Disordered' Ba(Mg1/3Ta2/3)O-3 and its ordering transition

摘要

The microstructure of the as-received disordered Ba(Mg1/3Ta2/3)O-3 (BMT) and BMT after ordering heat treatment was studied by electron diffraction and high-resolution electron microscopy (HREM). 'Disordered' BMT consists of short-range-ordered nanodomains; diffuse streaking along all (111) directions is present in the reciprocal space. HREM images show that the BaO3 framework is unfaulted; the defects occur on the B cation (Mg and Ta) sublattice and consist of 'chemical faults'. Such faults change the local composition, causing a local excess of either Mg or Ta. The overall 1:2 stoichiometry can be conserved by the occurrence of both types of fault. Heat treatments will remove these faults and yield 1:2 ordered nuclei; further annealing will make these ordered nuclei grow larger, inducing long-range-ordered orientation variants. [References: 3]