The microstructure of as-received disordered Ba(Mg1/3Ta2/3)O3, or that after an ordering heat-treatment, was studied by means of electron diffraction and high-resolution electron microscopy. The so-called disordered material consisted of short-range ordered nanodomains. Diffuse streaking along all <111> directions was present in reciprocal space. High-resolution electron microscopic images showed that the BaO3 framework was unfaulted. The defects occurred on the B-cation (Mg and Ta) sub-lattice and consisted of so-called chemical faults. Such faults changed the local composition, thus causing a local excess of either Mg or Ta. The overall 1:2 stoichiometry could be conserved by the occurrence of both types of fault. Heat treatments could remove these faults and yield 1:2 ordered nuclei. Further annealing could make these ordered nuclei grow larger; thus inducing long-range ordered orientation variants.

‘Disordered’ Ba(Mg1/3Ta2/3)O3 and its Ordering Transition. C.H.Lei, S.Amelinckx, G.Van Tendeloo: Philosophical Magazine A, 2002, 82[11], 2321-32