Evaluation of the 1:2 ordered structure of Ba(B′1/3B′′2/3)O3 perovskites along various zone axes using transmission electron microscopy

Abstract

The 1:2 ordered structure of Ba(B′_1/3B′′_2/3)O₃ perovskites was studied in detail by transmission electron microscopy from different projections (〈110〉_c, 〈111〉_c and 〈112〉_c) in Ba((Co, Zn, Mg)_1/3Nb_2/3)O₃ ceramics. For the 〈110〉_c and 〈112〉_c zone axes, the occurrence of 1/3{111}-type superlattice reflections in their corresponding selected area electron diffraction images directly revealed the 1:2 ordered structure. The most informative 〈110〉_c zone gave two sets of 〈111〉_c ordering variants, providing a convenient way to detect the twin boundaries. The 〈112〉_c zone axis variant with only one set of 〈111〉_c axes could be used to detect single anti-phase boundaries. In addition, the 〈111〉_c zone axis, which is parallel to the ordering direction, clearly showed the hexagonal symmetry of a 1:2 ordered structure in the corresponding high-resolution transmission electron microscopy image. For a completely ordered sample, there are always a certain proportion of areas without a superperiod lattice. These areas should also be the ordered domains, the variants of which are not perpendicular to the given zone axis.