Ferroelectric and Antiferroelectric Perovskites PbB′ 0.5 B′′ 0.5 O 3

This is a review of properties of PbB' 0.5 B'' 0.5 O 3 perovskites, which hold a special position among ferroelectric and antiferroelectric perovskites because of the presence of two sorts of B ions in the sublattice of the oxygen octahedra. The B' and B'' ions may be ordered, disordered or partially ordered, and this has a tremendous influence on the properties of these compounds. So, when one speaks about this class of perovskites, one should also indicate the degree of ion ordering in them. In this review, an analysis is made of specific features of phase transitions in perovskites with different degrees of ion ordering: diffuse phase transitions and relaxor properties in materials with ion disorder, so-called spontaneous phase transitions, and ferroelectric-to-antiferroelectric transformations at the ion ordering. Some related problems are also discussed.