Group-Theoretical Classification of Aristotypes of Cation and Anion Orders in Perovskites

Abstract

A group-theoretical classification of cation and anion orders of crystals with a perovskite structure is presented. Aristotypes are idealized structures (phases), from which the low-symmetry ordered modifications of perovskites are formed as a result of rotations and deformation of octahedra, as well as the cooperative Jahn–Teller effect and other physical phenomena. Seven aristotype classes have been distinguished, which are characterized by the atomic ordering in each of Wyckoff positions and simultaneous atomic ordering in several positions. The critical and secondary (improper) order parameters, describing the formation of ordered structures, are determined. The classification proposed makes it possible to systematize a variety of known phases, establish genetic structural links between low-symmetry ordered structures, and design new materials.