B-CATION ARRANGEMENTS IN DOUBLE PEROVSKITES

A survey of A'A''B'B''O6 double perovskites, which encompasses over 300 compounds synthesized from about 1950 to the present, shows that three distinct B-cation arrangements are known: random, rock salt, and layered. Examples are provided to illustrate the most common symmetries of these B-cation sublattices and to show how they can be assigned based on powder diffraction patterns. A comprehensive examination of the factors that influence B-cation arrangement, namely the charge, size, and electronic configuration of the B cations, and the A/B size ratio, is presented. Special consideration is given to the layered sublattice because of its rarity and its potential importance in two-dimensional materials, such as cuprate superconductors.