Fig. 1. Perovskite structure and composition.

(A) ABX₃, in the cubic single perovskite structure ($\mathit{P}\mathit{m}\overline{3}\mathit{m}$), where the A cation is surrounded by a network of corner-sharing BX₆ octahedra. (B) A₂BB′X₆, in the rock salt double perovskite structure ($\mathit{F}\mathit{m}\overline{3}\mathit{m}$), where the A cations are surrounded by an alternating network of BX₆ and B′X₆ octahedra. In this structure, inverting the B and B′ cations results in an equivalent structure. While the ideal cubic structures are shown here, perovskites may also adopt various noncubic structures. (C) Map of the elements that occupy the A, B, and/or X sites within the 576 compounds experimentally characterized as perovskite or nonperovskite at ambient conditions and reported in (17–19).