Evolutionary exploration of polytypism in lead halide perovskites.

The regular ABX cubic perovskite structure is composed of close-packed AX layers stacked along the 〈111〉 axis. An equivalent hexagonal close-packed network can also be formed, in addition to a series of intermediate polytype sequences. Internally, these correspond to combinations of face- and corner-sharing octahedral chains that can dramatically alter the physical properties of the material.