The structural complexity of perovskites.

A recent research direction related to ABX 3 perovskites is the use of molecules on the A and/or X-site, a development that has proved fruitful for photovoltaics, (improper) ferroelectrics and barocalorics. Replacing atoms by molecules increases the chemical space for the synthesis of materials with new properties, conceptually translating chemical, synthetic freedom to novel opportunities in material design. Here an information theory-based rating scheme is applied to obtain structural complexities across various perovskite classes. It is shown that chemical diversity is synonymous with increased structural complexity which scales with the size of the pseudocubic ReO 3 -type network and available distortion schemes. The results agree with chemical intuition and show that structural complexities serve as a valuable tool for identifying complex distortion schemes in perovskites such as octahedral tilts and shifts with unusual propagation vectors and deformations of the coordination network.