Symmetry-based approach to identify structural prototypes of ferroic phases

In previous work, we developed a systematic symmetry analysis using group-subgroup relations to construct representative structural models for ferroic phases in the form of supercells that satisfy a desired point symmetry but are built from the minical combination of lower-symmetry primitive cells [M. Kotiuga et al., arXiv:2107.04628]. This allowed us to identify structural prototypes (i.e., supercells that are lower in energy, per formula unit, than the higher-symmetry primitive cell and with real, positive phonon dispersions) of paraelectric barium titanate characterized by〈111〉local titanium displacements while preserving cubic point symmetry. Here, we extend this study to several other cubic perovskites and show that the metastability of these prototypes is related to the phonon instabilities of the 5-atom conventional cell and is dependent on volume, the latter often dictated by the filler A-site cation.¹ Furthermore, we investigate other lower-symmetry phases of perovskites in order to identify the structural prototypes of both ferroelectric and antiferroelectric phases of these materials.² This approach is general and can be used in any crystalline system to find candidate templates and efficiently search for prototypes.