Using a symmetry-based approach to identify structural prototypes from first principles

Many materials properties stem directly from the underlying crystal structure, which often exhibit orderings extending past a single chemical unit. In this seminar I will focus on paraelectric and ferroelectric phases of perovskites that exhibit a non-negligible degree of disorder using barium titanate as our primary test case. I will show how one can construct metastable prototypes of these phases through a symmetry analysis in tandem with density-functional-theory calculations. These prototypes can serve as minimal models which can be used to faithfully represent these phases in calculations and, being metastable, are local minima of the potential-energy landscape and therefore possess no structural instabilities. This methodology has allowed us to systematically explore and identify two structural prototypes for paraelectric barium titanate which possess titanium displacements while maintaining a cubic point symmetry and, furthermore, correspond to phonon instabilities of the 5-atom-primitive cell [PRR 4, L012042 (2022)]. I will discuss our results across the titanates, niobates and zirconates, as well as extensions to the lower-symmetry ferroelectric phases.