Polymorphism in Bi-based perovskite oxides: a first-principles study

TL;DR

This study uses a genetic algorithm to explore the complex polymorphic landscape of Bi-based perovskite oxides, revealing numerous minima and structural variations influenced by energy balances and strain conditions.

Contribution

It provides a comprehensive first-principles analysis of the polymorphism in Bi-based perovskites, identifying multiple stable and metastable phases and their dependence on strain and energy considerations.

Findings

Large number of energy minima compared to typical ferroelectric perovskites

Identification of charge-ordering structures in BiMnO₃

Existence of an inverse supertetragonal phase in bulk and under strain

Abstract

Under normal conditions, bulk crystals of BiScO$_3$ , BiCrO$_3$, BiMnO$_3$, BiFeO$_3$, and BiCoO$_3$ present three very different variations of the perovskite structure: an antipolar phase, a rhombohedral phase with a large polarization along the space diagonal of the pseudocubic unit cell, and a supertetragonal phase with even larger polarization. With the aim of understanding the causes for this variety, we have used a genetic algorithm to search for minima in the surface energy of these materials. Our results show that the number of these minima is very large when compared to that of typical ferroelectric perovskites like BaTiO$_3$ and PbTiO$_3$ , and that a fine energy balance between them results in the large structural differences seen. As byproducts of our search we have identified charge-ordering structures with low energy in BiMnO$_3$ , and several phases with energies that are similar to that of the ground state of BiCrO$_3$. We have also found that a inverse supertetragonal phase exists in bulk, likely to be favored in films epitaxially grown at large values of tensile misfit strain.