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

Abstract

Under normal conditions, bulk crystals of BiScO3, BiCrO3, BiMnO3, BiFeO3, and BiCoO3 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 BaTiO3 and PbTiO3, 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 BiMnO3, and several phases with energies that are similar to that of the ground state of BiCrO3. 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.

Supertetragonal Phases of Perovskite Oxides: Insights from Electronic Structure Calculations

“…Another curve showing the same tendency corresponds to supertetragonal P4mm BiFeO 3 , which is not the ground state of the bulk material, but it is very similar to the phase accessible when grown as thin films in the way described in the previous Section. For supertetragonal P4mm BiScO 3 and BiMnO 3 these results align with those previously reported for these oxides [37,41] regarding their potential to be realized experimentally (in the case of BiMnO 3 , supertetragonal structures that are slightly monoclinic are favored over the purely tetragonal P4mm phase [40,41] ). Finally, BiCrO 3 shows a behaviour that is more similar to BaTiO 3 than to his bismuth-based relatives.…”

“…Figure 2 (bottom panel) points towards a positive answer. The data in this graph is from Reference [40]; it shows how five bismuth-based perovskites of tetragonal P4mm symmetry behave with pressure, after our calculations using the PBEsol approximation. Among them, there is BiCoO 3 , which displays this P4mm phase in bulk in normal conditions.…”

“…Top panel: results for PbTiO 3 , taken from Reference [33] (local-density approximation; circles) and from Reference [31] (PBEsol approximation; squares). Bottom panel: results for Bi-based perovskites, taken from Reference [40].…”

“…While this is the case in the other bismuth-based perovskites, no supertetragonal phase seems available for BiCrO 3 in normal conditions. [40] The picture that emerges is one in which all perovskite oxides have the potential to become supertetragonal, if enough negative pressure is applied. Enough, in this context, might mean ambient conditions, like in the case of BiCoO 3 , and this is why crystals of this material can be synthesized with c/a = 1.27 in bulk.…”

First-principles screening of ABO3 oxides with two magnetic sublattices

“…An intensive investigation like this one, which involves numerous structural optimizations for varying compositions and spin arrangements, requires a computationally light method for it to be feasible. Additionally, DFT + U simulations have been shown to yield qualitatively and semiquantitatively correct results for many multiferroic and related compounds, including ferrites [33,34], manganites [35,36], and even nickelates [37,38] displaying exotic charge-and orbital-ordering effects. Further, DFT + U has been used to compute the parameters of suitable spin Hamiltonians that can be solved numerically to yield magnetic-ordering temperatures in agreement with experiment [39,40].…”