First-principles examination of low tolerance factor perovskites

Abstract

Perovskites are generally formed in the non‐polar Pnma phase. The materials found in the polar subgroup of Pnma are not common. This article reports how perovskites having a low tolerance factor display ferroelectric instabilities in artificially constrained Pnma phase. The bond length distribution and the bond valence sum were analyzed to examine the origin of the ferroelectric behavior of low tolerance factor materials. However, the ground state structure of low tolerance perovskite is not Pnma phase, but either ilmenite (R 3¯) or lithium niobate (R3c) phase. Here, epitaxial strain was used as a tuning parameter to stabilize the polar subgroup of Pnma. The rationalized principles from these studies will be valuable for designing new ferroelectric materials in the future.

Silver niobate perovskites: structure, properties and multifunctional applications

“…where r O , r A , and r B are the ionic radii of the O, A, and B ions, respectively. In some publications, an alternative expression has been proposed: 86,87 t ¼ r AÀO . ffiffi ffi…”

“…21) can be linked to its geometry by the tolerance factor ( t ) as discussed by Bartel et al , 85 where r O , r A , and r B are the ionic radii of the O, A, and B ions, respectively. In some publications, an alternative expression has been proposed: 86,87 where r A–O and r B–O are the bond lengths of A–O and B–O bonds, respectively. In some crystals, the interaction between A-/B-site cations and the O anion is not only based on ionic bonds, but also on covalent ones, which play an essential role in the origin of ferroelectricity.…”