Stabilizing ferroelectricity in alkaline-earth-metal-based perovskites (ABO3) via A- (Ca2+/Sr2+/Ba2+) and B-site (Ti4+) cationic radius ratio (RA /RB )

Abstract

Various distortion parameters for alkaline-earth-metal-based perovskites (A 2+B 4+O3) have been analyzed as a function of A- and B-site cationic radii R A and R B. The observed octahedral rotations and their associated mode amplitudes have shown an increasing trend with larger B-site cations, while a decreasing trend has been observed with larger A-site cations. Moreover, the analysis demonstrates that for incipient ferroelectrics like CaTiO3 and SrTiO3, having respective space groups Pnma (a -0 b +0 a -0) and Pm 3 m (a 00 a 00 a 00), ferroelectric displacements are achieved via cation manipulation, which is governed by the R A /R B parameter. The increase in R A /R B through substitutions on the A site may suppress octahedral rotations as well as A-site anti-polar displacements in CaTiO3 and can consequently lead to a ferroelectrically distorted BaTiO3-like P4mm (a 00 a 00 c 0+) phase via a cubic phase of SrTiO3, which has an intermediate R A /R B parameter. These results have been further corroborated by the calculated amplitudes of various frozen phonon modes associated with the cubic Pm 3 m Brillouin zone, responsible for symmetry breaking to tilt-oriented non-ferroelectric Pnma and ferroelectric P4mm phases. © 2022 International Union of Crystallography. All rights reserved.