Cooperative Couplings between Octahedral Rotations and Ferroelectricity in Perovskites

TL;DR

This paper reveals a dual nature of the interaction between octahedral rotations and ferroelectricity in perovskites, showing that their coupling can be cooperative rather than competitive, leading to novel ferroelectric behaviors.

Contribution

It introduces a unified model with high-order coupling terms explaining the dual AFD-FE interaction and predicts pressure-enhanced polarization in perovskites.

Findings

AFD and FE modes can cooperate in certain perovskites.

A new high-order coupling model explains the dual interaction.

Pressure can enhance ferroelectric polarization.

Abstract

The structure of ABO3 perovskites is dominated by two types of unstable modes, namely, the oxygen octahedral rotation (AFD) and ferroelectric (FE) mode. It is generally believed that such AFD and FE modes tend to compete and suppress each other. Here we use first-principles methods to show that a dual nature of the AFD-FE coupling, which turns from competitive to cooperative as the AFD mode strengthens, occurs in numerous perovskite oxides. We provide a unified model of such a dual interaction by introducing novel high-order coupling terms, and explain the atomistic origin of the resulting new form of ferroelectricity in terms of universal steric mechanisms. We also predict that such a novel form of ferroelectricity leads to atypical behaviors, such as an enhancement of the electric polarization under hydrostatic pressure.