Designing New Improper Ferroelectrics with a General Strategy

TL;DR

This paper introduces a universal design strategy for discovering new improper ferroelectric materials, expanding beyond traditional structures using density functional theory and substitution methods.

Contribution

A general design rule for improper ferroelectrics applicable to any system, enabling identification of new ferroelectric and multiferroic materials beyond known structures.

Findings

R-3c perovskite can become ferroelectric via B-site cation substitution

ZnSrO2 can be ferroelectric through anion substitution

Design approach can create new multiferroics like fluorine-doped LaMnO3

Abstract

The presence of a switchable spontaneous electric polarization makes ferroelectrics ideal candidates for the use in many applications such as memory and sensors devices. Since known ferroelectrics are rather limited, finding new ferroelectric (FE) materials has become a flourishing field. One promising route is to design the so-called hybrid improper ferroelectricity. However, the previous approach based on the Landau theory is not easily adopted to the systems that are unrelated to the Pbnm perovskite structure. To this end, we develop a general design rule that is applicable to any systems. By combining this rule with density functional theory calculations, we identify previously unrecognized classes of FE materials. It shows that the R-3c perovskite structure can become FE by substituting half of the B-site cations. ZnSrO2 with a non-perovskite layered structure can also be FE through the anion substitution. Moreover, our approach can be used to design new multiferroics as illustrated in the case of fluorine substituted LaMnO3.