Stabilization of highly polar BiFeO$_3$-like structure: a new interface design route for enhanced ferroelectricity in artificial perovskite superlattices

TL;DR

This paper demonstrates how interface engineering in BaTiO3/CaTiO3 superlattices can stabilize a highly polar BiFeO3-like phase in CaTiO3, enabling new pathways to create ferroelectric and multiferroic materials from nonpolar perovskites.

Contribution

It introduces a novel interface reconstruction mechanism that stabilizes a BiFeO3-like phase in CaTiO3, expanding the design space for ferroelectric and multiferroic materials.

Findings

Stabilization of a highly polar BiFeO3-like phase in CaTiO3 via interface reconstruction.

Identification of oxygen octahedron rotation patterns as key to phase stabilization.

Prediction of new ferroelectric materials from nonpolar perovskites through interface engineering.

Abstract

In ABO3 perovskites, oxygen octahedron rotations are common structural distortions that can promote large ferroelectricity in BiFeO3 with an R3c structure [1], but suppress ferroelectricity in CaTiO3 with a Pbnm symmetry [2]. For many CaTiO3-like perovskites, the BiFeO3 structure is a metastable phase. Here, we report the stabilization of the highly-polar BiFeO3-like phase of CaTiO3 in a BaTiO3/CaTiO3 superlattice grown on a SrTiO3 substrate. The stabilization is realized by a reconstruction of oxygen octahedron rotations at the interface from the pattern of nonpolar bulk CaTiO3 to a different pattern that is characteristic of a BiFeO3 phase. The reconstruction is interpreted through a combination of amplitude-contrast sub 0.1nm high-resolution transmission electron microscopy and first-principles theories of the structure, energetics, and polarization of the superlattice and its constituents. We further predict a number of new artificial ferroelectric materials demonstrating that nonpolar perovskites can be turned into ferroelectrics via this interface mechanism. Therefore, a large number of perovskites with the CaTiO3 structure type, which include many magnetic representatives, are now good candidates as novel highly-polar multiferroic materials [3].