Coupling between octahedral rotations and local polar displacements in WO3/ReO3 superlattices

TL;DR

This study uses first-principles calculations to explore how octahedral rotations and local polar displacements interact in WO3/ReO3 superlattices, revealing strain-induced enhancements and stability conditions.

Contribution

It demonstrates the coupling between octahedral rotations and polar displacements in superlattices, highlighting the effects of strain and layer thickness on structural stability and distortions.

Findings

Octahedral tilts do not propagate across materials in superlattices.

Strain couples with antiferroelectric displacements to enhance rotations in WO3 layers.

Thicker ReO3 layers (≥3 layers, Re fraction ≥50%) stabilize the superlattice and promote rotations.

Abstract

We model short-period superlattices of WO$_3$ and ReO$_3$ with first-principles calculations. In fully-relaxed superlattices, we observe that octahedral tilts about an axis in the planes of the superlattices do not propagate from one material, despite the presence of the corner-shared oxygen atoms. However, we find that octahedral rotation is enhanced within WO$_3$ layers in cases in which strain couples with native antiferroelectric displacements of tungsten within their octahedral cages. Resulting structures remain antiferroelectric with low net global polarization. Thermodynamic analysis reveals that superlattices with sufficiently thick ReO$_3$ layers, the absolute number being three or more layers and the Re fraction $\geq 50\%$, tend to be more stable than the separated material phases and also show enhanced octahedral rotations in the WO$_3$ layers.