Interplay of epitaxial strain and rotations in PbTiO$_3$/PbZrO$_3$ superlattices from first principles

TL;DR

This study uses first-principles calculations to explore how epitaxial strain influences structural phases and distortions in PbTiO3/PbZrO3 superlattices, revealing complex phase transitions driven by octahedral rotations and antipolar modes.

Contribution

It provides a detailed symmetry-based analysis of phase behavior and identifies the critical role of various distortions in strain-induced phase transitions in superlattices.

Findings

Identified three phase transitions with increasing in-plane lattice constant.

All phases exhibit significant oxygen octahedral rotations.

Antipolar distortion is key in high-tensile-strain phase.

Abstract

We present first-principles calculations of the structural phase behavior of the [1:1] \pzta\ superlattice and the \ptoa\ and \pzoa\ parent compounds as a function of in-plane epitaxial strain. A symmetry analysis is used to identify the phases and clarify how they arise from an interplay between different kinds of structural distortions, including out-of-plane and in-plane polar modes, rotation of oxygen octahedra around out-of-plane or in-plane axes, and an anti-polar mode. Symmetry-allowed intermode couplings are identified and used to elucidate the nature of the observed phase transitions. For the minimum-period [1:1] \pzta\ superlattice, we identify a sequence of three transitions that occur as the in-plane lattice constant is increased. All four of the phases involve substantial oxygen octahedral rotations, and an antipolar distortion is important in the high-tensile-strain phase. Inclusion of these distortions is found to be crucial for an accurate determination of the phase boundaries.