Mesoscopic theory of defect ordering-disordering transitions in thin oxide films

TL;DR

This paper develops a Landau theory to understand how strain influences defect ordering in thin oxide films, enabling control over defect superstructures for functional material applications.

Contribution

It introduces a theoretical framework for strain-induced defect ordering in thin oxide films, including analytical expressions for defect-ordered states and phase diagram analysis.

Findings

Strain and defect concentration significantly affect defect ordering phases.

Analytical phase diagrams show controllable defect superstructures.

Results suggest pathways to engineer functional properties via substrate selection.

Abstract

Ordering of mobile defects in functional materials can give rise to fundamentally new phases possessing ferroic and multiferroic functionalities. Here we develop the Landau theory for strain induced ordering of defects (e.g. oxygen vacancies) in thin oxide films, considering both the ordering and wavelength of possible instabilities. Using derived analytical expressions for the energies of various defect-ordered states, we calculated and analyzed phase diagrams dependence on the film-substrate mismatch strain, concentration of defects, and Vegard coefficients. Obtained results open possibilities to create and control superstructures of ordered defects in thin oxide films by selecting the appropriate substrate and defect concentration.