Oxygen vacancies in SrTiO$_{3}$ thin films at finite temperatures: A first-principles study

TL;DR

This study uses first-principles calculations to analyze oxygen vacancies in strained SrTiO$_{3}$ thin films, emphasizing the importance of thermal lattice excitations for accurate modeling of defect formation and diffusion.

Contribution

It introduces a comprehensive ab initio approach that incorporates lattice thermal excitations to better predict oxygen vacancy behavior in epitaxially strained SrTiO$_{3}$ thin films.

Findings

Thermal lattice excitations are essential for matching experimental formation energies.

Strain significantly influences oxygen ion diffusion barriers.

Thermal effects alter diffusion energy barriers depending on tensile or compressive strain.

Abstract

Epitaxially grown SrTiO$_{3}$ (STO) thin films are material enablers for a number of critical energy-conversion and information-storage technologies like electrochemical electrode coatings, solid oxide fuel cells and random access memories. Oxygen vacancies (${\rm V_{O}}$), on the other hand, are key defects to understand and tailor many of the unique functionalities realized in oxide perovskite thin films. Here, we present a comprehensive and technically sound ab initio description of ${\rm V_{O}}$ in epitaxially strained (001) STO thin films. The novelty of our first-principles study lies in the incorporation of lattice thermal excitations on the formation energy and diffusion properties of ${\rm V_{O}}$ over wide epitaxial strain conditions ($-4 \le \eta \le +4$%). We found that thermal lattice excitations are necessary to obtain a satisfactory agreement between first-principles calculations and the available experimental data on the formation energy of ${\rm V_{O}}$ for STO thin films. Furthermore, it is shown that thermal lattice excitations noticeably affect the energy barriers for oxygen ion diffusion, which strongly depend on $\eta$ and are significantly reduced (increased) under tensile (compressive) strain, also in consistent agreement with the experimental observations. The present work demonstrates that for a realistic theoretical description of oxygen vacancies in oxide perovskite thin films is necessary to consider lattice thermal excitations, thus going beyond standard zero-temperature ab initio approaches.