Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain

TL;DR

This paper investigates the local and long-range strain effects of vacancy defects in strontium titanate, providing new calculations of elastic dipole tensors and chemical strains that can be compared with experimental data.

Contribution

First calculations of elastic dipole tensors and chemical strains for point defects in perovskites, linking theoretical predictions with experimental observations.

Findings

Oxygen vacancy has a highly anisotropic elastic dipole tensor.

Chemical strain measurements constrain defect types in oxygen-poor samples.

Good agreement between calculated and experimental chemical strain for strontium vacancies.

Abstract

We present a study of the local strain effects associated with vacancy defects in strontium titanate and report the first calculations of elastic dipole tensors and chemical strains for point defects in perovskites. The combination of local and long-range results will enable determination of x-ray scattering signatures that can be compared with experiments. We find that the oxygen vacancy possesses a special property -- a highly anisotropic elastic dipole tensor which almost vanishes upon averaging over all possible defect orientations. Moreover, through direct comparison with experimental measurements of chemical strain, we place constraints on the possible defects present in oxygen-poor strontium titanate and introduce a conjecture regarding the nature of the predominant defect in strontium-poor stoichiometries in samples grown via pulsed laser deposition. Finally, during the review process, we learned of recent experimental data, from strontium titanate films deposited via molecular-beam epitaxy, that show good agreement with our calculated value of the chemical strain associated with strontium vacancies.