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

摘要

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