Defects and threshold displacement energies in SrTiO_3 perovskite using atomistic computer simulations

摘要

The mode and energy of simple defect incorporation in SrTiO_3 (vacancies and interstitials) is quantified using computer simulation techniques with an empirical partial charge model of interatomic forces, as well as using density functional theory calculations. Oxygen and strontium interstitials form split-interstitial configurations whereas titanium interstitials occupy channel positions. Defect migration energies and paths are also considered; interstitials are more mobile than vacancies, with a low predicted oxygen interstitial migration energy of around 0.3 eV. We also calculate the threshold displacement energy (E_d) for each atom type in SrTiO_3 perovskite using molecular dynamics simulations, by introducing a primary knock-on atom with a range of energies (20-250 eV) in principal crystallographic directions at 300 K. We find that all atom types are most easily displaced via direct replacement sequences on their own sublattices, which are extensive for Sr atoms due to focusson processes acting along channels. The weighted average threshold displacement energies (for use in TRIM-type calculations) are 50 eV for oxygen, 70 eV for strontium and 140 eV for titanium atoms. These computed energies for O and Sr are comparable to experimentally-derived values in perovskites, whereas the E_d for Ti is much higher; it is expected that the value reported here is more accurate due to experimental difficulties in distinguishing different types of defects.