Identification of Mn site in Mn-doped SrTiO 3 : First principles study

Abstract

Abstract Manganese can incorporate into perovskite SrTiO 3 at either on the Sr-site ( A -site) or Ti-site ( B -site) depending on the growth conditions. However, there is no clear explanation on what conditions lead to A -site or B -site occupations and what are the local structures around Mn. In this work, first-principles calculations were carried out to study Mn in SrTiO 3 under different growth conditions. The calculations showed that Mn prefers to substitute for Ti site under a wide range of growth conditions; indicating that the substitution it is difficult to avoid even when one intentionally tries to dope Mn into the A -site. Due to a large size difference, Mn cannot fit in the Sr site. Instead, a charged interstitial Mn has rather low formation energy, especially under O-poor conditions. In addition, Mn i can bind with Sr vacancy which has the compensating charge with a very high binding energy to form Mn i - V Sr complex. Mn i - V Sr has an equivalent chemical composition to Mn Sr . Therefore, one might view Mn i - V Sr as an off-center Mn Sr . In this view point, Mn A -site has a large cation off-centering consistent with experimental observations. We further relate our local structure models with the experiments by calculating the Mn K -edge x-ray absorption near-edge spectroscopy (XANES) spectra associated with Mn Ti , Mn Sr (on regular Sr lattice), and Mn i - V Sr or off-center Mn Sr defects to compare with the measured Mn K -edge XANES spectra. Our results show good agreement with the measured spectra.