Effect of oxygen vacancies on the electronic structure and dielectric properties of SrAl2O4: A first-principles study

Abstract

In this study, both the generalized gradient approximation (GGA) and the GGA-1/2 methods were applied to examine the effect of oxygen vacancies on the electronic and optical properties of bulk monoclinic SrAl2O4. Since the monoclinic structure of SrAl2O4 has two non-equivalent sites for oxygen atoms, we can distinguish between two kinds of oxygen vacancies (VO) in this material. These two kinds of VO are labeled VOI and VOII. Our results show that although these two types of vacancies have comparable formation energies, their electronic and optical properties are significantly different. The formation energy of the VO defect under Sr-rich, Al-rich, and O-poor conditions was less than 1 eV, which means that it could exist at high concentrations. Moreover, the results of density of states (DOS) analysis show that the oxygen vacancy had a deep donor defect featuring a fully occupied electronic level located deep in the band gap of SrAl2O4. This electronic level was located at Ev+2.9eV in case of VOI and at Ev+3.3eV in case of VOII. This defect induced a noticeable change in the spectrum of optical absorption of SrAl2O4. Our results show that the formation of oxygen vacancies can significantly enhance the UV absorption-related properties of this material.