Ab initio simulation of oxygen vacancies in LiMgPO4

Abstract

The electronic structure of olivine-type LiMgPO4 with neutral and charged oxygen vacancies (F centers) was studied using ab initio density functional theory (DFT) calculations. The F centers introduce the energy states within the band gap, which explain the two-stage experimental absorption spectra, as demonstrated the imaginary part of complex dielectric function calculated for all types of defects. The formation energies of neutral and charged vacancies in nonequivalent oxygen sites were analyzed as a function of the Fermi level. The dominant defects in LiMgPO4 should be doubly charged F 2+ or neutral F 0 depending on the location of the Fermi level in the band gap, while the magnetic F + centers appear only in a narrow range of the Fermi energy. These defects may serve as traps during irradiation and induce the thermoluminescence of LiMgPO4.