Interstitial-oxygen-atom diffusion in MgO

The atomic and electronic structure of the radiation-induced Frenkel defects Oᵢ⁰ in MgO crystals is calculated. A full-potential linear-muffin-tin-orbital method combined with a 16-atom supercell is used for the optimization of the interstitial defect geometry. It is found that energetically the most favorable ground state Oᵢ configuration is the (111) dumbbell centered at a regular oxygen site, whereas face-centered and cube-centered configurations are higher in energy by 1.45 eV and 3.57 eV, respectively. The (111) configuration is close in energy to the (110) configuration, which allows the dumbbell to rotate easily on a lattice site. In all these four cases the interstitial oxygen atom attracts considerable additional electron density from its nearest regular O^2- ions, which makes it close to the Oᵢ^- ion rather than a neutral atom. The mechanism and the relevant activation energy for Oᵢ diffusion are discussed in the light of available experimental data. {} 1996 The American Physical Society.