Interstitial-oxygen-atom diffusion in MgO

The atomic and electronic structure of the radiation-induced Frenkel defects (Formula presented) 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 (Formula presented) 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 (Formula presented) ions, which makes it close to the (Formula presented) ion rather than a neutral atom. The mechanism and the relevant activation energy for (Formula presented) diffusion are discussed in the light of available experimental data.