Collision cascades were investigated in MgO at energies ranging from 400eV to 5keV. Initial energy was imparted to the principle knock-on atom in the lattice and the cascade development was tracked by using classical molecular dynamics. Temperature accelerated dynamics was performed on representative defects to follow the behavior to experimental time scales. Molecular statics was used to calculate basic properties of these defects, while density functional theory calculations were used to verify the potential. In the cascades performed at the lowest energy, the lattice either reforms perfectly or, if residual defects remain, these consist of isolated interstitials and vacancies and charge-neutral Mg-O divacancies and di-interstitials. As the energy was increased to 5keV, isolated interstitials and di-interstitials remained the most common defects but more vacancy clustering could occur and interstitial defects consisting of up to seven atoms were observed. Molecular statics calculations find that the binding energy per atom of the interstitial clusters increased from 3.5 to over 5eV as the size increased from 2 to 16 atoms. Long-time-scale dynamics revealed that vacancies essentially never move at room temperature but that some interstitial clusters could diffuse quickly. Although tetra-interstitial interstitial clusters were essentially immobile, there was a long-lived metastable state of the hexa-interstitial that diffused one dimensionally on the nanosecond time scale at room temperature.

Dynamical Simulations of Radiation Damage and Defect Mobility in MgO. B.P.Uberuaga, R.Smith, A.R.Cleave, G.Henkelman, R.W.Grimes, A.F.Voter, K.E.Sickafus: Physical Review B, 2005, 71[10], 104102