Radiation damage in oxides

The kinetics of vacancy production have been studied in high-purity MgO powders after irradiation by 20 MeV protons. The rate of formation of cation vacancies fits a model of interstitial-vacancy recombination. Isochronal annealing curves show that the cation vacancy is destroyed over a narrow temperature range between 650 and 700 K. The absence of vacancy pairs formed during this process suggests the probable mechanism is the diffusion of interstitial magnesium ions to the vacancies with an activation energy of 2.7 eV. Comparison of the rate of initial anion defect production as a function of particle size of the powder indicates that the surface can compete with the vacancy as a trap for oxygen ions displaced from vacancies up to several tens of angstroms from the surface, thus reducing the vacancy-interstitial recombination process.