Radiation damage in oxides. II. Defect formation in CaO and SrO

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Abstract
For pt.I see abstr. A36337 of 1973. The formation of cation and anion vacancies has been studied in high purity CaO and SrO 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 isolated vacancy concentration is enhanced by thermal treatment at temperatures just below those at which the isolated vacancy begins to disappear. This is interpreted in terms of the decomposition of a vacancy-vacancy or vacancy-impurity aggregate. At slightly higher temperatures (640K for CaO) the isolated vacancy is converted to the vacancy-hydroxyl ion complex and isothermal data indicates close to 100% conversion. At higher temperatures the vacancy-hydroxyl ion complex is destroyed. The probable mechanism of the first process is vacancy diffusion with an activation energy of 1.8 eV, to a hydroxyl ion where the vacancy is trapped and partial charge compensation occurs. At higher temperatures it seems likely that diffusion of interstitial cations to the vacancy occurs with an activation energy of 3.1 eV. The efficiency of vacancy production is an order of magnitude less than that predicted for primary displacements confirming the importance of recombination between vacancies and those interstitials formed within a critical volume around the vacancy.

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