Radiation damage in the cation sublattice of alpha-Al₂O₃

Abstract

HVEM measurements in conjunction with optical measurements of electron-irradiation induced colour centres have enabled the displacement threshold energy of aluminium and oxygen in α-Al₂O₃ to be measured over a wide range of temperature. The thresholds were found to be temperature independent and had values of 18 ±3 eV for aluminium and 76 ±3 eV for oxygen. Dislocation loops were produced in the HVEM at high temperatures with 300 kV electrons at which energy only aluminium ions are displaced. The loops were found to be pure edge dislocations of interstitial character, lying on the basal plane with 6 = 1/3 [0001]. The loops are stoichiometric but faulted on the aluminium sublattice. A model is proposed by which cation displacement at high temperatures result in aluminium interstitials precipitating between basal planes with rapid diffusion of oxygen ions between the aluminium layers producing the faulted loops. Support for the model is provided by measurements of the activation energy for short range diffusion of oxygen vacancy centres. This was found to be 0.55 eV.