Electron-beam induced dissociation of dislocation loops in magnesia-alumina ceramics

Kinetics of interstitial-type dislocation loops in α-Al₂O₃ and MgO · Al₂O₃, which were induced by 6 keV Ar⁺ ions at 300 K, has been investigated under electron irradiation at 300-870 K by transmission electron microscopy. Dislocation loops disappeared during electron irradiation at energies of 100, 150 and 200 keV, where displacement damage is hardly induced in α-Al₂O₃ and MgO · Al₂O₃ with those electron energies. The disappearing rate of dislocation loops increases with decreasing electron energy and with decreasing irradiation temperature. Further, a portion of dislocation loops in α-Al₂O₃ has been found to grow under the subthreshold-energy electron irradiation, and the average size of the surviving dislocation loops decreases with irradiation at 300 K but increases at 370, 420 and 570 K. We have reached a conclusion that dislocation loops in α-Al₂O₃ and MgO · Al₂O₃ dissociate into isolated interstitials through ionizing radiation. The generated interstitial has been found to mostly recombine with radiation-induced vacancies at lower irradiation temperature (300 K) but to be absorbed to the surviving dislocation loops at higher temperature (370-570 K). The disappearing rate of loops is discussed in terms of a balance between the dissociation process by ionizing radiation and the diffusion process of the generated interstitials.