RADIATION-INDUCED ELECTRICAL DEGRADATION IN CRYSTALLINE AL2O3

Recent studies, simulating the behavior of insulating materials in a f usion device environment, show that under concurrent applications of r adiation, applied electric field, and elevated temperature, they suffe r degradation of their electrical properties. The goal of the present study is to address the mechanism of this radiation-induced electrical degradation and the defects involved. Our results show that when an A l2O3 crystal under a moderate electric field is irradiated with 1.8 Me V electrons at 773 K, the dc conductivity during and after irradiation increases rapidly above a critical dose and saturates after the condu ctivity increases by a factor of 10(3). There are two main conclusions . First, the electrical degradation is due to the charge of the electr ons and holes created during radiation, rather than due to displacemen ts of indigenous ions by elastic collisions with the energetic electro ns. Second, the defects attending the observed electrical degradation are dislocations. Transmission electron microscopy studies revealed re gions of large dislocation density distributed nonuniformly throughout the degraded area, with an overall average density of approximately 1 0(9) cm-2, as opposed to approximately 10(4) cm-2 in regions which wer e not electron irradiated nor subjected to an electric field. The conc entration of point defects, as characterized by optical absorption and electron paramagnetic resonance, was below detectable limit. In addit ion, no second phase was observed.