A REVIEW OF THE OPTICAL-PROPERTIES OF ANION LATTICE VACANCIES, AND ELECTRICAL-CONDUCTION IN ALPHA-AL2O3 - THEIR RELATION TO RADIATION-INDUCED ELECTRICAL DEGRADATION

Optical and thermal properties of anion vacancies are reviewed in some detail and shown unlikely to accommodate the formation of aluminum colloids below similar to 750 K. These colloids had been previously proposed to account for an anomalous conductivity which has been reported in alumina after prolonged irradiation at elevated temperature under an applied electric field. A survey of electrical conductivity measurements demonstrates that conduction in alumina below 1000 K is dominated by extrinsic effects. Given the low concentration of F-type centers observed in conjunction with anomalous conductivity, as compared with typical impurity levels, extrinsic effects similarly dominate after irradiation. Dislocations observed to accompany the anomalous conductivity are considered as possible low-resistant pathways. Alternative external current leakage paths are also considered.