OPTICAL AND ELECTRON-MICROSCOPY OF SAPPHIRE IRRADIATED WITH AN APPLIED ELECTRIC-FIELD AT 450-CENTER-DOT-C

Single crystal alpha-alumina (sapphire) has been irradiated with 1.8 MeV electrons at a temperature of 450 degrees C while subject to an electric field of 130 kV/m. At intervals during the course of the irradiation the electron beam was switched off and the electrical conductivity of the sapphire was measured at 450 degrees C. After a damage dose of similar to 10(-7) dpa the intrinsic electrical conductivity began to rise, increasing by four orders of magnitude after only 8 x 10(-6) dpa. The combination of displacement damage, electric field and temperature leading to increased electrical conductivity is known as the RIED effect (Radiation-Induced Electrical Degradation). Optical microscopy of the irradiated sapphire revealed thin disc shaped precipitates but only in the irradiated area of the sample subject to an electric field. TEM of the irradiated area showed that the precipitates consisted of an intimate mixture of alpha- and gamma-alumina with (<000(6)over bar> sapphire//((1) over bar (1) over bar 1) gamma-)alumina and (01(1) over bar 2) sapphire//(311) gamma-alumina. The relative orientations of alpha- and gamma-alumina show that a phase change is involved which has not been previously observed in bulk irradiated alumina.