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 M eV electrons at a temperature of 450 degrees C while subject to an ele ctric field of 130 kV/m. At intervals during the course of the irradia tion the electron beam was switched off and the electrical conductivit y of the sapphire was measured at 450 degrees C. After a damage dose o f similar to 10(-7) dpa the intrinsic electrical conductivity began to rise, increasing by four orders of magnitude after only 8 x 10(-6) dp a. The combination of displacement damage, electric field and temperat ure 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) ov er bar 2) sapphire//(311) gamma-alumina. The relative orientations of alpha- and gamma-alumina show that a phase change is involved which ha s not been previously observed in bulk irradiated alumina.