Optical and electron microscopy of sapphire irradiated with an applied electric field at 450°C

• Published in: Journal of nuclear materials Vol. 226; no. 3; pp. 286 - 292
• Main Authors: Pells, G.P., Hodgson, E.R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.1995; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Conductivity phenomena in semiconductors and insulators; Cross-disciplinary physics: materials science; rheology; Electronic transport in condensed matter; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Low-field transport and mobility; piezoresistance; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; Solid-phase precipitation; Solubility, segregation, and mixing; phase separation; Inorganic compounds; Phase transformations; Physical radiation effects; Electron beam; Experimental study; Precipitates; Alpha phase; Gamma phase; Sapphire; Electric field effects; Microstructure; Aluminium oxides; Electric conductivity
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/0022-3115(96)80001-8

Single crystal α-alumina (sapphire) has been irradiated with 1.8 MeV electrons at a temperature of 450°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°C. After a damage dose of ≈ 10−7 dpa the intrinsic electrical conductivity began to rise, increasing by four orders of magnitude after only 8 × 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 α- and γ-alumina with (0006¯) sapphire //(1¯11¯) γ-)alumina and (011¯2) sapphire //(311) γ-alumina. The relative orientations of α- and γ-alumina show that a phase change is involved which has not been previously observed in bulk irradiated alumina.