How the trapping of charges can explain the dielectric breakdown performance of alumina ceramics

The aim of this work is to bring new elements to the understanding of break down phenomena. Different alumina materials are studied in breakdown tests and by absorbed current measurement. The association of these two character isation methods displays correlations between breakdown strength, the abili ty to trap or diffuse electrical charges and microstructural parameters. Di fferent materials have been studied with a growing quantity of defects: str uctural defects in the single crystal, grain boundaries in very pure polycr ystalline alumina (99.99%), impurities in less pure polycrystalline alumina (99.8%), interfaces in the case of alumina with a dispersion of zirconia a nd finally the adding of sintering aids. It appears that materials capable of diffusing injected charges have higher breakdown values than those trapp ing charges locally. Two other favourable behaviours are characterized: tra pping charges at the injection point in order to limit the injection proces s, and trapping followed by reemission which relaxes the insulator and dela ys breakdown. (C) 2001 Elsevier Science Ltd. All rights reserved.