Key role of oxygen at zinc oxide varistor grain boundaries

Abstract

The electrical transport properties of zinc oxide varistors are correlated with the chemistry of their grain boundaries. An adsorbed layer of bismuth, about 5 Å thick, is necessary to create potential barriers at the grain boundaries. The height of these potential barriers depends sensitively on the excess amount of oxygen (∼1 monolayer) present at the interfaces between grains. This oxygen enrichment is influenced by thermal processing and by electrical degradation.