A Review of the Zinc Oxide Varistor.
HARRY DIAMOND LABS ADELPHI MD
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The nonlinear electrical characteristic of zinc oxide varistors is explored in terms of the ceramic sintering process, i. e., sintering temperature, oxide admixture, grain growth, intergranular layer thickness, etc. The property of non-ohmic conduction is traced to the presence of a segregated second-phase accumulation layer, which surrounds the ZnO grains, and acts as an insulating potential barrier. The transition region from ohmic to non-ohmic conduction prebreakdown region is explained by the Poole-Frenkel effect in which, for low applied fields, conduction takes place by thermal activation over the field-lowered barrier. In the highly conductive breakdown region, conduction corresponds with Fowler-Nordheim field-assisted tunneling. Although Space-Charge-Limited-Conduction SCLC theory is considered, it does not appear to be applicable. Author
- Electrical and Electronic Equipment