Oxide nonlinear conductors are granular electronic ceramic materials whose electrical behavior is dominated by grain boundary interfaces states. The material is typically comprised of relatively conducting oxide grains with electrical barriers at the grain boundaries induced by segregated impurity ions. Oxide nonlinear conductors can exhibit a highlynonlinear current-voltage relationship with a 5% change in voltage serving to increase the current flow an order of magnitude or more.
This review outlines our understanding of the microstructure, grain boundary properties and electrical behavior of these variable resistor or “varistor” granular materials. ZnO varistors currently have widespread application in protecting power and signal level electrical circuits against dangerous voltage surges and a brief overview will be given of the applications of this material.