Optical method for determining the grain resistivity in ZnO-based ceramic varistors

An optical technique for evaluating the grain resistivity in ZnO ceramic varistors is described. It is based on the existence of a rather sharp minimum in the infrared reflectance whose wavelength position depends on the free-electron density and hence on the ZnO grain resistivity. Values of resistivity obtained from optical measurements are in good agreement with those obtained using alternative evaluation techniques.