Temperature dependence of zinc oxide grain resistivity in ZnO varistor ceramics

Abstract

Temperature dependence of the bulk resistivity of zinc oxide grains in ZnO varistor ceramics was studied in the range 77–460 K. The pulse method was used for the measurement of the grain resistivity. In the examined temperature range the resistivity of ZnO grains exhibits the negative temperature coefficient (the resistivity is decreased with increase in temperature). Two activation energies of electrical conduction, 0.014 eV (below 270 K) and 0.048 eV (above 270 K) were observed. They are related to two shallow donor levels contributing to the electrical conduction of zinc oxide grains. It was shown that ZnO varistor ceramics with the higher grain resistivity have the higher low-field grain-boundary barrier height.