<i>C-t</i> Characteristics of Pr Doped ZnO Varistors

Abstract

C-t characteristics of ZnO varistors containing praseodymium oxide are examined. The effects of sintering temperature on the C-t characteristics are also discussed. C-t characteristics are found to be strongly connected with the electronic interface states at the grain boundaries and useful for characterizing the interface states. When samples were sintered below 1340°C, the interface states were discrete and monoenergetic at 0.8eV below the conduction band edge. However, samples which were sintered above 1360°C formed continuously distributed levels near 0.7eV below the conduction band edge. Moreover, the density of states and varistor voltage per grain boundary rapidly increased in this temperature range. These phenomena were explained by the oxygen evolution from Pr6O11 by the reduction to Pr2O3 during the sintering process.