Influence of Cr2O3 doping on the electrical characteristics of novel ZnO-Cr2O3-based varistor ceramics

Abstract

Novel ZnO-Cr2O3-based varistors can overcome the problems related to the volatile, high-cost and toxic components of conventional ZnO-Bi2O3-, ZnO-Pr6O11-, and ZnO-V2O5-based varistors. The influence of the varistor former with different doping levels, i.e., the Cr2O3, on the microstructure and electrical properties was examined and the optimal amount of Cr2O3 doping to enhance the electrical performance of ZnO-Cr2O3-based varistor ceramics was determined. The results showed that about 0.1 mol.% of Cr2O3 is optimal for the formation of the electrostatic double Schottky barriers with increased height at the grain boundaries (GBs) and thus an enhanced I-V nonlinearity (i.e., a coefficient of nonlinearity α = 73) and a lower leakage current (IL < 0.2 μA/cm2) in ZnO-Cr2O3-based varistor ceramics with an Eb of 383 V/mm. For larger additions of Cr2O3, a Ca3(CrO4)2 phase forms, which decreases the barrier height and leads to a lowering of α and an increase in IL.