Effect of sintering temperature on microstructure and nonlinear electrical characteristics of ZnO varistor

The nonlinear properties of ZBMCCS-based varistors, which are composed of ZnO-Bi2O3-MnO2-Cr2O3-Sb2O3-Co3O4 and SiO2 are studied inrelation to sintering temperature, in the range of 1280-1350 degrees C. The samples are investigated for grain morphology by using scanning electron microscope (SEM). These samples were examined by using X-ray diffraction patterns (XRD) and DC electrical measurements. X-ray diffraction analysis of the samples show the presence of ZnO, Zn2SiO4 willemite phase and Co2.33Sb0.67O4 spinel phases. The average grain size of ZnO increased as the sintering temperature increased from 2.57 to 6.84 mu m. In the examined temperature range, the breakdown field decreased from 2992 to 127 V/cm with the increase of sintering temperature. This system gives a relatively high nonlinearity coefficient alpha = 33.61 (at a sintering temperature of 1280 degrees C) with a low leakage current of 0.21 mA/cm(2).