Effect of Heat Treatment on Tolerance Characteristic for Electrical Degradation of Sb2O3-added ZnO Varistors

Abstract

The effects of the heat treatment of Bi-Mn-Co-Sb-added ZnO varistors on their electrical degradation were investigated. Before heat treatment, the degree of the tolerance characteristics of varistors for electrical degradation was smallest for the sample added Sb2O3 of 0.12 mol%. After heat treatment, the tolerance characteristic for electrical degradation was markedly improved. It was found that the tolerance characteristics for electrical degradation after heat treatment strongly depend on the amount of added Sb2O3. For the samples added Sb2O3, the tolerance characteristics for electrical degradation upon heat treatment is not affected by the intensity of the X-ray diffraction peak of the (004) plane for ZnO. For samples added Sb2O3 of 0.12mol% or less, The value of the non linearity index α of the voltage-current (V-I) characteristics after electrical degradation was proportional to the full width at half maximum (FWHM) of the X-ray diffraction peak at 29.4°for Zn2.33Sb0.67O4-type spinel particle for samples with heat treatment under various conditions. Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the existence of fine spinel particles at grain boundaries or triple points of ZnO grains. Furthermore, it is speculated that the improvement of tolerance characteristics for electrical degradation is due to the decrease in the ion mobility of O2- ions or Zn2+ ions due to their blocking by uniformly dispersed fine spinel particles at grain boundaries.