Effect of heat treatment on tolerance characteristic for electrical degradation of ZnO varistors with added Sb2O3

The effects of the heat treatment of ZnO varistors with added Bi-Mn-Co-Sb 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 with 0.12 mole-% of added Sb2O3. After heat treatment, the electrical degradation tolerance characteristic 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 with added Sb2O3, the tolerance characteristic 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 with 0.12 mole-% or less of added Sb2O3, the value of the nonlinearity index a of the voltagecurrent (VI) characteristic after electrical degradation was proportional to the full width at half maximum (FWHM) of the X-ray diffraction peak at 29.4 degrees for Zn2.33Sb0.67O4 spinel particles in samples subjected to 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 the electrical degradation tolerance characteristics is due to a decrease in the ion mobility of O2 ions or Zn2+ ions due to their blocking by uniformly dispersed fine spinel particles at grain boundaries. (C) 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 110, 2012; Published online in Wiley Online Library. DOI 10.1002/eej.21229