Effect of ZrO2 addition on tolerance characteristics of the electrical degradation of ZnO varistors

3 ZnO varistors with excellent electrical degradation tolerance characteristics were made by addition of Bi2O3-MnO2-Co3O4-Cr2O3-SiO2-Sb2O3-NiO. The electrical degradation tolerance characteristics were evaluated by varying the amount of ZrO2. The evaluation methods were voltagecurrent (VI) characteristics, X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion X-ray spectroscopy (EDX). Monoclinic and tetragonal ZrO2 and compounds derived from Zr were observed at both the grain boundaries and triple points. Moreover, the compounds derived from Zr with added Sb showed improved electrical degradation tolerance characteristics. On the other hand, monoclinic ZrO2 in particular degraded the electrical degradation tolerance characteristics. One factor in the improvement of the electrical degradation tolerance characteristics is that the mobility of oxide ions or interstitial Zn2+ ions might be hindered by the formation of compounds containing Zr, Sb, Si, and Bi atoms. The electrical degradation tolerance characteristics of ZnO varistors with added ZrO2 were better than those of varistors without addition of ZrO2 but subjected to heat treatment. (C) 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 1119, 2012; Published online in Wiley Online Library. DOI 10.1002/eej.21228