Relationship between grain boundaries and electrical degradation of ZnO varistors

AbstractThe effects of the electrical degradation characteristics and microstructure of Sb2O3‐added ZnO varistors were investigated by field emission scanning electron microscopy (FE‐SEM), energy dispersion X‐ray spectroscopy (EDX), optical microscopy, X‐ray diffraction (XRD), and voltage– current (V−I) characteristic measurement. The nonlinearity index α of the V−I characteristic for Bi‐Mn‐Co‐Sb2O3‐added ZnO varistors decreased with increasing amount of Sb2O3 after electrical degradation. Twin crystals of ZnO were formed by the addition of Sb2O3. The number of twin crystals with two c‐axes perpendicular to the twin plane increased and the number of twin crystals with two c‐axes parallel to the twin plane decreased with increasing addition of Sb2O3. It is suggested that electrical degradation is affected by a combination of orientations of ZnO grains containing twin planes and that a double Schottky barrier may not be formed in the twin plane. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 1– 9, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20493