Abstract

Commercial ZnO varistor ceramics are multi-component, with minor amounts of added oxides that play important roles, both in electrical sense and to control microstructure. The emphasis of this paper is mainly on improving the electrical properties and the effect of nano ZnO powder on varistor behavior. Ultra fine ZnO powders with crystallite size 3-10nm have been prepared by sol-gel auto combustion method. The synthesized powders characterized by X-ray diffraction (XRD), differential thermal analysis (DTA)/thermogravimetry analysis (TGA), transmission electron microscopy (TEM) and surface area using Brunauer–Emmett–Teller (BET) method. Different valance state elements in oxide form are additively doped with nano ZnO powder for fabrication of varistors. Sintering is performed at 850 to 1150°C with 4h soaking time. The varistor is characterized with respect to phase identification, crystallite size determination using X-ray Diffraction. The densification and microstructure analysis using scanning electron microscope (SEM) are also investigated. It is shown that the varistor is mainly consisting of ZnO, Zn₇Sb₂O₁₂ spinel and Bi₂O₃-rich phases. It can be produced having a sintered density ~99% of its theoretical density with grain size ~5-7mm and a maximum breakdown voltage 292 V/mm.

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