ZnO varistors with reduced amount of additives prepared by direct mixing of constituent phases

The aim of this work was to reduce number of additives using new method of preparation, refered as “direct mixing of the constituent phases”. The method is based on sintering of a mixture of constituent phases with the following compositions: ZnO phase uniformly doped with 0.1 mol% Mn2+ and 0.1 mol% Co2+, γ-Bi2O3 stabilized with Mn2+ and spinel phase of composition Zn1.86Co0.46Sb0.67O4 or Zn1.971Ni0.090Co0.030Cr0.247Mn0.090Sb0.545O4. The varistors sintered at 1030 °C showed good electrical properties, with nonlinearity coefficient reaching 50 and low values of leakage current. To improve microstructure some powder mixtures were intensively milled and further processed on the same way as unmilled powder mixtures. Electrical and microstructural properties of milled and unmilled samples were compared.