ZnO varistors from intensively milled powders

Two ways of application of intensive milling in ZnO varistors processing were compared. First was intensive milling of mixture of previously prepared constituent phases. In this case, intensive milling was applied only to obtain highly activated nanocrystalline varistor powder mixtures. Second application is intensive milling of simple mixture of oxides that could result not only in activation and formation of nanocrystalline powders, but also in mechanochemical reaction and synthesis of constituent phases. Powders and ceramics samples were characterized by XRD and SEM analysis, as well as by dc electrical measurements (nonlinearity coefficients, leakage current and breakdown field). Differences in microstructural and electrical properties of obtained varistors were discussed and optimal milling and processing conditions were recommended. The best electrical characteristics were found in sample Z1-DMCP-m, which exhibited leakage current of 2.5 μA/cm2, nonlinear coefficient reaching 58 and breakdown field of 8950 V/cm.