Effect of step sintering on breakdown voltage of varistors prepared from nanomaterials by sol gel route

ZnO varistor materials were prepared by a sol gel route with subsequent drying and calcination. Varistor discs fabricated from these materials were subjected to a two step sintering schedule. Therefore in a typical experiment, the samples were heated to 1000°C, then allowed to cool for over 30 min to 900°C and held there for 6 h. The results were compared with commercial varistor samples sintered in a similar way. Considerably higher breakdown voltages were obtained for the varistors made from nanosample (1192±30 V mm⁻¹) compared with the commercial samples (723±30 V mm⁻¹) sintered under the same experimental conditions. The sintered materials were characterised by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and density measurements.