Effects of vanadium and manganese concentrations on the composition, structure and electrical properties of ZnO-rich MnO2–V2O5–ZnO varistors

The composition, structure and electrical properties of ZnO-rich MnO2–V2O5–ZnO varistors have been analysed. Samples were prepared by a conventional powder route with 0.25–0.75 V2O5 mol% and 0.1–1.5 MnO2 mol% concentrations. All the microstructures consisted of ZnO grains with zinc vanadates as minority secondary phases. The quantity and type of zinc vanadates found depended on the cooling rate. α-Zn3(VO4)2 and Zn4V2O9 were found in air-cooled samples, whereas γ-Zn3(VO4)2 and Zn4V2O9 were found in samples cooled relatively slowly at 5 °C min−1. All samples exhibited non-linear current-voltage varistor behavior, with non-linear coefficients, α, ranging from 9.7 to 27.3. The electrical behaviour was relatively insensitive to the different rates of cooling. The highest values of α were obtained in slowly cooled samples when the MnO2 concentration was 0.25 mol% and when the V2O5 concentration was 0.5 mol%.