Electrical and microstructural characteristics of ZnO–Bi₂O₃-based varistors doped with rare-earth oxides

ZnO-based varistor samples with a relatively high Sb₂O₃ to Bi₂O₃ ratio of 5 were fired at 1200 °C and found to have a high threshold voltage (V_T) of 280 V/mm and a low energy-absorption capacity of 50 J/cm3. The introduction of rare-earth oxides (REO) increased the energy-absorption capacity of Pr₆O₁₁- and Nd₂O₃-doped samples to 110 J/cm3 while their threshold voltage (V_T) remained slightly above 300 V/mm. Doping with Pr₆O₁₁ and Nd₂O₃ altered the formation of the spinel phase and significantly changed its particle size and distribution which, as a result, had a positive effect on the energy-absorption capacity of the REO-doped samples. Doping with small amounts of Pr₆O₁₁ and Nd₂O₃ appears to be promising for the preparation of ZnO-based varistors with a high breakdown voltage and a high energy absorption capacity.