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 degreesC and found to have a high threshold voltage (V-T) of 280 V/mm and a low energy-absorption capacity of 50 J/cm(3). The introduction of rare-earth oxides (REO) increased the energy-absorption capacity of Pr6O11- and Nd2O3-doped samples to 110 J/cm(3) 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.