Effect of Cr₂O₃ Doping Amount on Microstructure and Electrical Properties of SnO₂ Varistor

With SnO₂ powder, CuO powder, Nb₂O₅ powder and Cr₂O₃ powder as raw materials,（98.95-x）SnO₂-1CuO-0.05Nb₂O₅-xCr₂O₃（x=0, 0.01, 0.02, 0.03, 0.05, mole fraction/%）varistor was prepared by powder metallurgy technique. The effect of Cr₂O₃ doping amount on the microstructure and electrical properties of the varistor was studied. The results show that with the increase of Cr₂O₃ doping amount, the relative density, shrinkage rate and average grain size of sintering samples first increased and then decreased. When the Cr₂O₃ mole fraction was 0.02%, the relative density and shrinkage rate of sintering sample were both the highest. When the Cr₂O₃ mole fraction was 0.01%, the grain size was the largest and the particle size distribution was the most uniform. With the increase of Cr₂O₃ doping amount, the voltage gradient of SnO₂ varistor increased, the leakage current density decreased first and then increased, and the nonlinear coefficient increased first and then decreased. When the mole fraction of Cr₂O₃ was 0.02%, the leakage current density was the smallest, the nonlinear coefficient was the largest, and the voltage gradient was high, indicating the best comprehensive electrical performance.