Influences of Bi_2O_3-B_2O_3 Glass Doping on Properties of ZnO-Bi_2O_3-TiO_2-based Varistors

The influences of Bi_2O_3-B-2O_3 glass additives on the microstructure and nonlinear electrical properties of ZnO-Bi_2O_3-TiO_2-based varistor were investigated.SEM images show that low melting Bi_2O_3-B_2O_3 glass can help to increase ZnO grain size and refine microstructure with uniform grain size distribution at 900℃through liquid phase sintering mechanism,whereas the grain size decreases with increasing ZnO-B_2O_3 glass addition resulting from non-melting ZnO-B_2O_3 glass pining the ZnO grain boundaries.The varistor ceramics with 2wt%Bi_2O_3-B_2O_3 glass addition own best nonlinear electrical properties with voltage gradient E_(1mA)=124.9V/mm,nonlinear coefficient a=46.2,leakage current density J_L=0.2μA/cm~2.For Bi_2O_3-B_2O_3 glass doped varistor,kinetic exponent n_B and apparent activation energy Q_B are only 2.15 and 146.2kJ/mol which are much lower than that of ZnO-B_2O_3 glass doped varistor.The results reveal that Bi_2O_3-B_2O_3 glass doping is more effective in improving the microstructure and electrical properties of ZnO-Bi_2O_3-TiO_2-based varistor than ZnO-B_2O_3 glass doping.