Influences of Bi2O3-B2O3 Glass Doping on Properties of ZnO-Bi2O3-TiO2-based Varistors

The influences of Bi2O3-B2O3 glass additives on the microstructure and nonlinear electrical properties of ZnO-Bi2O3-TiO2-based varistor were investigated. SEM images show that low melting Bi2O3-B2O3 glass can help to increase ZnO grain size and refine microstructure with uniform grain size distribution at 900 degrees C through liquid phase sintering mechanism, whereas the grain size decreases with increasing ZnO-B2O3 glass addition resulting from non-melting ZnO-B2O3 glass pining the ZnO grain boundaries. The varistor ceramics with 2wt% Bi2O3-B2O3 glass addition own best nonlinear electrical properties with voltage gradient E-1mA=124.9V/mm, nonlinear coefficient alpha=46.2, leakage current density J(L)=0.2 mu A/cm(2). For Bi2O3-B2O3 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-B2O3 glass doped varistor. The results reveal that Bi2O3-B2O3 glass doping is more effective in improving the microstructure and electrical properties of ZnO-Bi2O3-TiO2-based varistor than ZnO-B2O3 glass doping.