Study On The Microstructure And Properties Of ZnO - Varistor Ceramics Doped With TiO 2 Subcrystals With 6 O ₁₁

The method of microwave sintering is superior to conventional sintering for its volume heating. The work for preparing ZnO-based varistor have been studied with TiO2and Pr6O11doping. Results as follows:1) Grain of the samples doped with TiO2were coarser than pure ZnO. When the ratio of TiO2dopants was increased from2.25-2.75wt%, the average size of ZnO increased, the density was also increased, and new phase of Zn2TiO4formed. Meanwhile the dielectric constant of ZnO decreased, the value of impedance increased according.2) When Pr6O11doping was increased, the ratio of pores decreased, however the scale of grains increased as well as the density at the same temperature. The highest nonlinear coefficient of the sample sintered in1250℃is3.2,its breakdown voltage is269.2V and the leak current is0.365mA,which is the lowest. At the temperature of1250℃, sample doped0.5wt%Pr6O11got a highest breakdown voltage as well as the nonlinear coefficient, which is178.6V and2.9respectively, and the leak current is0.491mA.3) The highest nonlinear coefficient was got by doping0.5wt%TiO2and sintering at1200℃, and the breakdown voltage is717.8V, the leak current is0.296mA. When the ratio of TiO2dopants was increased, the contains of the spine phase of Pr2Ti2O7and Zn2TiO4forming. The nonlinear coefficient of sample was decreased at1250℃.4) The samples prepared by conventional sintering were denier than microwave sintering, however the samples prepared by microwave sintering were more uniform. And with the TiO2doping increasing, the sample sintered by conventional method owned higher dielectric constant and lower impedance.