Electrical Properties and Kinetic of Crystalline Grain Growth of Low-voltage ZnO Varistor Doped with Zn-B Glass

The effects of Zn-B glass additive on microstructure and electrical properties of low-voltage ZnO varistor were studied.The results show that ZnO varistor with x=0.1wt% obtains the optimal nonlinear electrical properties: E1mA=36.7V/mm,α=30.4,IL=0.1μA.The grain growth mechanism of low-voltage ZnO varistor doped with Zn-B glass is also investigated in terms of the phenomenological kinetic of crystalline grain growth.Based on the theory,the grain growth kinetic exponent n and apparent activation energy Q are calculated as 4.54 and 316.5kJ/mol for ZnO ceramics varistor sintered at the temperature below 1000℃.The grain growth mechanism is that non-melting Zn-B glass pins the ZnO grain boundaries,which inhibits the grain growth of ZnO varistor.However,n and Q value are 2.92 and 187kJ/mol at the temperature higher than 1000℃.It indicates that melting Zn-B glass wetting the ZnO grain boundaries creates a liquid phase sintering mechanism,which accelerates the grain growth of ZnO varistor.