Study on the Effect of Bi2O3 Addition on the Current Carrying Performance of ZnO varistors

In this paper, the effects of different Bi
2
O
3
content doping on the comprehensive electrical properties of ZnO varistors, especially the current carrying capability, were investigated under a multivariate complex formula. The results show that the comprehensive electrical properties are better when the Bi
2
O
3
content is 1.0 mol%, with a voltage gradient of 252.96 V/mm, a leakage current of 1.55 μA/cm
²
, a nonlinear coefficient of 54.47, a residual voltage ratio of 1.75, the ability to pass 18 times 2 ms square impulses with an amplitude of 300 A, a current carrying capacity of 21.6 A/cm
²
, and an energy absorption capacity of 179.7 J/cm
³
, The relationship between the microstructure and macroscopic electrical properties of ZnO varistor under different Bi
2
O
3
doping was investigated and analyzed by measuring the phase composition, microstructure, grain boundary parameters and impedance spectrum of ZnO varistor samples. The analysis shows that the proper amount of Bi
2
O
3
doping can accelerate the impurity ion distribution and reaction speed, grain growth is promoted by the infiltration of bismuth-rich liquid phase, grain sizes become larger, grain size inhomogeneity decreases, grain boundary components are more uniformly distributed, potential barrier increases, voltage gradient decreases, nonlinear coefficient increases, leakage current decreases; excessive Bi
2
O
3
doping will cause the spinel phase to ripen and agglomerate, and local accumulation occurs with bismuth-rich phase, which in turn hinders the grain growth and grain boundary composition segregation, making the microstructure and the uniformity of the grain boundary composition tend to deteriorate, and the varistor electrical properties deteriorate at the same time, the current carrying performance also becomes worse.