| ZnO varistor is widely used in all kinds of electronic circuits and electronic devices because of its excellent nonlinear coefficient and high surge current capability.Various models for their conduction mechanism were proposed.The most widely accepted model is back-to-back double Schottky barrier model.Based on the double Schottky barrier model,We use the control variable method to explore the influence of different doping conditions?semiconductor donor doping,replacing anion or cation sites?on the electrical properties of ZnO varistor.By analyzing the morphology,density and so on,the causes of different phenomena were analyzed.The aim of this paper is to study the effect of different donor dopants on the electrical properties of ZnO varistor,especially the influence of the material on the nonlinear characteristics and high surge current capability.In this paper,the influence of Al doping on ZnO varistor was studied.Al?NO3?3·9H2O can be used as donor additive,which can increase the carrier concentration of ZnO varistor,reduce the electrical resistivity.In addition,the introduction of Al3+to spinel phase enrichment inhibited grain growth.In industry,Al?NO3?3·9H2O solution was used to adopt Al3+,which is beneficial to the dispersion of the raw materials.In this study,Zinc oxide and Al?NO3?3·9H2O were mixed and presintered,the mixing ball milling method was adjusted,the dispersion of Al3+can be improved.The experimental results showed that in the range of0.02wt%0.05wt%,with the increase of Al3+doping amount,the grain size of ZnO varistor decreases and the varistor gradient increases.However,if the amount of Al3+is excessive,Al3+is enriched in the grain boundary layer.And experiment results also showed the improvement of high surge current capability by presintering method.The influence of donor type anionic dopant on the electrical properties of ZnO varistor ceramics was studied.F is used to replace Al,F and Al co-doping was investigated.The microstructure and electrical properties of F doped and F and Al co-doped were measured and analyzed.The results showed that F in the ZnO varistor mainly influence the grain size,instead of spinel phase and nonlinearity.The co doping of F and Al improves the electrical properties obviously.The two elements of F and Al have similar effects on the electrical properties of ZnO varistor ceramics.Comparing with those ZnO varistor which only doped Al3+or F-,F and Al co-doping improve the nonlinearity and high surge current capability.The influence of Cl doping on the ZnO varistor was also studied.The effect of different content of ZnCl2 content on the electrical properties of ZnO varistor was investigated.The experiment showed that the effect of doping Cl element on ZnO varistor is similar to the doping of Al element,which can provide free electrons and increase the concentration of grain carrier.According to microstructure analysis,when doping chlorine ion,the grain size and the spinel phase are affected.A certain amount of chlorine doping can reduce the grain size and increase the varistor voltage gradient.At the same time,the electric performance analysis showed that the introduction of Cl element improves the high current impulse withstand capability of the ZnO varistor.The introduction of Cl ions may also enhance the composite conduction mechanism of zinc gap and oxygen vacancy.When the doping amount is0.04mol%,the nonlinear coefficient and the ability to withstand large current are good,and the barrier height is also kept at a high value at high temperature. |
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