Study On Microstructure And Electrical Properties Of ZnO-Pr₆O₁₁ Varistor

Since the discovery of excellent electrical properties of ZnO varistors,ZnO varistors have been widely used in electronic circuits.In order to meet the special needs of different occasions,the electrical properties of ZnO varistors is usually changed by changing the dopant or the sintering schedule.In this paper,the optimum doping ratio and the optimum sintering temperature were obtained by doping of SiO₂,MnO₂,Er₂O₃ and changing the sintering temperature.First,the effect of SiO₂ doping on the properties of ZnO varistor was studied.The solid phase sintering method was used to prepare the samples according to the molar ratio of?97.0-x?mol%ZnO+0.5 mol%Pr₆O₁₁+0.5 mol%CoO+0.5mol%Cr₂O₃+0.5 mol%Y₂O₃+x mol%SiO₂,so as to make study on the relationship between the amount of SiO₂ doping and the properties of the Zn-Pr-based varistors.From the experimental analysis,it is concluded that the breakdown field strength increases from 137 V/mm to 434 V/mm and then decreases to 101 V/mm with increasing SiO₂ doping.When the SiO₂ content is1.5 mol%,the nonlinear coefficient???reaches the maximum?31?;when the SiO₂ content is 3.0 mol%,the breakdown field strength reaches the maximum and the leakage current is minimized?1.1?A/cm²?.When the SiO₂ doping amount is 1.5mol%,the dissipation factor reaches a minimum value;when the SiO₂ content is 4.5 mol%,the relative dielectric constant reaches a maximum value.In this experiment,the varistor with high nonlinear coefficient and low dissipation was obtained by SiO₂ doping.Next,the effect of MnO₂ doping on the properties of ZnO varistors was studied.Using a multi-component formulation,?97.5-x?mol%ZnO+1.0 mol%Pr₆O₁₁+0.5 mol%Y₂O₃+1 mol%V₂O₅+x mol%MnO₂ is selected as a formulation.In this paper,the effect of MnO₂ doping on the microstructure,phase composition,and the electrical properties of the ZnO varistor was investigated.From the experimental analysis,it is concluded that the average grain size of ZnO varistorgradually decreases with increasing MnO₂ doping.The sintered density decreases,and the breakdown field strength increases,the leakage current increases to a maximum of 61 and then decreases,the nonlinear coefficient increases first and then decreases with increasing MnO₂ doping.When the MnO₂content is 0.5 mol%,the obtained varistor has the best performance,for which,the breakdown field strength is up to 437 V/mm,the leakage current value is 2.4?A/cm²,and the nonlinear coefficient value is 66.Third,the effect of Er₂O₃ doping on the properties of ZnO varistors was studied.The samples were prepared according to?97.5-x?mol%ZnO+1.0 mol%Pr₆O₁₁+1 mol%V₂O₅+0.5 mol%Y₂O₃+x mol%Er₂O₃.This paper analyzes the relationship between structure and properties of ZnO varistor with increasing Er₂O₃ doping.The experimental data show that the average grain size of ZnO varistor gradually decreases,the sintering density increases,the breakdown field strength gradually increases,and the value of the nonlinear coefficient firstly increases and then decreases with increasing Er₂O₃ doping.The Leakage current increases to a maximum of 51 and then decreases with increasing Er₂O₃ doping.When the Er₂O₃ content is 1.0 mol%,the electrical properties of the ZnO varistor is optimal,for which,with the breakdown field strength is 355 V/mm,the nonlinear coefficient is 51,and the leakage current is 1.8?A/cm².Finally,96.5 mol%ZnO+1.0 mol%Pr6O11+1 mol%V2O5+0.5 mol%Y2O3+1.0 mol%Er2O3 was used to prepare the varistor sample.The sintering temperatures of 1150°C,1200°C,1250°C,and 1300°C were studied.With increasing sintering temperature,the breakdown field strength first decreases and then increases,and the nonlinear coefficient first increases and then decreases.When the sintering temperature is 1200°C,the nonlinear coefficient reaches the maximum value of 41,and the leakage current exhibits a minimum value of 1.8?A/cm2.Finally,when the sintering temperature is1200°C,the performance of the varistor is the most excellent.