Study Of The Properties Of High Absorption Pulse Resisted ZnO-Pr₆O₁₁ And ZnO-Bi₂O₃ Varistor

With the development of science and technology,electrical products are widely used.As an over–voltage protection device,varistors can protect the normal operation of the equipment though absorbing the impulsive which is induced by the over-voltage.The effects of sintering temperature and doping ions on the properties of ZnO–Pr₆O₁₁ and ZnO–Bi2O3 varistors,such as phase composition,microstructure,grain growth kinetics and electrical property,were sysmatically studied.The composition of the optimal characteristics of Zn O–Pr₆O₁₁ and ZnO–Bi2O3 varistors were obtained.Moreover,its application in power and photovoltaic were analyzed.Firstly,the effect of sintering temperature on microstructure structure and electrical properties of ZnO–Pr₆O₁₁ varistors was studied.The as-prepared Zn O–Pr₆O₁₁ varistors were composed of 96.0mol%ZnO,0.5mol%Pr₆O₁₁,0.5mol%Cr2O3,0.5mol%Co2O3,0.5mol%Y2O3,1.0mol%V₂O₅ and 1.0mol% Mn₃O₄.The results show that the average grain size of ZnO–Pr₆O₁₁ varistor increased as increasing the sintering temperature.As a contrast,the sintering density,the breakdown strength and the impedance decreased gradually as increasing the sintering temperature.However,the leakage current decreased firstly,and then increased.Besides that,the non–linearity coefficient and the grain boundary barrier height increased firstly and then decreased.When the sintering temperature reached 1100?,the leakage current reached the minimum value of 2.94?A/cm2 and the non–linearity coefficient reached the maximum value of 46.3 at the sintering temperature of 1100?.As a next step,we investigate the effects of Mn₃O₄ doping on the microstructure and electrical properties of ZnO–Pr₆O₁₁ varistor,which were composed of?97.0–x?mol%ZnO,0.5mol%Pr₆O₁₁,0.5mol%Cr2O3,0.5mol% Co2O3,0.5mol% Y2O3,1.0mol%V₂O₅,x mol%Mn₃O₄?where x=0.25,0.50,0.75,1.00,1.25,1.50?.The results show that,with the increase of Mn₃O₄ doping amount,the main crystal phase of varistor is hexagonal wurtzite structure of ZnO.However,the relative intensity of ZnO characteristic peaks decreased slightly,and the position shifted to high angle.Moreover,the surface hole of varistor decreased gradually,the average grain size decreased in the beginning and then increased,while the breakdown field strength,the grain boundary barrier height,the nonlinear coefficient,the leakage current and impedance increased firstly and then decreased.When the doping amount of Mn₃O₄ is 1.00mol%,the spinel phases in the varistor reached the most,the average grain size reached the minimum value of 1.44?m,the breakdown field strength reached the maximum value of 1128.6V/mm,the nonlinear coefficient is 46.3,which is only less 2.2 than the maximum value of 48.5.Based on the formulas of grain growth dynamics,the kinetic growth coefficient is 3.9,the activation energy in the grain growth process is 281.6 k J/mol,the grain boundary mobility is low,and the grain growth rate is slow.Thirdly,we investigate the effect of V₂O₅ doping on the microstructure structure and electrical properties of ZnO–Pr₆O₁₁ varistor,which were composed of?98.5–x?mol%ZnO,0.5mol%Pr₆O₁₁,1.0mol%Y2O3,x mol%V₂O₅?where x=0.25,0.50,0.75,1.00,1.25,1.50?.With the increase of the doping amount of V₂O₅,the intensity of the spinel phase PrVO4 characteristic peak increased gradually,while the intensity of Pr9O16 and Pr5O9 characteristic peaks decreased gradually,the average grain size,the grain boundary barrier height and the leakage current decreased firstly,then increased,while the breakdown field strength,the nonlinear coefficient and the impedance increased firstly then decreased.The composition of V₂O₅–doped ZnO–Pr₆O₁₁–based varistor is simple,but the performance is superior.When the doping amount of V₂O₅ reached 1.0mol%,Pr9O16 changed into Pr5O9;the grain size become uniform,and reached a minimum of 1.17?m;the impedance reached its maximum value,the leakage current reached the minimum value of 1.18?A/cm2,and the breakdown field strength reached the maximum value of 1099V/mm.Based on the formulas of grain growth dynamics,the kinetic growth coefficient is 4.1,the activation energy in the grain growth process is 292.8kJ/mol,the grain boundary mobility is low,and the grain growth rate is slow.Finally,we investigate the effect of Nb₂O₅ doping on the microstructure structure and electrical properties of ZnO–Bi2O3 varistor,which were composed of?97.5–x?mol%ZnO,0.5mol%Bi2O3,1.0mol%Y2O3,1.0mol%V₂O₅,x mol%Nb₂O₅?where x=0.5,1.0,1.5,2.0,2.5,3.0?.the main crystal phase of Zn O–Bi2O3 varistor was Zn O,and the grain boundary phase were mainly Bi3NbO7?Y3NbO7?BiYO3 and Nb₂O₅.With the increase of doping amount of Nb₂O₅,the relative intensity of Bi3NbO7 characteristic peak decreased gradually,while the relative intensity of Y3NbO7 characteristic peak increased gradually.The average grain size,grain boundary barrier height,leakage current decreased firstly and then increased,while the breakdown field strength,the nonlinear coefficient and the impedance firstly increased firstly and then decreased.the maximum value of the breakdown field strength was 472.8V/mm.When the doping amount of Nb₂O₅ is 1.5mol%,the leakage current reached the minimum value of 2.27?A/cm2,the nonlinear coefficient increased the maximum value of 32.4,and the breakdown field strength was 460.1V/mm,which is only less 12.7 V/mm than its maximum value.