Research On Doping Modification Of ZnBiMnNbO Base Varistor Ceramics

ZnO-Bi₂O₃?ZnBiO?based varistors have been widely used in electronic equipment and power systems due to their excellent nonlinear properties.And it has ever become the most widely applied varistor ceramic systems.In recent years,the widespread application of integrated circuits has put forward a higher demand for high performance ZnO based varistor ceramics also with the low temperature sintering ability,because they are more suitable for the fabrication of multi-layered low voltage varistors.The traditional ZnBiO and ZnO-Pr₆O₁₁?ZnPrO?base varistor ceramics have a small leakage current,but their sintering temperature is too high.In contrast,varistor ceramics of ZnO-V₂O₅?ZnVO?based system has a low sintering temperature but a much higher leakage current.As a result,ceramics of these two systems can't meet the above demand.To solve this problem,this study put forward a new ZnBiMnNbO based varistor by substituting V₂O₅ with Bi₂O₃ in the low temperature sintering ZnVMnNbO based varistor ceramics.Then the effects of Co₂O₃,sintering temperature variation within 875-925?,soaking time variation within 2-5h and the addition of a Ce-La composite dopant which is a semi-finished product collected on a local Rare Earth reefing line will be revealed.First,the effect of Bi and V as varistor forming element in ZnO based ceramics were studied under the condition of the same dopant environment and sintering temperature.The results show that the ZnBiMnNbO base varistors sintered at 900oC for three hours showed the optimum varistor properties:the nonlinear coefficient 31.83,the leakage current density3.75?A/cm² and the breakdown field 576.75 V/mm.These values are generally superior than those of similarly prepared ZnVMnNbO based varistor ceramics.This result shows that Bi is more efficient than V on acting as the varistor forming elements in ZnO based ceramics.With the increase of Co₂O₃ content in the range of 0-0.2 mol%,the density of ZnBiMnNbO basic varistor ceramics gradually increases.At the same time,the average grain diameter increases from 3.83 to 4.32?m.The addition of Co₂O₃ results in the formation of Bi_7.53Co_0.47O_11.921.92 as the new secondary phase.The results of the I-V test show that 0.1 mol%Co₂O₃ doped ZnBiMnNbO ceramic sintered at 850oC for 3h exhibits the optimum electrical performance characterized by the non-linear coefficient of 30.85,the breakdown voltage780.85 V/mm,and the leakage current density 3.1?A/cm².With the increase of La and Ce composite dopant in the range of?0-0.1mol%?,the density of ZnBiMnNbO based varistor ceramics gradually increases,and the average grain diameter decreases from 6.36 to 5.62?m.Meanwhile,CeO₂ and La₂O₃ precipitate at the grain boundaries as the new secondary phases.The results of the I-V test show that the RE containing ZnBiMnNbO based varistors sintered at 900oC for 4h has the optimum varistor properties:the the nonlinear coefficient is 44.11,the breakdown voltage field is 614.04 V/mm and the leakage current density is 2.04?A/cm².