Study On Effects Of Simultaneous Addition Of Sb₂O₃,Y₂O₃,SiO₂ And B₂O₃ To Bi-based ZnO Varistors On The Electrical Characteristic

ZnO-Bi2O3 based varistors are widely applied in the protection of electric power systems and integrated circuits because of the highly nonlinear voltage-current characteristics.In this thesis,the commercial ZnO-Bi2O3 based varistors has been improved by doping/or codoping Yttrium,Antimony,Silicon and Boron.Samples were made by using the solid-state reaction method.The electrical characteristics,microstructure,phase structure and element position were investigated using a V-I characteristics test,electrical degradation,XRD,SEM and EDS method and so on.Varistors with a higher varistor voltage,a higher resistance to electrical degradation and a low current density were fabricated.Results are as follows:1.The effects of adding Y2O3 0-4.0 mol%,Sb2O3 0～2.0mol%to a Bi-Mn-Co-Cr-Ni-added ZnO(a commercial composition)varistor on the nonlinear V-I characteristics,varistor voltage,resistance to electrical degradation,nonlinear index a and leakage current JL were investigated.The varistor voltage reached around 1000V/min by adding Y and Sb together,but decreased soon after short-term electrical degradation.The nonlinear coefficient was around 45.In addition,the relative dielectric constants εr was decreased obviously by adding Sb2O3,which indicated the reduction in formation of insulating regions along the grain boundary because of Sb addition.The leakage current was higher with Y-Sb additive.The nonlinear coefficient a decreased below 10 when the amount of Y2O3 was above 3.0mol%,indicating that the samples’non-linear characteristics nearly disappeared.2.SiO2 was doped from zero to 6.0 mol%into Bi-Mn-Co-Cr-Ni-added ZnO varistors together with 2.0 mol%Sb2O3 and 2.0mol%Y2O3.After altering the amount of Si in samples,the varistor voltage and resistance to electrical degradation were slightly improved,while the leakage current decreased significantly.The leakage current was below 10-5 A/cm2 when SiO2 amount was higher than 2.65mol%,and the nonlinear coefficient was stable about 40 before electrical degradation,then maintaining around 30 after electrical degradation.3.Added 0～2.0mol%of Boron in the samples above and adjusted Silicon amount separately with 0,2.65,5.0mol%.Samples with a good resistance to electrical degradation,a higher varistor voltage(900～1100V/mm),and the nonlinear coefficient around 45 to 55 were achieved.It was discovered that Boron has the ability to improve the resistance to electrical degradation.When 1.0 mol%of B2O3 was added,the leakage current density stayed below 10-5A/cm2 when high voltage was applied to samples at 130℃ high temperature status for a 20 hour period.4.It was found that the Bi2O3 in samples has two crystal phases,β and δ.The nonlinear coefficient a after electrical degradation was higher than others when δ-Bi2O3 was present.A Y-Sb-Bi component was formed when approximately 1mol%of B2O3 was added.It was investigated that this Y-Sb-Bi component has the ability to improve the resistance to electrical degradation.It was also observed that the resistance to electrical degradation was decreased when the willmite(Zn2SiO4)amount in samples increased.