Study On Preparation Of ZnO-Bi₂O₃ Varistor Ceramics At Low Temperature

ZnO varistor ceramics have been widely used in computers,household appliances,high-voltage electrical circuits,and high-power circuit devices because of their excellent pressure sensitive performance.At the same time,ZnO-Bi₂O₃ varistors are the most studied in varistor ceramics.With the development of integration,miniaturization and functionalization of electronic-electrical products,the preparation research and performance optimization of multilayer ZnO varistor ceramics have attracted more and more attention of researchers.In order to achieve the co-firing of silver paste and ZnO varistor and the optimization of electrical propertiesi,in this paper,the effect of low temperature sintering auxiliary additives?BST?,In₂O₃,Ga₂O₃,La₂O₃ and Co₃O₄ on the phase structure,microstructure,density and electrical properties of the ZnO-Bi₂O₃-MnO₂-SiO₂-TiO₂ varistor ceramics was studied by doping.besides,the mechanism of additives to optimize the electrical properties was investigated,and the low-temperature preparation of ZnO-Bi₂O₃ varistor ceramics with excellent properties was realized.This thesis came to the following main conclusions:1.Selected the ZnO-Bi₂O₃-MnO₂-SiO₂-TiO₂ system to study the performance of varistors,determined the molar ratio of Bi₂O₃,TiO₂,SiO₂ is 6:3:4,and realized the low temperature sintering of ZBMST varistors.The results of research show that,when the sintering temperature is 875?,ZBMST varistor have a comparatively high density with the relative density of 97.6%,voltage gradient of 717.1 V/mm,leakage current density of 0.38?A/cm²,nonlinear coefficient of 5.5,and it possess a relatively high dielectric constant and a low energy loss.2.By doping In₂O₃,Ga₂O₃,La₂O₃ into ZnO-Bi₂O₃-MnO₂-SiO₂-TiO₂ system respectively,the effect of additives on the structure and properties of the varistors was investigated,and the mechanism it modified the electrical properties was revealed.The results show that with 0.075 mol%In₂O₃ doping,In₂O₃ and ZnO are in solid solution and can promote the dispersion of the bismuth-rich phase.Doping In₂O₃ with a low forbidden band width can effectively improve the nonlinear coefficient;its voltage gradient is 816.6 V/mm,the leakage current density is 0.35?A/cm²,the nonlinear coefficient is increased to 15.7,and the dielectric loss is small.La₂O₃ is difficult to dissolve with ZnO,but La₂O₃ doping will promote MnO₂ and SiO₂ to dissolve in the bismuth-rich phase,refine the grain size,and slightly increase the nonlinear coefficient.Ga₂O₃ doping can significantly refine the ZnO grains,but due to its high band gap,its doping will reduce the nonlinear coefficient.3.By studying the structure and properties of ZnO-Bi₂O₃-MnO₂-SiO₂-TiO₂-Co₂O₃six-component varistor ceramics,the electrical properties of the varistor ceramics were optimized and improved.The results show that when the BST doping is 0.25mol%,the electrical performance of the varistor ceramic is the better,the voltage gradient is 301.2 V/mm,the leakage current is 0.028?A/cm²,and the nonlinear coefficient is 39.8;when the Co₂O₃ doping is 0.075 mol%,the pressure sensitivity is pretty good,the voltage gradient is 526.2 V/mm,the leakage current density is 0.027?A/cm²,the nonlinear coefficient is 43.4,and it has a low dielectric constant and a low energy loss.