Preparation And Study On Dielectric Properties Of BaTiO₃ Based AC High Voltage Ceramic Capacitor Dielectric

With the development of the national smart grid,ceramic capacitor used in power grid tends to be smaller and more lightweight.Thus the dielectric should have superior integrated dielectric properties.The modified Ba0.94Bi0.04Ti0.96Sn0.04O3(BBST)dielectric is provided with high dielectric constant and favorable dielectric temperature stability,it has been widely used in the fabrication of multilayer ceramic capacitors up to now.However,this material is rarely used in high voltage capacitors due to the poor alternating current(AC)breakdown strength,insulation and relatively large dielectric loss.Therefore,a series of research work has been carried out to reduce dielectric loss,improve AC breakdown strength and insulation of BBST ceramic in this dissertation.First,effects of the same mass ratio SiO2,Al2O3 and MgO addition on the phase composition,microstructure and dielectric properties of BBST ceramics were investigated.The experimental results show that both SiO2 and Al2O3 react with the matrix during the solid-state sintering process,new phases were generated then,which lead to the deterioration of dielectric constant and dielectric loss.While the added MgO doesn't react with matrix,it coexists with perovskite BBST phase in the BBST/MgO composite.This structure can benefit to optimize the AC breakdown strength,reduce dielectric loss and other properties of BBST matrix,indicating MgO is a desirable additive for BBST.The effects of MgO content on the microstructure and dielectric properties of the BBST/MgO composite ceramics were further investigated.The results show that MgO is uniformly distributed in BBST grain boundaries.Although MgO deteriorates dielectric constant of BBST,with the increase of MgO content in BBST/MgO composite ceramics,the densification is gradually enhanced,AC breakdown strength and insulation increases,dielectric loss decreases.This is mainly attributed to following reasons:MgO possesses high breakdown,low loss and high insulation.Also,MgO could optimize the microstructure of BBST-MgO composite ceramic.The results show that BBST10 added with 10wt%MgO has the best comprehensive dielectric properties,whose dielectric constant is 2010,dielectric loss is 0.0077 and average AC breakdown field strength is 36.7 kV/cm.Finally,the BBST 10 composite ceramics were further modified by rare earth addition.Compared with La2O3 and Nd2O3,Sm2O3 is more conducive to optimize AC breakdown strength and dielectric loss for BBST 10.With the increase of Sm2O3 content,both AC breakdown strength and dielectric loss of BBST10 become better.The AC breakdown strength of BBST10-1.5%Sm2O3 is as high as 60.9 kV/cm,which is nearly 1.7 times that of BBST10.Also,its dielectric loss is only 0.0017,which is lower 80%than BBST10.