Preparation And Electrical Properties Of BaTiO₃-Sr_0.7Bi_0.2TiO₃-Bi(Ni_2/3Nb_1/3)O₃-CaZrO₃ Ceramics

With the continuous development of Multilayer Ceramic Capacitors（MLCCs）towards miniaturization and high integration,people urgently need lead-free ceramic materials with good temperature stability and high energy storage density.However,the existing lead-free ceramic materials are difficult to meet actual needs.In this paper,BaTiO₃is selected as the functional ceramic matrix,and by the modification at A/B site of ceramics,the dielectric temperature stability,breakdown strength,energy storage density and energy storage efficiency are simultaneously improved.The main research content and results of the thesis are as follows:Firstly,（1-x）BaTiO₃-xSr_0.7Bi_0.2TiO₃binary solid solution ceramics（denoted as B100xSBT,x=0.04,0.08,0.12,0.16）were prepared by a solid phase reaction method.It is found that the addition of Sr_0.7Bi_0.2TiO₃（SBT）improves the dielectric temperature stability of the ceramics.The temperature coefficient of capacitance（TCC）of ceramics is reduced from-275%～22%to-82%～22%in the range of-55～200℃.The maximum polarization(P_max)is increased from15μC/cm²to 20μC/cm²,and the breakdown strength is increased from 30 kV/cm to 90kV/cm,resulting in a gradually increased effective energy storage density of ceramics.The dielectric temperature stability of the samples B12SBT and B16SBT can satisfy the X9V standard of the Electronics Industries Association（EIA）.The ceramics B12SBT have the best energy storage performance with effective storage energy density of 293 m J/cm³（2.18 times that of as-prepared BTO ceramics）,the energy storage efficiency of 44%under the breakdown field strength of 90 kV/cm.Secondly,（1-y）(0.88BaTiO₃-0.12Sr_0.7Bi_0.2TiO₃)-yBi(Ni_2/3Nb_1/3)O₃ternary solid solution ceramics（denoted as BS100yBNN,y=0.025,0.005,0.075,0.100）were also prepared by the solid state reaction method.It is found that the dielectric temperature stability is further improved as the content of Bi(Ni_2/3Nb_1/3)O₃（BNN）increases from 0.025 to 0.100.The range of TCC is reduced from-82%～22%to-56%～22%in the range of-55～200℃（meet the EIA X9U standard）.Moreover,as the BNN content increases,the relaxor characteristics of ceramics are enhanced,leading to a gradually increased effective energy storage density.The breakdown field strength of BS10BNN ceramics is 120 kV/cm,the effective energy storage density is 545 m J/cm³（4 times that of BTO ceramics）,and the energy storage efficiency reaches 89%.Finally,5 wt.%CaZrO₃（CZO）was added to（1-y）(0.88BaTiO₃-0.12Sr_0.7Bi_0.2TiO₃)-yBi(Ni_2/3Nb_1/3)O₃by a precipitation method to obtain quaternary solid solution ceramics BS100yBNNCZO（y=0.025,0.05,0.075,0.1）.It is found that all the experimental samples satisfy the EIA X9U standard.The addition of CZO can effectively increase the breakdown strength of the ceramics.The breakdown field strength of BS10BNNCZO ceramics is increased to 140 kV/cm,the effective energy storage density is 744 m J/cm³（5.55 times that of BTO ceramic）,and the energy storage efficiency reaches 91%.The purpose of improving the dielectric temperature stability and energy storage performance have been achieved in the as-prepared quaternary solid solution ceramics.It can provide a functional material basis for the next generation of energy storage ceramic capacitors.