The Preparation And Modification Of Barium Titanate Based Dielectric Ceramics

In this paper, barium titanate dielectric ceramics have been prepared by sol-gel method with titanium oxide, nitrate barium, strontium nitrate etc as raw materials, and citric acid,ethylene as complexing agent, meanwhile the best synthesis condition was studied. The x with the best dielectric properties has been confirmed through prepared(_1-x)BaTiO_3-xSrTiO₃ composite ceramics, and the dielectric properties of that have been improved by doping Mn²⁺to A site and B site, Bi³⁺ to A site based on it.When the pH was 4, n（CA）: n（metal ions） was 3:1, clear and stable precursor solution could be obtained, and when the synthesis temperature was 900 ℃for 2 hours, nano-sized barium titanate powders were obtained with excellent crystallinity and the size was about30⁴0nm. Ceramics with high density and excellent dielectric properties have been obtained when the sintering temperature was 1250℃for 2 hours, then relative reduction was 15.20%and apparent density was 5.547 g/cm³. In addition, the properties that erwas 1250.4, tand was0.049（f=1KHz）.（1-x）BaTiO_3-xSrTiO₃ composite ceramics with different x values were single perovskite structure, When x≧0.3, the grain became translating tetragonal phase to cubic phase. When the sintering temperature was 1225℃,the dielectric constant increased at first, then decreased sharply with the increasing of x values, meanwhile, the dielectric loss increased at first, then decreased, but increased again.When the x was 0.3, the dielectric properties were better that er achieved 2771.84, and the tand was 0.0695（f =1KHz）.Mn doping on A site could decrease the size of grain obviously, on the contrary, Mn doping on B site could promoted the ceramic sintering that the relative density could achieve92.79%, and the the grain size increased when the doping content x was low. However, the grain size would decrease when the doping content x was more than 0.03.When the x was 0⁰.008 for Mn doping on A site,(Ba_0.7Sr_0.3)_1-x Mn_xTiO₃ ceramics with different x values were single perovskite structure. The grain became translating cubic phase to tetragonal phase with the x increased to 0.006,0.008. The dielectric constant decreased with the increasing of x, and the dielectric loss decreased at fist then increased.When the x was0.006, the dielectric loss achieved minimum that the tand was 0.00848（T=1250℃, f=1KHz）.When the x was 0⁰.01 with Mn²⁺doping on B site of Ba_0.7Sr_0.3TiO₃, the phase were single tetragonal perovskite structure. When the x was 0.005, the phase formation was better.There were some unknown impure phase and the grain became translating cubic phase to tetragonal phase with the x increasing to 0.03⁰.05. The dielectric constant er increased at first then decreased with the increasing of x, and the dielectric constant achieved maximum when the x was 0.005, that the dielectric constant erwas 3245.38（T=1225℃, f=1KHz）, then the characteristic of dielectric constant-frequency was best. Meanwhile, the dielectric loss decreased with the increasing of x, the dielectric loss achieved minimum when the x was 0.05,that the tan d was 0.0041（T=1250℃, f=1KHz）, then the characteristic of dielectric lossfrequency was best.Bi³⁺doping on A site couldn’t alter the original single cubic perovskite structure of Ba_0.7Sr_0.3TiO₃. When the x was 0⁰.03, it promoted the ceramic sintering and the grain growing, then the density increased and the grain size was 4⁵μm. When the x was 0.03,(Ba_0.7Sr_0.3)_1-x Bi_x TiO₃ could obtain the best dielectric properties and dispersion characteristic,that the erwas 3345.25, and the tand was 0.0099（T=1200℃, f =1K Hz）.