Study On Ultra-fine (Ba, Sr)TiO₃ Powders And Ceramics

Strontium-barium titanate ceramics, which have been developed in recent decades years,. have been one of the most important functional ceramics and used as the basic raw materials in the composition of ceramic capacitors today. The research of preparation and properties of strontium-barium titanate ceramics has been a focal point in the field of inorganic solid chemistry. However, the study of strontium-barium titanate begins only in recent years inside and there is a lot of work to do.The preparation of homogeneous ultra-fine strontium-barium titanate powders with high purity by Sol-gel method was studied. Compared to conventional process, the synthesis temperature and sintering temperature is lower, saving energy, increasing the density of ceramics and improving the properties of ceramic products. The research of strontium-barium titanate ceramics properties and the effects of doping agent improves the properties and satisfies with more requirements in different fields.The ultra-fine BST powders and doped BST powders prepared by citrate-nitrate combustion method were studied. The BST powders were characterized using several techniques, such as TG/DSC,XRD,SEM and TEM, to determine particle size, composition, phase and morphology respectively. The influences of citrate acid volume,PH value,heat-treating temperature and dispersant(ethylene alcohol) volume on the properties of ultra-fine BST powders were investigated, to obtain the best amount of citrate acid volume and dispersant(ethylene alcohol) volume, the proper Ph value and heat-treating temperature. The results indicated that the properties of ultra-fine BST powders are prominent under the condition as follows: the PH value is 7, the ethylene alcohol volume is 2.25ml and the heat-treating temperature is 800℃. The phase structure of BST powders is cubical phase. The average grain size is 100nm. The particle morphology is irregularity spherical shape with conglobation.Ultra-fine Bi₄Ti₃O₁₂ powders were prepared by Sol-gel method . By means of TG/DSC,XRD,SEM and other test methods, the particle size, composition, phase and morphology of Bi₄Ti₃O₁₂ powders were analysed. The results indicate that the phase structure of Bi₄Ti₃O₁₂ powders is bismuth layer-structure and the average grain size is 70nm.BST mixed-powders were prepared by ultra-fine BST powders and additive BST powders doped with ultra-fine Bi₄Ti₃O₁₂ powders. The preparation of BST functional ceramics using BST mixed -powders was studied. The surface topography, microscopic structure and phase structure of ultra-fine BST ceramics were systematically analysed. The effects of sintering temperature and the doped amount of Bi₄Ti₃O₁₂ on the surface microscopic structure were studied. The dielectric properties of BST function ceramics were investigated by means of YY2814 automatic LCR meter, CJ2672 withstand voltage tester, TH2683 insulation resistance tester. The effects of sintering temperature, the additive amount of Bi₄Ti₃O₁₂ and trace elements on the dielectric properties of BST ceramics were studied.According to the study of different formula and technology of BST ceramics, the formula 5th was prominent. The sintering temperature is 1200℃and the average grain size of BST is 0.5um. The dielectric properties reach the level as follows: the dielectric constant is 2241, the dielectric loss is 0.0035, the compression strength is 7.36Kv/mm,the rate of insulation resistance is 10.43GΩ.cm and AC/C is-61.23%.