Synthesis Of Barium Strontium Titanate (Ba_0.7Sr_0.3TiO₃) Nanopowders By Sol-gel Method

Perovskite-sturcture barium strontium titanate (Ba_1-xSr_xTiO₃, BST) ceramics have been used in a wide range of applications owing to their promising properties. The preparation of the BST powders has been paid more attention because of the development of BST ceramics. The BST powders are usually prepared by solid state reaction required the high calcination temperature and long time. As one of the chemical synthesis methods the sol-gel method is able to provide high chemical purity, precise composition, and uniform microstructure. Therefore, the sol-gel method has been extensively employed in the preparation of many powder materials. In this dissertation we prepared the Ba_0.7Sr_0.3TiO₃ powders by sol-gel method. Thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), Infrared (IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the thermal decomposition behavior, the crystallization process, the particle size and morphology of the calcined powders. The major work is summarized as follows:Ba_0.7Sr_0.3TiO₃ nanopowders have been synthesized by sol-gel methods using barium acetate, strontium acetate and tetra-n-butyl titanate as Ba, Sr, Ti sources. The results indicated that single-phase and well-crystallized Ba_0.7Sr_0.3TiO₃ nanopowders could be obtained by a modified sol-gel process after calcining the dried gel at 900℃for 2 h in the presence of polyvinylpyrrolidone (PVP). It could be found that the use of PVP could resolve aggregation of particles efficiently producing the shape-controlled microstructure with narrow size distribution and uniform morphology. The separated and almost uniform particles at PVP/Ti ratio of 2:1 were formed with an average primary particle size around 90 nm.Ba_0.7Sr_0.3TiO₃ nanopowders were also successfully prepared by the citric acid gel method using barium nitrate, strontium nitrate and tetra-n-butyl titanate as Ba, Sr, Ti sources, and citric acid as complexing reagent. The results indicated that single-phase and well-crystallized Ba_0.7Sr_0.3TiO₃ nanopowders with particle size around 80 nm could be obtained after calcining the dried gel at 950℃for 2 h. The results show that the processes of the preparation of sol, sol to gel conversion and heating were affected by the pH value, the concentration of citric acid, water in sol and the heating process.