Study On Synthesis Of Ba_1-xSr_x TiO₃ (x=0–1) Superfine Powder Materials

Barium titanate (BaTiO₃), strontium titanate (SrTiO₃) and barium strontium titanate (Ba1-xSrxTiO₃), all belonging to perovskite structure, are all important electronic ceramic materials and are used extensively in electronic equipment, communication equipment, catalysis and so on. Therefore, the preparation of these electronic ceramic materials is hotspot of study for years. In this paper, we prepared BaTiO₃, SrTiO₃ and Ba1-xSrxTiO₃ by coprecipitation method, low-temperature combustion method, molten-salt method and molten hydrated salt method respectively, and the products were tested.Using Ba(NO₃)₂, TiO₂ and H₂C₂O₄·2H₂O as raw materials, highly pure and ultra-fine barium titanate powders were prepared by a prepared oxalate coprecipitation method. By means of XRD, FT-IR and SEM, the phase composition, purity, microstructure and particle size of products were characterized. The results show that the products with a high purity, tetragonal structure and spherical particle shape have a narrow particle size distribution that 80% are below 3μm and the average size is about 2.3μm. The formation process of BaTiO₃ was also studied by conbining TG-DTA analysis and the XRD results of products prepared at different temperatures.Strontium titanate nanopowders were prepared by a low-temperature combustion method, using Sr(NO₃)₂, Ti(OC₄H₉)4, citric acid (CA) and NH₄NO₃ as raw materials. XRD, SEM, TEM, and FT-IR were used to study the structure, morphology and constituent of products. The results show that the products prepared under the conditions of the mole ratio of Sr(NO₃)₂, TiO(NO₃)₂, CA and NH4NO₃ being 1 : 1 : 2 : 8 and the pH value of the precursor solution being 7 were well dispersed single cubic perovskite SrTiO₃ nanopowders with an average grain size of about 25 nm and a lattice constant a=0.3913 nm. The crystallization process of the SrTiO₃ particles was investigated by TG-DTA.Rod-shaped SrTiO₃ powders were synthesized by a molten-salt method. This method synthesized products from a reaction of SrCO₃ and self-made rod-shaped TiO₂ with a eutectic mixture of NaCl-KCl at 750 oC for 8 h. The products were characterized with XRD, FT-IR, SEM and TEM. The results show that the rod-shaped SrTiO₃ with a diameter of 0.2–1.0μm and a length of 2.0–7.0μm has a cubic perovskite structure and high purity, and these as-synthesized rods are all composed of small crystals. Furthermore, the formation mechanism of SrTiO₃ rods was also discussed.With molten-salt method, perovskite Ba0.7Sr0.3TiO₃ nanopowders whit hollow cube structure were prepared, using molten Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O as flux, reacted with anatase-TiO₂ at 180 oC. The products were characterized with XRD, SEM, TEM and HRTEM. The results show that products are well crystallization. The average edge length of these cubes is about 180 nm and each hollow cube is composed of many small crystals. The effects of various conditions on product morphology, structure and particle size were studied. The formation process of products was preliminarily discussed.