エマルジョン燃焼法で合成したチタン酸バリウムの粒子特性と焼結性 Characteristics and Sintering Behavior of Barium Titanate Powder Synthesized by Emulsion Combustion Method

Barium titanate (BaTiO_3) powder was synthesized using the emulsion combustion method (ECM) from a water-in-oil-type emulsion, in which a barium nitrate aqueous solution, a titania sol, kerosene and a surfactant were included, at a firing temperature of 850℃. Particle characteristics and sintering behavior of the synthesized particles were evaluated. The particles of the synthesized powder were nearly spherical in shape, 200-500 nm in diameter and polycrystalline. The diameter of the particle was almost consistent with that calculated from the size of the aqueous microsphere in the emulsion, the concentration of metal ions and the density of BaTiO_3. The X-ray diffraction (XRD) pattern showed that the main product (over 95%) was BaTiO_3 and that a small amount of Ba_2TiO_4 was synthesized. The compact of the synthesized powder was densified up to 90% of the theoretical density at a sintering temperature of 1200℃, which was 100℃ lower than that of the powder produced by the hydrothermal process. The fine polycrystalline structure of the ECM-made particles was considered to enhance the densification at a lower temperature. The sintered specimen showed a typical temperature dependence of dielectric constant in BaTiO_3, which included two peaks at 20 and 120℃, corresponding to orthorhombic-tetragonal and tetragonal-cubic phase transitions, respectively.