Sol-Gel Synthesis of Nano-Scaled BaTiO_3, BaZrO_3 and BaTi_0.5Zr_0.5O_3 Oxides via Single-Source Alkoxide Precursors and Semi-Alkoxide Routes

摘要

Sol-gel synthesis of nano-sized BaTiO_3, BaZrO_3 and BaTi_0.5Zr_0.5O_3 ceramics using alkoxide and semi-alkoxide routes has been investigated and the pervoskites obtained have been compared with respect to crystallisation temperature, crystallite size and compositional purity. Heterometal alkoxides containing two (for BaTiO_3 and BaZrO_3) and three (for BaTi_0.5Zr_0.5O_3) different metals were used as single-source precursors in the alkoxide route while semi-alkoxide syntahesis was preformed by reacting barium hydroxide or acetate with Ti and/or Zr alkoxides. Semi-alkoxide synthesis also produces stoichiometric and phase-pure oxides, however, at temperatures higher than 1000 deg C. At temperatures below 1000 deg C, BaCO_3 and small amounts of other undesired phases (e.g., BaTi2O_4) were present in the oxides derived from semi-alkoxide synthesis. Thermal behaviour, studied by TGA/DTAmeasurements, shows that thermal decomposition occurs in three major steps and depends on the educt composition and the synthes route. Among alkoxide derived powders, crystalline BaTi_0.5Zr_0.5O_3 phase is formed at 400 deg C while complete crystallisation of BaMO_3 ceramics occurs around 600 deg C. The cubic to tetragonal phase transition for BaTiO_3 is clearly observed at relatively low-temperature of 800 deg C. The stoichiometry and phase homogeneity of the obtained powders were demonstrated by energy dispersive X-ray analysns and powder diffractometry. The averaged crystallite size of the obtained nano-ceramics was evaluated using the FormFit programme. SEM and TEM observations revealed a high microstructural uniformity.