Phase Evolution and Nucleus Growth Observation of Solid-State BaTiO3 Powder Prepared by High-Energy Bead Milling for Raw Material Mixing

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The solid-state synthesis, phase evolution, and nucleus growth of the barium titanate (BaTiO3, BT) powder were investigated in this study. Rapid nucleus growth and precursor phase formation of BT were observed at a relatively low temperature of 600 °C by mixing BaCO3 (2 m2/g) and TiO2 (7 m2/g) with a high-energy bead mill. The decomposition of BaCO3 and the formation of the Ba2TiO4 phase were identified by transmission electron microscopy (TEM). On the basis of this observation, the weight loss observed at 600 °C in the derivative thermogravimetry (DTG) curve could also be explained. Furthermore, with increasing calcination temperature, single cubic BT with less than 80 nm fine nuclei/crystallites was observed at 900 °C, and tetragonal BT ($c/a > 1.008$) with an average particle size of 0.4 μm was obtained at 1000 °C. With regard to the dielectric properties of sintered ceramics, the relative permittivity ($\varepsilon_{\text{r}}$) increased with calcination temperature, and the Curie point also shifted to a progressively higher temperature. However, BT nucleus samples (with low calcination temperatures of 800 and 900 °C) could not satisfy the X7R requirement (Electric Industries Association Standard, the tolerance of capacitance from $-55$ to +125 °C is $\pm 15$%) until calcination temperature increased to 1000 °C.
2011-09-25