Phase evolution and nucleus growth observation of solid-state BaTiO ₃ powder prepared by high-energy bead milling for raw material mixing

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 (2m2/g) and TiO2 (7m2/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 80nm 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 (ε_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 ±15%) until calcination temperature increased to 1000 °C.