Solid-state synthesis of nano-sized BaTiO₃ powder with high tetragonality

A solid-state reaction method was used to synthesize nano-sized, Ca-doped BaTiO₃ powder with high tetragonality (=c/a) in order to increase the volumetric efficiency of multilayer ceramic capacitors (MLCCs). The reaction temperatures for three different starting material combinations were examined by thermogravimetric/differential thermal analysis (TG/DTA). Nano-sized starting materials and the mechanochemical activation of the needle-shaped BaCO₃ via high-energy milling were effective in decreasing the reaction temperature. In addition, the results showed that the tetragonality of fine Ca-doped BaTiO₃ could be enhanced by 2-step heat treatment, consisting of holding at 800 °C for 1 h followed by consecutive heating to the target temperature, without any significant grain growth than that of the conventional 1-step calcination. The synthesized particles heat-treated at 950 and 1,000 °C by 2-step heat treatment were confirmed by characterization to have an average size of 128 and 212 nm, and a tetragonality of 1.0097 and 1.0105, respectively, which are higher tetragonality values than those previously reported for similar sized particles.