Effects of heat treatment and particle size on the tetragonality of nano-sized barium titanate powder

Although fine BaTiO3 powders with high tetragonality (=c/a) are required to increase the volumetric efficiency of a multilayer ceramic capacitor in industry, the tetragonality decreases and disappears below a certain particle size. In order to check the effects of particle size and processing temperature on tetragonality, heat treatment and X-ray diffraction were performed using commercial hydrothermal BaTiO3 powders after adding different amounts of carbon black. Carbon black was burned out completely up to 600 °C during the heat treatment while acting as an effective particle growth inhibitor even at high temperature like 1100 °C. By changing the amount of carbon black, the synthesis of BaTiO3 particles having similar size at different processing temperatures was possible. Tetragonality depended linearly on the average particle size up to 330 nm, while showing a saturated value of 1.0105 for larger particles. Tetragonality was not a function of processing temperature for particles heat treated above 950 °C, which implied that the heat treatment above 950 °C was not helpful for the enhancement of tetragonality.