Reaction and precipitation mechanism in the low-temperature aqueous synthesis of BaTiO3

In past years it has been demonstrated the possibility to obtain nanosized powders of Barium Titanate by precipitation in aqueous medium through the reaction Ba(OH)2 + TiCl4 + 4NaOH -> BaTiO3 + 4NaCl + 3H2O carried out at atmospheric pressure and 80 °C. In this work, the precipitation process was studied by means of X-ray diffraction, specific surface area measurements and scanning electron microscopy. Two different mechanisms of precipitation and crystallisation are reported, depending on the concentration of cationic species. In particular, [Ba2+] plays a critical role. For concentrations higher than 0.11 M the reaction leads directly to fully crystalline round-shaped particles with size in the range 20-50 nm. At [Ba2+] = 0.06M the product is an amorphous Ti-rich precipitate (Ba/Ti = 0.4) which slowly transforms into faceted BaTiO3 particles by a dissolution-precipitation process. This conclusion is supported by SEM observation of the particle size and morphology, which are incompatible with in-situ transformation. For intermediate concentrations, amorphous and crystalline phases coexist in the precipitate.