Agglomerate-free BaTiO₃ particles by salt-assisted spray pyrolysis

Optimum conditions for the synthesis of nonagglomerated BaTiO₃ particles by salt-assisted spray pyrolysis (SASP) were investigated. The effect of particle residence time in the reactor and salt concentration on the crystallinity and surface morphology of BaTiO₃ was examined by x-ray diffraction and scanning electron microscopy. Mixtures of a metal chloride or nitrate salt, dissolved in aqueous precursor solutions, were sprayed by an ultrasonic atomizer into a five-zone hot-wall reactor. By increasing the salt concentration or the particle residence time in the hot zone, the primary particle size was increased, and its surface texture was improved compared to BaTiO₃ particles prepared by conventional spray pyrolysis. The SASP-prepared BaTiO₃ crystal was transformed from cubic to tetragonal by simply increasing the salt concentration at constant temperature and residence time. Further thermal treatments such as calcination or annealing are not necessary to obtain nonagglomerated tetragonal BaTiO₃ (200–500 nm) particles with a narrow size distribution. Increasing the carrier gas flow rate and decreasing the residence time in the hot zone resulted in cubic BaTiO₃ particles about 20 nm in diameter.