Nanostructured barium titanate thin films from nanoparticles obtained by an emulsion precipitation method

Spherical non-agglomerated BaTiO3 precursor particles of 3-5 nm size were prepared by an emulsion precipitation method that consisted of the complexation of Ba- and Ti-precursors in separate water-in-decane emulsions, followed by mixing and controlled precipitation upon reactive decomposition of tetramethyl ammonium hydroxide. Stable clear yellow dispersions with a final particle yield of ∼60% were obtained. In situ high temperature X-ray diffraction (XRD) measurements indicated that the initially amorphous particles crystallised into single-phase tetragonal BaTiO3 at 600 °C. Thin BaTiO3 films of 25-350 nm thickness were prepared from the precursor dispersions by spin coating or controlled deposition on Si wafers. The average crystallite size after annealing at 800 °C was approximately 26 nm, but some larger grains of 100-150 nm size were also observed. Fresnoite (Ba2TiSi2O8) was likely to be formed near the interface between the oxide layer of the Si substrate and the BaTiO3 film.