Nanostructure Development in Alkoxide-Carboxylate-Derived Precursor Films of Barium Titanate

The structural evolution in wet alkoxide-carboxylate sol gel precursor films of barium titanate upon drying was investigated by time-resolved small-angle X-ray scattering (SAXS). The morphology of as-dried amorphous precursor thin films was investigated by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Sols were prepared from titanium(IV) iso-propoxide in 2-methoxyethanol and barium acetate in acetic acid. The structures that were visible with SAXS could be divided into oligomeric structures with fractal-like scattering characteristics, and randomly packed agglomerates of nanoparticles of similar size. The fractal-like morphologies disappeared during film drying, probably because they were not stable in the absence of a solvent matrix. Only the ordered agglomerate-like structures remained in the as-dried films. EELS on as-dried films showed that spatial separation between barium and titanium-rich domains occurred during the drying of the thin films on a length scale of nanometers, depending on hydrolysis ratio. This demonstrates that as-dried films are not necessarily uniform on the mesoscopic level.