Solid-state and surface spectroscopic characterization of BaTiO3 fine powders

The bulk and surface structure of two BaTiO3 powders has been investigated by FT-IR and FT-Raman spectroscopies. A high-area sample (39 m2/g), produced by a hydrothermal method, cubic to XRD, appears to have lower symmetry to Raman spectroscopy, with unit-cell distortions similar to those of tetragonal ferroelectric BaTiO3. It contains BaCO3 impurities, leading to a bulk Ba/Ti ratio lower than 1, as also evidenced by Raman spectra. Bulk hydroxy groups are evident, possibly needed to balance such a charge defect. Calcination at 1223 K causes the disappearance of these impurities and converts this material in the usual tetragonal phase. The surface properties of both powders, investigated through water and pyridine adsorption, are similar and appear to be dominated by Ba2+ ions, so leading to a solid characterized by extremely weak Lewis acidity. An interpretation for the solid-state behavior of the starting powder is proposed.