Nanostructured TiO₂-based composites: structural, optical and electrical properties

Full text: Nanostructured TiO2-composite powders having tin, copper or zirconium oxide as the second compound were prepared by polyol. Short heat treatment at 500°C and subsequent observation on FEG-SEM showed the polyol precipitates were formed of TiO₂ micro platelets covered with the secondary oxide nanoparticles, being the TiO₂ anatase phase always the predominant one, as proved by XRD. Optical characterizations indicated much higher light absorbance for the powder having Cu than for TiO₂ single oxide, in the wavelength range from 250 to 2500 nm. Low and high temperature electrical measurements were performed in just powder pressed pellets and, particularly for the TiO₂-SnO₂ nanocomposite the curve of resistivity as a function of temperature under an applied electrical field showed an abrupt fall at about 450K, showing an important thermal stimulation on that region of temperature (Schottky Effect). The characteristics curves, electrical current as a function of the applied voltage, were investigated for the 343-450K temperature range and the graphics presented non-linear behavior indicating an interaction between the electrical field and the grain boundary potential barrier to the electrons. It was proposed a simplified model of electron transport throughout grains in which it is assumed that the existing barrier between titanium oxide grains was reduced due to the presence of SnO₂ nanoparticles on its surface, although the dominant role is still played by the TiO₂ phase. (author)