Bandgap studies on anatase titanium dioxide nanoparticles

Titanium dioxide, predominantly in the anatase phase with an average grain size of 5-10 nm, has been synthesized by the hydrazine method. These nanocrystalline particles show a blue shift in the absorption edge of the diffuse reflectance ultraviolet spectrum of about 10 nm compared to that of commercially available titania. Synthesized samples were characterized by X-ray diffraction and transmission electron microscopy for their structural properties and UV-Vis absorption spectroscopy for the bandgap studies. The absorption spectra show a linear fit for the direct transition. The optical and electrical properties of the samples have been studied and the Arrhenius plots of electrical conductivity both for the as-prepared anatase TiO2 and the one subsequently reduced in hydrogen atmosphere at 673 K show a distinct difference in the activation energy. The hydrogen-annealed sample shows a typical semiconducting behavior whereas the as-prepared sample indicates a phonon contribution to the conductivity around 300 K. (C) 2002 Elsevier Science B.V. All rights reserved.