Photoacoustic Spectra of Mixed TiO₂ Ultrafine Powders with Rutile and Anatase Structures

We have measured the optical absorption of mixed TiO 2 ultrafine powders with rutile and tanatase structures by photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of strongly scattered materials. The values of band-gap energies, E g , of the TiO 2 ultrafine powders with different rutile contents were determined by the theory of interband transition in semiconductors. The values of E g of rutile and anatase structures of TiO 2 ultrafine powders are 3.00 eV and 3.20 eV, respectively, obtained from PA intensity and PA phase spectra, indicating the usefulness of PA spectroscopy. Mixed TiO 2 ultrafine powders with rutile and anatase structures (20–140 nm diameters) were obtained by thermal oxidation of TiCl 4 . Rutile structure contents depend on the thermal oxidation temperature. The value of E g of a mixed TiO 2 ultrafine powder with rutile and anatase structures decreases continuously with the increase of the rutile content. This indicates that the apparent E g can be controlled by mixing the nanometer-sized TiO 2 powders with rutile and anatase structures, hence, we can control and obtain TiO 2 materials with an arbitrary apparent E g between rutile and anatase structures.