Photoacoustic spectra of mixed TiO2 ultrafine powders with rutile and anatase structures

We have measured the optical absorption of mixed TiO2 ultrafine powders wit h rutile and tanatase structures by photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of strongly scattered m aterials. The values of band-gap energies, E-g, of the TiO2 ultrafine powde rs with different rutile contents were determined by the theory of interban d transition in semiconductors. The values of E-g of rutile and anatase str uctures of TiO2 ultrafine powders are 3.00 CV and 3.20 eV. respectively, ob tained from FA intensity and PA phase spectra, indicating the usefulness of PA spectroscopy. Mixed TiO2 ultrafine powders with rutile and anatase stru ctures (20-140 nm diameters) were obtained by thermal oxidation of TiCl4. R utile structure contents depend on the thermal oxidation temperature. The v alue of E-g of a mixed TiO2 ultrafine powder with rutile and anatase struct ures decreases continuously with the increase of the rutile content. This i ndicates that the apparent E-g can be controlled by mixing the nanometer-si zed TiO2 powders with rutile and anatase structures, hence, we can control and obtain TiO2 materials with an arbitrary apparent E-g between rutile and anatase structures.