Anatase to rutile phase transition promoted by vanadium substitution in TiO2: A structural, vibrational and optoelectronic study

Abstract The anatase to rutile phase transition of TiO 2 which normally occurs at 750 °C, is reduced to temperatures below 600 °C by vanadium doping. The structural transformation is observed by a systematic study in the temperature range from 450 °C to 750 °C. The introduction of vanadium in rutile lattice is found to have impact on lattice parameters and particle size. This substitution also helps to reduce the bandgap of rutile TiO 2 to 1.76 eV from 3.04 eV upon 6 at% of vanadium doping. Vanadium induces additional donor level in forbidden region. XANES study confirms that vanadium is in mixed valence state of V 4+ and V 5+ and concentration of V 4+ increases with increasing doping amount and in the band gap region donor level due to V 4+ takes deeper position than V 5+ . As a result, the effective band gap decreases with increasing vanadium concentration. Anharmonicity of vibrational modes systimatically increases which indicates increasing phonon-phonon interaction with increasing doping concentration.