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 TiO2 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 TiO2 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 V4+ and V5+ and concentration of V4+ increases with increasing doping amount and in the band gap region donor level due to V4+ takes deeper position than V5+. 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. © 2017 Elsevier Ltd and Techna Group S.r.l.