Title: Doping anatase TiO2 with group V-b and VI-b transition metal atoms: a hybrid functional first-principles study,
Abstract: We investigate the role of transition metal atoms of group V-b (V, Nb, and
Ta) and VI-b (Cr, Mo, and W) as n- or p-type dopants in anatase TiO2 using
thermodynamic principles and density functional theory with the
Heyd-Scuseria-Ernzerhof HSE06 hybrid functional. The HSE06 functional provides
a realistic value for the band gap, which ensures a correct classification of
dopants as shallow or deep donors or acceptors. Defect formation energies and
thermodynamic transition levels are calculated taking into account the
constraints imposed by the stability of TiO2 and the solubility limit of the
impurities. Nb, Ta, W and Mo are identified as shallow donors. Although W
provides two electrons, Nb and Ta show a considerably lower formation energy,
in particular under O-poor conditions. Mo donates in principle one electron,
but under specific conditions can turn into a double donor. V impurities are
deep donors and Cr shows up as an amphoteric defect, thereby acting as an
electron trapping center in n-type TiO2 especially under O-rich conditions. A
comparison with the available experimental data yields excellent agreement.