Doping anatase TiO2 with group V-b and VI-b transition metal atoms: a hybrid functional first-principles study

摘要

We investigate the role of transition metal atoms of group V-b (V, Nb, andTa) and VI-b (Cr, Mo, and W) as n- or p-type dopants in anatase TiO2 usingthermodynamic principles and density functional theory with theHeyd-Scuseria-Ernzerhof HSE06 hybrid functional. The HSE06 functional providesa realistic value for the band gap, which ensures a correct classification ofdopants as shallow or deep donors or acceptors. Defect formation energies andthermodynamic transition levels are calculated taking into account theconstraints imposed by the stability of TiO2 and the solubility limit of theimpurities. Nb, Ta, W and Mo are identified as shallow donors. Although Wprovides 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 aredeep donors and Cr shows up as an amphoteric defect, thereby acting as anelectron trapping center in n-type TiO2 especially under O-rich conditions. Acomparison with the available experimental data yields excellent agreement.