Generalized Gradient Approximation plus U Study for Metallization Mechanism of Niobium-Doped Anatase Titanium Dioxide

I investigated the metallization mechanism of niobium(Nb)-doped anatase titanium dioxide (TiO2). There are recent calculations for Nb-doped TiO2 using the local density approximation (LDA) or generalized gradient approximation (GGA) method. I performed GGA+ U calculations to solve the problem. The obtained band gap and the defect state are expected to be improved by the GGA+ U method. I calculated the electronic structures of undoped, one-Nb-doped, and two-Nb-doped TiO2 per supercell. It was found that metallization is caused not by Mott transition with an overlap between the impurity and conduction bands but by the direct doping of an excess electron of Nb to the hybridized bands consisting mainly of Ti and Nb d-orbitals. (C) 2010 The Japan Society of Applied Physics