Effects of Nb doping concentration on TiO2 electricel conductivity and optical performance

Nowadays, in the reports of Nb heavy-doped TiO2, when the doping mole of Nb is in the range of 0.050 to 0.0625, there is a current controversy between the two experimental results about the minimum resistance of the doped systems. To solve this contradiction, the models of un-doped and the three different concentrations of Nb doped Ti1-xNbxO2 (x=0.03125, 0.050, 0.0625) have been set up based on the first-principles plane wave ultra-soft pseudo potential method of density functional theory; then the geometry optimization of all models is carried out; and the band structures, the density of states, and optical properties are calculated. Results reveal that under the condition of limited doping amount as in this paper, when the doping moles of Nb is increased, the volume, the total energy, and the formation energy of the doped system are increased; the doped system has a lower stability and is hard to be redoped; the relative electronic concentration, and the electron effective mass are increased; the migration rate is reduced, and the conductivity is thus reduced. The wider the optical band-gap, the more obvious the shift of absorption edge to the short wavelength side, the lower the absorptivity and reflectivity; and the transmittance is increased. these are in agreement with the experimental results.