A first-principle study of the effect of W-doping on physical properties of anatase TiO2

The experimental studies of the effect of W-doping on conductivity of anatase TiO2 have opposite conclusions when the W-doping concentration is in a range from 0.02083 to 0.04167. To solve the conflict, two supercell models for Ti0.97917W0.02083O2 and Ti0.95833W0.04167O2 are set up for optimizing their geometries and calculating their band structures and the densities of states based on the first-principles plane-wave norm-conserving pseudopotential of the density functional theory. The electron concentration, electron effective mass, electronic mobility, and electronic conductivity are calculated as well. The calculated results show that both electronic conductivity and conductive property of the doped system increase while the electron effective mass decreases, with the increase of W-doping concentration in the presence or absence of electron spin. The conductive property of Ti0.95833W0.04167O2 system is better than that of Ti0.97917W0.02083O2 system, which is further proved by the analyses of ionization energy and Bohr radius. To analyze the stability and formation energy of W-doped anatase TiO2, two more supercell models for Ti0.96875W0.03125O2 and Ti0.9375W0.0625O2 are set up combined with the geometry optimization. The calculated results show that the total energy and the formation energy increase while the stability of the doped system decreases, with the increase of W-doping concentration in a range from 0.02083 to 0.04167 in the presence or absence of electron spin. Meanwhile the W-doping becomes more difficult. A comparison of the doped system with the pure anatase TiO2 shows that the lattice constant along the a-axis of the W-doped anatase TiO2 increases, and its lattice constant along the c-axis and volume increase as well. The calculated results agree with the experimental results. The doped system becomes a half-metal diluted magnetic semiconductor with a room temperature ferromagnetism in the presence of electron spin.