Atomic Control of Conductivity Versus Ferromagnetism in Wide-Gap Oxides Via Selective Doping: V, Nb, Ta in AnataseTiO2

We identify two general types of electronic behaviors for transition-metal impurities that introduce excess electrons in oxides. (i) The dopants introduce resonant states inside the host conduction band and produce free electrons; (ii) the dopants introduce a deep gap state that carries a magnetic moment. By combining electronic structure calculations, thermodynamic simulations, and percolation theory, we quantify these behaviors for the case of column V-B dopants in anatase ${\mathrm{TiO}}_2$. Showing behavior (i), Nb and Ta dopants can convert the insulator ${\mathrm{TiO}}_2$ into a transparent conductor. Showing behavior (ii), V dopants could convert nonmagnetic ${\mathrm{TiO}}_2$ into a ferromagnet. Whether a dopant shows behavior (i) or (ii) is encoded in its atomic $d$ orbital energy.