First-principles microscopic calculations were made of the formation energy, electrical activity, and magnetic moment of Co dopants and various native defects in anatase. Based upon these results, equilibrium thermodynamics were used to predict the resultant carrier concentration, the average magnetic moment per Co atom and the dominant oxidation state of Co. The predicted values were in good agreement with experiment, assuming O-poor growth conditions. In this regime, a substantial fraction of Co dopants occupied interstitial sites as donors. The incomplete compensation of these donors by substitutional Co acceptors then led to the experimentally observed n-type behavior.

Theory of Dopants and Defects in Co-Doped TiO2 Anatase. J.M.Sullivan, S.C.Erwin: Physical Review B, 2003, 67[14], 144415 (7pp)