Theory of dopants and defects in Co-doped TiO2 anatase
Abstract
We report first-principles calculations of the formation energy, equilibrium concentration, electrical activity, and magnetic moment of Co dopants and a variety of native defects in TiO2 anatase for growth conditions ranging from O-poor to O-rich. We find that under O-rich growth conditions, the electronic and magnetic properties of Co-doped samples are predicted to be quite different from that observed experimentally. In particular, the material is predicted to be insulating rather than n-type, with an average magnetic moment per Co in disagreement with experiment, and Co oxidation state of IV rather than the measured value of II. On the other hand, for conditions corresponding to O-poor growth, the predicted properties agree well with experimental observations. Moreover, we find that under these conditions, a substantial fraction of Co dopants occupy interstitial sites as donors. We suggest that the observed n-type behavior results from the incomplete compensation of these donors by substitutional Co acceptors, which drives the Fermi level near the conduction band edge and leads to thermal excitation of electrons from interstitial Co into the conduction band. We also find that O vacancies occur in concentrations much too small to play any significant role in the Co-doped samples.Keywords
All Related Versions
This publication has 0 references indexed in Scilit: