COMPUTER-SIMULATION STUDY OF THE DEFECT CHEMISTRY OF RUTILE TIO2

We examine the defect chemistry of rutile TiO2 using computer simulati on techniques. The stable valencies of dopant transition metal ions in TiO2 are calculated to be Nb(V), V(III), Fe(III) and Cr(III). We find that Cr3+, Al3+, Ga3+, V3+ and Fe3+ dissolve preferentially at substi tutional sites in TiO2 with charge compensation by oxygen vacancies ra ther than Ti4+ interstitials, although experimentally both are observe d. Nb5+ is calculated to dissolve preferentially at substitutional sit es with charge compensation being facilitated via Ti(III) ions or tita nium vacancies. The solution enthalpy of Nb5+ is reduced by the introd uction of Al3+ into the lattice. The solution enthalpy is further redu ced when we consider bound Al3+/Nb5+ clusters.