Geometry and ordering of defects in non-stoichiometric rutile

Abstract

The geometry of point defects in TiO2-x rutile has been investigated using periodic density functional calculations. A reconstruction of the vacancy site with a neighbouring Ti4+-ion displaced to an interstitial site was predicted to be thermodynamically favourable. A similar reconstruction of an interstitial site does not lead to a lower energy. Energies of various ordered patterns of the defects were compared, including that in the shear planes. A particular favourable ordering was found in the (132) shear planes for O-vacancies and in the (121) shear planes for Ti-interstitials. Comparison of the defect formation energies revealed that in highly non-stoichiometric rutile Ti-interstitials are more stable than O-vacancies. However, the difference between the formation energies decreases rapidly as rutile becomes more stoichiometric, indicating that at a very low defect concentrations O-vacancies may be the majority type defect. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.