Unveiling Oxygen Vacancy Superstructures in Reduced Anatase Thin Films

Oxygen vacancies are known to play a crucial role in tuning the physical propertiesand technological applications of titanium dioxide TiO2. Over the last decades, defects insubstoichiometric TiO2have been commonly associated with the formation of TinO2n−xMagnéliphases, which are extended planar defects originating from crystallographic shear planes. Bycombining advanced transmission electron microscopy techniques, electron energy-loss spectros-copy and atomistic simulations, we reach new understanding of the oxygen vacancy inducedstructural modulations in anatase, ruling out the earlier shear-plane model. Structural modulationsare instead shown to be due to the formation of oxygen vacancy superstructures that extendperiodically inside thefilms, preserving the crystalline order of anatase. Elucidating the structure ofoxygen defects in anatase is a crucial step for improving the functionalities of such material systemand to engineer devices with targeted properties.