The structure and chemistry of the TiO2-rich surface of SrTiO3(001)

Oxide surfaces are important for applications in catalysis and thin film growth. An important frontier in solid-state inorganic chemistry is the prediction of the surface structure of an oxide. Comparatively little is known about atomic arrangements at oxide surfaces at present, and there has been considerable discussion concerning the forces that control such arrangements. For instance, one model suggests that the dominant factor is a reduction of Coulomb forces(1); another favours minimization of 'dangling bonds' by charge transfer to states below the Fermi energy(2). The surface structure and properties of SrTiO3-a standard model for oxides with a perovskite structure-have been studied extensively(3-14). Here we report a solution of the 2 x 1 SrTiO3 (001) surface structure obtained through a combination of high-resolution electron microscopy and theoretical direct methods. Our results indicate that surface rearrangement of TiO6-x units into edge-sharing blocks determines the SrO-deficient surface structure of SrTiO3. We suggest that this structural concept can be extended to perovskite surfaces in general.