Polarity on the SrTiO3 (111) and (110) surfaces

Relying on the results obtained by a total energy, semi-empirical Hartree-F ock method, we discuss polarity effects at the (111) and (110) surfaces of SrTiO3. For these orientations, we consider some prototypical (1 x 1) confi gurations, which differ by their surface composition and the coordination n umber of the surface atoms. We argue that the compensation for these polar orientations is achieved through anomalous fillings of surface states, whic h, in principle, should be detectable by surface spectroscopies. The compen sation does not imply a partial filling, so that all these surfaces keep th eir insulating character. The thermodynamic stability of the different conf igurations is also analyzed, and we conclude that, consistently with the ex perimental observations, these surfaces are relatively stable, especially w hen compared with polar faces of more ionic oxides, such as MgO(111). The e fficiency of SrTiO3 for screening the strong electrostatic perturbation ass ociated to the polar orientations is invoked to explain such a behavior. (C ) 1999 Elsevier Science B.V. All rights reserved.