Radiation defects on SrTiO3 polar and nonpolar surfaces

Using the INDO quantum-chemical computational method we focus on oxygen-vacancy and F center defects on the non-polar (001) and polar (110) SrTiO3 surfaces considering both cubic and tetragonal lattices of the material. The results obtained for the lattice relaxation around the defects on the polar (110) surface point to the significant role of the Coulomb interaction in this semi-ionic material. However, in the case of the oxygen vacancies the analysis of the electronic density redistribution leads to the conclusion that these defects make material more covalent due to the stronger hybridization between the O 2p and Ti 3d states. Wave functions of the F centers are found on the two defect-closest Sr atoms in an agreement with the available scanning microscopy and spectroscopy data and pointing to localization of two electrons within the O vacancy region. The analysis of the properties of O vacancies and F centers on the non-polar (001) surface points to somewhat different pattern. In particular, the wave functions of the F centers are found on the defect-nearest Ti atoms and are rather extended. One of the absorption energies obtained by the ΔSCF method matches the experimentally observed value of 2.1 eV found in fast-electron irradiation of strontium titanate.

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