Publication No.64



A. Stashans, S. Serrano, J. Ortiz. Radiation defects on 
SrTiO3 polar and non-polar surfaces - SPIE Proceedings, 
2003, Vol. 5122, p. 264-270.

Abstract:
	Using the INDO quantum-chemical computational method we focus 
on oxygen-vacancy and F centre 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 hybridisation between the O 2p and Ti 
3d states. Wave functions of the F centres are found on the two defect-
closest Sr atoms in an agreement with the available scanning microscopy 
and spectroscopy data and pointing to localisation of two electrons 
within the O vacancy region. The analysis of the properties of O 
vacancies and F centres on the non-polar (001) surface points to somewhat 
different pattern. In particular, the wave functions of the F centres 
are found on the defect-nearest Ti atoms and are rather extended. One 
of the absorption energies obtained by the DSCF method matches the 
experimentally observed value of 2.1 eV found in fast-electron 
irradiation of strontium titanate. 




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