Publication No.53



A. Stashans, S. Serrano, J. Ortiz. Radiation defects on SrTiO3 
polar and non-polar surfaces - 3rd Int. Conf. Advanced Opt. 
Mater. Devices, Riga (Latvia), 2002, p. 30. 

Abstract:
	Strontium titanate (SrTiO3) is a widely utilised electronic 
material. Surface oxygen vacancies in SrTiO3 play a central role in 
many technologically important reactions and processes. Therefore, 
it is necessary and important to investigate the effect of surface 
oxygen vacancies on the electronic, structural and optical properties 
of the SrTiO3 surfaces.
	In the present work using a 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 this material. The optimisation of perfect 
surfaces, done by us before [1,2], shows considerable differences 
between two cases. 
	The obtained results of structure relaxation around the oxygen 
vacancies and F centres 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 O vacancies and F centres on the 
non-polar (001) surface point to somewhat different pattern. In 
particular, the wave functions of the F centres are found on the 
defect-nearest Ti atoms being 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 [3]. 

[1] A. Stashans, F. Erazo, J. Ortiz, and P. Valverde, Phil. 
    Mag. B, 81, 1977 (2001).
[2] A. Stashans and S. Serrano, Surf. Sci., 497, 285 (2002). 
[3] N. N. Lebedeva, Soviet Phys. Solid St., 34, 869 (1992). 




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