Publication No.58



H. Pinto, S. Elliott, A. Stashans. Theoretical study of structural 
and optical properties of F-centres in tetragonal BaTiO3 - 3rd 
Int. Conf. Advanced Opt. Mater. Devices, Riga (Latvia), 
2002, p. 43. 

Abstract:
	Using the density functional theory (DFT) within the local 
density approximation (LDA) [1] and a method based on the Hartree-
Fock (HF) approximation [2], we study the structural, electronic and 
optical properties of F-centres (two electrons in an oxygen-vacancy) 
in the tetragonal lattice of the perovskite-type BaTiO3 crystal. In 
this phase, the F-centre has two non-equivalent positions due to the 
two different O atoms; namely, the F-centre situated in the Ti-O-Ti 
chains along the [001] polarisation axes (Fz) and the F-centre situated 
in the Ti-O-Ti chains laying within the x-y plane  (Fx-y). Both cases 
are considered in our study.
	The obtained results point out that the crystal structure 
containing Fz centre is energetically more stable than that of the 
Fx-y centre. The two electrons of the F-centre are found to be localised 
on the two adjacent Ti ions and their ground state is composed mainly 
of Ti 3dz2 atomic orbital. Besides, we have computed the allowed optical 
transitions in the F-centre using the so-called delta SCF method. As 
a result the obtained absorption energies are found to be equal to 
1.47 eV for the Fz centre and 3.07 eV and 4.27 eV for the Fx-y centre. 

[1] V. Milman, B. Winkler, J. A. White, C. J. Pickard, M. C. Payne, 
    E. V. Akhmatskaya, and R. H. Nobes, Int. J. Quant. Chem., 77, 895 
    (2000).  
[2] E. V. Stefanovich, E. K. Shidlovskaya, A. L. Shluger, and M. A. 
    Zakharov, Phys. Status Solidi B, 160, 529 (1990).




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