Publication No.68



H. Pinto, S. Elliott, A. Stashans. Theoretical study of 
structural and optical properties of F-centers in tetragonal 
BaTiO3 - SPIE Proceedings, 2003, Vol. 5122, p. 303-309.

Abstract:
	Using the density functional theory (DFT) within the local 
density approximation (LDA) and a method based on the Hartree-Fock 
(HF) approximation, we study the structural, electronic and optical 
properties of F-centers (two electrons in an oxygen-vacancy) in the 
tetragonal lattice of the perovskite-type BaTiO3 crystal. In this 
structure the F-center has two non-equivalent positions due to the 
two different O atoms; namely, the F-center situated in the Ti-O-Ti 
chains along the [001] polarization axes (Va0) and the F-center 
situated in the Ti-O-Ti chains within the x-y plane (Vb0). Both cases 
are considered in our study. The obtained results point out that the 
crystal structure containing Va0 centre is energetically more stable 
than that of the Vb0 center. The two electrons of the F-center are 
found to be localized 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 for the F-center using the 
so-called DSCF method. As a result the obtained absorption energies 
are found to be equal to 1.47 eV for the Va0 center as well as 3.07 
and 4.27 eV for the Vb0 center. 




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