Publication No.9



A. Stashans, F. Vargas. Studies of F-type centres in SrTiO3 crystal. 
- 18th Europ. Phys. Soc. Conf., Montreux (Swwitzerland), 2000, 
p. 111.

Abstract:
	We have used the modified for crystals advanced quantum-chemical method and 
periodic LUC model to study F type centres (one and two electrons trapped by an O 
vacancy) in SrTiO3 crystal. The computations have been carried out for cubic and 
tetragonal phases of the material. 
	The geometry optimisation has been done. As a result we have obtained that 
Ti, Sr and O atoms move outwards the F-type symmetrically in the cubic and 
asymmetrically in the tetragonal phases, respectively. The atomic displacements are 
equal to 0.13 A, 0.08 A and 0.06 A for the Ti, Sr and O atoms, respectively, in the 
cubic phase. For the tetragonal phase considerably larger displacements for Sr and O 
atoms were obtained along the ferroelectric c axis. The relaxation energies are 1.6 
eV and 3.2 eV for cubic and tetragonal lattices, respectively. 
	The two electrons were found to be well localised on the two closest Ti 
atoms. The studies are made in a way to compare the results with those with the 
F+ centre. 




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