Publication No.36



P. Sánchez, A. Stashans. Computational studies of Nb-doped
SrTiO3 - 11th Int. Conf. Rad. Eff. Insulators, Lisbon 
(Portugal), 2001.

Abstract:
	Due to the extensive applications in the electronic industry 
and its unusual properties, SrTiO3 crystal has attracted a great deal 
of attention. The modified for crystals quantum-chemical method and a 
periodic large unit cell (LUC) model was used to study this material. 
We have been working with LUCs of 40 and 135 atoms substituting one 
Ti atom by one Nb atom. This kind of doping increases the charge of 
the system by one electron leading to the relaxation of the surrounding 
O and Sr atoms.
	As it is known, the directions <100> and <010> are completely 
equivalent due to the symmetry of the tetragonal phase of the crystal.  
That is why the relaxation of the atoms along these axes is the same 
and is equal to 0.06 Ĺ for the Sr atoms in the plane under the impurity 
and 0.11 Ĺ for the Sr atoms in the plane above it.  The oxygen atoms 
have movements of 0.08 Ĺ, 0.07 Ĺ and 0.05 Ĺ, depending on their position 
around the impurity.
	The relaxation was performed taking into account the fact that 
the tetragonal phase of this crystal presents a ferroelectric behaviour.  
This implies the presence of a spontaneous electric dipole along the z-axis, 
which changes due to the doping. This produces a different kind of motion 
along the z-axis for both kinds of atoms.  We have found that the strontium 
and oxygen atoms have the opposite displacements along the ferroelectric 
axis. We suppose that this fact evidences a local change in the electric 
dipole of the crystal due to the impurity presence.




Back to the main page of our research centre