Publication No.30



E. Patiño, A. Stashans, R. Nieminen. Quantum chemical 
study of effects produced by Nb- and La-doping in BaTiO3 
- 7th Conf. Europ. Cer. Soc., Brugge (Belgiium), 2001.

Abstract:
	The effects produced on BaTiO3 due to Nb and La doping 
have been studied. The investigation has been performed using 
developed for crystals quantum chemical method based on the 
Molecular Orbital theory.
	Under the influence of Nb impurity in both phases, cubic 
and tetragonal, the geometry relaxation shows a symmetric character, 
i.e., outward displacements of bariums and inward displacements of 
oxygens, which belong to the vicinity of the defect. The relaxation 
energy is found to be equal to 1.69 eV and 5.44 eV in cubic and 
tetragonal phases, respectively. In both phases the extra electron 
belonging to Nb transfers from the local energy level within the 
band gap to the conduction band.
	Under the influence of La impurity, in the cubic phase, 
the lattice distortion shows a non-symmetric pattern. Although 
titaniums move away symmetrically by 0.07 Å, the oxygen displacements 
are asymmetric along only one crystallographic axis by 0.02 Å. In 
the tetragonal phase only oxygens move towards the La impurity by 
0.06 Å while the titaniums remain motionless. The calculated 
relaxation energy is equal to 0.84 eV in cubic and 0.52 eV in 
tetragonal phases, respectively. In both phases the extra electron 
remains in the local energy level within the band gap.




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