Publication No.13 A. Stashans, F. Erazo. Structural and electronic properties due to the Nb-doping in cubic and orthorhombic phases of CaTiO3 crystal. - 14th Int. Conf. Def. Insulat. Mat., Johannnesburg (South Africa), 2000, p. 66. Abstract: By means of the modified for crystals quantum-chemical method and periodic large unit cell (LUC) model we study influence of Nb atom impurity upon the structural and electronic properties of the CaTiO3 crystal. The computations are carried out in a manner to compare the obtained results for two different crystallographic phases, cubic and orthorhombic. The geometry optimization is carried out in order to find the equilibrium spatial structures of both crystal structures as well as to predict the most stable configurations of the Nb atom in these crystalline lattices. The studies are done using 80-atom LUCs. This corresponds to 16-times (4x2x2) extension of the primitive 5-atom cubic unit cell and 4-times (2x2x1) extension of the primitive 20-atom orthorhombic unit cell. The obtained relaxation energies are found to be equal to 3.83 eV and 15.04 eV for the impurity-doped cubic and orthorhombic lattices, respectively. In our mind, this points out to the fact that the orthorhombic lattice is more compact and Nb-impurity presents major perturbation there as in the case of the cubic lattice. This leads to the large magnitude of the relaxation energy. There are also considerable differences in a way in which Nb atom influences the band structure of two phases. While for the cubic crystal we do not find any unusual features, the transfer of extra electron from the local energy level within the band-gap to the conduction band is found for the orthorhombic crystal. This explains the electrical conductivity augmentation observed in a number of experimental studies [1]. [1] K. Ueda, H. Yanagi, H. Hosono, and H. Kawazoe, Phys. Rev. B, 56, 12998 (1998).
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