Quantum-chemical studies of Nb-doped CaTiO3

There exists experimental evidence that several properties of the CaTiO3 crystal, such as electrical conductivity and ferroelectricity, strongly depend on the Nb doping. In particular, if the concentration of Nb impurities is sufficiently high, a drastic increase in the electrical conductivity is observed. A supercell model and periodic quantum-chemical calculation scheme are used to study pure and Nb-doped crystals. The geometry optimization is carried out in order to find the equilibrium spatial structures of both cubic and orthorhombic phases, as well as to predict the most stable configurations of the Nb atom in these crystalline lattices. The obtained relaxation energies of 3.83 eV for the cubic phase and 15.04 eV for the orthorhombic phase are discussed, and their difference is explained. The composition of the electronic energy bands is analysed in comparison with the available experimental data. The increase in the electrical conductivity in the Nb-doped material for the orthorhombic phase is proved.