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The combination effect of substitutional impurities of group IVB–VIB transition metals on the oxygen vacancy formation energy in rutile titania was studied by the projector augmented wave method within density functional theory. The pair interaction energy of impurity atoms was estimated depending on the interatomic distance. It was shown that the interaction in the Zr + Zr, Hf + Hf and Nb + Ta pairs leads to the energy preference of their orientation along the <100> direction at a distance of the lattice parameter a. The Mo + Mo and Nb + Mo pairs prefer to orient along the [001] direction at a distance of the lattice parameter c. If the impurity atoms are farther than the third neighbors, then their interaction can be neglected. It was found that the change in the oxygen vacancy formation energy due to doping with several impurities can be estimated as the sum of the energy changes due to single impurity divided by a coefficient whose value depends on the mutual arrangement of the impurity atoms. [ABSTRACT FROM AUTHOR]

The total energies of a number of Ti–Si intermetallic phases are calculated by the projector augmented-wave method. It is shown that the formation enthalpies of Ti5Si3 and TiSi are almost equal. The peculiarities of the density of electronic states of the considered titanium silicides and its evolution with increasing silicon content are discussed. The formation energies of doped titanium silicides Ti5Si3 and TiSi are calculated depending on the position of the impurity on different sublattices. It is established that the elements of the 3d-period prefer to replace titanium in Ti5Si3, while the elements of the second half of the 3d‑period substitute silicon in TiSi. The effect of impurities on the relative stability of compounds is studied. It is shown that almost all the considered elements except Cu, Zn, Al, and Ga increase the stability of the Ti5Si3 phase with respect to TiSi. The obtained results agree with the available experimental data. [ABSTRACT FROM AUTHOR]

The influence of simple and transition metal impurities, as well as interstitial impurities (B, C, and N), on the oxygen adsorption on the Ti5Si3 titanium silicide surface has been studied using the of projector augmented wave method within the electron density functional theory. It has been shown that titanium-substituting impurities belonging to the latter halves of the 3d–5d periods cause most significant changes in the adsorption energy. In addition, simple metals and interstitial impurities reduce the oxygen–surface interaction. By analyzing local electron densities of states, charge density difference distribution, charge transfer, and the overlap population of oxygen bonds to nearest-neighbor atoms, we have revealed special aspects of impurity influence on chemical bonding between the titanium silicide surface and oxygen. Factors responsible for an increase/decrease in the adsorption energy of oxygen on the doped surface are discussed. A correlation between the change in adsorption energy and the electronegativity of impurities has been found. [ABSTRACT FROM AUTHOR]

The atomic and electronic structure of the Al2O3/Ti5Si3 interface has been calculated for the first time by the method of projected augmented waves within the electron density functional theory. The values of the adhesion energy are determined depending on the cleavage plane. It is shown that the work of separation obtained for the plane passing through the interplanar distance closest to the interface in titanium silicide is significantly less than that at the interface. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures, the elastic moduli, the vibrational frequencies, and the thermodynamic characteristics of the Ti5Si3 titanium silicide are calculated by the projector augmented wave method within the density functional theory. The Fermi surface is calculated and the electron velocity on all its four sheets is estimated. An analysis of the spatial dependence of linear compressibility, Young's modulus, and shear modulus demonstrates their weak anisotropy, and the anisotropy of Poisson's ratio is more pronounced. The phonon spectrum of the titanium silicide is calculated and its thermodynamic characteristics are estimated. On the whole, the calculation results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures, the elastic moduli, the vibrational frequencies, and the thermodynamic characteristics of the Ti5Si3 titanium silicide are calculated by the projector augmented wave method within the density functional theory. The Fermi surface is calculated and the electron velocity on all its four sheets is estimated. An analysis of the spatial dependence of linear compressibility, Young's modulus, and shear modulus demonstrates their weak anisotropy, and the anisotropy of Poisson's ratio is more pronounced. The phonon spectrum of the titanium silicide is calculated and its thermodynamic characteristics are estimated. On the whole, the calculation results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The formation energies of oxygen vacancies and the migration barriers of oxygen in TiO2 with a rutile structure have been calculated by the projector augmented-wave method within the electron density functional theory. We have derived analytical expressions for the temperature-dependent diffusion coefficients along two crystallographic directions using Landman's method and calculated the activation energies and the pre-exponential factor. The temperature-dependent diffusion coefficient is shown to be in good agreement with the experiment and with the results obtained previously by the statistical method. The influence of impurities on the diffusion properties of oxygen in the oxide is discussed. [ABSTRACT FROM AUTHOR]

The formation energies of oxygen vacancies and the migration barriers of oxygen in TiO2 with a rutile structure have been calculated by the projector augmented-wave method within the electron density functional theory. We have derived analytical expressions for the temperature-dependent diffusion coefficients along two crystallographic directions using Landman's method and calculated the activation energies and the pre-exponential factor. The temperature-dependent diffusion coefficient is shown to be in good agreement with the experiment and with the results obtained previously by the statistical method. The influence of impurities on the diffusion properties of oxygen in the oxide is discussed. [ABSTRACT FROM AUTHOR]

The article presents a study on the mechanism of carbon dioxide (CO2) radical formation in biological and synthetic apatites. The study used tooth enamel from human molars, pig molars and incisors, and cortical bones of cows which were irradiated with cobalt (Co) γ-rays, and examined by electron paramagnetic resonance (EPR). A Varian E12 X-band EPR spectrometer was used to measure EPR at room temperature. The study observed that the higher the characteristic energy of the radiation, the larger the contribution of orthorhombic radicals were.