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A sample of lutetium carboboride LuB2C was synthesized from a mixture of lutetium hydride, boron and carbon by annealing in argon. The temperature dependence of the heat capacity Cp(T) (2-300 K) and lattice parameters a(T), b(T), and c(T) (5-300 K) of the carboboride was experimentally determined. The experimental values of the heat capacity were fitted with the approximation Cp(T) = aT + ΣCD + CE + CTLS(T). Here the first term is the electronic contribution, the second is the sum of the Debye components, the third is the Einstein contribution, and the fourth is the contribution to the heat capacity due to the vibrations of the two-level systems which are formed in the Lu-subsystem due to the asymmetry of the B-C atomic arrangement around the Lu3+-ions and, as a consequence, the possible transition of the lutetium atoms between spatially close, but energetically non-equivalent positions. A strong anisotropy of the thermal expansion of the carboboride was revealed. Along the c axis the coefficient of thermal expansion monotonically increases; in the basal plane, the expansion is practically not observed. The temperature dependence of the unit cell volume Vu(T) has been analyzed in the Debye-Einstein approximation taking into account the electronic contribution and effect of two-level systems. The values of the Gruneisen parameters corresponding to different modes of the phonon spectrum of the carboboride have been determined. The frequencies of the lattice vibrations, determined in a Raman scattering experiment, are in satisfactory agreement with the parameters obtained from Cp(T) using the Debye-Einstein approximation. Using ab initio band theory methods and an exchange-correlation functional in the PBE form in the VASP package, it was established that the total energies of these two crystal structures differ by no more than 0.01 eV f.u.-1. Calculations of the thermodynamic properties of LuB2C yielded similar results for orthorhombic and tetragonal phases of the carboboride.

*Özışık, Hacı ( Aksaray, Yazar ) *Deligöz, Engin ( Aksaray, Yazar ), The characteristics of the electronic and phonon subsystems of lanthanum tetraboride (LaB4) studied using first-principles calculations. The calculated lattice parameters, as well as the positions of atomic, are satisfactorily consistent with the experimental data. The partial densities of states, band structure, Fermi surface, phonon dispersion curve of LaB4 are calculated and analysed. The reliability of the calculation results is confirmed by a satisfactory agreement between the calculated thermodynamic parameters of LaB4 (temperature changes in heat capacity, entropy, Gruneisen parameter and volume modulus) with experimental data.

The electronic structure was calculated by the first-principle methods of quantum chemistry and the parameters of the electric field gradient near the 7Li nuclei of the double molybdate LiBi(MoO4)2 were determined. Analysis of the NMR spectra revealed that the states of the 7Li nuclei in LiBi(MoO4)2 in the cation sublattice do not differ, whereas in the NaBi(MoO4)2, the Na atoms in Bi positions have different populations and electric field characteristics.

The electronic band structure, frequency-dependent dielectric function and absorption spectra of the anatase containing oxygen vacancy or doped with bismuth or carbon have been calculated with the aid of the pseudopotential plane-wave method. Basing on the calculated data, the available experimental data on the visible light absorption are discussed. The main conclusion is that the Bi 3+ ions cannot replace the Ti 4+ ions in the structure of anatase. The conclusion is confirmed by the calculations of the energy of the defect formation. The visible light absorption can be explained by the presence of the carbon impurities or additional phases, probably Bi 2 O 3 or Bi 4 Ti 3 O 12 .

Electronic structure, chemical bonding and charge distribution in cubic and tetragonal zirconium hydrides were studied using the non-empirical self-consistent band (LMTO-GF) and cluster ( X α DV ) methods. The influence of hydrogen and zirconium vacancies on the electronic spectrum of hydrides was considered. The influence of the introduction of additional octahedrally coordinated hydrogen atoms on the features of the energetic states in ZrH 2 is discussed.