X-ray emission spectra and electronic structure of VO,VN, VC

The experimental K_β5 and L_α emission spectra for vanadium and K_α spectra for nonmetal are studied for vanadium monoxide, nitride and carbide. Using the spectra unfolding the experimental molecular orbital diagrams have been obtained. By the semiempirical Mulliken-Wolfsberg-Helmholz method with the self-consistency on charges and configurations the calculations of electronic structure of clusters [VO₆]^10?, [VN₆]^15? and [VC₆]^20? have been carried out. The results of calculations are compared with the X-ray data. The effects of chemical bonding and charge densities on metal atoms in VO, VN, VC are discussed.     

X-ray emission spectra and chemical bonding in TiC,TiN and TiO

The experimental X-ray emission spectra of titanium carbide, nitride and oxide have been obtained. Quantum-chemical calculations of the electronic structure of clusters in TiC, TiN and TiO have been carried out by the semiempirical Mulliken-Wolfsberg-Helmholtz method with self-consistency on charges and configurations. The results of these calculations are in good agreement with the X-ray spectroscopy data and offer a reasonable explanation of the experimental spectra. Chemical bonding and electronic structure of the compounds are discussed. Ionicity is shown to increase from TiC to TiO according to the electronegativity principle, the calculated charges on the metal ions being close to experimental estimates. The role of metal-metal and metal-nonmetal interactions in the chemical bonding is analysed. Vacancy models for TiO and their effect on the X-ray emission spectra are investigated. By the CNDO method with configurational interactions the optical spectrum of titanium carbide has been calculated. It is shown that this spectrum may be interpreted from the results for the [TiC₆] cluster, without introducing the Lye-Logothetis band scheme with negative charge on the metal ion.     

Physical properties and electronic structure of TaC-HfC solid solutions

The results of investigations of the physical properties and electronic structure in the Hf _x Ta_1?x solid solutions have been generalized. The N ₃ X-ray emission spectra Ta in hafnium and tantalum carbides have been investigated for the first time. Peak locations and intensities have been compared with the results of calculations of the electron band structure of Hf _x Ta_1?x C alloys with x = 0, 0.25, 0.5, and 0.75. It has been found that the inversion of peak intensities with increasing hafnium concentration is due to a nonmontonic variation in the density of Ta 5d states in the valence band of these compounds.     

Electronic structure and properties of the ground state of copper in semiconducting cuprates

The spin-polarized discrete variational X_a method is used to calculate clusters that model the electronic structures of CuO, La₂CuO₄, and Nd₂CuO₄. It, is shown that in each of the compounds the unoccupied portion of the valence band involves mainly the O2p states, the contributions from the Cu3d orbitals being significantly smaller. The effects of the nature of holes in the valence band and of the structure of the close environment of copper on the low-energy CuK spectra and the X-ray photoelectron spectra of the above systems are discussed. Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences. Translated fromZhumal Struktumoi Khimii, Vol. 36, No. 4, pp. 636–643, July–August., 1995. Translated by I. Izvekova     

Characterization of oxide layers formed on electrochemically treated Ti by using soft X-ray absorption measurements

The oxide layers of electrolytic oxidized titanium (Ti) were characterized using Ti L_2,3 and O K edge X-ray absorption. The spectra show that the structure of the oxide layers that are formed during a 1 min treatment are dependent on the concentration of the electrolyte (H₂SO₄ or Na₂SO₄) with which the Ti surface was treated, and also on the magnitude of the potential that was applied during the anodic oxidation process (100 V or 150 V). It is found that a potential of 150 V and an electrolyte concentration of 0.5 M or 1.0 M produces a layer of TiO₂ having rutile crystal structure.     

Chemical shifts in the x-ray emission spectra of MgB<Subscript>2</Subscript> and their correlation with the electronic structure

The x-ray emission spectra of magnesium diboride MgB₂ are measured. It is found that the Mg L_2,3 and B K_α emission lines are shifted with respect to the spectra of the pure metals toward the low-energy range. The band calculations of the MgB₂ diboride in the framework of the full-potential linearized muffin-tin orbital (LMTO) method demonstrate that the electron populations of the shells in both components of MgB₂ are higher than those of pure metals. This increase in the electron populations is associated with the crystal contraction and manifests itself in low-energy shifts of the emission lines.     

σ and π-band dispersion of graphite from polarized resonant inelastic X-ray scattering measurements

Resonant inelastic X-ray scattering of highly oriented pyrolytic graphite (HOPG) is observed above the C 1s threshold at different polarization angles. It is shown that combining the polarization and excitation energy dependence of X-ray emission spectra makes it possible to perform quantitative band mapping selective to the chemical bonding (σ and π).     

The electronic structure,x-ray photoelectron and emission spectra of YOF

The results of electronic structure calculations for YOF are presented, making use of Xα-DVM together with experimental X-ray photoelectron and emission spectra for this compound. Three versions of calculations have been performed, depending on the relation between oxygen and fluorine charges in the [YO₄F₄] cluster. The interpretation of experimental spectra is carried out on the basis of these calculations.