X-ray spectroscopy studies of the electronic structure and band-structure calculations of cubic TaCxN1-x carbonitrides

The electronic structure of almost stoichiometric cubic (NaCl structure) tantalum carbonitrides TaCxN₁₋x synthesized under high pressure-high temperature conditions (7-10 GPa and 2100-2400°C) was studied employing X-ray photoelectron spectroscopy (XPS), Xray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS). The XPS valence-band and core-level spectra, the XES Ta Lβ ₅, C Kα and N Kα bands (reflecting energy distributions of mainly the Ta 5d-, C 2p- and N 2p-like states, respectively), as well as the XAS Ta LIII edges (unoccupied Ta d-like states) were derived and compared on a common energy scale for the compounds TaC₀.₉₈, TaC₀.₅₂N₀.₄₉ and TaN₀.₉₇ obtained under the mentioned high pressure-high temperature conditions. To investigate the influence of substitution of carbon atoms by nitrogen in the cubic TaCxN₁₋x system, the cluster self-consistent calculations of the electron density of states for cubic TaC, TaC₀.₅N₀.₅ and TaN compounds were carried out with the FEFF8 code. In the present work a rather good agreement of the experimental and theoretical results for the electronic structure of the TaCxN₁₋x system under consideration was obtained

The Chemical Bonding in Crystals with Chalcopyrite Structure

Experimentally with x-ray spectroscopy method and theoretically using the cluster approach of the local coherent potential method the particularities of chemical bonds of the semiconductors AgGaS2, AgInS2, CuGaS2, CuInS2 have been investigated. The fluorescent x-ray emission K-bands and the absorption K-spectra (XANES) of sulphur in the compounds investigated were obtained with resolution 0.2 eV. For upper part of the valence bands the electron structure is due to the occupied d-states of the noble metal (Ag, Cu), which mix with the delocalized p-states of S. The significant mixture of these states shows the strong covalent bond of S atom with noble metal atom.'The three maxima splitting of these states confirms the resonance character of the interaction of these atoms. The similarity of results for both chalcopyrite and zinc-blend stuctures proves, that the short-range ordering determines the electronic energy structure of these tetrahedral semiconductors

Ti L-Spectrum XANES and Electron Structure of the System Ti-Al-C

The electron structure and Ti L -absorption edge in the system Ti-Al-C have been studied theoretically using the local coherent potential method of the multiple scattering theory. The alculated local partial electron density of states of Ti made it possible to study the influence of Al on the electron structure of this material and its Ti L-absorption spectrum. It was shown that in the ternary system comparing with the binary titanium carbide the first maximum of the titanium unoccupied d-states nearly disappeared and the intensity of the second one fell more than twice. These calculations are in a good correspondence with the experimental Ti L-spectra and indicate that the contribution of Ti s-states to XANES can be neglected

MODEL CALCULATION OF THE ELECTRON ENERGY STUCTURE OF DIAMOND, BN AND BeCN2

The electronic energy structure of the row of similar compounds: diamond (C), BN, and BeCN2 has been investigated. It was found for BeCN2 that the top of the valence band is formed by p-states of N, whereas the bottom of the conduction band - by s-states of Be and C. The width of the energy forbidden band Eg in BeCN2 - was estimated. The comparison of the calculated partial and total electron densities of states of diamond and BN with x-ray K-spectra of emission and absorption and with x-ray electron spectra was carried out. The corresponding partial electron states of diamond and BN were also compared with corresponding densities of states of BeCN2

X-Ray Spectroscopic Studies of some Compounds with the same Chemical Formula and Different Crystal Structure

With the x-ray spectroscopy method two groups of semiconducting compounds are investigated. The first group consists of: CdIn2S4 (spinel type structure; F d 3 m – Ok7), CdGa2S4 and HgGaA ( the "defective" chalcopyrite; I 4- – S42). To the second group belong: Tl3TaS4 (that is made of coordinative tetrahedra [TaS4] and of structure units [TlS8]; I 4- 3 m – T43 ) and isostructural compounds Tl3TaS4 and TI3AsS4 (the structural type K3PS4; [formula: see text])- flnorescent K-emission bands and absorption K-spectra (XANES) of sulphur in compounds investigated are received with the resolution about 0.2 eV. The primary L2,3-emission bands of S have been studied using RSM-500 with resolution 0.4 eV. The electron energy structure of the valence bands are similar in isoelectronic compounds CdIn2S4, CdGa2S4 and HgGa2S4 that follows from the likeness of the forms of the x-ray emission bands in these compounds. At the same time the absorption SK-spectra (XANES) are alike only for CdGa2S4 and HgGa2S4 and differ significantly with SK-spectrum of CdIn2S4, that is due to the difference of S-atom sorroundings in these compounds. The similarity of the forms of all x-ray spectra in isostructural and isoelectronic compounds Tl3PS4 and Tl3AsS4 proves the likeness of the electron-energy structure in these compounds and of the environment of S-atom in these compounds. The emission and absorption spectra of S in Tl3TaS4 differ from ones of Tl3PS4 and Tl3AsS4, that is due to the fact, that Ta-atom is not isoelectronic to atoms of P and As, that results in the difference of S-atom surroundings and the electron-energy structure

Determination of Muffin-Tin Potential by XANES

A scheme of the MT-potential construction by using experimental data is proposed. It is based on the inverse problem solution in the theory of many-centre shape resonances. Input data are positions Ei and widths Γi of maxima in XANES corresponding to shape resonances. The MT potential within atomic spheres is considered in the form Vat(r)+∑n an rn where Vat is a given atomic potential, and the coefficients an are chosen so that calculated and experimental characteristics of resonances are close at most