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Abstract The structure of Ge 20 Sb 10 S 70 , Ge 23 Sb 12 S 65 and Ge 26 Sb 13 S 61 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements at the Ge and Sb K-edges as well as Raman scattering. For each composition, large scale structural models were obtained by fitting simultaneously diffraction and EXAFS data sets in the framework of the reverse Monte Carlo (RMC) simulation technique. Ge and S atoms have 4 and 2 nearest neighbors, respectively. The structure of these glasses can be described by the chemically ordered network model: Ge-S and Sb-S bonds are always preferred. These two bond types adequately describe the structure of the stoichiometric glass while S-S bonds can also be found in the S-rich composition. Raman scattering data show the presence of Ge-Ge, Ge-Sb and Sb-Sb bonds in the S-deficient glass but only Ge-Sb bonds are needed to fit diffraction and EXAFS datasets. A significant part of the Sb-S pairs has 0.3–0.4 Å longer bond distance than the usually accepted covalent bond length (∼2.45 Å). From this observation it was inferred that a part of Sb atoms have more than 3 S neighbors. Highlights • Structural models of GeSbS glasses consistent with multiple datasets are constructed. • Structure of these glasses can be described by the chemically ordered network model. • Ge and S atoms obey the Mott-rule and have 4 and 2 nearest neighbors, respectively. • Long Sb-S bonds were observed, suggesting that SbS 5 units may exist in this system. [ABSTRACT FROM AUTHOR]

Abstract: X-ray absorption fine structure (XAFS) studies of Ni nanograins embedded in carbonaceous films were performed basing on the K edge spectra of nickel. A series of samples containing various doses of Ni doped to the film during the deposition was studied. The crystalline structure and chemical constitution of formed nanograins were found dependent on the nickel dose. They change along the series from those similar to bulk structure of metallic Ni towards amorphous form of NiO. The Fourier transform fitting analysis based on Ni fcc and NiO rock salt models showed for all samples a significant reduction of the range of atomic order around Ni as compared to appropriate bulk materials. The changes in an oxide content rate in the nanograins were evaluated by fitting the coefficients of the linear combination spanned on two the most distinct measured XAFS spectra. We have found that low oxygen inflow resulted in formation of amorphous NiO, but saved the metallic core of grains. High oxygen uptake resulted in thorough grain oxidation. [Copyright &y& Elsevier]

We report on the use of X-ray absorption spectroscopy as a tool for the identification of the phases formed in the technological process of composite preparation. A composite is a mixture of several compounds and, in many cases, the use of traditional X-ray diffraction to determine the phases can be difficult because of the small amount of phases present. X-ray absorption studies (XANES and EXAFS) of the c-BN Ti/TiN layered system are presented. These materials are models of the powdered composites used in industry for tool production. XANES and EXAFS analyses showed that, after annealing up to 1300 °C, a TiB2 phase is formed, but the chemical bonding of the Ti atoms differs slightly from that of standard TiB2 powder, showing the presence of defects in site occupancy. Assuming that the X-ray absorption spectral shape is a linear combination of the spectra of all the components, we estimated the kind and limits of other phase inclusions. [Copyright &y& Elsevier]

An EXAFS study of indium substituted CdCr2Se4 magnetic semiconductors is presented. Thin films of the compositions Cd1−yCr2−2xIny+2xSe4 with 2x=0.00, 0.11, 0.27 and y=0.14, 0.11, 0.00, respectively, were prepared by the radio frequency (RF) sputtering technique. From the Cr–K edge and Se–K edge EXAFS spectra the information on the local atomic environments around Se and Cr sites was obtained. With indium substitution the second nearest neighbour shell of the Cr site, which consists of Cr and possibly In ions, splits into two shells. The splitting increases with the increasing amount of indium. Direct current magnetisation measurements have shown that the samples with y=0 or x=0 are in the spin glass state and the samples with x≠0 and y≠0 are in the randomly canted state. These changes of magnetic properties are attributed to the differences of local environments as observed in the EXAFS measurements. [Copyright &y& Elsevier]

Transparent n-type niobium-doped titanium dioxide thin films (TiO 2 :1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb K-edges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S = 155 μV/K) for n-type TiO 2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW m−1 K−2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequency-domain thermoreflectance experiments, a thermal conductivity value of 1.3 W m−1 K−1 was obtained for the optimized TiO 2 :Nb film. (a, b) Radial distribution functions (RDFs) G(R) calculated from the coordinates of atoms in a TiO 2 5 × 5 × 2 supercell at 300 K, for 5% and 10% of dopant Nb atoms. Dashed (black and red) curves are for RDFs G (Ti–O) and G (Ti–Ti) in anatase TiO 2 at T = 300 K. (c, d) Fragments of the RMC 5a × 5b × 2c supercells for c) 5% of Nb and d) 10% of Nb atoms. Image 1 • Nb-doped TiO 2 films exhibit pronounced thermoelectric properties with very high Seebeck coefficient. • Maximum power factor and figure of merit values of 1.0 mW m−1 K−2 and 0.18. • Detailed information on local structure from radial distribution at Ti–K and Nb–K absorption edges. [ABSTRACT FROM AUTHOR]