Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

EXAFS study of titanium and zinc environments during nucleation in a cordierite glass

Abstract: Nucleation is studied in a magnesium aluminosilicate glass containing ZnO and TiO2 as nucleating agents. Characterization of the phase morphology in the first stages of crystallization is performed with X-ray diffractometry and electron microscopy. X-ray absorption spectroscopy (EXAFS and edge structure) is used to provide information on the environment of zinc and titanium atoms. From the earliest stages of nucleation, important changes of the environments of these atoms are found. Titanium, which is four-fold coordinated in glass, gradually becomes six-fold coordinated as nucleation occurs. The arrangement of titanium second neighbours which differs markedly from that in glass even in the first stages of heat-treatment supports the hypothesis of Al2TiO5 being the first crystalline phase containing titanium. Zinc atoms keep four-fold coordination during the process with a disorder larger than in the parent glass in the earliest steps, decreasing as zinc is embedded in a crystalline phase. In that phase, second neighbours of zinc seem to be predominantly zinc and titanium atoms, proving that zinc and titanium are major components in the first crystallized phases.

X-ray Raman scattering as a substitute for soft-x-ray extended x-ray-absorption fine structure.

Abstract: We have recorded x-ray Raman-scattering spectra from graphite and diamond with high resolution and good signal-to-noise (S/N) ratio by excitation with hard x rays from synchrotron radiation. The scattering spectra show characteristics predicted by the theory. The observed scattering spectrum for graphite was not exactly the same as the absorption spectrum, possibly because of polarization effects in the anisotropic materials. In the case of diamond powder, however, oscillations identical with those found in the extended x-ray-absorption fine structure (EXAFS) spectrum were observed, and from an analysis employing the formula used for EXAFS, interatomic distances were obtained. Thus, it is experimentally confirmed for the first time that x-ray Raman spectroscopy by using hard x rays can supply the same information as the soft-x-ray EXAFS. X-ray Raman spectroscopy can thus be a substitute for EXAFS to determine the local structure around low-atomic-number elements whose EXAFS study is plagued with inherent experimental difficulties.

High-Temperature XAS Study of Fe2SiO4 Liquid: Reduced Coordination of Ferrous Iron

Abstract: X-ray absorption spectroscopy (XAS) of Fe(2+) in Fe(2)SiO(4) liquid at 1575 kelvin and 10(-4) gigapascal (1 bar) shows that the Fe(2+) -O bond length is 1.98 +/- 0.02 angstroms compared with approximately 2.22 angstroms in crystalline Fe(2)SiO(4) (fayalite) at the melting point (1478 kelvin), which indicates a decrease in average Fe(2+) coordination number from six in fayalite to four in the liquid. Anharmonicity in the liquid was accounted for using a data analysis procedure. This reduction in coordination number is similar to that observed on the melting of certain ionic salts. These results are used to develop a model of the medium-range structural environment of Fe(2+) in olivine-composition melts, which helps explain some of the properties of Fe(2)SiO(4) liquid, including density, viscosity, and the partitioning of iron and nickel between silicate melts and crystalline olivines. Some of the implications of this model for silicate melts in the Earth's crust and mantle are discussed.

The Absorption Coefficient of Nitrogen Pentoxide in the Ultraviolet and the Visible Absorption Spectrum of NO3

Abstract: Absorption spectrograms have been made of the gaseous system N2O5–O3 during the decomposition of the ozone and into the subsequent decomposition of the N2O5, placing these in time such that one was taken when the system consisted essentially of only N2O5 and oxygen. From such spectrograms as the last mentioned, the absorption coefficient, α10, of N2O5 has been measured over the wave‐length range 3800–2850A. The value rises steadily from approximately 0.002 at the first wave‐length to approximately 0.52 at 2850A. The absorption coefficient curve continues to rise to shorter wave‐lengths and qualitative observations indicated no maximum as far as 2400A. No absorption which could be attributed to N2O5 could be observed in the 4500A region. Absorption spectrograms of NO3 in the visible are given. In a study using low dispersion of the influence of oxygen on the absorption spectrum of NO2, no noticeable effect was observed.

Near edge x-ray absorption fine structure study of benzene adsorbed on metal surfaces: Comparison to benzene cluster complexes

Abstract: Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been used to study benzene adsorbed on several close-packed metal surfaces [Au(111), Rh(111), Pt(111), and Ru(0001)] under the same experimental conditions. The NEXAFS spectra reveal significant differences with regard to the shapes and positions of resonances and the dichroism observed for the resonance intensities. These differences correlate directly with the binding energy and can be attributed to differences in the electronic coupling of the benzene molecule to the substrate and to adsorption in- duced changes in the molecular structure of the benzene molecule. A comparison to the NEXAFS spectra recorded for the benzene metal cluster complexes [Ru(η6–C6H6)(CH3CN)3]2+ and Ru3(CO)9(μ3:η2:η2:η2–C6H6) indicates that the μ3-arene complex, where the benzene ring is bonded to three metal atoms, can be regarded as a reasonable cluster analog for the adsorption of benzene on the Ru(0001) transition metal surface.