Search results for "Extended X-ray absorption fine structure"
showing 10 items of 193 documents
Synyhesis, structure, spectroscopy and redox chemistry of square-planar nickel(II) complexes with tetradentate o-phenylenedioxamidates and related li…
2005
[EN] A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N¿-methyloxamidate) (L1) and related o-phenylene(N¿-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate) (L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)¿L1 complex presents an intense MLCT band in the UV region (¿max = 357 nm) and a distinctive 1 s ¿ 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni¿N(amidate) bond lengths (1.85¿1.93 Å) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typi…
Local structure and dynamics of wurtzite‐type ZnO from simulation‐based EXAFS analysis
2014
Conventional methods of EXAFS data analysis are often limited to the nearest coordination shells of the absorbing atom due to the difficulties in accurate accounting for the so-called multiple-scattering effects. Besides, it is often difficult to resolve the non-equivalent groups of atoms in a single coordination shell due to strong correlation between structural parameters. In this study we overcome these problems by applying two different simulation-based methods, i.e., classical molecular dynamics (MD) and reverse Monte with evolutionary algorithm (EA), to the analysis of the Zn K-edge EXAFS data for wurtzite-type bulk ZnO. The RMC/EA-EXAFS method allowed us to separate the contributions…
The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)
2016
AbstractWe present new data about the chemical and structural characteristics of bauxite residue (BR) from Greek Al industry, using a combination of microscopic, analytical, and spectroscopic techniques. SEM-EDS indicated a homogeneous dominant “Al-Fe-Ca-Ti-Si-Na-Cr matrix”, appearing at the microscale. The bulk chemical analyses showed considerable levels of Th (111 μg g−1), along with minor U (15 μg g−1), which are responsible for radioactivity (355 and 133 Bq kg−1 for 232Th and 238U, respectively) with a total dose rate of 295 nGy h−1. Leaching experiments, in conjunction with SF-ICP-MS, using Mediterranean seawater from Greece, indicated significant release of V, depending on S/L ratio,…
EXAFS and XANES analysis of oxides at the nanoscale
2014
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Local structure of nanosized tungstates revealed by evolutionary algorithm
2015
Nanostructured tungstates, such as CoWO4 and CuWO4, are very promising catalytic materials, particularly for photocatalytic oxidation of water. The high catalytic activity of tungstate nanoparticles partially is a result of their extremely small sizes, and, consequently, high surface-to-volume ratio. Therefore their properties depend strongly on the atomic structure, which differ significantly from that of the bulk material. X-ray absorption spectroscopy is a powerful technique to address the challenging problem of the local structure determination in nanomaterials. In order to fully exploit the structural information contained in X-ray absorption spectra, in this study we employ a novel ev…
X-ray absorption spectroscopy studies of the off-center Ni2+ions in Ni c Mg 1-c O solid solutions
1996
In this work we present the x-ray absorption spectroscopy study of NicMg1-cO (0.01 <EQ c <EQ 1) solid solutions. The extended x-ray absorption fine structure (EXAFS) above the Ni K-edge was analyzed using the multi-shell fitting procedure. It was found that nickel ions are located in a distorted environment and shift upon dilution to the off- center positions. This fact follows from two main results: (1) in the first shell, the average Ni- O distance increases linearly upon dilution; (2) in the second shell, the average Ni-Ni distance remains unchanged and decreases slightly at low nickel concentration while the dependence of the Ni-Mg distance has a break at c approximately equals 0.6 and …
Mn, Fe, Zn and As speciation in a fast-growing ferromanganese marine nodule
2004
The speciation of Mn, Fe, As and Zn in a fast-growing (0.02mm/yr), shallow-marine ferromanganese nodule has been examined by micro X-ray fluorescence, micro X-ray diffraction, and micro X-ray absorption spectroscopy. This nodule exhibits alternating Fe-rich and Mn-rich layers reflecting redox variations in water chemistry. Fe occurs as two-line ferrihydrite. The As is strictly associated with Fe and is mostly pentavalent, with an environment similar to that of As sorbed on or coprecipitated with synthetic ferrihydrite. The Mn is in the form of turbostratic birnessite with ~;10 percent trivalent manganese in the layers and probably ~;8 percent corner-sharing metal octahedra in the interlayer…
Quantitative analysis of rhenium in irradiated tungsten
2021
Abstract Pure tungsten (W), irradiated to 3.5 dpa in a target of the Swiss neutron spallation source (SINQ), was characterized using high-sensitivity HPGe gamma ray spectroscopy to identify the present radionuclides. Synchrotron X-ray absorption spectroscopy was used to quantify the amount of Re produced in the irradiated W. An atomic concentration of 0.61% Re in the irradiated W was determined from the height of the L3-edge X-ray absorption edge jump. Analysis of the local atomic structure from the extended X-ray absorption fine structure (EXAFS) spectra indicates that rhenium (Re) produced in the system is mainly coordinated by W atoms and partly coordinated by void defects. First-princip…
Induced optical absorption and ITS relaxation in LiNbO3
1999
Abstract Electron pulse induced absorption spectra and their decay kinetics have been investigated in LiNbO3 crystals with various Li/Nb ratios rasnging from congruent to stoichiometric composition. It is shown that the absorption spectra, the optical density and the decay kinetics depend on the Li/Nb ratio. The rising front of the induced absorption is too fast to be resolved. The room temperature decay, characterized by the half-lifetime Δt, is faster in the stoichiometric crystal (∼ 750 ns) than in the congrruent crystal (∼ 3.5 μs).
The role of yttrium and titanium during the development of ODS ferritic steels obtained through the STARS route: TEM and XAS study
2018
Abstract Oxide Dispersion Strengthened Ferritic Steels (ODS FS) are candidate materials for structural components in future fusion reactors. Their high strength and creep resistance at elevated temperatures and their good resistance to neutron radiation damage is obtained through extremely fine microstructures containing a high density of nanometric precipitates, generally yttrium and titanium oxides. This work shows transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) characterization of Fe-14Cr-2W-0.3Ti-0.24Y ODS FS obtained by the STARS route (Surface Treatment of gas Atomized powder followed by Reactive Synthesis), an alternative method to obtain O…