Search results for "extended x-ray absorption fine structure"
showing 10 items of 193 documents
Defects in yttrium aluminium perovskite and garnet crystals: atomistic study
2000
Native and impurity point defects in both yttrium aluminium perovskite (YAP) and garnet (YAG) crystals are studied in the framework of the pair-potential approximation coupled with the shell model description of the lattice ions. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. The calculated values of the distortion caused by the antisite YAl x in the lattice turn out to be in an excellent agreement with the EXAFS measurements. In non-stoichiometric compounds, the calculated reaction energies indicate that excess Y2 O3 or Al2 O3 is most likely to be accommodated by the forma…
New Regularization Method for EXAFS Analysis
2007
As an alternative to the analysis of EXAFS spectra by conventional shell fitting, the Tikhonov regularization method has been proposed. An improved algorithm that utilizes a priori information about the sample has been developed and applied to the analysis of U L3‐edge spectra of soddyite, (UO2)2SiO4⋅2H2O, and of U(VI) sorbed onto kaolinite. The partial radial distribution functions g1(UU), g2(USi), and g3(UO) of soddyite agree with crystallographic values and previous EXAFS results.
Combining EXAFS and XRay Powder Diffraction to Solve Structures Containing Heavy Atoms
2005
Determination of structures using x-ray powder diffraction is complicated if the reflection intensities are mainly influenced by the scattering from heavy atoms and the atomic coordinates of light atoms remain uncertain. A method like EXAFS, which is sensitive to short range order, gives reliable atomic distances in the surroundings of heavy atoms with a precision of ±0.02 A. The probability for obtaining the complete structure from x-ray powder diffraction increases if one includes parameters derived from EXAFS measurements as restraints during the procedure of structure solving. We demonstrate the potential of combining EXAFS and x-ray powder diffraction by solving the structure UO2[H2AsO…
Cooperative Spin‐Crossover Behaviour in Polymeric 1D Fe II Coordination Compounds: [{Fe(tba) 3 }X 2 ]· n H 2 O
2007
A new family of 1D cooperative spin-crossover polymers with general formula [{Fe(tba)3}X2]·nH2O [tba = N-(4H-1,2,4-triazol-4-yl)benzamide; X = CF3SO3–, n = 2 (1), n = 0 (4); BF4–,n = 3 (2), n = 0 (5); 4-CH3C6H4SO3–, n = 3 (3), n = 0 (6)] has been synthesised and characterised using a series of spectroscopic methods, X-ray powder diffraction, magnetic susceptibility measurements and differential scanning calorimetry. The copper analogue of 1, [{Cu(tba)3}(CF3SO3)2]·3H2O (7), has also been synthesised and its crystal structure solved at 293 K. Compound 7 crystallises in the P space group. The bidentate N-(4H-1,2,4-triazol-4-yl)benzamide ligand bridges the copper ions through the 1,2-nitrogen p…
Interplay between local structure, vibrational and electronic properties on CuO under pressure
2020
The electronic and local structural properties of CuO under pressure have been investigated by means of X-ray absorption spectroscopy (XAS) at Cu K edge and ab initio calculations, up to 17 GPa. The crystal structure of CuO consists of Cu motifs within CuO4 square planar units and two elongated apical Cu-O bonds. The CuO4 square planar units are stable in the studied pressure range, with Cu-O distances that are approximately constant up to 5 GPa, and then decrease slightly up to 17 GPa. In contrast, the elongated Cu-O apical distances decrease continuously with pressure in the studied range. An anomalous increase of the mean square relative displacement (EXAFS Debye-Waller, s2) of the elong…
Photochemical Synthesis of Water-Soluble Gold Nanorods: The Role of Silver Ions in Assisting Anisotropic Growth
2009
The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by stat…
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…
Low temperature X-ray absorption spectroscopy study of $CuMoO_{4}$ and $CuMo_{0.90}W_{0.10}O_4$ using reverse Monte-Carlo method
2020
Radiation physics and chemistry 175, 108411 (2020). doi:10.1016/j.radphyschem.2019.108411
Atomistic simulations of the FeK-edge EXAFS in FeF3using molecular dynamics and reverse Monte Carlo methods
2016
Atomistic simulations of the experimental Fe K-edge extended x-ray absorption fine structure (EXAFS) of rhombohedral (space group ) FeF3 at T = 300 K were performed using classical molecular dynamics and reverse Monte Carlo (RMC) methods. The use of two complementary theoretical approaches allowed us to account accurately for thermal disorder effects in EXAFS and to validate the developed force-field model, which was constructed as a sum of two-body Buckingham-type (Fe–F and F–F), three-body harmonic (Fe–F–Fe) and Coulomb potentials. We found that the shape of the Fe K-edge EXAFS spectrum of FeF3 is a more sensitive probe for the determination of potential parameters than the values of stru…
Crossing the boundary between face-centred cubic and hexagonal close packed: the structure of nanosized cobalt is unraveled by a model accounting for…
2014
The properties of nanostructured cobalt in the fields of magnetic, catalytic and biomaterials depend critically on Co close packing. This paper reports a structural analysis of nanosized cobalt based on the whole X-ray diffraction (XRD) pattern simulation allowed by the Debye equation. The underlying structural model involves statistical sequences of cobalt layers and produces simulated XRD powder patterns bearing the concurrent signatures of hexagonal and cubic close packing (h.c.p. and f.c.c.). Shape, size distribution and distance distribution between pairs of atoms are also modelled. The simulation algorithm allows straightforward fitting to experimental data and hence the quantitative …