scholarly journals Transformation from pyrochlore to fluorite by diffraction and X-ray spectroscopy

2014 ◽  
Vol 70 (a1) ◽  
pp. C234-C234
Author(s):  
Brendan Kennedy ◽  
Peter Blanchard ◽  
Emily Reynolds ◽  
Zhaoming Zhang
Keyword(s):  
Diffraction Data ◽  
Pyrochlore Structure ◽  
Structural Evolution ◽  
Atomic Scale ◽  
Fluorite Phase ◽  
Edge Structure ◽  
X Ray ◽  
Coordination Numbers ◽  
Spectroscopy Studies ◽  
X Ray Absorption

We have studied the long-range average and local structures in a number of zirconium containing materials of the type A2B2O7 ( A = Ln or Y; B = Zr, Hf or Sn) using synchrotron X-ray and neutron powder diffraction and X-ray absorption spectroscopy. Studies of the system Gd2-xTbxZr2O7 include neutron diffraction data, obtained at λ ≍ 0.497 Å to minimise absorption, not only provide evidence for independent ordering of the anion and cation sublattices, but also suggest that the disorder transition across the pyrochlore-defect fluorite boundary of Ln2Zr2O7 is rather gradual. In general we observe that while the diffraction data indicate a clear phase transition from ordered pyrochlore to disordered defect-fluorite at specific compositions corresponding to a critical ionic radius ratio of the A and B cations (rA/rB) x ~ 1.0-1.2, X-ray absorption near-edge structure (XANES) results reveal a gradual structural evolution across the compositional range. These findings provide experimental evidence that the local disorder occurs long before the pyrochlore to defect-fluorite phase boundary as determined by X-ray diffraction, and the extent of disorder continues to develop throughout the defect-fluorite region. Where possible the experimental results were supplemented by ab initio atomic scale simulations, which provide a mechanism for disorder to initiate in the pyrochlore structure. Further, the coordination numbers of the cations in both the defect-fluorite and pyrochlore structures were predicted, and the trends agree well with the experimental XANES results. X-ray absorption measurements at the Zr L3-edge, which showed a gradual increase in the effective coordination number of the Zr from near 6-coordinate in the pyrochlore rich samples to near 7-coordinate in the defect fluorites.

X-ray absorption near the edge structure and X-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

2009 ◽  
Vol 18 (7) ◽  
pp. 2734-2738 ◽  
Author(s):  
Zhang Hui ◽  
Liu Ying-Shu ◽  
Wang Bao-Yi ◽  
Wei Long ◽  
Kui Re-Xi ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Iron Films ◽  
Edge Structure ◽  
X Ray ◽  
Spectroscopy Studies ◽  
X Ray Absorption

X-ray absorption spectroscopy studies for the determination of adsorption binding modes of selenium oxoanions onto iron and manganese based nanomaterials

2012 ◽  
Vol 1480 ◽  
Author(s):  
Christina M. Gonzalez ◽  
Jason G. Parsons ◽  
Jeffrey Hernandez ◽  
Jorge L. Gardea-Torresdey
Keyword(s):  
Absorption Spectroscopy ◽  
Binding Modes ◽  
Edge Structure ◽  
X Ray ◽  
Microwave Assisted ◽  
Spectroscopy Studies ◽  
X Ray Absorption ◽  
Binding Mechanisms ◽  
Iron And Manganese

ABSTRACTIncreasing concentrations of selenium oxoanions in the environment are placing many animals at risk for reproduction failure and deformities. The understanding of binding mechanisms of selenium oxoanions to iron and manganese based oxide minerals could lead to enhanced understanding of selenium mobility in the environment. In this study, the binding mechanisms of selenium oxoanions, selenite and selenate, to non microwave-assisted and microwave-assisted synthetic Fe3O4, Mn3O4, and MnFe2O4 nanomaterials were investigated through the use of X-ray absorption spectroscopy. The X-ray absorption near-edge structure (XANES) spectroscopy studies revealed the oxidation state of selenite and selenate remains the same after binding occurs to all nanomaterials in pH 2, 4, or 6 environments. The binding modes of selenite and selenate were determined to be bidentate binuclear through use of Extended x-ray absorption fine structure (EXAFS) and were independent of nanomaterials, synthetic technique, and pH.

scholarly journals The Atomic-Scale Interaction of Bioactive Glasses with Simulated Body Fluid

2005 ◽  
Vol 480-481 ◽  
pp. 21-26 ◽  
Author(s):  
L.J. Skipper ◽  
F.E. Sowrey ◽  
D.M. Pickup ◽  
R.J. Newport ◽  
K.O. Drake ◽  
...  
Keyword(s):  
Simulated Body Fluid ◽  
Body Fluid ◽  
Sol Gel ◽  
Atomic Scale ◽  
X Ray Diffraction ◽  
Bioactive Glasses ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

The formation of a carbonate-containing hydroxyapatite, HCAp, layer on bioactive calcium silicate sol-gel glass of the formula (CaO)0.3(SiO2)0.7 has been studied in-vitro in Simulated Body Fluid (SBF). Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR) measurements have been performed with results showing the formation of a significantly amorphous HCAp layer after less than 5 hours in solution.

scholarly journals Neural network assisted analysis of bimetallic nanocatalysts using X-ray absorption near edge structure spectroscopy

2020 ◽  
Vol 22 (34) ◽  
pp. 18902-18910 ◽  
Author(s):  
Nicholas Marcella ◽  
Yang Liu ◽  
Janis Timoshenko ◽  
Erjia Guan ◽  
Mathilde Luneau ◽  
...  
Keyword(s):  
Neural Network ◽  
Local Structure ◽  
Bimetallic Nanoparticles ◽  
Edge Structure ◽  
X Ray ◽  
Coordination Numbers ◽  
Rich Information ◽  
Bimetallic Nanocatalysts ◽  
Assisted Analysis ◽  
X Ray Absorption

Trained neural networks are used to extract the first partial coordination numbers from XANES spectra. In bimetallic nanoparticles, the four local structure descriptors provide rich information on structural motifs.

Stoichiometric Study of Iron Sulfide Prepared by Mechanochemical Reaction

2007 ◽  
Vol 561-565 ◽  
pp. 2099-2102 ◽  
Author(s):  
Chung Kwei Lin ◽  
Chin Yi Chen ◽  
Pee Yew Lee ◽  
Chih Chieh Chan
Keyword(s):  
Ball Milling ◽  
Nearest Neighbor ◽  
Iron Sulfide ◽  
Structural Evolution ◽  
High Energy ◽  
Mechanochemical Reaction ◽  
Iron Sulfides ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

In the present study, pure elemental powders of Fe and S were mixed to give the desired compositions of Fe50S50. A SPEX 8000D high-energy ball mill was used to synthesize iron sulfide powders under an Ar-filled atmosphere. The prepared powders were examined by conventional X-ray diffractometry and synchrotron X-ray absorption spectroscopy. The experimental results revealed that mechanochemical reactions occurred during the ball milling process for all the compositions. The Fe50S50 phase was obtained after ball milling for 20 h. Extended X-ray absorption fine structure (EXAFS) results revealed that the nearest neighbor bond lengths of the radial distribution function (RDF) for iron decreased when iron sulfides formed. X-ray absorption near edge structure (XANES) of S K-edges distinguished better the structural evolution of these iron sulfides.

Ab Initio XAFS and XANES Standards

1993 ◽  
Vol 307 ◽  
Author(s):  
J. J. Rehr ◽  
S. I. Zabinsky ◽  
R. C. Albers
Keyword(s):  
Fine Structure ◽  
Ab Initio ◽  
Multiple Scattering ◽  
State Of The Art ◽  
Experimental Measurements ◽  
Edge Structure ◽  
X Ray ◽  
Coordination Numbers ◽  
X Ray Absorption ◽  
Better Than

ABSTRACTAb initio x-ray-absorption fine structure (XAFS) and x-ray-absorption near edge structure (XANES) standards are developed for molecules and solids. These standard XAFS spectra are obtained from ab initio XAFS calculations, using an automated code, FEFF, which we have extended to include multiple-scattering (MS) and XANES calculations. Our treatment is based on state-of-the-art curved-wave MS theory. Sample results are presented and compared with experiment. We find that these theoretical standards are comparable with experimental measurements, yielding distance determinations better than 0.02 Å and coordination numbers better than 20%. Our approach also gives a new MS interpretation of the σ* shape-resonances in XANES.

scholarly journals Opportunities and challenges of applying advanced X-ray spectroscopy to actinide and lanthanide N-donor ligand systems

2022 ◽  
Vol 29 (1) ◽  
Author(s):  
Tim Pruessmann ◽  
Peter Nagel ◽  
Laura Simonelli ◽  
David Batchelor ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Donor Ligands ◽  
Physical Processes ◽  
Edge Structure ◽  
Donor Ligand ◽  
X Ray ◽  
Trivalent Lanthanides ◽  
Novel Technique ◽  
Trivalent Actinides ◽  
Spectroscopy Studies ◽  
X Ray Absorption

N-donor ligands such as n-Pr-BTP [2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine] preferentially bind trivalent actinides (An3+) over trivalent lanthanides (Ln3+) in liquid–liquid separation. However, the chemical and physical processes responsible for this selectivity are not yet well understood. Here, an explorative comparative X-ray spectroscopy and computational (L 3-edge) study for the An/Ln L 3-edge and the N K-edge of [An/Ln(n-Pr-BTP)3](NO3)3, [Ln(n-Pr-BTP)3](CF3SO3)3 and [Ln(n-Pr-BTP)3](ClO4)3 complexes is presented. High-resolution X-ray absorption near-edge structure (HR-XANES) L 3-edge data reveal additional features in the pre- and post-edge range of the spectra that are investigated using the quantum chemical codes FEFF and FDMNES. X-ray Raman spectroscopy studies demonstrate the applicability of this novel technique for investigations of liquid samples of partitioning systems at the N K-edge.

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