Determination of the cation distribution in Fe2Ni(PO4)2using isotopic substitution and powder neutron diffraction

2003 ◽  
Vol 36 (6) ◽  
pp. 1361-1367 ◽  
Author(s):  
Paul F. Henry ◽  
Mark T. Weller ◽  
Chick C. Wilson
Keyword(s):  
Neutron Diffraction ◽  
Time Of Flight ◽  
Neutron Diffraction Study ◽  
Data Set ◽  
X Ray ◽  
X Ray Scattering ◽  
Powder Neutron Diffraction ◽  
Combined Data ◽  
Ray Scattering

The distribution of divalent iron and nickel over the two metal sites with differing coordination geometry in Fe2Ni(PO4)2, sarcopside, has been investigated using time-of-flight powder neutron diffraction of nickel isotopically substituted materials. Data from four separate samples were collected using HRPD at ISIS, containingnatNi,58Ni,60Ni and62Ni, under identical conditions. The occupancy of iron on theM(1) site was found to be 0.290 (1) from a combined-data-set Rietveld refinement of the three isotopically substituted samples, compared with 0.26 (4) and 0.26 (15) respectively from this and a previous time-of-flight powder neutron diffraction study using natural-abundance nickel, and 0.366 (6) and 0.376 (3) using anomalous X-ray scattering techniques. A critical comparison of isotope substitution neutron diffraction and anomalous X-ray scattering methods for distinguishing nickel and iron from powder data is presented.

Rapid structure determination of the hydrogen-containing compound Cs2C2O4·H2O by joint single-crystal X-ray and powder neutron diffraction

2007 ◽  
Vol 63 (3) ◽  
pp. 426-432 ◽  
Author(s):  
Mark T. Weller ◽  
Paul F. Henry ◽  
Mark E. Light
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Data ◽  
Structure Determination ◽  
Neutron Diffraction Data ◽  
Data Set ◽  
X Ray ◽  
Neutron Diffractometer ◽  
Powder Neutron Diffraction

The structure determination of caesium oxalate monohydrate using single-crystal X-ray diffraction, powder neutron diffraction data and a combination of both has been undertaken. Results show that even for hydrogen-containing materials data collected rapidly on a high-flux neutron diffractometer improve the refinement such that accurate positional and thermal displacement parameters can be extracted for all atom types. This contrasts with structural models extracted from either data set alone that demonstrate the inherent limitations of the individual diffraction methods. The rapidity with which useful neutron diffraction data has been collected from hydrogen-containing compounds, 10 min in this study, indicates that the technique should be widely applicable allowing the facile and accurate extraction of hydrogen positions for many compounds.

Determination of the distribution of elements with similar electron counts: a practical guide for resonant X-ray scattering

2013 ◽  
Vol 46 (3) ◽  
pp. 769-778 ◽  
Author(s):  
Simon Welzmiller ◽  
Philipp Urban ◽  
Felix Fahrnbauer ◽  
Loredana Erra ◽  
Oliver Oeckler
Keyword(s):  
Element Distribution ◽  
Data Sets ◽  
Data Set ◽  
X Ray ◽  
X Ray Scattering ◽  
Multiple Data ◽  
Straightforward Method ◽  
Distribution Of Elements ◽  
Ray Scattering

This article attempts to present straightforward and easy-to-understand guidelines for the determination of element distribution in compounds lacking X-ray scattering contrast because they have similar electron counts. Different sources of anomalous dispersion correction terms (especially Δf′ values) are compared with respect to their suitability, reliability and quality. Values from databases are compared with Δfvalues calculated from fluorescence spectra and those refined from single-crystal diffraction data, using both reference crystals without scattering contrast problems and crystals containing elements with similar electron counts. The number of data sets required to determine reliably the element distribution and the optimum wavelengths to be used are discussed. Joint multiple data set refinements are suitable for the refinement of multiply mixed occupancies of elements lacking scattering contrast. The most straightforward method of obtaining Δf′ values depends on the complexity of the problem to be solved and the precision required.

scholarly journals Size and Concentration Determination of Colloidal Nanocrystals by Small-Angle X-Ray Scattering

2018 ◽  
Author(s):  
Jorick Maes ◽  
Nicolo Castro ◽  
Kim De Nolf ◽  
Willem Walravens ◽  
Benjamin Abécassis ◽  
...  
Keyword(s):  
Band Gap ◽  
Small Angle ◽  
Accurate Determination ◽  
Band Gap Energy ◽  
Colloidal Nanocrystals ◽  
X Ray ◽  
Absolute Scale ◽  
X Ray Scattering ◽  
Ray Scattering

<div> <div> <div> <p>The accurate determination of the dimensions of a nano-object is paramount to the de- velopment of nanoscience and technology. Here, we provide procedures for sizing quasi- spherical colloidal nanocrystals (NCs) by means of small-angle x-ray scattering (SAXS). Using PbS NCs as a model system, the protocols outline the extraction of the net NC SAXS pattern by background correction and address the calibration of scattered x-ray intensity to an absolute scale. Different data analysis methods are compared, and we show that they yield nearly identical estimates of the NC diameter in the case of a NC ensemble with a monodisperse and monomodal size distribution. Extending the analysis to PbSe, CdSe </p> </div> </div> <div> <div> <p>and CdS NCs, we provide SAXS calibrated sizing curves, which relate the NC diameter and the NC band-gap energy as determined using absorbance spectroscopy. In compari- son with sizing curves calibrated by means of transmission electron microscopy (TEM), we systematically find that SAXS calibration assigns a larger diameter than TEM calibration to NCs with a given band gap. We attribute this difference to the difficulty of accurately sizing small objects in TEM images. To close, we demonstrate that NC concentrations can be directly extracted from SAXS patterns normalized to an absolute scale, and we show that SAXS-based concentrations agree with concentration estimates based on absorption spectroscopy.</p></div></div></div>

Diffuse x-ray scattering from InGaAs/GaAs quantum dots

2003 ◽  
Vol 799 ◽  
Author(s):  
Rolf Köhler ◽  
Daniil Grigoriev ◽  
Michael Hanke ◽  
Martin Schmidbauer ◽  
Peter Schäfer ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Synchrotron Radiation ◽  
Diffuse Scattering ◽  
Data Evaluation ◽  
X Ray ◽  
X Ray Scattering ◽  
Gaas Matrix ◽  
Wetting Layers ◽  
Ray Scattering

ABSTRACTMulti-fold stacks of In0.6Ga0.4As quantum dots embedded into a GaAs matrix were investigated by means of x-ray diffuse scattering. The measurements were done with synchrotron radiation using different diffraction geometries. Data evaluation was based on comparison with simulated distributions of x-ray diffuse scattering. For the samples under consideration ((001) surface) there is no difference in dot extension along [110] and [-110] and no directional ordering. The measurements easily allow the determination of the average indium amount in the wetting layers. Data evaluation by simulation of x-ray diffuse scattering gives an increase of Incontent from the dot bottom to the dot top.

scholarly journals Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites

2009 ◽  
Vol 42 (2) ◽  
pp. 259-264 ◽  
Author(s):  
Xinguo Hong ◽  
Quan Hao
Keyword(s):  
Structure Determination ◽  
Heavy Atom ◽  
Unit Cell ◽  
Wide Angle ◽  
X Ray ◽  
X Ray Scattering ◽  
Molecular Envelope ◽  
Waxs Data ◽  
Ray Scattering

Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the programGASBORat 5 Å resolution (qmax= 1.25 Å−1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2σ level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax= 0.25 Å−1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination ofFSEARCHand WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement.

Analysis of Nanopowders by Small-Angle X-Ray Scattering Method’s

2012 ◽  
Vol 7 (4) ◽  
pp. 107-116
Author(s):  
Sergey Bardakhanov ◽  
Ludmila Vikulina ◽  
Vladimir Lysenko ◽  
Andrey Nomoev ◽  
Sergey Poluyanov ◽  
...  
Keyword(s):  
Distribution Function ◽  
Size Distribution ◽  
Small Angle ◽  
Electron Accelerator ◽  
Size Distribution Function ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

The possibility of application of small-angle X-ray scattering (SAXS) for nanopowders analysis was studied. The research for eight silica powders (including four powders obtained by the authors with help of electron accelerator) was conducted. The possibility of application of small angle X-ray scattering for determination of size distribution function of nanoparticles was shown

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