Location and energy of interstitial hydrogen in the1∕1approximantW-TiZrNiof the icosahedralTiZrNiquasicrystal: Rietveld refinement of x-ray and neutron diffraction data and density-functional calculations

2006 ◽  
Vol 73 (18) ◽  
Author(s):  
R. G. Hennig ◽  
E. H. Majzoub ◽  
K. F. Kelton
Keyword(s):  
Neutron Diffraction ◽  
Rietveld Refinement ◽  
Diffraction Data ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Neutron Diffraction Data ◽  
X Ray ◽  
Interstitial Hydrogen

scholarly journals When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical

2017 ◽  
Vol 73 (4) ◽  
pp. 544-549 ◽  
Author(s):  
Ariste Bolivard Voufack ◽  
Nicolas Claiser ◽  
Claude Lecomte ◽  
Sébastien Pillet ◽  
Yves Pontillon ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Diffraction Data ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Organic Radical ◽  
Neutron Diffraction Data ◽  
Nitronyl Nitroxide ◽  
X Ray ◽  
Complete Active Space ◽  
Polarized Neutron

Joint refinement of X-ray and polarized neutron diffraction data has been carried out in order to determine charge and spin density distributions simultaneously in the nitronyl nitroxide (NN) free radical Nit(SMe)Ph. For comparison purposes, density functional theory (DFT) and complete active-space self-consistent field (CASSCF) theoretical calculations were also performed. Experimentally derived charge and spin densities show significant differences between the two NO groups of the NN function that are not observed from DFT theoretical calculations. On the contrary, CASSCF calculations exhibit the same fine details as observed in spin-resolved joint refinement and a clear asymmetry between the two NO groups.

Powder diffraction studies of synthetic calcium and lead apatites

2000 ◽  
Vol 53 (8) ◽  
pp. 679 ◽  
Author(s):  
Jean Y. Kim ◽  
Ronald R. Fenton ◽  
Brett A. Hunter ◽  
Brendan J. Kennedy
Keyword(s):  
Neutron Diffraction ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Lattice Parameters ◽  
Neutron Diffraction Data ◽  
X Ray ◽  
Lead Compounds ◽  
Calcium Compounds ◽  
Cation Sites

The crystal structures of M10(PO4)6X2, where M = Ca or Pb and X = OH¯, F¯, Cl¯ or Br¯, have been determined by Rietveld refinement of powder synchrotron X-ray and neutron diffraction data. All the compounds are hexagonal with space group P 63/m. For the calcium compounds, the lattice parameters are a = 9.4302(5), 9.3475(3), 9.5902(6), 9.6482(6) and c = 6.8911(2), 6.8646(1), 6.7666(2), 6.7788(2) Å, for X = OH¯, F¯, Cl¯, Br¯, respectively. For the lead compounds, the corresponding lattice parameters are a = 9.8612(4), 9.7547(5), 9.9767(4), 10.0618(3) and c = 7.4242(2), 7.2832(2), 7.3255(1), 7.3592(1) Å. In these compounds there are two cation sites, a channel of M(I) atoms and a triangle of M(II) atoms. The anion interacts most strongly with the M(II) atoms with the interaction dictating the position of the anion relative to the M(II) triangle. In Ca10(PO4)6X2, the F¯ ion sits within the triangle planes, while the larger OH¯ and Cl¯ anions are disordered above and below the M(II) triangles. The even larger Br¯ is midway between two triangles at (0, 0, ). Despite the larger size of the isostructural lead compounds, no anions are found in the triangles. The F¯, Cl¯ and Br¯ ions are at (0, 0, ) and the OH¯ ion is disordered at (0, 0, z). This difference in behaviour is possibly related to the lead 6s electrons. In this paper, the experimental results are presented and possible reasons for the observed differences are discussed.

Design of a novel Peltier-based cooling device and its use in neutron diffraction data collection of perdeuterated yeast pyrophosphatase

2010 ◽  
Vol 43 (5) ◽  
pp. 1113-1120 ◽  
Author(s):  
Esko Oksanen ◽  
François Dauvergne ◽  
Adrian Goldman ◽  
Monika Budayova-Spano
Keyword(s):  
Data Collection ◽  
Neutron Diffraction ◽  
Diffraction Data ◽  
Catalytic Mechanism ◽  
Inorganic Pyrophosphatase ◽  
Neutron Diffraction Data ◽  
Cooling Device ◽  
Data Set ◽  
X Ray ◽  
X Ray Crystallography

H atoms play a central role in enzymatic mechanisms, but H-atom positions cannot generally be determined by X-ray crystallography. Neutron crystallography, on the other hand, can be used to determine H-atom positions but it is experimentally very challenging. Yeast inorganic pyrophosphatase (PPase) is an essential enzyme that has been studied extensively by X-ray crystallography, yet the details of the catalytic mechanism remain incompletely understood. The temperature instability of PPase crystals has in the past prevented the collection of a neutron diffraction data set. This paper reports how the crystal growth has been optimized in temperature-controlled conditions. To stabilize the crystals during neutron data collection a Peltier cooling device that minimizes the temperature gradient along the capillary has been developed. This device allowed the collection of a full neutron diffraction data set.

Measurement of Atomic Elastic Constants by Pulsed Neutron Powder Diffraction

1992 ◽  
Vol 36 ◽  
pp. 577-583
Author(s):  
A. C. Lawson ◽  
G. H. Kwei ◽  
J. A. Goldstone ◽  
B. Cort ◽  
R. I. Sheldon ◽  
...  
Keyword(s):  
High Temperature ◽  
Neutron Diffraction ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Elastic Constants ◽  
Diffraction Data ◽  
High Temperature Superconductors ◽  
Neutron Powder Diffraction ◽  
Neutron Diffraction Data ◽  
Pulsed Neutron

AbstractWe have developed a technique for determining the atomic elastic constants from measurements of the Debye-Waller factors. The Debye-Waller factors are obtained by Rietveld refinement of time-of-flight neutron diffraction data and interpreted in terms of an atomic Debye-Waller temperature. The method is applicable to powders and to materials that must be encapsulated for safety or environmental reasons. We will illustrate our technique with applications to actinide metals, to metallic hydrides and to high-temperature superconductors.

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