Double Bent Crystal Monochromator for High Resolution Neutron Powder Diffraction

2013 ◽  
Vol 28 (S2) ◽  
pp. S351-S359 ◽  
Author(s):  
P. Mikula ◽  
M. Vrána ◽  
J. Šaroun ◽  
B.S. Seong ◽  
W. Woo
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Angular Resolution ◽  
Polycrystalline Sample ◽  
Neutron Powder Diffraction ◽  
Diffraction Experiment ◽  
Neutron Diffraction Experiment ◽  
Bent Crystal ◽  
Neutron Wavelength

Recent results of focusing and reflectivity properties of the dispersive double-bent-crystal monochromator have shown that it could be succesfully used in high resolution neutron diffraction experiment. By using a standard polycrystalline sample of α-Fe, the resolution of the diffraction performance in the vicinity of the scattering angle 2θS = 90o for the neutron wavelength λ= 0.162 nm was tested in detail. It has been found that for thin (1.3 mm) bent second crystal the angular resolution represented by FWHM of diffraction profiles was 1x10−3 rad for 211 and 200 reflections and about 3x10−3 rad for 220 reflection.

High Resolution Neutron Powder Diffraction Study of the Tubular Phase Bi4Sr8Cu5O19+x

1989 ◽  
Vol 169 ◽  
Author(s):  
M.T. Caldés ◽  
J.M. Navarro ◽  
A. Fuertes ◽  
X. Obradors ◽  
C. Miravitlles ◽  
...  
Keyword(s):  
Structural Change ◽  
High Resolution ◽  
Neutron Diffraction ◽  
Diffraction Study ◽  
Powder Diffraction ◽  
Neutron Powder Diffraction ◽  
Diffraction Experiment ◽  
Antiferromagnetic Ordering ◽  
Powder Neutron Diffraction ◽  
Diffraction Patterns

AbstractA high resolution neutron powder diffraction experiment has been performed on Bi4Sr8Cu5O19+x. The structure is well described in the space group Fmmm with the oxygen atoms in the bismuth planes appearing disordered in intermediate positions between NaCl and bridging sites as occurs in the superconductors Bi2Sr2Can‐1CunO4n+2. Temperature dependence study of powder neutron diffraction patterns between 1.5K and 998K does not show any relevant structural change neither evidence of antiferromagnetic ordering in this sample.

Use of Neutron Diffraction for Describing Texture of Isostatically-Pressed Molybdite Powders

2005 ◽  
Vol 105 ◽  
pp. 83-88 ◽  
Author(s):  
H. Sitepu ◽  
Heinz Günter Brokmeier
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Quantitative Description ◽  
Neutron Powder Diffraction ◽  
Powder Diffraction Data ◽  
Neutron Powder Diffraction Data ◽  
Pole Figures ◽  
Diffraction Patterns ◽  
Excellent Tool

The modelling and/or describing of texture (i.e. preferred crystallographic orientation (PO)) is of critical importance in powder diffraction analysis - for structural study and phase composition. In the present study, the GSAS Rietveld refinement with generalized spherical harmonic (GSH) was used for describing isostatically-pressed molybdite powders neutron powder diffraction data collected in the ILL D1A instrument. The results showed that for texture in a single ND data of molybdite the reasonable crystal structure parameters may be obtained when applying corrections to intensities using the GSH description. Furthermore, the WIMV method was used to extract the texture description directly from a simultaneous refinement with 1368 whole neutron diffraction patterns taken from the sample held in a variety of orientations in the ILL D1B texture goniometer. The results provided a quantitative description of the texture refined simultaneously with the crystal structure. Finally, the (002) molybdite pole-figures were measured using the GKSS TEX2 texture goniometer. The results showed that neutron diffraction is an excellent tool to investigate the texture in molybdite.

scholarly journals Neutron diffraction investigation of the temperature dependence of crystal structure and thermal motions of red HgI2

2007 ◽  
Vol 63 (6) ◽  
pp. 828-835 ◽  
Author(s):  
Dieter Schwarzenbach ◽  
Henrik Birkedal ◽  
Marc Hostettler ◽  
Peter Fischer
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Soft Mode ◽  
Layer Structure ◽  
Neutron Powder Diffraction ◽  
Force Constants ◽  
Quantum Oscillator ◽  
Thermal Displacement ◽  
Tetrahedral Layer

The structure of, and anisotropic thermal motions in, the red semiconductor tetrahedral layer structure of HgI2 have been studied with neutron powder diffraction as a function of temperature from 10 to 293 K. Average thermal displacement parameters U eq of the two atoms are comparable in size at 10 K, but U eq(Hg) increases considerably faster with temperature than U eq(I), the Hg—I bond being highly non-rigid. The anisotropic displacement tensor U (I) is strongly anisotropic with one term about twice as large as the others, while U (Hg) is nearly isotropic. All displacement tensor elements, except U 22(I), increase faster with temperature than harmonic quantum oscillator curves indicating a softening of the isolated-atom potentials at large amplitudes. A lattice dynamical model provides arguments that the anisotropic thermal motions of I are dominated by a soft mode with a wavevector at the [½ ½ 0] boundary of the Brillouin zone consisting essentially of coupled librations of the HgI4 tetrahedra, and by translations of the entire layer. The large vibration amplitudes of Hg suggest weak Hg–I force constants compared with the I–I force constants, allowing Hg to move quite freely inside the tetrahedra. The libration mode induces dynamic deformations of the Hg—I bond with twice its frequency. This provides a mechanism for the anharmonicity and may explain the lightening of the color from red to orange upon cooling at ca 80 K.

High Resolution Neutron Powder Diffraction Studies of the Ferroelastic Phase Transition in LaNbO4

1989 ◽  
Vol 166 ◽  
Author(s):  
W I F David
Keyword(s):  
Phase Transition ◽  
High Resolution ◽  
Powder Diffraction ◽  
Structural Phase ◽  
Strain Tensor ◽  
Neutron Powder Diffraction ◽  
Line Broadening ◽  
Neutron Powder Diffraction Data ◽  
Ferroelastic Phase Transition ◽  
Principal Axes

ABSTRACTAnalysis of high resolution neutron powder diffraction data of ferroelastic LaNbO4 indicates a monoclinic to tetragonal structural phase transition that is accompanied by anomalous line broadening. The origins of this line broadening have been investigated using a novel modification of the Rietveld technique. The results show that strain broadening is associated with the ferroelastic phase transition both above and below the transition temperature. This anomalous ‘microstrain’ is well-described by a second rank strain tensor, the principal axes of which are collinear with the spontaneous lattice strain. This phenomenon may be a general feature of proper ferroelastic phase transitions.

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