Convergent-beam neutron crystallography

2004 ◽  
Vol 37 (5) ◽  
pp. 778-785 ◽  
Author(s):  
W. M. Gibson ◽  
A. J. Schultz ◽  
J. W. Richardson ◽  
J. M. Carpenter ◽  
D. F. R. Mildner ◽  
...  
Keyword(s):  
Focal Length ◽  
Single Crystal Sample ◽  
Polycapillary Optics ◽  
Crystal Sample ◽  
Integrated Intensity ◽  
Neutron Wavelength ◽  
Powder Samples ◽  
Focal Spot Diameter ◽  
Convergent Beam ◽  
Pulsed Neutron

Two monolithic polycapillary optics of different focal length and beam convergence are employed to investigate the use of focusing lenses for the neutron convergent-beam method for time-of-flight crystallography with a broad neutron wavelength bandwidth. The optic of short output focal length (15.5 mm) with a beam convergence of 16.8 (10)° has a focal spot diameter of ∼100 µm for 3.2 Å neutrons. For an MnF2single-crystal sample of this diameter on a pulsed neutron source, this lens gives an expected integrated intensity gain of ∼100 for a 020 Bragg peak. Further measurements on a powder diffractometer show that the expected diffracted beam intensities for Ni have gains in excess of 500 for powder samples of this diameter. The degradation of resolution is minimized in the backscattering geometry.

Origin of Paramagnetic Defect in Single Crystal and Ceramic B4C

1987 ◽  
Vol 97 ◽  
Author(s):  
E. L. Venturini ◽  
D. Emin ◽  
T. L. Aselage
Keyword(s):  
Single Crystal ◽  
Angular Dependence ◽  
Esr Spectra ◽  
Single Crystal Sample ◽  
Paramagnetic Defect ◽  
Crystal Sample ◽  
Spin Resonance ◽  
Integrated Intensity ◽  
Increasing Temperature ◽  
Positively Charged

ABSTRACTWe compare electron spin resonance (ESR) spectra of B4C samples made by three methods. The samples are 1) two ceramics made by hot-pressing boron and carbon powders, 2) a polycrystal made by carbothermic reduction, and 3) a single crystal grown from a palladium metal melt. All samples show remarkably similar spectra between 2 and 100 K. In particular, all samples show a single Lorentzian absorption, a linewidth that decreases with increasing temperature, and an inverse temperature dependence of the integrated intensity. The integrated intensity of the paramagnetic spin signal corresponds to a density of 2×1019/cm2 localized spins. Having a single crystal sample enables us to meaningfully measure the angular dependence of the ESR linewidth. This angular dependence is consistent with the paramagetic centers being unpaired electrons centered on the central carbon atoms of positively charged C-C-C intericosahedral chains. These chains appear to replace 0.5 % of the positively charged C-B-C intericosahedral chains which occur in B4C.

Structure Information From Electron Diffraction Intensities

1990 ◽  
Vol 48 (2) ◽  
pp. 516-517
Author(s):  
J. Gjønnes ◽  
N. Bøe ◽  
K. Gjønnes
Keyword(s):  
Computational Effort ◽  
Unit Cell ◽  
Small Unit ◽  
Structure Information ◽  
Dispersion Surface ◽  
Integrated Intensity ◽  
The One ◽  
Image Position ◽  
Convergent Beam ◽  
Beam Patterns

Structure information of high precision can be extracted from intentsity details in convergent beam patterns like the one reproduced in Fig 1. From low order reflections for small unit cell crystals,bonding charges, ionicities and atomic parameters can be derived, (Zuo, Spence and O’Keefe, 1988; Zuo, Spence and Høier 1989; Gjønnes, Matsuhata and Taftø, 1989) , but extension to larger unit cell ma seem difficult. The disks must then be reduced in order to avoid overlap calculations will become more complex and intensity features often less distinct Several avenues may be then explored: increased computational effort in order to handle the necessary many-parameter dynamical calculations; use of zone axis intensities at symmetry positions within the CBED disks, as in Figure 2 measurement of integrated intensity across K-line segments. In the last case measurable quantities which are well defined also from a theoretical viewpoint can be related to a two-beam like expression for the intensity profile:With as an effective Fourier potential equated to a gap at the dispersion surface, this intensity can be integrated across the line, with kinematical and dynamical limits proportional to and at low and high thickness respctively (Blackman, 1939).

scholarly journals Stability and equation of state of face-centered cubic and hexagonal close packed phases of argon under pressure

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Agnès Dewaele ◽  
Angelika D. Rosa ◽  
Nicolas Guignot ◽  
Denis Andrault ◽  
João Elias F. S. Rodrigues ◽  
...  
Keyword(s):  
Equation Of State ◽  
Single Crystal ◽  
Single Crystal Sample ◽  
Moderate Pressure ◽  
Face Centered Cubic ◽  
Experimental Conditions ◽  
Crystal Sample ◽  
Hexagonal Close Packed ◽  
Face Centered ◽  
Fcc Phase

AbstractThe compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: $$V_0$$ V 0 = 38.0 Å$$^3$$ 3 /at, $$K_0$$ K 0 = 2.65 GPa, $$K'_0$$ K 0 ′ = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure ($$\le$$ ≤ 20 GPa).

scholarly journals Analysis and Mapping of Detailed Inner Information of Crystalline Grain by Wavelength-Resolved Neutron Transmission Imaging with Individual Bragg-Dip Profile-Fitting Analysis

2021 ◽  
Vol 11 (11) ◽  
pp. 5219
Author(s):  
Yosuke Sakurai ◽  
Hirotaka Sato ◽  
Nozomu Adachi ◽  
Satoshi Morooka ◽  
Yoshikazu Todaka ◽  
...  
Keyword(s):  
Crystal Orientation ◽  
Perfect Crystal ◽  
Imaging Method ◽  
Transmission Imaging ◽  
Profile Fitting ◽  
Imaging Results ◽  
Integrated Intensity ◽  
Small Change ◽  
Integrated Intensities ◽  
Pulsed Neutron

As a new method for evaluating single crystals and oligocrystals, pulsed neutron Bragg-dip transmission analysis/imaging method is being developed. In this study, a single Bragg-dip profile-fitting analysis method was newly developed, and applied for analyzing detailed inner information in a crystalline grain position-dependently. In the method, the spectrum profile of a single Bragg-dip is analyzed at each position over a grain. As a result, it is expected that changes in crystal orientation, mosaic spread angle and thickness of a perfect crystal can be evaluated from the wavelength, the width and the integrated intensity of the Bragg-dip, respectively. For confirming this effectiveness, the method was applied to experimental data of position-dependent Bragg-dip transmission spectra of a Si-steel plate consisting of oligocrystals. As a result, inner information of multiple crystalline grains could be visualized and evaluated. The small change in crystal orientation in a grain, about 0.4°, could be observed by imaging the Bragg-dip wavelengths. By imaging the Bragg-dip widths, both another grain and mosaic block in a grain were detected. Furthermore, imaging results of the integrated intensities of Bragg-dips were consistent with the results of Bragg-dip width imaging. These small crystallographic changes have not been observed and visualized by previous Bragg-dip analysis methods.

Extending the temperature sensing range using Eu3+ luminescence up to 865 K in a single crystal of EuPO4

2019 ◽  
Vol 21 (29) ◽  
pp. 16329-16336 ◽  
Author(s):  
Suchinder K. Sharma ◽  
Thomas Köhler ◽  
Jan Beyer ◽  
Margret Fuchs ◽  
Richard Gloaguen ◽  
...  
Keyword(s):  
Single Crystal ◽  
Temperature Sensing ◽  
Single Crystal Sample ◽  
Coupling Scheme ◽  
Excitation Wavelength ◽  
Crystal Sample ◽  
Sensing Range

Extending the temperature sensing range up to 865 K using an appropriate choice of excitation wavelength and coupling scheme in a single crystal sample of EuPO4.

scholarly journals Stationary beam full-field transmission helium ion microscopy using sub-50 keV He+: Projected images and intensity patterns

2019 ◽  
Vol 10 ◽  
pp. 1648-1657
Author(s):  
Michael Mousley ◽  
Santhana Eswara ◽  
Olivier De Castro ◽  
Olivier Bouton ◽  
Nico Klingner ◽  
...  
Keyword(s):  
Ion Irradiation ◽  
Ion Beam ◽  
Far Field ◽  
Ion Scattering ◽  
Full Field ◽  
Helium Ion ◽  
Powder Samples ◽  
Convergent Beam ◽  
Surface Diffraction ◽  
Possible Cause

A dedicated transmission helium ion microscope (THIM) for sub-50 keV helium has been constructed to investigate ion scattering processes and contrast mechanisms, aiding the development of new imaging and analysis modalities. Unlike a commercial helium ion microscope (HIM), the in-house built instrument allows full flexibility in experimental configuration. Here, we report projection imaging and intensity patterns obtained from powder and bulk crystalline samples using stationary broad-beam as well as convergent-beam illumination conditions in THIM. The He+ ions formed unexpected spot patterns in the far field for MgO, BN and NaCl powder samples, but not for Au-coated MgO. The origin of the spot patterns in these samples was investigated. Surface diffraction of ions was excluded as a possible cause because the recorded scattering angles do not correspond to the predicted Bragg angles. Complementary secondary electron (SE) imaging in the HIM revealed that these samples charge significantly under He+ ion irradiation. The spot patterns obtained in the THIM experiments are explained as artefacts related to sample charging. The results presented here indicate that factors other than channeling, blocking and surface diffraction of ions have an impact on the final intensity distribution in the far field. Hence, the different processes contributing to the final intensities will need to be understood in order to decouple and study the relevant ion-beam scattering and deflection phenomena.

Polycapillary focusing optic for small-sample neutron crystallography

2002 ◽  
Vol 35 (6) ◽  
pp. 677-683 ◽  
Author(s):  
W. M. Gibson ◽  
A. J. Schultz ◽  
H. H. Chen-Mayer ◽  
D. F. R. Mildner ◽  
T. Gnäupel-Herold ◽  
...  
Keyword(s):  
Quartz Crystal ◽  
Sample Volume ◽  
Small Sample ◽  
Diffraction Measurement ◽  
Small Crystals ◽  
Diffraction Peaks ◽  
Convergent Beam ◽  
Pulsed Neutron ◽  
Intense Spot ◽  
Pulsed Neutron Source

The relatively low flux from neutron sources means that structural analysis using neutron diffraction requires large crystals that are often not available. The feasibility of a polycapillary focusing optic to produce a small intense spot of size < ∼0.5 mm for small crystals has been explored and such an optic has been tested both on a monochromatic and on a polychromatic beam. In a diffraction measurement from an α-quartz crystal using a 2.1° convergent beam from a pulsed neutron source, six diffraction peaks in the 1.5–4 Å wavelength bandwidth transmitted by the optic were observed. These diffraction spots show an intensity gain of 5.8 ± 0.9 compared with a direct beam diffracting from the same sample volume as that illuminated by the convergent beam.

A Comparison of Small Angle Neutron Scattering and X-Ray Diffraction Studies of Cobalt Precipitates in A Cu-0.95 at. % Co Alloy

1986 ◽  
Vol 82 ◽  
Author(s):  
S. Spooner ◽  
S. Iida ◽  
B. C. Larson
Keyword(s):  
Small Angle ◽  
Large Angle ◽  
Detailed Comparison ◽  
Scattering Data ◽  
Single Crystal Sample ◽  
X Ray Diffraction ◽  
Data Set ◽  
Crystal Sample ◽  
X Ray ◽  
Angle Scattering

ABSTRACTA detailed comparison of small-angle scattering (SANS) and large angle x-ray diffraction methods of characterization of precipitates was undertaken. Cobalt-rich precipitates on the order of 50 Å developed after a 17 hour anneal at 570°C were studied in a single crystal sample with SANS and with diffuse x-ray scattering near the (400)Bragg peak. Each scattering data set was analyzed independently in terms of a distribution of precipitate sizes; a detailed comparison is made of the size distribution obtained. A small interparticle interference effect is seen.

Stability of High-Spin State of Iron in β-NaFeO2

2020 ◽  
Vol 855 ◽  
pp. 177-182
Author(s):  
Mochammad Yan Pandu Akbar ◽  
Rieko Ishii ◽  
Agustinus Agung Nugroho
Keyword(s):  
Single Crystal ◽  
High Spin ◽  
Spin State ◽  
High Spin State ◽  
Polycrystalline Sample ◽  
Single Crystal Sample ◽  
Structural Refinement ◽  
Crystal Sample ◽  
The Stability ◽  
Crystal Volume

We investigated the stability of the high-spin state of the iron β-NaFeO2 based on the structural refinement. The oxidation of the Fe2+ ion in the as-synthesized sample is evidenced by its green color. Due to its sensitivity in air and CO2, this compound will decompose into a reddish Fe3+ state. The smaller crystal volume of the decomposed compound is mainly related to the shorter ionic radius of the high-spin state Fe3+ and this result will be compared to the single crystal sample. In contrast to the polycrystalline sample, the decomposition single crystal sample only taking place on the surface of the as-grown crystal.

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