scholarly journals Accurate Measurement of Powder Diffraction Intensities Using Synchrotron Radiation

1988 ◽  
Vol 41 (3) ◽  
pp. 403 ◽  
Author(s):  
W Parrish ◽  
M Hart
Keyword(s):  
Synchrotron Radiation ◽  
Structure Refinement ◽  
Specimen Preparation ◽  
Instrument Function ◽  
Beam Geometry ◽  
Profile Fitting ◽  
Powder Samples ◽  
Parallel Beam Geometry ◽  
Integrated Intensities ◽  
Wavelength Selectivity

This paper reviews the advantages of synchrotron radiation for obtaining accurate values of the integrated intensities of powder samples for crystal structure refinement. The higher accuracy than conventional X-ray tube focusing methods results from the parallel beam geometry which has a symmetrical constant instrument function, higher intensity and resolution and easy wavelength selectivity. The importance of specimen preparation and the profile fitting function are discussed.

Crystal-structure refinement by profile fitting and least-squares analysis of powder diffractometer data

1983 ◽  
Vol 16 (6) ◽  
pp. 611-622 ◽  
Author(s):  
G. Will ◽  
W. Parrish ◽  
T. C. Huang
Keyword(s):  
Least Squares ◽  
Structure Refinement ◽  
Specimen Preparation ◽  
Crystal Structure Refinement ◽  
Instrument Function ◽  
X Ray ◽  
Profile Fitting ◽  
Fitting Method ◽  
The Individual ◽  
Integrated Intensities

The refinement of crystal structures using X-ray powder data in a two-stage method is described. (1) The integrated intensities of the individual reflections are derived by a profile fitting method in which the profile shapes are accurately defined using an experimentally determined instrument function and the sum of Lorentzian curves. (2) These values are then used in a powder least-squares refinement for structure determination. The results obtained with three simple structures (silicon, quartz and corundum) gave R(Bragg) values of 0.7 to 2.5%. The necessity of correcting for preferred orientation and the importance of proper specimen preparation are also discussed.

Parallel Beam and Focusing X-ray Powder Diffractometry

1988 ◽  
Vol 32 ◽  
pp. 481-488
Author(s):  
W. Parrish ◽  
M. Hart
Keyword(s):  
Lattice Parameter ◽  
Particle Sizes ◽  
Parallel Beam ◽  
Instrument Function ◽  
X Ray ◽  
Experimental Profile ◽  
Beam Geometry ◽  
Parallel Beam Geometry ◽  
Integrated Intensities ◽  
Voigt Function

AbstractComparison of results using synchrotron radiation and X-ray tubes requires a knowledge of the fundamentally different profile shapes inherent in the methods. The varying asymmetric shapes and peak shifts in focusing geometry limit the accuracy and applications of the method and their origins are reviewed. Most o f the focusing aberrations such as specimen displacement, flat specimen and θ-2θ mis-setting do not occur in the parallel beam geometry. The X-ray optics used in synchrotron parallel beam methods produces narrow, symmetrical profiles which can be accurately fit with a pseudo-Voigt function, They have the same shape in the entire pattern. Only the width increases as tanθ due to wavelength dispersion but with higher resolution systems dispersion can be eliminated. The constant instrument function contribution to the experimental profile shape is an important advantage in studies involving profile shapes, e.g., small particle sizes and microstrains, and accurate integrated intensities. The absence of systematic errors leads to more precise lattice parameter determinations.

Accuracy and Precision of Intensities in X-Ray Polycrystalline Diffraction

1982 ◽  
Vol 26 ◽  
pp. 35-44 ◽  
Author(s):  
W. Parrish ◽  
T. C. Huang
Keyword(s):  
Structure Refinement ◽  
Silicon Powder ◽  
Absolute Intensity ◽  
Preferred Orientation ◽  
Average Intensity ◽  
Profile Fitting ◽  
Powder Samples ◽  
Crystallite Sizes ◽  
The Absolute ◽  
Integrated Intensities

AbstractThe integrated and peak intensities of a series of silicon powder samples of various crystallite sizes were measured with a computer automated diffractometer and a profile fitting method (PFM). The accuracy of the PFM was better than 0.003% in computing the integrated intensities. The PFM gave more precise values than would be expected from counting statistics of the peak intensity. The average difference between each measurement and the average intensity was 0.5% with little dependence oo the absolute intensity. Crystallite sizes have a large effect and it is essential to rotate the specimen around the diffraction vector. The best results were obtained with <10 μm particles. Larger sizes decrease the absolute intensities and change the relative intensities. Structure refinement using the POWLS (powder least squares refinement) program showed the presence of (111) preferred orientation even in the <10 μm specimens. R(Bragg) decreased from 4.3% to 0.7% by including the preferred orientation correction in the refinement.

scholarly journals Influence of Sample-Movement on Particle-Randomization of Powder Samples in the Parallel-Beam Geometry

1997 ◽  
Vol 29 (1-2) ◽  
pp. 27-37
Author(s):  
K. Burger ◽  
J. Ihringer
Keyword(s):  
High Resolution ◽  
Rotation Axis ◽  
Bragg Reflection ◽  
Parallel Beam ◽  
X Ray ◽  
Beam Geometry ◽  
Powder Samples ◽  
Parallel Beam Geometry ◽  
Diffraction Patterns ◽  
Integrated Intensities

Today, from powder X-ray diffraction the scientists want to obtain high resolution diffraction patterns with reliable Bragg-reflection intensities. Two well-known and closely connected obstacles on the way are texture and particle randomization of the sample, which strongly influence the measured intensities. In the work presented here, we examine the second problem.Especially with high resolution diffractometers, for well crystallized or highly absorbing samples the number of contributing crystals in the powder is too small, thus introducing significant errors in the profiles and measured intensities of Bragg-reflections. This may be the major source of inaccuracy in data used for structure determination. Calculations of the error of the integrated intensities are presented, for the high resolution, parallel beam geometry at a synchrotron X-ray source. Results exhibit errors of 40 % in the range of highest resolution for a sample of 3 μm crystals of corundum, with the sample at rest. To enhance randomization, several methods of sample-movement are considered. A new effective method is proposed, where the rotation axis of the flat sample-disk is slightly inclined out of the diffraction plane.

Intensity enhancement in asymmetric diffraction with parallel-beam synchrotron radiation

1993 ◽  
Vol 26 (6) ◽  
pp. 774-777 ◽  
Author(s):  
H. Toraya ◽  
T. C. Huang ◽  
Y. Wu
Keyword(s):  
Synchrotron Radiation ◽  
Incident Angle ◽  
Parallel Beam ◽  
Intensity Enhancement ◽  
Radiation Data ◽  
Profile Fitting ◽  
Diffraction Patterns ◽  
Integrated Intensities ◽  
Radiation Laboratory ◽  
Limited Height

An intensity enhancement obtained from asymmetric diffraction with a fixed incident angle α has been studied. Parallel-beam synchrotron radiation with λ = 1.54 Å (Stanford Synchrotron Radiation Laboratory) and λ = 1.53 Å (Photon Factory) was used to collect powder diffraction patterns of Si, CeO2 (α = 5 and 10°) and monoclinic ZrO2 (α = 10°). The synchrotron-radiation data were analyzed using single-reflection profile fitting and whole-powder-pattern fitting techniques. The integrated intensities in the asymmetric diffraction were compared with those of symmetric diffraction obtained by the conventional θ–2θ scanning technique. An intensity, after correction for a limited height of counter aperture, was enhanced by factors of 1.8 (α = 5°) and 1.7 (α = 10°) at the maximum in asymmetric diffraction and its magnitudes agreed well with those calculated from theory.

Integration of neutron time-of-flight single-crystal Bragg peaks in reciprocal space

2014 ◽  
Vol 47 (3) ◽  
pp. 915-921 ◽  
Author(s):  
Arthur J. Schultz ◽  
Mads Ry Vogel Jørgensen ◽  
Xiaoping Wang ◽  
Ruth L. Mikkelson ◽  
Dennis J. Mikkelson ◽  
...  
Keyword(s):  
Single Crystal ◽  
Structure Refinement ◽  
Time Of Flight ◽  
Reciprocal Space ◽  
One Dimensional ◽  
Profile Fitting ◽  
Neutron Time ◽  
Fixed Radius ◽  
Integrated Intensities ◽  
Fitting In

The intensity of single-crystal Bragg peaks obtained by mapping neutron time-of-flight event data into reciprocal space and integrating in various ways is compared. These methods include spherical integration with a fixed radius, ellipsoid fitting and integration of the peak intensity, and one-dimensional peak profile fitting. In comparison to intensities obtained by integrating in real detector histogram space, the data integrated in reciprocal space result in better agreement factors and more accurate atomic parameters. Furthermore, structure refinement using integrated intensities from one-dimensional profile fitting is demonstrated to be more accurate than simple peak-minus-background integration.

Energy-dispersive powder profile refinement using synchrotron radiation

1978 ◽  
Vol 11 (3) ◽  
pp. 165-172 ◽  
Author(s):  
A. M. Glazer ◽  
M. Hidaka ◽  
J. Bordas
Keyword(s):  
Synchrotron Radiation ◽  
Structural Parameters ◽  
Structure Refinement ◽  
Powdered Material ◽  
Instrument Function ◽  
Solid State Detector ◽  
Near Future ◽  
State Detector ◽  
Profile Refinement ◽  
Sample Environment

Results of powder-profile refinement using a solid-state detector with synchrotron radiation are presented. The data are collected very rapidly and the usual structural parameters are refined together with line-shape, zero error and instrument function. The results are in excellent agreement with previously published parameters. The rapidity and precision of the method means that it will be possible in the near future to find structural parameters of a powdered material in a few s or min and thus allow simultaneous structure refinement with changing sample environment.

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.

Betaine arsenate, (CH3)3NCH2COO · D3AsO4: structure refinement using multiple-wavelength synchrotron radiation data

1997 ◽  
Vol 212 (9) ◽  
Author(s):  
S. Kek ◽  
M. Grotepaß-Deuter ◽  
K. Fischer ◽  
K. Eichhorn
Keyword(s):  
Crystal Structure ◽  
Synchrotron Radiation ◽  
Room Temperature ◽  
Structure Refinement ◽  
Temperature Phase ◽  
Space Group ◽  
Radiation Data ◽  
Multiple Wavelength

AbstractThe crystal structure of deuterated betaine arsenate, (CHThe both paraelectric and ferroelastic room-temperature phase of betaine arsenate crystallizes in space group

X-ray Diffraction Studies of Polycrystalline Thin Films Using Glancing Angle Diffractometry

1988 ◽  
Vol 32 ◽  
pp. 311-321 ◽  
Author(s):  
R.A. Larsen ◽  
T.F. McNulty ◽  
R.P. Goehner ◽  
K.R. Crystal
Keyword(s):  
Thin Films ◽  
Deep Penetration ◽  
X Ray Diffraction ◽  
Parallel Beam ◽  
X Ray ◽  
Beam Geometry ◽  
Polycrystalline Thin Films ◽  
Glancing Angle ◽  
Parallel Beam Geometry

AbstractThe use of conventional θ/2θ diffraction methods for the characterization of polycrystalline thin films is not in general a satisfactory technique due to the relatively deep penetration of x-ray photons in most materials. Glancing incidence diffraction (GID) can compensate for the penetration problems inherent in the θ/2θ geometry. Parallel beam geometry has been developed in conjunction with GID to eliminate the focusing aberrations encountered when performing these types of measurements. During the past yearwe developed a parallel beam attachment which we have successfully configured to a number of systems.

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