Solving crystal structures from powder diffraction data
TL;DR: In this article, high resolution powder data from both neutron and X-ray (synchrotron) sources have been used to estimate the possibility of direct structure determination from powder data.
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Abstract: High resolution powder data from both neutron and X-ray (synchrotron) sources have been used to estimate the possibility of direct structure determination from powder data Two known structures were resolved by direct methods with neutron and X-ray data With synchrotron X-ray data, the measured range of data was insufficient for a structure analysis, but the R-factor calculations showed the intensities extracted from the profile data to be of acceptable quality The results were used to estimate the largest structure that might be solved using routine techniques It was found that the limit would be near twenty atoms in the asymmetric part of a centro-symmetric structure
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Synchrotron X-Ray Powder Diffraction
Abstract: The application of synchrotron X-ray radiation to powder diffraction is described. A perfect Si double-crystal monochromator at the Cornell High Energy Synchrotron Source (CHESS) was used in conjunction with Si, Ge, LiF and Al2O3 analyzers to investigate resolution and intensity characteristics at selected wavelengths between 1.07 and 1.54 A. The results obtained with Ge at 1.54 A gave a resolution Δd/d of 5 × 10−4 at 2θ = 30°, falling to 2 × 10−4 at 2θ = 140°. Analysis of the peak shapes is described in detail, with particular emphasis on the asymmetry observed at angles below 50° due to axial divergence effects. With a simple correction to allow for these, the peak shapes are found to be well represented by a convolution of Gaussian and Lorentzian components, the respective peak widths of these being related to the intrinsic resolution and sample broadening effects. It is pointed out that the use of a crystal analyzer should eliminate shifts in the Bragg-peak positions owing to the displacement-type aberrations which occur with conventional focusing-type diffractometers. Except for a constant zero error, the mean discrepancy in observed and calculated peak positions between 0 and 90° for reference samples CeO2, Al2O3 and NiO is found to be only about 0.003°. Finally, some general remarks are made about the application of the Rietveld profile technique to structural analysis from synchrotron powder diffraction data.
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Structure determination of α -CrPO 4 from powder synchrotron X-ray data
TL;DR: In this paper, the structure of α-CrPO4 was solved from powder X-ray data obtained at the Brookhaven National Synchrotron Light Source, and confirmed by a Rietveld analysis of neutron data collected with the diffractometer Dla at the Institut Laue-Langevin, Grenoble.
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Data Collection Strategies for Constant Wavelength Rietveld Analysis
R. J. Hill,I. C. Madsen +1 more
TL;DR: In this article, the Rietveld method is used for the analysis of powder diffraction data and the entire pattern is calculated using a model for the positions of the peaks (the unit cell parameters), their intensities (dependent on the atomic positional and thermal parameters, preferred orientation, etc.) and their widths and shapes, together with a description of the background.
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