A Minicomputer and Methodology for X-Ray Analysis

Parrish, W.; Ayers, G. L.; Huang, Ting

doi:10.1007/978-1-4613-3096-7_40

Cited by 11 publications

(3 citation statements)

References 4 publications

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“…The IBM Series/1 minicomputer X-ray analysis automation system was used for automated data collection (Parrish, Ayers & Huang, 1980, 1982. It permitted a number of all day/night runs without operator attention to be set up.…”

Section: Computer Automation and Data Reductionmentioning

confidence: 99%

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

Will¹,

Parrish²,

Huang³

1983

J Appl Cryst

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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.

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Section: Computer Automation and Data Reductionmentioning

confidence: 99%

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

Will¹,

Parrish²,

Huang³

1983

J Appl Cryst

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“…around the axis normal to the surface greatly improves the particle size statistics by bringing many more particles into reflecting positions (Parrish and Huang 1983). Oscillating the specimen over a small angular range has been used (Yukino and Uno 1986).…”

Section: Specimen Qualitymentioning

confidence: 99%

Accurate Measurement of Powder Diffraction Intensities Using Synchrotron Radiation

Parrish¹,

Hart²

1988

Aust. J. Phys.

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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. 11.. IntroductionRecent developments of synchrotron radiation powder diffraction methods have renewed interest in X-ray crystal structure refinement and determination using powder samples. Analyses using conventional X-ray tube focusing methods have had limited use and rather low precision mainly because of problems arising from the varying asymmetric profile shapes and the complex instrument function. In contrast, neutron diffraction powder data have simple Gaussian profile shapes and have been successfully used to determine hundreds of crystal structures by the Rietveld method.The synchrotron radiation parallel beam powder method has a simple constant instrument function and the patterns have high peak-to-background. It has important advantages over neutrons in the much higher intensity which allows recording a high quality pattern for structure analysis in a few hours, and in the easy wavelength selectivity to optimise the experiment.For a given sinO/A range, single crystal diffraction patterns have many more reflections than powder patterns. A number of reflections are intrinsically superimposed in powder patterns (e.g. 333/511), and there are usually many overlaps forming clusters of reflections. The experimental data must, therefore, be of the highest quality to approach single crystal analysis. Two related factors are also of the highest importance, the specimen preparation and the profile fitting procedure. These topics form the subject of this paper.A number of structures have been solved recently using different synchrotron radiation powder methods.

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“…All these functions are symmetric and some kind of asymmetry must be introduced to model a real X-ray peak. To allow for this asymmetry Parrish et al (1980) used three overlapping Lorentzians per peak in their profile fitting procedure.…”

Section: Introductionmentioning

confidence: 99%

Learned Peak Shape Functions for Powder Diffraction Data

Hepp¹,

Baerlocher²

1988

Aust. J. Phys.

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Aust. J. Phys., 1988,41,229-36 An algorithm is described for the determination of an experimental (learned) peak shape function, which has been used succesfully in crystal structure refinements from powder data. The function gives an optimal fit to almost any peak shape since it is not based on an analytical expression. It is determined from a single peak in a pattern by first fitting this peak with the proposed algorithm which ensures that the function is smooth and has only one maximum and two inflection points. The learned function is then normalised and decomposed into a symmetric and an asymmetric part. These are stored in tabulated form, permitting linear interpolation. As with an analytical function, a FWHM and asymmetry function describing the 26 dependence of the peak shape can be applied.

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A Minicomputer and Methodology for X-Ray Analysis

Cited by 11 publications

References 4 publications

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

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

Accurate Measurement of Powder Diffraction Intensities Using Synchrotron Radiation

Learned Peak Shape Functions for Powder Diffraction Data

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