Search results
Results from the WOW.Com Content Network
Rietveld refinement is a technique described by Hugo Rietveld for use in the characterisation of crystalline materials. The neutron and X-ray diffraction of powder samples results in a pattern characterised by reflections (peaks in intensity) at certain positions.
The Wyckoff positions are named after Ralph Wyckoff, an American X-ray crystallographer who authored several books in the field.His 1922 book, The Analytical Expression of the Results of the Theory of Space Groups, [3] contained tables with the positional coordinates, both general and special, permitted by the symmetry elements.
The accuracy of this quantitative analysis of sample composition is affected by various factors. Many elements will have overlapping X-ray emission peaks (e.g., Ti K β and V K α, Mn K β and Fe K α). The accuracy of the measured composition is also affected by the nature of the sample.
The Scherrer equation, in X-ray diffraction and crystallography, is a formula that relates the size of sub-micrometre crystallites in a solid to the broadening of a peak in a diffraction pattern. It is often referred to, incorrectly, as a formula for particle size measurement or analysis.
[6] [3] The beam used in SAD is broad illuminating a wide sample area. In order to analyze only a specific sample area, the selected area aperture in the image plane is used. This is in contrast with nanodiffraction, where the site-selectivity is achieved using a beam condensed to a narrow probe. [3]
An X-ray diffraction pattern of a crystallized enzyme. The pattern of spots (reflections) and the relative strength of each spot (intensities) can be used to determine the structure of the enzyme. The relative intensities of the reflections provides information to determine the arrangement of molecules within the crystal in atomic detail.
XAS is an interdisciplinary technique and its unique properties, as compared to x-ray diffraction, have been exploited for understanding the details of local structure in: glass, amorphous and liquid systems; solid solutions; doping and ionic implantation of materials for electronics; local distortions of crystal lattices; organometallic compounds
The decadic absorbance of a scattering sample is defined as −log 10 (R+T) or −log 10 (1−A). For a non scattering sample, R = 0, and the expression becomes −log 10 T or log( 1 / T ), which is more familiar. In a non-scattering sample, the absorbance has the property that the numerical value is proportional to sample thickness.