ensuite de mener un affinement de structure dans de bonnes conditions. En , Rietveld ,  a introduit une procédure d’affinement de structure à partir. 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. The powder diffraction option (Rietveld refinement + leBail technique) was implemented in Dušek,M., Petříček,V., Wunschel,M., Dinnebier,R.,E. & Van .
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Rietveld refinement is a technique described by Hugo Rietveld for use in the afifnement 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 height, width and position of these reflections can be used to determine many aspects of the material’s structure.
Rietveld refinement – Wikipedia
The Rietveld method uses a least squares approach to refine a theoretical line profile until it matches the measured profile. The introduction of this technique was a significant step forward in the diffraction analysis of powder samples as, unlike other techniques at that time, it was able to deal reliably with strongly overlapping reflections.
This terminology will be used here although the technique is equally applicable to alternative scales such as x-ray energy or neutron time-of-flight.
The only wavelength and technique independent scale is in reciprocal space units or momentum transfer Qwhich is historically rarely used in powder diffraction but very common in all other diffraction and optics techniques.
The shape of a powder diffraction reflection is influenced by the characteristics of the beam, the experimental arrangement, and the sample size and shape.
In the case of monochromatic neutron sources the convolution of the various effects has been found to result in a reflex almost exactly Affniement in shape. At very low diffraction angles the reflections may acquire an asymmetry due to the vertical divergence of the beam.
Rietveld used a semi-empirical correction factor, A s to account for this asymmetry. At a given position more than one diffraction peak may contribute to the profile. The width of the diffraction peaks are found to broaden at higher Bragg angles. This angular dependency was originally represented by.
In powder samples there is a tendency for plate- or rod-like crystallites to align themselves along the axis of a cylindrical sample holder. In solid polycrystalline samples the production of the material may result in greater volume fraction of certain crystal orientations commonly referred to as texture.
In such cases the reflex intensities will vary from that predicted for a completely random distribution. Rietveld allowed for moderate cases of the former by introducing a correction factor:.
The principle of the Rietveld Method is to minimise a function M which analyzes the difference between a calculated profile y calc and the observed data y obs. Rietveld defined such an equation as:.
From Wikipedia, the free encyclopedia. Retrieved from ” https: Crystallography Diffraction Neutron-related techniques.