Dear Lennart, In the microstructure analysis you aim at, one should take into account different contributions to the peak broadening: instrumental, crystal size, microstrain, and stacking faults. Using only two reflections (111 and 200) one can not allow for all these contributions independently and correctly. You should use as many reflections as possible from the whole powder pattern range up to the highest diffraction angles you can reach. Regarding the model of stacking faults in MAUD, it has a shortcoming in that it does not allow for the influence of faults on peak intensities. See our recent discussion: http://www.mail-archive.com/rietveld_l@ill.fr/msg05464.html http://www.mail-archive.com/rietveld_l@ill.fr/msg05469.html
Best regards, Leonid ******************************************************* Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660036, Akademgorodok 50/24, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid ******************************************************* ________________________________ From: Lennart Leich <lennart.le...@gmail.com> To: Rietveld_l@ill.fr Sent: Friday, March 20, 2015 11:30 PM Subject: Determination of Microstrain using MAUD Hello everyone, first I want to introduce myself. My name is Lennart Leich, I am 24 years old and I study mechanical engineering at the „Ruhr-Universität-Bochum“ in Germany. My area of specialisation is materials science and materials engineering. At the moment I writing my bachelor thesis with the topic: „Determination of the stacking fault energy of different fcc metals using X-ray’s” at the chair of materials engineering. As microstructure analysis using diffraction is not well known at our institute we start powder diffraction using bragg-brentano geometry on the pure elements nickel, gold and copper and later on a chrome-nickel steel. We want to determine the stacking fault energy by comparing diffractograms of annealed and cold-worked powders as described in [1]. I plan to do Rietveld Refinement using the Software MAUD to determine the microstrain. Steps in MAUD: 1. load file data of diffractogram *.xy, *.cif and the file of instrumental broadening (MAUD tutorial – Instrumental Broadening Determination is already done) into MAUD 2. refine the (111) and (200) peak separated 3. free parameters for background, scale, basic phase and refine. finally free parameters for Line-Broadening model and the size-strain model (both Popa) and refine. Is my approach generally correct? Is it necessary to have “good” starting parameters for refinement, which I have to calculate previously, to be physically correct? As you all know and I have learned require such Refinements a lot of experience, which I not have. I think one occuring problem during refinement is to distinguish, wether a refinement is physically correct or just a “good” mathematical function, that describes the diffractograms shape. Therefore I subscribe to this mailinglist to discuss some of my problems regarding my work. Thanks in advance. Best Regards Lennart Leich [1] R. P. Reed and R. E. Schramm - „Relationship between stacking-fault energy and x-ray measurements of stacking-fault probability and microstrain“
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