This exercise provides a tutorial example of how to use the GSAS software package with the EXPGUI interface to perform Rietveld analysis. The following pages show how to use EXPGUI to perform the same tutorial refinement for Nickel powder, presented in the GSAS manual. The GSAS manual is included with the distributions of the GSAS programs (see above). The manual can be found EXPGUI website.
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For a Rietveld refinement, it is essential that the powder data is properly collected. Click on the Scaling menu and unflag the Refine option of the Scale Histogram scale factor.
Flag the Extract Fobs flag for the reflection intensity extraction. Everything which can be seen in the Fox main window is saved. Practical advices and suggestions are also given together with literature citations. Data collection Prior to the quantitative phase analysis one is generally sopposed to have a preliminary qualitative phase analysis in order to determine: For a Rietveld refinement, it is essential that the powder data is properly collected.
A guide training exercise of quantitative phase analysis using EXPgui_百度文库
The conversion can be achieved using one of the many freeware avialable programs. Unfortunately the fit of the background is not yet acceptable. It is time now to define a background function and prepare it for the refinement. Expgiu complex systems with their problems of phase identification, chemical ecpgui, microabsorption, preferred orientation, excessive peak overlap can only reduce the levels of accuracy and precision that can be attained. Especially microabsorption effects are very hard to handle.
The manual is what you should cite when publishing a structure refined with GSAS [and of course you will cite it: I personally use ConvX www.
Programs (downloads, links and basic instructions)
Click on the Scaling menu and unflag the Refine option of the Scale Histogram scale factor. As you can see, the fit of the background is still very poor as well as the peak intensities.
Remember mannual change 1 or a couple of things and refine and probably allow only small changes – damping to 8 or 9. Documentation is found at B. To get the refinement started you need three files: Further tutorials and information on GSAS can be found on: Larson and Robert B.
On the other hand, the peak positions seem fairly good that is the peaks are correctly centred for both phases. Remember that you exxpgui create several of these objects simultaneously limited only by memory! At the end of the Rietveld process, the refined phase fractions are converted into weight fractions and rescaled to the values of the original mixture by the ratio between the refined Xs,c and the known Xs amount of added standard.
There are other codes e. You can run that one from the main Fox directory.
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To my experience ,when there is just one preferred orientation direction it is better and safer to use the MD model because the SH model gives a better fit but the physical meaning can be lost if too many coefficients of the polynomial manuxl refined. The final result with stadard deviation is: Do a speedtest of Fox takes about 2mn. The manual is what you should cite when publishing a structure refined with GSAS [and of course you will cite it: In some cases e.
The interest in this area is predicted to increase if one considers that the appealing nano-science world describes crystal-size dependent properties of systems that cover a broad range between the crystalline and the amorphous state. Friday 16 September Site to search This website. They are still pretty large at this point. GSAS General Structure Analysis System is a comprehensive system for the refinement of structural models manuaal both x-ray and neutron diffraction data.
You can change the numbers to give the section of the detector you kanual. A special attention is devoted to the refinement strategy which is of paramount importance to achieve a sound result. In Mineralogy 20, The scattering contribution of any amorphous component possibly expgul in the sample is a part of the background and the above normalisation equation does not include it.
Programs (downloads, links and basic instructions) | UNSW Chemistry
Modern Powder Diffraction Rev. The glass fraction is then 1 — 0. See the FAQ for a few more details. Science Forum, De La Torre, A. Structure manuwl can be taken from crystal structure databases such as ICSD see http: The misfit is large as you will see.
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