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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You can run that one from the main Fox directory.
Manual – FOX, Free Objects for Crystallography Wiki
When convergence is reached, a significant improvement of the fit is observed: Executable versions of GSAS are distributed more-or-less freely but the source code is not distributed. In the following sections, all the operations to start and run a refinement with EXPGUI are fully described in order to mwnual the reader be able to reproduce the result for the specific example.
Put a title to this experiment file say: Finally click Add atoms. See the FAQ for a few more details. The misfit is large as you will see. Repeat every time you want to update the old result with a new one. The refinement is described in detail step by step.
In the example, the phases are known a priory but that was just a test case! One of the problems in the quantification of the amorphous phase using the internal standard methods is that the standard may not be fully crystalline.
Someone may claim this result is expvui for publication but if you give a close look at the graphic profiles, you will see expguii the the fit of the background is still very poor Fig.
Manual last edited The site with everything structural: Modern Powder Diffraction Rev. Click on the LS Controls menu and put a number of cycles for the refinement I suggest The principal GSAS site is ftp: When convergence is reached, a significant improvement of the fit is observed: LST file which is huge now as it contains all the results of the refinement cycles, check the final weight estimates.
Factors to consider prior to data collection are the geometry of the diffractometer for Bragg-Brentano geometries it is important that the incident beam is kept on the sample at all angles to ensure a constant-volume condition. You can plot in space under below or in a new screen beside.
EXPGUI automatically goes to the last cycle of refinement and highlight expguo lines with the agreement factors. See this page on Fox support for CIF import. Repeat the described actions to see the plots after the next refinements cycles.
Please note that the data file QPA. This means that if the amnual is performed, the background usually has to be re-estimated and resubtracted several times during a refinement.
I suggest to set the initial values of the phase fractions to a large value Remember that you can create several of these objects simultaneously limited only by memory! GSAS You need to put in a folder the following files: Click New Column and highlight phase 1 and histogram in the first column and phase 2 and histogram in the second column, and save. Click New Column and highlight phase 1 and histogram in the first column and phase 2 and histogram in the second column, and save.
It is expgyi important to remember that these effects can be minimised by reducing the particle size or by using a more penetrating radiation, otherwise they should be corrected using for example the Brindley model.
Programs (downloads, links and basic instructions)
DAT are available upon request from the author. Here you will find information on the programs we use in our group – links to download sites and some starting points or links to fantastic getting started guides.
Although this is addressed to the beginner, it is strongly encouraged to time some time exgpui read the milestones papers by McCusker et al.
Another possibility with the background is to estimate it by linear interpolation between selected points between peaks and then subtracted. An advantage of the pseudo-Voigt is that it allows the Gaussian and Expgi components of the peak shape to be introduced in a physically intuitive way to model the overall line broadening which furnishes useful information about the microstructure of the sample McCusker et al.
Sample selection and preparation The example reported here is a full description of a Rietveld refinement using EXPGUI for the determination of the phase weights in a polyphasic mixture containing an amorphous phase. Remember me on this computer.
As you can see, the fit of the background is still very poor as well as the peak intensities. Let the procedure reach convergence. De la Torre, A. There are other codes e.