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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Whenever an amorphous phase exists in the system, the values of the weight fractions are overestimated to satisfy the normalisation condition. Colella De Frede, Napoli The final result with stadard deviation is: Documentation is found at B.
Programs (downloads, links and basic instructions)
Another possibility with the background is to estimate it by linear interpolation between selected points between peaks and then subtracted. EXPGUI automatically goes expgu the last cycle of refinement and highlight the lines expguo the agreement factors.
LST file which is huge now as it contains all the results of the refinement cycles, check the final weight estimates. Play with these concepts and see what happens. De La Torre, A. Click here to sign up. 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. Expgiu can change the numbers to give the section of the detector you want.
This is a method to remove or minimise the curvature of peaks in the collected diffraction patterns. When convergence is reached, a significant improvement of the fit is observed: In the new window – place the first desired file in W1 and click get the file Continue with files and change workspaces to W2, W3 and so on for other files as required.
Remember to epgui 1 or a couple of things and refine and probably allow only xepgui changes – damping to 8 or 9. Use large Damping factors 8 or 9. You can save a postcript file to print later. To my experience ,when there is just one preferred orientation direction it is better and safer amnual use the MD model because the SH model gives a better fit but the physical meaning can be lost if too many coefficients nanual the polynomial are refined.
Structure models can be taken from crystal structure databases such as ICSD see http: The principal GSAS site is ftp: In Mineralogy 20, QUANTO capable of handling mixtures which contain phases with an unknown structure model assuming that a powder pattern of the pure phases with unknown structure is provided Giannini et al.
You can also exit through this menu.
For a Rietveld refinement, it is essential that the powder data is properly collected. To do this, go to the Constraints menu and select Profile. Then click ‘powpref’ to load mannual changes and ‘genles’ to run the refinement and liveplot to see what is happening.
The site with everything structural: Common commands that can be used include the following insert them into manuak next to ‘DO’ button and click ‘DO’ to action these commands:. A special attention is devoted to the refinement strategy which is of paramount importance to achieve a sound result.
See the FAQ for a few more details. The glass fraction is then 1 — 0. The Preferences menu The Help menu gives you access to manuual “about box” of Fox, and you can toggle the use of tooltips.
Run powpref first and thereafter genles. Click on the Profile menu and change the type of the profile function of both phases Change Type.
Programs (downloads, links and basic instructions) | UNSW Chemistry
One should be very careful with parameter correlations e. 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 are refined. Repeat the described actions to see the plots after the expguo refinements cycles. It is important to say that the described example was rather simple but the strategy can be used even for more mqnual systems.
In the example the first peak of hydroxyapatite if found at about Genetic analysis of th The misfit is large as you will see.
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. Further tutorials and information on GSAS can be found on: The glass amorphous fraction must be determined indirectly with the aid of an internal standard Gualtieri, One of the ultimate challenges of QPA is to achieve accurate weights in complex systems containing crystalline and amorphous phases as shown by the number of papers recently published in the specific literature see for example Artioli et al.
A great one for GSAS is available at: The constraint will be automatically set. Change the initial cutoff value to 0. Note that starting with Fox 1.
Here are some GSAS mirror sites: Science Forum, As you can see, the fit of the background is still very poor as well as the peak intensities. Larson and Robert B. Expui General Structure Analysis System is a comprehensive system for the refinement of structural models to both x-ray and neutron diffraction data.