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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A special attention is devoted to the refinement strategy which is of paramount importance to achieve a sound result. Repeat the same espgui Phase 2. The scattering contribution of any amorphous component possibly existing in the sample is a part of the with Mi and Vithe unit cell mass and volume, respectively. In the example, the phases are known a priory but that was just a test case!
Run powpref first and thereafter genles. Colella De Frede, Napoli GSAS General Structure Analysis System is a comprehensive system for the refinement of structural models to both x-ray and neutron diffraction data. There are other codes e.
The glass amorphous fraction must be determined indirectly with the aid of an internal standard Gualtieri, In the example the first peak of hydroxyapatite if found at about When convergence is reached, a significant improvement of the fit is observed: The specific problem is usually solved using an internal standard, suitably chosen, manuao is added in a known amount to the investigated mixture and treated as a mixture component itself.
Use large Damping factors 8 or 9. Flag the Extract Fobs flag for the reflection intensity extraction.
Repeat every time you want to update the old result with a new one. You can run that one from the main Fox directory. Flag the Extract Fobs flag for the reflection intensity extraction.
Finally click Add atoms. In the following sections, all the operations to start and run a refinement with EXPGUI are fully described in order to let the reader be able to reproduce the result for the specific example.
Structure models can be taken from crystal structure databases such as ICSD see http: Structure models The starting structure models were corundum from Ishizawa et al.
Manual – FOX, Free Objects for Crystallography Wiki
Click on Edit Background and chose the function type and number of terms. Log In Sign Up. 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. More complex systems with their problems of phase identification, chemical substitutions, microabsorption, preferred orientation, excessive peak overlap can only reduce the levels of accuracy and precision that can be attained.
You can change the numbers to give the section of the detector you want. To do this, go to the Constraints menu and select Profile. Click here to sign up.
Programs (downloads, links and basic instructions)
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. You can also exit through this menu. You can save a postcript file to print later. majual
The principal GSAS site is ftp: I suggest to set the expghi values of the phase fractions to a large value Unfortunately the fit of the background is not yet acceptable. This is a method to remove or minimise the curvature of peaks in the collected diffraction patterns.
The Preferences menu The Help menu gives you access to the “about box” of Fox, and you can toggle the use of tooltips. The final result with stadard deviation is: Cement and Concrete Res. Science Forum, Manua, automatically goes to the last cycle of refinement and highlight the lines with the agreement factors. The refinement is described in detail step by step.