Difference between revisions of "Preferred orientation in EXPGUI/GSAS"
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is a bit more flexible, and is the one I would suggest starting with. | is a bit more flexible, and is the one I would suggest starting with. | ||
Slides at the bottom of the page give more info on both approaches. | Slides at the bottom of the page give more info on both approaches. | ||
Also, there are some hints & help can be found on the ccp14 website here: | |||
http://sdpd.univ-lemans.fr/du-sdpd/nexus/ccp14/web/solution/gsas/spher_h2.htm | |||
For Debye-Scherrer geometry, the spherical harmonics terms of omega, chi & phi should be set to (0,0,0). I'm told that the default values of omega, chi & phi (0,90,0) are appropriate for Bragg-Brentano diffraction. Also, according to "experience" (aka Bob Von Dreele), texture is "rare" for Debye-Scherrer data, changing these (0,0,0) terms is really needed. | |||
It is suggested to start with a low order number for the spherical harmonic correction, and slowly increase the order number. If preferred orientation is present, this should starting improving the fit. | |||
You can also see pages 141-144 of the GSAS Manual for a full description of the coordinate systems and Eulerian rotation angles used for spherical harmonics texture. | |||
or for more about Spherical Harmonics in GSAS, refer to: | |||
Von Dreele, R. B. (1997). Quantitative texture analysis by Rietveld refinement. J. Appl. Cryst. 30, 517-525. | |||
or | |||
for more about | |||
The slides below are taken from ''GSAS Parameters & Controls'' chapter of Brian Toby's excellent series of [http://www.aps.anl.gov/Xray_Science_Division/Powder_Diffraction_Crystallography/ web-based GSAS/EXGUI tutorials]. | |||
Revision as of 15:51, 12 September 2011
In GSAS/EXGUI has implemented 2 approaches to deal with preferred orientation
1) March-Dollase correction requires that you state specific hkl values.
2) Spherical harmonics correction (Orientational Distribution Function) is a bit more flexible, and is the one I would suggest starting with.
Slides at the bottom of the page give more info on both approaches.
Also, there are some hints & help can be found on the ccp14 website here: http://sdpd.univ-lemans.fr/du-sdpd/nexus/ccp14/web/solution/gsas/spher_h2.htm
For Debye-Scherrer geometry, the spherical harmonics terms of omega, chi & phi should be set to (0,0,0). I'm told that the default values of omega, chi & phi (0,90,0) are appropriate for Bragg-Brentano diffraction. Also, according to "experience" (aka Bob Von Dreele), texture is "rare" for Debye-Scherrer data, changing these (0,0,0) terms is really needed.
It is suggested to start with a low order number for the spherical harmonic correction, and slowly increase the order number. If preferred orientation is present, this should starting improving the fit.
You can also see pages 141-144 of the GSAS Manual for a full description of the coordinate systems and Eulerian rotation angles used for spherical harmonics texture.
or for more about Spherical Harmonics in GSAS, refer to:
Von Dreele, R. B. (1997). Quantitative texture analysis by Rietveld refinement. J. Appl. Cryst. 30, 517-525.
The slides below are taken from GSAS Parameters & Controls chapter of Brian Toby's excellent series of web-based GSAS/EXGUI tutorials.
