Date: Wed, 30 May 2001 19:30:14 -0800 To: rietveld_l@ill.fr From: Sergey Ushakov [svushakov@ucdavis.edu] Subject: spherical harmonics in GSAS question Dear All, Could somebody give me a hint on what should be omega, phi and chi angles ideally for Bragg-Bretano geometry (or tell why they should change)? Thanks in advance, Sergey ---------------------------------- Sergey Ushakov post-doc University of California at Davis Thermochemistry Facility Dept. of Chem.Engr.&Mat.Sci. One Shields Ave., Davis, CA 95616 ph 530/754-5863 fax 530/752-9307 |
Date: Thu, 31 May 2001 10:42:23 -0400
From: "Brian H. Toby" [Brian.Toby@nist.gov]
Organization: NIST Center for Neutron Research
To: rietveld_l@ill.fr
Subject: Re: spherical harmonics in GSAS question
Under normal circumstances, you can leave the spherical harmonics
orientation angles as zero. Their purpose is for pole figure analysis,
where you are doing multiple measurements, with your sample in different
orientations (or with detectors in various positions relative to your
sample).
Brian
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Brian H. Toby, Ph.D. Leader, Crystallography Team
Brian.Toby@NIST.gov NIST Center for Neutron Research, Stop 8562
voice: 301-975-4297 National Institute of Standards & Technology
FAX: 301-921-9847 Gaithersburg, MD 20899-8562
http://www.ncnr.nist.gov/xtal
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Date: Thu, 31 May 2001 10:43:56 -0600 To: rietveld_l@ill.fr From: vondreele@lanl.gov (Bob Von Dreele) Subject: Re: spherical harmonics in GSAS question Dear Sergey (& All), The default values of omega, chi & phi (0,90,0), which you will find under 'A' in histogram editing, are appropriate for Bragg-Brentano diffraction geometry. For Debye-Scherrer geometry these should be set to (0,0,0). Since experience has shown that texture is "rare" for D-S data, changing these is rarely needed. The sample rotation angles found in the spherical harmonics texture menu are only needed for "full" texture analysis to correct for small sample orientation errors. If you "tilt" the sample then the appropriate values must be changed to reflect the rotation of the sample. See p141-144 of the GSAS Manual for a full description of the coordinate systems and Eulerian rotation angles used for spherical harmonics texture. Bob Von Dreele |