Changeset 4960 for trunk


Ignore:
Timestamp:
Jun 15, 2021 1:36:25 PM (3 months ago)
Author:
vondreele
Message:

update documentation for "Texture implementation"

File:
1 edited

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  • trunk/GSASIIobj.py

    r4924 r4960  
    10841084For reducing the effect of texture in a structural refinement
    10851085there are entries labeled preferred orientation in each phase's
    1086 data tab. Two different
    1087 approaches can be used for this, the March-Dollase model and
    1088 spherical harmonics.
     1086data tab. Two different approaches can be used for this, the March-Dollase
     1087model and spherical harmonics.
     1088
    10891089For the March-Dollase model, one axis in reciprocal space is designated as
    10901090unique (defaulting to the 001 axis) and reflections are corrected
     
    10991099
    11001100The second method for reducing the effect of texture in a structural
    1101 refinement is to create a probability surface as an expansion in
    1102 terms spherical harmonic functions. Only functions consistent with
     1101refinement is to create a crystallite orientation probability surface as an
     1102expansion in terms spherical harmonic functions. Only functions consistent with
    11031103cylindrical diffraction suymmetry and having texture symmetry
    11041104consistent with the Laue class of phase are used and are allowed,
    1105 so the higher the symmetry
    1106 the fewer terms that are available for a given spherical harmonics order.
    1107 For use of this correction, select the lowest order that provides
     1105so the higher the symmetry the fewer terms that are available for a given spherical harmonics order.
     1106To use this correction, select the lowest order that provides
    11081107refinable terms and perform a refinement. If the texture index remains close to
    11091108one, then the correction is not needed. If a significant improvement is
     
    11111110gives an even larger improvement.
    11121111
    1113 To characterize texture in a material, one needs data collected with the
     1112To characterize texture in a material, generally one needs data collected with the
    11141113sample at multiple orientations or, for TOF, with detectors at multiple
    11151114locations around the sample. In this case the detector orientation is given in
    11161115each histogram's Sample Parameters and the sample's orientation is described
    11171116with the Euler angles specifed on the phase's Texture tab, which is also
    1118 where the texture type (cylindrical, rolling,...) and the sherical
     1117where the texture type (cylindrical, rolling,...) and the spherical
    11191118harmonic order is selected. This should not be used with a single dataset and
    11201119should not be used if the preferred orientations corrections are used.
     
    11321131about K and Chi-s is a rotation about J.
    11331132
     1133Three typical examples:
     1134    1) Bragg-Brentano laboratory diffractometer: Chi=0
     1135    2) Debye-Scherrer counter detector; sample capillary axis perpendicular to diffraction plane: Chi=90
     1136    3) Debye-Scherrer 2D area detector positioned directly behind sample; sample capillary axis horizontal; Chi=0
     1137            NB: The area detector azimuthal angle = 0 in horizontal plane to right as viewed from x-ray source & 90 at vertical "up" direction
     1138           
    11341139ISODISTORT implementation
    11351140------------------------------
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