Dear Davide,
This is obtain from the help of X'Pert HighScore Plus, I have write the
formula due to image mode.
Lorentz-Polarization correction:
The Lorentz-Polarization factor LP is:
*LP= [1 + POL Cos(2theta).Cos(2theta)]/[Sintheta.Sintheta.Costheta]*
POL describes the additional polarization factor when a monochromator is
used:
POL=Cos(2theta_m).Cos(2theta_m)
where 2/θ/_m *(2theta_m)* is the diffraction angle of the monochromator.
This formula is valid for mosaic monochromators, like pyrolytic graphite.
The incident-beam monochromators have less mosaicity, they are between a
mosaic and a perfect single crystal. A value close to that of a mosaic
crystal is most likely.
For a perfect single crystal the following formula applies:
POL=Cos(2theta_m)
For the *X'Celerator monochromator* the formula:
POL = 1/cos² 2/θ/ _XCmon
is used, where 2/θ/ _XCmon is the diffraction angle of the X'Celerator
monochromator.
Table of *POL* values for powder diffraction *monochromators* according
to the formulas above:
Monochromator Wavelength [Å] Material Reflection /d/-spacing [Å]
2/θ/_m [°] POL
Cu diffr. beam 1.54184 C (002) 3.3570 26.55 0.800
Cu X'Celerator 1.54184 C (002) 3.3570 26.55 1.25
Co diffr. beam 1.78897 C (002) 3.3570 30.91 0.736
Co X'Celerator 1.78897 C (002) 3.3570 30.91 1.359
Cr diffr. beam 2.29100 C (002) 3.3570 39.90 0.588
Mo diffr. beam
old *(< 2002)* 0.71073 C (004) 1.6785 24.45 0.829
Mo diffr. beam
new *(≥ 2002)* 0.71073 C (002) 3.3570 12.13 0.956
Fe diffr. beam 1.93735 C (002) 3.3570 33.54 0.695
Cu hybride 2-bounce 1.54184 Ge (220) 2.0002 45.30 0.494
Co hybride 2-bounce 1.78897 Ge (220) 2.0002 53.13 0.359
Cu incid. beam (K-Alpha1 only) 1.54056 Ge (111) 3.2660 27.28 0.790
- 0.888
Co incid. beam (K-Alpha1 only) 1.78897 Ge (111) 3.2660 31.79 0.722
- 0.850
All K-beta filters All wavelengths - - - -
1.000
All mirrors All wavelengths - - - - 0.999
The */PANalytical/* diffracted beam monochromators (flat and curved) are
all made of pyrolytic graphite. The reflection used is C(002) for Cu,
Co, Cr and Fe. For Mo the C(004) reflection was used, a newer design
changed to the (002) for more intensity. The incident beam monochromator
(Johansson type) is made of germanium. The reflection used for CuK/α/1
and CoK/α/1 is Ge(111).
In our case, we use a Nickel Filter, then the polarization is equal to 1.000
Davide Levy wrote:
Dear all,
which is the best value for the polarization in GSAS when you have a data
collected on 'XPERT diffractometer with a Xcellerator detector?
Thank you
Davide
--
Dr. François Goutenoire
Maître de Conférences, IUT Le Mans
Laboratoire des Oxydes et Fluorures, UMR6010
Avenue Olivier Messiaen,
72085 Le Mans, Cedex 9
