Variable entrance and receiving slits seem to be the current best choice
for commercially available powder diffractometers (conventional X-rays,
Bragg-Brentano) in the scope of good resolution and limited problems in
whole pattern fitting.
Among the best patterns I have treated recently :
LaB6 Al2O3
NIST SRM 660 NIST SRM 1976
U 0.00310 0.00444
V 0.00112 0.00149
W 0.00112 0.00156
Rp 8.9% 8.1% (background subtracted,
peak only)
7.9% 5.9% (background not
subtracted, peak only)
2-Theta range 18-148 24-147.5
2-Theta Degrees
FWHM values : 0.0381 0.0452 24
in 2-Theta 0.0405 0.0480 30
degrees 0.0481 0.0569 50
0.0585 0.0693 70
0.0731 0.0867 90
0.0951 0.1130 110
0.1333 0.1589 130
0.1948 0.2327 146
Both patterns measured in the same conditions (CuKalpha1+2 ; same slits ;
conventional X-ray tube..).
Fit with a Rietveld program in "lFobsl" extracting mode (no structure).
Questions are :
1- One can hear sometimes that variable slits lead to irreproducible
measurements, is that true ?
2- Has anybody better results with an in-laboratory apparatus (eventually
Kalpha1) on both aspects (FWHM and Rp) for theses well known standards ?
(message distributed on sci_tech_xtal and rietveld@xtal.cmc.uab.edu)
Armel LE BAIL armel@ONE.univ-lemans.fr
Laboratoire des Fluorures
Universite du Maine
72017 Le Mans Cedex
FRANCE