> We are still trying to tackle the problem of accurately fitting X'Pert Pro
> XRD data with fundamental parameter peaks. There seems to be some kind of
> difference between actual Soller slit acceptance angles and the values
> required by XFit. We have two sets of Soller slits : 0.04 rad and 0.02 rad.
> If I can still convert angles correctly (I'm beginning to doubt this), this
> means acceptance angles of 2.3 deg and 1.15 deg. When these values are
> applied to our spectrum of corundum (just a test sample we've taken that we
> intend to replace by silver behenate or some other standard), the peaks come
> out way too small and we need values of around 6 deg and 3 deg to get the
> data to come out right. I don't suppose the strain or crystallite size
> corrections should be that important (or are they ?) so we didn't use these.
>
> Anybody ?
>
> Sven Van den Berghe
Refining on Crystallite size and strain in XFIT as part of
fundamental parameters fitting is important.
Refer to the XFIT tutorials at:
Fitting Lab XRD data using Fundamental Parameters Approach
http://www.ccp14.ac.uk/tutorial/xfit-95/fun1.htm
Fundamental Parameters Peak Profiling on lab XRD data for
Auto-Indexing and Structure Solution
http://www.ccp14.ac.uk/tutorial/xfit-95/liti/rwfunpar.htm
(this also shows you how to constrain the crystallite
size and strain parameters to all the fitted peaks)
--------
My main concern is about using Corundum as a good
standard to get a lock on these parameters(?).
May favourite would be to use Annealed Cubic (IA3) Y2O3 -
10.6 Angstrom - which is very good for looking into
alignment and the machine settings. Especially as it
has some good relatively low angle peaks which would be
most affected by the Sollers Slits.
------
Also, with the old Philips 1050 style of diffractometer with
wide optics, the diffracted beam sollers could be taken out
easily. Is it possible to physically measure the acceptance
angle? One of the major points of fundamental parameters
profile fitting is you are refining on real physical parameters
with respect to the geometry elements of the instrument. So
they can be verified by physical measurement.
Cheers,
Lachlan.
--
Lachlan M. D. Cranswick
Collaborative Computational Project No 14 (CCP14)
for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703 Fax: +44-1925-603124
E-mail: [EMAIL PROTECTED] Ext: 3703 Room C14
http://www.ccp14.ac.uk
