The preferred orientation (PO) problem is recurrent at the rietveld_l.
This is normal since PO is one of the biggest problem...
Given that a neutron experiment is very expensive, some
recommendations should be inside of the powder neutron...
Armel is right that preferred orientation can often be a problem with X-ray data, but it is wrong to assume that this was indeed the case with Zhijian Fan's neutron data from LaNi4.25Al0.75. PO is not usually a problem with neutrons, unless you have very plate- or needle-like crystallites and then shake the sample to pack them. Was that the case ?
The reason FullProf asks "Are you really dealing with preferred orientation?" (the original question) is that you may get a slightly lower R-factor if you refine more parameters, but you should have a physical reason for doing that (as Peter Zavalij said). The objective of RR is not just to get the lowest possible R-factor :-)
Alan.
Dr Alan W. Hewat, Diffraction Group Leader.
Institut Laue-Langevin, BP 156X Grenoble FRANCE 38042
fax (33)4.76.20.76.48 tel (33)4.76.20.72.13 (or .26 Mme Guillermet)
<[EMAIL PROTECTED]>
http://www.ill.fr/dif/AlanHewat.htm
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