> I have a philosophic question for you: the structure obtained by NPD
> are better than the ones found by XRPD? I explain a little bit more my
> question, I studied a MgAlFeO4 spinel both by NDP and XRPD from RT to
> 1000°C.
Rather than continue to discuss philosophy, the following paper seems
relevant. Look to see why neutrons rather than X-rays were chosen for this
particular problem. Perhaps the authors will themselves comment via the
Rietveld list.
"Cation partitioning versus temperature in (Mg0.70 Fe0.23) Al1.97 O4
synthetic spinel by in situ neutron powder diffraction".
Pavese, A.; Artioli, G.; Russo, U.; Hoser, A.(1999)
Physics and Chemistry of Minerals 26, 242-250
> Precision of CW neutron machines is
> frequently not so high as X-ray diffractometers, but this problem is
> masked in Rietveld by extremely (artficialy) low e.s.d.'s of lattice
> parameters.
Hmm?? With CW neutron machines, the wavelength is sometimes not well
defined so there may be a scale error in the refined lattice parameters.
Lattice dimensions are then precise but not accurate until they have been
corrected for this scale error. But that has nothing to do with the
accuracy with which the atom coordinates are determined.
Of course, if you can collect both neutron and x-ray data, especially
synchrotron data, on similar samples at the same temperature, you may
improve accuracy by performing a combined refinement, but that is often
not possible. And again, it was not the question - "Neutron or X-ray" (for
this particular metal oxide).
______________________________________________
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
<[EMAIL PROTECTED]> +33.476.98.41.68
http://www.NeutronOptics.com/
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