Jaap wrote :
>Finally Armel, in my view an attempt the split the Rietveld community in
>two, i.e. in house X-ray and central facility neutrons, is artificial. By
>teh way did you note that someone called Mark Weller was on your neutron
>list as well. As far as I know, he has been working in Southampton for
>some time now. So there is hope for ordinairy university based scientist
>to use neutrons!
But the question was about using both. I don't know if Mark Weller
published combined X-ray and neutron refinements. Am I so far
from the truth if I estimate the number of published works combining
X-ray and neutron in a single refinement to, say less than 20 cases ? I
would like to see, in the 10 next years, this number increase to, say, 1000,
for being convinced that this is really a way that should be adopted.
But I do not believe it. Such combined refinements will stay anecdotal
(or elitist if you prefer), reserved to specific cases, or to those having
easy access to both radiations.
Nobody among the readers has already tried to combine both kind of
data and finally preferred to publish the neutron data only, for
avoiding pain and lightening the discussion ?-)). I will not send the
first stone... I do have published separate neutron and X-ray refinements
and compared the results (JSSC 89, 1990, 282-291, or Eur. J. Solid
State Inorg. Chem. 15, 1988, 551-563). This is not really a problem
to publish independent refinement on neutron and X-ray data. I do
agree that in a few cases (may be the 20 cases cited above), a combined
refinement was really fruitful (speaking of V atoms comes certainly to
mind, but why not prepare an isomorphous sample without V ?-).
Rare is not always beautiful.
All the best,
Armel
PS- take the Rietveld Round Robin PbSO4 X-ray pattern and omit
the O atoms, you will have RB~15%. Make a Fourier difference
and you will see if the "light" atoms are so light, when using good data.
When I remember my crystallography courses 25 years ago, maybe,
I see the decomposition of the structure factor by atom pairs. O atoms
are involved not only in O-O pairs, but also in Pb-O and S-O pairs,
fortunately. In many cases, like Li2TbF6, or LiSbWO6 and so on, I had
no difficulty to see the Li atoms in the Fourier syntheses, by X-ray.
Hence not a large need of neutrons, but in a few cases.
Armel Le Bail - Universite du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/
