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Re: [sdpd] negative debye-waller factors.
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<font size=3>At 08:48 AM 3/19/01 +0100, you Dezzane wrote:<br>
>dear colleagues,<br>
><br>
>one short question abour refinements:<br>
><br>
>, <br>
>BP46, domaine univeristaire<br>
>38402 GRENOBLEsometimes, usually when the diffraction patterns
is<br>
>beautifull (large grain size), the overall<br>
>Debye-waller factor used for X-ray refinement always<br>
>goes to negative values. What is the origin of this<br>
>and how to solve it ?<br>
><br>
Does the same thing happen with neutron powder diffraction patterns
of the same material? If not ( as I suspect) the problem is likely to
absorption due to surface roughness, which reduces the intensity of
low angle reflections more than the high angle ones. And that, of
course, leads to negative "temperature factors". See Sparks
Kumar, et al., In Advances in X-ray Analysis (1992)<br>
<br>
Hope this helps,<br>
Ray Young </font><br>
<div>Prof. R. A. Young</div>
<div>School of Physics</div>
<div>Georgia Institute of Technology</div>
<div>Atlanta, GA 30332 USA</div>
<div>Tel: 404-894-5208</div>
<div>FAX 404-894-9958</div>
<div>e-mail r.young...@physics.gatech.edu</div>
<br>
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