1) Wrong geometrical corrections (LP factor, etc.)
2) Beam overflow at low angles
3) Surface roughness effects
4) Absorption, sample thickness, etc.
5) Correlation with the background trace
etc.
Have you carefully controlled all these effects?
Try collecting in the same experimental conditions a standard sample: Si, quartz or LaB6, and see!
Regards
N.Masciocchi
At 18.03 31/01/05, you wrote:
I'm getting started with GSAS and in all my refinements i get stuck with negative thermal parameters no matter what i do. Is there any tip to get rid of this problem or maybe do i need to learn a little bit more?
Thanks
Norberto Masciocchi, Prof.
Dipartimento di Scienze Chimiche e Ambientali,
Universit� dell'Insubria, via Valleggio 11, 22100 Como (Italy)
Phone: +39-031-326227; FAX: +39-031-2386119
[EMAIL PROTECTED]
http://scienze-como.uninsubria.it/masciocchi/
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Y �sa es en el fondo la mejor definici�n del homo sapiens. (J.Cort�zar)
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