gsas question

Ram SESHADRI ( (no email) )
Thu, 4 Sep 1997 18:52:54 -0600

>I am doing a dual refinement of xray and neutron data using gsas. The
>xray data was collected at room temperature and the neutron data was
>collected at 4K. The problem is that the 2 histograms share the same atom
>parameter file where the temperature factors are located for each atom.
>Since the different data was collected under such different conditions the
>temperature factors should be quite different. Is there any way to
> vary the temperature factors separately for each histogram?
>
>thanks,
>Laurel Basciano

The only Rietveld program that can help you is XND which will allow you to
declare different temperatures for the different histograms and include the
temperature dependence in the structural model.

See for example:

R.Seshadri, C.Martin, M.Hervieu, B.Raveau and C.N.R.Rao,
Structural evolution and electronic properties of La1+xSr2-xMn2O7,
Chem. Mater. 9 (1997) 270.

XND can be found at http://rx-crg1.polycnrs-gre.fr/public/xnd/xnd.html

but it cannot help you if the neutron data is TOF.

You worry about thermal parameters being different: The lattice parameters
should be vastly different between 4K and RT (unless you have a ZTE material).

Cheers

Ram

-- Dr. Ram SESHADRIAnorganische Chemie, Johannes Gutenberg UniversitatBecherWeg 24, Mainz D55099 Germany. Phone(FAX): +49 6131 39 4417(5380)email/net: seshadri@Indigotrem1.chemie.uni-mainz.de