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Re: [sdpd] Indexing problem
Dear Cristian,
I do not know what is your compound, but looking on your webpage I have
seen that one of the themes of your laboratory (even if you are listed
with other subject) is the interaction of hydrogen with the solid. Is
not your compound a metal hydride? In that case you can imagine that the
compound has desorbed during the data collection, so you have different
lattice parameters at low and high 2theta regions. And maybe even
different crystal symmetry ...
Best wishes
Radovan
>Dear all,
>
>I encounter a (serious) problem when trying to index an X-ray powder
>pattern. The data was measured on a good diffractometer (Philips X-
>celerator, Cu Kalpha1;-Brag-Brentano geometry) (lowest FWHM~0.06 °) with
>a step of 0.016° and a lot of counting time. The sample has a perovskite
>like structure and undergoes a number of structural transitions when
>heating. Triclinic at room temperature (I have refined this one), unknown
>intermediary temperature phase, and a tetragonal high temperature phase
>(I have refined this one too). When indexing with the majority of the
>available software (Dicvol, Treor, Ito&) alone or in the Crysfire suite,
>in the front of the list I get a monoclinic cell a=7.86 b=7.68 c= 7.72
>A and Beta~90.3° with rather good agreement factors (M20 about 180).
>Refining the cell in FullProf, gives a perfect fit for the low 2Theta
>pattern (2Theta<80°), but at high 2Theta values there are some shifts in
>the positions or the reflections. I have thought that this could came
>from some instrumental error, but the tetragonal high temperature phase
>give a perfect fit even in this are, so I have excluded this possibility.
>
>Is someone has any idea or maybe has encountered the same kind of
>problem, please help me. Thank you in advance
>
>=====
>Cristian PERCA
>Laboratoire de Physico-Chimie de l'Etat Solide
>Bât. 414 - Université Paris XI
>91405 ORSAY Cedex - France
>http://www.u-psud.fr/chimsol
>Tél : 01 69 15 48 04
>cristian.perca...@lpces.u-psud.fr
>cristianperca...@yahoo.com
>
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>Yahoo! Groups Links
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--
Radovan Cerny
Laboratoire de Cristallographie
24, quai Ernest-Ansermet
CH-1211 Geneva 4, Switzerland
Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08
mailto : Radovan.Cerny...@cryst.unige.ch
URL : http://www.unige.ch/sciences/crystal/cerny/rcerny.htm
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