Dear Breogan,
just three small additions:
(i) .25 Å is a lot, if the lattice parameter in that direction is 4 Å,
but much less if it is 40 Å....
(ii) Definitely, as Peter indicated, partial exchange of guest molecules
could be responsible for the differences. This could then be indicated
by a broadening of the peaks .
(iii) If there is a texture as you have described, one could also
consider the possibility that differently oriented crystals in your
specimen have different lattice parameters. That is (effectively) the
case in the case of residual macrostress, but may be also conceivable
(as a slightly exotic case) in the case composition variations.... This
could be checked by measuring the lattice parameters in transmission and
reflection geometry.
Best regards
Andreas
On 05.02.2014 20:11, Breogan Pato Doldan wrote:
I would like to thank you both.
It is a small mismatch (about 0.25 A).
Due to the structure of the compound and its porosity it really makes
sense that the exchange of the guest inside the cavity can affect the
lattice.
Regards
------------------------------------------------------------------------
*De: *"Peter Stephens" <peter.steph...@stonybrook.edu>
*Para: *"Breogan Pato Doldan" <breogan.p...@udc.es>,
"rietveld_l@ill.fr" <Rietveld_L@ill.fr>
*Enviados: *Miércoles, 5 de Febrero 2014 11:55:59
*Asunto: *Re: Preferred orientation and lattice parameters
How much mismatch? If you're getting a good profile fit, I'd be
inclined to doubt that it is a consequence of preferred orientation.
You could mix your sample with another material (corundum powder,
cork) to try to reduce the degree of preferred orientation, and see if
that makes a difference.
Instead of a Le Bail fit, you could try a full Rietveld to see if the
powder really is the same phase as the single crystal. One could also
imagine that a powder would be more facile in exchanging solvent with
the environment, which could affect lattice parameters.
On Wed, Feb 5, 2014 at 1:37 PM, Breogan Pato Doldan
<breogan.p...@udc.es <mailto:breogan.p...@udc.es>> wrote:
Dear rietvelders,
I have carried out the single crystal resolution and the PXRD Le
Bail refinement of a Metal Organic Framework.
The compound crystalizes as needles and there is a clear in-plane
preferred orientation along the c-axis.
There is a mismatch between the single crystal and the Le Bail
refinement data in the lattice parameter c.
Could this mismatch be due to the preferred orientations?
Regards,
Breogán Pato Doldán,
Fundamental Chemistry Department.
Faculty of Sciences. University of A Coruña
Rúa da Fraga 10, 15008, A Coruña. Spain.
Tel: +34 981167000 ext. 2061 <tel:%2B34%20981167000%20ext.%202061>
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Max-Planck-Institut fuer Intelligente Systeme
(ehemals Max-Planck-Institut fuer Metallforschung)
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