Re: [sdpd] structure and structureless lattice determination

[Armel Le Bail <alb...@cristal.org>]

>Has any work been done comparing the lattice dynamics during a structural 
>transition for a sample (such as in situ heating) obtained using a 
>structureless and structure refinement? Such as cell volume during a 
>transition obtained with and without structure refinement.
>
>Any references?

You can find comparison with traditional cell parameter refinement
from previously extracted peak positions :
http://www.ccp14.ac.uk/poster-talks/iucr2002/
http://www.ccp14.ac.uk/poster-talks/iucr2002/sld040.htm

But finding a reference showing a serious comparison
of the cell parameters quality from either the Rietveld or the
Pawley/Le Bail methods, I don't know. The test results would
strongly depend on the data resolution and structure
complexity, and would not be possible in the case of
unkown structures (no Rietveld fit possible - but cell
parameters are remaining hypothetical until the Rietveld fit
becomes possible).

If all phases are well defined in your system, you may take
the risk to apply only the Pawley/Le Bail methods. However, be
prepared to a question from the reviewer of your manuscript,
something like "and what about a Rietveld refinement ?".

If some phase(s) in your system have not any confirmed crystal
structure, and you limit yourself to a Pawley/Le Bail fit, be prepared
to have your paper rejected, possibly. However, I have myself braved
that risk once successfully in the following paper, using the Pawley
method :-)
"Crystal structure and thermal behaviour of H2Ti3O7: a new
defective ramsdellite form from Li+/H+ exchange on Li2Ti3O7",
A. Le Bail and J.L. Fourquet, Mat. Res. Bull. 27, 75-85 (1992).

There was so few data (neutrons, large wavelength) that the
structure refinement would have been dubious as well. Some
intermediate phases during the thermal decomposition of
H2Ti3O7 remain a bit hypothetical... But nice evolutions of
(hypothetical) cell parameters and volumes are presented ;-).

Best,

Armel


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