[sdpd] Inappropriate

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

Hi,

Comments on a recent negative paper about the Le Bail
method (iterative application of the Rietveld decomposition
formula with cell restraints, but without structural
model, in order to extract intensities):

================================================
"Lattice parameter measurement using Le Bail versus structural
(Rietveld) refinement: A caution for complex, low symmetry
systems", V. K. Peterson, Powder Diffraction, 20 (2005) 14-17.

Abstract : The measurement of lattice parameters using the Le Bail
method  was shown to be inappropriate for a complex, low
symmetry, structure, even with high resolution synchrotron diffraction
data. The method failed as a result of ambiguous indexing in
the absence of constraints on diffraction intensities, that
arise when a structural model is used, combined with the large
number of reflections. A caution for the use of the Le Bail
and other whole-powder pattern decomposition methods is
presented, particularly for high reflection density data.
=============================================

Is that true ?

Yes, absolutely and obviously. The door was wide open
to such a conclusion. I certainly have written something
similar somewhere.

Other inappropriate conditions already described alsewhere:
the use of a negative background leading to negative intensities.

Best wishes,

Armel




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