On 08/29/2018 04:15 AM, Le Bail Armel wrote:
Hi,
After the IUCr Monograph on Crystallography 13 (2002)
entitled "Stucture Determination from Powder Diffraction Data"
you may find in the preface :
"Although the Rietveld method of structure refinement from powder
diffraction data is often loosely considered to be synonymous with structure
determination, it is not. The Rietveld method only comes into play in the
final stage of the structure solution process when an approximate structural
model has been found."
WIF David, K Shankland, LB McCusker, C Baerlocher
A clear distinction having my complete agreement.
Armel
Armel,
Although the above statement may be generally true, I can provide a counter
example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E.
Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a
high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we
only had a powder - no single crystals. From data measured at ESRF, we used GSAS
to isolate the peaks of interest for the unknown phase, and used program TREOR
to autoindex the unknown and identify the impurity phases. We then extracted
intensities using the LeBail method, and determined the structure using direct
methods with program SIRPOW. The structure was then refined with GSAS. We were
even able to locate the H atom from Fourier maps!
Even 20 years ago, it was possible to determine the structure from X-ray powder
patterns.
Larry
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Please do NOT attach files to the whole list <alan.he...@neutronoptics.com>
Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
