Absolutely important that people understand that the Rietveld method is structure refinement and not solution, but as Larry points out sometimes you can get a more out of it if you’re clever… and have no other choice! Here’s a second example:
Stubbs et al., 2010, Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O], American Mineralogist 95 (8-9): 1132-1140 which is a bit of a brute-force approach to implying structures of some uranyl phosphates in a synchrotron heating experiment. Joanne Stubbs sorted through known structures of related materials and used observed trends in refinements to select similar structures to further investigate. Able to then postulate reasonable structures which then refined to the observed data and provided insight into this interesting group of materials. Not the standard way to employment of Rietveld Refinement and certainly not true structural solutions, but a smart, useful, and rather satisfying application nonetheless. Best- David David Elbert Hopkins Extreme Materials Institute Malone Hall Johns Hopkins University 3400 N. Charles St Baltimore, MD 21218 (410) 516-5049 elb...@jhu.edu > On Aug 29, 2018, at 12:09 PM, Larry Finger <larry.fin...@lwfinger.net> wrote: > > 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/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 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/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
