Dear Kotaro, The same rule of line broadening was observed in beta phase of Mg(BH4)2, and was explained as ordering of twin domains, in other words microtwinning which creates a superstructure to the even,even,even subcell. If the twinning probability is not 100%, then the odd,odd,odd reflections broaden till they disappear. You may find an inspiration in
Acta Cryst. (2007). B63, 561-568 [ doi:10.1107/S0108768107022665<http://dx.doi.org/10.1107/S0108768107022665> ] Structure of unsolvated magnesium borohydride Mg(BH4)2 J.-H. Her<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Her,%20J.-H.>, P. W. Stephens<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Stephens,%20P.W.>, Y. Gao<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Gao,%20Y.>, G. L. Soloveichik<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Soloveichik,%20G.L.>, J. Rijssenbeek<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Rijssenbeek,%20J.>, M. Andrus<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Andrus,%20M.> and J.-C. Zhao<http://scripts.iucr.org/cgi-bin/citedin?search_on=name&author_name=Zhao,%20J.-C.> In Fullprof there are few models of line broadening, but I do not know whether any of them can be used for your case. In Topas you may create any model of line broadening using the macro language. Hope it helps Radovan Radovan Cerny Laboratoire de Cristallographie, DQMP Université de Genève 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : radovan.ce...@unige.ch URL : http://www.unige.ch/sciences/crystal/cerny/rcerny.htm De : rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] De la part de Kotaro SAITO Envoyé : vendredi 31 juillet 2015 09:15 À : Rietveld_l@ill.fr Objet : Selective peak broadening - interpretation and handling in FullProf Dear Rietvelders, There is two things I would like to ask. 1. Physical interpretation of selective peak broadening I have a difficulty in interpreting selective peak broadening in my TOF data of quaternary Heusler alloy. All peaks for all-odd hkl reflections show significant broadening (about 25% increase from the instrumental resolution for small d range and 100% increase for large d range). Other peaks for all-even hkl stay in the instrumental resolution for whole d range. If hkl reflections for one specific direction show broadening, it might be easier to interpret. But this time, it is not the case. (eg. 111 reflection shows significant broadening but 222 does not.) If I write the sample's chemical formula as ABCD, 4 sites in the Heusler alloy along [111] direction seems to be (A,B)-(C,D)-(C,D)-(A,B) with different site mixing ratio according to brief analysis. One thing I have noticed is that each lattice plane for all-odd hkl consists of one sublattice. For the case of 111 reflection, which is the easiest case, first plane at the origin consists only (A,B). Second plane consists only (C,D), and so on. This holds for other all-odd hkl reflections Does anyone know good literatures to get some hints for this? I have checked “Defect and Microstructure Analysis by Diffraction” by Snyder, Fiala, and Bunge, but I couldn’t find descriptions about selective peak broadening. 2. Handling selective peak broadening in FullProf The manual says “there is a number of size models built into FullProf corresponding to particular sets of reflections that are affected from broadening.” But I only find Size-Model=14 and -2 (to -9) in the manual for that purpose. Are there any models other than these? And, does anyone know what Size-Model=14 is? The manual only shows a result using Size-Model=14 (Figure 2) without any explanations. I have already tried Size-Model=-2 and it works well but not sufficient for 111 peak which shows the largest broadening. (and it does not gives me any physical interpretation, of course.) Best, Kotaro //================//================// Kotaro SAITO High Energy Accelerator Research Organization Institute of Materials Structure Science 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan //================//================// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>> Send commands to <lists...@ill.fr<mailto: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/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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