Dear Radovan and Leonid,
Thanks for your comments.
Both papers are very interesting and seem to contain good hints for my case.
Now I am confusing when I compare peak width vs. 2th in constant wave profiles
and peak width vs. d in TOF.
When I plot FWHM/d vs. d, FWHM/d of all-odd peaks increases with increasing d.
(Note these FWHM are obtained with multiple peak fitting with simple Gaussian.)
In other words, peak broadening is large for small hkl peaks.
Here is the plot. (not an attachment file!)
https://www.dropbox.com/s/uzm0fv3q8ljoq5o/Layout0.pdf?dl=0
On the other hand, for example Fig.3 in Leonid’s paper
(http://dx.doi.org/10.1107/S00218898114X), peak broadening is larger for
large 2th, which means large hkl peaks.
If the peak broadening in my TOF data has a similar origin as two papers which
Radovan and Leonid showed, is it acceptable to have such different hkl
dependence between TOF and 2th data? Or do I miss some basic points about
diffraction?
Best regards,
Kotaro
//////
Kotaro SAITO
High Energy Accelerator Research Organization
Institute of Materials Structure Science
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
//////
> 2015/07/31 17:13、Radovan Cerny のメール：
>
> 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 ]
>
> Structure of unsolvated magnesium borohydride Mg(BH4)2
>
> J.-H. Her, P. W. Stephens, Y. Gao, G. L. Soloveichik, J. Rijssenbeek, M.
> Andrus and J.-C. Zhao
>
>
>
> 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 Energ
