> Alan and Maxim,

Thanks for the comment and the article.
I relieved that I know the point.

> Leonid,
Yes, the instrumental resolution itself increases with d (or TOF).
But it is still strange for me that only all-odd peaks show different 
d-dependence from CeO2 and other all-even peaks in terms of slope in the 
delta-d/d vs d plot.

Now, I think a similar situation as high temperature phase of Mg(BH4)2 occurs 
in my quaternary Heusler sample.
For all-odd hkl, structure factor is F_hkl=4(f_A-f_C)+/-4i(f_B-f_D). Here, A-D 
denote four fcc sublattices in Heusler alloys, or 4a,4c,4b,4d sites in F-43m.
If there exist ABCD and CDAB type domains, those domain have out-of-phase 
scattering for all-odd reflections and same story as Mg(BH4)2 can be applied.
But still I don’t understand why peak widths show such strong dependence on d 
(or TOF).

Concerning attachment files.
This time I use Dropbox but I don’t guarantee it as an image archive because 
the image might be removed by me a few years later when I clean up my folders.

//================//================//
  Kotaro SAITO
  High Energy Accelerator Research Organization
  Institute of Materials Structure Science
  1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
//================//================//

> 2015/08/04 19:34、Alan Hewat <alan.he...@neutronoptics.com> のメール:
> 
> On 4 August 2015 at 11:54, Kotaro SAITO <kotaro.sa...@kek.jp> wrote:
> Or do I miss some basic points about diffraction?
> 
> I won't try to address your specific material... and I'm being called to 
> lunch :-) But for beginners who may be lost in these technical papers, I will 
> attempt the following trivial explanation
> 
> If you have a layered material where two layers A and B are slightly 
> different you will have super-structure reflections. These will be as sharp 
> as the main reflections (from the average structure) if the order of the 
> layers is perfectly regular ABABABAB...
> 
> But if the layers only have short-range order eg ABABBABAAB... then these 
> superlattice reflections will be broadened, and even completely washed out if 
> the order between layers is completely random. Otherwise the width delta-d of 
> the superstructure reflections will give you the short range order length - 
> the shorter the correlation length the broader the superlattice reflections. 
> 
> Obviously delta-d doesn't depend on the d-spacing between layers, only on the 
> length of their order. So the broadening is constant in d-space as usually 
> plotted for TOF neutron diffraction.
> 
> For angular dispersion eg with a constant x-ray or neutron wavelength, 
> Bragg's law 2d.sin(theta)=lambda comes in. If you differentiate Bragg's law 
> you will find a simple relation between delta-d and delta-2theta, the line 
> broadening for angular dispersion measurements.
> 
> Alan. 
> (Everything should be as simple as possible... but no simpler.)
> BTW, thanks for using dropbox instead of an attachment. That's the way to 
> go...
> -- 
> ______________________________________________
>    Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE 
> <alan.he...@neutronoptics.com> +33.476.98.41.68
>         http://www.NeutronOptics.com/hewat
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