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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