[Ifeffit] Coordination of ball-milled alloys

Alejandro Fernandez-Martinez fernande at ill.fr
Wed May 9 11:51:47 CDT 2007

Thanks for your help.

To paraphrase, the sample is not a random mixture of Cr and Fe in a
bcc lattice, which seems a little strange to me, as bcc Cr and Fe have
very similar lattice constants -- I don't know whether they form a
uniform solid solution, but you are studying this sample, so it might
not be as simple as a random substitution, right???     Do you know
the fraction of Fe atoms that has been alloyed?    Do you know how
much of the sample is crystalline, and what the defect density is?

I know exactly the percentage of Fe atoms that have not been alloyed. 
They come from the fact that in the ball milling we used powder of Fe 
with bigger grain size than Cr powder and that the milling time was not 
very long, so some Fe did not have enough time to alloy.

The issue with the short range may bue due to inhomogeneities in the 
sample combined with the instability of the beam that day (I was one of 
the first XAS users of that beamline..).

>By the way, any such issue would completely negate the assertion that
>there is a simple relation between the diffraction <u^2> and XAFS
>sigma^2.  The assertion that sigma^2 <= 2<u^2> definitely assumes that
>all atoms are on a single set of lattice points.   For example, it is
>not a very useful guideline for amorphous systems.
This is a very interesting comment. Thanks a lot.


Alejandro Fernandez-Martinez
Institut Laue-Langevin
6, rue Jules Horowitz - B.P. 156
38042 Grenoble Cedex 9, France

Tel: +33 (0)
Fax: +33 (0)4
fernande at ill.fr

Geochimie de l'Environnement
BP 53
38041 Grenoble Cedex

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