Re: [Ifeffit] Coordination of ball-milled alloys

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 and XAFS sigma^2. The assertion that sigma^2 <= 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. Alex -- Alejandro Fernandez-Martinez Institut Laue-Langevin 6, rue Jules Horowitz - B.P. 156 38042 Grenoble Cedex 9, France Tel: +33 (0)4.76.20.75.71 Fax: +33 (0)4 76.20.76.48 fernande@ill.fr -- Geochimie de l'Environnement LGIT - UJF BP 53 38041 Grenoble Cedex France