[Ifeffit] Coordination of ball-milled alloys
Alejandro Fernandez-Martinez
fernande at ill.fr
Fri May 4 13:18:17 CDT 2007
Dear all,
I am quite new to XAS data analysis, maybe you can help me with a little
problem I have.
I am trying to fit EXAFS data at Cr K-edge of a bcc Fe30Cr70 alloy
synthesized by ball-milling. For those who don't know it, this technique
is very effective in alloying metals but introduces a lot of structural
defects in the structure. This is clearly seen in neutron diffraction
data (with DW 2 times larger than DWs of a Cr reference and larger FWHMs).
When fitting the EXAFS data without any specific constrain (only for
distances) I get DWs on the same order of magnitude for the Cr-foil than
for the alloy, and a very reduced coordination of N1=2.3 (compare with
N1=8 for the Cr-foil) for the first neighbour (without physical sense?).
In order to take into account the larger DWs for the alloyed sample (as
found in diffraction data) I have constrained the minimum value of the
DWs to a value double than the DWs of the Cr-foil. This gives me an
increase of the N for the first shell, but at the same time, I have to
refine lambda (photoelectron mean free path) in order to correct the
excesive decay introduced by the DW exponential in the EXAFS formula,
and to get a good fit. Then I get a more physically understandable N1=5.5.
- The 1st question is: do you think the logical discourse that I have
followed until now is correct? I don't have idea on how much some
quantities as lambda should or not be refined.
- 2nd question: what dou you think about the use of diffraction data as
constraint for EXAFS data analysis?
Many thanks in advance!
cheers,
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 at ill.fr
--
Geochimie de l'Environnement
LGIT - UJF
BP 53
38041 Grenoble Cedex
France
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