Sebastiano, You are correct that EXAFS is relatively insensitive to atoms that are nearby on the periodic table. This is because the backscattering amplitudes and phase shifts are functions of, in part, Z number. In the case of stochastic replacement of a host atom by a dopant on the exact position of the lattice site, it can be difficult or impossible to distinguish nearby atoms. However, if the introduction of the dopant is accompanied by a distortion to the lattice, the situation might be a lot friendlier. In that case, you may be able to notice two (or more) distances in the neighboring shells, one of which can be explained by the host atom and the other(s) by the dopant. Even better, you can measure data at the edges of both host and dopant and corefine the data. That additional information might be enough to figure out what's going on. I also think that your case -- an alloy -- might be a good candidate for high energy diffraction using PDF analysis methods. PDF, or PDF combined with EXAFS, might help for your problem. Good luck, B On Tuesday 15 May 2007, Cammelli Sebastiano wrote:
Dear
I am Sebastiano and I am working on some metallic alloy composed by several diluted elements in a Fe matrix. The main elements are: Cu, Cr < 0.5at%; Mn, Ni < 1.5at%, I collected some spectra at different K edge (Mn, Ni, Cu). Submitting this alloy by annealing treatment (775K) and neutron irradiation, some clusters are expected mainly composed by Cu; Ni and Mn play an important role but it is not so clear. Some problems rise when I try to analyze these data:
"It is known" that it is not so easy to recognize by EXAFS the difference from near elements as Fe and Mn (Z=26,25) and Cu, Ni (29,28) because these elements has a similar electronic distribution. Performing the analysis by Artemis I found some 'realistic' value of Mn Fe and Ni in the first and second shell (Cu K edge), have these values any physical meaning since I cannot distinguish element as Fe and Mn?
Do you know any tricks that could help me? Maybe the right answer is that EXAFS is not enough to investigate these alloys, but if I cannot distinguish the different atoms, which kind of quantitative information could I get? The interatomic distances are important but which is the meaning of distance between the absorber (Cu) and an unknown atom (Fe or Mn, Cr or Mn, Cu or Ni?)?
Thank you help and for your time.
Sebastiano
Sebastiano.cammelli@psi.ch
Paul Scherrer Institute, Villigen 5232 (CH)
-- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/