Re: [Ifeffit] EXAFS signal from dopant atoms

Hi Eugenio, If it is possible to measure the EXAFS of B and/or C edges, you can also do a multiedge refinement like this paper. http://journals.aps.org/prb/pdf/10.1103/PhysRevB.66.224405 Guanghui 2015-09-17 发件人：Carlo Segre 发送时间：2015-09-17 10:06 主题：Re: [Ifeffit] EXAFS signal from dopant atoms 收件人："XAFS Analysis using Ifeffit" 抄送： Hi Eugenio: This only partly depends on the actual concentration of your dopant atom. Just becuaseit is a low concentration does not mean the signal is necessarily in the noise. If you set up your experiment correctly and collect sufficient data you can get quite a good signal from even a low concentration. What you will see in the EXAFS, if the structure is well-ordered, is the fact that the C atom is surrounded by a bunch of A atoms at whatever distance will be typical for a dopant atom of this kind. You will also see further "shells" which will likely be mostly B atoms. As you increase the concentration of C atoms, you might not see too much difference in the near neighbor A atom environment but you will be seeing a second shell with more and more C atoms replacing the B atoms. There are many more nuances to this but it is not a great idea to put a lot of presumptions into your structural model since you might bias the results of the analysis. Good luck Carlo On Thu, 17 Sep 2015, Eugenio Paris wrote:

Dear all,

I have a very general question about EXAFS analysis. Let's take as example a binary system AB in which i am substituting the atom B with another atom C so that we have AB(1-x)C(x). Let us imagine that we know the structure of binaries AB and AC with Rab and Rac atomic distances and we know that in AB(1-x)C(x) the substitutional site will be 100% the B-site.

If I measure the EXAFS spectrum of atom C as a function of "x" what can I expect for the EXAFS oscillations? My idea is that when "x" is very small the EXAFS will be highly noisy and damped, while as "x" increases the oscillations will become more evident above the noise level.

How to model this situation to get information on C-A bond? In Athena I can start with the .cif file of AC structure with full occupancy and obtain the distance and the DWF for the A-C bond but.. how to treat the signal-to-noise ratio? I mean, as "x" decreases I think there must be a leaking out of the EXAFS signal, should this effect be introduced in S0^2? Or can it affect the effective number of neighbors?

Hope I explained myself, thank you!

Eugenio Paris PhD student, University of Rome (Italy)

-- Carlo U. Segre -- Duchossois Leadership Professor of Physics Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit