[Ifeffit] EXAFS signal from dopant atoms

[Guanghui Zhang]

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 <segre at iit.edu>
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"<ifeffit at millenia.cars.aps.anl.gov>
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 at iit.edu   http://phys.iit.edu/~segre   segre at debian.org 
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