[Ifeffit] [Ext] Analyzing EXAFS data on Artemis

Matthew Marcus mamarcus at lbl.gov
Thu May 27 14:34:22 CDT 2021

If you go beyond first shell, then you'll need to take into account the 
Se-Se paths in Li2Se.  That may be your best way of detecting Li2Se.

On 5/27/2021 12:03 PM, Carlo Segre wrote:
> Hi Deltsidis:
> Using Artemis, you can compare the calculated Fourier Transforms of the 
> Se-Fe and Se-Li paths to see if the latter will actually be visible.  I 
> suspect that it will not if it is an impurity phase with small phase 
> fraction.  I would probably start with only Se-Fe and see how well it 
> can fit the data.
> The eins(T, thetae) is the temperature dependent term.  What is missing 
> the static disorder that needs to be added into the sigma^2 to account 
> for the temperature independent residual disorder.
> Carlo
> On Thu, May 27, 2021 at 9:43 AM Alexandros Deltsidis 
> <adeltsidis at iesl.forth.gr <mailto:adeltsidis at iesl.forth.gr>> wrote:
>     Dear mailing list,
>     I am currently analyzing some EXAFS data. I am studying a Lix(C5H5N)FeSe
>     system in a temperature grid that extends from 20 K to 300 K and I
>     have 4
>     such datasets which correspond to different amount of doping (x). Right
>     now, im focusing on fitting the 1st coordination cell, in Artemis
>     for the
>     Se K-edge. My starting model is the simple P4/nmm FeSe. So, in my system
>     the 1st coordination cell, in the Se K-edge, corresponds to the Se
>     (absorber) - Fe (backscatterer) pair. I have 2 questions:
>     1) I realize now, that I have a certain impurity in the high doping
>     range
>     on my system, namely Li2Se. I try to include a scattering path from the
>     respective Li2Se crystal model in my fits, since a Se (absorber) - Li
>     (backscatterer) pair is present in the R-range of my fit in the Forward
>     Fourier Transform. My question here is if this makes sense since Li is
>     much smaller scatterer compared to Se. In other words, does it make
>     sense
>     to look for physical parameters (Li-Se bond length and DW factor
>     respectively) of a signal (Se-Li) that is "tucked" in below the main
>     peak
>     coming from the "majority" Se-Fe signal in the FFT?
>     2)Also, I'm attempting to extract an Einstein temperature for each of
>     those datasets, by utilizing the "eins(T, thetae)" function
>     implemented in
>     Artemis. What is the equation that is parametrized here? Does it include
>     the s0^2 offset term that accounts for the overall configuration
>     disorder
>     in the system? And if that is the case is there same way to separate it
>     from the temperature dependent s^2 term?
>     Thank you in advance,
>     Deltsidis Alexandros
>     PS:I am attaching a png. file exported from Artemis that is relative
>     to my
>     question 1)
>     Ph.D candidate,
>     Institute of Electronic Structure and Laser (IESL),
>     Foundation for Research and Technology - Hellas
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> -- 
> Carlo U. Segre -- Duchossois Leadership Professor of Physics
> Professor of Materials Science & Engineering
> Director, Center for Synchrotron Radiation Research and Instrumentation
> Illinois Institute of Technology
> Voice: 312.567.3498            Fax: 312.567.3494
> segre at iit.edu <mailto:segre at iit.edu> http://phys.iit.edu/~segre 
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