[Ifeffit] [Ext] Analyzing EXAFS data on Artemis

[Carlo Segre]

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> 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   http://phys.iit.edu/~segre   segre at debian.org
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