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@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 (FORTH)_______________________________________________
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