[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.
mam
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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