[Ifeffit] La2Zr2O7 EXAFS fitting

Scott Calvin scalvin at sarahlawrence.edu
Fri Aug 14 07:01:13 CDT 2015

Hi Herve,

I haven’t looked at your project file, but the 1.80 A peak is not that big a surprise, as peaks in the Fourier transform typically show up 0.3 to 0.5 angstroms lower than the corresponding half-path length, due to the effects of the potential of the absorbing and scattering atoms. In other words, the Fourier transform is not a radial distribution function, although it’s correlated to one.

The interaction between the two similar path lengths further complicates peak location, since it can establish a “beating” between the two signals.

Under the circumstances, a peak at 1.80 angstrom is not remarkable.

The peak at 1.28 angstrom, on the other hand, is well in to the background region for this compound, and does not need to correspond to a path.

The fact that the Fourier transform is not a radial distribution function is why some sort of comparison to a standard is necessary. For Ifeffit users, that typically means fitting to a so-called “theoretical standard,” that is, a computed spectrum, using Artemis. It could also mean comparison to a well-chosen series of measured materials (“empirical standards”). But it is not possible to just look at the Fourier transform and read off bond lengths.

—Scott Calvin
Sarah Lawrence College

On Aug 14, 2015, at 4:41 AM, herve muguerra <herve.muguerra at neel.cnrs.fr<mailto:herve.muguerra at neel.cnrs.fr>> wrote:

Dear All,

First of all, I am still very new in EXAFS analysis, so please excuse me
for any misunderstandings.

My sample is a crystalized La2Zr2O7 thin layer (thickness = 100 nm) on a
NiW substrate and we have realized EXAFS measurements by grazing angle
under primary vacuum at Lathanum L3 edge (ESRF, Grenoble, France).

My objectives are to establish the local distortions due to the
different constraints in the oxide thin layer.

The La2zr2O7 crystalized in a pyrochlore structure (SG = Fd-3m ; a =
First scattering path
La-O2.1                                2.3352A
La-O1.1                                2.6453A

But I have a problem: I observe the first peaks at 1.28A and 1.80A on
the EXAFS spectra as a function of R.

How do you explain this feature?

Can you point me in the right direction for these issues?

I attached the project file La_80_LZO_1000.prj of my sample:
LAHM045 to LAHM50 = 6 different scans
La_80_LZO_1000 = Data merge


Best regards

Hervé Muguerra
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Ifeffit at millenia.cars.aps.anl.gov<mailto:Ifeffit at millenia.cars.aps.anl.gov>

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