[Ifeffit] E0 in Co3O4

Manuel MONTE CABALLERO manuel.monte at esrf.fr
Fri Oct 27 04:41:14 CDT 2017

Dear Jesús,

Why will you choose the maximum at 7722 eV?
I will choose the first one (ignoring the pre-edge), around 7718 eV.

The problem here, could be that in Co3O4 you have one atom of Co(II) and 
two of Co(III) so, there are absorbing at different energies.
But the EXAFS is common so, and error will happen no matter which 
maximum you choose.
I have a CoO spectra and the maximums of the derivative (again ignoring 
the pre-edge) appear at 7717, 7721 and 7725 eV.
If you had a Co2O3 spectra (I don't) you can compare and decide to 
choose the E0 which is closer to that of the Co2O3 as in Co3O4 you have 
more Co(III).

Also, if you make three copies of the spectra and select a different E0 
for each one you can see how it affect the x(k) and the Fourier 
transform (to R).
The first E0 (7718 eV) make x(k) to have higher intensity (resulting in 
higher intensity of peaks in R).
But the third one (7722) creates an extra feature below 1 in the R space 
(for k range 3-9 or 3-10).

Usually I will just choose the first one or, compare some and see what 
Probably, the different will not so high to make you worry too much.



On 25/10/2017 17:11, Jesús Eduardo Vega Castillo wrote:
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> Dear list,
> I enclose an Athena project with a XAFS spectrum of Co3O4 with a 
> metallic Co reference.
> Athena by default has chosen E0 at the absolute maximun of the 
> derivative curve (at 7727.8eV) which in my opinion is too high because 
> it is at the white line zone.
> I believe that E0 should be the previous maximun in the derivative at 
> around 7722eV, which would be at the rising edge.
> Am I wrong?
> I would appreciate some help with the criterion to determine the right 
> value.
> Yours,
> Jesús
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