Dear Carlos,

My understanding is that you would like to explore the ratio of Co (or Co ions) either in octahedral phase or tetrahedral phase.

Please be referred to a similar issue at https://millenia.cars.aps.anl.gov/pipermail/ifeffit/2013-July/006759.html

If your samples are in forms of crystalline, you may want to use X-ray diffraction technique. Performing a Rietveld refinement for the obtained XRD patterns can give you the required results.

If your samples are amorphous, you may want to measure XANES spectra, then perform fitting for those using the Athena package, to get the percentage of Co.

EXAFS fitting for 2 phases might give you more information than the above-mentioned stoichiometry. That can be done using the Artemis package.

The EXAFS equation for a mixture of materials contributing to the measured edge is given in the following reference:

"Scott Calvin, XAFS for Everyone, CRC Press, Boca Raton, 2013 p. 342."

The following paper is highly recommended for your reference

S. Kelly, R. Ingalls, F. Wang, B. Ravel, and D. Haskel, Phys. Rev. B 57, 7543-7550 (1998).

Furthermore, from the Co K-edge spectrum, that is proportional to the absorption per atom of Co, you can also calculate the volume fraction in a cubic centimeter of material. 

To do so, you need to firstly obtain the (short-ranged) lattice parameter (in angstrom) of each phase from an EXAFS fitting with an R-factor less than 0.02.
Then the volume (in angstrom cube) of the unit cell of each phase is known. Given that the number of Co atoms /unit cell is known for each phase, the ratio of moles of Co in octahedral phase to total moles of Co for 1 cm³ of sample can be conveniently calculated. This value is equivalent to the volume fraction (%) in 1 cm³ of the sample.

Good luck with your analysis.

Sincerely,

Bokky, D.C. Nguyen

Postdoctoral Fellow at IoP, Academia Sinica, Taiwan

-----Original message-----
From:Carlos Triana Estupinan<ctrianae@unal.edu.co>
To:XAFS Analysis using Ifeffit<ifeffit@millenia.cars.aps.anl.gov>
Date: Fri, 05 Jul 2019 20:37:15
Subject: [Ifeffit] Inversion Degree

Dear

All

Dear

I have EXAFS spectra for spinel Co3O4, and I have to determine the inversion degree X, or the cation distribution of Co at the octaedral and tetraedrical sites.

The EXAFS fitting can be performed employing two clusters of atoms, one having the absorbing atom in tetrahedral site and one having the absorbing atom in octahedral site. However, I do not know how to exactly determine the fraction of cations in octahedral or tetraedral sites from fitting the spectra with two sites independently.

Could you please tell me how exactly should I proced, can I define a EXAFS fitting parameter giving me the cation distribution of Co at the octaedral and tetraedrical sites. If so, how can I do it.

Thanks and best regards,

--

Carlos Augusto Triana Estupiñan
M.Sc. Sciences - Physics
Physicist
Tel: +57 322 256-2309

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