Hi R.,

I understand that the pre-edge corresponds to a transition that is normally forbidden by symmetry, while the absorption edge represents the transition from the core level to the continuum.

In Fundamentals of EXAFS, Figure 7.3 shows that the absorption edge shifts when iron changes from its metallic state to +2 and +3 oxidation states. The caption states:

"Fe K-edge XANES of Fe metal and several Fe oxides, showing a clear relationship between edge position and formal valence state."

As the edge position is unclear for me in the LST compound, should it be the point of maximum slope?

The LST peak at 4975 eV could correspond to the B peak reported by Rossi et al. (DOI: 10.1103/PhysRevB.100.245207), which is an aspect I am not entirely familiar with. I reviewed the paper by Farges (DOI: 10.1103/PhysRevB.56.1809) and did not observe anything similar. This is the first time I have seen the B peak so intense; previously, I have encountered lower-energy peaks with higher intensity, likely due to distortions in the local symmetry.

I understand that the pre-edge is more related to local symmetry than to the oxidation state, based on the manuscripts I mentioned. Could you please clarify this further?

I am confused by this sentence:

"The peak position for LTS-213 is approximately 4970 eV, which agrees well with that for rutile TiO₂ with a valence of titanium species in the 4+ oxidation state."

I will check the tutorials, I always catch something new.

Best regards,

On Fri, Feb 28, 2025 at 2:04 AM Robert Gordon via Ifeffit <ifeffit@millenia.cars.aps.anl.gov> wrote:

Hi B. Have you had any lessons on XAFS? i. e. attended an XAFS course offered by many synchrotrons and related institutions. Do you know the difference between pre-edge features and absorption edge? In the plot you provided, the edge positions

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Hi B.

Have you had any lessons on XAFS? i.e. attended an XAFS course offered by many synchrotrons and related
institutions.

Do you know the difference between pre-edge features and absorption edge?
In the plot you provided, the edge positions are clearly different.

Formal oxidation state is a convenient way to count electrons.

Edge position is governed by how the screening of the nucleus of the absorber is affected
by the type and arrangement of near neighbours - orbitals involved in bonding and extent of
charge transfer between absorber and ligands...hence the usefulness of XAFS as a technique
for characterising local environments.

Still confused? Start here: https://xafs.xrayabsorption.org/tutorials.html

-R.

On 2025-02-26 11:31 p.m., Benito Melas via Ifeffit wrote:
Hi all, I was following this article about Li2TiS3 https: //pubs. acs. org/doi/full/10. 1021/acs. inorgchem. 4c03864 and found this Ti edge XANES figure The authors claim The peak position for LTS-213 is approximately 4970 eV, which agrees well with

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Hi all,
I was following this article about Li2TiS3

https://pubs.acs.org/doi/full/10.1021/acs.inorgchem.4c03864

and found this Ti edge XANES figure

The authors claim

The peak position for LTS-213 is approximately 4970 eV, which agrees well with that for rutile TiO2 with a valence of titanium species in the 4+ oxidation state.

Should we use the pre-edge to determine the oxidation state? Is it reliable, or should we use E₀ and compare it with references of well-known oxidation states?

In addition, TiS2, in which titanium is also in the 4+ oxidation state, shows pre-edge peaks at 4968–4971 eV. (21) Considering the titanium oxidation state in the raw materials, the stability of the titanium species, and the XANES results, the oxidation state of the titanium species in LTS-213 is likely to be 4+.

The second conclusion is even more unclear.

Would you help me see if I am missing something in my understanding of oxidation states using XANES?

Best, B.
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