This paper has data on various Ti oxides and considers the effects of 
crystal symmetry and valence.  It's EELS, not XANES, but close enough.
	mam

On 2/28/2025 8:44 AM, Robert Gordon via Ifeffit wrote:
> Hi B. A correlation between formal oxidation and edge shift from metal 
> (metal = pure covalent) to oxides can certainly be observed. If you 
> consider Fe bonded to O in a variety of compounds (i. e. not just Fe- 
> oxides), you will see that for different
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> Hi B.
> 
> A correlation between formal oxidation and edge shift from metal (metal 
> = pure covalent) to oxides
> can certainly be observed. If you consider Fe bonded to O in a variety 
> of compounds (i.e. not just Fe-oxides),
> you will see that for different formal valence, the edge positions 
> cluster. They are not all the same
> for a given formal valence. This occurs due to changes in the Fe-O 
> interaction when the O also interacts
> with something else. The pre-edge can also show this. A particularly 
> beautiful paper illustrating this is
> by Petit, Farges, Wilke and Sole (J. Synchrotron Rad. (2001). 8, 
> 952-954) for an assortment of Fe minerals.
> 
> For the LI2TiS3 compound in the plot you provided, I would take the edge 
> position (XAFS Eo) to be
> about 4975. I would want to look at the derivative and look at the first 
> peak in the derivative of the
> main rising edge (i.e., yes, max slope). Similarly for r-TiO2, I would 
> consider the edge position to be
> about 4978 eV. The difference in  edge position between two Ti species 
> with formal oxidation of +4
> would be attributed to the differing bonding environments. With Ti-S 
> more covalent than Ti-O, one
> wold expect the Ti-S compound to have a smaller edge shift from the 
> metal than the Ti-O compound.
> 
> "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."
> 
> 
> The authors observe peaks in close proximity for two compounds with 
> differing bonding environments
> (Ti-O vs Ti-S) and note that one of these compounds has Ti with a formal 
> valence of +4.
> 
> What the authors have not done is a systematic study of correlations 
> between pre-edge peak positions for
> Ti-containing compounds where Ti is bonded to sulphur or oxygen. Any 
> conclusions based on one
> comparison are likely highly influenced by observer bias. They made a 
> compound called Li2TiS3,
> and they want to say S-2, Li+1 ergo Ti+4. They are being somewhat 
> carefree in their interpretation
> of the limited data. If they had at least compared to TiS2, it would be 
> a more valid comparison.
> 
> Formal oxidation state is convenient for electron counting. For XAFS 
> edge position, what influences
> that is governed by the extent of charge transfer to/from the local 
> environment about the absorber.
> Correlations with formal oxidation state can be established for similar 
> environments (i.e. ligand type),
> but even that will show subtleties for variations in environment.
> 
> When analyzing and interpreting data, don't overreach.
> 
> -R.
> 
> 
> 
> 
> On 2025-02-28 6:10 a.m., Benito Melas wrote:
>>
>> 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://urldefense.us/v3/__https://xafs.xrayabsorption.org/__;!!G_uCfscf7eWS!ab6KdUGBKgpF84sYz_wvhzdB5_gip4F2qgfvZ5QBXTNbZFT4X05s_JViCpSy83dY9Hs9suoVImmyl04EKnkEchQUoegHWfN4$
>>     tutorials.html <https://urldefense.us/v3/__https://
>>    xafs.xrayabsorption.org/tutorials.html__;!!G_uCfscf7eWS!
>>     cuRhpnCFtMGCgmgTnagYtXR0UFimCoj7yflO8wdOKWgzg6RAC71KlWOwJG9r7NjTmZzwRsQXjhTBDrCRI5s8T3E5RzjmkYcHtbYSTVY$>
>>
>>     -R.
>>
>>
>>
>>     On 2025-02-26 11:31 p.m., Benito Melas via Ifeffit wrote:
>>>     Hi all, I was following this article about Li2TiS3 https: //
>>>     pubs. acs. org/doi/full/10. 1021/acs. inorgchem. 4c03864 and
>>>     found this Ti edge XANES figure The authors claim The peak
>>>     position for LTS-213 is approximately 4970 eV, which agrees well with
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>>>     This message came from outside your organization.
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>>>     Hi all,
>>>     I was following this article about Li2TiS3
>>>
>>>     https://urldefense.us/v3/__https://pubs.acs.org/doi/full/10.1021/acs.inorgchem.4c03864__;!!G_uCfscf7eWS!ab6KdUGBKgpF84sYz_wvhzdB5_gip4F2qgfvZ5QBXTNbZFT4X05s_JViCpSy83dY9Hs9suoVImmyl04EKnkEchQUoXB1CGi-$
>>>     <https://urldefense.us/v3/__https://pubs.acs.org/doi/
>>>    full/10.1021/acs.inorgchem.4c03864__;!!G_uCfscf7eWS!
>>>     dgbg7xRHFkgxNOkmL0Kq2to4N0TuOb4sIXHq_EEsewBDLy86AfRm3KvSGxgT5yzUccLRLvGZQO-OqW3np26v-1bbQHGacJAM$>
>>>
>>>     and found this Ti edge XANES figure
>>>
>>>     image.png
>>>     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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>>
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> 
> 
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