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
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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