[Ifeffit] No shift in XANES absorption peak

[Claudia Schnohr]

Dear Disha,

In principle, yes, there can be a change of bond length without a  
notable change of the XANES. But it also depends on how large the bond  
length changes are that you observe.

I have studied a lot of semiconductor alloys, for example (In,Ga)P or  
Cu(In,Ga)Se2 where the Ga and In atoms share the same lattice site.  
They are always coordinated to four P or Se atoms, respectively, but  
the bond lengths change by 0.02 to 0.03 A because the size of the unit  
cell changes with In/Ga ratio. At the same time, the Ga and In XANES  
is completely unaffected by a change of the In/Ga ratio. If you are  
interested in this, you may have a look at Phys. Rev. B 85, 245204  
(2012), J. Appl. Phys. 116, 093703 (2014), or Appl. Phys. Rev. 2,  
031304 (2015).

This is just to say that, yes, in some special cases you can have a  
change of bond length without a change of XANES. There can be lot's of  
other things going on, too :)

Cheers, Claudia



----- Nachricht von Disha Gupta <dsha.91 at gmail.com> ---------
      Datum: Mon, 11 Jun 2018 18:29:49 +0800
        Von: Disha Gupta <dsha.91 at gmail.com>
Antwort an: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
    Betreff: Re: [Ifeffit] No shift in XANES absorption peak
         An: ifeffit at millenia.cars.aps.anl.gov


> Dear Dr Carlo
>
> The edges are almost identical. The pre-edge intensity change isn't that
> significant I feel. I did the Artemis fittings with the coordination
> numbers fixed. Maybe I can try varying the coordination numbers and see if
> it gives a different result.
> I have attached the images of the pre-edge and main peak.
>
>
>
>
>
> Thanks and Regards
> Disha
>
>
>
>
> From: Carlo Segre <segre at iit.edu>
> Date: Mon, Jun 11, 2018, 12:34
> Subject: Re: [Ifeffit] No shift in XANES absorption peak
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
>
>
>
> Hi Disha:
>
> it would be good to see the XANES you are referring to.  Are the edges
> identical or do they change but not shift significantly?  Is the
> coordination number also constant?  Generally, the bond distance will
> change with oxidation state if the coordination number is constant but if
> the coordination number changes, then there could be a change in bond
> length too.
>
> Cheers,
>
> Carlo
>
>
> On Mon, 11 Jun 2018, Disha Gupta wrote:
>
>> Dear All
>>
>> Firstly, I would like to say sorry if I have missed out on this discussion
>> before but it would be great if you could help me out.
>> I have been analyzing some Mn K-edge XAS data for some battery materials.
>> While the XANES data shows no shift in the main absorption peak which
> means
>> that there is no oxidation change happening, however, when I am fitting
> the
>> data in Artemis, I can see a shift in the bond lengths suggesting an
>> oxidation change. Is it possible that bond lengths change even though
> XANES
>> spectra show no change?
>>
>>
>> Thank you and Kind Regards
>> Disha
>>
>
> --
> Carlo U. Segre -- Duchossois Leadership Professor of Physics
> Interim Chair, Department of Chemistry
> Director, Center for Synchrotron Radiation Research and Instrumentation
> Illinois Institute of Technology
> Voice: 312.567.3498            Fax: 312.567.3494
> segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org
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>
> Disha Gupta
> Graduate Student
> School of Materials Science and Engineering
> Nanyang Technological University (NTU), Singapore
> +65 84087404
> DISHA001 at e.ntu.edu.sg
>
>
> On Mon, Jun 11, 2018 at 11:34 AM, Disha Gupta <dsha.91 at gmail.com> wrote:
>
>> Dear All
>>
>> Firstly, I would like to say sorry if I have missed out on this discussion
>> before but it would be great if you could help me out.
>> I have been analyzing some Mn K-edge XAS data for some battery materials.
>> While the XANES data shows no shift in the main absorption peak which means
>> that there is no oxidation change happening, however, when I am fitting the
>> data in Artemis, I can see a shift in the bond lengths suggesting an
>> oxidation change. Is it possible that bond lengths change even though XANES
>> spectra show no change?
>>
>>
>> Thank you and Kind Regards
>> Disha
>>


----- Ende der Nachricht von Disha Gupta <dsha.91 at gmail.com> -----



-- 
PD Dr. Claudia S. Schnohr
Institut für Festkörperphysik
Friedrich-Schiller-Universität Jena
Max-Wien-Platz 1
D-07743 Jena
Germany

Tel: +49 3641 947333
Fax: +49 3641 947302