Re: [Ifeffit] Ti data problem

[Qingying Jia]

Hi Carlo,

  In many transition metal oxide cases like this, what would be the more
proper E0, the position of the apex of the first derivative peak or the
second one that is usually higher than the first peak, or it really
depends? I have seen people using either. In this particular case, it seems
like using E0 of 4967 eV (the first derivative peak position) gives cleaner
and more reasonable FT-EXAFS.

  Regards,
  Jia

On Mon, Aug 8, 2016 at 5:05 PM, Carlo Segre  wrote:

>
> Hi Siliang:
>
> The first thing is that you have misidentified the edge position.  Itis
> way too high in all the data sets.
>
> Put it at the inflection point of the main rise in the absorption curve
> and you will find that the problem is much reduced.
>
> The second thing is that you have a very bad backgrund problem in your
> data and, in my estimation your usable data range is no moe than k=2 to
> k=8.  In fact, my suggestion is that you truncate the data by setting the
> spline range to end at 8.  The FT range should probably be set at 2-8 or
> even 2-7 (somewhere in that range and put a window sill of dk=2 to get rid
> of some of the ringing.
>
> Once you do those things the data will look much more reasonable.
>
> These data could probably have used some longer counting times.  Where did
> you take the data?
>
> Carlo
>
> On Mon, 8 Aug 2016, Siliang Chang wrote:
>
> Dear all,
>>
>>
>>
>> I am new to XAFS data analysis. I?m currently working on the XAFS data of
>> atomic layer deposited mixed oxide thin film: SnTiOx. I have both Sn and
>> Ti
>> K edge data, and was able to fit Sn edge using a model of (Sn,Ti)O2 solid
>> solution. However, Ti data really confuses me (please see attached file).
>> With Rbkg set to 1, there is a doublet in 1-2 Å region in every data, this
>> is something I have never seen in the literature. I?m wondering if this is
>> normal? Does this mean I should set a larger Rbkg value, say, around 1.5?
>>
>>
>>
>> I?ve tried to fit the abovementioned Ti data using several models:
>> anatase,
>> rutile, (Sn,Ti)O2 solid solution, perovskite (N is fixed at 6 for all of
>> those), so far no success. I would really appreciate if you can comment on
>> my data processing, any suggestions are welcomed, as I?m new to this, I?m
>> not sure if I?m doing it the right way.
>>
>>
>>
>> Thank you very much.
>>
>>
>>
>> Best regards,
>>
>> Siliang Chang
>>
>>
>>
>>
>>
>>
>>
> --
> 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: 312.567.3498Fax: 312.567.3494
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Re: [Ifeffit] Nearest neighbor statistics in a random alloy

[Qingying Jia]

Hi Felix,


Your assumptions are not correct because the model you use is not a
representative unit cluster model. Basically the following three equations
are always correct for foil:

 NPt-Pt+NPt-Co=12

NCo-Co+NCo-Pt=12

NCo-Pt/NPt-Co=9

And the specific values for the coordination number can be determined if
you know the orderness of the structure. As for the random distribution of
Pt and Co in foil,

NPt-Pt/NPt-Co=9

or equivalently,

NCo-Pt/NCo-Co=9,

Then you can get

NPt-Pt=10.8, and NPt-Co=1.2

The results will be different if the structure is ordered.


  Regards,

On Fri, Jun 23, 2017 at 9:02 AM, Felix E. Feiten 
wrote:

> Dear all,
>
> I am fitting a Pt9Co1 foil sample.
> I assume the sample to be basically fcc platinum with every 10th atom
> randomly replaced by cobalt.
>
> Here are the assumptions I make:
>
> 1. every atom has 12 nearest neighbors
>
> 2. every Pt atom has (on average) 10.7 Pt nearest neighbors and 1.3 Co
> nearest neighbors
>
> 3. every Co atom has (on average) 11.7 Pt nearest neighbors and 0.3 Co
> nearest neighbors
>
> I have been told that assumptions 2 and 3 are not precise. Here is what
> I'm confused about:
>
> In order to determine the number of Pt or Co nearest neighbors I looked at
> an ensemble of 13 atoms:
> 1 absorber and 12 scatterers/nearest neighbors.
> I assume that the Pt/Co ratio in this ensemble is 9/1 and therefor,
> statistically, 1.3 out of those 13 atoms should be Co. That means that if
> Co is the central atom only 0.3 Co atoms are remaining for the 12 nearest
> neighbors. On the other hand, if Pt is the central atom, (all) 1.3 Co atoms
> are remaining for the 12 nearest neighbors.
>
> I have been told that the ratio of Pt/Co should be 9/1 in the 12 nearest
> neighbors, not in the 12 atoms including the central atom (quote: "because
> we have a bulk sample").
>
> But I do not understand why.
>
> Can someone please explain the correct answer to me?
>
> With kind regards,
>
> Felix
>
>
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Re: [Ifeffit] No shift in XANES absorption peak

[Qingying Jia]

Hi Disha,

  For such a huge shit of bond distance, the corresponding lattice constant
change should be readily seen by XRD. It will also shift the XANES edge
slightly.

  Regards,

On Mon, Jun 11, 2018 at 10:58 AM, Disha Gupta  wrote:

> Dear Claudia, Qingying Jia, Matt
>
> Thank you so much for your responses :)
>
> The shift in bond length I see is almost around 0.1-0.12 Angstrom, which
> is not small enough to ignore. I think the coordination might be changing,
> if not the oxidation state. I will redo the Artemis calculations with N as
> a variable again to see if that helps. Because keeping my N constant
> actually gave me pretty low Debye-Waller values and R factor was also below
> 5% so I was assuming the fits were reliable.
>
> I was also thinking maybe Mn is undergoing partial oxidation, however, in
> bulk we do not see that change in the main XANES absorption peak. I am not
> sure if that can be a possibility.
>
> Thanks a lot again!
> Kind Regards
> Disha
>
>
> Disha Gupta
> Graduate Student
> School of Materials Science and Engineering
> Nanyang Technological University (NTU), Singapore
> +65 84087404
> disha...@e.ntu.edu.sg
>
>
> On Mon, Jun 11, 2018 at 10:14 PM,  cars.aps.anl.gov> wrote:
>
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>>
>> Today's Topics:
>>
>>1. Re: Demeter on Windows 10 does not work (sikolen)
>>2. Re: No shift in XANES absorption peak (Claudia Schnohr)
>>3. Re: No shift in XANES absorption peak (Qingying Jia)
>>4. Re: Demeter on Windows 10 does not work (Matt Newville)
>>5. Re: No shift in XANES absorption peak (Matt Newville)
>>
>>
>> --
>>
>> Message: 1
>> Date: Mon, 11 Jun 2018 13:39:03 +0200
>> From: sikolen 
>> To: XAFS Analysis using Ifeffit 
>> Subject: Re: [Ifeffit] Demeter on Windows 10 does not work
>> Message-ID: 
>> Content-Type: text/plain; charset=UTF-8; format=flowed
>>
>> Thanks Kathy,
>>
>> It seems the problem is really with the wrong path... Now I see how to
>> fix it.
>>
>> Vadim
>>
>>
>> On 2018-06-08 17:07, Kathy Dardenne wrote:
>> > Dear Vadim,
>> >
>> > I am running  myself Demeter 0.9.26, 64bit under win10 and do not have
>> > such
>> > trouble. But your description is similar to the problem occurring with
>> > the
>> > previous release of Demeter 0.9.26 pre2 (old path for gnuplot
>> > executable in
>> > ini file leading the same effect), did you download the actual version
>> > for
>> > Demeter 0.9.26? this later trouble is fixed and Demeter runs smoothly
>> > with
>> > win7 and win10.
>> >
>> > Kathy
>> >
>> > -Message d'origine-
>> > De?: Ifeffit  De la part de
>> > sikolen
>> > Envoy??: vendredi 25 mai 2018 10:01
>> > ??: ifeffit@millenia.cars.aps.anl.gov
>> > Objet?: [Ifeffit] Demeter on Windows 10 does not work
>> >
>> >
>> > Dear all,
>> >
>> > I've just changed my loving Windows-7 to the new Windows-10. I've
>> > installed
>> > Demeter (v.0.9.26, 64-bit), but it does not work: cmd-Windows appears
>> > for
>> > the a couple of seconds and disappears forever. Is it already known
>> > problem
>> > of the OS? Sorry, may be  this question already appeared here, I just
>> > missed
>> > it.
>> >
>> > Vadim
>> > --
>> > ***
>> > Dr. Vadim Sikolenko
>> > Senior Scientist
>> > Frank Laboratory of Neutron Physics
>> > vadim.sikole...@jinr.ru
>> > Skype: svadimm
>> > **
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Re: [Ifeffit] No shift in XANES absorption peak

[Qingying Jia]

Hi Disha,

  The shift in bond distance in this case, is not necessarily associated
with the change of oxidation state. It can be simply caused by the
insertion/removal of Li/Na or whatever depending on your battery type
during the charge/discharge, which sometimes changes the oxidation state of
Mn slightly, sometimes doesn't.

  Regards,

On Sun, Jun 10, 2018 at 11:34 PM, 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
>
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Re: [Ifeffit] [Ext] Deglitch the data

[Qingying Jia]

Agree. Took a quick look at your spectrum. The IrOx seems to be extremely
amorphous without much Ir-Ir interactions. The dip is around 11 (A-1) in
the k-space. So you may just truncate anything beyond that dip and the
remaining spectrum should carry most useful information and be fitable, at
least for the first shell Ir-O bond.

On Sun, Jul 16, 2023 at 11:13 PM Carlo Segre  wrote:

> Hi Kavya:
>
> What you have are not glitches but shifts in the absolute absorption
> probably due to bubbles or droplets moving through the beam.  You can tell
> these from crystal glitches because the glitches are sharp and occur at the
> same energy in every scan while these are likely to move around from scan
> to scan.  In my experience, this kind of change in the spectrum is not
> correctable.  Hopefully you have lots of scans and only some of them have
> these artifacts and can be thrown out.
>
> Carlo
>
> On Sun, Jul 16, 2023 at 10:00 PM Shailendra 
> wrote:
>
>> Hi, IFEFFIT community,
>>
>> I am Rachna, a Ph.D. student working on IrO2 based OER catalyst.  I am a
>> new XAS user. Recently, we recorded some XAS on amorphous IrO2 electrode
>> samples however some of the samples show a dip in adsorption at high
>> energy. The glitches are similar to the one in the attached photo. I am
>> attaching the Athena file for the measurements too. I was wondering if
>> there is a way to remove such glitches.
>> I would greatly appreciate any tips or tricks you may have for dealing
>> with this situation.
>>
>> Thanks,
>> Kavya Rachna
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>
>
> --
> Carlo U. Segre (he/him) -- Duchossois Leadership Professor of Physics
> Professor of Materials Science & Engineering
> Director, Center for Synchrotron Radiation Research and Instrumentation
> Illinois Institute of Technology
> Voice: 312.567.3498Fax: 312.567.3494
> se...@iit.edu   http://phys.iit.edu/~segre   se...@debian.org
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Re: [Ifeffit] [Ext] Question about EXAFS fitting of mixtures

[Qingying Jia]

EXAFS fit will not tell apart. XANES analysis with or without LCA will.

On Mon, May 15, 2023 at 7:09 PM Soyoung Kim  wrote:

> Dear all,
>
> While fitting EXAFS for tiny Pt nanoparticles, a simple question occurred
> to me. For these two scenarios:
> 1. All Pt atoms are coordinated to 3 O atoms and 3 Pt atoms each.
> 2. Half of the Pt atoms are coordinated to 6 O atoms and half to 6 Pt
> atoms.
>
> If we fit only single-scattering paths, would it be possible to tell apart
> these two scenarios with EXAFS fitting? What about linear combination
> analysis of the XANES?
>
> Thank you,
> Soyoung
>
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