[Ifeffit] Ifeffit Digest, Vol 89, Issue 3

[Varadarajan Sridharan]

Dear Matt,
  I agree to your point.
  AS of now I am not attempting to fit the Ca substituted system for two
reasons
  1.I am specifically looking for the "cause" for the structure in the
second peak. The structure
    is present in the calculated CdO Chi(R) plot itself.
 2. Apart from that when I tried to put in Ca in the ATOM, Ca is not at all
appearing in the list
    after running ATOM.
Can you help me out in this matter as well.
Thanking you
---- Varadarajan Sridharan

On Tue, Jul 6, 2010 at 10:30 PM,
<ifeffit-request at millenia.cars.aps.anl.gov>wrote:

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> Today's Topics:
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>   1. Re: Clarification needed on the structured 2nn peak
>      (Matt Newville)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 6 Jul 2010 07:52:16 -0500
> From: Matt Newville <newville at cars.uchicago.edu>
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Clarification needed on the structured 2nn peak
> Message-ID:
>        <AANLkTinjUxHwVBBkCBiONWnNNptLnpSKpI9mnri3HbBv at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Dear Varadarian,
>
> I didn't look at your attachments, but have you considered that there
> might be some Cd-Ca in the second shell?   I didn't see what value of
> x you had in Cd(1-x)CaxO, but if the oxides form a solid solution one
> might naively expect the second shell to have  (1-x) Cd and x Ca
> coordination.   Ca and Cd scatter photoelectrons  differently enough
> to be distinguishable in the EXAFS.  It might be that there is extra
> disorder too, say if the typical Cd-Ca distance was different from the
> typical Cd-Cd distance.
>
> Cheers,
>
> --Matt
>
> On Tue, Jul 6, 2010 at 7:29 AM, Varadarajan Sridharan
> <varadu.sridh at gmail.com> wrote:
> > Greetings to all
> >
> > ?? I am a beginner to EXAFS.
> >
> > ? Recently I had carried out Cd K-edge EXAFS? measurements on Cd1-xCaxO
> > solid solution. The end members CdO and CaO belong to same crystal
> structure
> > Fm-3m.
> >
> > ?? I had analysed the spectrum with Atthena and fitted with Arthemis. I
> am
> > attaching the Athena project file (***.prj) and that of Arthemis project
> > file (***.apr) for your reference.
> >
> > Athena:
> >
> > ?? As per the crystal structure of CdO, the first nearest neighbour is at
> > 2.345 A corresponding to Cd-O1 inter atomic distance and 2nn distance is
> > 3.3.16 A corresponding to Cd-Cd1 inter atomic distance. Though I am able
> get
> > the first peak in chi(R) plot at expected position, I am having some
> > problems for the second peak. The second peak has features; main one and
> a
> > shoulder. The main peak itself appears at lower R compared to expected
> one.
> > Intensity of the shoulder increases with Ca substitution at the expense
> of
> > main peak itself.
> >
> > ??????????? Can any one comment on this?
> >
> > ???? My predicament: If I associate, based on the structure of second
> peak,
> > bimodal distribution for the Cd-Cd1 interatomic distance, the difference
> of
> > 0.4 A is 11%. This value gives me an uneasy feeling. Is it possible to
> > accommodate this difference within the setting of F m-3m?
> >
> > ????????????????????????????????? OR
> >
> > ???????????????????????????????? It is due the multi scattering is the
> > problem?
> >
> > Arthemis:
> >
> > For CdO: ?The k^3 weighted chi fitting, I agree is far from satisfaction.
> > Std of delR is a bothering point. I had included 20 paths. Even for the
> CdO
> > with F m-3m, the calculated second peak has a shoulder at lower R. I
> could
> > see a small contribution from path 4. But I am not sure if that is all.
> >
> > How to float the individual GDS parameter for each and every path? What
> can
> > be done to improve the fitting?
> >
> > Thanking you all in advance
> >
> > Varadarajan Sridharan
> >
> > ----------------------------------
> >
> > Condensed matter Physics Division
> >
> > Materials Science division
> >
> > Indira Gandhi Centre for Atomic Research
> >
> > Kalpakkam 603 102
> >
> > India
> >
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> End of Ifeffit Digest, Vol 89, Issue 3
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