Re: [Ifeffit] Ifeffit Digest, Vol 89, Issue 3

6 Jul 2010


      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,
wrote:
...
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Today's Topics:
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 
To: XAFS Analysis using Ifeffit 
Subject: Re: [Ifeffit] Clarification needed on the structured 2nn peak
Message-ID:
       
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
...
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
On Tue, Jul 6, 2010 at 7:29 AM, Varadarajan Sridharan
 wrote:
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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