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Today's Topics:

  1. Re: Hexagonal WO3 (Carlo Segre)
     (Ying Zhou, Anorganisch-Chemisches Inst.)


----------------------------------------------------------------------

Message: 1
Date: Mon, 24 Nov 2008 19:47:48 +0100
From: "Ying Zhou, Anorganisch-Chemisches Inst." <ying.zhou@aci.uzh.ch>
Subject: Re: [Ifeffit] Hexagonal WO3 (Carlo Segre)
To: segre@agni.phys.iit.edu, XAFS Analysis using Ifeffit
       <ifeffit@millenia.cars.aps.anl.gov>
Message-ID: <web-16396377@idmailbe2b.unizh.ch>
Content-Type: text/plain;charset=iso-8859-1;format="flowed"

Dear Carlo

Thanks very much for your nice suggestions. This is really what I want to
know.

Best wishes
Ying


On Mon, 24 Nov 2008 11:33:02 -0600 (CST)
 Carlo Segre <segre@iit.edu> wrote:
>
> Hi Yordy:
>
> I have removed all the previous emails to keep the message short...
>
> On Sat, 22 Nov 2008, Yordy Licea Fonseca wrote:
>
>> Hi Carlo and Ying,
>>
>> Does it means that if the sample is a random solid solution at
>>experimental
>> temperature, in principle, you would be able to simulate the EXAFS spectra
>> whichever be the Mo/W ratio in the second shell coordination in the
>> Feff.inp, am I right?
>>
>
> I am not quite sure what you are getting at but I think that the answer is
> yes.  What you needto do is to have a single scattering path for each of
> the two possibilities in the second shell (Mo or W) along with the first
> shell path to O and then start fitting with minimal parameters.  For
> example, if you know that the total number of atoms in the second shell is
> 12 for this structure (and you are reasonably sure that this is the
> correct structure), you can constrain the sum of the two occupation
> factors to be equal to 12 provided that you have a reasonable
> understanding of what the amplitude reduction factor might be.  You can
> also start by constraining the delta R and sigma-squareds for the two
> paths until you are sure that the fit makes sense and is stable.
>
> If you have data from both W and Mo edges, you have more leeway in your
> fitting and you can begin to make a model which tries to figure out if
> there is clustering of one kind of atom in the structure.  There are a
> number of papers in the literature that do this (off the top of my head I
> can think of one in particular by Shibata and Bunker for Au/Ag
> nanoparticles but there are surely many more).  Ultimately you can develop
> a nice model but the one thing that you can't really do too much is
> include multiple scattering paths which include the atoms which are
> substituted for one another.
>
> Hope this answers your question,
>
> Carlo
>
> --
> Carlo U. Segre -- Professor of Physics
> Associate Dean for Special Projects, Graduate College
> Illinois Institute of Technology
> Voice: 312.567.3498            Fax: 312.567.3494
> segre@iit.edu   http://www.iit.edu/~segre   segre@debian.org
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