[Ifeffit] Hexagonal WO3 (Carlo Segre)

[Ying Zhou, Anorganisch-Chemisches Inst.]

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 at 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 at iit.edu   http://www.iit.edu/~segre   segre at debian.org
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