Re: [Ifeffit] Hexagonal WO3 (Carlo Segre)

Dear Carlo, Thank you very much. The point is that we have obtained a Co Mo/W O4 solid solution. It seems to me a very similar problem to that posted by Ying. Good luck in yor work, Yordy 2008/11/25

Send Ifeffit mailing list submissions to ifeffit@millenia.cars.aps.anl.gov

To subscribe or unsubscribe via the World Wide Web, visit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit or, via email, send a message with subject or body 'help' to ifeffit-request@millenia.cars.aps.anl.gov

You can reach the person managing the list at ifeffit-owner@millenia.cars.aps.anl.gov

When replying, please edit your Subject line so it is more specific than "Re: Contents of Ifeffit digest..."

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." Subject: Re: [Ifeffit] Hexagonal WO3 (Carlo Segre) To: segre@agni.phys.iit.edu, XAFS Analysis using Ifeffit Message-ID: 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 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 _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

End of Ifeffit Digest, Vol 69, Issue 17 ***************************************

-- Yordy E. Licea Fonseca Departamento de Físico-Química Instituto de Química-IQ/UFRJ Laboratório de Catálise Heterogênea Rio de Janeiro, RJ, CEP 21.949-909 Brasil Email: yliceafonseca@gmail.com