Anatoly: Thanks so much. Jhonny Huertas Flores Rio de Janeiro-Brasil

From: ifeffit-request@millenia.cars.aps.anl.gov Subject: Ifeffit Digest, Vol 113, Issue 13 To: ifeffit@millenia.cars.aps.anl.gov Date: Sat, 14 Jul 2012 16:19:14 -0500

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1. Re: Ifeffit Digest, Vol 113, Issue 11 (Anatoly I Frenkel) 2. "RE: Contents of Ifeffit digest..." (johnny huertas)

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Message: 1 Date: Sat, 14 Jul 2012 19:13:01 +0000 From: Anatoly I Frenkel To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Ifeffit Digest, Vol 113, Issue 11 Message-ID: <545F89325F51764C902D37B42C9F4D53135B1B44@YUWEXCPM12.yuad.uds.yu.edu> Content-Type: text/plain; charset="iso-8859-1"

Hi Jhonny,

This article on AgBr(x)Cl(1-x) explains how to do this type of analysis, and if there are still questions, look for other articles (in Phys. Rev. B and Phys. Rev. Lett.) on mixed ionic salts, by the same authors:

https://pubweb.bnl.gov/~frenkel/BUCKLING-PHB/buckledPHB.pdf

It is a model independent way to find local composition of Br and Cl around Ag. You are better off doing that (limit it to the 1st shell analysis) rather than using particular configurations you are proposing, and then see if you get the same composition (x) for Ag-Br as you obtain for composition y corresponding to the Br-Br coordination number found from Br K-edge. That will mean that your alloy is random. Otherwise, there may be either short range order or segregation that you will be able to identify by comparing x and y in each individual case. Rely on XRD results also, to tell whether you really have a solid solution or not.

If you only measured Ag edge, you still can make some conclusions but you should rely on the bulk composition to compare the "x" and "y".

Anatoly

________________________________ From: ifeffit-bounces@millenia.cars.aps.anl.gov [ifeffit-bounces@millenia.cars.aps.anl.gov] on behalf of johnny huertas [johnnyhf@hotmail.com] Sent: Saturday, July 14, 2012 1:51 PM To: Lista fe IFEFFIT Subject: Re: [Ifeffit] Ifeffit Digest, Vol 113, Issue 11

Hi Matt: Thanks for your response. First of all I am beginner in this issue. Because of my little experience I don't know exactly how to specify my problem but I think you write an interesting phrase in your response: "are you asking if you can distinguish random substitution from ordered substitution? I'm not sure why the Ag-Br and Ag-Cl parameters would be the same". I don't know how to create a robust fitting model to distinguish random substitution from ordered substitution of the example found in Bruce site about AgBr(1-x)Clx. What are the parameters that I must consider to fit the spectra and to verify if exist random or ordered substitution? I am attaching a document very explicit about this. Thanks again.

Jhonny Huertas Flores Rio de Janeiro-Brasil

...

From: ifeffit-request@millenia.cars.aps.anl.gov Subject: Ifeffit Digest, Vol 113, Issue 11 To: ifeffit@millenia.cars.aps.anl.gov Date: Sat, 14 Jul 2012 12:00:01 -0500

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Today's Topics:

1. problems (johnny huertas) 2. Re: problems (Matt Newville)

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Message: 1 Date: Fri, 13 Jul 2012 22:21:50 +0000 From: johnny huertas To: Subject: [Ifeffit] problems Message-ID: Content-Type: text/plain; charset="iso-8859-1"

Members of list: I have some problems to resolve a question. I have been working a lot in fit the AgBr(1-x)Clx example of FEFFIT site. My fits were good in my opinion, but I don't know how to identify the Br and Cl atomic distribution around Ag (random or specific?). I didn't find any example about this in the site. Conversely I have made some attempts to identify such distribution. I have made two fits preparing for each one feff file, a feff file puting Br and Cl atoms in face and other in medirian position around Ag knowing the CN=6 of this central atom and fiting only the first shell. Unfortunatelly I don't have found satisfactory results because the paremeter are equal in both cases. I would like you help showing a similar example. Thanks. Jhonny Huertas Flores Rio de Janeiro-Brasil