Re: [Ifeffit] How to input atoms in solid solution for Artemis

Thank you all for the help. Fuxiang On Thu, Jun 23, 2016 at 10:19 PM, Matt Newville wrote:

Fuxiang,

On Thu, Jun 23, 2016 at 4:47 PM, Fuxiang Zhang wrote:

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Hi, Scott,

In fact, I have a series of single crystal Ni-Fe alloys (Fm-3m) with known atomic ratio, and measured both Fe and Ni edges for samples and standards. I just want to see if there's any difference between the local bonding environment of Fe and Ni, such as R, N and sigma2. Now using the suggested method by Matt by changing atoms in FEFF.inp file, I can only get ss, deltr and E0 from fitting (I don't know how to refine N and R).

You can refine N and deltaR for any scattering path. R is Reff + deltaR, so that *is* refining R. When you say "I don't know how to refine N and R", I'm left unsure what part you do and do not know. There are lots of on-line examples and documentation. If you're having trouble, it might help to ask a specific question.

...

But the fitting with Ni (or Fe) edge can only generate the same R and deltr for Ni-Ni and Ni-Fe pairs.

I'm sorry, I don't understand. In principle, the Ni-Ni distance and Ni-Fe distances can be different, of course.

Fitting the edges of Ni and Fe will yield a little difference in the R and

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deltr. Which results should I believe, or something wrong I am using the program because I cannot generate different R for Ni-Ni and Ni-Fe pairs with the same data set. Many thanks for your suggestions and helps.

I can't tell whether you're saying you do not know how to tell Artemis to refine different distances for Ni-Ni and Ni-Fe, or that when you do tell it to do this that the result is that the two distances are the same.

As said earlier, unless you're looking at some weird situation, I would expect measuring distances and coordination numbers separately for Ni-Ni, Ni-Fe, Fe-Fe, and Fe-Ni to be very, very hard. My recollection (could be wrong) is that the nominal near-neighbor distances for fcc Ni and bcc Fe are both around 2.48 Ang. With Z different by only 2, I would not expect these to be distinguishable.

But the program definitely allow you to try....

--Matt Newville

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