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

[Matt Newville]

Fuxiang,


On Thu, Jun 23, 2016 at 4:47 PM, Fuxiang Zhang <zhangfx at umich.edu> wrote:

> 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
> 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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