Tony --

> Should I fit EXAFS spectra of a doped material and the same material, but
> oxidized and reduced (three spectra) simultaneously? In my opinion: yes, as
> I am looking for small differences. Is varying one Eo for the three samples
> the right approach?
> I am also wondering, should I vary one Eo for samples with different doping
> concentrations?
>
I think you need to be more specific about what your samples are and
what you're trying to learn from them.   For example, I could read
your question as meaning you have samples of
    Mn K edge for Mn doped into silicon  ("a doped material")
    Si K edge of pure silicon              ("same material, reduced")
    Si K edge of quartz                      ("same material, oxidized")

In which case, I don't see that see much to be gained by fitting the
spectra together.

In general, one fits multiple spectra together when it is expected
that there is a relationship between the different coordination
environments, most usually a simple relationship between the g(R)'s
for the different samples.

E0 is typically different for each sample.  There are situations where
they can be constrained to be the same, such as spectra are all on the
same sample at different temperatures.

For more specific answers, please ask more specific questions.

--Matt
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