[Ifeffit] The most important fitting parameters

[Bridget Ingham]

Dear all,

I am trying to use EXAFS, along with other techniques, to attempt to find
information about an unknown structure. It is an organic-inorganic hybrid
material, EDX reveals Cu1-W1-O4 as the stoichiometry of the inorganic
component, which we are most interested in structurally. We have not been
able to solve the structure from XRD, although not for want of trying.

I started off with CuWO4 as the model compound and constrained the fitting
parameters:
- take all 1st oxygen shells (x6 at slightly different distances) and give
them all amp1, dr1*reff, enot and ss1
- take all 1st copper shells (x2) and give them both amp2, dr2*reff, enot
and ss2
- take all 2nd oxygen shells (x6), amp3, dr3*reff, enot, ss3
- take all 1st tungsten shells (x6), amp4, dr4*reff, enot, ss4

This gave me 13 parameters with 14.8 independent points.

(Other factors: fitted in kw=2&3, k-range 2-9, used Athena with default
background subtraction parameters as the chi(k) from that seemed sensible.
The data were collected at SSRL, beamline 11-2, in transmission.)

I was happy with the final result (R-factor 0.014), but am just wondering if
this is a sensible way to go about doing things - bearing in mind I am not
sure of the structure in the first place. Any hints or advice would be much
appreciated. I should have collected data at the tungsten edge as well, as
it is not that much higher in energy from Cu, but this didn't occur to me
until later.

Regards,
Bridget

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