[Ifeffit] Calculating Ce oxidation state at the L3 edge

[Bruce Ravel]

On 05/16/2017 01:31 PM, Stephanie Laga wrote:
>
> I have a (hopefully) quick question about calculating oxidation state of
> CeO2 at the L3 edge.
>
> When calculating ox state by taking the ratio of peak areas, is the
> pre-edge feature for Ce included in this calculation? This point isn't
> clear to me from looking at various papers.
>
> I've attached an image from Bernardi 2015, which shows that the %Ce III
> calculation doesn't include the fitted pre-edge feature A. I'm not sure
> why this would not be included? Is this because we only consider 2p > 5d
> transitions and the pre-edge is 2p > 4f (forbidden) transition?
>


I am not sufficiently knowledgeable about CeO2 specifically to answer 
your question specifically.  However, there are some general principles 
that apply.

The concept here is to come up with a set of peak shapes that describe 
the shapes of the end member spectra.  Those two sets of peaks, taken 
together, represent the contribution to the spectra from each end 
member.  Sum the areas of each set of peaks, that represents the 
contribution.

You then fit all of both sets of peaks to an unknown spectrum and sum up 
each set.  You now have enough information to quantify the amount of 
each end member.

So, in general, yes, you would include the fitted peak A because that is 
part of your quantification metric.  So, I disagree with the formula in 
the figure you attached.  But peak A is small, so neglecting it has 
scant impact on the result.

Some caveats:

1. You must be very careful about normalization.  If you do not 
normalize consistently, then you will introduce systematic error in the 
phase quantification.

2. You must use the same step-like function for both end members and for 
the unknowns.  If the step function changes, then the areas under the 
peaks will change, introducing systematic error.

It would be interesting to compare this to linear combination analysis 
to see if you get the same answers....

HTH,
B

-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
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