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@bnl.gov
National Institute of Standards and Technology
Synchrotron Science Group at NSLS-II
Building 743, Room 114
Upton NY, 11973
Homepage: http://bruceravel.github.io/home/
Software: https://github.com/bruceravel
Demeter: http://bruceravel.github.io/demeter/
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