[Ifeffit] Vanadium-Chromium Prussian Blue Analog XANES fitting

Adora Graham abaldwin2242 at gmail.com
Thu Jul 30 18:38:45 CDT 2015


First of all, I am still very new to XAS analysis, so please excuse any
misunderstandings I may have.

I have a series of compounds nominally consisting of KxVx[Cr(CN)6] Prussian
blue analogs (where x is ~1) with Cr(III) and presumably V(II) present in
the system. From other evidence, the V(II) may be oxidizing to V(III). I
have XAS data collected at the V and Cr K-edges from APS and have been
struggling through trying to analyze my data using Athena.

I am trying to get two things out of this data:

First, I would like to get the oxidation state of the Vanadium sites. If
they are not V(II), to get the ratio of V(II) to V(III) present, if
possible. I have been trying to follow a similar analysis to Wong (Phys.
Rev. B, 1984, 30, 10, 5596-5610). However, I seem to be running into the
issue of finding standards with a similar ligand set to my sample. I have
XAS data for the following standards: VO, V2O3, V2O4, V2O5, V(acac)3,
VO(acac), VOSO4, and VSO4. I start with VSO4 as my initial vanadium source,
so that could be useful for a comparison. Our initial idea was to use the
vanadium oxides to give a standard curve to then extrapolate the oxidation
state of my compound, but using this gives me an oxidation state of ~4.2
which seems unreasonable for my system. I am kind of lost otherwise as to
what else I could do with this.

Second, I would like to get the ratio of V to Cr. I was told I could
compare the un-normalized K-edge heights of the vanadium to that of the
chromium to get this ratio. This doesn't seem right, as I would think that
there should be some relative intensity factor involved. Also, this gives
me a fairly unreasonable value of 4:1, since XPS measurements give me
values of around 1:1.

Can you point me in the right direction for these issues?

I've also attached the project files for one of my samples.

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