[Ifeffit] Vanadium-Chromium Prussian Blue Analog XANES fitting

Adora Graham abaldwin2242 at gmail.com
Thu Jul 30 22:49:46 CDT 2015


I have attached a copy of the correlation plot that I am using. I could
also send more information as to how I am picking the peaks (which might
also be the problem here), but that would take significantly more time to
generate at this point.

I was using the main edge values reported in Wong's paper (in red), since
one of my standards (VSO4) does not have a pre-edge peak, so it wouldn't be
comparable. The main edge value I get for VOSO4 differs by ~0.6eV compared
to Wong's reported value, so I think I'm adjusting things correctly. I
actually have access to the raw data from J. Mater. Chem., 2011, 21,
5580  (with permission from Dr. Whittaker-Brooks), which I am using as
several of my standards (in black).

I have a feeling that my main issue is the difference in attached atoms (CN
vs. O) of my compound compared to the standards. What do you think?


On Thu, Jul 30, 2015 at 6:12 PM, Chris Patridge <patridge at buffalo.edu>

> The standard curve using V standard, how are you making the curve?  You
> probably know from the Wong paper that there are pre edge features for the
> vanadium oxide species. We used a very similar method to assign oxidation
> states to doped vanadium oxide compounds between 3-5. The method gave us
> results that were consistent with other evidence.
> Chris
> Sent from my iPhone
> On Jul 30, 2015, at 7:38 PM, Adora Graham <abaldwin2242 at gmail.com> wrote:
> Hello,
> 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.
> Thanks,
> Adora
> <AGB02-083-Cr merged.prj>
> <AGB02-083-V merged.prj>
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