[Ifeffit] Vanadium-Chromium Prussian Blue Analog XANES fitting

[Chris Patridge]

If you have Dr. Whittaker-Brooks data then you have the work we did on vanadium oxides. You can look at some of the other vanadium papers we did. 

Chris

Sent from my iPhone

> On Jul 30, 2015, at 11:49 PM, Adora Graham <abaldwin2242 at gmail.com> wrote:
> 
> Chris, 
> 
> 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?
> 
> Regards, 
> Adora
> 
>> On Thu, Jul 30, 2015 at 6:12 PM, Chris Patridge <patridge at buffalo.edu> wrote:
>> 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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> 
> <XAS main edge correlations.pdf>
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