Re: [Ifeffit] Vanadium-Chromium Prussian Blue Analog XANES fitting

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 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> _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit