[Ifeffit] from Rui Si at SSRF: help needed

[Scott Calvin]

Hi Rui,

Since XRD indicates your material is phase pure, I can think of three likely contributors as to why the 3 angstrom peak is "missing."

First is that you never actually plotted the model. You plotted the magnitude of individual paths from the model, but you did not sum the paths and plot the magnitude of the result. Your paths 2, 3, and 4 all show considerable amplitude around 3 angstroms, but the magnitude plot does not show phase. It is quite possible for those paths to add out of phase, and thus partially cancel. You should try summing the paths and plotting the result.

Second, Co3O4 is a spinel, and has two different absorbing sites for cobalt (the tetraehdrally and octahedrally coordinated ones). It very much looks to me like you only did a feff calculation for one of those sites. You need to calculate for both sites. Since there are two octahedral sites for every tetrahedral one, you need to weight the octahedral sites twice as heavily when you do the sum (you can use the S02 path parameter to affect weighting).

Finally, you didn't include any multiple-scattering paths. Multiple-scattering paths are significant contributors to spinel spectra in that region of the Fourier transform.

--Scott Calvin
Sarah Lawrence College


On Jul 15, 2014, at 5:25 AM, Bruce Ravel <bravel at bnl.gov> wrote:

> 
> 
>    (1) Why the second peak (ca. 3 Å) in experimental data is missing in
>        the Co3O4 model?
>