Hi Robert,

Thanks for responding, I don’t think that there was any formation of Cr6+ in the beam. The edge position or rest of the spectra didn’t change with repeated scans, it was just the variation in a single pre-edge peak.

Thanks again,

Rachel

From: Robert Gordon via Ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Sent: Thursday, 21 August 2025 4:02 AM
To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Cc: Robert Gordon <moyie.institute@gmail.com>
Subject: [Ifeffit] Re: Variation in pre-edge intensity with replicate scans without change in EXAFS

Hi, Any chance of a Cr6+ contaminant? The very pronounced pre-edge feature of Cr6+ in chromate appears to align well with the second feature in Cr3+ (Cr2O3). If that contaminant is being reduced in the beam, that might explain what you are seeing.

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Hi,

Any chance of a Cr6+ contaminant? The very pronounced pre-edge feature of Cr6+ in chromate

appears to align well with the second feature in Cr3+ (Cr2O3). If that contaminant is being reduced

in the beam, that might explain what you are seeing.

e.g. https://www2.ung.si/~arcon/_borders/xas/xanes/xanes.htm

-R.

On Wed, Aug 20, 2025 at 5:30 AM Rachel Pepper via Ifeffit <ifeffit@millenia.cars.aps.anl.gov> wrote:

Hi everyone, I’ve got some XAS data at the Cr K edge for Cr-doped alumina (i. e. ruby) powder samples (Cr 0. 1-1 atomic%) where we are seeing a reduction in one of the pre-edge peaks with replicate scans. There are three sets of samples;

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Hi everyone,

I’ve got some XAS data at the Cr K edge for Cr-doped alumina (i.e. ruby) powder samples (Cr 0.1-1 atomic%) where we are seeing a reduction in one of the pre-edge peaks with replicate scans. There are three sets of samples; each made by a different synthetic method.

We did do the repeat scans on the same spot on the samples and noted this change after the data was collected, which means that the change might be a result of beam damage. However, the results are odd because:

The reduction in intensity is consistent across different Cr concentrations for samples made by the same method, but is not observed for all preparation methods
The XAFS does not show the same systematic variation with replicate scans which suggests that this change in the pre edge is not due to a structural change
The edge position doesn’t change with repeat scans
We have compositional data for these samples, and there are no significant impurities
I’ve worked up the XAFS data in Artemis and there doesn’t seem to be significant differences in the structures of the samples prepared by the three different methods. For all methods, it looks like there is a second Cr atom in the second coordination shell, which is also supported by luminescence data.

I’ve looked online and found a computational study where intensity differences in ruby samples may be related to electron spin (doi: 10.1238/Physica.Topical.115a00191, doi: 10.1039/b926499j), but I’m not sure if this is a sensible explanation – I’m still quite new to this technique.

Has anyone come across anything similar, or does anyone know why we might have seen this in our samples?

I’ve attached some images of the pre-edge and XAFS regions for the scans to illustrate what I’m asking about.

Thank you,

Rachel

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