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://urldefense.us/v3/__https://www2.ung.si/*arcon/_borders/xas/xanes/xanes.htm__;fg!!G_uCfscf7eWS!Z4Fuo27w3E3LSMjq5mTa8j6CnnXHgficBY4OO-XWOXw1wu8MYNM-ayFo5L_mrHRyzl-Mn0ZSomMyQ3TbGxsphs4Qn0idEluu0D8K2aE$ -R. On Wed, Aug 20, 2025 at 5:30 AM Rachel Pepper via Ifeffit < [email protected]> 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; > ZjQcmQRYFpfptBannerStart > This Message Is From an External Sender > This message came from outside your organization. > > ZjQcmQRYFpfptBannerEnd > > 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: > > 1. 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 > 2. 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 > 3. The edge position doesn’t change with repeat scans > 4. We have compositional data for these samples, and there are no > significant impurities > 5. 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 > ifeffit mailing list: > https://millenia.cars.aps.anl.gov/mailman3/lists/ifeffit.millenia.cars.aps.anl.gov/ > > to unsubscribe, send mail to [email protected] >
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