In synchrotron XRD of Ni/Ni3Al I have found low angle peak with twice bigger interpalanar distance than 111 (2.06 A) at 4.12 A. Can it be instrumental artefact?
Such type of peaks doesn't relate to instrumental errors. Unidentified peaks in this case could be due to a possible second phase, you should exam this possibility first which is the most probable if not try the second choice of super lattice
as i see from the graph there are other unnamed other peaks, you should take all peaks for your analysis. Analysts unidentified peaks separately for both cases suggested above
Could you please show your original XRD image. How is your data masking?. Another possibility is as Dr. Omar suggested, there is a possibility of second phase.
@ Omar M S
Thank you, superlattice is reasonable, but one thing bothers me, this are quite common alloys. why no one found it before?
@ Sorb Yesudhas
In file there is image exported from .mar3450 file. Unfortunately I don't know anything about masking.
I don't know what was the wavelength and X-ray spot size that you have used for this measurement. The data is very spotty because you didn't ground the sample well. If the sample is not powdered well (soft grounding for nearly three hours until the sample size become ~1 micron), then for the incoming X-ray beam, bigger size particles in your sample will act like single crystals. If too many spots are on the rings, then the observed intensity will be different from the actual intensity. You can’t do proper fitting with this kind of data. Using Fit2D or Dioptas software, you need to mask big spots and then integrate to convert the 1D image to 2D pattern. My opinion is that you need to repeat the measurement and this data you can use for preliminary analysis. Since you have two well defined rings at the beginning (first two rings), therefore your sample may not be pure.
Please have a look at the synchrotron XRD carried out under high pressure and the red colour represents the masking. The brodness of rings is due to the merging of more than one peak.
Thank you for your comment I will take care of that in future, these were my first samples measured this way.
Other unidentified on the picture peaks are from Cr7C3. I just didn't name them. I have different scans from extracted Cr7C3 from this alloy and I Cr7C3 is not source of the peak at 4.12 A .
May be some impurities would have incorporated while grounding or some unreacted component of the sample may contribute this extra peak. Since synchrotron radiation is extremely intense and having very high energy and flux, even the presence of small traces of the impurity also it will detect.
I have studied this sample extensively using SEM and TEM and no other phases were found (We didn't check it for that super lattice).
XRD was performed on bulk 4x4x20 sample cut from casting I don't believe that impurity will give only one peak exactly at two times higher interplanar distance in comparison to 111 (Ni, Ni3Al) I have 7 other samples with other compositions with the same effect.
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