I have performed powder XRD ( Rigaku smart-lab X-ray powder diffractometer - RINT2200 ) on my sintered samples. The base intensity of two different samples sometimes varies hugely even though the pattern is perfect, such as one in order of 103, while other is in order of 105. I usually grind the sintered samples before performing XRD. So does the size of powder particles after grinding cause this? If so, why?
Are the samples chemically equivalent or could fluorescence be an issue?
Dear Sai,
The intensity of diffraction is related to several points. The structural factor is responsible for the overall intensity. Atoms belonging to a plane in the structure contributes to some extent to the final intensity of a particular peak. The influence relates to the (hkl), Miller index of the plane.
For instance, the final intensity, let say for the (111) plane, is the sum of the contribution of all atoms that belong to that specific plane.
Based on that, if you have a loss of stoichiometry, it impacts the final intensity of that plane to which the lost atom belongs.
Some other intensity effects are a result of:
1 - Crystal size: smaller sizes usually results in larger FWHM and so lower intensity.
2 - Imperfections: if the final crystallinity of your sample is not as good as expected, the defects all over the lattice affect the final intensity.
3 - Sample holder improper prepared: if some preferred orientation occurs in the sample preparation, relative intensities differ from the expected ones. Have in mind that the capillary mounted sample for transmission is by far better than the usual powder sample holder preparation. Spray dry prepared samples are the best ones.
4 - Sample inhomogeneity: based on size, length, or the preparation itself.
5 - overlapped intensities: if you have polymorph, other phases such as reactants in the sample, they may overlap some peaks, usually clearly observable in the correction matrix.
6 - Isomorphic substitution: if another one substitutes some atom, the electron density may vary significantly, implying in a different structural factor.
7 - Interstitial substitution: atoms outside of the special positions of your space group may result in intensities variation of the diffraction pattern.
8 - Measure setup: if some orientation is present, and you measure in static mode (no sample spinning), you may orient the X-ray beam related to crystals in your sample. This problem is crucial in needle-like crystals. They need consistent crush.
Best regards,
WNM
Respected Pal Baggethun,
All the sample are chemically equivalent. They are various wt% of Carbon in MgB2 sintered powder. I think there is no issue of fluorescence.
Respected Wagner Da Nova Mussel,
Thank you for your insight. In all samples, the peak intensities after normalizing, match with the database. But the base values (before normalizing) between two similar samples are different by a few orders.
For example, take XRD specimens i) a and ii)b-made from MgB2 with 2 wt% and 3 wt% carbon added respectively. The XRD pattern when normalized looks almost same, but the intensities for specimen a are in order of 10^3, while that of specimen b are in order of 10^5. Hence i was wondering what might be the reason.
Thank you
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