I am new to the XRD, and when I analyzing the Au particle (micron size), I see some abnormal split of the peaks happened. I suspects that the splitting is due to the K alpha 1 and K alpha 2 of the copper. I doing the XRD on d8 advance power XRD machine. And I have done the SEM to confirm that the Au is pure. I check up some of the K alpha 1 and K alpha 2 splitting, it seem like they would cause 0.2% of difference in the d spacing( which is confirmed my all five peaks), but the intensity should be around 2:1, also the splitting should be more obvious with the increasing of the 2 Theta, those two are not my case. I wonder what should I do to confirm if it is due to the K alpha 1 and K alpha 2 splitting.
Dear Xingyu Chen,
Almost every XRD phase analysis software has the option to show you the spectral lines (K alpha 1/2... K beta and so on). Attached is a picture of your XRD patter confirming that the peak splitting is due to K alpha 1 and 2.
Dear Xingyu Chen,
In your pattern, the FWHM of the reflection varies for the diffraction peaks. The first (111) is much more narrow than the second (200) etc For that reason the split between Kalpha 1 and 2 "appears" not to increase systematically with 2Theta. Look at this systematic behavior:
hkl 2Theta width
111 38.2 narrow
222 81.7 narrow
200 44.4 wide
220 64.6 wide
311 77.6 wide
Since 111 and 222 are narrow, and all other hkl combinations are wider, a likely reason for this behavior is that the shape of your particles might be anisotropic probably "nanorods" along [111], which means that the diameter along [200] will be smaller, resulting in broader diffraction maxima.
Rietveld type programs can describe this with some effort, forget the so called Scherrer equation, it gives a course size estimate of size at best. To fully characterize the particle needs to be simulated with a full atomistic model and the powder pattern be calculated with the Debye-Scattering-Equation.
Keep in mind that you need the instrumental resolution if you want to determine accurate sizes.
R. B. Neder
Dear Dr.Neder,
Here is the SEM image of this nanoparticle, it looks like it has an intrinsic twins. Could that be implied that the crystal is thus anisotropic instead of causing by Kalpha1 and Kalpha2?
Your presumption is right. Only point to remember is splitting takes place only at higher angle. If you find splitting at lower angles that is below 50 degree, you have to be cautious. Reason may be many, like phase transformation, presence of impurity, alignment of deffractometer and so forth and so on.
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