I have obtained a Peak in XRD that's 10 degrees before the start of the peaks in the ICDD so I want to know is it acceptable? and what could cause this as other shifts are nearly Identical
Dear Imtenan Elmanzalawi ,
10° is a lot.
Matching of peaks should be in the 0,01° regime.
In your case, you should have a look at the x-ray wave lengths in use.
They have to match also.
If different wave lengths were taken, you are able to match the 2theta axes of both XRD pattern via the Bragg law...
Start with:
lambda1 = 2d*sin(theta1) & lamda2=2d*sin(theta2),
further calculation is straightforward...
Good luck and
best regards
G.M.
Dear Imtenan Elmanzalawi ,
in addition to Dr Gerhard Martens answer, the CCDC cards database is based on experimental deposited PXRD, they are not standards. They are real samples, measured by the authors compiled in the database. They pass through a check routine for basic descriptions errors and added to the database.
Therefore, your sample may present some dislocation due to characteristics not present in the reference, or present in the pattern used as reference not present in you sample.
Nevertheless, taking into account the correct wavelength, preparation, measurement setup, and adequate reference pattern the difference in peak position needs to be very low, as already stated.
Best regards,
WNM
Dear Imtenan Elmanzalawi ,
just an amendment:
a peak showing up for example at about 60° (in 2theta) for a Cu tube ( Cu K-alpha at ~1,54A) based XRD pattern will show up at about 70° (in 2theta) for a Co tube ( Co K-alpha at ~1,79A) based XRD pattern of the same sample.
However, the shift is not constant, but depends on the theta (2theta) value.
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