# Effect of dopant size on XRD peak shift

If we add an impurity atom (doping) to the crystalline struture of another material and take the XRD of the doped material what kind of peak shift can we expect. For the better description of my question i have added an image below

In the image black bold line ($2\theta$) is the standard XRD peak of a material; blue ($2\theta ^{L}$) and green ($2\theta ^{R}$) dotted lines are the peak shift caused due to the doping of impurity atom. Can you tell me if there is any relationship between dopent size and peak shift (right/left dotted lines).

• Well, for one thing I'd say that, if the doping changes the lattice parameters then the XRD peak shifts in the opposite direction: So, if the dopant leads to an increase in the lattice constant then the diffraction angle $2 \theta$ decreases. But I fear your question might be a bit too general and it is difficult to make general predictions about what happens to the XRD shift when you dope the material. But then again, I'm no expert in this field and there might very well exist general guidelines that I'm not aware of. – Philipp Sep 6 '13 at 10:49

Doping, not to confuse with alloying, introduces a low amount of impurities or more generally point defects in a crystal. The overall periodicity of the system is thus not changed and no shift should be expected in XRD. However doping introduces some disorder that makes XRD peaks broader.

The peak shift in the xrd is based on the dopant size. If the dopant size is smaller than the base metal it occupies the interstitial position leading to change in the lattice structure and the d-spacing between the atoms become less and there is an increase in the x-ray diffraction resulting in higher angles ($$2\theta^R$$). And vice versa when the dopant size is larger than the base metal. Lower angles ($$2\theta^L$$) is attained with increase in d spacing.

Sometimes, dopants can go to the interstitial site of the target material. We can say this makes some distortions happen.That actually change the crystal structure. Then we can see the certain peak position changes.

Also, misalignment can make peak position changes.So we have to operate the machine properly. calibration is very important.

Strain and stress of the materials can make XRD peak shift as well.

Good luck.

• The OP's question was 'Can you tell me if there is any relationship between dopent size and peak shift?' This does not answer that question and so I am flagging it for deletion. – bon Jun 15 '15 at 10:31