I got the XRD pattern for undoped and 6% and 9 % Ni doped ZnO NPs. It is clear that there is no NiO peak and not change the crustal structure with Ni doping. But, 6 % Ni doped ZnO XRD peaks shift to lower angle as compared with a pure ZnO NPs. However, 9% Ni doped ZnO XRD peaks shift to higher angle as compared with a pure ZnO NPs.
Hi Sajith,
it is a surprising, unexpected result; do you have checked your theta/2-theta scale?
Is your sample thickness the same for the 0%, the 6% and the 9% Ni doped sample? Otherwise you may have different surface levels of your sample surface with respect to the x-ray beam; thus shifting the theta scale a little bit. But I must admit that significant +/ - theta shifts are not easily achieved by different surface positions. This leads to the question on how much are these +/- shifts in theta?
A second option may be that perhaps your zero point of your theta scale might be not right in at least one of your cases.
From the x-ray spectroscopic point of view it is interesting that by the introduction of Ni into the sample (ZnO) the Cu K-beta lines and thus the corresponding XRD peaks will be significantly reduced relative to the Cu K-alpha based peaks due to the appearence of the attenuation caused by the Ni-K-edge in the sample system. But from this apect I do not expect any +/- peak shift in theta.
Gerhard's points are good. Post the data so we can see how much shift you have. You could add a small amount of a crystalline standard material like Si or Al2O3 in order to calibrate your peak positions.
Hi Ian,
adding a standard material for having a calibrated theta scale is a good idea.
So Sajith is then able to exclude all issues with respect to theta scale. Very good!
Dear Professor Martens
Thank you very much for your valuable answer. I have checked all 2-theta value .Also i cheeked 12 % Ni doped ZnO NPs. It also shift to higher angle as 9% doped ZnO NPs.
Hi Sajith,
thanks for your answer.
Assuming now your 2-theta scale is right. For bulk ZnO I would expect either a gradual increase of lattice spacing or a gradual decrease of lattice spacing with increasing Ni doping amount.
For your ZnO nano-particles this is obviously not the case.
Therefore I think the large surface area compared to the volume of the NPs may be responsible for your measured effect.
Do you have perfomed the doping after formation of the ZnO NPs?
If so, I think there showed up compressive stresses in the NP surface when a few (6% case) Ni atoms attach the surface and partly move into the NP, thus giving rise to tensile stresses (larger d-spacing) inside the NP.
With increasing doping (9% and 12%) the stress in the surface change from compressive to tensile ones due to more accumulation of Ni at the surface, giving rise to compressive stresses inside the NP (lower d-spacing). May be that there a closed Ni layer is built up in these cases.
But please pay attention: These thoughts are pure brain storming like speculations.
For looking deeper into this scenario you have in additon to the peak shift to look at the peak widths and at the peak profiles. The latter may be asymmetric too.
As Ian J. Slipper suggested above, you should share the data with her. She is an expert in this field and has got the tools and has got a very lot of experience in analyzing XRD spectra.
I very much agree with Gerhard Martens the change of peak positions means change of d spacing or in other words lattice parameters.
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