As you can read in any tetbook on XRD (for example, D.B. Cullity), among the most frequent cases, peak shift can be caused by strain or by changes in chemical composition. In case of strain resulting from a planar stress - very likely in a thin layer - peaks in a typical theta-2theta scansion will be shifted to lower angle for compressive stress and to higher angle for tensile stress. Change in stoichometry can produce similar effects, but for ZnO films I'd expect more likely a strain effect. A psi-tilt (or omega-tilt) measurement could demonstrated if strain is the (main) reason for the observed effect: see textbooks for X-ray residual stress analysis

As you can read in any tetbook on XRD (for example, D.B. Cullity), among the most frequent cases, peak shift can be caused by strain or by changes in chemical composition. In case of strain resulting from a planar stress - very likely in a thin layer - peaks in a typical theta-2theta scansion will be shifted to lower angle for compressive stress and to higher angle for tensile stress. Change in stoichometry can produce similar effects, but for ZnO films I'd expect more likely a strain effect. A psi-tilt (or omega-tilt) measurement could demonstrated if strain is the (main) reason for the observed effect: see textbooks for X-ray residual stress analysis

Yes I am agree with P. Scardi answer, shift in XRD peaks arises due to strain contribution in the sample preparation.

thanks this information is very useful and can I get that book about XRD from internet?

Sidra, I would check your university library, but there are some excellent online features out there including this one from the University of Cambridge:

http://www.doitpoms.ac.uk/tlplib/index.php

Nur, another reason could be a so-called zero error, meaning that the sample is not in the calibrated position. To separate this from strain one indication could be that both the high and low angle peaks are shifted by the same amount. If the sample is strained the shifts will normaly be greater at high angles than low angles.

shifts in peaks positions mean that the unit cell increase or decrease respect to your "ideal" model. just to be sure, try to measure one of your samples with some standard (LaB6, Si, Y2O3, etc, the one in which the reflections do not overlap too much with the reflections of your sample) and then determine and refine the lattice parameters and adjust with the standard. Then you will see if the deviations arise from your sample or is a problem of calibration of the diffractometer. hope it can help you

Certainly, it is pretty interesting and fruitful discussion. A good chance to learn more about strain analysis via XRD. I think, you should look your substrate peaks. If there is also a similar change as you have for your thin films then it could be misalignment etc. Otherwise, it is compressive stress (decrease in 2*theta), or tensile stress (increase in 2*theta).

Nur, the shifting of peaks is due to change in d-spacing of planes i.e. change in lattice parameter. The d-spacing change can be caused by strain or stress. Generally, the residual strain or stress results in increase in FWHM of peaks. Other wise change of d-spacing in nano-materials is well reported and attributed to the change in lattice parameters at nano-meter scales due to enhance surface forces.

The shifting may occur due to substitution or doping your compound with any external source(frenkel/schottky defects)....left and right depends upon the ionic radii of the particular source you may have used.

I agree with others: Peak shift may be due to strain (crystal defects) – crack – dislocation- surface roughness for one element: For alloy and composite materials added interference effect

Firstly, I agree with the P. Scardi answer, shift in XRD peaks could be due to strain contribution, which is a macrostress. Secondly, the shift is also can be duo to the zero drift from XRD equipment. Thirdly, the shift XRD peaks can also be caused by temperature. And in your sample, I think the strain could be one important reason. In addition, I think you should also exclude the error influence from the expand of peaks duo to the small grain size of nanostructure.

To me this question is interesting because it is fundamental and even after a century past the Braggs' Nobel Prize https://www.flickr.com/photos/85210325@N04/11604959265/, we are still confronted with the same paradigm, ambivalence. XRD data and results should be precise and unequivocal. However, it is clear from not only this discussion but numerous others both on RG (Research Gate) and LI (LinkedIn) that the "fat lady hasn't sung yet" (the end of the show isn't near yet) on this topic.

I hope to share some of my experimental data with various materials to help shine the light on this "dimly lit path" perhaps. Therefore, with much humility and deference to those who have already made vital comments, here are my observations and opinions:

1. Post and display your data in order to fully take advantage of the super-expertise available on RG & LI.

2. Post specific details such as substrate used, film thickness, sample prep., other data such as optical micrographs, SEM, AFM, TEM etc.

3. Never try to analyze a linear diffractogram without an internal or external "standard" for calibration. "Trust but verify", "Доверяй, но проверяй", "Doveryay, no proveryay"

4. In your case, the substrate would be an ideal "relative standard" if crystalline. What is it? How close are the substrate reflections to the film reflections? Post your data.

5. "electrochemical deposition process" - Can we assume that you are creating a "film" on a substrate? Please define it unambiguously.

6. Try to be engaged in the discussion and not abscond (MIA) after popping the question.

7. Hypothesize, but confirm by the process of elimination.

8. BTW How do you normally confirm the precise positioning of the sample surface on the diffractometer axis? Do most of you assume this, or do you verify for each sample? Especially, if not powder.

Even with all these challenges the conventional linear diffractogram has been successfully used by most of us for nearly a century now. So if you don't mind the Rip Van Winkle Factor (long tedious data acquisition times), continue to use the method. If not, switch to the more modern 2D detector and 2D diffractograms (a Million to Billion advantage). You may always use the nearly extinct ancient tool (photographic film) if you cannot afford the modern real time 2D imaging tools for XRD. Don't forget that the Braggs, Ewald, Laue, Guinier, Weissmann and others in the past did use film to record the ever-present 2D XRD signal in each experiment. Neglecting the 2D diffraction pattern would invariably result in the "hand waving" and lack of precision many of us have to contend with presently.

More to come……….

https://www.flickr.com/photos/85210325@N04/11343736043/

Please review this RG discussion for more details:

https://www.researchgate.net/post/Is_this_a_reasonable_way_to_eliminate_effects_of_sample_surface_misalignment_with_the_diffractometer_axis_Theta-2Theta_Diffractograms

Use of internal standards and addressing sample surface misalignment w.r.t diffractometer axis.

Notice that without the Aluminum (111), (200) & the (220) peaks emanating from the fixed Aluminum sample holder, it would have been impossible to tell the cause of the shift in the other peaks. After adjusting the profiles so that these 3 Aluminum peaks coincide, the rest of the peaks lineup well with each other. This cause of XRD peak shift must be eliminated before one can draw any precise conclusions regarding XRD peak shifts.

Since we are recording only one side (relative to the incident beam) of the Debye-Scherrer arcs in conventional diffractometery the "zero offset" is not easily perceived. However, if one was observing the D-S arcs on either side of the (000) incident beam such misalignment would be amply apparent. It would still serve well to employ a "known standard" such as we have in the Aluminum holder diffraction pattern (spectrum) common to all the diffractograms.

Anders, can I know for a strained sample why is that the shift is high at large angles than at low angles? It would be very helpful if i can get some reference for this as I got similar results for one of my thin films? Thanks.

Rm, the Bragg equation indicates that at higher angles a shift due to a change in the unit cell will be larger for a high 2theta than a low one. By differentiating the Bragg equation with respect of 2 theta this becomes apparent.

Thanks for that. I need one more clarification. You said that if there is an instrumental error with zero position, the shift would be same at higher and lower angles whereas it will be more prominent for the strained sample. Can you kindly check the below link where I got a different answer that for sample misalignment the shift will be prominent  at higher angles? Your answer will be really appreciated.

https://www.researchgate.net/post/Can_someone_advise_me_on_XRD_2_theta_position_shift_for_222_plane_but_not_for_111

Sorry, Rm, your question eluded me last summer and I was only now aware of it!

If you do the maths you will find that zero errors are actually less prominent at high to very high degrees 2 theta. I work with large to very large unit cells meaning that I don't normally measure above 50 degrees 2 theta and the zero error is more or less constant (it actually has a cosine dependence on theta) as the shift also depends on the ratio between the diffractometer radius and the sample misalingment. For my system, this ratio is about 1000. However, from your other question you talk about a shift of as much as 2 degrees 2 theta, something I don't believe could be due to your sample being missaligned.

For strain, this is also not typically a very large effect on peak positions, but can act in both shifting the peak due to the lattice parameters changing slightly if uniform or by adding asymmetry to the peak if non-uniform.

Hope this helps!

The peak shift can arise from the non-alignment of sample during experiment and at high temperature. The sample may have experienced residual stresses. The second circumstance however, is most uncommon but can happen. The best thing to do is to repeat the test again at least three times.

Large size ions shift XRD to low angle side while samll size ions shift it to the high angle side....

Are u sure @P. Scardi that lower angle means compressive? I think its tensile? Pls Correct if I'm wrong.

Dear Nur,

It is caused by strain, texture and temperature effect.

Ashish

you need to do two corrections . 1-slit wedth

2-background line and remove amorphous content

Dear Ganesha Krishna V S ,

you are right. With respect to stress/strain:

tensile stress will decrease diffraction angle and compressive stress will increase diffraction angle.

There is unfortunately an error above.

http://pd.chem.ucl.ac.uk/pdnn/peaks/size.htm