In which angular range are your scans, which geometry do you use, which energy too?

Might be that you just miss the diffraction points in reciprocal space.

are you sure you get the carbonate!!

It is always best to double check carbonation results with TGA in addition to XRD. As Mohamed A. Elbagerma suggested, not always are carbonation products actually carbonates. See my attached publication for examples of this.

Also, be mindful that hydrated magnesium carbonates (e.g. hydromagnesite) have diffraction patterns with broad peaks that can be mistaken for amorphous materials, in which case minor phases with sharp peaks may appear to be dominant. Use Rietveld refinement to distiguish between mass fraction quantities.

Article Distinguishing between carbonate and non-carbonate precipita...

Thanks Bojan, Mohamed and Rafael. Actually I did carbonation experiments with different mixtures of calcium, magnesium and calcium+magnesium. I just have problem with XRD for magnesium. TGA results and adding HCl to solid precipitate shows it should be probably nesquehonite (MgCO3(H2O)3). I have no idea why I just have problem in identifying the solid carbonate from magnesium carbonation. The angle I used was 2-90, 40kv and 15mA. Bojan what do you mean by "miss the diffraction points in reciprocal space"

Rafael, In order to do quantification by Rietveld method I need to find which potential components are available in my sample. Unfortunately it just shows 5 sharp peaks which matches with Al and it can come form just sample holder as I don't have Al in my sample. Now the question is why this happens considering I repeated the scanning several times but result is still the same. 

Rafael's suggestions are very good, the one thing I think you should try is to run a background scan of the sample holder alone, then run it with your sample, then simply subtract the sample holder run from the sample holder plus sample run. It could be that the sample holder reflections are far higher than the sample itself, so you need to discount the holder immediately. Also using a smaller step size, say 0.05 degree may be of use.

Also, what software database are you using to identify your sample ? I would recommend the PDF-2 (Powder diffraction file 2), but this is quite expensive. The basic databases that you get with Panalytical etc are not very good as they do not allow for crystallographic phase changes. If you do as I suggested above, then send me a) Your original RAW file, then b) The new RAW file with background subtracted, I can use my software to try to determine your compositions.

Thanks Christopher! Although I used smaller step size (0.01) but maybe your suggestion to run with and without sample can help. With your answer I think maybe the reason is the smaller reflection intensity of precipitate rather than sample holder. 

Thank you :)

Thanks Fabrizio! Definitely I will try that :)

Dear Tahareh,

I thought about the step size but yours should be fine. If the peak is really sharp, then it comes from sample holder or something else. You can try to measure just sample holder to see whether there is some difference or not. If this stays, might be that your carbonate peaks are not very intensive and therefore they are not visible due to the scaling to the order of magnitude of the very sharp and intensive one. I would try to measure from 3 deg. (for instance, I agree with Fabrizio) up to the sharp peak and then to continue after the peak. Let's hope that you find what you are looking for.

Best regards.

Thanks for your help Bojan! Sure, I'll do that :)

Hi are you student ph

Synthesis at ambient temperature may form an amorphous or quasi-amorphous structures without sharp diffraction peaks. Small absorption coefficient makes the sample transparent and the holder diffraction pattern is dominant. Try change the scale or use logarithmic or square root scale in order to observe weak signal. Usually you can form a crystalline material by heat treatment but pay attention to do it in the right atmosphere (in wich your substance is stable. 

Could you post an image of your diffractogram? This would help enormously.

First I wonder, why do you start at 2° in 2Theta? I would alway first simulate a diffractogram in order to determine the meaningful 2Theta range. If there all reflections can be interpreted all should be fine. If some peaks appear which cannot be indexed you should also include smaller angles in order to see ho big the usit cell is. 

If your peak would be Aluminium I am surprized that you see only one (at least it was written "the Al peak"). If your sample holder is of Aluminium ( is this really the case?) you should see all reflections, even if the sheet used is highly textured. That somebody uses Al single crystal as sample holder I've never heard about. Si sample holders are not that rare since quite easy to get, but Al? 

I would really recommend to post a pattern that we can see which kind of signal do you get.

Attached is a XRD simulation of a mixture of Al (red) and MgCO3 (trigonal Mg carbonate) for Cu radiation (this innformation is still missing: Which radiation you are using?). If these are the substances you are talking about the diffractogram should show these peak positions. Of course, if your Mg-phase is different, forget the Mg-carbonate reflections. It also shows you that in case of Al as secondary signal the MgCo3 signal is clearly weaker. The plot shows a mixture of 80% carbonate and only 20% Al. Nevertheless the Al peaks are still higher :-).

Thanks Gert. I used the Cu radiation and I just decided this range from 2 to 90 as we normally do. I attached the XRD for solid phase obtained from 10 and 15 minutes reaction time. Interestingly, despite the same measuring condition, these two XRD are quietly different. I could identify Chlorartinite and magnesite in 10 min precipitate but for 15 minutes and after that (20-30 and 60 min) I got the same peak of Al. 

Thank you :)

At least it is clear that you measured Aluminium. The hump I would also explain as amorphous or nanocrystalline phase. For nanocrystalline state the broad "wave" on the background can stay which appears at the same position where the sharp peaks later appear. If you would simulate the spectra with very small grain size (a few usit cells) you would probably get a similar signal. You could try to determine the radial distribution function in order to determine the nearest neighbors but this is perhaps easier nowadays using the techniques F. Konrad described.