Say I have hydroxyapatite compound, doped with cobalt. Now there are two impurity peaks which comes. The question is how to decide that this new peak correspond to this element/compound. Say for example, the possibility are calcium phosphate, cobalt phosphate and etc. Now according to me, the first logic is to see the possible byproducts from the chemical reaction to synthesize hydroxyapatite. The second is to see whether the refinement for that impurity cif file gives low chi square. But I wanted to know, say there are two elements/compounds which i think of from the cif file. Their intensity in their respective compound is higher/lower, whereas in my case that intensity peak is very low. So does the refinement data looks through or it just see, at that particular 2theta, peaks comes so it will refine accordingly. Or say we do not know about refinement at all and we have the cif, so how do we decide whether this peak is from this compound. I basically want to know in respect of xrd only and from any other techniques.
Dear friend,
I also get some impurity peaks in my xrd data. For confirming the phase of these extra peaks I follow the steps:
1) Comparing the data with other literature review.
2) Predicting the possible compounds that may be formed according to the literature review.
3) Checking the experimental data with the standard PDF file using the Xpert Highscore software (You can ask to the XRD machine operator for checking this)
4) Refining the data with the main phase along with the cif of the secondary phase using some software.( Iam using fullprof)
These are the steps that I followed till now. If there is mistakes expert can correct and that will be helpful in our research.
Thank You
Hello,
I follow the same steps as the one provided by Haobam Samananda Singh .
If you need to choose between equivalent structure (let say calcium phosphate and cobalt phosphate, with the same space group but different chemical content), the relative intensities for each peaks on XRD will be different, and the cell parameters will be different between both materials (meaning the peaks will not appear at the exact same angle) so in most case you will be able to find the proper one. If you have "pure" (no solid solution / mixed cations) cobalt phosphate in your sample, cell parameters should not move (much) from the one in the reported cif of cobalt phosphate. And same reasoning for calcium phopsphate (with cif of calcium phosphate). So most of the time you can tell.
Sometimes it might be quite difficult for impurities / small intensities, and really difficult depending on sample preparation : preferred orientation will have an impact on intensities, zero level of your sample will have an impact on ° of your peak, and so on. Remember that you might see at first glance 1-2 peaks of your impurities, but there are several other peaks intensities (hidden by some peaks of your main phase), that could help to conclude (while refining with fullprof for example).
If you really need to know, you can sometimes uses other experiments (such as SEM EDX), to measure chemical content in some particles of your material (if you are missing Cobalt content in your main phase, it is likely that the impurities are Cobalt phosphate, and so on).
Kind regards,
Hello Anshul Sharma
This is an important question for those who synthesize compounds with doped elements. First, let's talk about hydroxyapatite. A very common byproduct is Calcium Triphosphate, and I have seen it in more than one refinement I have done before. So you have to keep in mind that a refinement may be conducted with the usual hydroxyapatite phase but also with Calcium triphosphate phase. About the doped atom, you would have to get a high resolution measurement, and a concentration of the dopant that makes difference in XRD pattern compared to the pure hydroxyapatite. So, everything is about how much you can detect.
You asked if it was possible to identify the dopant by the peaks position. If your doping was "perfect", I mean the cobalt atom is perfectly substituted in calcium site, with no changing in unit cell structure, there should not be any new peaks, because the structure remained the same. But in real, many things can happen, as structure changes and new byproducts. I suggest you start by the most probable: Hydroxyapatite and calcium triphosphate. Then, if there are other peaks, you start to look for some cobalt structures.
Some times we can't identify other structures because the refinement chi square is already low. We know that we have added a dopant, but the refinement is already very good if we don't consider it. But you know you have a dopant, and there are other analysis that proves the new element is there, then you should try to refine with it, as long as it makes sense. It would be very strange if your refinement points 50% of dopant, but some other analysis says 5%.
Go for it and try the refinement. And reply if you need help.
Best regards,
Dr. Ricardo Tadeu
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