I have produced crystals of two metals and a ligand separately while using a published procedure but used a different solvent instead. The x-ray diffraction patterns of my synthesized materials are different from the published. However, their fluorescence spectra have similar features as the published. One of the spectra has one pronounced (high intensity) peak than the published. Is there any explanation?
Dear Golafale,
Fluorescence spectrum give you quantitative information about the elements in your sample whereas X-ray diffraction pattern give you information about the geometry of the crystal lattice and values of the lattice parameters. Then you can obtain similar fluorescence spectra for two different crystal structures i.e. CdS fluorescence spectrum will give you 50% Cd and 50% S, whereas the crystal structure can be zincblende or wurzite.
Best regards,
Pedro
No, if the PXRD patterns are different, then you have two different structures.
Dear Saki,
you may suffer from preferred orientation artifacts. Do you obtain your diffractograms from powder sample and what is about the published work; also powder?
Differences in XRD peak heights are easily achieved.
Laura already pointed to the powder aspect.
Comparing XRD peak heights is always a critical isssue. When in addition strain is present in your sample, peak broadening shows up, which in consequence decrease the peak height. So please take care when comparing peak heights.
Crystal lattice is maily identified by the peak positions as already pointed out by Pedro above.
Pedro, I think that is exactly what I am dealing with. I was wonder if two different crystal structures can give similar fluorescence spectrum.
Laura, thanks; I certainly understand that but the similarity in spectra features confused me.
Gerhard, I compared the powder pattern with the simulated (published work). Thanks for helping.
Does the published work specify if it was recorded on a flat plate sample holder or in a capillary? A capillary measurement will normally be moreprecise, also for your own sample, and less prone to preferred orientation. You should also do a Pawley, or even better Rietveld, fit on your pattern to determine if the unit cell and atomic positions are similar to the published work.
Dear Golafale,
First of all, are you talking about X-ray fluorescence spctre and X-ray diffraction?
If the answer are yes, you should have in mind that the two tecniques are usefull for different things.
The first one are used for chemical quantification, as Gallardo said, and the second for crystalograph informations.
This means that for a certain class of materials, named polimorphs, it's posible to obtain similar fluorescence spectre but a totally different X-ray pattern. For example, the same formula Al(OH)3, there are 4 differents minerals associated, gibbsite, bayerite, doyleite, and nordstrandite. This happens because the arrangemet of atoms in the structure are dfifferent in each mineral, so as theirs proprieties, as Mccormick said.
In other hand, a unmatching X-ray fluorescence spectre indicates different atom proportion on the cristals formula. Hematite (Fe2O3) and Magnetite (Fe3O4) will indicate iron on the spectre, but the proportion will be different.
In a second instance, you should consider that X-ray diffraction are applicable only to cristaline materials type. So, if there are a possibility of your sample be amorphous, you will not obtain a "real" diffraction pattern. Lundvall suggested a Rietveld refinement, this realy could help you.
Another observation point is about compatibility between source and your sample, in both cases. They have to be compatible, avoiding background noise and other associated errors. But it should be a minor concern since you're using a literature procedure.
I hope to had helped.
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