The above is the X-ray diffraction diagram from the iron nano sample that I synthesized from green tea extract. Could you please explain the characteristic peak at the 80-degree position?
Dear Van Triệu ,
please provide more details on your measurement. Which iron phase did you expect to have obtained? How much sample did you use, what is the sample support, the diffractometer type, the wave length.
Your blue markers seem to indicate pure Iron in the bcc phase, and it should be clear that you do not have any of that in your sample. Them main peaks at 25° and 42° 2Theta looks rather like an amorphous material, or a very small nanoparticle in the size range 2 nm diamter. This might be remnants of the organic educts? How clean do you expect your sample to be?
Dear R. B. Neder ,
In the X-ray diffraction diagram above, I used one sample, which was placed on a holder of unknown material. The type of machine used is PXRD D8-ADVANCE with a wavelength of 0.15406 nm (CuKα). The peaks at 25 and 42 Theta, according to the reference literature, are from amorphous carbon and graphite. I expect that my sample would yield pure iron combined with carbon. I have tested the magnetism of my powder sample with a magnet, and it showed magnetism, but based on the diffraction peaks obtained, I cannot determine the form of iron.
Thank you for sharing the information!
Dear Van Triệu ,
I agree with R. B. Neder . One type of material I have deal before, that show very broad peaks, is the ferrihydrite, which contains lameles of iron and oxygen, with water between them. Another point is, you told us that you are synthesizing pure iron nanoparticles. Iron is known for being very reactive to oxygen, and will rapidly oxidize to Fe2+ and Fe3+, so, probably, you will not have pure Iron (Fe0) nanoparticles, unless you protected the nanoparticles in some way (For example, core shell synthesis). I am not sure, we need more information about the synthetic procedure, however, I believe you obtained a iron oxide or iron hydroxide compound, with graphite as a separated phase.
Another point is, which reference that says that amorphous carbon has a peak in diffraction experiment? This seems very contra intuitive, since amorphous materials will not present any organization and thus no diffraction peaks.
Also, the X-ray diffraction intensity are very small for all the peaks, you can also try to change the slit to improve X-ray counts and increase the intensity, trying to change the setup parameters, and you can also use a zero intensity substrate that you could use small amount of powder (The zero intensity substrate for PXRD normally is a cleaved silicon wafer in a certain orientation) .
Best regards,
GG
A quick search on the powder diffraction pattern of amorphous carbon did not show me any pattern beyond 60° 2Theta @ CuKalpha. Any higher order peaks will be extremely low in intensity.
According to a compilation of Fe-C (BCC) (Liu Cheng, A. Boetttger, Th.H. de Keijser, E.J. Mittemeijer, Scripta metallurgica, 1990, 24, 509) lattice parameters shows that the lattice parameter changes from 2.8665A up to roughly 3.08A with increasing Carbon content (8 Atom% max). This change in the lattice parameter is sufficient to shift the Fe reflections down in 2Theta to values where the peaks in your pattern seem to be. See attached calculated powder diffraction pattern for a=3.05A and a sphere of 20 A diameter. With the relative intensities, I do not think that this explains your 80° 2Theta peak.
Check the composition of your sample, how much Fe is there compared to C? Can you prepare a pure carbon sample and run the powder pattern for this by itself. As there is a small peak at ~16° 2Theta I suspect that you have some organics/polymers in your sample that may introduce more order, thus increasing peaks at high 2Theta as well.
I guess you might produce (Fe,C) under very reducing conditions. The other magnetic Fe phase would be magnetite Fe3O4, peaks would be at much lower 2Theta.
Generally, run the powder pattern with at least twice the counting time to reduce the noise, as all peaks are broad you can double the step width without loosing too much information.
Gustavo Henrique de Magalhães Gomes All amorphous materials do show short range order between the first to (roughly) third/fourth neighbor atoms. These reasonable well defined interatomic distances most certainly produce at least a first, so called "first sharp diffraction" peak, even if this is commonly roughly 5 to 10° FWHM @CuKalpha. Check out the literature on "Glass" diffraction pattern as examples.
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