Dear Nadal,

I think the two peaks around 7° and 19° do not belong to Fe3O4.

They may arise from your capping material. Large organic (chain) molecules are able to show very broad amorphous like XRD peaks.

Your 7° and 19° peaks are much broader than the Fe3O4 peaks above 30°.

Do you have got a reference pattern of your oleic acid matrix without the nanoparticles?

If not, you should perform such a reference scan. Please use the same sample thickness, the same support *) and the same temperature.

Good luck.

*) the two peaks may alternatively arise from the sample support.

Dear Nadal,

I think the two peaks around 7° and 19° do not belong to Fe3O4.

They may arise from your capping material. Large organic (chain) molecules are able to show very broad amorphous like XRD peaks.

Your 7° and 19° peaks are much broader than the Fe3O4 peaks above 30°.

Do you have got a reference pattern of your oleic acid matrix without the nanoparticles?

If not, you should perform such a reference scan. Please use the same sample thickness, the same support *) and the same temperature.

Good luck.

*) the two peaks may alternatively arise from the sample support.

There are few datacards which says that Fe3O4's highest intensity peak comes at ~18.3 (01-074-1909) and ~19.8deg (01-076-0955) 2theta (Cu Ka). Whereas, Most of the cards shows max intensity peak at ~35deg. So, I suggest to follow the procedure mentioned by Dr. Martens.

" Could it be possible that the crystal structure is BCT instead of FCC? "

I am not a big fan to mix up terms. As far as I know the terms bct (body-centered tetragonal) and fcc (face centered cubic) are exclusively related to Fe phases martensite and austenite (and corresponding metal phase). BCT used in your explanation is possibly a tetragonal I-lattice, e.g. a space-group type like I 4/m mm, whereas FCC would be an F lattice as in space-group types F m-3m (for Fe). However, magnetite has a space-group F d-3m, i.e. the only shared part is the F lattice (Which might be the reason that people mix F and fcc). Therefore, any mixture of terms is not very helpful and only shows that people usually do not understand what they are standing for and simply use them since it looks "impressive". For me it is always hard to follow a text if crystallographic terms are improperly used since I always have to find out what do they want to say? Is it reasonable or only some fancy part of a sentence?

Anyway, a cubic F lattice becomes automatically a tetragonal I lattice in case of a tiny distortion or shift of atoms (i.e. the peak positions either only slightly shift or do not shift at all but their intensity changes slightly which can have also other reasons so that it is hard to differentiate between the real reason). In other words, a small change of the lattice or structure is very likely not the reason for the observed change. Your peaks are anyway quite broad which might be caused by the size of the nano particles but also any other loss of the perfect translation symmetry (e.g. stacking faults, maghemite).

Hello Nadal,

So far the peak at ~7, it might be from any possible contamination or the change in the geometry of the crystal, but it shows from some researcher that Fe3O4 could have a peak at ~19. You may easily find such work on google search, better any scholarly search.

Krishna Joshi : Well...between 18-19° there is indeed the 111, but at ~ 37° is the 222 as second order reflection with a comparable intensity (1/3 less than 111). I would assume that if your assumption of a 111 would be correct, at 37° a clearly higher intense reflection should appear. The visible reflection at ~35° seems to be the much more intense 311 (ten times higher predicted as 111).

The entire diffractogram seems to display only additionally the 400 (43°) and the 440 (62.5°) which is either an indication of a strong texture...or a metastable phase like wuestite (FeO). However, then the visible 311 does not match because for wuestite is no reflection at 35° but only 37°.

Such simple simulations I recommend to do using software like PowderCell.

Dear Nadal,

the main diagnostic peaks of magnetite are: (220) ~30 degrees, (311) 100% ~ 36 degrees, (222) low intensity ~ 37-38 degrees and the (422), (511) and (440) between 50 - 65 degrees for Cu tube.

You are getting oleic acid capped with Fe3O4. Have in mind that, the particles may absorb high amounts of diffracted X-ray from the capped material, once they are not entirely free of oleic acid.

In some characteristics conditions, there will be a crystallization of oleic acid and their intermediates. Check the possible crystallization.

Also, consider the different sizes and final encapsulated oleic acid in the magnetite particles. The obtention of Magnetite as hollow spheres depends only on the synthesis setup.

Are the synthesis conditions very oxidative? Is it possible to still have Fe2+ after organics introduction in the process? Are the final materials black in any way? Brown? Orange/red? How confident to have got magnetite?

The idel situation would test the magnetization, nevertheless can be hard to do in nano-materials.

Low angle organics diffraction peaks are usually expected, take care and check the reactants of the system (all your starting materials) carefully.

Be sure there is no residue of the reactants, and all peaks can safely correlate with one phase final product.

Otherwise, considering changes in symmetry are the only speculation.

Depending on the synthesis amounts and pathways, end up with encapsulated magnetite would be expected, resulting in the very low intensity of the (311) ~ 100% in your diffraction.

Best regards,

WNM

I believe it is something related to oleic acid. I had 2 hypotheses:

1) Although I tend to believe those peaks are too narrow to belong to a liquid, it is likely that the fatty acid chains capping the particles are more ordered than in liquid phase and less ordered than in the crystalline phase. Monoclinic crystalline oleic acid has important peaks at roughly 6.6° and 18.9° 2theta (for Cu Ka radiation).

2)The other thing I was phantasizing about is whether some solid "iron oleate" could form as an impurity phase. While apparently iron oleate exists, I haven't found its crystal structure on any database, nor any other metal-oleate. So mine is pure speculation and also I do not know your synthesis conditions so I don't know if it is even possible to form it.