I want to measure the stoichiometry of Fe3O4 nanoparticles synthesized in our lab. What are the possible ways to get that?
You can do neutron diffraction if you have enough amount of powder sample and refine the stoichiometry by doing Rietveld analysis. Does the sample show Verwey transition at low temperature? If so then by measuring the transition temperature you will be able to estimate the stoichiometry as well. But this is an indirect method.
Since the spinel Fe oxides allow the full range of stoichiometries ranging from magnetite to maghemite, the stoichiometry may also be or become inhomogeneous across the particle upon exposure to atmosphere (and/or change in reducing environment etc.). X-ray absorption and X-ray magnetic dichroism in particular have proven to be useful in quantifying the stoichiometry, including site distribution.
Check the paper by E. Pellegrin et al. in physica status solidi (b) (1999, if I remember correctly), and those papers quoting it (we did in some of our work).
As with neutron diffraction proposed by Tapan above you need access to large scale facility to do these experiments (synchrotron radiation).
Alternatively, high quality EELS in (S)TEM might be an option.
What is the average particle size of your sample? Have you you put some surfactant molecules to protect your nanoparticles? If you have surfactant molecules containing H atoms then the polarized neutron diffraction method can be used to separate soin incoherent scattering from H.
Thank you very much for your answers. It will be really helpful for me. The average particle size is 7 nm and the particles are coated with oleylamine. So H atoms are there.
Some of the samples show Verwey transition, but some of them do not. That is one of the reason to check the stoichiometry.
Well you should do neutron diffraction with polarized neutrons. You can do that only at ILL (D7) and also FRM II (DNS). About a g sample will OK.
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