Iron oxides, especially the Fe3O4 and γ-Fe2O3 phases, play a significant role in potential applications of nanomaterials due to their suitable features such as biocompatibility, magnetic and optoelectronic properties. Moreover, it is convenient to use Fe3O4 for some applications, such as Li-ion batteries, because of its combined valence states of iron. Therefore, it is highly desired to distinguish the two, otherwise similar, iron oxide phases and to evaluate the degree of Fe3O4 stoichiometry. Genuinely, a proper characterization of these compounds can be problematic due to their similar structures and the common occurrence of non-stoichiometric iron oxide forms and their mixtures in the nanosystems. In this respect, 57Fe Mössbauer spectroscopy is regarded as a powerful tool for the identification of different forms of iron oxides as well as for the distinguishing between core-shell structures and mixtures. The present contribution is focused on theoretical 57Fe Mössbauer spectra of Fe3O4, γ-Fe2O3 and their different degrees of stoichiometry, with regards to the correct evaluation of the spectra. 57Fe Mössbauer spectra of two distinct levels of non-stoichiometric γ-Fe2O3 and Fe3O4 were modelled and discussed. Furthermore, theoretical examples of 57Fe Mössbauer spectra of Fe3O4/γ-Fe2O3 mixture of 1/1 particle ratio and a core-shell structure, where Fe3O4 core takes up 75% of the particle’s volume, are presented.Keywords: γ-Fe2O3, Fe3O4, stoichiometry, mixtures, 57Fe Mössbauer spectroscopy
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