Distribution of Iron Atoms in Nonequivalent Crystallographic Sites of Fe7C3 Carbide in Core–Shell Nanostructures

The structure and magnetic properties of iron carbide nanoparticles encapsulated into carbon shells, obtained as a result of ferrocene transformations at a pressure of 8 GPa and different temperatures, have been investigated by powder X-ray diffraction, transmission electron microscopy, and Mossbauer spectroscopy. It is found that the main crystalline carbide states are hexagonal phase Fe7C3 and cementite Fe3C, whose relative contents are determined by the treatment temperature. Mossbauer spectroscopy was used to identify three nonequivalent states of iron atoms in the structural sites of Fe7C3 hexagonal lattice. It is established that the occupancies of these sites differ from the known values for the bulk material, which is related to the specific features of structure formation under conditions of high pressure and temperature.