Mössbauer spectroscopy has been used to examine the effect of increasing copper ion concentration on the iron distribution in CuxFe3−xO4(0⩽x⩽0.9). For x⩽0.37, fast electron exchange among octahedral iron ions occurs as in Fe3O4, suggesting that the itinerant electrons associated with the octahedral Fe2+ ions remain delocalized in the sublattice. At high values of x (x⩾0.59), however, the itinerant electrons become localized in a small fraction of exchange-coupled iron ions. The relative numbers of distinguishable cations making up the complements of the octahedral sites of the copper ferrites are determined.
Studies of the room temperature Mössbauer spectra of MxFe3−xO4 (where M = Cu, Cd, or Ti; and O⩽x⩽1) together with the measurements of unit cell dimension and electrical conductivity indicate that a significant change in the electronic properties of each system occurs around the intermediate composition (x∼0.5). The samples with low values of x(<0.5) retain the characteristics of Fe3O4, while those with high values of x(>0.6) behave as semiconductors as the sixth 3d electron of Fe2+ ion becomes localized.
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