Crystallographic study of cobalt treatment on γ-Fe2O3

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Abstract
Chemical analysis and x‐ray diffraction measurements of samples during the reaction of cobalt treatment were carried out to study the mechanism of reaction. X‐ray diffraction, TEM observation, and magnetic measurements of core γ‐Fe2O3 and the modified particles were performed to investigate the crystal growth of cobalt ferrite on core γ‐Fe2O3 particles. From chemical analysis of Fe2+ and total‐iron ions in the reacting suspension and x‐ray diffraction measurements of samples during the reaction, it is clear that the lattice constant becomes larger due to the formation of cobalt ferrite on core γ‐Fe2O3 without decrement of Fe2+/total‐iron ratio. So, cobalt ferrite on core γ‐Fe2O3 particles is formed not by the oxidation of added Fe2+ ions, but by the electron transfer from Fe(OH)2 to core material. From x‐ray diffraction measurements, I400/I311, I220/I311, and I111/I311 were calculated. While I400/I311 and I220/I311 are almost constant, only I111/I311 increases with increasing the amount of cobalt and ferrous ions added. These results show that cobalt ferrite is preferentially grown on (111) plane which is the close‐packed plane of spinel lattice.