Morphology and composition tailoring of CoxFe3-xO4 nanoparticles

Nano-octahedra of cobalt ferrite CoxFe3-xO4 (1 <= x < 2), with a broad size distribution around 1520 nm, were synthesized by a hydrothermal method using nitrates as precursors. For the first time, single-phased nano-octahedra of cobalt-rich ferrite CoxFe3-xO4 (x = 1.5) were synthesized. The nano-octahedra are crystallized in a normal spinel structure, with tetrahedral sites occupied by Co2+. This specific octahedral shape was obtained with anionic, cationic, and nonionic surfactants. The nature of the surfactant influenced the chemical composition of the powder and the size of the nano-octahedra. The {100} truncation of the octahedra is more pronounced for the small particles. For the first time, single-phased nanoparticles with as much as x = 1.8 cobalt were synthesized with ethylene glycol as solvent. These nanoparticles, around 8 nm in size, have no specific shape and possess a lacunar spinel structure similar to maghemite. The samples were characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy.