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Formation mechanism and shape control of monodisperse magnetic CoFe 2O 4 nanocrystals
N. Bao, L. Shen, W. An, , C.H. Turner, A. Gupta
Published in
2009
Volume: 21
   
Issue: 14
Pages: 3458 - 3468
Abstract
The formation mechanism and shape control of monodisperse magnetic cobalt ferrite CoFe 2O 4 nanocrystals produced by thermolysis of a stoichiometric Co 2+Fe 2 3+ 3+-oleate complex in organic solution has been investigated. Synthesis of the pure ternary CoFe 2O 4 inverse spinel phase, without formation of any intermediate binary cobalt and iron oxides, is favored by the close thermal decomposition temperature of the Co2+-oleate and Fe3+-oleate precursors. For reaction temperatures between 250 and 320 °C, the nucleation and growth dynamics dictate the size and shape evolution of the nanocrystals. Prenucleation of CoFe 2O 4 occurs at 250-300 °C but without any growth of nanocrystals, because the monomer concentration is lower than the critical nucleation concentration. For temperatures in the range of 300-320 °C,which is above the thermolysis temperature of the mixed Co 2+Fe 2 3+ 3+-oleate complex, the monomer concentration increases rapidly resulting in homogeneous nucleation. Atomic clusters of CoFe 2O 4 with size<2 nm are initially formed at 314 °C that then grow rapidly when the temperature is raised to 320 °C in less than a minute. The shape of the CoFe 2O 4 nanocrystals can be reproducibly controlled by prolonging the aging time at 320 °C, evolving from initial spherical, to spherical-to-cubic, cubic, corner-grown cubic, or starlike shapes. Thus, with careful choice of reaction parameters, such as the precursor concentration and the heating rate, it is possible to achieve large-scale synthesis of shape-controlled monodisperse CoFe 2O 4 nanocrystals with high yield. © 2009 American Chemical Society.
About the journal
JournalChemistry of Materials
ISSN08974756