TY - JOUR
T1 - Size effect on the crystal phase of cobalt fine particles
AU - Kitakami, Osamu
AU - Sato, Hisateru
AU - Shimada, Yutaka
AU - Sato, Futami
AU - Tanaka, Michiyoshi
PY - 1997/1/1
Y1 - 1997/1/1
N2 - We have synthesized Co fine particles with the average diameter (Formula presented) of less than 500 Å by sputtering Co in a somewhat high inert-gas pressure. It has been found that there is a close relationship between the particle size and the crystal phase; that is, pure fcc (β) phase for (Formula presented) a mixture of hcp (α) and β phases for (Formula presented) and α phase with inclusion of a very small amount of β phase for (Formula presented) Precise structural characterizations have revealed that the β particles are multiply twinned icosahedrons and the α particles are perfect single crystals with external shape of a Wulff polyhedron. In order to explain the size effect on the crystal phase of Co fine particles, we have performed theoretical calculations for total free energies of an α single crystal, a β single crystal, and a multiply twinned β icosahedron. The present calculations well explain the size dependence of the crystal phase of the Co fine particles, and have revealed that the stabilization of β phase, confirmed by previous studies, is the intrinsic effect caused by the small dimensionality of fine particles. Moreover, the phase transformations that occurred in annealing experiments can also be explained by the theory.
AB - We have synthesized Co fine particles with the average diameter (Formula presented) of less than 500 Å by sputtering Co in a somewhat high inert-gas pressure. It has been found that there is a close relationship between the particle size and the crystal phase; that is, pure fcc (β) phase for (Formula presented) a mixture of hcp (α) and β phases for (Formula presented) and α phase with inclusion of a very small amount of β phase for (Formula presented) Precise structural characterizations have revealed that the β particles are multiply twinned icosahedrons and the α particles are perfect single crystals with external shape of a Wulff polyhedron. In order to explain the size effect on the crystal phase of Co fine particles, we have performed theoretical calculations for total free energies of an α single crystal, a β single crystal, and a multiply twinned β icosahedron. The present calculations well explain the size dependence of the crystal phase of the Co fine particles, and have revealed that the stabilization of β phase, confirmed by previous studies, is the intrinsic effect caused by the small dimensionality of fine particles. Moreover, the phase transformations that occurred in annealing experiments can also be explained by the theory.
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U2 - 10.1103/PhysRevB.56.13849
DO - 10.1103/PhysRevB.56.13849
M3 - Article
AN - SCOPUS:0000307412
VL - 56
SP - 13849
EP - 13854
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
SN - 0163-1829
IS - 21
ER -