Crystal(编程语言)
材料科学
相(物质)
结晶学
单晶
BETA(编程语言)
粒径
物理
化学
物理化学
量子力学
计算机科学
程序设计语言
作者
Osamu Kitakami,Hiromu Sato,Yutaka Shimada,F. Sato,Michiyoshi Tanaka
出处
期刊:Physical review
日期:1997-12-01
卷期号:56 (21): 13849-13854
被引量:467
标识
DOI:10.1103/physrevb.56.13849
摘要
We have synthesized Co fine particles with the average diameter $(D)$ of less than 500 \AA{} 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 (\ensuremath{\beta}) phase for $D<~200\AA{},$ a mixture of hcp (\ensuremath{\alpha}) and \ensuremath{\beta} phases for $D\ensuremath{\sim}300\AA{},$ and \ensuremath{\alpha} phase with inclusion of a very small amount of \ensuremath{\beta} phase for $D>~400\AA{}.$ Precise structural characterizations have revealed that the \ensuremath{\beta} particles are multiply twinned icosahedrons and the \ensuremath{\alpha} 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 \ensuremath{\alpha} single crystal, a \ensuremath{\beta} single crystal, and a multiply twinned \ensuremath{\beta} 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 \ensuremath{\beta} 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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