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The Pseudostable Phase

Published online by Cambridge University Press:  26 February 2011

Ryoichi Kikuchi
Affiliation:
Dept. Materials Science & Engnrg, UCLA, Los Angeles, CA 90024-1595
Tetsuo Mohri
Affiliation:
Dept. Metallurgical Engineering, Hokkaido Univ., Sapporo 060, Japan
Brent Fultz
Affiliation:
California Institute of Technology, Pasadena, CA 91125
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Abstract

The basic nature of kinetic processes is examined theoretically. When an isothermal development of order is studied theoretically, sometimes an ordered phase different from the final equilibrium one transiently predominates, while the free energy (Fsys) decreases monotonically although very slowly. There is another category of kinetic changes for which the convenient interpretation is that the Fsys surface itself changes in time. In this second category, a state can initially be a local minimum of Fsys and thus can be called a ‘metastable’ state, but after a certain time, as the Fsys surface itself changes, a kinetic path appears along which Fsys decreases and the system can change along it. To include both categories, the concept of the PSEUDOSTABLE phase is proposed. It is shown that even in the nucleation process, Fsys for the entire system decreases monotonically, although the local free energy may fluctuate.

Type
Research Article
Copyright
Copyright © Materials Research Society 1992

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