Spinodal in a Liquid-Face-Centered Cubic Phase Separation(Condensed matter: structure and mechanical and thermal properties)

概要

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A van der Waals model is introduced to describe liquid-bcc-fcc phase transitions and phase separations, including unstable and metastable regions. We introduce translational order parameters, or degree of a crystalline ordering, for bcc and fcc structures. Combining a van der Waals theory for an imperfect gas with these translational order parameters, we derive the free energy, which is given by one conserved order parameter (concentration) and nonconserved order parameters (degree of a crystalline order). We calculate the phase diagrams on the temperature-concentration plane and find bcc and fcc unstable regions, a bcc-fcc phase separation, and a liquid-bcc-fcc triple point. We also calculate temporal evolution of structure factors for concentration and for crystalline order, depending on a quench temperature and concentration and find a new spinodal decomposition, driven by the instability of a fcc ordering.
2006-08-15