Theoretical Investigation of Lattice Thermal Vibration Effects on Phase Equilibria Within Cluster Variation Method

Continuous Displacement Cluster Variation Method is employed to study binary phase equilibria on the two dimensional square lattice with Lennard-Jones type pair potentials. It is confirmed that the transition temperature decreases significantly as compared with the one obtained by conventional Cluster Variation Method. This is ascribed to the distribution of atomic pairs in a wide range of atomic distance, which enables the system to attain the lower free energy. The spatial distribution of atomic species around a Bravais lattice point is visualized. Although the average position of an atom is centred at the Bravais lattice point, the maximum pair probability is not necessarily attained for the pairs located at the neighboring Bravais lattice points. In addition to the real space information, k-space information are calculated in the present study. Among them, the diffuse intensity spectra due to short range ordering and atomic displacement are discussed.

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Theoretical Investigation of Fe-Based Phase Equilibria from the First-Principles

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.3127 ◽

2005 ◽

Vol 475-479 ◽

pp. 3127-3130 ◽

Cited By ~ 2

Author(s):

Ying Chen ◽

Shuichi Iwata ◽

Tetsuo Mohri

Keyword(s):

Theoretical Investigation ◽

Phase Stability ◽

First Principles ◽

Cluster Variation Method ◽

High Accuracy ◽

Variation Method ◽

Transition Temperatures ◽

Spin Polarized ◽

Cluster Variation ◽

Effective Cluster

Theoretical investigation of the phase equilibira of three kinds of Fe-based alloys, Fe-Ni, Fe-Pd and Fe-Pt systems is attempted by combining FLAPW total energy calculations and Cluster Variation Method. It is revealed that the magnetism plays a crucial role in the phase stability and spin polarized calculation is indispensable. The experimental L10-disorder transition temperatures are reproduced with fairly high accuracy. Thermal vibration effects incorporated based on the Debye-Gruneisen model further improve the calculated transition temperatures. Furthermore, the influence of the various effective cluster interactions on phase stability is calculated systematically.

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Application of Continuous Displacement Cluster Variation Method to Study Phase Equilibria

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.1496 ◽

2010 ◽

Vol 654-656 ◽

pp. 1496-1499

Author(s):

Tetsuo Mohri

Keyword(s):

Transition Temperature ◽

Phase Equilibria ◽

Lattice Distortion ◽

Cluster Variation Method ◽

Variation Method ◽

Study Phase ◽

Local Lattice Distortion ◽

Local Lattice ◽

Cluster Variation ◽

Continuous Displacement

Cluster Variation Method (CVM) has been widely recognized as one of the most reliable theoretical tools to study phase equilibria in metallic alloy systems. The conventional CVM, however, does not allow atomic local displacements and, therefore, calculated results often encounter various inconveniences such as the overestimation of transition temperatures. Continuous Displacement Cluster Variation Method (CDCVM) was proposed to circumvent such deficiencies of the conventional CVM. Preliminary studies on an order-disorder phase diagram based on CDCVM indicate that the transition temperature is shifted downward reproducing experimental tendencies. In the present study, lattice thermal vibration effects are also incorporated through Morse potential. It is concluded that the local lattice distortion effects are quite effective to reduce the transition temperature.

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