Anharmonicity, mechanical instability, and thermodynamic properties of the Cr-Re σ-phase

Mauro Palumbo; Suzana G Fries; Alain Pasturel; Dario Alfè

doi:10.1063/1.4869800

Anharmonicity, mechanical instability, and thermodynamic properties of the Cr-Re σ-phase

J Chem Phys. 2014 Apr 14;140(14):144502. doi: 10.1063/1.4869800.

Authors

Mauro Palumbo¹, Suzana G Fries¹, Alain Pasturel², Dario Alfè³

Affiliations

¹ ICAMS, Ruhr University Bochum, Universität Str. 150, D-44801 Bochum, Germany.
² SIMAP, UMR CNRS-INPG-UJF 5266, BP 75, F-38402 Saint Martin d'Hères, France.
³ Department of Earth Sciences, Department of Physics and Astronomy, London Centre for Nanotechnology and Thomas Young Centre@UCL, University College London, Gower Street, London WC1E 6BT, United Kingdom.

PMID: 24735300
DOI: 10.1063/1.4869800

Abstract

Using density-functional theory in combination with the direct force method and molecular dynamics we investigate the vibrational properties of a binary Cr-Re σ-phase. In the harmonic approximation, we have computed phonon dispersion curves and density of states, evidencing structural and chemical effects. We found that the σ-phase is mechanically unstable in some configurations, for example, when all crystallographic sites are occupied by Re atoms. By using a molecular-dynamics-based method, we have analysed the anharmonicity in the system and found negligible effects (~0.5 kJ/mol) on the Helmholtz energy of the binary Cr-Re σ-phase up to 2000 K (~0.8T(m)). Finally, we show that the vibrational contribution has significant consequences on the disordering of the σ-phase at high temperature.