Thermo-physical properties of body-centered cubic iron-magnesium alloys under extreme conditions |
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Authors: | K. Ká das,R. Ahuja,B. Johansson,O. Eriksson |
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Affiliation: | a Applied Materials Physics, Department of Materials Science and Engineering, The Royal Institute of Technology, SE-10044, Stockholm, Swedenb Research Institute for Solid State Physics and Optics, H-1525 Budapest, P.O. Box 49, Hungaryc Materials Theory, Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120, Uppsala, Sweden |
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Abstract: | Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C′). Magnesium alloying significantly increases C′ of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in detail. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth’s inner core as provided by seismic observations. |
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Keywords: | A. Fe alloys D. Elasticity D. Dynamical stability E. Ab initio |
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