Thermodynamics, lattice stability and defect structure of strontium silicides via first-principles calculations
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abstract
The thermodynamics of the Sr-Si system is of fundamental importance for the understanding of eutectic modification of Al-Si alloys. At the same time, strontium silicides have recently been found to have potential applications in electronic devices. Renewed research efforts have led to a re-evaluation of the phase equilibria in this system, resulting in the discovery of previously undetected stable intermetallic compounds. In this work, we investigate the finite temperature thermodynamic properties of the stable (and metastable) Sr-Si intermetallics. The vibrational properties of the intermetallic compounds are calculated within harmonic theory, with quasi-harmonic corrections to account for the effects of thermal expansion. The total free energies of the compounds are computed considering vibrational and electronic contributions, as well as weak anharmonic corrections. The ground state of the system is predicted and compared to previous experimental and computational results. The vibrational properties of the compounds seem to be dominated by the presence or absence of strong covalent Si-Si bonds. This is found to be directly related to the structural features of the compounds, namely, the connectivity between Si ions. Finally, the nature of the structural phase transition observed in the SiSr2 is examined and the point defect responsible for the non-stoichiometry of the high-temperature polymorph at this composition is identified. 2009 Elsevier B.V. All rights reserved.
