The vibrational thermodynamic properties of ordered and disordered fcc-based alloys in three aluminum transition-metal (TM) systems, Al-TM (TM=Ti, Zr, and Hf), are computed by first principles methods employing supercell calculations and the transferable-force-constant (TFC) approach. In order to obtain accurate values for the high-temperature limit of the vibrational mixing entropies in these systems, it is necessary to parametrize the dependence of the force constants on both the equilibrium bond length and the TM concentration in the TFC method. Provided this concentration dependence is accounted for, the TFC approach is shown to lead to predictions for the vibrational mixing entropy accurate to within approximately 20%. The utility of the TFC method is demonstrated by its application to the calculation of vibrational entropies of mixing for approximately 30 structures in each of the three Al-TM systems, facilitating the construction of well converged vibrational-entropy cluster expansions. The calculations yield large and negative values for the vibrational mixing entropies of both ordered and disordered alloys, with an overall magnitude of up to 1.0 kB /atom, and ordering entropies (i.e., the difference between the vibrational entropy of ordered and disordered phases at the same composition) in the range of 0.2-0.3 kB /atom for concentrated alloys. Calculated results are shown to be in good agreement with experimental data available for the Al-Ti system.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Mar 28 2007|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics