Vibrational entropies of alloying and compound formation: experimental trends

Using phonon density-of-states data from the literature, the vibrational en tropies of formation were calculated for 32 different alloys and intermetal lic compounds in the harmonic approximation. The vibrational entropies of f ormation span a wide range from -0.64k(B) to +0.55k(B) atom(-1) The change in vibrational entropy when a minority species is substituted for a majorit y species was also calculated. These vibrational entropies of alloying rang ed from -0.39k(B) to +1.0k(B) atom(-1). Some correlations of the vibrationa l entropies to the thermophysical properties of the elements are reported. Correlations of vibrational entropies to predictions of a bulk Debye model were unsuccessful because the Debye temperature emphasizes a minority of ph onons that have low energies. Good correlation was found between the vibrat ional entropy of formation and the differences in metallic radii of the all oy species. The vibrational entropies of alloying for L1(2), A15 and Laves phase compounds were most successfully correlated to the mass ratio of the solute and matrix atoms.