Vibrational entropies of alloying and compound formation: Experimental trends

Abstract

Using phonon density-of-states data from the literature, the vibrational entropies of formation were calculated for 32 different alloys and intermetallic compounds in the harmonic approximation. The vibrational entropies of formation 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 majority species was also calculated. These vibrational entropies of alloying ranged from -0.39k_B to +1.0k_Batom⁻¹. Some correlations of the vibrational 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 phonons that have low energies. Good correlation was found between the vibrational entropy of formation and the differences in nietallic radii of the alloy species. The vibrational entropies of alloying for L1₂, A15 and Laves phase compounds were most successfully correlated to the mass ratio of the solute and matrix atoms.