Magnitude and Origin of the Difference in Vibrational Entropy between Ordered and DisorderedFe3Al

The difference in vibrational entropy between chemically disordered and $D{O}_3$-ordered ${\mathrm{Fe}}_3$Al was measured by calorimetry to be (0.10 ± 0.03) ${\mathit{k}}_{\mathit{B}}$/atom at high temperatures, with the ordered alloy having the lower vibrational entropy. Analysis of the vibrational modes of the ordered and disordered alloys with a Born-von Kármán model showed that the lower vibrational entropy of the ordered alloy originates from high-frequency optical modes involving large-amplitude vibrations of the aluminum-rich sublattice.