Vibrational entropy of ordered and disorderedNi3Al

We have measured the difference in vibrational entropy of ${\mathrm{Ni}}_3$Al in two states of chemical order: as a disordered fcc solid solution, and as the equilibrium L$1_2$ ordered structure. Data were obtained from three independent methods: low-temperature calorimetry, temperature-dependent x-ray diffractometry, and temperature-dependent extended electron energy loss fine structure spectrometry. We estimate that at high temperatures, the vibrational entropy of chemically disordered ${\mathrm{Ni}}_3$Al is 0.3${\mathit{k}}_{\mathit{B}}$/atom greater than for ordered ${\mathrm{Ni}}_3$Al.