Vibrational entropy of ordered and disordered Ni3Al

We have measured the difference in vibrational entropy of Ni3Al in two states of chemical order: as a disordered fcc solid solution, and as the equilibrium L12 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 Ni3Al is 0.3kB/atom greater than for ordered Ni3Al.