An experimental study of the difference in vibrational entropy between ordered and disordered Fe3Al

The difference in vibrational entropy between disordered and DO3-ordered Fe3Al was measured by calorimetry to be (0.10 +/- 0.03) k(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 Karman model showed that the lower vibrational entropy of the ordered ahoy originates from high-frequency optical modes involving the vibration of the aluminum-rich sublattice. These modes are consistent with the large changes in local vibrational amplitudes of Al atoms upon ordering that were measured by extended electron energy loss fine structure spectrometry.