An Inelastic Nuclear Resonant Scattering Study of Partial Entropies of Ordered and Disordered Fe3Al

ABSTRACTInelastic nuclear resonant scattering spectra were measured on alloys of Fe3Al that were chemically disordered, partially-ordered, and DO3-ordered. The phonon partial DOS for 57Fe atoms were extracted from these data, and the change upon disordering in the partial vibrational entropy of Fe atoms was obtained. By comparison to previous calorimetry measurements, it is shown that the contribution of the Fe atoms to the vibrational entropy is a factor of 10 smaller than that of the Al atoms. With the assistance of Born – von Kárán model calculations on the ordered alloy, it is shown that differences in the vibrational entropy originate primarily with changes in the optical modes upon disordering. The phonon DOS of 57Fe was found to change systematically with chemical short range order in the alloy. It is argued that changes in the vibrational entropy originate primarily with changes in the chemical short-range order in the alloy, as opposed to long-range order.