Inelastic neutron scattering of γ-iron, and the determination of the elastic constants by lattice dynamics

The physical properties of the various phases of iron have been the subject of numerous of numerous theoretical and experimental investigations. Of particular interest is the appearance of the fcc γ-phase between approximately 1,200 K and 1,670 K. The authors were able to growth in situ single crystals of fcc iron of sufficient size to perform an inelastic neutron scattering study of the lattice dynamics of this phase of iron. The phonon dispersion curves along the [00ξ],[ξξ0] and [ξξξ] symmetry directions were measured at 1,428 K. A limited number of phonons were also measured at 1,227 K and 1,640 K to assess the temperature dependence of the phonon frequencies. The data collected at 1,428 K were used to evaluate the elastic constants, the phonon density of states and the lattice contribution to the specific heat. The measured dispersion curves of γ-Fe are qualitatively similar to those of Ni (measured at 296 K) and Ni0.3Fe0.7 (measured at 296 and 573 K)