Lattice dynamics of Cu3Au in the ordered and disordered states

The phonon dispersion relations of ordered and disordered Cu3Au have been measured at room temperature using inelastic neutron scattering techniques. The dispersion curves for the disordered state are very similar to those for pure Cu, while the curves for the ordered state are considerably different from those expected with the assumption that Cu-Au forces are identical to Cu-Cu forces in Cu. Born-von Karman fits to those data are given. The results how that in the ordered state Cu-Au forces are more than five times as strong as Cu-Cu forces. Each force in the disordered state can be regarded as the average of the corresponding forces in the ordered state.