Lattice dynamics of theA15compoundNb3Sb

The phonon dispersion curves of ${\mathrm{Nb}}_3$Sb have been studied by inelastic neutron scattering. All the branches have been determined in the main symmetry directions and the results are analyzed with Born—von Kármán models of different complexity. A model with general forces up to the eighth-nearest neighbors gives excellent agreement with experiment. However, a rather good description of the dispersion curves is obtained with a model including axially symmetric forces up to the third-nearest neighbors, which indicates that these interactions are dominant. Temperature effects were found to be very small. Additional experiments were performed on polycrystalline samples to determine directly the phonon density of states. Our results obtained on ${\mathrm{Nb}}_3$Sb are compared with the available phonon data on ${\mathrm{Nb}}_3$Sn.