Lattice dynamics and related diffusion properties of intermetallics: II. Ni₃Sb

The phonon dispersion of the intermetallic Ni_72.5Si_27.5 has been studied by inelastic neutron scattering in its high-temperature phase of DO₃ structure, stable above 530°C. The dispersion has been examined at a temperature of 600°C; some selected branches were also studied at 530°C (i.e. very close to the phase transition) and at 900°C. In general, the phonons are very strongly damped and some branches have not been found at all. For transverse phonons with [ξξ0] propagation, the frequency does not change as a function of the temperature, but the widths become larger towards higher temperatures. The migration enthalpy and several other thermodynamic quantities have been calculated from the densities of states. The anomalous behaviour of the alloy is related to high vacancy densities.