The Transition from Zero- to First-Sound Phonon Propagation in Lead at High Temperatures

Wavevector dependences of the transverse phonon energy widths, determined by neutron scattering, in monocrystalline lead provide evidence for a transition from a zero-sound, collision-free mode of high-frequency phonon propagation to a first-sound, collision-dominated regime at about 500 to 550 K. Hence the propagation of phonons having wavelengths on the scale of the interatomic spacing is heavily damped, similarly to that in the liquid state, prior to melting.