Phonon dispersion in NaF in the region between zero and first sound, measured by inelastic neutron scattering

Abstract

This is the first inelastic neutron scattering experiment covering the transition region between zero and first sound. Measurements in NaF were performed in a wavevector region 0.06<or=q/qmax<or=0.25 at 295, 500, 600 and 700K. The experimental data cover the zero-sound region at room temperature and the transition region near first sound at 700K. We show that it is possible to describe the frequency dependence of the sound velocities by use of an averaged thermal-photon lifetime. The isothermal elastic constants and the averaged phonon lifetimes are determined at each temperature, and the zero-sound elastic constants at room temperature.