Phonon Spectra in TaC and HfC

Abstract

Phonon dispersion curves have been measured by one-phonon coherent inelastic neutron scattering in the high-symmetry directions of TaC at room temperature and at 4.2°K (superconducting transition temperature $T_c\approx 10$°K). Pronounced structure is observed in the [001] and [110] directions for the longitudinal acoustic modes and, to some extent, for the longitudinal optic modes. By contrast, HfC ($T_c<1\mathrm{}$°K) exhibits little or no structure in these modes.