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\ifmmode^\circ\else\textdegree\fi{}K (superconducting transition temperature ${T}_{c}\ensuremath{\approx}10$\ifmmode^\circ\else\textdegree\fi{}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 (${T}_{c}<1$\ifmmode^\circ\else\textdegree\fi{}K) exhibits little or no structure in these modes.