Lattice Dynamics of KN3

In this paper we report the measurement of several acoustic-phonon modes in K${\mathrm{N}}_3$. Results for the longitudinal and doubly degenerate transverse modes along the [$00\mu$] directions and the longitudinal and one transverse mode (polarized along the $c$ axis) propogating along the [$\mu \mu 0$] direction are presented. The measurements are compared with a calculation based on a rigidion model. The model includes point charges at the position of the cation and at the center of the anion. The short-range repulsive interaction is a modified Huggins-Mayer potential with the cation treated as spherical and the anion as an ellipsoid of revolution. Adequate agreement is obtained with the present neutron-scattering measurement and with recent infrared and Raman results.