The lattice dynamics of antimony

Inelastic neutron scattering measurements are reported of the frequencies of the normal modes of vibration of antimony at room temperature. Results are presented for the frequencies of phonons with reduced wavevectors in the , and directions of the reciprocal lattice, and polarized in one of the mirror planes. Bornvon Karman models with general tensor forces extending to the ninth-nearest neighbours of each atom are unable to fit the data to within the accuracy of the measurements. Comparisons are made with phonon dispersion curves for bismuth by scaling all frequencies with the ionic plasma frequency. Marked differences between the scaled dispersion curves at small wavevectors are attributed to the effects of spin-orbit coupling on the wavevector dependence of the dielectric constant. At the zone boundaries, the phonon frequencies are less sensitive to details of the screening, but it seems important to include the effects of covalency if calculations of the phonon frequencies are to agree with experiment.