Phonon Spectrum of Scandium Metal by Inelastic Scattering of Neutrons

The phonon dispersion relations along the principal symmetry axes of the hexagonal close-packed metal scandium have been measured at room temperature by means of inelastic neutron scattering. The results have been analyzed in terms of a sixth-neighbor modified axially symmetric force-constant model. Both the dispersion curves and the force-constant model are qualitatively similar to those obtained for yttrium metal and yield long-range interactions in the basal plane, but interactions which decrease rapidly in the direction normal to the basal plane. A qualitative discussion is also given concerning the directional nature of the bonding in hcp metals from a consideration of the electron-phonon matrix elements. Evidence has been found for an anomaly along the ${\Delta }_1$ branch reflecting the nesting feature of the Fermi surface along that direction. An unsuccessful search has been made for paramagnon-type excitations in this metal down to 4.2 K.