ANOMALOUS LATTICE-DYNAMICS IN INTERMEDIATE-VALENCE CENI

The low-energy phonon modes of the intermediate-valence system CeNi an d the isostructural reference compound LaNi have been measured at room temperature by inelastic neutron scattering in the scattering planes (001) and (100). In general, the frequencies of the acoustic and lower optical-phonon branches are found to be appreciably lower in CeNi. Th is effect is especially dramatic for the acoustic modes propagating al ong the a and b directions. Maximum softening was observed near the zo ne boundary, where it can exceed 20% for some of the branches. These d ata represent the most pronounced effect of electron-lattice coupling in a Ce-based intermediate-valence compound that we are aware of.