Anomalous phonon softening in intermediate-valence CeNi

Inelastic neutron scattering measurements of the phonon dispersion in CeNi have been performed in the [1 0 0]/ [0 1 0] plane at temperatures between 1 0 and 295 K. A general softening of the acoustic phonon frequencies with re spect to T = 295 K is observed at low temperatures for all measured longitu dinal and transverse branches. The largest effect occurs at the zone bounda ry. Anomalies are observed in the temperature dependencies of the energies of several modes, showing either a minimum or a maximum in the range 100 K < T < 200 K. This behaviour is indicative of an unusually strong coupling o f valence fluctuations and lattice vibrations. (C) 1999 Elsevier Science B. V. All rights reserved.