PHONON ANOMALIES IN THE INTERMEDIATE-VALENCE COMPOUND CE0.9PR0.1NI5

The phonon dispersion curves of the intermediate valence alloy Ce0.9Pr 0.1Ni5 and the integral valence reference alloys LaNi5 and PrNi5 have been investigated by coherent inelastic neutron scattering on a triple -axis spectrometer. The lowest zone-center optic mode in Ce0.9Pr0.1Ni5 is distinctly softer than in the reference alloys. Despite the smalle r lattice volume of the Ce-based alloy there is no hardening of acoust ic and optic phonon branches with respect to the reference systems. Th e observed effects are interpreted as features of the f-d -hybridisati on due to the intermediate valence state of the cerium ion.