Observation of phonon anomalies in the intermediate-valence compoundCePd3

We report measurements of the phonon dispersion relation in intermediate-valence ${\mathrm{CePd}}_3$. The longitudinal-acoustic modes show a distinct softening above 100 K and a temperature-dependent broadening and splitting at higher temperatures. Especially in the 〈100〉 direction the longitudinal modes differ from those of other ${\mathrm{Cu}}_3$Au structures. A good fit of the room-temperature dispersion curves is given by a 16-parameter Born–von Kármán model with a breathing force as an additional degree of freedom.