Phonon density-of-states in bcc and hcp Eu metal under high pressure measured by151Eu nuclear inelastic scattering of synchrotron radiation

We present the first study of the phonon density-of-states (DOS) of mixed-valent (m.v.) Eu metal in the bcc-phase at 10 GPa and in the hcp-phase at 17 GPa using 151Eu nuclear inelastic scattering of synchrotron radiation. In both cases, features in the phonon-DOS exhibit shifts to lower energies when compared with stable divalent or trivalent rare-earth metals with larger molar volumes. These anomalous properties are caused by the strong m.v. state of Eu in both phases, determined independently by 151Eu nuclear forward scattering, and are discussed in conjunction with a recent study of the Sm phonon-DOS in divalent and m.v. SmS.