Phonon density-of-states in bcc and hcp Eu metal under high pressure measured by ¹⁵¹Eu nuclear inelastic scattering of synchrotron radiation

Abstract

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.

Keywords:

• Eu metal
• high pressure
• mixed valence
• phonon spectroscopy
• ¹⁵¹Eu nuclear inelastic scattering

Acknowledgements

This work was supported by the BMBF (05 KS4PPB/4) and the DFG (WO 209/12-3). We want to thank Ilya Sergueev for his expert help with the installation of the monochromator and the KB optics, and Harald Müller for his advice with the argon glove box. We are thankful to Svetoslav Stankov for making available the results on Eu metal at ambient pressure prior to publication.