[en] Single-crystal x-ray diffraction from clathrate-II NaxSi136 (x = 24) prepared by a new technique reveals the exceptionally large Na@Si-28 atomic displacement parameter (U-eq) is strongly temperature dependent, and can be attributed to low-energy rattling modes associated with the Na guest. Inelastic neutron scattering (INS) spectra collected from NaxSi136 powder specimens (x = 3, 23) confirm the presence of low-energy guest-derived phonon modes for Na@Si-28 and Na@Si-20. The lower energy Na@Si-28 rattler mode falls in the frequency range of the silicon host acoustic phonons, indicating the possibility for interaction with these phonons. The presence of these low-energy modes combined with the ability to controllably vary the guest content presents a unique opportunity for exploring the influence of guest-framework interactions on the lattice dynamics in intermetallic clathrates.
Disciplines :
Physics
Author, co-author :
Beekman, M.; Department of Physics, University of South Florida, Tampa, FL 33620, USA
Hermann, Raphaël ; Université de Liège - ULiège > Département de physique > Département de physique
Möchel, Anne ; Université de Liège - ULiège > Doct. sc. (chimie - Bologne)
Juranyi, F.; Laboratory for Neutron Scattering, ETH Zuerich and Paul Scherrer Institut
Nolas, G. S.; Department of Physics, University of South Florida
Language :
English
Title :
A study of low-energy guest phonon modes in clathrate-II NaxSi136 (x = 3, 23, and 24)
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