Einstein Modes in the Phonon Density of States of the Single-Filled Skutterudite Yb${}_{0.2}$Co${}_4$Sb${}_{12}$

Abstract

Measurements of the phonon density of states by inelastic neutron \emph{time-of-flight} scattering and specific heat measurements along with first principles calculations, provide compelling evidence for the existence of an Einstein oscillator ("\emph{rattler}") at ${\omega }_{E1}\approx$ 5.0 meV in the filled skutterudite Yb${}_{0.2}$Co${}_4$Sb${}_{12}$. Multiple dispersionless modes in the measured density of states of Yb${}_{0.2}$Co${}_4$Sb${}_{12}$ at intermediate transfer energies (14 meV $\le$ \emph{$\omega$} $\le$ 20 meV) are exhibited in both the experimental and theoretical \emph{density-of-states} of the Yb-filled specimen. A peak at 12.4 meV is shown to coincide with a second Einstein mode at \emph{${\omega }_{E2}\approx$} 12.8 meV obtained from heat capacity data. The local modes at intermediate transfer energies are attributed to altered properties of the host CoSb${}_3$ cage as a result of Yb-filling. It is suggested that these modes are owed to a complementary mechanism for the scattering of heat-carrying phonons in addition to the mode observed at ${\omega }_{E1}\approx$ 5.0 meV. Our observations offer a plausible explanation for the significantly-higher \textit{dimensionless figures of merit} of filled skutterudites, compared to their parent compounds.

9 pages, 6 figures

References in corpus (3)

• Lattice dynamics and reduced thermal conductivity of filled skutterudites
• Heavy Fermion Behavior, Crystalline Electric Field Effects, and Weak Ferromagnetism in SmOs_{4}Sb_{12}
• 123Sb-NQR study of unconventional superconductivity in the filled skutterudite heavy-fermion compound PrOs4Sb12 under high pressure up to P = 3.82 GPa

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