Abstract
Measurements of the phonon density of states by inelastic neutron time-of-flight scattering and specific-heat measurements along with first-principles calculations, provide compelling evidence for the existence of an Einstein oscillator (rattler) at in the filled skutterudite . Multiple dispersionless modes in the measured density of states of at intermediate transfer energies are exhibited in both the experimental and theoretical density of states of the Yb-filled specimen. A peak at 12.4 meV is shown to coincide with a second Einstein mode at obtained from heat-capacity data. The local modes at intermediate transfer energies are attributed to altered properties of the host 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 . Our observations offer a plausible explanation for the significantly higher dimensionless figures of merit of filled skutterudites, compared to their parent compounds.
- Received 20 May 2010
DOI:https://doi.org/10.1103/PhysRevB.82.174301
©2010 American Physical Society