Impact of Rattlers on Thermal Conductivity of a Thermoelectric Clathrate: A First-Principles Study

Abstract

We investigate the role of rattling guest atoms on the lattice thermal-conductivity of a type-I clathrate Ba${}_8$Ga${}_{16}$Ge${}_{30}$ by first-principles lattice dynamics. Comparing phonon properties of filled and empty clathrates, we show that rattlers cause 10-fold reductions in the relaxation time of phonons by increasing the phonon-phonon scattering probability. Contrary to the resonant scattering scenario, the reduction in the relaxation time occurs in a wide frequency range, which is crucial for explaining unusually low thermal-conductivities of clathrates. We also find that the impact of rattlers on the group velocity of phonons is secondary because the flattening of phonon dispersion occurs only in a limited phase space in the Brillouin zone.

10 pages, 10 figures

References in corpus (1)

• Glasslike vs. crystalline thermal conductivity in carrier-tuned Ba8Ga16X30 clathrates (X = Ge, Sn)

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