Hopping Processes Explain T-linear Rise of Thermal Conductivity in Thermoelectric Clathrates above the Plateau

Abstract

Type-I clathrate compounds with off-center guest ions realize the phonon-glass electron-crystal concept by exhibiting almost identical lattice thermal conductivities ${\kappa }_{\mathrm{L}}$ to those observed in network-forming glasses. This is in contrast with type-I clathrates with on-center guest ions showing ${\kappa }_{\mathrm{L}}$ of conventional crystallines. Glasslike ${\kappa }_{\mathrm{L}}$ stems from the peculiar THz frequency dynamics in off-center type-I clathrates where there exist three kinds of modes classified into extended(EX), weakly(WL) and strongly localized(SL) modes as demonstrated by Liu $et.al.$, Phys. Rev. B $\text{93}$, 214305(2016). Our calculated results based on the hopping mechanism of SL modes via anharmonic interactions show fairly good agreement with observed $T$-linear rise of ${\kappa }_{\mathrm{L}}$ above the plateau. We emphasize that both the magnitude and the temperature dependence are in accord with the experimental data of off-center type-I clathrates.

References in corpus (2)

• Glasslike vs. crystalline thermal conductivity in carrier-tuned Ba8Ga16X30 clathrates (X = Ge, Sn)
• Cage-size control of guest vibration and thermal conductivity in Sr8Ga16Si30-xGex

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