Structural, transport, and thermal properties of the single-crystalline type-VIII clathrate Ba8Ga16Sn30

Huo Dexuan

Sakata Takeaki

Sasakawa Tetsuya

Avila M. A.

Tsubota Masami

Iga Fumitoshi

Fukuoka Hiroshi

Yamanaka Shoji

Aoyagi S.

Takabatake Toshiro

Physical Review B

We report the electrical resistivity rho, Hall coefficient RH, thermoelectric power S, specific heat C, and thermal conductivity kappa on single crystals of the type-VIII clathrate Ba8Ga16Sn30 grown from Sn-flux. Negative S and RH over a wide temperature range indicate that electrons dominate electrical transport properties. Both rho(T) and S(T) show typical behavior of a heavily doped semiconductor. The absolute value of S increases monotonically to 243 µV/K with increasing temperature up to 550 K. The large S may originate from the low carrier concentration n = 3.7×1019 cm–3. Hall mobility µH shows a maximum of 62 cm2/V s around 70 K. The analysis of temperature dependence of µH suggests a crossover of a dominant scattering mechanism from ionized impurity to acoustic phonon scattering with increasing temperature. The existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is evidenced by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K. This local vibration of Ba atoms should be responsible for the low thermal conductivity (1.1 W/m K at 150 K). The potential of type-VIII clathrate compounds for thermoelectric application is discussed.

Physics [ 420 ]

eng

American Physical Society

Copyright (c) 2006 American Physical Society

[ISSN] 1098-0121

[NCID] AA11187113

[DOI] 10.1103/PhysRevB.71.075113

[DOI] http://dx.doi.org/10.1103/PhysRevB.71.075113