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P. Tomes, M. Ikeda, Gaku Eguchi, M. Baitinger, H. Nguyen, M. Mihalkovic, P. Popcevic, C. Allio, C. Krellner, P. Lory, S. Pailhès, V. Giordano, H. Euchner, A. Smontara, N. Barisic, M. Boissieu, Y. Grin, S. Paschen:
"Anisotropic heat and charge transport in the cubic clathrate Ba8Au6-xGe40+x";
Vortrag: SCTE2018, The 21st International Conference on Solid Compounds of Transition Elements, Wien; 25.03.2018 - 29.03.2018.

A good thermoelectric material exhibits, in addition to large thermopower, low phonon thermal conductivity and high electrical conductivity. Type-I clathrates, which show promise for thermoelectric application, exhibit remarkably low phonon thermal conductivities, and there is wide consensus that the cage-like crystal structure is of central importance to this phenomenon. The type-I clathrate Ba8Au6−xGe40+x possesses six tetrakaidecahedra and two dodecahedra cages per unit cell, and each cage encapsulates a weakly-bonded Ba atom. This material is particularly interesting for phonon transport studies because the rattling motion of Ba is associated with a very low characteristic energy [Pierre-Franc ̧ois Lory et al., Nat. Commun. 8, 491 (2017)].
In this presentation we report electrical and thermal transport properties of single-crystalline Ba7.81Au5.33Ge40.67. Remarkably, both the electrical resistivity and the phonon thermal conductivity show pronounced anisotropy. We observed a reduced electrical conductivity but an enhanced phonon thermal conductivity along the [110] direction. Electronic band structure calculations reveal pronounced anisotropy for the same direction. We suggest that strong electron-phonon coupling is at the origin of the observed phenomena.