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Thermoelectric properties of Ba 8 Au 5.25 Ge 40.3 □ 0.45 type - I clathrate

The Ba - containing type - I clathrates show promising thermoelectric (TE) properties [1]. Therefore, Ba - Au - Ge type - I clathrates are thus of interest for TE applications as well [2]. Both p - and n - type conductivity were found in the Ba - Au - Ge system, depending on Au content. Here we present the measurements of the electrical and thermal transport on the p - type single crystal Ba 8 Au 5.25 Ge 40.3 □ 0.45 along [001], [110] and [111] directions. The sample shows a semiconducting - like behavior. The Hall coefficient R H exhi bits a positive sign, pointing on the dominance of electron - like conduction. The Hall mobility μ H below ~ 100 K follows approximately T - 3/2 law, while above 100 K the μ H is temperature independent, which denotes on neutral - impurity scattering. Thermal conductivity κ , measured by steady state method and 3ω method, is rather low with κ ~ 1 Wm - 1 K - 1 at room temperature. It is interesting to point out that the electrical resis tivity, R H and κ along [110] direction revealed a different magnitude compared to [001] and [111] directions. It seem reasonable to assume that this observation is due to different electron - phonon coupling for different directions, as it will be shown by l ow - temperature κ data. [1] A. Saramat, G. Svensson, A. Palmqvist, C. Stiewe, E. Mueller, D. Platzek, S. Williams, D. Rowe, J. Bryan, and G. Stucky, J. Appl. Phys. 99 , 023708 (2006). [2] H. Zhang, H. Borrmann, N. Oeschler, C. Candolfi, W. Schnelle, M. Schmidt, U. Burkhardt, M. Baitinger, J. - T. Zhao, Y. Grin, Inorg. Chem. 50 , 1250 (1250). We acknowledge financial support from the Austrian Science Fund (FWF project TRP 176 - N22) and from the German Research Foundation (DFG project SPP 1386 - nanOcla)

Ba-Au-Ge type I clathrates; thermoelectric properties

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