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A. Zolriasatein, X. Yan, E. Bauer, P. Rogl, A. Shokuhfar, S. Paschen:
"Influence of PCA on thermoelectric properties and hardness of nanostructured Ba-Cu-Si clathrates";
Road Materials and Pavement Design, 87 (2015), S. 883 - 890.

Nanostructuring has been considered an effective approach to enhance the thermoelectric (TE) performance of materials by reducing their lattice thermal conductivity. In the present study, we show the influence of a process control agent (PCA) for ball milling, Stearic acid (SA), on the nano- and microstructure and thermoelectric properties of type-I clathrates in the Ba-Cu-Si system, which are promising candidates for TE applications. The SA effectively reduces cold welding and prevents particle agglomeration during ball milling. Consequently, it increases the powder yield and the milling efficiency. Smaller grain/crystallite sizes are obtained in the as-milled powders than without SA. Importantly, the SA forms nano-layers around the clathrate particles, which inhibit the grain growth during the hot pressing process used for powder compaction. Therefore, smaller grain sizes are also obtained in the hot-pressed samples. They show increased hardness and reduced thermal conductivity but also increased electrical resistivity. However, as the phonon transport is more strongly degraded than the charge transport, we observe 15% enhancement in the dimensionless thermoelectric figure of merit ZT by adding the PCA.

http://dx.doi.org/10.1016/j.matdes.2015.08.096