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A2: Medium temperature materials
The ideal thermoelectric material combines high electrical conductivity and thermopower with low thermal conductivity. In this regard, the intermetallic type-I clathrates show promise with their exceedingly low lattice thermal conductivities. In many intermetallic compounds cerium is known to lead, through the Kondo interaction, to strong correlation phenomena including the occurrence of giant thermopowers at low temperatures. We report on the successful incorporation of cerium and some other rare-earth elements as guest atoms into the clathrate crystal structure, and on the synthesis of the materials in single phase form. The physical properties of the rare-earth clathrates are discussed. We observe a 50% enhancement of the thermopower in cerium-containing clathrate compared with a rare earth-free reference material. Importantly, this enhancement occurs at high temperatures and we suggest that a rattling-enhanced Kondo interaction underlies this effect [1].
[1] A. Prokofiev, A. Sidorenko, K. Hradil, M. Ikeda, R. Svagera, M.Waas, H.Winkler, K. Neumaier, and S. Paschen. Thermopower enhancement by encapsulating cerium in clathrate cages. Nature Mat. 12 1096-1101 (2013)
We acknowledge financial support from the Austrian Science Fund (Project TRP 176-N22 and 1623-N16) and the European Research Council (Advanced Grant QuantumPuzzle, no. 227378.