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Thermopower enhancement by encapsulating cerium in clathrate cages

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The increasing worldwide energy consumption calls for the design of more efficient energy systems. Thermoelectrics could be used to convert waste heat back to useful electric energy if only more efficient materials were available. 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 conductivities1. Here we report the successful incorporation of cerium as a guest atom into the clathrate crystal structure. In many simpler intermetallic compounds, this rare earth element is known to lead, through the Kondo interaction, to strong correlation phenomena including the occurrence of giant thermopowers at low temperatures2. Indeed, we observe a 50% enhancement of the thermopower compared with a rare-earth-free reference material. Importantly, this enhancement occurs at high temperatures and we suggest that a rattling-enhanced Kondo interaction3 underlies this effect.

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Figure 1: Structure and quality characterization of the clathrate Ce–BAS.
Figure 2: Transport properties of Ce–BAS and La–BAS.
Figure 3: Thermopower comparison with the rare-earth-free reference material BAS.
Figure 4: Thermodynamic properties of the investigated clathrates.

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Change history

  • 06 November 2013

    In the version of this Letter originally published online, in Fig. 1a caption, '2a (6c)' should have read '2a (6d)'. This error has now been corrected in all versions of the Letter.


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We acknowledge financial support from the Austrian Science Fund (projects P19458-N16, TRP 176-N22 and I623-N16) and the European Research Council (Advanced Grant QuantumPuzzle, no. 227378), and help from T. Pippinger and R. Miletich-Pawliczek (Vienna University) during single-crystal XRD measurements on La–BAS. TEM images were made by J. Bernardi and M. Stöger-Pollach at USTEM (Vienna University of Technology).

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A.P. and S.P. designed the research. A.P. synthesized the material; A.S., M.I., R.S., M.W., H.W., K.N. and K.H. performed the measurements. A.P., A.S., H.W., K.H. and S.P. analysed the data. A.P., A.S. and S.P. prepared the manuscript.

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Correspondence to A. Prokofiev or S. Paschen.

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Prokofiev, A., Sidorenko, A., Hradil, K. et al. Thermopower enhancement by encapsulating cerium in clathrate cages. Nature Mater 12, 1096–1101 (2013).

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