Thermopower enhancement by encapsulating cerium in clathrate cages

• Published in: Nature materials Vol. 12; no. 12; pp. 1096 - 1101
• Main Authors: Prokofiev, A., Sidorenko, A., Hradil, K., Ikeda, M., Svagera, R., Waas, M., Winkler, H., Neumaier, K., Paschen, S.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2013; Nature Publishing Group
• Subjects: 639/301/119/997; 639/301/299/2736; 639/301/930; Biomaterials; Cerium; Clathrates; Condensed Matter Physics; Conductivity; Crystal structure; Earth; Energy consumption; Energy management; Heat transfer; High temperature; Intermetallics; letter; Low temperature; Materials Science; Nanotechnology; Optical and Electronic Materials; Photovoltaic cells; Rare earth elements; Solar energy; Thermal conductivity; Waste heat
• DOI: 10.1038/nmat3756
• ISSN: 1476-1122; 1476-4660

Clathrate materials have been the subject of intense investigation because of their beneficial properties, in particular their low thermal conductivities. Now, improved thermopower at high temperatures arising from strong electron correlation effects has been achieved in a type-I clathrate containing cerium guest atoms. 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 conductivities 1 . 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 temperatures 2 . 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 interaction 3 underlies this effect.