Heterostructures of skutterudites and germanium antimony tellurides – structure analysis and thermoelectric properties of bulk samples
Heterostructures of germanium antimony tellurides with skutterudite-type precipitates are promising thermoelectric materials due to low thermal conductivity and multiple ways of tuning their electronic transport properties. Materials with the nominal composition [CoSb2(GeTe)_(0.5)]_x(GeTe)_(10.5)Sb_2Te_3 (x = 0–2) contain nano- to microscale precipitates of skutterudite-type phases which are homogeneously distributed. Powder X-ray diffraction reveals that phase transitions of the germanium antimony telluride matrix depend on its GeTe content. These are typical for this class of materials; however, the phase transition temperatures are influenced by heterostructuring in a beneficial way, yielding a larger existence range of the intrinsically nanostructured pseudocubic structure of the matrix. Using microfocused synchrotron radiation in combination with crystallite pre-selection by means of electron microscopy, single crystals of the matrix as well as of the precipitates were examined. They show nano-domain twinning of the telluride matrix and a pronounced structure distortion in the precipitates caused by GeTe substitution. Thermoelectric figures of merit of 1.4 ± 0.3 at 450 °C are observed. In certain temperature ranges, heterostructuring involves an improvement of up to 30% compared to the homogeneous material.
© 2015 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Received 26th May 2015, Accepted 31st July 2015, First published online 31 Jul 2015. Financial support from the European Union (European Social Fund, NFG ''Effiziente Energienutzung: Neue Konzepte und Materialien'') and the Deutsche Forschungsgemeinschaft (Grant OE530/1-2) is gratefully acknowledged. The authors thank Dr Gavin B. Vaughan, Dr Jonathan Wright and Dr Loredana Erra (ESRF, Grenoble) for their support during the synchrotron measurements (project HS-4625). We are indebted to Prof. Dr Wolfgang Schnick (LMU Munich) for his generous support of this work. Tom Faske, Christina Fraunhofer and Sabine Hübner are acknowledged for help with some preliminary syntheses. GJS acknowledges support of DoE EFRC-S3TEC Award DE-SC0001299.
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