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High-efficiency thermoelectric Ba8Cu14Ge6P26: bridging the gap between tetrel-based and tetrel-free clathrates

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Abstract

A new type-I clathrate, Ba8Cu14Ge6P26, was synthesized by solid-state methods as a polycrystalline powder and grown as a cm-sized single crystal via the vertical Bridgman method. Single-crystal and powder X-ray diffraction show that Ba8Cu14Ge6P26 crystallizes in the cubic space group Pm[3 with combining macron]n (no. 223). Ba8Cu14Ge6P26 is the first representative of anionic clathrates whose framework is composed of three atom types of very different chemical natures: a transition metal, tetrel element, and pnicogen. Uniform distribution of the Cu, Ge, and P atoms over the framework sites and the absence of any superstructural or local ordering in Ba8Cu14Ge6P26 were confirmed by synchrotron X-ray diffraction, electron diffraction and high-angle annular dark field scanning transmission electron microscopy, and neutron and X-ray pair distribution function analyses. Characterization of the transport properties demonstrate that Ba8Cu14Ge6P26 is a p-type semiconductor with an intrinsically low thermal conductivity of 0.72 W m−1 K−1 at 812 K. The thermoelectric figure of merit, ZT, for a slice of the Bridgman-grown crystal of Ba8Cu14Ge6P26 approaches 0.63 at 812 K due to a high power factor of 5.62 μW cm−1 K−2. The thermoelectric efficiency of Ba8Cu14Ge6P26 is on par with the best optimized p-type Ge-based clathrates and outperforms the majority of clathrates in the 700–850 K temperature region, including all tetrel-free clathrates. Ba8Cu14Ge6P26 expands clathrate chemistry by bridging conventional tetrel-based and tetrel-free clathrates. Advanced transport properties, in combination with earth-abundant framework elements and congruent melting make Ba8Cu14Ge6P26 a strong candidate as a novel and efficient thermoelectric material.

Graphical abstract: High-efficiency thermoelectric Ba8Cu14Ge6P26: bridging the gap between tetrel-based and tetrel-free clathrates

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Publication details

The article was received on 09 Aug 2017, accepted on 28 Sep 2017 and first published on 29 Sep 2017


Article type: Edge Article
DOI: 10.1039/C7SC03482B
Citation: Chem. Sci., 2017, Advance Article
  • Open access: Creative Commons BY license
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    High-efficiency thermoelectric Ba8Cu14Ge6P26: bridging the gap between tetrel-based and tetrel-free clathrates

    J. Wang, O. I. Lebedev, K. Lee, J. Dolyniuk, P. Klavins, S. Bux and K. Kovnir, Chem. Sci., 2017, Advance Article , DOI: 10.1039/C7SC03482B

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