High-efficiency thermoelectric Ba8Cu14Ge6P26: bridging the gap between tetrel-based and tetrel-free clathrates. Issue 12 (10th October 2017)

• Record Type: Journal Article
• Authors: Wang, Jian; Lebedev, Oleg I.; Lee, Kathleen; Dolyniuk, Juli-Anna; Klavins, Peter; Bux, Sabah; Kovnir, Kirill
• Is Part Of: Chemical science. Volume 8:Issue 12(2017)
• Page Start: 8030
• Page End: 8038
• Publication Date: 2017-10-10
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7sc03482b
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Synergy between tetrel- and pnictide-based clathrates: synthesis, crystal structure, and transport properties of a Ba8 Cu14 Ge6 P26 . Abstract : A new type-I clathrate, Ba8 Cu14 Ge6 P26, 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 Ba8 Cu14 Ge6 P26 crystallizes in the cubic space group Pm 3̄ n (no. 223). Ba8 Cu14 Ge6 P26 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 Ba8 Cu14 Ge6 P26 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 Ba8 Cu14 Ge6 P26 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 Ba8 Cu14 Ge6 P26 approaches 0.63 at 812 K due to a high power factor of 5.62 μW cm −1 K −2 . The thermoelectric efficiency of Ba8 Cu14 Ge6 P26 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. Ba8 Cu14 Ge6 P26 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 Ba8 Cu14 Ge6 P26 a strong candidate as a novel and efficient thermoelectric material.