Copper-Rich Thermoelectric Sulfides: Size-Mismatch Effect and Chemical Disorder in the [TS 4 ]Cu 6 Complexes of Cu 26 T 2 Ge 6 S 32 (T=Cr, Mo, W) Colusites

• Published in: Angewandte Chemie International Edition Vol. 58; no. 43; pp. 15455 - 15463
• Main Authors: Pavan Kumar, Ventrapati, Guélou, Gabin, Lemoine, Pierric, Raveau, Bernard, Supka, Andrew R, Al Rahal Al Orabi, Rabih, Fornari, Marco, Suekuni, Koichiro, Guilmeau, Emmanuel
• Format: Journal Article
• Language: English
• Published: Germany 21.10.2019
• Subjects: colusites; disorder; thermoelectric properties; mismatch; sulfides
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201908579

Herein, we investigate the Mo and W substitution for Cr in synthetic colusite, Cu Cr Ge S . Primarily, we elucidate the origin of extremely low electrical resistivity which does not compromise the Seebeck coefficient and leads to outstanding power factors of 1.94 mW m  K at 700 K in Cu Cr Ge S . We demonstrate that the abnormally long iono-covalent T-S bonds competing with short metallic Cu-T interactions govern the electronic transport properties of the conductive "Cu S " framework. We address the key role of the cationic size-mismatch at the core of the mixed tetrahedral-octahedral complex over the transport properties. Two essential effects are identified: 1) only the tetrahedra that are directly bonded to the [TS ]Cu complex are significantly distorted upon substitution and 2) the major contribution to the disorder is localized at the central position of the mixed tetrahedral-octahedral complex, and is maximized for x=1, i.e. for the highest cationic size-variance, σ .