Copper‐Rich Thermoelectric Sulfides: Size‐Mismatch Effect and Chemical Disorder in the [TS4]Cu6 Complexes of Cu26T2Ge6S32 (T=Cr, Mo, W) Colusites

• Published in: Angewandte Chemie 2019-10, Vol.131 (43), p.15601-15609
• 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: Article
• Language: English
• Subjects: Cations; Chemical Sciences; Chemistry; Chromium; Colusite; Condensed Matter; Copper; Cristallography; Electrical resistivity; Electron transport; Größenfehlpassung; Inorganic chemistry; Material chemistry; Molybdenum; Organic chemistry; Physics; Seebeck effect; Strukturfehlordnung; Substitutes; Sulfide; Tetrahedra; Thermoelektrische Eigenschaften; Transport properties; Tungsten
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201908579

Herein, we investigate the Mo and W substitution for Cr in synthetic colusite, Cu26Cr2Ge6S32. 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−1 K−2 at 700 K in Cu26Cr2Ge6S32. 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 “Cu26S32” 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 [TS4]Cu6 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, σ2. Ziemlich unangepasst: Nicht passende Kationengrößen in gemischt oktaedrisch‐tetraedrischen Komplexen stören die Ladungstransporteigenschaften von Colusiten. Die direkte Beziehung zwischen Größenfehlanpassung, struktureller Fehlordnung und chemischer Bindung im leitfähigen „Cu26S32”‐Gerüst wurde hergeleitet und mit den thermoelektrischen Eigenschaften korreliert.