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

Ventrapati Pavan Kumar (1) , Gabin Guélou (1) , P. Lemoine (2) , Bernard Raveau (1) , Andrew R Supka (3) , Rabih Al Rahal Al Orabi (3, 4) , Marco Fornari (3) , Koichiro Suekuni (5) , Emmanuel Guilmeau (1)

1 CRISMAT - Laboratoire de cristallographie et sciences des matériaux
2 ISCR - Institut des Sciences Chimiques de Rennes
3 CMU - Central Michigan University
4 Solvay (France)
5 Kyushu University

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.

Keywords: Conductive network; Size mismatch; Colusite; Thermoelectric properties; Sulfides; Colusites; Disorder; Mismatch; Thermoelectric; Sulfide

Domains: Chemical Sciences; Coordination chemistry; Chemical Sciences; Cristallography; Chemical Sciences; Material chemistry

Ventrapati Pavan Kumar, Gabin Guélou, P. Lemoine, Bernard Raveau, Andrew R Supka, et al.. Copper‐Rich Thermoelectric Sulfides: Size‐Mismatch Effect and Chemical Disorder in the [TS4]Cu6 Complexes of Cu26T2Ge6S32 (T=Cr, Mo, W) Colusites. Angewandte Chemie International Edition, 2019, 58 (43), pp.15455-15463. ⟨10.1002/anie.201908579⟩. ⟨hal-02307079⟩