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Copper‐Rich Thermoelectric Sulfides: Size‐Mismatch Effect and Chemical Disorder in the [ T S 4 ]Cu 6 Complexes of Cu 26 T 2 Ge 6 S 32 ( T =Cr, Mo, W) Colusites
Author(s) -
Pavan Kumar Ventrapati,
Guélou Gabin,
Lemoine Pierric,
Raveau Bernard,
Supka Andrew R.,
Al Rahal Al Orabi Rabih,
Fornari Marco,
Suekuni Koichiro,
Guilmeau Emmanuel
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201908579
Subject(s) - seebeck coefficient , octahedron , crystallography , electrical resistivity and conductivity , tetrahedron , copper , metal , thermoelectric effect , chemistry , covalent bond , materials science , thermoelectric materials , cationic polymerization , crystal structure , thermodynamics , physics , metallurgy , organic chemistry , quantum mechanics
Herein, we investigate the Mo and W substitution for Cr in synthetic colusite, Cu 26 Cr 2 Ge 6 S 32 . 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 Cu 26 Cr 2 Ge 6 S 32 . 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 26 S 32 ” 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 [ T S 4 ]Cu 6 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 2 .