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High Power Factors of Thermoelectric Colusites Cu 26 T 2 Ge 6 S 32 ( T = Cr, Mo, W): Toward Functionalization of the Conductive “Cu–S” Network
Author(s) -
Pavan Kumar Ventrapati,
Supka Andrew R.,
Lemoine Pierric,
Lebedev Oleg I.,
Raveau Bernard,
Suekuni Koichiro,
Nassif Vivian,
Al Rahal Al Orabi Rabih,
Fornari Marco,
Guilmeau Emmanuel
Publication year - 2019
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201803249
Subject(s) - seebeck coefficient , materials science , electronegativity , octahedron , crystallography , metal , thermoelectric effect , copper , electrical resistivity and conductivity , condensed matter physics , thermal conductivity , thermodynamics , crystal structure , physics , chemistry , metallurgy , quantum mechanics , composite material
The introduction of hexavalent T 6+ cations in p‐type thermoelectric colusites Cu 26 T 2 Ge 6 S 32 ( T = Cr, Mo, W) leads to the highest power factors among iono‐covalent sulfides, ranging from 1.17 mW m −1 K −2 at 700 K for W to a value of 1.94 mW m −1 K −2 for Cr. In Cu 26 Cr 2 Ge 6 S 32 , ZT reaches values close to unity at 700 K. The improvement of the transport properties in these new sulfides is explained on the basis of electronic structure and transport calculations keeping in mind that the relaxation time is significantly influenced by the size and the electronegativity of the interstitial T cation. The rationale is based on the concept of a conductive “Cu–S” network, which in colusites corresponds to the more symmetric parent structure sphalerite. A detailed structural analysis of these colusites shows that the distortion of the conductive network is influenced by the presence in the structure of mixed octahedral–tetrahedral [ T S 4 ]Cu 6 complexes where the T cations are underbonded to sulfur and form metal–metal interactions with copper, Cu– T distances decreasing from 2.76 Å for W to 2.71 Å for Cr. The interactions between these complexes are responsible for the outstanding electronic transport properties. By contrast, the thermal conductivity is not significantly affected.