Designing a Thermoelectric Copper-Rich Sulfide from a Natural Mineral: Synthetic Germanite Cu22Fe8Ge4S32

Ventrapati Pavan Kumar (1) , Laura Paradis-Fortin (1, 2) , P. Lemoine (2) , Vincent Caignaert (1) , Bernard Raveau (1) , Bernard Malaman (3) , Gérard Le Caër (4) , Stéphane Cordier (2) , Emmanuel Guilmeau (1)

1 CRISMAT - Laboratoire de cristallographie et sciences des matériaux
2 ISCR - Institut des Sciences Chimiques de Rennes
3 IJL - Institut Jean Lamour
4 IPR - Institut de Physique de Rennes

This study shows that the design of copper-rich sulfides by mimicking natural minerals allows a new germanite-type sulfide Cu22Fe8Ge4S32 with promising thermoelectric properties to be synthesized. The Mössbauer spectroscopy and X-ray diffraction analyses provide evidence that the structure of our synthetic compound differs from that of the natural germanite mineral Cu26Fe4Ge4S32 by its much higher Cu(+)/Cu(2+) ratio and different cationic occupancies. The coupled substitution Cu/Fe in the Cu26-xFe4+xGe4S32 series also appears as a promising approach to optimize the thermoelectric properties. The electrical resistivity, which decreases slightly as the temperature increases, shows that these materials exhibit a semiconducting behavior, but are at the border of a metallic state. The magnitudes of the electrical resistivity and Seebeck coefficient increase with x, which suggests that Fe for Cu substitution decreases the hole concentration. The thermal conductivity decreases as the temperature increases leading to a moderately low value of 1.2 W m(-1) K(-1) and a maximum ZT value of 0.17 at 575 K.

Keywords: Minerals; Physical and chemical processes; Cations; Thermoelectrics; Crystal structure

Domains: Chemical Sciences; Physics [physics]

Ventrapati Pavan Kumar, Laura Paradis-Fortin, P. Lemoine, Vincent Caignaert, Bernard Raveau, et al.. Designing a Thermoelectric Copper-Rich Sulfide from a Natural Mineral: Synthetic Germanite Cu22Fe8Ge4S32. Inorganic Chemistry, 2017, 56 (21), pp.13376-13381. ⟨10.1021/acs.inorgchem.7b02128⟩. ⟨hal-01640116⟩