Local-Disorder-Induced Low Thermal Conductivity in Degenerate Semiconductor Cu22Sn10S32

S-based semiconductors are attracting attention as environmentally friendly materials for energy-conversion applications because of their structural complexity and chemical flexibility. Here, we show that the delicate interplay between the chemical composition and cationic order/disorder allows one to stabilize a new sphalerite derivative phase of cubic symmetry in the Cu-Sn-S diagram: Cu 22 Sn 10 S 32 . Interestingly, its crystal structure is characterized by a semiordered cationic distribution, with the Cu-Sn disorder being localized on one crystallographic site in a long-range-ordered matrix. The origin of the partial disorder and its influence on the electronic and thermal transport properties are addressed in detail using a combination of synchrotron X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy, theoretical modeling, and transport property measurements. These measurements evidence that this compound behaves as a pseudogap, degenerate p-type material with very low lattice thermal conductivity (0.5 W m -1 K -1 at 700 K). We show that localized disorder is very effective in lowering κ L without compromising the integrity of the conductive framework. Substituting pentavalent Sb for tetravalent Sn is exploited to lower the hole concentration and doubles the thermoelectric figure of meri ZT o 0.55 at 700 K with respect to the pristine compound. The discovery of this semiordered cubic sphalerite derivative Cu 22 Sn 10 S 32 furthers the understanding of the structure-property relationships in the Cu-Sn-S system and more generally in ternary and quaternary Cu-based systems.