Low thermal conductivity in ternary Cu4Sn7S16 compound

This paper describes Cu4Sn7S16 material as a potential thermoelectric comprising low cost and non-toxic elements, whose complex crystal structure permits intrinsic low thermal conductivity. We begin by identifying two different synthesis approaches to obtain pure and fully dense samples, using conventional sealed tube and mechanical alloying methods combined with Spark Plasma Sintering. We then confirm the complex rhombohedral structure (R-3m, a ∼ 7.37 Å, c ∼ 36.02 Å) using both Rietveld refinement of powder X-ray diffraction patterns and High Resolution Transmission Electron Microscopy (HRTEM) analyses. Finally, we characterize the electrical and thermal properties at high temperatures on highly dense samples. The electrical behavior is also shown for the first time to change from semiconducting to metallic behavior according to sample preparation, suggesting that the material is highly sensitive to cationic site occupancy and Cu:Sn:S ratio. The complex crystallographic structure of Cu4Sn7S16 causes low thermal conductivity, which is found below 1.1 W/mK above room temperature. The focus of this paper is to drawn attention to the way in which complex structures specifically designed to induce intrinsic low thermal conductivity can be potentially attractive thermoelectrics, even in materials that are intrinsically poor conductors.