Low-Temperature Structure and Thermoelectric Properties of Pristine Synthetic Tetrahedrite Cu12Sb4S13

Abstract

We have examined the low-temperature crystal structure and thermoelectric properties of unsubstituted synthetic tetrahedrite, Cu12Sb4S13, a parent compound for modern state-of-the-art thermoelectric materials for midtemperature heat-to-power conversion. The crystal structure, space group I43m, was probed by X-ray powder diffraction with synchrotron radiation at different temperatures within the range of 10–293 K. It displays subtle changes at the temperature of the metal-to-semiconductor transition (MST) near 90 K, at which a concerted displacement of two independent atoms occurs without symmetry reduction. The displacement of the sulfur atom toward the face of the Cu6 octahedron, the shift of the copper atom toward the triangle S3 plane composed of two independent sulfur atoms, and a sharp elongation of the Cu—Sb separation upon the MST largely affect the transport properties of Cu12Sb4S13. It displays sharp increase in electrical resistivity and a maximum in thermopower below the MST. On the contrary, ...