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 I4̅3m, 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, the lattice part of thermal conductivity increases smoothly in the entire temperature range. Low thermal conductivity of Cu12Sb4S13 is associated with the quazi-localized out-of-plane rattling of three-coordinated copper atoms, which softens with decreasing temperature responding to subtle structural changes upon the MST.

Thermoelectric Properties of Magnesium-Doped Tetrahedrite Cu12−xMgxSb4S13

“…A second dip is observed near 85 K which closely corresponds to the metal-toinsulator transition accompanied by a distortion of the cubic unit cell. [37] The introduction of a small amount of Mg significantly enhances the first anomaly with a rather abrupt decrease between 300 and 200 K from 1.1 to 0.55 W m-1 K-1, respectively. This stronger decrease, which corresponds to the temperature range where the hysteretic behavior is observed in the electrical resistivity, is mainly due to the higher  values measured in this sample compared to the ternary compound.…”

First-principles study of electronic transport and structural properties of Cu12Sb4S13 in its high-temperature phase

“…1). This result is not surprising since, in tetrahedrite at low temperatures, there are hints of a structural transition happening around 70 K that modifies the size of the cell and introduces distortions in the local symmetry for T < 70 K; this transition is object of an active experimental investigation 2,[31][32][33][34] . In addition, the instability at low temperatures emerges also from DFT calculations of the phonon spectrum of the high-T symmetric phase 1 .…”

Disorder-driven glasslike thermal conductivity in colusite Cu26V2Sn6S32Candolfi1, Guélou2, Bourgès3 et al. 2020Phys. Rev. Materials283390View full textAdd to dashboardCite

“…Upon cooling, none of the samples experience a phase transition in contrast to their cousin sulfides tetrahedrites, of general chemical formula Cu 12 Sb 4 S 13 , where structural distortions or exsolution process (i.e. a phase separation into two isostructural phases of distinct chemical compositions) have been evidenced below 300 K. [26][27][28][29][30][31] Further thermodynamic evidence of the role of the disorder on the thermal transport is provided by the specific heat measurements shown in After subtracting the electronic contribution, the lattice specific heat ℎ , plotted as ℎ / 3 versus to more clearly emphasize the low-energy features, show the presence of specific heat in excess of the Debye contribution for both compounds that peaks near = 15 and 17 K for the H and L samples, respectively. Such an excess has also been observed in tetrahedrites and is often found in cage-like systems for which the low-energy dynamics of the entrapped atoms dominates ℎ at low temperatures.…”