International audienceWe report the evaluation of the thermoelectric performance of polycrystalline p-type SnSe, a material in which unprecedented values of the thermoelectric figure of merit ZT have been recently discovered in single crystals. Besides anisotropic transport properties, our results confirm that this compound exhibits intrinsically very low thermal conductivity values. The electrical properties show trends typical of lightly doped, intrinsic semiconductors with thermopower values reaching 500 mu V K-1 in a broad temperature range. An orthorhombic-to-orthorhombic transition sets in at 823 K, a temperature at which the power factor reaches its maximum value. A maximum ZT of 0.5 was obtained at 823 K, suggesting that proper optimization of the transport properties of SnSe might lead to higher ZT values. These findings indicate that this system represents an interesting experimental platform for the search of highly efficient thermoelectric materials

The single phase clathrate-I Ba(8)Ge(43)square(3) (space group Ia3d (no. 230), a = 21.307(1) A) was synthesized by quenching the melt between cold steel plates. Specimens for physical property measurements were characterized by microstructure analysis and X-ray diffraction on polycrystalline samples as well as single crystals. Transport properties including thermopower, electrical resistivity, thermal conductivity and specific heat were investigated in a temperature range of 2-673 K. The electrical resistivity exhibits a metal-like temperature dependence below 300 K turning into a semiconductor-like behaviour above 300 K. The analysis of the specific heat at low temperature indicates a finite density of states at the Fermi level, thus corroborating the metallic character below 300 K. The temperature dependence of the specific heat was modelled assuming Einstein-like localized vibrations of Ba atoms inside the cages of the Ge framework. A conventional crystal-like behaviour of the thermal conductivity with a low lattice contribution (kappa(l)(300 K) = 2.7 W m(-1) K(-1)) has been evidenced.

The ability of some materials with a perfectly ordered crystal structure to mimic the heat conduction of amorphous solids is a remarkable physical property that finds applications in numerous areas of materials science, for example, in the search for more efficient thermoelectric materials that enable to directly convert heat into electricity. Here, we unveil the mechanism in which glass-like thermal conductivity emerges in tetrahedrites, a family of natural minerals extensively studied in geology and, more recently, in thermoelectricity. By investigating the lattice dynamics of two tetrahedrites of very close compositions (Cu12Sb2Te2S13 and Cu10Te4S13) but with opposite glasslike and crystal thermal transport by means of powder and single-crystal inelastic neutron scattering, we demonstrate that the former originates from the peculiar chemical environment of the copper atoms giving rise to a strongly anharmonic excess of vibrational states.

We present a detailed study of the evolution of the electrical, galvanomagnetic, and thermodynamic properties of polycrystalline Ag x Mo 9 Se 11 compounds for 3.4 ≤ x ≤ 3.8 at low temperatures (2−350 K). In agreement with density functional theory calculations, the collected data show an overall gradual variation in the transport properties from metallic to semiconducting behavior on going from x = 3.4 to 3.8. The results evidence subtle variations in the electronic properties with the Ag content, typified by both positive and negative phonon-drag effects together with thermopower and Hall coefficient of opposite signs. Analysis of the data suggests that these features may be due to peculiarities of the dispersion of the valence bands in the vicinity of the chemical potential. A drastic influence of the Ag content on the thermal transport was evidenced by a pronounced change in the temperature dependence of the specific heat below 10 K. Nonlinearities in the C p (T 3 ) data are correlated to the concentration of Ag atoms, with an increase in x resulting in a more pronounced departure from a Debye law. The observed behavior mirrors that of ionic conductors, suggesting that Ag x Mo 9 Se 11 for x ≥ 3.6 might belong to this class of compounds.