ABSTRACT
Tetrahedrites, a class of earth-abundant minerals, exhibit extremely low thermal conductivity values making them promising candidates for thermoelectric applications at high temperatures. Herein, we extend investigations on these materials to specimens substituted on both the Cu and Sb sites by reporting on the thermoelectric properties of polycrystalline Cu12-xCoxSb4-yTeyS13 in a wide range of temperatures (2-700 K). All prepared samples exhibit p-type heavily-doped semiconducting behavior with relatively low electrical resistivity values. These substitutions have little influence on the thermal conductivity, which remains very low in the whole temperature range (â¼0.7 W m(-1) K(-1)). Although the double-substituted samples exhibit higher ZT values with respect to the parent tetrahedrite Cu12Sb4S13, the maximum ZT of 0.80 reached at 700 K for (x,y) = (0.82, 0.41) remains comparable to the values obtained in compounds solely substituted with Co or Te.
ABSTRACT
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.
ABSTRACT
Synthesis of PbTe nanoparticles has been performed by pulsed laser fragmentation of PbTe micron-sized powders in distilled water with a Nd:YAG laser. The influence of various experimental parameters (wavelength, treatment duration, and output energy) on the yield of fragmentation, the size and the crystallographic structure of the nanoparticles produced has been investigated. Characterization of the nanopowders was performed by X-ray diffraction analyses and transmission electron microscopy observations. Thanks to a careful control of the synthesis parameters, PbTe nanoparticles with an average diameter close to 6 nm and exhibiting a sharp distribution in size have been produced.
ABSTRACT
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.
ABSTRACT
Polycrystalline Mo(3)Sb(7-x)Te(x) samples with nominal Te concentrations of x=0.0, 0.3, 1.0, 1.6 and 2.2 have been synthesized by a powder metallurgical route. High temperature thermoelectric properties measurements including thermopower (300-900 K), electrical resistivity (300-800 K) and thermal conductivity (300-1000 K) were carried out. The temperature and compositional variations of the thermopower can be satisfactorily explained by assuming a single parabolic band model with dominant acoustic phonon scattering. However, such a simple model fails to describe the electronic thermal conductivity for low Te concentration. The dimensionless figure of merit, ZT, increases on increasing both the temperature and the Te content to reach a maximum value of 0.3 at 800 K that can be extrapolated to â¼0.6 at 1000 K for Mo(3)Sb(5.4)Te(1.6).
ABSTRACT
Temperature dependences of the magnetic susceptibility, specific heat, and electrical resistivity have been measured for the Mo(3)Sb(7) compound in the 0.6-350 K range. This compound exhibits bulk superconductivity occurring at 2.25 K and follows the Kadowaki-Woods relation, A/gamma(2)=1.0 x 10(-5) microOmega x cm(K x mol/mJ)(2), as a heavy-fermion system does. We show, from experimental evidence and theoretical argument, that Mo(3)Sb(7) can be classified as a coexistent superconductor-spin fluctuation system. The McMillan equation including paramagnon effects was found to give an accurate estimation of the transition temperature.
