Reliability Investigation of Silicide-Based Thermoelectric Modules.

The reliability and failure mechanisms of silicide-based thermoelectric modules (-type Mg(Si,Sn)/-type HMS) were investigated thanks to two types of thermal tests with either a fixed or a cycling thermal gradient, under different atmospheres. The hot interfaces of the thermoelectric modules were analyzed by scanning electron microscopy and X-ray diffraction after the reliability tests. The current thermoelectric modules do not exhibit any failure mechanism under ambient air for a hot side temperature of 250 °C for tests conducted either during 500 h at a fixed temperature gradient or after 1000 thermal cycles.

Thermal Stability of MgSiSn under Oxidation Conditions.

The use of MgSiSn under air in thermoelectric modules in the mid-temperature range of 400-600 °C is linked to its ability to resist oxidation. In this study, oxidation experiments performed at 400 °C under air evidenced the stability of the material, either under static conditions (up to 100 h) or under severe heating-cooling cyclic conditions (up to 400 cycles), showing its ability to be used in a reliable way at this temperature. By combining thermogravimetry, scanning electron microscopy, temperature X-ray diffraction analysis, and mechanical and thermodynamic considerations, a mechanism is proposed explaining how MgSiSn further undergoes decomposition with time under air when treated above 500 °C.

Residual resistivity as an independent indicator of resonant levels in semiconductors.

Distortion of the density of states induced by specific impurities, a mechanism known as resonant level (RL), is an efficient strategy to enhance the thermoelectric performances of metals and semiconductors. So far, experimental signatures identifying the resonant nature of an impurity have relied on the so-called Ioffe-Pisarenko plot that enables visualizing the induced thermopower enhancement at specific carrier concentrations. However, this method cannot solely discern RL from other possible band-structure-related sources of thermopower enhancement such as band-shape modifications or band convergence.

Transport properties of polycrystalline SnTe prepared by saturation annealing.

Because the binary chalcogenide SnTe is an interesting Pb-free alternative to the state-of-the-art thermoelectric material PbTe, significant efforts were devoted to the optimization of its thermoelectric properties over the last few years. Here, we show that saturation-annealing treatments performed at 823, 873 or 973 K under Sn-rich conditions provide a successful strategy to prepare polycrystalline samples with a controlled concentration of Sn vacancies. Both scanning transmission electron microscopy and Mössbauer spectroscopy demonstrate the absence of Sn-rich areas at the grain boundaries in the saturation-annealed samples.

Electronic Band Structure and Transport Properties of the Cluster Compound AgTlMoSe.

Mo-based cluster compounds are a large class of materials with complex crystal structures that give rise to very low lattice thermal conductivity. Here, we report on the crystal structure and transport property measurements (5-800 K) of the novel Tl-filled compound AgTlMoSe. This compound adopts a crystal structure described in the rhombohedral R3 c space group [ a = 9.

Thermoelectric properties of the tetrahedrite-tennantite solid solutions CuSbAsS and CuCoSbAsS (0 ≤ x, y ≤ 4).

Tetrahedrites, a class of copper- and sulfur-rich minerals, exhibit inherently very low lattice thermal conductivity and adjustable electronic properties that make them interesting candidates for thermoelectric applications. Here, we investigate the influence of isovalent As substitution on the Sb site on the structural and transport properties (5-700 K) of the two solid solutions Cu12Sb4-xAsxS13 and Cu10Co2Sb4-yAsyS13 (0 ≤ x, y ≤ 4). Electronic band structure calculations predict that As has only a weak influence on the valence bands and hence, on the p-type metallic character of Cu12Sb4S13.

Inelastic neutron scattering study of the lattice dynamics of the homologous compounds (PbSe)(BiSe) (m = 1, 2 and 3).

We report on the inelastic response of the homologous compounds (PbSe)5(Bi2Se3)3m for m = 1, 2 and 3 followed in a broad temperature range (50-500 K) using high-resolution powder inelastic neutron scattering experiments. These results are complemented by low-temperature measurements of the specific heat (2-300 K). The evolution of the anisotropic crystal structure of these compounds with varying m, built from alternate Pb-Se and mBi-Se layers, only weakly influences the generalized phonon density of states.

An Sn-induced resonant level in β-AsTe.

Distortion of the density of states by an impurity-induced resonant level has been shown to provide an effective strategy to improve the thermoelectric performance of semiconductors such as Bi2Te3, PbTe or SnTe. Here, combining first-principles calculations and transport property measurements, we demonstrate that Sn is a resonant impurity that distorts the valence band edge in p-type β-As2Te3. This remarkable effect is characterized as a prominent, sharp peak in the electronic density of states near the Fermi level.

Synthesis and transport properties of the Te-substituted homologous compounds PbBiSeTe (0 ≤ x ≤ 1.0).

The crystal structure and transport properties (2-723 K) of the homologous compound Pb5Bi6Se14 with partial substitution of Te for Se are studied by means of powder X-ray diffraction, scanning electron microscopy, electrical resistivity, thermopower, thermal conductivity and Hall effect measurements. Polycrystalline samples of Pb5Bi6Se14-xTex (0 ≤ x ≤ 1.0) were prepared by a two-step synthesis method based on the pseudo-binary PbSe-Bi2Se3 phase diagram combined with Te substitution in the PbSe precursor.

Crystal Structure and Transport Properties of the Homologous Compounds (PbSe)(BiSe) (m = 2, 3).

We report on a detailed investigation of the crystal structure and transport properties in a broad temperature range (2-723 K) of the homologous compounds (PbSe)(BiSe) for m = 2, 3. Single-crystal X-ray diffraction data indicate that the m = 2, 3 compounds crystallize in the monoclinic space groups C2/m (No. 12) and P2/m (No.

Improved Thermoelectric Properties in Melt-Spun SnTe.

SnTe has been the focus of numerous experimental and theoretical studies over the last years owing to its high thermoelectric performances near 800 K when appropriately doped. Here, we demonstrate that melt-spinning, an ultrafast-quenching synthesis technique, followed by spark plasma sintering results in enhanced values in polycrystalline SnTe. To illustrate the impact of this technique, the results are contrasted with those obtained on two polycrystalline samples prepared by direct quenching of molten SnTe and without quenching.

Synthesis, Crystal Structure, and Transport Properties of the Hexagonal Mo Cluster Compound AgRbMoSe.

Mo-based cluster compounds are promising candidates for thermoelectric applications at high temperatures due to their very low lattice thermal conductivity values. Here, we report on a detailed investigation of the crystal structure and transport properties measured in a wide range of temperatures (2-800 K) of polycrystalline AgRbMoSe. Single-crystal X-ray diffraction shows that this compound crystallizes in the hexagonal space group P6/m.

Effect of Isovalent Substitution on the Electronic Structure and Thermoelectric Properties of the Solid Solution α-AsTeSe (0 ≤ x ≤ 1.5).

We report on the influence of Se substitution on the electronic band structure and thermoelectric properties (5-523 K) of the solid solution α-AsTeSe (0 ≤ x ≤ 1.5). All of the polycrystalline compounds α-AsTeSe crystallize isostructurally in the monoclinic space group C2/m (No.

Cu Insertion Into the Mo12 Cluster Compound Cs2Mo12Se14: Synthesis, Crystal and Electronic Structures, and Physical Properties.

Mo-based cluster compounds are promising materials for high-temperature thermoelectric applications due to their intrinsic, extremely low thermal conductivity values. In this study, polycrystalline cluster compounds Cs2CuxMo12Se14 were prepared for a wide range of Cu contents (0 ≤ x ≤ 2). All samples crystallize isostructurally in the trigonal space group R3̅.

X-ray characterization, electronic band structure, and thermoelectric properties of the cluster compound Ag2Tl2Mo9Se11.

We report on a detailed investigation of the crystal and electronic band structures and of the transport and thermodynamic properties of the Mo-based cluster compound Ag2Tl2Mo9Se11. This novel structure type crystallizes in the trigonal space group R3̅c and is built of a three-dimensional network of interconnected Mo9Se11 units. Single-crystal X-ray diffraction indicates that the Ag and Tl atoms are distributed in the voids of the cluster framework, both of which show unusually large anisotropic thermal ellipsoids indicative of strong local disorder.

Neutron diffraction, electronic band structure, and electrical resistivity of Mo(3-x)Ru(x)Sb(7).

Neutron diffraction experiments and Korringa-Kohn-Rostoker with coherent potential approximation electronic band structure calculations as well as electrical resistivity measurements have been performed on polycrystalline Mo(3-x)Ru(x)Sb(7) samples for 0 < or = x < or = 1. Neutron diffraction studies have been undertaken at room temperature and extended down to 4 K to get a better understanding of the crystalline structure modifications as the Ru content increases. Both structural and chemical characterizations have unambiguously revealed a solubility limit of the Ru atoms close to 0.