This work reports enhanced thermoelectric properties of transparent thin films. The influence of the composition, thickness and deposition method has been studied, reaching a ZT > 0.1 at room temperature.

recovery. [ 1 ] The search for high performance materials has continued to improve the relatively low conversion effi ciency of thermoelectric materials. The effi ciency is defi ned by the dimensionless fi gure of merit, zT = S 2 Tσ /( κ E + κ L ), where, S , σ , T , κ L , and κ E are the Seebeck coeffi cient, electrical conductivity, absolute temperature, and the lattice and electronic components of the thermal conductivity, respectively. Pb chalcogenides have received considerable attention amongst existing thermoelectric materials due to the relatively high thermoelectric conversion effi ciencies for both n-type [ 2 ] and p-type [ 3,4 ] compounds.Intrinsic semiconducting lead chalcogenides (PbQ, Q = Te, Se, S) can be tuned to p-type through substitution of monovalent sodium on the lead sublattice. [ 5,6 ] Although, sodium has been the most viable dopant for lead chalcogenides, [ 3,7,8 ] its solubility limits to ≈2 at% in PbS, [ 9 ] ≈0.9 at% in PbSe, [ 9 ] and a maximum of ≈0.7 at% in PbTe. [ 10 ] The exceptionally high thermoelectric performance of ≈2 has been reported for a 2 at% Na-doped multiphase nanostructured PbTe, [ 4,11,12 ] ≈1.6 for 2 at% Na-doped nanostructured multiphase PbSe [ 13 ] and ≈1.2 for 2.5 at% Nadoped nanostructured multiphase PbS. [ 14 ] However, the mechanisms by which these high thermoelectric effi ciencies have been achieved in multiphase compounds with dopant concentrations above the solubility level of the matrix have not been studied systematically. Little attention has been given to the effect of the inhomogeneous distribution of sodium between the component phases on the thermoelectric properties of multiphase compounds. Here, we have explored the thermoelectric properties of multi phase nanostructured quaternary (PbTe) 0.65 (PbS) 0.25 (PbSe) 0.1 compounds at various Na-dopant concentrations.Strategies aiming to improve the power factor (S 2 σ) through tuning of the electronic band structure near the Fermi level, include resonant states, [ 15,16 ] multiple bands, [ 14,17 ] manipulating the band gap, [18][19][20] and/or modulation doping. [21][22][23] During the last decade, tremendous efforts have also been devoted to reducing the lattice thermal conductivity of bulk thermoelectric materials by nanostructuring. [ 4,8,24 ] Multiphase lead chalcogenides compounds invariably exhibit higher zT values than those of their constituent phases. This is attributed to the combined effects of: band engineering resulting from the effects of alloying; a reduction in the lattice thermal conductivity, which Despite the effectiveness of sodium as a p-type dopant for lead chalcogenides, its solubility is shown to be very limited in these hosts. Here, a high thermoelectric effi ciency of ≈2 over a wide temperature range is reported in multiphase quaternary (PbTe) 0.65 (PbS) 0.25 (PbSe) 0.1 compounds that are doped with sodium at concentrations greater than the solubility limits of the matrix. Although these compounds present room temperature thermoelectric effi ciencies similar to sodium doped PbT...

We review the current status of low-cost magnesium-based thermoelectric materials in relation to other materials.

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Magnesium-based thermoelectric materials (Mg2X, X = Si, Ge, Sn) have received considerable attention due to their availability, low toxicity, and reasonably good thermoelectric performance. The synthesis of these materials with high purity is challenging, however, due to the reactive nature and high vapour pressure of magnesium. In the current study, high purity single phase n-type Mg2Ge has been fabricated through a one-step reaction of MgH2 and elemental Ge, using spark plasma sintering (SPS) to reduce the formation of magnesium oxides due to the liberation of hydrogen. We have found that Bi has a very limited solubility in Mg2Ge and results in the precipitation of Mg2Bi3. Bismuth doping increases the electrical conductivity of Mg2Ge up to its solubility limit, beyond which the variation is minimal. The main improvement in the thermoelectric performance is originated from the significant phonon scattering achieved by the Mg2Bi3 precipitates located mainly at grain boundaries. This reduces the lattice thermal conductivity by ~50% and increases the maximum zT for n-type Mg2Ge to 0.32, compared to previously reported maximum value of 0.2 for Sb-doped Mg2Ge.

Narrow band-gap lead chalcogenides have been developed for several optical and electronic applications. However, band-gap energies of the ternary and quaternary alloys have received little attention compared with the parent binary phases. Here, we have fabricated single-phase ternary (PbTe) 1– x (PbSe) x and quaternary (PbTe) 0.9– y (PbSe) 0.1 (PbS) y and (PbTe) 0.65– z (PbSe) 0.35 (PbS) z alloys and shown that although lattice parameters follow Vegard’s law as a function of composition, the band-gap energies exhibit a substantial bowing effect. The ternary (PbTe) 1– x (PbSe) x system features a smaller bowing parameter predominantly due to the difference in electronegativity between Se and Te, whereas the larger bowing parameters in quaternary alloys are generated from a larger crystal lattice mismatch and larger miscibility gap. These findings can lead to further advances in tuning the band-gap and lattice parameters for optical and electronic applications of lead chalcogenides.

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Joining metallic alloys can be an intricate task, being necessary to take into account the material characteristics and the application in order to select the appropriate welding process. Among the variety of welding methods, pulsed laser technology is being successfully used in the industrial sector due to its beneficial aspects, for which most of them are related to the energy involved. Since the laser beam is focused in a concentrated area, a narrow and precise weld bead is created, with a reduced heat affected zone. This characteristic stands out for thinner material applications. As a non-contact process, the technique delivers flexibility and precision with high joining quality. In this sense, the present review addresses the most representative investigations developed in this welding process. A summary of these technological achievements in metallic metals, including steel, titanium, aluminium, and superalloys, is reported. Special attention is paid to the microstructural formation in the weld zone. Particular emphasis is given to the mechanical behaviour of the joints reported in terms of microhardness and strength performance. The main purpose of this work was to provide an overview of the results obtained with pulsed laser welding technology in diverse materials, including similar and dissimilar joints. In addition, outlook and remarks are addressed regarding the process characteristics and the state of knowledge.