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In this reply, we stress again the discovery that the lattice size effect is indicated to also contribute to the Seebeck coefficient.

We investigated the feasibility of the co-doping effect of zinc and chromium for copper and vanadium substitution, respectively, and reported the first successful Cr incorporation within the bulk Sn-based colusite structure.

Pristine and Co-doped MoS2 nanosheets, containing a dominant 1T phase, have been densified by spark plasma sintering (SPS) to produce a nanostructured arrangement. The structural analysis by X-ray powder diffraction revealed that the reactive sintering process transforms the 1T-MoS2 nanosheets into their stable 2H form despite a significantly reduced sintering temperature and time testifying to the fast kinetics of phase change. Together with the phase conversion, the SPS process promoted a strong texturing of the nanosheets, which drives additional scattering processes and alters the electronic and thermal transport properties. In the pristine sample, it produced one of the lowest thermal conductivities ever reported on MoS2 with a minimal value of 0.66 W/m·K at room temperature. The effect of Co substitution in the final sintered samples is not significant, compared to the pristine MoS2 sample, except for a non-negligible improvement of the electrical conductivity by a factor of 100 in the high-Co content (6% by mass) sample.

Alongiside the growing demand for wearable and implantable electronics, the development of flexible thermoelectric (FTE) materials holds great promise and has recently become a highly necessitated and efficient method for converting heat to electricity. Conductive polymers were widely used in previous research; however, n-type polymers suffer from instability compared to the p-type polymers, which results in a deficiency in the n-type TE leg for FTE devices. The development of the n-type FTE is still at a relatively early stage with limited applicable materials, insufficient conversion efficiency, and issues such as an undesirably high cost or toxic element consumption. In this work, as a prototype, a flexible n-type rare-earth free skutterudite (CoSb3)/poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) binary thermoelectric film was fabricated based on ball-milled skutterudite via a facile top-down method, which is promising to be widely applicable to the hybridization of conventional bulk TE materials. The polymers bridge the separated thermoelectric particles and provide a conducting pathway for carriers, leading to an enhancement in electrical conductivity and a competitive Seebeck coefficient. The current work proposes a rational design towards FTE devices and provides a perspective for the exploration of conventional thermoelectric materials for wearable electronics.

In the present study, we have focused on the elaboration of control of Te-doped CoSb3 thin films by RF magnetron sputtering which is an attractive technique for industrial development of thermoelectric (TE) thin films. We have successfully synthesized sputtering targets with a reliable approach in order to obtain high-quality films with controlled stoichiometry. TE properties were then probed and revealed a reliable n-type behavior characterized by poor electrical transport properties. Tellurium substitution was realized by co-sputtering deposition and allowed obtaining a significant enhancement of the power factor with promising values of PF ≈ 0.21 mW m−1 K−2 near room temperature. It is related to the Te doping effect which leads to an increase of the Seebeck coefficient and the electrical conductivity simultaneously. However, despite this large improvement, the properties remained far from the bulk material and further developments are necessary to improve the carrier mobility reduced by the thin film formatting.

International audience; We report here a rich variation of the thermoelectric properties of a series of Cu-Sn based thiospinels of composition CuM1+xSn1-xS4 upon partial substitution at the Sn-site with a variety of transition elements (M = Ti, V, Cr, Co). The optimized synthesis and processing conditions we used enabled us to realize highly densified and homogeneous compounds. The V-series was found to exhibit the lowest performing thermoelectric properties, whereas Co and Ti substituted compounds showed moderate thermoelectric properties with a maximum figure of merit (zT(max)) of similar to 0.02 and similar to 0.07 at 673 K, respectively. In contrast, the Cr substituted compounds exhibited better thermoelectric performance with zT similar to 0.2 at 673 K for the composition CuCr1.2Sn0.8S4. Both p- and n-type compounds were obtained; specifically, the Co and Ti series were found to be n-type, and the Cr series was found to be p-type. Besides the suppressed thermal transport, the attractive thermoelectric properties with the Cr-series can be attributed to the simultaneous increase of the Seebeck coefficient and electrical conductivity with increasing temperature, thus resulting in an improved power factor. Experimental and DFT theoretical calculations also predict a considerable interaction between the carriers and magnetic moments, contributing to a higher effective mass, thus leading to higher thermopower and power factor for the Cr-series. Computed electronic density of states and band structures, in agreement with the experimental findings, envisaged n-type half-metallic character for the CuTi1+xSn1-xS4 paramagnetic compounds, n-type conducting behavior for the CuCo1+xSn1-xS4 compounds, p-type weak half-metallic character for the CuV1+xSn1-xS4 compounds, and p-type semiconducting behavior for the CuCr1+xSn1-xS4 ferromagnetic compounds. Computation of the electronic transport coefficients using the Boltzmann transport equation also suggests a better thermoelectric property, especially the thermopower, for the Cr-series when compared to its Ti/V/Co counterparts.

The crystallographic and transport properties of thin films fabricated by pulsed laser deposition and belonging to the Sm y (Fe x Ni1-x )4Sb12 filled skutterudite system were studied with the aim to unveil the effect exerted by temperature and duration of thermal treatments on structural and thermoelectric features. The importance of annealing treatments in Ar atmosphere up to 523 K was recognized, and the thermal treatment performed at 473 K for 3 h was selected as the most effective in improving the material properties. With respect to the corresponding bulk compositions, a significant enhancement in phase purity, as well as an increase in electrical conductivity and a drop in room temperature thermal conductivity, were observed in annealed films. The low thermal conductivity, in particular, can be deemed as deriving from the reduced dimensionality and the consequent substrate/film interfacial stress, coupled with the nanometric grain size.

International audience; GeTe, which undergoes phase transition between low symmetric rhombohedral to high symmetric cubic phase between 550-700 K (depending on the dopant and composition) and its alloys have widely been considered as promising candidates for mid-temperature range thermoelectrics. A variety of dopants have been tried in the past to improve further the thermoelectric performance of GeTe. In this work, an extensive experimental-and theoretical-based screening of transition (Y, Zr, Hf, V, Nb, Mo, and Ru) and rare-earth elements (La, Pr) that were not used in the past, are studied to explore if they can be of any potential use as dopants in thermoelectric GeTe. Out of these studied dopants, Ru, Nb, Pr, V, and Mo were found to be detrimental, Y and Hf to be reasonable, and Zr and La to be more promising. The transition or rare-earth dopant dependent variation in transport properties and thermoelectric performance of GeTe is corroborated with a concoction of factors ranging from modifications of the band gap, energy difference between the two valance band maxima, magnetic character, nature of the dopant or impurity state and their position with regard to the Fermi level, secondary cubic GeTe phase, etc. Contrary to the classical approaches where intrinsic Ge vacancies (that are inherently formed due to the thermodynamic nature of GeTe) are suppressed to improve their thermoelectric performance, an opposite approach is adopted in this work. Here by intentionally creating more electrically dormant Ge vacancies and modulating/balancing it with Zr-doping, an improved figure of merit, zT ~1.3 at 673 K is obtained for Ge-deficient Ge0.98Zr0.005Te compound, thanks to the suppression of the lattice contribution to the thermal conductivity arising due to the large density of planar defects in these vacancy-induced compounds. These optimized Ge-deficient Zr-doped materials when codoped with Sb, results in effective convergence of electronic band valleys by tuning the crystal field effect and reduced thermal transport, thus yielding a high zT ~1.8 at 723 K. This work not only screens a directory of dopant elements to enrich the current state of the knowledge on GeTe-based compounds, but also indicates that the strategy of creation and synchronization of Ge-vacancies with a certain dopant is an alternative and effective route for enhancing zT.

International audience; We describe here a new, easy and scalable route for synthesising colusites by using mechanical-alloying and reactive spark plasma sintering, together with the thermoelectric behaviour of zinc-substituted derivatives, Cu26-xZnxV2Sn6S32 (0 ≤ x ≤ 2). X-ray diffraction analysis coupled with transmission electron microscopy evidences the high crystallinity of the as-synthesized samples. In the pristine compound, an intrinsic exsolution phenomenon leads to the formation of two distinguishable colusite phases. Additional neutron powder diffraction results support the substitution of Zn in the tetrahedral Cu sites and 119Sn Mössbauer spectroscopy analyses prove the presence of only Sn4+ in colusite irrespective of the Zn content (x ≤ 2). The mechanical properties denote a wide homogeneity of the samples despite a significant impact of the exsolution on the microstructure. The Zn for Cu substitution provides electron doping, decreasing the holes concentration. High temperature thermoelectric properties in the p-type series Cu26-xZnxV2Sn6S32 are reported. The highest power factor of 0.92 mW m-1 K-2 at 700 K is found for x = 1, with a corresponding ZT value of 0.4. © The Royal Society of Chemistry 2016.