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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.

The crystallographic and transport properties of thin films fabricated by pulsed laser deposition and belonging to the Sm

In this work, a series of Bi2Te3/X mol% MoS2 (X = 0, 25, 50, 75) bulk nanocomposites were prepared by hydrothermal reaction followed by reactive spark plasma sintering (SPS). X-ray diffraction analysis (XRD) indicates that the native nanopowders, comprising of Bi2Te3/MoS2 heterostructure, are highly reactive during the electric field-assisted sintering by SPS. The nano-sized MoS2 particles react with the Bi2Te3 plates matrix forming a mixed-anion compound, Bi2Te2S, at the interface between the nanoplates. The transport properties characterizations revealed a significant influence of the nanocomposite structure formation on the native electrical conductivity, Seebeck coefficient, and thermal conductivity of the initial Bi2Te3 matrix. As a result, enhanced ZT values have been obtained in Bi2Te3/25 mol% MoS2 over the temperature range of 300–475 K induced mainly by a significant increase in the electrical conductivity.

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

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.

Funder: White Rock Foundation, Funder: Jardine Foundation, Funder: Cambridge Commonwealth European and International Trust, Coordination nanosheets are an emerging class of 2D, bottom-up materials having fully π-conjugated, planar, graphite-like structures with high electrical conductivities. Since their discovery, great effort has been devoted to expand the variety of coordination nanosheets; however, in most cases, their low crystallinity in thick films hampers practical device applications. In this study, mixtures of nickel and copper ions are employed to fabricate benzenehexathiolato (BHT)-based coordination nanosheet films, and serendipitously, it is found that this heterometallicity preferentially forms a structural phase with improved film crystallinity. Spectroscopic and scattering measurements provide evidence for a bilayer structure with in-plane periodic arrangement of copper and nickel ions with the NiCu2 BHT formula. Compared with homometallic films, heterometallic films exhibit more crystalline microstructures with larger and more oriented grains, achieving higher electrical conductivities reaching metallic behaviors. Low dependency of Seebeck coefficient on the mixing ratio of nickel and copper ions supports that the large variation in the conductivity data is not caused by change in the intrinsic properties of the films. The findings open new pathways to improve crystallinity and to tune functional properties of 2D coordination nanosheets.

Filled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Smy(FexNi1−x)4Sb12-filled skutterudite system. Films were deposited under vacuum conditions by the pulsed laser deposition (PLD) method on fused silica substrates, and the deposition temperature was varied. The effect of the annealing process was studied by subjecting a set of films to a thermal treatment for 1 h at 423 K. Electrical conductivity σ and Seebeck coefficient S were acquired by the four-probe method using a ZEM-3 apparatus performing cycles in the 348–523 K temperature range, recording both heating and cooling processes. Films deposited at room temperature required three cycles up to 523 K before being stabilized, thus revealing the importance of a proper annealing process in order to obtain reliable physical data. XRD analyses confirm the previous result, as only annealed films present a highly crystalline skutterudite not accompanied by extra phases. The power factor of annealed films is shown to be lower than in the corresponding bulk samples due to the lower Seebeck coefficients occurring in films. Room temperature thermal conductivity, on the contrary, shows values comparable to the ones of doubly doped bulk samples, thus highlighting the positive effect of interfaces on the introduction of scattering centers, and therefore on the reduction of thermal conductivity.

We report thermal conductivity (κ) above 300 K for perovskite ferroelectrics BaTiO3 (T c ≈ 402 K) and PbTiO3 (763 K), as well as antiferroelectrics PbZrO3 (503 K) and PbHfO3 (476 and 433 K). BaTiO3 and PbTiO3 show similar κ in the paraelectric phase. In contrast, smaller and glasslike κ is found above T c for PbZrO3 and PbHfO3, signifying the presence of large anharmonic distortions in the paraelectric phase. Low-temperature heat capacity on PbZrO3 shows a lack of glasslike thermal behavior in the antiferroelectric phase.

A novel heterogeneous catalytic nanomaterial based on a molybdenum cluster-based halide (MC) and a single-layered copper hydroxynitrate (CHN) was first prepared by colloidal processing under ambient conditions. The results of the elemental composition and crystalline pattern indicated that CHN was comprehensively synthesized with the support of the MC compound. The absorbing characteristic in the ultraviolet and near-infrared regions was promoted by both of the ingredients. The proper chemical interaction between the materials is a crucial reason to modify the structure of the MCs and only a small decrease in the magnetic susceptibility of CHN. The heterogeneous catalytic activity of the obtained MC@CHN material was found to have a high efficiency and excellent reuse when it is activated by hydrogen peroxide (H2O2) for the degrading reaction of the organic pollutant at room temperature. A reasonable catalytic mechanism was proposed to explain the distinct role of the copper compound, Mo6 compound, and H2O2 in the production of the radical hydroxyl ion. This novel nanomaterial will be an environmentally promising candidate for dye removal., Graphical abstract

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.

In the present study, we have focused on the elaboration of control of Te-doped CoSb

The influence of structural disorder on the thermal transport in the colusite $\mathrm{C}{\mathrm{u}}_{26}{\mathrm{V}}_{2}\mathrm{S}{\mathrm{n}}_{6}{\mathrm{S}}_{32}$ has been investigated by means of low-temperature thermal conductivity and specific heat measurements (2--300 K), $^{119}\mathrm{Sn}$ M\"ossbauer spectroscopy and temperature-dependent powder inelastic neutron scattering (INS). Variations in the high-temperature synthesis conditions act as a key parameter for tuning the degree of disorder in colusite compounds. Intriguingly, we find that all synthesized samples are disordered, the degree of which varies with the synthesis conditions used. M\"ossbauer data clearly evidence that Sn atoms do not solely occupy the $6c$ site of the crystal lattice but are present on possibly both the Cu and V sites, leading to a random distribution of these three cations within the unit cell. Increasing the disorder in these materials tends to lead to a smearing out of the main features in the phonon density of states measured by INS. Although the evolution of the inelastic signal upon warming is well described by a quasiharmonic approximation, elastic properties calculations indicate large average Gr\"uneisen parameters, consistent with those determined experimentally from thermodynamic data. Increasing the level of disorder results in a decreased average Gr\"uneisen parameter suggesting that the lowered lattice thermal conductivity is not driven by enhanced anharmonicity. These results provide experimental evidence to support that the remarkable changeover in the lattice thermal conductivity from crystalline to glasslike is solely driven by enhanced disorder accompanied by local lattice distortions.

International audience; A complete thiospinel solid solution CuCoxTi2-xS4 (0 ≤ x

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.

International audience; In/ZnO bulk compounds have been synthesized using a simple solid-state process. In this study, both the structural features and thermoelectric properties of the Zn1-xInxO series with ultralow indium content (0

International audience; A recently introduced photothermal method, the photothermoelectric (PTE) calorimetry is proposed for the first time in order to detect phase transitions. The capability of both back (BPTE) and front (FPTE) detection configurations in detecting phase transitions is analyzed. It was found that the back detection configuration, with optically opaque sample and thermally thick sample and TE sensor, is very suitable for phase transitions detection; the information, in this configuration, can be collected from both amplitude and phase of the BPTE signal and the amplitude has the possibility of amplifying the critical anomaly of the thermal parameters. In the FPTE configuration, the information about phase transition is contained only in the amplitude of the signal. Using the PTE method, the well-known ferro-paraelectric phase transition of triglycinesulphate (TGS), tacking place at about 49 °C, was investigated. Comparison with the photopyroelectric (PPE) method is performed. © 2015 Elsevier B.V. All rights reserved.

International audience; Bulk polycrystalline samples in the series Ti1-xNbxS2 (0 ≤ x ≤ 0.075) were prepared using mechanical alloying synthesis and spark plasma sintering. X-ray diffraction analysis coupled with high resolution transmission electron microscopy indicates the formation of trigonal TiS2 by high energy ball-milling. The as-synthesized particles consist of pseudo-ordered TiS2 domains of around 20-50 nm, joined by bent atomic planes. This bottom-up approach leads, after spark plasma sintering, to homogeneous solid solutions, with a niobium solubility limit of x = 0.075. Microstructural observations evidence the formation of small crystallites in the bulk compounds with a high density of stacking faults. The large grain boundary concentration coupled with the presence of planar defects, leads to a substantial decrease in the thermal conductivity to 1.8 W/mK at 700 K. This enables the figure of merit to reach ZT = 0.3 at 700 K for x = 0.05, despite the lower electron mobility in mechanically alloyed samples due to small crystallite/grain size and structural defects. © 2015 Elsevier Ltd.

The photopyroelectric (PPE) technique is one of the photothermal (PT) methods mostly used for phase transitions investigations. In this paper, we want to compare the PPE results with those obtained using another, recently developed PT method [the photothermoelectric (PTE) calorimetry] for the same purpose of detecting phase transitions. The well-known ferro-paraelectric phase transition of TGS, taking place at a convenient temperature (about $$49\, {}^{\circ }\hbox {C}$$ ), has been selected for demonstration. A comparison of the two PPE and PTE methods, both in the back detection configuration (in the special case of optically opaque sample and thermally thick regime for both sensors and sample) shows that they are equally suitable for phase transitions detection. Performing a proper calibration, the amplitude and phase of the signals can be used in order to obtain the critical behaviour of all sample’s static and dynamic thermal parameters.

Équipe 103 : Composés intermétalliques et matériaux hybrides; International audience; This paper describes Cu4Sn7S16 material as a potential thermoelectric comprising low cost and non-toxic elements, whose complex crystal structure permits intrinsic low thermal conductivity. We begin by identifying two different synthesis approaches to obtain pure and fully dense samples, using conventional sealed tube and mechanical alloying methods combined with Spark Plasma Sintering. We then confirm the complex rhombohedral structure (R-3m, a similar to 7.37 angstrom, c similar to 36.02 angstrom) using both Rietveld refinement of powder X-ray diffraction patterns and High Resolution Transmission Electron Microscopy (HRTEM) analyses. Finally, we characterize the electrical and thermal properties at high temperatures on highly dense samples. The electrical behavior is also shown for the first time to change from semiconducting to metallic behavior according to sample preparation, suggesting that the material is highly sensitive to cationic site occupancy and Cu:Sn:S ratio. The complex crystallographic structure of Cu4Sn7S16 causes low thermal conductivity, which is found below 1.1 W/mK above room temperature. The focus of this paper is to drawn attention to the way in which complex structures specifically designed to induce intrinsic low thermal conductivity can be potentially attractive thermoelectrics, even in materials that are intrinsically poor conductors.