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Ge doped In 2 O 3 bulks were prepared by dry uniaxial compaction or slip casting shaping methods followed by a conventional or microwave sintering. Density of slip casted Ge doped In 2 O 3 samples after conventional sintering reaches bulk density close to the theoretical one thanks to an optimized particles arrangement in the slip casted green bulks. Combined with a fast microwave sintering, slip casted bulks possess submicrometer grain size due to limited grain growth. A significant decrease of the electrical resistivity has been measured in slip casted samples sintered by conventional heat treatment. In bulk specimens sintered by microwave heating, a simultaneous increase of electrical resistivity and decrease of the thermal conductivity is observed. From room temperature to 1000 K in air, slip casted samples sintered by conventional or microwave sintering exhibit similar thermoelectric figure of merit ( ZT ) values. [ABSTRACT FROM AUTHOR]

Abstract: Zn1−x Ni x O dense ceramics were prepared from Zn1−x Ni x O nanoparticles with x varying from 0 to 0.06. These nanoparticles were synthesized by liquid route. In the sintered samples, the solubility limit of Ni in the Zn1−x Ni x O wurtzite structure was found to be 0.03. The increase of x until 0.03 led to a significant raise in both electrical conductivity (σ) and absolute value of Seebeck coefficient (|S|). Ni-richer samples (x >0.03) contained in addition a small amount of Ni rich secondary phase (Zn y Ni z O) with a cubic structure similar to NiO. The thermoelectric properties of all samples were investigated from room temperature to 1000K. All doped samples showed a n-type semiconducting conductivity. For Ni contents higher than x =0.03, the increase of the secondary phase content induced a decrease in σ and |S|. The highest power factor (0.6mWm−1 K−2) and ZT (0.09) were found for Zn0.97Ni0.03O at 1000K. [Copyright &y& Elsevier]

Abstract: Thermoelectric performances on cobaltite ceramics can be changed by doping followed by grain orientation methods. This can be performed by the Laser Floating Zone (LFZ) method on samples with different substitutions in the Rock Salt sublattice. In this work, Bi2−x Pb x Ca2Co1.7O y (x =0.0, 0.2, 0.4 and 0.6) ceramics have been directionally grown at 30mm/h. In all the cases, samples show a microstructure composed, mainly, of alternated grains of the thermoelectrical phase and the solid solution Bi(Pb)–Ca–O, with small CoO inclusions. It has been found an important improvement on the resistivity and thermopower for samples with 0.4 Pb substitution, leading to power factor values higher than usual in misfit cobaltites obtained by conventional solid state routes. [Copyright &y& Elsevier]

Abstract: In this work, polycrystalline samples of the substituted n =3 Ruddlesden-Popper Ca4−x RE x Mn3O10 phase were prepared by solid-state reaction (RE, rare earth=Ce, Nd, Sm, Eu, Gd, Dy). Single phased samples were synthesized for sintering times larger than 150h at 1350°C. Complete thermoelectric characterizations were performed from 5 to 390K, in terms of electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ). As expected, the substitution of Ca by different rare earth elements leads to a significant modification of the thermoelectric properties. With substitution level as low as 1.25at.%, a remarkable decrease of the electrical resistivity is observed. The influence of this cationic substitution on the thermal conductivity (κ), Seebeck coefficient (S), and the figure of merit ZT is also discussed. In this study, the best one reaches 5.8×10−3 at 300K for the Ca3.95Eu0.05Mn3O10 composition, a value 6 times higher than the ZT exhibited by the beginning Ca4Mn3O10 sample. [Copyright &y& Elsevier]

Abstract: Thermoelectric performances of cobaltite ceramics can be improved raising the electrical conductivity. This can be performed by increasing the size of grains and aligning them along a preferential direction by the Laser Floating Zone (LFZ) method. In this work, Bi2Sr2Co1.8O x ceramics have been directionally grown at three different speeds, i.e. 15, 30 and 50 mm/h. Their microstructure and thermoelectric properties are significantly influenced by the LFZ growth conditions. In all cases, the microstructure exhibits alternate cobaltite layers with secondary phases and small CoO inclusions, particularly when the growth is performed at high speeds (30 and 50 mm/h). The thermopower is, nevertheless, higher than usual while electrical resistivity values are similar to those obtained by conventional solid state routes, leading to relatively high power factor values. This result is probably linked to the stacking of different BiSrCoO layers and/or to oxygen vacancies. [Copyright &y& Elsevier]

Abstract: Sintered, textured and single crystal products of the layered misfit [Bi0.81CaO2]2[CoO2]1.69 cobaltite have been successfully synthesized and characterized. Based on structure and texture models, the orientation distribution of the hot-forged sample was successfully analysed by neutron diffraction. The results gave a clear description of the fiber texture with c-axes of the plate-like grains aligned parallel to the hot-forging direction. In terms of transport properties, the decrease of the electrical resistivity according to the degree of alignment and crystallinity of the materials evidenced the important role of the texturation and the strong anisotropy existing in these misfit layered cobaltites. [Copyright &y& Elsevier]

Abstract: The performance of a thermoelectric material can be increased when the electrical conductivity is raised. This could be performed by aligning grains along a preferential direction using, for example, the laser floating zone (LFZ) method. This technique has indeed demonstrated its potentiality to increase the electrical conductivity on various ceramic materials. Moreover, with this technique, it is possible to grow samples at higher rates than with other techniques owing to the large thermal gradients developed at the melt-solid interface. The large grain sizes obtained by LFZ lead to samples with improved properties. This paper reports the synthesis of thermoelectric bars by the LFZ technique. The properties (electrical resistivity (ρ) and thermopower) of directionally solidified Bi-based cobaltite rods are determined and correlated with the structural features (XRD and SEM-EDX). [Copyright &y& Elsevier]

The electrical performance of a hot-forming Bi:2223 compounds prepared by modifying the characteristics of the starting precursor powders and of YBa2Cu3Oy superconducting fabrics are investigated. The single domain Y123 fabrics are processed by an infiltration process from precursor Y2O3 cloths which having dimensions of thick films (∼100 μm) and posses the structure replica of precursor Y2O3 fabrics. Transport critical currents exceeding 2.1×104 A/cm2 at 77 K, 0 T and 3.9×104 A/cm2 at 65 K in self field are measured for Bi-2223 samples. For fabric samples, transport Jc measurements in self field showed the transition between the superconducting state and the flux-flow regime to occur at a critical current density (Jc) of 5.5×104 A/cm2 at 77 K. Quench tests at 77 K on the fabric samples using pulsed currents up to 5Jc with a duration of 25 ms are discussed. [Copyright &y& Elsevier]

Using the combination of standard ceramic processing and an infiltration technique, single domain superconductor foam of Y123 has been prepared. In this report we present magneto-transport measurements of these foams. The investigations reveal superconducting properties being similar to those of bulk melt processed materials. The magnetic hysteresis vs field measurements show a high anisotropy of the critical current density up to Jcab/Jcc∼7, in good agreement with the observation of a strong texture as determined from neutron diffraction measurements. [Copyright &y& Elsevier]

(1− x )Ca 3 Co 4 O 9 / x Co 3 O 4 composites samples with x =0, 10, 20 and 50 vol% have been prepared by solid state reaction and sintered by spark plasma sintering. Their thermoelectric properties have been studied in the range 323–1000 K. No reaction occurs between Co 3 O 4 and Ca 3 Co 4 O 9 particles during the high temperature treatment. The addition of Co 3 O 4 particles within a Ca 3 Co 4 O 9 matrix strongly influences the thermoelectric properties. The powerfactor decreases as the Co 3 O 4 content increases. As the thermal conductivity increases, this leads to lower ZT values. These modifications of the thermoelectric properties are consistent with the compressive strain on Ca 3 Co 4 O 9 originating from the mismatch of thermal expansion coefficients of Ca 3 Co 4 O 9 and Co 3 O 4 . [ABSTRACT FROM AUTHOR]

Abstract: Thermoelectric performances of misfit cobaltites can be controlled by grain orientation and/or by cation substitution. Both processes have been simultaneously performed by directional solidification at 0.03m/h, using the laser floating zone technique, of Bi2−x Pb x Sr2Co1.8O y (with x =0.0, 0.2, 0.4 and 0.6). The microstructure has shown two different main phases as a function of Pb content, a Co-poor phase for low Pb content (0.0 and 0.2) and a Co-rich one for higher Pb substitution. These microstructural changes are reflected on the thermoelectric properties leading to an important decrease on the resistivity and increase of thermopower for samples with 0.4Pb substitution. Both improvements lead to power factor values higher than usual in textured misfit cobaltites. [Copyright &y& Elsevier]

Architectured wires containing 61 restacked Copper Clad Aluminum (CCA) wires were cold-drawn down to a diameter of 1 mm without intermediate annealing. Samples were taken at intermediate diameters of 3 mm and 1.7 mm to observe the wire structure at different steps. Independently of the wire diameter, the structure did not exhibit any porosity and initial CCA wires were uniformly distributed inside the structure with constant equivalent diameters. Post-elaboration annealing treatments performed on CCA and architectured wires led to the formation of Al 2 Cu, AlCu and Al 4 Cu 9 intermetallic compounds (IMC). It was shown that IMC growth kinetics do not depend on the wire diameter, indicating no marked influence of the plastic deformation. The volume fraction of IMC strongly increased with the reduction of the diameter and impacted the electrical resistivity of the architectured wire. The equivalent resistivity has been easily computed by a linear rule of mixture model, with three electrical resistances in parallel (Al, Cu and IMC), weighted by their respective volume fraction. This model allowed extracting a mean resistivity of IMCs of 4.5 μΩ·cm. It also demonstrated that this restacking drawing process, without any intermediate annealing treatment is an interesting method for the elaboration of architectured wires with optimized functional properties. [ABSTRACT FROM AUTHOR]

Pure ZnO and single Al-doped ZnO compounds without secondary phase have been obtained by SPS process. Starting powders prepared by co-precipitation have been synthesized. The sintered pellets exhibit different texture degree but similar isotropic shaped grains. Sintering mechanisms are proposed for both powders, explaining the different texture and grain size evolutions as a direct consequence of the differences observed in both compounds. The influence of texture and grain morphology on the thermoelectric properties is studied. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fabrication of nanostructured skutterudites ZnO or PbTe/In0.2Co4Sb12. [•] Thermal conductivity modeling accounts for experimental results. [•] Greater lattice thermal conductivity decrease in In0.2Co4Sb12 than in CoSb3. [•] A max ZT of 1.05 is obtained at 700K in a 2wt% ZnO-containing sample. [Copyright &y& Elsevier]

Abstract: Addition of nanoparticles into bulk materials is one of the strategies designed to synthesize thermoelectric materials with superior efficiency. The presence of nanoparticles is expected to act as a barrier of the heat transport due to an increased amount of nanoscopic interfaces and to enhance the electronic properties via quantum confinement effects. Here, this approach was applied to the skutterudite CoSb3 matrix in which different amounts of ZnO (2–12wt.%) nanoparticles were introduced. The samples were densified by spark plasma sintering and characterized by X-ray diffraction and scanning electron microscopy. The thermoelectric properties were investigated in a broad temperature range (2–800K) to better assess the influence of the ZnO nanoparticles. The nanostructured materials showed a significant enhancement in the thermopower values combined with a slight decrease in the thermal conductivity. A small amount of ZnO nanoparticles (2wt.%) has a beneficial influence on the dimensionless thermoelectric figure of merit ZT suggesting that introducing stable oxide nanoparticles may be an interesting way to improve the thermoelectric properties of skutterudite compounds. [Copyright &y& Elsevier]

Abstract: The synthesis of Bi2Ca2Co1.7O x misfit compounds by different processing routes, i.e. classical solid-state, and two solution methods namely sol–gel via nitrates and a polymer route, has been investigated. A comparison among the final products has been performed using DTA, TGA, X-ray diffraction, scanning electron microscopy, and thermoelectric characterizations. All the samples obtained by solution synthesis show a very important increase in ZT, as compared to the solid state prepared samples, due to a significant decrease in the electrical resistivity values. [Copyright &y& Elsevier]

Abstract: Indium oxide ceramics doped with different doping levels of germanium (from 0 to 10at.%) were prepared with nano-sized powders obtained by citrate gel process. Ge for In substitution in the In2O3 bixbyite structure below the solubility limit (about 0.5–1 atom%) leads to a large decrease in the electrical resistivity and the absolute value of the Seebeck coefficient. X-ray diffraction and scanning electron microscopy show the presence after sintering of well dispersed secondary phases In2Ge2O7 when the Ge solubility in the In2O3 matrix is passed. The thermal properties measurements confirm that the decrease in the lattice thermal conductivity observed in these composite materials can be attributed to the presence of insulating In2Ge2O7 phases. Furthermore, preliminary microwave sintering experiments have been tested in order to keep the nanoscale after sintering. Particular nano–microstructures were obtained due to minimal grain growth induced by this rapid sintering process. [Copyright &y& Elsevier]

Abstract: Electronic band structure calculations using the augmented spherical wave method have been performed for CuCrO2. For this antiferromagnetic () semiconductor crystallizing in the delafossite structure, it is found that the valence band maximum is mainly due to the t2g orbitals of Cr3+ and that spin polarization is predicted with per Cr3+. The structural characterizations of CuCr1−x Mg x O2 reveal a very limited range of Mg2+ substitution for Cr3+ in this series. As soon as , a maximum of 1% Cr ions are substituted by Mg site is measured in the sample. This result is also consistent with the detection of Mg spinel impurities from X-ray diffraction for . This explains the saturation of the Mg2+ effect upon the electrical resistivity and thermoelectric power observed for . Such a very weak solubility limit could also be responsible for the discrepancies found in the literature. Furthermore, the measurements made under magnetic field (magnetic susceptibility, electrical resistivity and Seebeck coefficient) support that the Cr4+ “holes”, created by the Mg2+substitution, in the matrix of high spin Cr3+ () are responsible for the transport properties of these compounds. [Copyright &y& Elsevier]

Abstract: The manufacturing of thermoelectric modules from conventional materials is well established and widely commercially available. However, fabrication of modules based on oxide materials has been recently emerging and there exist very few reports on their performance. The oxide nature of the thermoelectric elements and the processing specifications involving very high temperatures make the fabrication a difficult task and different from that of conventional thermoelectric modules. In this work we describe (i) the fabrication of thermoelectric modules based on oxide bulk and foam materials of Ca3Co4O9 and Ca0.95Sm0.05MnO3 and (ii) the metal to ceramic contact preparation. The open porous foam structures of thermoelectric materials make it possible to design efficient thermoelectric modules for waste heat sources involving gaseous and liquid media. The possibility of direct large area physical contact of thermoelectric foam elements with hot media will make them efficient electric power generators. The open porous thermoelectric materials with introduced porosities can be good candidates to confine phonons (lattice vibrations) in order to reduce the thermal conductivity if the pores can be made sufficiently small. The performances of the modules were evaluated and possible factors limiting their theoretical performance are discussed. A parameter representing the quality of the modules termed the manufacturing factor (MF) representing the cumulative effect of various factors involved in the fabrication process is introduced and evaluated for the modules and compared to other reported modules. [Copyright &y& Elsevier]