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We report a detailed description of an innovative route of a melt spinning (MS) technique combined with a subsequent spark plasma sintering process in order to obtain high performance p-type Bi0.52Sb1.48Te3 bulk material, which possesses a unique low-dimensional structure. The unique structure consists of an amorphous structure, 5–15 nm fine nanocrystalline regions, and coherent interfaces between the resulting nanocrystalline regions. Measurements of the thermopower, electrical conductivity, and thermal conductivity have been performed over a range of temperature of 300–400 K. We found that MS technique can give us considerable control over the resulting nanostructure with good thermal stability during the temperature range of 300–400 K and this unique structure can effectively adjust the transport of phonons and electrons, in a manner such that it is beneficial to the overall thermoelectric performance of the material, primarily a reduction in the lattice thermal conductivity. Subsequently, this results in a maximum figure of merit ZT value of 1.56 at 300 K for p-type Bi0.52Sb1.48Te3 bulk material. This ZT value is over a 50% improvement of that of the state of the art commercial Bi2Te3 materials. We also report results of thermal cycling of this material for over one hundred cycles between 300–400 K. Our work offers an innovative route for developing high performance bismuth telluride based alloys and devices, which have even broader prospects for commercial applications. This technique may also be applicable to other thermoelectric materials. [ABSTRACT FROM AUTHOR]

Thermoelectricity has been recognized as an environmentally friendly energy conversion technology due to its ability to directly achieve conversion between heat and electricity for a long time. β-Zn4Sb3 has attracted considerable interest as promising thermoelectric material in the moderate temperature range (500 K–900 K), which is the temperature range of most industrial waste heat sources. In this paper, first we present the structure of β-Zn4Sb3 and the traditional doping strategy used to enhance its performance. Next, we review the details of some new methods utilized for improving the thermoelectric properties of β-Zn4Sb3 and its thermal stability as well as reliability. Finally, the review finishes with highlighting some promising strategies for future research directions in the material. [ABSTRACT FROM AUTHOR]

Thermoelectric half-Heusler compounds with the nominal composition (Ti0.33Zr0.33Hf0.33)NiSn were synthesized and exposed to operating conditions, i.e., elevated temperatures and oxidizing atmosphere. As-prepared samples were found to be a stable multiphase system consisting of Ti- and (Zr,Hf)-rich phases with half-Heusler structure. The influence of an oxidizing atmosphere at elevated temperatures on the sample was studied in- and ex situ by optical and electron microscopy and thermal analysis. Exposure to air resulted in surface oxidation starting at T = 545 K. During a defined heat treatment the Ti-rich phase decomposed while the (Zr,Hf)-rich phase was stable. In situ Atomic Force Microscopy and Scanning Kelvin Probe Force Microscopy experiments confirmed that interfaces, especially grain boundaries, are most prone to phase decomposition. [ABSTRACT FROM AUTHOR]

Abstract: In this article, a rapid and cost-effective melt spinning (MS) subsequently combined with a spark plasma sintering (SPS) process was utilized to prepared n-type Bi2(Te1−x Se x )3 (x = 0.0–1.0) solid solutions from high purity single elemental chunks. The substitution of tellurium by selenium has significant impacts on the electrical and thermal transport properties of the Bi2(Se x Te1−x )3 compounds in a manner which can be well understood using a valence bond rule and the corresponding change in band gap. Furthermore, the selenium substitution effectively adjusts the carrier density allowing an optimum value of ∼5 × 10−19 cm−3. As a result, a maximum ZT of 1.05 at 420 K was achieved for the Bi2(Se0.2Te0.8)3 sample which also shows an improved average ZT of ∼0.97 in the entire measurement temperature range. By adopting the same p-type legs, the module fabricated by the MS-SPS Bi2(Se0.2Te0.8)3 material which acts as n-type legs shows ∼10% enhancement in thermoelectric conversion efficiency compared with the module fabricated by n-type zone melted ingots. [Copyright &y& Elsevier]

Abstract Oxide materials are of current interest as high-temperature thermoelectrics in the automotive and manufacturing energy-harvesting sectors due to high chemical robustness, low toxicity and low cost. Driven by a need to improve the thermoelectric performance of n-type oxides to the level of p-type analogues, ceramics and composites based on donor-doped SrTiO 3 are considered as a promising material. Here Nb-doped SrTiO 3 with Nb content of 10 and 15% as well as Sr/(Nb + Ti) ratio of 1.00 and 0.98 was mixed with 0.6 wt. % of graphene oxide (GO) prepared by Hummer-based method and conventionally sintered in atmosphere of H 2 /N 2 to reduce both Nb-doped SrTiO 3 and GO. Addition of reduced GO in combination with introduction of Sr vacancies provides a synergistic effect of fastening charge transport and thereby increasing electrical conductivity σ and suppressing the thermal conductivity κ. These factors, together with a moderate Seebeck coefficient S , result in a high power factor PF = S 2 × σ up to ∼1.98 mW/(K2m) and thermoelectric figure of merit ZT = PF × T / κ up to 0.29. These findings offer further prospects for seeking high performance SrTiO 3 -based thermoelectrics by modification with reduced GO. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

We report small-angle neutron scattering studies on the microstructure network in bulk (Bi,Sb)2Te3 synthesized by the melt-spinning (MS) and the spark-plasma-sintering (SPS) process. We find that rough interfaces of multiscale microstructures generated by the MS are responsible for the large reduction of both lattice thermal conductivity and electrical conductivity. Our study also finds that subsequent SPS forms a microstructure network of ∼10 nm thick lamellae and smooth interfaces between them. This nanoscale microstructure network with smooth interfaces increases electrical conductivity while keeping a low thermal conductivity, making it an ideal microstructure for high thermoelectric efficiency. [ABSTRACT FROM AUTHOR]

Abstract This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous co-doping with aluminum. At 1100–1223 K mixed-doped samples demonstrated around ∼2.3 times increase in ZT as compared to single-doped materials, reaching ∼0.12. The simultaneous presence of aluminum and zirconium imposes a synergistic effect on electrical properties provided by their mutual effects on the solubility in ZnO crystal lattice, while also allowing a moderate decrease of the thermal conductivity due to phonon scattering effects. At 1173 K the power factor of mixed-doped Zn 0.994 Al 0.003 Zr 0.003 O was 2.2–2.5 times higher than for single-doped materials. Stability tests of the prepared materials under prospective operation conditions indicated that the gradual increase in both resistivity and Seebeck coefficient in mixed-doped compositions with time may partially compensate each other to maintain a relatively high power factor. [ABSTRACT FROM AUTHOR]

Abstract: β-Zn4Sb3 compounds doped with minute amounts of Cd were synthesized by the MS-SPS technique, which involves melt spinning (MS) followed by spark plasma sintering (SPS), and the microstructures, thermoelectric and thermodynamic properties were systematically characterized. The non-equilibrium MS-SPS technique generates multi-scale nanostructures in the MS-prepared ribbon-shape samples and the resulting compacted bulk materials. These unique multiple nanostructures result in substantial reductions in lattice thermal conductivities, particularly for samples with a large number of ZnSb nanodots with sizes of 10–30nm. Meanwhile, Cd-doping remarkably improves the electrical properties of the (Zn1− x Cd x )4Sb3 compounds by a slight decrease in electrical conductivity and an apparent enhancement of the Seebeck coefficient. Therefore, the dimensionless figure of merits are significantly improved and the maximum value reaches ∼1.30 for the (Zn0.99Cd0.01)4Sb3 sample at 700K, representing ∼13% and ∼23% improvements compared with the undoped MS-SPS sample and the 1% Cd-doped melting ingot, respectively. In particular, this value shows no degradation after 10 heat cycles from 300 to 700K or 30h annealing at 680K in vacuum, whereas the ZT of neat sample decreases by ∼20% to a relatively low value of ∼1.0 after 30h annealing. The enhanced thermal stability of ZT along with the suppressing effect on the low-temperature α–β phase transition clearly indicates a large improvement in thermodynamic stability as a result of minute Cd-doping. All the above-mentioned benefits make the minute Cd-doped β-Zn4Sb3 compound prepared by the MS-SPS technique a promising candidate for mid-range temperature thermoelectric power generation applications. [Copyright &y& Elsevier]