Fu-Hua Sun

Thermoelectric SnS and SnS-SnSe solid solutions prepared by mechanical alloying and spark plasma sintering: Anisotropic thermoelectric properties

P–type SnS compound and SnS1−xSex solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS–pressurizing direction in the temperature range 323–823 Κ. SnS compound and SnS1−xSex solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m−1 K−1 at 823 K for the composition SnS0.5Se0.5. With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS0.2Se0.8 along the parallel direction.

Ultrafast breathing humidity sensing properties of low-dimensional Fe-doped SnO2 flower-like spheres

Low-dimensional Fe-doped SnO2 flower-like nanospheres are synthesized by a simple template- and surfactant-free hydrothermal method. Interestingly, the hierarchical nanostructures not only show a low dimension (the diameter is ca. 200 nm), but also present a dramatic humidity sensitivity compared with the undoped ones. These obviously enhanced properties are probably ascribed to the strong affinity of Fe3+ ions on the SnO2 (101) interface in the alkaline conditions and the complex band configuration of the γ-Fe2O3/SnO2 Schottky contact. 2% Fe-doped SnO2 humidity sensors exhibit outstanding thermal stability (weight loss less than 2.5%), exceptionally fast response/recovery speed (<1@4 s, 95% relative humidity), as well as ultrahigh humidity sensitivity (S = 6479.5). Besides, Fe-doped SnO2 sensors possess excellent breathing sensing properties, superior to most of the reported SnO2-based humidity sensors under the same conditions. These results open the door for ultrafast breathing sensing and the potential application of touchless user interfaces to traditional metal oxide based humidity sensors.

Powder metallurgically synthesized Cu12Sb4S13 tetrahedrites: phase transition and high thermoelectricity

Cu12Sb4S13 tetrahedrite with intrinsically low lattice thermal conductivity has been identified as a promising thermoelectric material with earth-abundant and environmental-friendly resource, but as a natural mineral its synthesis process has not been established. This work studied a powder metallurgical process combining mechanical alloying (MA) and spark plasma sintering (SPS) to synthesize Cu12Sb4S13−x (x = 0, 0.1, 0.2, 0.3 and 0.4) compounds. It is found that single-phased Cu12Sb4S13−x bulks could be synthesized by the MA-SPS process, but tended to become powdered naturally in air at room temperature. Interestingly, this weathering-like phenomenon could be effectively suppressed when the MA-SPS process was repeated. Consequently, a high ZT value of up to 0.65 at 723 K was achieved at a nominal composition of Cu12Sb4S12.7, which is close to the best value of 0.70 obtained in Cu12Sb4S13 tetrahedrites prepared by the melting method, although the present process is more simple and cost-effective. In addition, in this study temperature-dependent phase transitions were investigated to explore the reasons for the weathering-like phenomenon observed in synthetic Cu12Sb4S13 tetrahedrites.

Enhanced thermoelectric performance of Cu 12 Sb 4 S 13− δ tetrahedrite via nickel doping

Cu12Sb4S13 tetrahedrite has received great attention as an earth-abundant and environmental-friendly thermoelectric material. This work aims to uncover the thermoelectric performance-enhancing effect and the mechanism of nickel doping on tetrahedrite. A series of Cu12−xNixSb4S13−δ (x = 0.5, 0.7, 1.0, 1.5 and 2.0) compounds were synthesized by mechanical alloying combined with spark plasma sintering. It is found that the thermal conductivity sharply reduces with increasing Ni content over the entire temperature range, < 0.9 W m−1 K−1, accompanied with an enhanced thermoelectric power factor. The model predicted that the reduced lattice thermal conductivity is attributed to mid-frequency phonon scattering, caused by precipitates and dislocations resulting from Ni doping. Consequently, a high ZT value up to 0.95 at 723 K was achieved for Cu11NiSb4S13−δ, corresponding to a ∼46% increase over non-doped Cu12Sb4S13−δ. Furthermore, the cyclic measurement showed that the Ni-doped tetrahedrites displayed high chemical stability.摘要Cu12Sb4S13是一种储量丰富、 环境友好的天然矿物, 被热电领域普遍关注. 本研究旨在揭示Ni掺杂提高黝铜矿材料热电性能的机理. 采用机械合金化(MA)结合放电等离子体烧结(SPS)的方法制备出Cu12−xNixSb4S13−δ (x = 0.5, 0.7, 1.0, 1.5, 2.0)样品. 实验结果表明, 在测量温度范围内(323–723 K), 随着Ni含量的增加, 样品的热导率急剧下降(< 0.9 W m−1 K−1), 同时热电功率因子逐渐增加. 理论模型计算表明, 晶格热导率的降低主要来源于Ni掺杂引起的析出相及位错对中频声子的强散射作用. 由于较低的热导率和较高的功率因子, Cu11NiSb4S13−δ 样品在723 K时获得最高ZT值0.95, 相对于未掺杂样品, 其热电性能提高了46%. 同时, 热循环测试表明, 通过Ni掺杂提高了黝铜矿热电材料的化学稳定性.

Lead-free MnTe mid-temperature thermoelectric materials: facile synthesis, p-type doping and transport properties

MnTe has been found to exhibit good thermoelectric properties at medium temperature recently, but the electrical transport properties, especially the interaction between magnetism and carriers, are still not fully understood and the synthesis process reported is mainly composed of melting. Herein, we present a facile method combining mechanical alloying (MA) and spark plasma sintering (SPS) to fabricate high purity MnTe. Carrier concentration is well tuned by sodium doping, resulting in a high power factor over 900 μW m−1 K−2 and a maximum ZT value exceeding 1.0 at 873 K. The electrical transport properties are analyzed by the single parabolic band model. Additionally, different electrical transport properties induced by the magnetic transformation were discussed and clarified by first-principles calculation, including the increase of carrier concentration, decrease of mobility and enhancement of the density-of-state (DOS) effective mass. The high thermoelectric performance reveals the potential of MnTe as a promising candidate for medium-temperature thermoelectric materials.

MnS Incorporation into Higher Manganese Silicide Yields a Green Thermoelectric Composite with High Performance/Price Ratio

Abstract Thermoelectric materials that can directly convert heat to electrical energy offer a viable solution for reducing the usage of fossil energy by harvesting waste heat resources. Higher manganese silicide (HMS) is a naturally abundant, eco‐friendly, and low‐cost p‐type thermoelectric semiconductor with high power factor (PF); however, its figure of merit (ZT) is limited by intrinsically high thermal conductivity (κ). For effectively enhancing the thermoelectric performance of HMS and avoiding the use of expensive or toxic elements, such as Re, Te, or Pb, a green p‐type MnS with high Seebeck coefficient (S) and low κ is incorporated into the HMS matrix to form MnS/HMS composites. The incorporation of MnS leads to a 31% reduction of κ and a 10% increase of S. The ZT value increases by ≈48% from 0.40 to 0.59 at 823 K. Correspondingly, performance/price ratio is first proposed to evaluate the practical value of thermoelectric materials, which is higher than those of the vast majority of current thermoelectric materials. This study provides an overview of enhancing ZT of HMS and reducing costs, which may also be applicable to other thermoelectric materials.

Melt‐Centrifuged (Bi,Sb)2Te3: Engineering Microstructure toward High Thermoelectric Efficiency

Microstructure engineering is an effective strategy to reduce lattice thermal conductivity (κl ) and enhance the thermoelectric figure of merit (zT). Through a new process based on melt-centrifugation to squeeze out excess eutectic liquid, microstructure modulation is realized to manipulate the formation of dislocations and clean grain boundaries, resulting in a porous network with a platelet structure. In this way, phonon transport is strongly disrupted by a combination of porosity, pore surfaces/junctions, grain boundaries, and lattice dislocations. These collectively result in a ≈60% reduction of κl compared to zone melted ingot, while the charge carriers remain relatively mobile across the liquid-fused grains. This porous material displays a zT value of 1.2, which is higher than fully dense conventional zone melted ingots and hot pressed (Bi,Sb)2 Te3 alloys. A segmented leg of melt-centrifuged Bi0.5 Sb1.5 Te3 and Bi0.3 Sb1.7 Te3 could produce a high device ZT exceeding 1.0 over the whole temperature range of 323-523 K and an efficiency up to 9%. The present work demonstrates a method for synthesizing high-efficiency porous thermoelectric materials through an unconventional melt-centrifugation technique.