Boosting the thermoelectric performance of p-type heavily Cu-doped polycrystalline SnSe via inducing intensive crystal imperfections and defect phonon scattering

In this study, we, for the first time, report a high Cu solubility of 11.8% in single crystal SnSe microbelts synthesized via a facile solvothermal route. The pellets sintered from these heavily Cu-doped microbelts show a high power factor of 5.57 μW cm−1 K−2 and low thermal conductivity of 0.32 W m−1 K−1 at 823 K, contributing to a high peak ZT of ∼1.41. Through a combination of detailed structural and chemical characterizations, we found that with increasing the Cu doping level, the morphology of the synthesized Sn1−xCuxSe (x is from 0 to 0.118) transfers from rectangular microplate to microbelt. The high electrical transport performance comes from the obtained Cu+ doped state, and the intensive crystal imperfections such as dislocations, lattice distortions, and strains, play key roles in keeping low thermal conductivity. This study fills in the gaps of the existing knowledge concerning the doping mechanisms of Cu in SnSe systems, and provides a new strategy to achieve high thermoelectric performance in SnSe-based thermoelectric materials

Eco-Friendly SnTe Thermoelectric Materials: Progress and Future Challenges

As a key type of emerging thermoelectric material, tin telluride (SnTe) has received extensive attention because of its low toxicity and eco-friendly nature. The recent trend shows that band engineering and nanostructuring can enhance thermoelectric performance of SnTe as intermediate temperature (400–800 K) thermoelectrics, which provides an alternative for toxic PbTe with the same operational temperature. This review highlights the key strategies to enhance the thermoelectric performance of SnTe materials through band engineering, carrier concentration optimization, synergistic engineering, and structure design. A fundamental analysis elucidates the underpinnings for the property improvement. This comprehensive review will boost the relevant research with a view to work on further performance enhancement of SnTe materials.</p

Effect of brazing temperature on the shear strength of Inconel 600 joint

In this study, Inconel 600 alloy was brazed by using Cusil ABA which is an active filler alloy in a high-vacuum condition under a pressure of 1×10 Pa. Three brazing temperatures (830, 865, and 900 °C) were chosen based on the solidus temperature of AgCuTi filler alloy in order to investigate the effects of these temperatures on the performance of the brazed joint. Brazing processes were carried out over a period of time (15 min) to ensure that the filler alloy was melted completely. The performance of the brazing process was evaluated in terms of bonding strength by shear test, whereas microstructural analysis was performed to investigate the bonding morphology. The results revealed that a maximum value of shear strength (223.32 MPa) was obtained at a brazing temperature of 865°C compared with other temperatures. It was also observed morphologically that the highest shear strength was influenced by the formation of two reaction layers that crossed in the center of the brazed area due to interdiffusion effect of several constituents from the Inconel 600 alloy and active brazing filler

Vacuum brazing of sapphire with Inconel 600 using Cu/Ni porous composite interlayer for gas pressure sensor application

In this research, sapphire as a ceramic was brazed to Inconel 600 as a metal with a commercially available Cusil ABA (63Ag-1.75Ti-35.25Cu) filler foil as braze alloy where Cu/Ni porous composite introduced as an interlayer so it could be used in a particular gas pressure sensor application. Several brazing processes were carried out in a high vacuum furnace in order to investigate the effects of brazing parameters on the joint interface and mechanical properties. The common brazing temperature and time were in the ranges of 830-900°C and 15-30min respectively, while vacuum pressure was remained constant at 1×10Pa. SEM-EDS and XRD analyses of the joint microstructure and interface composition revealed five distinct phases; NiTi, AlNi, CrTi, FeNiTi (TiO). The brazing area formed two "ocean" structures near to Inconel and sapphire interfaces whereas a reaction layer was developed at the surface of Inconel 600. Under the mechanical property analyses the brazed joint at 900°C for 30min obtained the maximum shear strength of 58.5MPa which is adequate for particular gas pressure sensor application

Ag doping induced abnormal lattice thermal conductivity in Cu2Se

Superionic Cu2Se-based thermoelectric materials have attracted extensive attention in recent years due to their ultralow lattice thermal conductivity and high dimensionless figure of merit (zT). Inspired by the effectiveness of heavy-element doping in reducing lattice thermal conductivity in various thermoelectric materials, we investigate the Ag-doping effects on the thermoelectric properties of Cu2Se nanocrystals made via a facile solvothermal method and subsequently spark plasma sintering. Based on the single parabolic band model analysis of thermoelectric properties, it has been found that the isoelectronic Ag dopant leads to an enhanced carrier concentration and significantly reduced carrier mobility, as well as a reduced electrical conductivity and power factor. Moreover, the reduced disorder-level of cations leads to an extraordinarily enhanced lattice thermal conductivity. All these result in a zT reduction for Ag-doped Cu2Se. This work systematically studies the influence of Ag dopants on the thermoelectric performance of Cu2Se and indicates that the Ag-doping is less promising in enhancing it

Effect of Surface States on Joining Mechanisms and Mechanical Properties of Aluminum Alloy (A5052) and Polyethylene Terephthalate (PET) by Dissimilar Friction Spot Welding

In this research, polyethylene terephthalate (PET), as a high-density thermoplastic sheet, and Aluminum A5052, as a metal with seven distinct surface roughnesses, were joined by friction spot welding (FSW). The effect of A5052’s various surface states on the welding joining mechanism and mechanical properties were investigated. Friction spot welding was successfully applied for the dissimilar joining of PET thermoplastics and aluminum alloy A5052. During FSW, the PET near the joining interface softened, partially melted and adhered to the A5052 joining surface. The melted PET evaporated to form bubbles near the joining interface and cooled, forming hollows. The bubbles have two opposite effects: its presence at the joining interface prevent PET from contacting with A5052, while bubbles or hollows are crack origins that induce crack paths which degrade the joining strength. On the other hand, the bubbles’ flow pushed the softened PET into irregularities on the roughened surface to form mechanical interlocking, which significantly improved the strength. The tensile-shear failure load for an as-received surface (0.31 μ m Ra) specimen was about 0.4–0.8 kN while that for the treated surface (&gt;0.31 μ m Ra) specimen was about 4.8–5.2 kN

Realizing high thermoelectric properties of SnTe via synergistic band engineering and structure engineering

Lead-free tin telluride (SnTe) has been drawn enormous attention recently due to their potential applications in the mid-temperature thermoelectric power generation. In this study, we systematic investigated the thermoelectric properties of In/Sr co-doped SnTe via first principles density functional theory calculation, coupled with extensive structural characterizations and property measurements. From which, we found that the co-doping of In and Sr in SnTe can significantly improve the electrical transport properties through unique interplay of band structure modifications, and the reduced lattice thermal conductivity can be achieved via strong phonon scattering by point defects, nanoprecipitates, and grain boundaries. Consequently, a record high power factor of ∼33.88 μWcm−1K−2 and a peak figure of merit of ∼1.31 has been achieved at 823 K for the Sn0.925In0.025Sr0.05Te pellet. This study indicates that In/Sr co-doping can effectively make incorporation of resonant levels, band degeneracy, band gap tuning and nanostructuring, leading to the achieving high thermoelectric performance of SnTe material

Polycrystalline SnSe with extraordinary thermoelectric property via nanoporous design

Nanoporous materials possess low thermal conductivities derived from effective phonon scatterings at grain boundaries and interfaces. Thus nanoporous thermoelectric materials have full potential to improve their thermoelectric performance. Here we report a high ZT of 1.7 ± 0.2 at 823 K in p-type nanoporous polycrystalline SnSe fabricated via a facile solvothermal route. We successfully induce indium selenides (InSey) nanoprecipitates in the as-synthesized SnSe matrix of single-crystal microplates, and the nanopores are achieved via the decompositions of these nanoprecipitates during the sintering process. Through detailed structural and chemical characterizations, it is found that the extralow thermal conductivity of 0.24 W m–1 K–1 caused by the effective phonon blocking and scattering at induced nanopores, interfaces, and grain boundaries and the high power factor of 5.06 μW cm–1 K–2 are derived from a well-tuned hole carrier concentration of 1.34 × 1019 cm–3 via inducing high Sn vacancies by self-doping, contributing to high ZTs. This study fills the gap of achieving nanoporous SnSe and provides an avenue in achieving high-performance thermoelectric properties of materials

Solvothermal synthesis of high-purity porous Cu1.7Se approaching low lattice thermal conductivity

Superionic Cu2−xSe has attracted extensive research interest as a promising thermoelectric material with low lattice thermal conductivity (~0.6Wm−1 K−1 at 773 K) and high figure of merit, zT. Here, we demonstrated that β-Cu2−xSe can be synthesized via a facile solvothermal method. By modifying the Cu/Se ratio to control the reaction kinetic condition, impurities, such as Cu2O, Cu and Cu3Se2, can be suspended and in turn lead to highpurity Cu1.7Se. After spark plasma sintering (SPS), porous Cu1.7Se pellet can be sintered and has a relatively low lattice thermal conductivity of ~0.24Wm−1 K−1 at 773 K. From the single parabolic band prediction, a high zT of ~1.6 at 773 K could be realized if the carrier concentration, nH, can be optimized to ~1×1020 cm−3 at the same low lattice thermal conductivity. Our study indicates that porous Cu1.7Se is promising to achieve high zT with proper nH-optimization