This study reaffirmed the high effectiveness of co-doping strategies in enhancing the figure of merit zT of both p- and n-type Bi2Te3-based materials. Sb/Ag and W/Cl co-doping simultaneously optimized the carrier concentration and suppressed the lattice thermal conductivity in p-type Bi2Te2Se and n-type Bi2Te2.7Se0.3, respectively. The effectiveness of Sb/Ag and W/Cl co-doping was supported by the density of states obtained from first-principles electronic structure calculations using, for each co-doped composition, a single large supercell containing all relevant dopants. Moreover, it was demonstrated that the thermoelectric properties of Bi2Te3-based systems were highly sensitive to synthesis conditions. For example, the sign of the Seebeck coefficient of the samples prepared in this study was opposite to that reported previously. A zT of similar to 0.94 at 400 K was obtained for p-type BiSb0.95Ag0.05Te2Se, while a zT of similar to 0.92 at 325 K was obtained for n-type Bi1.9995W0.0005Te2.697Se0.3Cl0.003. The p-type BiSb0.95Ag0.05Te2Se and the n-type Bi1.9995W0.0005Te2.697Se0.3Cl0.003, both possessing high power factors and high zT values, exhibited slightly different electrical and thermal transport properties ( rho n kappa p / rho p kappa n similar to 0.8 , where rho and kappa represent the electrical resistivity and thermal conductivity of respective materials). However, the finite element simulation confirmed that a module composed of these materials exhibited high output power and high conversion efficiency, even when the p- and n-type legs were designed with identical geometries, such as cross-sectional area and height.

Silver selenide (Ag2Se) is a promising n-type thermoelectric material for near-room-temperature energy harvesting due to its high electrical conductivity and low lattice thermal conductivity. In this study, Ag2Se-based composites were synthesized using a cold sintering process (CSP), enabling densification at low temperature under applied pressure. Reduced graphene oxide (RGO) was incorporated into the Ag2Se matrix in small amounts (0.25–1.0 wt.%) to enhance thermoelectric performance. Structural analysis confirmed phase-pure β-Ag2Se, while SEM and TEM revealed homogeneous RGO dispersion and strong interfacial adhesion. RGO addition led to a reduced carrier concentration due to carrier trapping by oxygen-bearing functional groups, resulting in decreased electrical conductivity. However, the absolute Seebeck coefficient increased with RGO content, maintaining a balanced power factor. Simultaneously, RGO suppressed thermal conductivity to below 0.75 W m−1 K−1 at room temperature. The optimal composition, 0.75 wt.% RGO, exhibited the highest average zT of 0.98 across the temperature range from room temperature to 383 K. These results demonstrate that combining the CSP with RGO incorporation offers a scalable and cost-effective strategy for enhancing the thermoelectric performance of Ag2Se-based materials.

Spin-Hall thermopiles have been previously proposed as a means to enhance the spin Seebeck effect (SSE). However, the use of platinum (Pt) for spin detection drives costs high and proves an impediment for scalability. In this work, a cost-effective spin-Hall thermopile constructed from opposite spin-Hall angle ferromagnets, cobalt (Co) and iron (Fe), is reported. The devices are fabricated using a standard sputter-coated yttrium iron garnet (YIG) substrate that serves as the spin injector, and thermally evaporated Co and Fe strips that enable spin detection. When serially connected to form a (YIG/Co, Fe) thermopile structure, measurements indicate a significant enhancement of the spin voltage that results from the additive spin contributions of the opposite spin-Hall angle ferromagnets and the anomalous Nernst effect (ANE) that they exhibit. The YIG/Co, Fe thermopile reported here offers a cost-effective alternative to Pt-based thermopiles and the possibility of large-scale implementation to realize future thermoelectric generators.

The generation of spin voltage by heat, known as the spin Seebeck effect (SSE), involves the injection of spin current from a ferromagnetic to a normal metal. In this study, the shunting effect in SSE is investigated within a hybrid structure consisting of iron (Fe) and cobalt (Co) films deposited on a Si-wafer substrate using thermal evaporation [Si/Fe(500 nm)/Co(10 nm)]. Spin voltage measurements performed in the in-plane configuration revealed a voltage reversal in the Co film and Fe film. However, in the hybrid structure (Si/Fe/Co), the voltage signal exhibited consistent directionality. This intriguing observation hints at a potential shunting effect, wherein the voltage influence from the Fe layer contributes to the Co film. Consequently, it is deduced that a significant shunting effect occurs when the resistivity of Fe is approximately three orders of magnitude lower than that of the Co film. This insight sheds light on the intricate dynamics of spin thermoelectric applications, emphasizing the role of material properties in optimizing performance.

The concept of a 'phonon-liquid electron-crystal' has received significant interest in recent years, with copper selenide (Cu2Se) emerging as one of the high-performance thermoelectric materials within this framework. This study focuses on the fabrication of Cu2Se bulk pellets through a low-temperature sintering method known as cold sintering process (CSP). The introduction of a liquid phase (thiol-amine solution) in this process facilitates the dissolution and precipitation of ion/atom clusters, resulting in sample densification. Remarkably, a sample density of nearly 90 % is achieved at a low sintering temperature of only 473 K. Furthermore, this CSP approach preserves the morphology of the Cu2Se precursor powders and effectively inhibits grain growth. Consequently, the lattice thermal conductivity of the CSP samples is significantly reduced, attributed to enhanced grain boundary phonon scattering. This leads to a substantial improvement in the figure-of-merit (ZT), increasing from 0.65 at 800 K in the hot-pressed sample to 2.13 at 800 K in the CSP sample. The advantages of CSP can be extended beyond Cu2Se, as it holds promise for enhancing the performance of various high-performance thermoelectric materials.

This study presents the fabrication of a highly reliable and thermally stable thermoelectric module using ternary half-Heusler (HH) compounds. The n-type and p-type legs were synthesized from NbCoSn and NbFeSb based materials, respectively. The thermoelectric properties of the HH compounds were enhanced through alloying with Ni doping in n-type NbCo1-xNixSn and Mn doping in p-type NbFe1-xMnxSb. Trace amounts of secondary phases were observed in both compounds using X-ray diffraction analysis. Nevertheless, doping improved the power factor as well as the figure-of-merit (zT) in both cases. The n-type NbCo0.90Ni0.10Sn and p-type NbFe0.96Mn0.04Sb compounds were chosen as thermoelectric legs based on optimized design for a 2 pi-module using a 3D finite element analysis and their matching thermal expansion coefficients. The constructed module exhibited a power density of 1.74 W cm(-2) with a conversion efficiency of approximately 1% when connected to the hot and cold sides at temperatures of 873 K and 293 K, respectively. These modules, fabricated from all HH compounds, demonstrated consistent and dependable thermoelectric performance, along with reproducibility, thus indicating their potential for practical applications.

In this article, we report on a low-cost instrument for the versatile measurement of spin caloritronics phenomena such as the spin Seebeck effect (SSE), anomalous Nernst effect (ANE) anisotropic magnetoresistance (AMR), and anomalous Hall effect (AHE). Solenoid coils provide a uniform variable magnetic field while the sample was sandwiched between thermal baths and measured in a vacuum chamber. Our results show excellent magnetic field uniformity (±0.37 mT) within the magnet gap and high stability of the generated temperature difference (±0.07 K). For verifying the effectiveness of our instrument, Yttrium Iron garnet (YIG)/Co structure was used to measure the SSE, AMR, and AHE, while a SiO2/Co structure was used for measuring the ANE. Our SSE measurements of the YIG/Co structure were found to be comparable with that of a commercially available instrument. We can therefore conclude that our low-cost and versatile instrument can be used to effectively observe spin Caloritronics phenomena.

Amorphous Fe-Ti-Sb (FTS) thin film was prepared on a 0.3-µm SiO2/Si wafer by a DC magnetron sputtering method to investigate the spintronic thermoelectric (STE) properties based on the anomalous Nernst effect (ANE) and spin Seebeck effect (SSE). A platinum (Pt) ultra-thin layer was coated on top FTS (Pt/FTS) thin film surface to be used for the spin Hall detector. The crystal structure, morphology, composition and magnetic characteristics of as-deposited FTS and Pt/FTS thin films were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and vibrating sample magnetometry (VSM), respectively. As a result, the crystal structure and morphology displayed a metallic-glass type within the amorphous phase and a smooth surface. The magnetic characterization showed that an ANE and SSE of FTS thin film to yield a spin Seebeck coefficient (Ss) of around 0.35 µV K− 1.

In this study, we report on the observation of spin current in opposite spin Hall angle materials of polycrystalline bulk-Fe3O4/Co and polycrystalline bulk-Fe3O4/Fe spin Seebeck effect (SSE) devices. In contrast to prior works, a facile and low-cost hot-pressing powder metallurgy process was employed to manufacture the polycrystalline bulk-Fe3O4 samples. The crystal structure, magnetization properties, and electrical resistivity characterizations of the fabricated bulk-Fe3O4, which were performed using x-ray diffraction, vibration sample microscope, and four-point probe, respectively, revealed excellent agreement with those of conventional Fe3O4. By taking advantage of the fact that the SSE signal in our devices is typically contaminated with the anomalous Nernst effect (ANE), we show that the total thermo-voltage obtained from our devices can be enhanced by the significant ANE signals exhibited by the Co and Fe spin detectors. Importantly, the ANE contributions could be filtered out from the main signal by independent measurements of the ANE voltage in SiO2/Co and SiO2/Fe systems, thereby allowing the approximate extraction of the SSE voltage. Our experiments reveal that the polarity of the measured ANE (and pure SSE voltages) are opposite to each other in the bulk-Fe3O4/Co and bulk-Fe3O4/Fe structures, thus proving the opposite spin-hall angles character of these materials. The findings of this work provide a pathway for further exploration of methods through which the thermo-voltage output in future spin-Hall thermopile devices may be improved using materials manufactured via a facile, low-cost, and easily scalable process.

The transverse thermoelectric voltage in the Au/Ni foil bilayer system has been investigated due to the combination of the spin Seebeck effect (SSE) and the anomalous Nernst effect (ANE) at room temperature. It is found that the transverse thermoelectric voltage proportionally increases with increasing applied temperature difference and approaches a constant value when the magnetization of the Ni foil reaches a saturation state. The measured thermoelectric voltage signal, about 0.424 ± 0.005 μV at 5 K of temperature difference, is the combination of the ANE signal from the Ni foil and the SSE signal from the Au/Ni foil bilayer system. The SSE and ANE coefficients are determined from the observed voltages, temperature difference, and dimension of the sample. Consequently, the SSE coefficient is found to be 2.5 times larger than the ANE coefficient. Moreover, the special dimensionless figure of merit for SSE is much greater than the obtained from ANE about 7 times. The work demonstrates the enhancement of the thermoelectric voltage due to the superposition of the SSE and ANE in the single bilayer system.

ABSTRACT Melt electrospinning is a suitable process for fabricating fibers by molting polymers. The melt electrospinning system includes a high voltage supply, a syringe pump, a fiber collector and a heating system. Therefore, the purpose of this study was to design and construct the syringe pump and the heating system of the melt electrospinning system. The syringe pump was driven by a stepper motor that controlled by a microcontroller "Arduino". A temperature controller of the heating system controlled the maximum temperature up to 400 °C through a band heater. To demonstrate the functionality of the fabricated melt electrospinning system, polycaprolactone (PCL) fibers were fabricated. The results showed that the melt electrospinning system could successfully fabricate PCL fibers which had slightly rough surface with diameter of micrometer range.

Melt-electrospun polycaprolactone (PCL) fibers were fabricated by using NaCl as an additive. The size and morphology of the PCL fibers could be controlled by varying the concentration of the additive. The smallest size of the fibers (2.67 ± 0.57) µm was found in the sample with 8 wt% NaCl, which was an order of magnitude smaller than the PCL fibers without the additive. The melt-electrospun fibers were characterized using the differential scanning calorimeter (DSC), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) techniques. Interestingly, a trace of NaCl was not found in any melt-electrospun fiber. The remaining PCL after melt-electrospinning was evaporated by annealing, and the NaCl residual was found in the glass syringe. The result confirmed that the NaCl additive was not ejected from the glass syringe in the melt-electrospinning process. Instead, the NaCl additive changed the viscosity and the polarization of the molten polymer. Two parameters are crucial in determining the size and morphology of the electrospun fibers. The higher NaCl concentration could lead to higher polarization of the polymer melt and thus a stronger electrostatic force, but it could also result in an exceedingly high viscosity for melt-electrospinning. In addition, the absence of NaCl in the melt-electrospun PCL fibers is advantageous. The fibers need not be cleaned to remove additives and can be directly exploited in applications, such as tissue engineering or wound dressing.