Search Results (632)

Bismuth (Bi)-doped indium oxide (In₂O₃) has emerged as a promising thermoelectric material due to its tunable electrical and thermal properties. This study investigates the effects of Bi-doping on the thermoelectric performance of In₂O₃, focusing on its electrical conductivity, band structure, carrier concentration, mobility, Seebeck coefficient, power factor, thermal conductivity, and overall thermoelectric figure of merit (ZT). The incorporation of Bi into the In₂O₃ lattice significantly enhances the material’s electrical conductivity, attributed to the increased carrier concentration resulting from Bi acting as an effective dopant. However, this doping also leads to a broadening of the bandgap, which influences the electronic transport properties. The Seebeck coefficient (absolute value) is observed to decrease with Bi-doping, a consequence of the elevated carrier concentration. Despite this reduction, the overall power factor improves due to the substantial increase in electrical conductivity. Furthermore, Bi-doping effectively reduces both the total thermal conductivity and the lattice thermal conductivity of In₂O₃. This reduction is primarily due to enhanced phonon scattering caused by the introduction of Bi atoms, which disrupt the lattice periodicity and introduce point defects. The combined improvement in electrical conductivity and reduction in thermal conductivity results in a significant enhancement of the thermoelectric figure of merit (ZT) with highest ZT value increased from 0.055 to 0.402 at 973 K. The optimized Bi-doped In₂O₃ samples demonstrate a ZT value that surpasses that of undoped In₂O₃, highlighting the potential of Bi-doping for advancing thermoelectric applications. This work provides a comprehensive understanding of the underlying mechanisms governing the thermoelectric properties of Bi-doped In₂O₃ and offers valuable insights into the design of high-performance thermoelectric materials for energy conversion technologies. Full article

Mechanical alloying (MA) has been proven to be an energy-efficient synthetic route for the development of high-performance thermoelectric (TE) materials. Higher Manganese Silicide (HMS) phases of the general formula Mn(Si_1−xAl_x)_1.75 (0 ≤ x ≤ 0.05) were prepared by MA implementing a short-time ball-milling process. Powder XRD and SEM analysis were carried out to validate the HMS phases, while small amounts of the secondary phase, MnSi, were also identified, especially for the Al-doped products. Electrical transport properties measurements showed that Al substitution causes an effective hole doping. A remarkable increase in electrical conductivity is observed for the Al-doped phases, while the corresponding reduction in the Seebeck coefficient is indicative of the increase in carrier density. Despite the small percentages of MnSi detected in Al-doped phases, an improvement in TE efficiency is achieved in the series Mn(Si_1−xAl_x)_1.75 (0 ≤ x ≤ 0.05). The 2.5% Al-doped phase exhibits a maximum figure-of-merit (ZT) of 0.43 at 773 K. Moreover, in an effort to utilize recycled silicon byproducts from photovoltaic (PV) manufacturing, Al-doped phases are developed by MA using two types of Si kerf. The two kerf-based products exhibit lower TE efficiencies, due to the increased amounts of the metallic MnSi phase. Full article

Hybrid thermoelectric generators (HTEGs) play a pivotal role in sustainable energy conversion by harnessing waste heat through the Seebeck effect, contributing to global efforts in energy efficiency and environmental sustainability. In practical sustainable energy systems, HTEG output performance is significantly influenced by uncertainties in the operational parameters (such as temperature differences and load resistance), material properties (including Seebeck coefficient and resistance), and structural configurations (like the number of series/parallel thermoelectric components), which impact both efficiency and system stability. This study employs the Sobol-sequence-sampling method to characterize these parameter uncertainties, analyzing their effects on HTEG output power and conversion efficiency using mean values and standard deviations as evaluation metrics. The results show that higher temperature differences enhance output performance but reduce stability, a larger load resistance decreases performance while improving stability, thermoelectric materials with high Seebeck coefficients and low resistance boost efficiency at the expense of stability, increasing series-connected components elevates performance but reduces stability, parallel configurations enhance power output yet decrease efficiency and stability, and greater contact thermal resistances diminish performance while enhancing system robustness. This research provides theoretical guidance for optimizing HTEGs in sustainable energy applications, enabling the development of more reliable, efficient, and eco-friendly thermoelectric systems that balance performance with environmental resilience for long-term sustainable operation. Full article

Optimizing thermoelectric (TE) performance in two-dimensional materials has emerged as a pivotal strategy for sustainable energy conversion. This study systematically investigates the regulatory mechanisms of uniaxial strain (−2% to +2%), temperature (300–800 K), and out-of-plane electric fields (0–1.20 eV/Å) on the thermoelectric properties of monolayer MoS₂ via first-principles calculations combined with Boltzmann transport theory. Key findings reveal that uniaxial strain modulates the bandgap (1.56–1.86 eV) and carrier transport, balancing the trade-off between the Seebeck coefficient and electrical conductivity. Temperature elevation enhances carrier thermal excitation, boosting the power factor to 28 × 10¹⁰ W·m⁻¹·K⁻²·s⁻¹ for p-type behavior and 27 × 10¹⁰ W·m⁻¹·K⁻²·s⁻¹ for n-type behavior at 800 K. The breakthrough lies in the exceptional suppression of lattice thermal conductivity (κ₁) by out-of-plane electric fields—at 1.13 eV/Å, κ₁ is reduced to single-digit values (W·m⁻¹·K⁻¹), driving ZT to ~4 for n-type MoS₂ at 300 K. This work demonstrates that synergistic engineering of strain, temperature, and electric fields effectively decouples the traditional trade-off among the Seebeck coefficient, conductivity, and thermal conductivity, providing a core optimization pathway for 2D thermoelectric materials via electric field-mediated κ₁ regulation. Full article

Thermocouples can be combined into thermopiles to sense heat differences or achieve localized heating and cooling. However, integrating them into textiles using yarns is not straightforward, and chemical methods face challenges like complex processing, poor scalability, and voltage non-uniformity. This study employs conventional weaving to fabricate textile-based thermocouples and thermopiles for wearable sensing and potential cooling applications, with a focus on protective clothing. Using stainless steel and nickel-coated carbon yarns, we demonstrate a more stable thermocouple than those made with chemical or welded methods, with minimal fabric damage. Four conductive yarns, stainless steel, carbon fiber (CF), and nickel-coated carbon fiber (NiFC), were woven and laser-cut to form thermocouples using three different binding types to connect them. Inox1–NiFC was the most efficient thermocouple, achieving the highest Seebeck coefficient of 21.87 µV/K with Binding 3. Binding 3 also reduced contact resistance by 66% across all configurations. Slightly lower but comparable performance was seen with Inox1–NiFC/Binding 2 (21.83 µV/K) and Inox2–NiFC/Binding 1 (15.79 µV/K). In contrast, FC-based thermocouples showed significantly lower Seebeck values: 5.67 µV/K (Inox2–FC/Binding 2), 5.43 µV/K (Inox1–FC/Binding 3), and 5.06 µV/K (Inox2–FC/Binding 1). A woven thermopile with three junctions made with the optimal binding and thermocouple combination generated an average of 55.54 µV/K and about 500 µV at small temperature differences (4–5 °C), with a linear voltage response suitable for sensing. While thermal sensing proved effective, Peltier cooling needs further optimization. This method offers a stable, low-cost, and scalable platform for textile-integrated thermoelectric systems, with strong potential for use in uniforms and other protective garments. Full article

Ultrasonic testing (UT) is a vital nondestructive testing (NDT) technique used to evaluate the integrity of materials and structures. However, conventional excitation signals often suffer from significant attenuation in highly attenuative materials, resulting in low signal energy and poor signal interpretation. Coded excitation techniques, such as the Barker code and the complementary Golay code (CGC), have been used to enhance signal energy and signal-to-noise ratio. Yet, Barker codes are limited by short sequence lengths, while CGC requires two transmission events, reducing time efficiency. This paper proposes a novel excitation method: the Barker-convolved mutually orthogonal Golay complementary code (BMOGCC). By convolving the Barker code with the mutually orthogonal Golay complementary code (MOGCC), BMOGCC combines the advantages of both, including flexibility in code length, improved signal amplitude, low sidelobe levels, and enhanced time efficiency. Performance was evaluated using numerical simulations and laboratory experiments, with key indices including the peak sidelobe level (PSL), mainlobe gain (MG), and temporal resolution. The results show that BMOGCC achieves a significantly higher MG than either the Barker code or MOGCC alone while maintaining a low PSL and preserving the temporal resolution. These findings demonstrate that BMOGCC is effective and efficient for coding excitation signals in ultrasonic testing, offering improved signal quality and measurement time efficiency. Full article

Ag₂Se has attracted significant attention as a promising alternative to Bi₂Te₃ for near-room-temperature thermoelectric (TE) applications. In this study, flexible Ag₂Se thin films were fabricated via magnetron sputtering under different sputtering power settings, followed by post-deposition annealing to optimize their TE properties. Structural and compositional analyses confirmed the successful synthesis of Ag₂Se films with high crystallinity. Additionally, tuning the sputtering power and annealing temperatures can effectively enhance the electrical conductivity, Seebeck coefficient, and overall power factor. A significant power factor of ~17.4 µW·cm⁻¹·K⁻² at 100 °C was achieved in the 30 W sputtering power and 300 °C annealing sample, pointing out the huge potential of Ag₂Se thin films as self-powered flexible devices. Full article

Famatinite (Cu₃SbS₄) is an earth-abundant, nontoxic material with potential for thermoelectric energy generation applications. Herein, rapid, energy-efficient, and facile one-pot modified polyol synthesis was utilized to produce gram-scale quantities of phase-pure famatinite (Cu_2.7M_0.3SbS₄, M = Cu, Zn, Mn) nanoparticles (diameter 20–30 nm) with controllable and stoichiometric incorporation of transition metal dopants on the Cu-site. To produce pellets for thermoelectric characterization, the densification process by spark plasma sintering was optimized for individual samples based on thermal stability determined using differential scanning calorimetry and thermogravimetric analysis. Electronic transport properties of undoped and doped famatinite nanoparticles were studied from 225–575 K, and the thermoelectric power factor was calculated. This is the first time electronic transport properties of famatinite doped with Zn or Mn have been studied. All famatinite samples had similar resistivities (>0.8 mΩ·m) in the measured temperature range. However, the Mn-doped famatinite nanomaterials exhibited a thermoelectric power factor of 10.3 mW·m⁻¹·K⁻¹ at 575 K, which represented a significant increase relative to the undoped nanomaterials and Zn-doped nanomaterials engendered by an elevated Seebeck coefficient of ~220 µV·K⁻¹ at 575 K. Future investigations into optimizing the thermoelectric properties of Mn-doped famatinite nanomaterials are promising avenues of research for producing low-cost, environmentally friendly, high-performing thermoelectric materials. Full article

Defensive pessimism, an important emotion regulation and motivation strategy, has increasingly attracted scholarly attention in psychology. Recently, sensor-based methods have begun to supplement or replace traditional questionnaire surveys in personality research. However, current approaches for collecting vital signs data face several challenges, including limited monitoring durations, significant data deviations, and susceptibility to external interference. This paper proposes a novel approach using a NiCr/NiSi alloy film temperature sensor, which has a K-type structure and flexible piezoelectric pressure sensor to identify and predict defensive pessimism personality traits. Experimental results indicate that the Seebeck coefficients for K-, T-, and E-type thermocouples are approximately 41 μV/°C, 39 μV/°C, and 57 μV/°C, respectively, which align closely with national standards and exhibit good consistency across multiple experimental groups. Moreover, radial artery frequency experiments demonstrate a strong linear relationship between pulse rate and the intensity of external stimuli, where stronger stimuli correspond to faster pulse rates. Simulation experiments further reveal a high correlation between radial artery pulse frequency and skin temperature, and a regression model based on the physiological sensor data shows a good fit (p < 0.05). These findings verify the feasibility of using temperature and flexible piezoelectric pressure sensors to identify and predict defensive pessimism personality characteristics. Full article

In this work, bio-based thermoelectric composites were developed using acrylated epoxidized soybean oil (AESO) as the polymer matrix and bismuth telluride (Bi₂Te₃) as the thermoelectric filler. The materials were formulated for both UV-curing and thermal-curing processes, with a focus on Digital Light Processing (DLP) 3D printing. Although UV curing proved ineffective at high filler concentrations due to the light opacity of Bi₂Te₃, thermal curing enabled the fabrication of stable, homogeneously dispersed composites. The samples were thoroughly characterized through rheology, FTIR, TGA, XRD, SEM, and density measurements. Thermoelectric performance was assessed under a 70 °C temperature gradient, with Seebeck coefficients reaching up to 51 µV/K. Accelerated chemical degradation studies in basic media confirmed the degradability of the matrix. The results demonstrate the feasibility of combining additive manufacturing with sustainable materials for low-power thermoelectric energy harvesting applications. Full article

Na₀.₈₉Co_0.90Me_0.10O₂ (Me = Cr, Ni, Mo, W, Pb, and Bi) ceramic samples were prepared using a solid-state reaction method, and their crystal structure, microstructure, and electrical, thermal, and thermoelectric properties were investigated. The effect of the nature of the doping metal (Me = Cr, Ni, Mo, W, and Bi) on the structure and properties of layered sodium cobaltite Na_0.89CoO₂ was analyzed. The largest Seebeck coefficient (616 μV/K at 1073 K) and figure-of-merit (1.74 at 1073 K) values among the samples studied were demonstrated by the Na_0.89Co_0.9Bi_0.1O₂ solid solution, which was also characterized by the lowest value of the dimensionless relative self-compatibility factor of about 8% within the 673–873 K temperature range. The obtained results demonstrate that doping of layered sodium cobaltite by transition and heavy metal oxides improves its microstructure and thermoelectric properties, which shows the prospectiveness of the used doping strategy for the development of new thermoelectric oxides with enhanced thermoelectric characteristics. It was also shown that samples with a higher sodium content (Na:Co = 0.89:1) possessed higher chemical and thermal stability than those with a lower sodium content (Na:Co = 0.55:1), which makes them more suitable for practical applications. Full article

This study investigates the application of additive manufacturing (AM) in fabricating transverse thermoelectric (TTE) composites, demonstrating the feasibility of this methodology for TTE material synthesis. Zinc oxide (ZnO), a wide-bandgap semiconductor with moderate thermoelectric performance, and copper (Cu), a highly conductive metal, were selected as base materials. These were formulated into stable paste-like feedstocks for direct ink writing (DIW). A custom dual-nozzle 3D printer was developed to precisely deposit these materials in pre-designed architectures. The resulting structures exhibited measurable transverse Seebeck effects. Unlike prior TE research primarily focused on longitudinal configurations, this work demonstrates a novel AM-enabled strategy that integrates directional compositional anisotropy, embedded metal–semiconductor interfaces, and scalable multi-material printing to realize TTE behavior. The approach offers a cost-effective and programmable pathway toward next-generation energy harvesting and thermal management systems. Full article

Eskebornite (CuFeSe₂), a member of the I–III–VI₂ ternary semiconductor family, was explored in this study as a potential thermoelectric material, offering new insights into its synthesis, structural characteristics, and transport behavior. Structurally analogous to chalcopyrite (CuFeS₂)—an extensively studied antiferromagnetic semiconductor—eskebornite remains relatively underexplored, particularly regarding its solid-state synthesis and thermoelectric performance. To address this gap, pure eskebornite was synthesized via mechanical alloying followed by hot pressing, a method that enables the fine control of its phase composition and microstructural features. The synthesized undoped CuFeSe₂ exhibited p-type nondegenerate semiconducting behavior, with electrical conductivity increasing monotonically over the temperature range of 323–623 K, indicative of thermally activated carrier transport. Simultaneously, a decreasing trend in thermal conductivity with temperature was observed, likely resulting from intensified phonon scattering, which serves to suppress heat transport and enhance the thermoelectric efficiency by maintaining a thermal gradient across the material. A peak in the Seebeck coefficient occurred between 473 and 523 K, suggesting the onset of intrinsic carrier excitation and a transition in dominant carrier transport mechanisms. The material exhibited a maximum power factor of 1.55 μWm⁻¹K⁻², while the dimensionless thermoelectric figure of merit (ZT) reached a peak value of 0.37 × 10⁻³ at 523 K. Although the ZT remains low, these results underscore the potential of eskebornite as a thermoelectric candidate, with substantial room for optimization through chemical doping, microstructural engineering, or nanostructuring approaches to enhance the carrier mobility and reduce the lattice thermal conductivity. Full article

The monitoring of peripheral electrical bioimpedance (EBI) variations is a promising method that has the potential to replace invasive or burdensome techniques for cardiovascular measurements. Segmental or continuous recording of peripheral pulse waves can serve as a basis for calculating prognostic markers like pulse wave velocity (PWV) or include parameters such as pulse transit time (PTT) or pulse arrival time (PAT) for noninvasive blood pressure (BP) estimation, as well as potentially novel cardiovascular risk indicators. However, several technical, analytical, and interpretative aspects need to be resolved before the EBI method can be adopted in clinical practice. Our goal was to investigate and improve the application of EBI, executing its comparison with other cardiovascular assessment methods in patients hospitalized for coronary catheterization procedures. Methods: We analyzed data from 44 non-acute patients aged 45–74 years who were hospitalized for coronary catheterization at East Tallinn Central Hospital between 2020 and 2021. The radial EBI and electrocardiogram (ECG) were measured simultaneously with central and contralateral pressure curves. The Savitzky–Golay filter was used for signal smoothing. The Hankel matrix decomposer was applied for the extraction of cardiac waveforms from multi-component signals. After extracting the cardiac component, a period detection algorithm was applied to EBI and blood pressure curves. Results: Seven points of interest were detected on the pressure and EBI curves, and four with good representativeness were selected for further analysis. The Spearman correlation coefficient was low for all but the central and distal pressure curve systolic upstroke time points. A high positive correlation was found between PWV measured both invasively and with EBI. The median value of complimentary pulse wave velocity (CPWV), a parameter proposed in the paper, was significantly lower in patients with normal coronaries compared to patients with any stage of coronary disease. Conclusions: With regard to wearable devices, the EBI-derived PAT can serve as a substrate for PWV calculations and cardiovascular risk assessment, although these data require further confirmation. Full article

The development of thermoelectric modules based on skutterudite materials requires stable, low-resistance interfaces between segments operating at different temperature ranges. This study investigates the microstructure, thermoelectric performance, and thermal stability of the following two joints: In_0.4Co₄Sb₁₂/Co₄Sb_10.8Te_0.6Se_0.6 (n-type) and CeFe₃Co_0.5Ni_0.5Sb₁₂/In_0.25Co₃FeSb₁₂ (p-type), fabricated by pulse plasma sintering (PPS). Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses confirmed the formation of well-bonded interfaces without pores or cracks. Aging at 773 K for 168 h did not result in morphological or chemical degradation, and phase composition remained unchanged according to X-ray diffraction (XRD). Surface Seebeck coefficient mapping and contact resistance measurements showed negligible changes after annealing, confirming electrical stability. To provide context for potential applications, theoretical energy conversion efficiencies were estimated based on measured thermoelectric properties, yielding 13.2% and 10.1% for the n- and p-type segmented legs, respectively. Additionally, measured coefficients of thermal expansion (CTE) indicated low mismatch between jointed materials, supporting good mechanical compatibility. The results demonstrate that the selected material combinations are thermally, chemically, and electrically stable and can be effectively used in segmented thermoelectric legs for intermediate-temperature applications. Full article