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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Spin-Dependent Thermoelectric Power of Nanoislands

The Seebeck effect explains the generation of electric voltage as a result of a temperature gradient. Its efficiency, defined as the ratio of the generated electric voltage to the temperature difference, is sensitive to local inhomogeneities that alter the scattering rate and the density of the conduction electrons. Spin-polarized Seebeck tunneling generates a distinct thermovoltage in spin-up and spin-down charge transport channels, which, as a key to spin caloritronics, focuses on transport phenomena related to spin and heat. Here, we report spatially resolved measurement of the spin-dependent thermovoltage in a tunneling junction formed by ferromagnetic Co nanoislands and a Ni tip using spin-dependent scanning tunneling thermovoltage microscopy (SP-STVthM). We resolve the nanoscale thermoelectric powers with respect to spin polarization, nanoisland size, stacking order of Co layers on a Cu substrate, and local sample heterogeneities. The observed thermally generated spin voltages are supported by first-principles and model calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A heat flux sensor leveraging the transverse Seebeck effect in elemental antimony

Certain configurations of anisotropic single crystal materials can generate a thermoelectric voltage orthogonal to an induced temperature gradient. This phenomenon is known as the Transverse Seebeck Effect (TSE) and can be leveraged to fabricate simple and robust heat flux sensors. Only a small number of materials have been considered as TSE-based transducers and, among these, few have been developed into sensors with ruggedization against chemical and mechanical degradation. Here, we report on the fabrication and characterization of a rugged TSE-based heat flux sensor using prismatic antimony single crystals. The heat flux sensor was tested under static and dynamic heating scenarios. The sensor has a linear responsivity of 16.8 µV/(W/cm2) to heat fluxes spanning more than two orders of magnitude and a time constant of 4.4 s. The sensor’s response to localized heating, probed with a laser scanning technique, validated that the transduction mechanism is primarily the TSE by ruling out a sizable contribution from the conventional Seebeck effect. Finite element analysis corroborated that components used in the sensor package are the primary determinants of the time constant and the decrement of the responsivity from its theoretical maximum. Design principles that may be applied to elicit a faster transient response or higher responsivity are proposed. Furthermore, the results establish single crystal antimony as a promising transducer material for heat flux measurement systems and demonstrate potential effects of ruggedization on sensor performance.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Conformal High-Power-Density Half-Heusler Thermoelectric Modules: A Pathway toward Practical Power Generators

Thermoelectric generators (TEGs) exploiting the Seebeck effect provide a promising solution for waste heat recovery. Among the large number of thermoelectric (TE) materials, half-Heusler (hH) alloys are leading candidates for medium- to high-temperature power generation applications. However, the fundamental challenge in this field has been inhomogeneous material properties at large wafer diameters, insufficient power output from the modules, and rigid form factors of TE modules. This has restricted the transition of TEGs in practical applications for over three decades. Here, we successfully demonstrate large diameter wafers with uniform TE properties, high-power conformal hH TE modules for high-temperature application, and their direct integration on flue gas platforms, such as cylindrical tubes, to form large area flexible TEGs. This new conformal architecture design provides a breakthrough toward medium-/high-temperature TEGs over the conventional BiTe- and polymer-based flexible TEG design. In this work, a variable fill factor and greater flexibility due to the conformal design result in higher device performance as compared to conventional rigid TEG devices. Modules with 72-couple hH legs exhibit a device high-power-density of 3.13 W cm-2 and a total output power of 56.6 W under a temperature difference of 570 degrees C. These results provide a promising pathway toward widespread utilization of thermoelectric technology into the waste heat recovery application and will have a significant impact on the development of practical thermal to electrical converters.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Thermoelectrics: From longitudinal to transverse

Thermoelectric power generation is a promising technology to realize a sustainable society because it directly converts thermal energy into electricity in a solid. Conventional thermoelectric generation is driven by the Seebeck effect, discovered by T.J. Seebeck in 1821, in which a charge current J c is generated in the direction parallel to a temperature gradient ∇T, the longitudinal geometry. Here, the ratio between the generated longitudinal electromotive force and applied ∇T is defined as the Seebeck coefficient. As shown in Figure 1A, a thermoelectric module based on the Seebeck effect typically consists of many pairs (128 for a 12V unit) of p-type and n-type conductors alternately arranged and connected in series. Since the Seebeck coefficient of a p-type (n-type) conductor is positive (negative), the thermopower in each element adds to the total output in the Seebeck module. This configuration is needed to achieve a practical voltage because each element only supplies millivolts but limits the use of thermoelectric generators. The efficiency of thermoelectric generators is characterized by the thermoelectric figure of merit, zT. Despite a 3-fold improvement in zT resulting from materials research over the last two decades, little progress has been made in their practical use; this is ascribed to the technological challenges in contact technology. The contacts on the hot side are subject to thermal degradation. All contacts (512 for a 12V unit) add electrical and thermal contact resistances that reduce the device efficiency to a fraction of that promised by the materials.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Enhanced thermoelectric performance of SnSe by controlled vacancy population

Abstract The thermoelectric performance of SnSe strongly depends on its low-energy electron band structure that provides high density of states in a narrow energy window due to the multi-valley valence band maximum (VBM). Angle-resolved photoemission spectroscopy measurements, in conjunction with first-principles calculations, reveal that the binding energy of the VBM of SnSe is tuned by the population of Sn vacancy, which is determined by the cooling rate during the sample growth. The VBM shift follows precisely the behavior of the thermoelectric power factor, while the effective mass is barely modified upon changing the population of Sn vacancies. These findings indicate that the low-energy electron band structure is closely correlated with the high thermoelectric performance of hole-doped SnSe, providing a viable route toward engineering the intrinsic defect-induced thermoelectric performance via the sample growth condition without an additional ex-situ process. Graphical Abstract

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Anomalous Nernst and Seebeck coefficients in epitaxial thin film Co 2 MnAl x Si 1 - x and Co 2 FeAl

Here we have measured the Seebeck and anomalous Nernst coefficients and corresponding transverse and longitudinal thermoelectric conductivities from 2 to 400 K in thin film (thickness t ~10 nm) Co 2 MnAl x Si 1-x (0 ≤ x ≤ 1) and Co 2 FeAl grown by molecular beam epitaxy (MBE). A large (-14 A m -1 K -1 at 300 K) anomalous component of the transverse thermoelectric conductivity is observed in Co 2 MnAl, especially as contrasted to Co 2 MnSi (0.28 A m -1 K -1 at 300 K). This enhancement is likely due to Weyl points close to the Fermi level of Co 2 MnAl which disappear as x decreases.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High thermoelectric figure of merit of porous Si nanowires from 300 to 700 K.

Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies. Among different high-temperature thermoelectrics materials, silicon nanowires possess the combined attributes of cost effectiveness and mature manufacturing infrastructures. Despite significant breakthroughs in silicon nanowires based thermoelectrics for waste heat conversion, the figure of merit (ZT) or operating temperature has remained low. Here, we report the synthesis of large-area, wafer-scale arrays of porous silicon nanowires with ultra-thin Si crystallite size of ~4 nm. Concurrent measurements of thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (S) on the same nanowire show a ZT of 0.71 at 700 K, which is more than ~18 times higher than bulk Si. This ZT value is more than two times higher than any nanostructured Si-based thermoelectrics reported in the literature at 700 K. Experimental data and theoretical modeling demonstrate that this work has the potential to achieve a ZT of ~1 at 1000 K.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Boride-based Ceramic Super-high Temperature Thermocouples in Harsh Environments (Final Scientific/Technical Report)

An electromotive force (emf) can be generated along a temperature gradient between the cold end and hot end of a thermoelectric material, termed the Seebeck effect. Based on the Seebeck effect, metallic alloys have been extensively employed to detect temperatures for centuries, named thermocouples. However, commercially available thermocouple alloys suffer from limitations, such as oxidation, chemical degradation, and poor long-term stability under high-temperature harsh environments. This DOE-funded project aimed to develop high-temperature, chemically tolerant thermocouples suitable for operation in extreme environments relevant to semiconducting thermoelectric materials. The research focused on boride-based semiconducting thermoelectric compounds as candidates for next-generation thermocouples with enhanced oxidation resistance, chemical stability, and thermal robustness under conditions representative of charcoal-fired electricity facilities. During the funded years, boride materials were synthesized using an arc-plasma technique under ambient air and argon atmospheres, enabling scalable and cost-effective production compared with conventional boride fabrication methods. The synthesized borides were processed into nanostructured powders, followed by consolidation into dense bulk materials using a spark plasma sintering (SPS) bottom-up approach. Comprehensive characterization was performed, including microstructural analysis, electrical transport measurements, and optical and thermal property evaluation. Both p-type and n-type boride electric legs were fabricated and integrated into boride-based thermocouples. The thermal and irradiation stabilities of the boride nanomaterials and bulk thermoelectric materials were systematically evaluated to assess suitability for long-term operation in harsh environments. Additionally, 12 students were broadly hands-on trained spanning the full research workflow, including word processing and technical editing (e.g., LATEX for manuscript and poster preparation), data collection and analysis (using Python and related libraries and hardware interfaces), sample preparation (including arc-plasma synthesis and spark plasma sintering), and advanced characterization techniques (such as X-ray diffraction, UV–vis spectroscopy, electron microscopy, differential thermal analysis (DTA), and Seebeck coefficient measurements, etc). Overall, this project demonstrated the feasibility of boride-based thermoelectric materials as durable high-temperature thermocouples, providing a promising pathway toward robust temperature sensing technologies aligned with DOE energy infrastructure and extreme-environment monitoring needs.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2024

An Advanced Cooling Device for Concentrated Photovoltaic Systems

Concentrated photovoltaics (CPV) have the potential to significantly enhance the energy conversion utilization of solar panels and reduce solar generation costs, making them a crucial area of advancement in solar power generation technology. However, the concentration of sunlight can lead to overheating of solar panels, resulting in a notable reduction in both the efficiency of solar power generation and the lifespan of the panels. This challenge remains the predominant technical hurdle that hinders the application of concentrated photovoltaic power generation technology. In this study, we propose a new cooling method for concentrated photovoltaic power generation systems via an integrated approach of incorporating Phase-Change Thermal Storage (PCTS) and Thermoelectric Generator (TEG) technology. This new method not only enhances the overall system's electricity generation efficiency but also effectively resolves the technical challenge of concentrated photovoltaic panel overheating issues, ensuring the continuity of concentrated photovoltaic power generation and extending the lifespan of solar panels and their components. In order to make full use of the wasted heat generated by photovoltaic power generation and effectively improve the power generation efficiency of the system, this work developed a phase change heat storage device based on a phase change material. This device uses the temperature difference between day and night to recover wasted heat from photovoltaic power generation. Through integration with the thermoelectric power generation system, thermal energy can be converted into electrical energy. In addition, the Peltier effect of thermoelectric materials is used to construct a photovoltaic panel overheating protection system, which significantly improves the reliability and service life of the system.

14 SOLAR ENERGY↗
DOE OSTI2024

An Advanced Cooling Device for Concentrated Photovoltaic Systems

Concentrated photovoltaics (CPV) have the potential to significantly enhance the energy conversion utilization of solar panels and reduce solar generation costs, making them a crucial area of advancement in solar power generation technology. However, the concentration of sunlight can lead to overheating of solar panels, resulting in a notable reduction in both the efficiency of solar power generation and the lifespan of the panels. This challenge remains the predominant technical hurdle that hinders the application of concentrated photovoltaic power generation technology. In this study, we propose a new cooling method for concentrated photovoltaic power generation systems via an integrated approach of incorporating Phase-Change Thermal Storage (PCTS) and Thermoelectric Generator (TEG) technology. This new method not only enhances the overall system's electricity generation efficiency but also effectively resolves the technical challenge of concentrated photovoltaic panel overheating issues, ensuring the continuity of concentrated photovoltaic power generation and extending the lifespan of solar panels and their components. In order to make full use of the wasted heat generated by photovoltaic power generation and effectively improve the power generation efficiency of the system, this work developed a phase change heat storage device based on a phase change material. This device uses the temperature difference between day and night to recover wasted heat from photovoltaic power generation. Through integration with the thermoelectric power generation system, thermal energy can be converted into electrical energy. In addition, the Peltier effect of thermoelectric materials is used to construct a photovoltaic panel overheating protection system, which significantly improves the reliability and service life of the system.

Gou, Yimeng↗
DOE OSTI2021

Negligible spin–charge conversion in Bi films and Bi/Ag(Cu) bilayers

Spin pumping experiments using ferromagnetic metals have reported highly efficient spin–charge conversion in Bi and at the Bi/Ag interface, possibly due to the inverse Rashba–Edelstein effect. However, longitudinal spin Seebeck effect experiments using the yttrium iron garnet ferrimagnetic insulator in Bi films and Bi/Ag bilayers do not show evidence of appreciable spin-to-charge conversion except the large Nernst signal inherent to Bi. These contrasting conclusions highlight the differences between magnetic metals and magnetic insulators as spin current injectors. Only the detected voltages that adhere to the inverse spin Hall effect of j C = (2e/h)θ SH j S x σ are due to spin currents.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Thermoelectric heating and cooling–integrated dishwasher with thermal energy storage

Household dishwashers must address several performance goals: maximize washing and drying performance, while minimizing cycle duration, energy consumption, and water consumption. This study develops and examines a novel thermoelectric heating and cooling (TEHC) system with thermal energy storage applied to a household dishwasher (DW), aiming to improve the energy and drying performance of a commercially-available dishwasher while maintaining its washing performance, water consumption, and cycle duration. Experimental testing conducted on the novel TEHC-DW system demonstrates an 8.7% reduction in total energy consumption, lowering the per-cycle usage to 0.952 kWh, and a 40% reduction in energy consumption for internal water heating. The novel TEHC-DW system also demonstrates better drying performance, shortening the drying time by 42% to reach the same remaining moisture content as a commercially-available system. In addition, a resistance-capacitance network model is developed that predicts total drying time, total energy consumption, and the highest temperature reached in the tub (53.4 °C). The model accuracy is validated with experimental data (within ±1 K), and the model functions as a design tool via a parametric study to evaluate the next-generation design and the effect of the number of thermoelectric modules and thermoelectric driving force (i.e., current). Overall, this study demonstrates the potential for TEHC technology to improve energy efficiency and drying performance in household dishwashers.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

The Importance of Avoided Crossings in Understanding High Valley Degeneracy in Half‐Heusler Thermoelectric Semiconductors

Abstract Half‐Heusler (hH) compounds are promising candidates for inexpensive, low‐toxicity thermoelectric materials. It is well known that engineering electronic bands with high valley degeneracy is an effective approach for enhancing the performance of thermoelectric materials, and there are several routes for achieving high valley degeneracy in hH systems. For instance, there are multiple locations in the first Brillouin zone where the valence band maximum can be found (at the Γ‐, L‐, or W‐point), and there are two competing low‐lying conduction bands at the X‐point, where the conduction band minimum is located. By converging the multiple valence band and conduction band extrema, the valley degeneracy, and hence, performance of these materials can be improved. Here, group theoretical and tight‐binding approaches, in addition to first‐principles density functional theory calculations, are used to study the chemical origins of various band extrema in both the n‐type and p‐type compounds, with particular focus on ZrNiSn and NbFeSb. Specifically, the importance of avoided crossings is explained. The results of this work can be used to better understand and develop design strategies for engineering better performing hH thermoelectrics.

Brod, Madison K.↗
DOE OSTI2024

Influence of metal organic framework glasses on thermoelectric properties of AgSb 0.96 Zn 0.04 Te 2 alloy

In recent years, a significant number of chalcogenides-based thermoelectric (TE) materials have been investigated theoretically and experimentally. However, the efficiency of TE materials is often limited by physical and chemical stability issues. Therefore, it is crucial to identify additive materials that can reduce thermal conductivity and improve the efficiency of crystalline TE materials. One well-known approach to lower thermal conductivity is introducing porosity into the material structure, which helps scatter phonon energy. Metal-organic framework (MOF) crystalline materials, known for their porosity and physical and chemical stability, offer unique advantages in TE applications. In this study, we investigate the influence of 20 weight% amorphous Zeolitic Imidazolate Framework (ZIF)-62 to p-type AgSb 0.96 Zn 0.04 Te 2 (ASTZ), a well-known TE material. We synthesized composites, ASTZ, ASTZ-Zn, and ASTZ-Co, by sintering ASTZ with amorphous ZIF-62(Zn) and ZIF-62(Co) respectively. The addition of amorphous ZIF-62(Zn) leads to a significant enhancement in the Seebeck coefficient of ASTZ increasing from 151 µV/K to 229 µV/K at 586K. Moreover, the thermal conductivity of the ASTZ TE materials drops drastically from 0.491 Wm -1 K -1 to around 0.22 Wm -1 K -1 at 623K with the addition of either amorphous ZIF-62(Zn) or ZIF-62(Co). Remarkably, ASTZ containing amorphous ZIF-62(Zn) achieves a maximum thermoelectric figure of merit (zT max ) of approximately 0.078 at 573K, surpassing any MOF-based thermoelectric material reported to date. In conclusion, these findings highlight the potential of amorphous ZIF-62 as an effective additive for enhancing the properties of thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Large language model-driven database for thermoelectric materials

Thermoelectric materials have the ability to convert waste heat into electricity, offering a valuable solution for energy harvesting. However, their widespread use is hindered by low conversion efficiency, the reliance on expensive rare earth elements, and the environmental and regulatory concerns associated with lead-based materials. A fast and cost-effective way to identify highly efficient thermoelectric materials is through data-driven methods. These approaches rely on robust and comprehensive datasets to train models. Although there are several databases on thermoelectric materials, there is still a need to collect and integrate experimental data from peer-reviewed research articles to capture diverse compositions and properties of materials. Here, in this work, we developed a comprehensive database of 7,123 thermoelectric compounds, containing key information such as chemical composition, structural detail, seebeck coefficient, electrical and thermal conductivity, power factor, and figure of merit (ZT). We used the GPTArticleExtractor workflow, powered by large language models (LLM), to extract and curate data automatically from the scientific literature published in Elsevier journals. This process enabled the creation of a structured database that addresses the challenges of manual data collection. The open access database could stimulate data-driven research and advance thermoelectric material analysis and discovery.

Database↗
DOE OSTI2021

Microstructure and heteroatom dictate the doping mechanism and thermoelectric properties of poly(alkyl-chalcogenophenes)

Heteroatom substitution can favorably alter electronic transport in conductive polymers to improve their thermoelectric performance. Here we report the spectroscopic, structural, and thermoelectric properties of poly(3–(3',7'-dimethyloctyl) chalcogenophenes) or P3RX doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), where the heteroatom [X = thiophene (T), selenophene (Se), tellurophene (Te)], the doping methodology, and extent of doping are systematically varied. Spectroscopic measurements reveal that while all P3RX polymers are appreciably doped, the doping mechanism is inherently different. Poly(3-hexylthiophene) (P3HT, used as a control) and poly(3–(3',7'-dimethyloctyl)tellurophene) (P3RTe) are doped primarily via integer charge transfer (ICT), whereas poly(3–(3',7'-dimethyloctyl)selenophene) (P3RSe) and poly(3–(3',7'-dimethyloctyl)thiophene) (P3RT) are doped via charge transfer complex (CTC) mechanisms. Despite these differences, all polymers saturate with roughly the same number of F4TCNQ counterions (1 dopant per 4 to 6 heterocycles), reinforcing the idea that the extent of charge transfer varies with the doping mechanism. Grazing incidence wide-angle x-ray scattering measurements provide insight into the structural driving forces behind different doping mechanisms—P3RT and P3RSe have similar microstructures in which F4TCNQ intercalates between the π-stacked backbones resulting in CTC doping (localized carriers), while P3HT and P3RTe have microstructures in which F4TCNQ intercalates in the alkyl side chain region, giving rise to ICT doping (delocalized carriers). These structural and spectroscopic observations shed light on why P3HT and P3RTe obtain electrical conductivities ca. 3 S/cm, while P3RT and P3RSe have conductivities <10–3 S/cm under the same thin film processing conditions. Ultimately, this work quantifies the effects of heteroatom, microstructural ordering, extent of doping, and doping mechanism, thereby providing rational guidance for designing future thermoelectric polymer-dopant systems.

36 MATERIALS SCIENCE↗