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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Proton irradiation effects on the thermoelectric properties in single-crystalline Bi nanowires

The effects of proton irradiation on the thermoelectric properties of Bi nanowires (Bi-NWs) were investigated. Single crystalline Bi-NWs were grown by the on-film formation of nanowires method. The devices based on individual Bi-NWs were irradiated with protons at different energies. The total number of displaced atoms was estimated using the Kinchin-Pease displacement model. The electric conductivity and Seebeck coefficient in the Bi-NW devices were investigated before and after proton irradiation at different temperatures. Although the Seebeck coefficient remained stable at various irradiation energies, the electrical conductivity significantly declined with increasing proton energy up to 40 MeV.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The effect of structural vacancies on the thermoelectric properties of (Cu₂Te){sub 1–x}(Ga₂Te₃) x

We have studied the effects of structural vacancies on the thermoelectric properties of the ternary compounds (Cu₂Te) 1–x (Ga₂Te₃) x (x=0.5, 0.55, 0.571, 0.6, 0.625, 0.667 and 0.75), which are solid solutions found in the pseudo-binary phase diagram for Cu₂Te and Ga₂Te₃, and possesses tunable structural vacancy concentrations. This materials system is not suitable due to the cost and scarcity of the constituent elements, but the vacancy behavior is well understood and will provide a valuable test case for other systems more suitable from the standpoint of cost and abundance of raw materials, which also possesses these vacancy features, but whose structural characterization is lacking at this stage. We find that the nominally defect free phase CuGaTe₂ possess the highest ZT (ZT=S²T/ρκ, where S is the Seebeck coefficient and ρ is the electrical resistivity κ is the thermal conductivity and T is the absolute temperature) which approaches 1 at 840 K and seems to continuously increase above this temperature. This result is due to the unexpectedly low thermal conductivity found for this material at high temperature. The low thermal conductivity was caused by strong Umklapp (thermally resistive scattering processes involving three phonons) phonon scattering. We find that due to the coincidentally strong scattering of carriers by the structural defects that higher concentrations of these features lead to poor electrical transport properties and decreased ZT. - Graphical abstract: Thermal conductivity and zT as a function of temperature for a series of compounds of the type (Cu₂Te) 1–x (Ga₂Te₃)x (x=0.5, 0.55, 0.571, 0.6, 0.625, 0.667 and 0.75). Highlights: • All the samples show p-type semiconducting behavior in the temperature dependence of the Seebeck and Hall coefficients. • The increased carrier concentration and the introduction of vacancies diminish the carrier mobility and power factor. • The low temperature k decreases significantly as the Ga₂Te₃ content increases due to increasing point defects. • The highest ZT ~ 1.0 at 840 K among the samples in this study was found in CuGaTe₂, which contains no vacancies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Thermoelectric Properties of Au- Containing Type-I Clathrates Ba8AuxGa16-3xGe30+2x

Type I clathrates, with compositions based on Ba8Ga16Ge30, are a class of promising thermoelectric materials due to their intrinsically low thermal conductivity. It has been demonstrated previously that the thermoelectric performance can be improved by transition metal substitution of the framework atoms. In this study, the effects of Au substitution for Ga/Ge on thermal and electrical transport properties of type I clathrate compounds have been investigated. Polycrystalline samples with a large range of Au content have been synthesized using conventional solid state techniques with the actual compositions of resulting materials approximately following Zintl-Klemm rules. The charge carrier type changes from electrons (n) to holes (p) as the Au content increases. The Seebeck coefficient (S) and power factor (S2/ where is the electrical resistivity) were improved by Au substitution and the resulting overall thermoelectric properties were enhanced by Au substitution with a thermoelectric figure of merit ZT ~ 0.63 at temperature T = 740 K for the composition Ba8Au5.47Ge39.96. The results presented herein show that Au-containing type I clathrates are promising p-type thermoelectric materials for high temperature applications.

Clathrates↗
DOE OSTI2019

High Thermoelectric Power Factor in Intermetallic Co Si Arising from Energy Filtering of Electrons by Phonon Scattering

Intermetallic compounds are usually poor thermoelectrics due to the high electronic densities of states at the Fermi level and concomitantly low Seebeck coefficients. However, intermetallic B20-type CoSi has been experimentally shown to attain remarkably large negative values of the Seebeck coefficient. We provide a theoretical explanation for this surprising fact using state-of-the-art first-principles calculations with explicit treatment of electron-phonon interactions. We find that the unique band structure of CoSi, which has both massless and heavy fermion bands near the Fermi level, facilitates strong scattering of the low-energy electrons by phonons into the heavy band, resulting in effective energy filtering and high thermal voltage. Our study predicts that a very large thermoelectric power factor of 80 μ W cm -1 K -2 or higher is experimentally accessible in the 300–600 K range and highlights a general principle for identifying intermetallic compounds with large thermopower.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Thermoelectric performance of co-doped SnTe with resonant levels

Some group III elements such as Indium are known to produce the resonant impurity states in IV-VI compounds. The discovery of these impurity states has opened up new ways for engineering the thermoelectric properties of IV-VI compounds. In this work, resonant states in SnTe were studied by co-doping with both resonant (In) and extrinsic (Ag, I) dopants. A characteristic nonlinear relationship was observed between the Hall carrier concentration (n{sub H}) and extrinsic dopant concentration (N{sub I}, N{sub Ag}) in the stabilization region, where a linear increase of dopant concentration does not lead to linear response in the measured n{sub H}. Upon substituting extrinsic dopants beyond a certain amount, the n{sub H} changed proportionally with additional dopants (Ag, I) (the doping region). The Seebeck coefficients are enhanced as the resonant impurity is introduced, whereas the use of extrinsic doping only induces minor changes. Modest zT enhancements are observed at lower temperatures, which lead to an increase in the average zT values over a broad range of temperatures (300–773 K). The improved average zT obtained through co-doping indicates the promise of fine carrier density control in maximizing the favorable effect of resonant levels for thermoelectric materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Electronic structure of epitaxial half-Heusler Co 1-x Ni x TiSb across the semiconductor to metal transition

In this paper, we report on the growth, electronic, and surface properties of the electron-doped half-Heusler series Co 1-x Ni x TiSb (001) grown by molecular beam epitaxy. High-quality epitaxial growth of thin films is achieved on InP (001) substrates using an InAlAs buffer layer for all nickel concentrations. The semiconductor to metal transition as a function of substitutional alloying was examined using electrical transport, Seebeck measurements, and angle-resolved photoemission spectroscopy (ARPES). Temperature-dependent electrical transport measurements of films with composition x ≤ 0.1 exhibit thermally activated behavior while x > 0.1 exhibit metallic behavior. Smooth, highly ordered film surfaces can be achieved following ex-situ transfer of the films and subsequent desorption of a sacrificial, protective antimony capping layer. Using this transfer technique, ARPES experiments were performed to investigate the effects of nickel alloying on the electronic band structure. Finally, an electron pocket is observed below the Fermi level at the bulk X point for compositions x > 0.1, in accordance with the crossover from semiconducting to metallic behavior observed in the transport measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Synthesis and evaluation of lead telluride/bismuth antimony telluride nanocomposites for thermoelectric applications

Heterogeneous nanocomposites of p-type bismuth antimony telluride (Bi{sub 2-x}Sb{sub x}Te{sub 3}) with lead telluride (PbTe) nanoinclusions have been prepared by an incipient wetness impregnation approach. The Seebeck coefficient, electrical resistivity, thermal conductivity and Hall coefficient were measured from 80 to 380 K in order to investigate the influence of PbTe nanoparticles on the thermoelectric performance of nanocomposites. The Seebeck coefficients and electrical resistivities of nanocomposites decrease with increasing PbTe nanoparticle concentration due to an increased hole concentration. The lattice thermal conductivity decreases with the addition of PbTe nanoparticles but the total thermal conductivity increases due to the increased electronic thermal conductivity. We conclude that the presence of nanosized PbTe in the bulk Bi{sub 2-x}Sb{sub x}Te{sub 3} matrix results in a collateral doping effect, which dominates transport properties. This study underscores the need for immiscible systems to achieve the decreased thermal transport properties possible from nanostructuring without compromising the electronic properties. - Graphical abstract: PbTe nanoparticles introduced into p-type Bi{sub 2}Te{sub 3} by incipient wetness results in decreased lattice thermal conductivity, but also acts as an electronic dopant, resulting in an overall decrease in thermoelectric performance. Highlights: Black-Right-Pointing-Pointer Composites of PbTe nanoparticles in Bi{sub 2-x}Sb{sub x}Te{sub 3} were formed by incipient wetness. Black-Right-Pointing-Pointer PbTe nanoparticles leads to decreased {kappa}{sub l}, consistent with phonon scattering. Black-Right-Pointing-Pointer PbTe nanoparticles lead to decreased S and {rho}, due to increased carriers. Black-Right-Pointing-Pointer Collateral doping from PbTe leads to decreased ZT with increasing concentration. Black-Right-Pointing-Pointer Immiscible systems are preferred for improved ZT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Oxygen adsorption and electronic transport properties of Fe-substituted YBaCo{sub 4}O{sub 7} compounds

Graphical abstract: - Highlights: • The conduction mechanism of YBaCo{sub 4}O{sub 7} system was established. • The effect of Fe substitution on the electronic transport was discussed. • The effect of oxygen adsorption/desorption processes on the transport properties was investigated. - Abstract: YBaCo{sub 4−x}Fe{sub x}O{sub 7} (0.0 ≤ x ≤ 0.8) samples were prepared by the solid-state reaction method and the effect of Fe substitution and oxygen adsorption/desorption on the electronic transport properties was investigated from room temperature to 900 °C. Fe for Co substitution results in a slight decline in the oxygen storage capacity at lower temperature (200–400 °C) and an increase of the phase-decomposition temperature at higher temperature (700–900 °C). Both the hole concentration and mobility are reduced in the Fe-containing compositions. Electrical resistivity, Seebeck coefficient, and conduction activation energy increase with the increasing Fe content. A close correlativity between oxygen adsorption and electronic transport behavior was observed in YBaCo{sub 4−x}Fe{sub x}O{sub 7} system. Oxygen adsorption decreases the electrical resistivity and Seebeck coefficients because of the increase of hole concentration at lower temperature and the phase decomposition at higher temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Processing and Thermoelectric Properties of TiNiSn Materials: A Review

The half-Heusler alloy TiNiSn is a promising material for high-temperature thermoelectric applications due to its good thermal stability and semiconductor-like electrical properties. Numerous synthesis techniques have been utilized to make TiNiSn, but a comparative study on its thermoelectric properties with respect to processing parameters has not been reported. Based on published experimental data, primary melting methods, such as arc melting or induction levitation melting, do not have a noticeable effect on the final thermoelectric properties, although choice of densification technique and annealing parameters correlate with each thermoelectric property. Thermal conductivity (2.47-6.08 W/m K), governed by lattice scattering effects, was maximized with high density from the spark plasma sintering (SPS) technique as well with low inclusions of metallic impurities and interstitial Ni defects from low-temperature, non-densified processes. Electrical resistivity (4.75-30 µΩ m), inversely related to thermal conductivity, is minimized when density is maximized and chemical defects are favorable from using SPS. All reported TiNiSn alloys contain intermetallic impurities, imparting a global trend of lowered electrical resistivity. Seebeck coefficient (− 273.20 to − 50.71 µV/K), proportional to electrical resistivity, is maximized when charge carrier concentration is minimized by eliminating phase impurities and Ni defects. Porosity has been observed to scatter low-energy electrons, which can increase Seebeck coefficient and electrical resistivity, although no statistical significance is found. An ideal TiNiSn alloy should have intermediate values of all interconnected thermoelectric properties to maximize ZT. Future research work should strive to include quantitative phase analysis to better characterize the contributions of Ni defects and impurity phases toward thermoelectric properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermoelectric Properties of Nanocrystalline Silicon Films Prepared by Hot-Wire and Plasma-Enhanced Chemical-Vapor Depositions

We report thermoelectric measurements over a temperature range of 80 K to 300 K of heavily boron-doped nanocrystalline silicon films prepared by hot-wire and plasma-enhanced chemical-vapor depositions. The nanocrystalline silicon films were doped by either gaseous deposition precursors or post-deposition ion implantation, resulting in boron concentrations ranging from 1 -2 x 10 20 cm -3 to 3 x 10 21 cm -3 . Reasonable values of the Seebeck coefficient and electrical conductivity were obtained at 300 K, comparable to many other research work. We also report thermal conductivity measurements on these films before doping, which we use to estimate their prospective thermoelectric efficiency. These measurements show values as low as 0.76 W/mK at 300 K which depend highly upon the grain sizes of the nc-Si films. We find that post-deposition doping by ion-implantation is more effective at enhancing the power factor than gaseous doping, and the power factor is only weakly dependent upon doping concentration for the films doped by ion implantation. We conclude that improvements of the thermoelectric efficiency of nc -Si films may depend more on a reduction of their thermal conductivity than doping optimization. The small grain sizes and the low thermal conductivity of the undoped nc -Si films accomplished in this work are therefore encouraging developments.

14 SOLAR ENERGY↗
DOE OSTI2011

Transport and optical properties of heavily hole-doped semiconductors BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2}

Experimental and theoretical studies of the electronic and optical properties of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} are reported. Experimental data include the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, and lattice constants for T{<=}300K, and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2x10{sup 18} and 5x10{sup 19} cm{sup -3} near room temperature for the selenide and telluride, respectively. The corresponding mobilities are near 15 cm{sup 2} V{sup -1} s{sup -1} for both materials. Optical measurements reveal a transition near 1.8 eV in BaCu{sub 2}Se{sub 2}, while no similar feature was observed for BaCu{sub 2}Te{sub 2}. First principles calculations indicate both materials are direct or nearly direct gap semiconductors with calculated gaps near 1.0 eV and 1.3 eV for the telluride and selenide, respectively, and predict weak absorption below about 2 eV. Transport properties calculated from the electronic structure are also presented. - Graphical abstract: Combined experimental and theoretical study of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} to assess potential for photovoltaic and thermoelectric applications. Highlights: > Comparative experimental and theoretical study of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2}. > Measured and calculated optical and transport properties. > Temperature dependence of lattice parameters and transport properties. > Hall and Seebeck coefficient measurements indicate heavy hole doping. > Good agreement between measured and modeled room temperature Seebeck coefficients.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Thermal creation of electron spin polarization in n-type silicon

Conversion of heat into a spin-current in electron doped silicon can offer a promising path for spin-caloritronics. Here, we create an electron spin polarization in the conduction band of n-type silicon by producing a temperature gradient across a ferromagnetic tunnel contact. The substrate heating experiments induce a large spin signal of 95 μV, corresponding to 0.54 meV spin-splitting in the conduction band of n-type silicon by Seebeck spin tunneling mechanism. The thermal origin of the spin injection has been confirmed by the quadratic scaling of the spin signal with the Joule heating current and linear dependence with the heating power.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Simultaneous enhancements of thermopower and electrical conductivity in quasi-one-dimensional α -YbAlB 4 single crystal

We report the thermoelectric properties of valence fluctuating material α-YbAlB 4 along a-, b-, and c-axes. The temperature dependence of the Seebeck coefficient for all axes shows negative peaks at around 250 K, which is close to the Kondo scale. Interestingly, the absolute value of the Seebeck coefficient along c-axis (-7 μV K -1 at 250 K) is larger than those along a- and b-axes (-50 μV K -1 at 250 K) although the electrical resistivity along c-axis is about four times lower than those along a- and b-axes. As a result, a very large thermoelectric power factor of ~14.5 mW m -1 K -2 is realized along c-axis at 200 K, which is ten times larger than those along a- and b-axes. The anisotropies in electrical resistivity and Seebeck coefficient, respectively, have different origins of Fermi surface and the c-f hybridization, realizing the simultaneous enhancements of thermopower and electrical conductivity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of preparation procedure and nanostructuring on the thermoelectric properties of the lead telluride-based material system AgPb{sub m}BiTe{sub 2+m} (BLST-m)

We report on the preparation and thermoelectric properties of the quaternary system AgPb{sub m}BiTe{sub 2+m} (Bismuth-Lead-Silver-Tellurium, BLST-m) that were nanostructured by mechanical alloying. Nanopowders of various compositions were compacted by three different methods: cold pressing/annealing, hot pressing, and short term sintering. The products are compared with respect to microstructure and sample density. The thermoelectric properties were measured: thermal conductivity in the temperature range from 300 K to 800 K and electrical conductivity and Seebeck coefficient between 100 K and 800 K. The compacting method and the composition had a substantial impact on carrier concentration and mobility as well as on the thermoelectric parameters. Room temperature Hall measurements yielded carrier concentrations in the order of 10{sup 19 }cm{sup −3}, slightly increasing with increasing content of the additive silver bismuth telluride to the lead telluride base. ZT values close to the ones of bulk samples were achieved. X-ray diffraction and transmission electron microscopy (TEM) showed macroscopically homogeneous distributions of the constituting elements inside the nanopowders ensembles, indicating a solid solution. However, high resolution transmission electron microscopy (HRTEM) revealed disorder on the nanoscale inside individual nanopowders grains.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

High figure of merit and thermoelectric properties of Bi-doped Mg{sub 2}Si{sub 0.4}Sn{sub 0.6} solid solutions

The study of Mg{sub 2}Si{sub 1−x}Sn{sub x}-based thermoelectric materials has received widespread attention due to a potentially high thermoelectric performance, abundant raw materials, relatively low cost of modules, and non-toxic character of compounds. In this research, Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}Bi{sub y} solid solutions with the nominal Bi content of 0≤y≤0.03 are prepared using a two-step solid state reaction followed by spark plasma sintering consolidation. Within this range of Bi concentrations, no evidence of second phase segregation was found. Bi is confirmed to occupy the Si/Sn sites in the crystal lattice and behaves as an efficient n-type dopant in Mg{sub 2}Si{sub 0.4}Sn{sub 0.6}. Similar to the effect of Sb, Bi doping greatly increases the electron density and the power factor, and reduces the lattice thermal conductivity of Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} solid solutions. Overall, the thermoelectric figure of merit of Bi-doped Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} solid solutions is improved by about 10% in comparison to values obtained with Sb-doped materials of comparable dopant content. This improvement comes chiefly from a marginally higher Seebeck coefficient of Bi-doped solid solutions. The highest ZT∼1.4 is achieved for the y=0.03 composition at 800 K. - Graphical abstract: (a)The relationship between electrical conductivity and power factor for Sb/Bi-doped Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}(Sb/Bi){sub y} (0<y≤0.03) solid solutions. (b)The correlation between temperature and the combination of the lattice and the bipolar terms of thermal conductivity of Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}Bi{sub y} (0≤y≤0.03) solid solutions. (c)Temperature dependent dimensionless figure of merit ZT of Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 1−y}Bi{sub y} (0≤y≤0.03) solid solutions. - Highlights: • Bi doped Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} showed 15% enhancement in the power factor as compared to Sb doped samples. • Bi doping reduced κ{sub ph} of Mg{sub 2.16}Si{sub 0.4}Sn{sub 0.6} due to stronger point defect scattering. • The highest ZT=1.4 at 800 K was achieved for Mg{sub 2.16}(Si{sub 0.4}Sn{sub 0.6}){sub 0.97}Bi{sub 0.03}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Improved Thermoelectric Performance of p-type Skutterudite YbxFe4-yPtySb12 (0.8 x 1, y = 1 and 0.5)

Thermoelectric performance of p-type skutterudites currently lags that of the corresponding n-type materials and improvement of this important class of materials have become the focus of considerable research effort world-wide. Recent calculations find promising band structural features in p-type skutterudite materials of the type AeFe3NiSb12 ( Ae = Ca, Sr, or Ba) which could potentially lead to excellent thermoelectric properties. Recent work on the Yb- filled analog of the these formulations (YbFe3NiSb12) however finds that the onset of intrinsic conduction at lower than expected temperatures deteriorates the performance above 500 K leading to poor performance in the temperature range of interest for automotive waste heat recovery applications. We therefore seek a way to increase the band gap in order to find a way to minimize the deleterious effects of intrinsic conduction. Here we present ab initio band structure calculations and the synthesis and thermoelectric properties of YbxFe4-yPtySb12 (0.8 x 1, y = 1 and 0.5). Ab initio calculations find that the band gap increases for YbFe3PtSb12 as compared to the Ni-containing analog, though no such increase in the band gap energy was found for as compared to YbFe3.5Ni0.5Sb12. The y = 1 samples shows a characteristic transition to intrinsic conduction with a decrease in the Seebeck coefficient at temperatures above 700 K. The increased carrier concentration in y = 0.5 virtually eliminates any evidence of intrinsic conduction and the Seebeck coefficients for these samples increase monotonically up to 750 K, resulting in power factors approaching 27 W/cm K2 at 750 K. These power factors combined with low thermal conductivity result in a ZT = 0.9 at 750 K for Yb0.95Fe3.5Pt0.5Sb12.

skutterudite↗
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↗