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Sample records for enhanced thermoelectric performance

  1. Enhanced thermoelectric performance of rough silicon nanowires.

    PubMed

    Hochbaum, Allon I; Chen, Renkun; Delgado, Raul Diaz; Liang, Wenjie; Garnett, Erik C; Najarian, Mark; Majumdar, Arun; Yang, Peidong

    2008-01-10

    Approximately 90 per cent of the world's power is generated by heat engines that use fossil fuel combustion as a heat source and typically operate at 30-40 per cent efficiency, such that roughly 15 terawatts of heat is lost to the environment. Thermoelectric modules could potentially convert part of this low-grade waste heat to electricity. Their efficiency depends on the thermoelectric figure of merit ZT of their material components, which is a function of the Seebeck coefficient, electrical resistivity, thermal conductivity and absolute temperature. Over the past five decades it has been challenging to increase ZT > 1, since the parameters of ZT are generally interdependent. While nanostructured thermoelectric materials can increase ZT > 1 (refs 2-4), the materials (Bi, Te, Pb, Sb, and Ag) and processes used are not often easy to scale to practically useful dimensions. Here we report the electrochemical synthesis of large-area, wafer-scale arrays of rough Si nanowires that are 20-300 nm in diameter. These nanowires have Seebeck coefficient and electrical resistivity values that are the same as doped bulk Si, but those with diameters of about 50 nm exhibit 100-fold reduction in thermal conductivity, yielding ZT = 0.6 at room temperature. For such nanowires, the lattice contribution to thermal conductivity approaches the amorphous limit for Si, which cannot be explained by current theories. Although bulk Si is a poor thermoelectric material, by greatly reducing thermal conductivity without much affecting the Seebeck coefficient and electrical resistivity, Si nanowire arrays show promise as high-performance, scalable thermoelectric materials.

  2. Engineering Nanostructural Routes for Enhancing Thermoelectric Performance: Bulk to Nanoscale.

    PubMed

    Mohanraman, Rajeshkumar; Lan, Tian-Wey; Hsiung, Te-Chih; Amada, Dedi; Lee, Ping-Chung; Ou, Min-Nan; Chen, Yang-Yuan

    2015-01-01

    Thermoelectricity is a very important phenomenon, especially its significance in heat-electricity conversion. If thermoelectric devices can be effectively applied to the recovery of the renewable energies, such as waste heat and solar energy, the energy shortage, and global warming issues may be greatly relieved. This review focusses recent developments on the thermoelectric performance of a low-dimensional material, bulk nanostructured materials, conventional bulk materials etc. Particular emphasis is given on, how the nanostructure in nanostructured composites, confinement effects in one-dimensional nanowires and doping effects in conventional bulk composites plays an important role in ZT enhancement.

  3. Engineering Nanostructural Routes for Enhancing Thermoelectric Performance: Bulk to Nanoscale

    PubMed Central

    Mohanraman, Rajeshkumar; Lan, Tian-Wey; Hsiung, Te-Chih; Amada, Dedi; Lee, Ping-Chung; Ou, Min-Nan; Chen, Yang-Yuan

    2015-01-01

    Thermoelectricity is a very important phenomenon, especially its significance in heat-electricity conversion. If thermoelectric devices can be effectively applied to the recovery of the renewable energies, such as waste heat and solar energy, the energy shortage, and global warming issues may be greatly relieved. This review focusses recent developments on the thermoelectric performance of a low-dimensional material, bulk nanostructured materials, conventional bulk materials etc. Particular emphasis is given on, how the nanostructure in nanostructured composites, confinement effects in one-dimensional nanowires and doping effects in conventional bulk composites plays an important role in ZT enhancement. PMID:26913280

  4. Enhanced Thermoelectric Performance of Hybrid Nanoparticle-Single-Molecule Junctions

    NASA Astrophysics Data System (ADS)

    Zerah-Harush, Elinor; Dubi, Yonatan

    2015-06-01

    It was recently suggested that molecular junctions would be excellent elements for efficient and high-power thermoelectric energy-conversion devices. However, experimental measurements of thermoelectric conversion in molecular junctions indicate rather poor efficiency, raising the question of whether it is indeed possible to design a setup for molecular junctions that will exhibit enhanced thermoelectric performance. Here we suggest that hybrid single-molecule-nanoparticle junctions can serve as efficient thermoelectric converters. The introduction of a semiconducting nanoparticle introduces new tuning capabilities, which are absent in conventional metal-molecule-metal junctions. Using a generic model for the molecule and nanoparticle with realistic parameters, we demonstrate that the thermopower can be of the order of hundreds of microvolts per degree kelvin and that the thermoelectric figure of merit can reach values close to 1, an improvement of 4 orders of magnitude over existing measurements. This favorable performance persists over a wide range of experimentally relevant parameters and is robust against disorder (in the form of surface-attached molecules) and against electron decoherence at the nanoparticle-molecule interface.

  5. Enhanced thermoelectric performance of carbon nanotubes at elevated temperature.

    PubMed

    Jiang, P H; Liu, H J; Fan, D D; Cheng, L; Wei, J; Zhang, J; Liang, J H; Shi, J

    2015-11-07

    The electronic and transport properties of the (10, 0) single-walled carbon nanotube are studied by performing first-principles calculations and semi-classical Boltzmann theory. It is found that the (10, 0) tube exhibits a considerably large Seebeck coefficient and electrical conductivity which are highly desirable for good thermoelectric materials. Together with the lattice thermal conductivity predicted by non-equilibrium molecular dynamics simulations, the room temperature ZT value of the (10, 0) tube is estimated to be 0.15 for p-type carriers. Moreover, the ZT value exhibits strong temperature dependence and can reach to 0.77 at 1000 K. Such a ZT value can be further enhanced to as high as 1.9 by isotopic substitution and chemisorptions of hydrogen on the tube surface.

  6. Phase Transition Enhanced Thermoelectric Performance in Copper Chalcogenides

    NASA Astrophysics Data System (ADS)

    Brown, David; Day, Tristan; Borup, Kasper; Christensen, Sebastian; Iversen, Bo; Snyder, G. Jeffrey

    2014-03-01

    Thermoelectric effects are characterized by the Seebeck coefficient or thermopower, which is related to the entropy associated with charge transport. For example, coupling spin entropy with the presence of charge carriers has enabled the enhancement of zT in cobalt oxides. We demonstrate that the coupling of a continuous phase transition to carrier transport in Cu2Se over a broad (360-410 K) temperature range results in a dramatic peak in thermopower, an increase in phonon and electron scattering, and a corresponding doubling of zT (to 0.7 at 406 K), and a similar but larger increase over a wider temperature range in the zT of Cu1.97Ag0.03Se (almost 1.0 at 400K). The use of structural entropy for enhanced thermopower could lead to new engineering approaches for thermoelectric materials with high zT and new green applications for thermoelectrics. Resnick Sustainibility Institute.

  7. Enhanced thermoelectric performance and anomalous seebeck effects in topological insulators.

    PubMed

    Xu, Yong; Gan, Zhongxue; Zhang, Shou-Cheng

    2014-06-06

    Improving the thermoelectric figure of merit zT is one of the greatest challenges in material science. The recent discovery of topological insulators (TIs) offers new promise in this prospect. In this work, we demonstrate theoretically that zT is strongly size dependent in TIs, and the size parameter can be tuned to enhance zT to be significantly greater than 1. Furthermore, we show that the lifetime of the edge states in TIs is strongly energy dependent, leading to large and anomalous Seebeck effects with an opposite sign to the Hall effect. These striking properties make TIs a promising material for thermoelectric science and technology.

  8. Enhanced thermoelectric performance in graphitic ZnO (0001) nanofilms

    NASA Astrophysics Data System (ADS)

    Li, Yan-Li; Fan, Zheyong; Zheng, Jin-Cheng

    2013-02-01

    We investigate the thermoelectric properties of ultrathin graphitic ZnO (0001) nanofilms based on first-principles calculations and Boltzmann transport theory. Staircase-like densities of states induced by quantum confinement in the nanofilms give rise to improved Seebeck coefficients and electrical conductivities. The optimized figure of merit for the single-layer graphitic ZnO (0001) nanofilm is estimated to be 0.6 at 300 K, which is about 120 times larger than that of bulk ZnO (0.005). Our results suggest that the graphitic ZnO (0001) nanofilms can be designed for high performance thermoelectric applications.

  9. Enhanced thermoelectric performance of SnSe based composites with carbon black nanoinclusions

    NASA Astrophysics Data System (ADS)

    Li, J. C.; Li, D.; Xu, W.; Qin, X. Y.; Li, Y. Y.; Zhang, J.

    2016-10-01

    Recently, a single crystalline SnSe and its sodium doped compound are reported to have an ultralow thermal conductivity and a high thermoelectric figure of merit. However, the highest thermoelectric figure of merit for polycrystalline SnSe-based materials is not larger than 1. In this study, we report a high thermoelectric figure of merit 1.21 at 903 K for poly-crystalline SnSe, realized by incorporating a proper proportion of carbon black as nano-inclusions. The exceptional performance arises from the enhanced power factor, coming from an increased electrical conductivity at high temperatures.

  10. Thermoelectric Performance Enhancement by Surrounding Crystalline Semiconductors with Metallic Nanoparticles

    NASA Technical Reports Server (NTRS)

    Kim, Hyun-Jung; King, Glen C.; Park, Yeonjoon; Lee, Kunik; Choi, Sang H.

    2011-01-01

    Direct conversion of thermal energy to electricity by thermoelectric (TE) devices may play a key role in future energy production and utilization. However, relatively poor performance of current TE materials has slowed development of new energy conversion applications. Recent reports have shown that the dimensionless Figure of Merit, ZT, for TE devices can be increased beyond the state-of-the-art level by nanoscale structuring of materials to reduce their thermal conductivity. New morphologically designed TE materials have been fabricated at the NASA Langley Research Center, and their characterization is underway. These newly designed materials are based on semiconductor crystal grains whose surfaces are surrounded by metallic nanoparticles. The nanoscale particles are used to tailor the thermal and electrical conduction properties for TE applications by altering the phonon and electron transport pathways. A sample of bismuth telluride decorated with metallic nanoparticles showed less thermal conductivity and twice the electrical conductivity at room temperature as compared to pure Bi2Te3. Apparently, electrons cross easily between semiconductor crystal grains via the intervening metallic nanoparticle bridges, but phonons are scattered at the interfacing gaps. Hence, if the interfacing gap is larger than the mean free path of the phonon, thermal energy transmission from one grain to others is reduced. Here we describe the design and analysis of these new materials that offer substantial improvements in thermoelectric performance.

  11. Enhanced thermoelectric performance of spark plasma sintered copper-deficient nanostructured copper selenide

    NASA Astrophysics Data System (ADS)

    Tyagi, Kriti; Gahtori, Bhasker; Bathula, Sivaiah; Jayasimhadri, M.; Singh, Niraj Kumar; Sharma, Sakshi; Haranath, D.; Srivastava, A. K.; Dhar, Ajay

    2015-06-01

    We report the thermoelectric properties of nanostructured Cu-deficient Cu2Se, which was synthesized by high energy ball milling followed by spark plasma sintering. Our method obtained a significant enhancement in the thermoelectric figure of merit (ZT), i.e., ~1.4 at 973 K, which was ~30% higher than its bulk counterpart. This enhancement in the thermoelectric performance was due mainly to a significant reduction in the lattice thermal conductivity, which was attributed to enhanced phonon scattering at various length scales by nanoscale defects as well as abundant nanograin boundaries. The nanoscale defects were characterized by transmission electron microscopy of the nanostructured Cu2-xSe samples, which formed the basis of the ZT enhancement.

  12. Enhanced thermoelectric performance in the Rashba semiconductor BiTeI through band gap engineering.

    PubMed

    Wu, Lihua; Yang, Jiong; Zhang, Tiansong; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2016-03-02

    Rashba semiconductors are of great interest in spintronics, superconducting electronics and thermoelectrics. Bulk BiTeI is a new Rashba system with a giant spin-split band structure. 2D-like thermoelectric response has been found in BiTeI. However, as optimizing the carrier concentration, the bipolar effect occurs at elevated temperature and deteriorates the thermoelectric performance of BiTeI. In this paper, band gap engineering in Rashba semiconductor BiTeI through Br-substitution successfully reduces the bipolar effect and improves the thermoelectric properties. By utilizing the optical absorption and Burstein-Moss-effect analysis, we find that the band gap in Rashba semiconductor BiTeI increases upon bromine substitution, which is consistent with theoretical predictions. Bipolar transport is mitigated due to the larger band gap, as the thermally-activated minority carriers diminish. Consequently, the Seebeck coefficient keeps increasing with a corresponding rise in temperature, and thermoelectric performance can thus be enhanced with a ZT  =  0.5 at 570 K for BiTeI0.88Br0.12.

  13. Enhanced thermoelectric performance in the Rashba semiconductor BiTeI through band gap engineering

    NASA Astrophysics Data System (ADS)

    Wu, Lihua; Yang, Jiong; Zhang, Tiansong; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2016-03-01

    Rashba semiconductors are of great interest in spintronics, superconducting electronics and thermoelectrics. Bulk BiTeI is a new Rashba system with a giant spin-split band structure. 2D-like thermoelectric response has been found in BiTeI. However, as optimizing the carrier concentration, the bipolar effect occurs at elevated temperature and deteriorates the thermoelectric performance of BiTeI. In this paper, band gap engineering in Rashba semiconductor BiTeI through Br-substitution successfully reduces the bipolar effect and improves the thermoelectric properties. By utilizing the optical absorption and Burstein-Moss-effect analysis, we find that the band gap in Rashba semiconductor BiTeI increases upon bromine substitution, which is consistent with theoretical predictions. Bipolar transport is mitigated due to the larger band gap, as the thermally-activated minority carriers diminish. Consequently, the Seebeck coefficient keeps increasing with a corresponding rise in temperature, and thermoelectric performance can thus be enhanced with a ZT  =  0.5 at 570 K for BiTeI0.88Br0.12.

  14. Enhanced thermoelectric performance of nanostructured topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect

    Sun, G. L.; Li, L. L.; Qin, X. Y. Li, D.; Zou, T. H.; Xin, H. X.; Ren, B. J.; Zhang, J.; Li, Y. Y.; Li, X. J.

    2015-02-02

    To enhance thermoelectric performance by utilizing topological properties of topological insulators has attracted increasing attention. Here, we show that as grain size decreases from microns to ∼80 nm in thickness, the electron mobility μ increases steeply from 12–15 cm{sup 2} V{sup −1} s{sup −1} to ∼600 cm{sup 2} V{sup −1} s{sup −1}, owing to the contribution of increased topologically protected conducting surfaces. Simultaneously, its lattice thermal conductivity is lowered by ∼30%–50% due to enhanced phonon scattering from the increased grain boundaries. As a result, thermoelectric figure of merit, ZT, of all the fine-grained samples is improved. Specifically, a maximum value of ZT = ∼0.63 is achieved for Bi{sub 2}Se{sub 3} at T = ∼570 K.

  15. Enhanced thermoelectric performance of amorphous Nb based oxynitrides

    NASA Astrophysics Data System (ADS)

    Music, Denis; Geyer, Richard W.; Hans, Marcus

    2015-12-01

    Using density functional theory, amorphous Nb0.27Ru0.06O0.56N0.10 was designed to facilitate a combination of an enhanced Seebeck coefficient and low electrical resistivity. Based on a positive Cauchy pressure, ductile behavior is expected. To verify these predictions, the transport and mechanical properties of amorphous thin films were evaluated. Metallic electrical resistivity and the Seebeck coefficient of -94 μV K-1 are obtained, which is consistent with our predictions. As there is no crack formation, these samples can be perceived as ductile. We demonstrate that the power factor can be increased by an order of magnitude, while keeping the thermal fatigue low.

  16. Remarkable enhancement in thermoelectric performance of BiCuSeO by Cu deficiencies.

    PubMed

    Liu, Yong; Zhao, Li-Dong; Liu, Yaochun; Lan, Jinle; Xu, Wei; Li, Fu; Zhang, Bo-Ping; Berardan, David; Dragoe, Nita; Lin, Yuan-Hua; Nan, Ce-Wen; Li, Jing-Feng; Zhu, Hongmin

    2011-12-21

    A significant enhancement of thermoelectric performance in layered oxyselenides BiCuSeO was achieved. The electrical conductivity and Seebeck coefficient of BiCu(1-x)SeO (x = 0-0.1) indicate that the carriers were introduced in the (Cu(2)Se(2))(2-) layer by Cu deficiencies. The maximum of electrical conductivity is 3 × 10(3) S m(-1) for Bicu(0.975)Seo at 650 °C, much larger than 470 S m(-1) for pristine BiCuSeO. Featured with very low thermal conductivity (∼0.5 W m(-1) K(-1)) and a large Seebeck coefficient (+273 μV K(-1)), ZT at 650 °C is significantly increased from 0.50 for pristine BiCuSeO to 0.81 for BiCu(0.975)SeO by introducing Cu deficiencies, which makes it a promising candidate for medium temperature thermoelectric applications.

  17. Enhanced thermoelectric performance of (Ba,In) double-filled skutterudites via randomly arranged micropores

    SciTech Connect

    Yu, Jian; Zhao, Wen-Yu E-mail: zhangqj@whut.edu.cn; Wei, Ping; Zhu, Wan-Ting; Zhou, Hong-Yu; Liu, Zhi-Yuan; Tang, Ding-Guo; Lei, Bing; Zhang, Qing-Jie E-mail: zhangqj@whut.edu.cn

    2014-04-07

    Porous (Ba,In) double-filled skutterudite materials with pore diameter about 1–4 μm were prepared by the decomposition of metastable ZnSb inclusions induced by the Zn sublimation. Transport measurements revealed that the Seebeck coefficient was increased due to the electron filtering effect induced by nanostructures in the surfaces of pores, the electrical conductivity was almost unchanged because of the percolation effect of conducted network composed of filled skutterudites, and the lattice thermal conductivity was dramatically suppressed due to the enhanced pore-edge boundary scattering of long-wavelength phonons. As a result, a maximum ZT of 1.36 was obtained, increased by 22.5% as compared to that of the bulk material with same chemical composition. This work demonstrates that by introducing porous structures is thought to be an efficient approach to improve the thermoelectric performance of bulk materials.

  18. Conducting grain boundaries enhancing thermoelectric performance in doped Mg2Si

    NASA Astrophysics Data System (ADS)

    Muthiah, Saravanan; Pulikkotil, Jiji; Srivastava, A. K.; Kumar, Ashok; Pathak, B. D.; Dhar, Ajay; Budhani, R. C.

    2013-07-01

    The thermoelectric properties of Pb doped Mg2Si, synthesized using reactive sintering employing spark plasma sintering, are investigated and are compared with other dopants reported in literature. While a moderate decrease in Seebeck coefficient and thermal conductivity is observed for 2 at. % of Pb doping in Mg2Si, a substantial enhancement in the material's thermoelectric figure-of-merit is observed, which is due to an enormous increase in its electrical conductivity. A brick-layer model is proposed to explain these results, wherein the inter-granular electronic conductivity is facilitated by Pb (or Mg2Pb) phases at grain boundaries, which is supported by microstructural evidences.

  19. Ultrahigh power factor and enhanced thermoelectric performance of individual Te/TiS2 nanocables.

    PubMed

    Li, Rui; Dui, Jingna; Fu, Yunlong; Xu, Yanling; Zhou, Shaomin

    2016-10-14

    Here, we present the successful fabrication of Te/TiS2 heterostructure nanocables with enhanced thermoelectric (TE) performance by a two-step route (a facile solvothermal approach for Te nanowires and then the Te nanowires are used as templates for the controllable growth of the Te/TiS2 nanocables), which is scalable for practical nanodevice applications. The heterostructure nanocables of different sizes can be prepared by varying the synthetic composition. Measurements of the Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ) are carried out on the same nanowires over a temperature range of 2-350 K. The heterostructure nanocables show an ultrahigh power factor (S(2) σ) with a maximum value of 0.58 Wm(-1) K(-2), which comes from a high electrical conductivity and a strongly enhanced Seebeck coefficient. The figure of merit (ZT) can reach 1.91 at room temperature from a single nanocable with a diameter of 60 nm, which is thought to contribute to the formation of the hetero-phase core/shell structure. These results are expected to open up new application possibilities in nanoscale TE devices based on individual Te/TiS2 heterostructure nanocables.

  20. Nanostructured Bi(2-x)Cu(x)S3 bulk materials with enhanced thermoelectric performance.

    PubMed

    Ge, Zhen-Hua; Zhang, Bo-Ping; Liu, Yong; Li, Jing-Feng

    2012-04-07

    Nanostructured Bi(2-x)Cu(x)S(3) (x = 0, 0.002, 0.005, 0.007, 0.01, 0.03) thermoelectric polycrystals were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) methods. The effect of Cu content on the microstructure and thermoelectric property of Bi(2-x)Cu(x)S(3) bulk samples was investigated. It was found that the subtle tailoring of Cu content could reduce both the electrical resistivity and the thermal conductivity at the same time, and consequently enhancing the thermoelectric property. A low electrical resistivity of 1.34 × 10(-4)Ω m(-1) and a low thermal conductivity of 0.52 W m(-1) K(-1) were obtained for the Bi(1.995)Cu(0.005)S(3) sample at 573 K. The low thermal conductivity is supposed to be due to the nanoscopic Cu-rich regions embedded in the host matrix. A peak ZT value of 0.34 at 573 K was achieved for the Bi(1.995)Cu(0.005)S(3) composition, which is the highest value in the Bi(2)S(3) system reported so far.

  1. Thermoelectric Performance Enhancement of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Composite Films by Addition of Dimethyl Sulfoxide and Urea

    NASA Astrophysics Data System (ADS)

    Kong, Fangfang; Liu, Congcong; Xu, Jingkun; Huang, Yao; Wang, Jianmin; Sun, Zhi

    2012-09-01

    Significant enhancement of thermoelectric (TE) performance was observed for free-standing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) composite films obtained from a PEDOT:PSS aqueous solution by simultaneous addition of dimethyl sulfoxide (DMSO) and different concentrations of urea. The electrical conductivity was enhanced from 8.16 S cm-1 to over 400 S cm-1, and the maximum Seebeck coefficient reached a value of 18.81 μV K-1 at room temperature. The power factor of the PEDOT:PSS composite films reached 8.81 μW m-1 K-2. The highest thermoelectric figure of merit ( ZT) in this study was 0.024 at room temperature, which is at least one order of magnitude higher than most polymers and bulk Si. These results indicate that the obtained composite films are a promising thermoelectric material for applications in thermoelectric refrigeration and thermoelectric microgeneration.

  2. Thermoelectric performance enhancement of calcium cobaltite through barium grain boundary segregation.

    PubMed

    Carvillo, Paulo; Chen, Yun; Boyle, Cullen; Barnes, Paul N; Song, Xueyan

    2015-09-21

    We report the dramatic increase of the Seebeck coefficient S and thermoelectric performance of calcium cobaltite Ca3Co4O9+δ ceramics through non-stoichiometric addition of minute amount of Ba. The nominal chemistry of polycrystal pellets are Ca3BaxCo4O9+δ (x = 0, 0.01, 0.05, and 0.1). At 323 K, S of Ca3Co4O9+δ is 135 μV K(-1), whereas S of Ba incorporated Ca3Ba0.05Co4O9+δ is 162.5 μV·K(-1), which is the highest S value near room temperature regime reported for calcium cobaltite. The increase of S for Ca3Ba0.05Co4O9+δ sample is accompanied by the decrease of the electrical resistivity ρ, resulting in high power factor S(2)/ρ of 843 μW·m(-1) K(-2) at 1007 K. Moreover, the thermal conductivities κ of Ca3BaxCo4O9+δ decrease with the increase of the Ba addition. The figure-of-merit ZT for Ca3Ba0.05Co4O9+δ reaches 0.52 at 1073 K and a factor of 2.5 increment in comparison with undoped Ca3Co4O9+δ. Nanostructure examinations show that the added Ba segregated at the Ca3Co4O9+δ grain boundaries, while the Ca3Co4O9+δ grain interior is free of Ba. Performance enhancement is attributed to the carrier filtering effect caused by the Ba segregation. In addition, Ba segregation promotes the better crystal alignment and the development of crystal texture.

  3. Synthesis, characterization and enhanced thermoelectric performance of structurally ordered cable-like novel polyaniline-bismuth telluride nanocomposite.

    PubMed

    Chatterjee, Krishanu; Mitra, Mousumi; Kargupta, Kajari; Ganguly, Saibal; Banerjee, Dipali

    2013-05-31

    Bismuth telluride (Bi₂Te₃) nanorods and polyaniline (PANI) nanoparticles have been synthesized by employing solvothermal and chemical oxidative processes, respectively. Nanocomposites, comprising structurally ordered PANI preferentially grown along the surface of a Bi₂Te₃ nanorods template, are synthesized using in situ polymerization. X-ray powder diffraction, UV-vis and Raman spectral analysis confirm the highly ordered chain structure of PANI on Bi₂Te₃ nanorods, leading to a higher extent of doping, higher chain mobility and enhancement of the thermoelectric performance. Above 380 K, the PANI-Bi₂Te₃ nanocomposite with a core-shell/cable-like structure exhibits a higher thermoelectric power factor than either pure PANI or Bi₂Te₃. At room temperature the thermal conductivity of the composite is lower than that of its pure constituents, due to selective phonon scattering by the nanointerfaces designed in the PANI-Bi₂Te₃ nanocable structures. The figure of merit of the nanocomposite at room temperature is comparable to the values reported in the literature for bulk polymer-based composite thermoelectric materials.

  4. Resonant enhancement in nanostructured thermoelectric performance via electronic thermal conductivity engineering

    NASA Astrophysics Data System (ADS)

    Patil, Urvesh; Muralidharan, Bhaskaran

    2017-01-01

    The use of an asymmetric broadening in the transport distribution, a characteristic of resonant structures, is proposed as a route to engineer a decrease in electronic thermal conductivity thereby enhancing the electronic figure of merit in nanostructured thermoelectrics. Using toy models, we first demonstrate that a decrease in thermal conductivity resulting from such an asymmetric broadening may indeed lead to an electronic figure of merit well in excess of 1000 in an idealized situation and in excess of 10 in a realistic situation. We then substantiate with realistic resonant structures designed using graphene nano-ribbons by employing a tight binding framework with edge correction that match density functional theory calculations under the local density approximation. The calculated figure of merit exceeding 10 in such realistic structures further reinforces the concept and sets a promising direction to use nano-ribbon structures to engineer a favorable decrease in the electronic thermal conductivity.

  5. Enhanced thermoelectric performance of Nb-doped SrTiO3 by nano-inclusion with low thermal conductivity.

    PubMed

    Wang, Ning; Chen, Haijun; He, Hongcai; Norimatsu, Wataru; Kusunoki, Michiko; Koumoto, Kunihito

    2013-12-09

    Authors reported an effective path to increase the electrical conductivity while to decrease the thermal conductivity, and thus to enhance the ZT value by nano-inclusions. By this method, the ZT value of Nb-doped SrTiO3 was enhanced 9-fold by yttria stabilized zirconia (YSZ) nano-inclusions. YSZ inclusions, located inside grain and in triple junction, can reduce the thermal conductivity by effective interface phonon scattering, enhance the electrical conductivity by promoting the abnormal grain growth, and thus lead to the obvious enhancement of ZT value, which strongly suggests that, it is possible to not only reduce the thermal conductivity, but also increase the electrical conductivity by nano-inclusions with low thermal conductivity. This study will give some useful enlightenment to the preparation of high-performance oxide thermoelectric materials.

  6. Computer modeling of thermoelectric generator performance

    NASA Technical Reports Server (NTRS)

    Chmielewski, A. B.; Shields, V.

    1982-01-01

    Features of the DEGRA 2 computer code for simulating the operations of a spacecraft thermoelectric generator are described. The code models the physical processes occurring during operation. Input variables include the thermoelectric couple geometry and composition, the thermoelectric materials' properties, interfaces and insulation in the thermopile, the heat source characteristics, mission trajectory, and generator electrical requirements. Time steps can be specified and sublimation of the leg and hot shoe is accounted for, as are shorts between legs. Calculations are performed for conduction, Peltier, Thomson, and Joule heating, the cold junction can be adjusted for solar radition, and the legs of the thermoelectric couple are segmented to enhance the approximation accuracy. A trial run covering 18 couple modules yielded data with 0.3% accuracy with regard to test data. The model has been successful with selenide materials, SiGe, and SiN4, with output of all critical operational variables.

  7. Enhanced thermoelectric performance of a quintuple layer of Bi{sub 2}Te{sub 3}

    SciTech Connect

    Zhang, J.; Liu, H. J. Cheng, L.; Wei, J.; Shi, J.; Tang, X. F.; Uher, C.

    2014-07-14

    The electronic structure of a quintuple layer (QL) of Bi{sub 2}Te{sub 3} is calculated using the first-principles pseudopotential method. It is found that the band gap of an isolated QL is considerably larger than that of bulk Bi{sub 2}Te{sub 3}. The electronic transport of the QL is, then, evaluated using the semiclassical Boltzmann theory within the relaxation time approximation. By fitting the energy surface from first-principles calculations, a suitable Morse potential is constructed and used to predicate the lattice thermal conductivity via equilibrium molecular dynamics simulations. By optimizing the carrier concentration of the system, the ZT of Bi{sub 2}Te{sub 3} QL can be enhanced to a relatively high value. Moreover, the ZT value exhibits strong temperature dependence and can reach as high as 2.0 at 800 K. This value can be further increased to 2.2 by the substitution of Bi atoms with Sb atoms, giving nominal formula of (Bi{sub 0.25}Sb{sub 0.75}){sub 2}Te{sub 3}. The significantly enhanced ZT value makes QL a very appealing candidate for thermoelectric applications.

  8. Key to enhance thermoelectric performance by controlling crystal size of strontium titanate

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Ye, Xinxin; Yaer, Xinba; Wu, Yin; Zhang, Boyu; Miao, Lei

    2015-09-01

    One-step molten salt synthesis process was introduced to fabricate nano to micrometer sized SrTiO3 powders in which effects of synthesis temperature, oxide-to-flux ratios and raw materials on the generation of SrTiO3 powders were examined. 100 nm or above sized pure SrTiO3 particles were obtained at relatively lower temperature of 900∘C. Micro-sized rhombohedral crystals with a maximum size of approximately 12 μm were obtained from SrCO3 or Sr(NO3)2 strontium source with 1:1 O/S ratio. Controlled crystal size and morphology of Nb-doped SrTiO3 particles are prepared by using this method to confirm the performance of thermoelectric properties. The Seebeck coefficient obtained is significantly high when compared with the reported data, and the high ratio of nano particles in the sample has a positive effect on the increase of Seebeck coefficient too, which is likely due to the energy filtering effect at large numbers of grain boundaries resulting from largely distributed structure.

  9. Enhanced thermoelectric performance in TiNiSn-based half-Heuslers.

    PubMed

    Downie, R A; MacLaren, D A; Smith, R I; Bos, J W G

    2013-05-14

    Thermoelectric figures of merit, ZT > 0.5, have been obtained in arc-melted TiNiSn-based ingots. This promising conversion efficiency is due to a low lattice thermal conductivity, which is attributed to excess nickel in the half-Heusler structure.

  10. Enhanced Thermoelectric Performance in Cu-Intercalated BiTeI by Compensation Weakening Induced Mobility Improvement.

    PubMed

    Wu, Lihua; Yang, Jiong; Chi, Miaofang; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2015-09-23

    The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization.

  11. Enhanced Thermoelectric Performance in Cu-Intercalated BiTeI by Compensation Weakening Induced Mobility Improvement

    PubMed Central

    Wu, Lihua; Yang, Jiong; Chi, Miaofang; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2015-01-01

    The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization. PMID:26394841

  12. Enhanced thermoelectric performance in Cu-intercalated BiTeI by compensation weakening induced mobility improvement

    SciTech Connect

    Wu, Lihua; Yang, Jiong; Chi, Miaofang; Wang, Shanyu; Wei, Ping; Zhang, Wenqing; Chen, Lidong; Yang, Jihui

    2015-09-23

    The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. Ultimately, these results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization.

  13. Enhanced thermoelectric performance in Cu-intercalated BiTeI by compensation weakening induced mobility improvement

    DOE PAGES

    Wu, Lihua; Yang, Jiong; Chi, Miaofang; ...

    2015-09-23

    The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by amore » factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. Ultimately, these results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization.« less

  14. Current Pulses Momentarily Enhance Thermoelectric Cooling

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey; Fleurial, Jean-Pierre; Caillat, Thierry; Chen, Gang; Yang, Rong Gui

    2004-01-01

    The rates of cooling afforded by thermoelectric (Peltier) devices can be increased for short times by applying pulses of electric current greater than the currents that yield maximum steady-state cooling. It has been proposed to utilize such momentary enhancements of cooling in applications in which diode lasers and other semiconductor devices are required to operate for times of the order of milliseconds at temperatures too low to be easily obtainable in the steady state. In a typical contemplated application, a semiconductor device would be in contact with the final (coldest) somewhat taller stage of a multistage thermoelectric cooler. Steady current would be applied to the stages to produce steady cooling. Pulsed current would then be applied, enhancing the cooling of the top stage momentarily. The principles of operation are straightforward: In a thermoelectric device, the cooling occurs only at a junction at one end of the thermoelectric legs, at a rate proportional to the applied current. However, Joule heating occurs throughout the device at a rate proportional to the current squared. Hence, in the steady state, the steady temperature difference that the device can sustain increases with current only to the point beyond which the Joule heating dominates. If a pulse of current greater than the optimum current (the current for maximum steady cooling) is applied, then the junction becomes momentarily cooled below its lowest steady temperature until thermal conduction brings the resulting pulse of Joule heat to the junction and thereby heats the junction above its lowest steady temperature. A theoretical and experimental study of such transient thermoelectric cooling followed by transient Joule heating in response to current pulses has been performed. The figure presents results from one of the experiments. The study established the essential parameters that characterize the pulse cooling effect, including the minimum temperature achieved, the maximum

  15. High Performance Bulk Thermoelectric Materials

    SciTech Connect

    Ren, Zhifeng

    2013-03-31

    Over 13 plus years, we have carried out research on electron pairing symmetry of superconductors, growth and their field emission property studies on carbon nanotubes and semiconducting nanowires, high performance thermoelectric materials and other interesting materials. As a result of the research, we have published 104 papers, have educated six undergraduate students, twenty graduate students, nine postdocs, nine visitors, and one technician.

  16. Enhancement of thermoelectric performance in composite materials through locally-modulated doping

    NASA Astrophysics Data System (ADS)

    Adams, Michael J.; Jin, Hyungyu; Heremans, Joseph P.

    2015-03-01

    Composites of organic or inorganic constituents are often considered as a way to yield high thermoelectric figure of merit. The limit of this approach is set by the effective medium theory, which demonstrates formally that a composite of two materials A and B cannot have higher figure of merit than the highest of either A or B, in the absence of interaction between A and B. In this work, we show that this limit can be lifted by introducing into a host material a second phase that behaves differently vis-a-vis electrons than vis-a-vis phonons. This phase consists of electrically and thermally insulating islands of material that locally dope the semiconducting host. Doped material near the islands provides electrically conductive volumes for charge carriers. Phonons, unaffected by local doping, are scattered by the islands. Thermopower is less affected by the doped regions than electrical conductivity, by an intrinsic mathematical property of the effective medium theory. We employ this concept in Bi1-xSbx alloys and in p-type (Bi1-xSbx)2 Te3 compounds, which are known as good thermoelectric materials at cryogenic and room temperatures, respectively. Experimental transport data and the local microscopic characterizations of the samples are presented. Supported by DOE US-China Clean Energy Research Center SubK 3002041929, and by AFOSR MURI FA9550-10-1-0533.

  17. Spinodally Decomposed PbSe-PbTe Nanoparticles for High-Performance Thermoelectrics: Enhanced Phonon Scattering and Unusual Transport Behavior.

    PubMed

    Kim, Min-Seok; Lee, Woo-Jin; Cho, Ki-Hyun; Ahn, Jae-Pyoung; Sung, Yun-Mo

    2016-07-26

    Dramatic enhancements in the figure of merit have been obtained in bulk thermoelectric materials by doping, band engineering, and nanostructuring. Especially, in p-type thermoelectrics, high figure of merits near 2.0 have been reported in a few papers through the reduction in lattice thermal conductivity and the advancement in power factors. However, there exists no report on the n-type systems showing high figure of merits because of their intrinsically low Seebeck coefficients. Here, we demonstrate that a nanostructured bulk n-type thermoelectric material that was assembled by sintering spinodally decomposed lead chalcogenide nanoparticles having a composition of PbSe0.5Te0.5 reaches a high figure of merit of 1.85. The spinodally decomposed nanoparticles permit our thermoelectric material to have extremely low lattice thermal conductivity and a high power factor as a result of nanostructuring, electronic optimization, insertion of an impurity phase and phase change in local areas. We propose that this interesting concept would be one of the promising approaches that overcome limitation arising from the fact that most parameters in the figure of merit are closely correlated.

  18. Unexpected high-temperature stability of β-Zn4Sb3 opens the door to enhanced thermoelectric performance.

    PubMed

    Lin, Jianping; Li, Xudong; Qiao, Guanjun; Wang, Zhao; Carrete, Jesús; Ren, Yang; Ma, Lingzhi; Fei, Youjian; Yang, Baifeng; Lei, Lei; Li, Ju

    2014-01-29

    β-Zn4Sb3 has one of the highest ZT reported for binary compounds, but its practical applications have been hindered by a reported poor stability. Here we report the fabrication of nearly dense single-phase β-Zn4Sb3 and a study of its thermoelectric transport coefficients across a wide temperature range. Around 425 K we find an abrupt decrease of its thermal conductivity. Past this point, Zn atoms can migrate from crystalline sites to interstitial positions; β-Zn4Sb3 becomes metastable and gradually decomposes into Zn(hcp) and ZnSb. However, above 565 K it recovers its stability; in fact, the damage caused by decomposition can be repaired completely. This is key to its excellent thermoelectric performance at high temperature: the maximum ZT reaches 1.4. Molecular dynamics simulations are used to shed light on the microscopic behavior of the material.

  19. Enhancement of thermopower of TAGS-85 high-performance thermoelectric materials by doping with the rare earth Dy

    SciTech Connect

    Levin, Evgenii; Budko, Serfuei; Schmidt-Rohr, Klaus

    2012-04-10

    Enhancement of thermopower is achieved by doping the narrow-band semiconductor Ag{sub 6.52}Sb{sub 6.52}Ge{sub 36.96}Te{sub 50} (acronym TAGS-85), one of the best p-type thermoelectric materials, with 1 or 2% of the rare earth dysprosium (Dy). Evidence for the incorporation of Dy into the lattice is provided by X-ray diffraction and increased orientation-dependent local fields detected by {sup 125}Te NMR spectroscopy. Since Dy has a stable electronic configuration, the enhancement cannot be attributed to 4f-electron states formed near the Fermi level. It is likely that the enhancement is due to a small reduction in the carrier concentration, detected by {sup 125}Te NMR spectroscopy, but mostly due to energy filtering of the carriers by potential barriers formed in the lattice by Dy, which has large both atomic size and localized magnetic moment. The interplay between the thermopower, the electrical resistivity, and the thermal conductivity of TAGS-85 doped with Dy results in an enhancement of the power factor (PF) and the thermoelectric figure of merit (ZT) at 730 K, from PF = 28 μW cm{sup −1} K{sup −2} and ZT ≤ 1.3 in TAGS-85 to PF = 35 μW cm{sup −1} K{sup −2} and ZT ≥ 1.5 in TAGS-85 doped with 1 or 2% Dy for Ge. This makes TAGS-85 doped with Dy a promising material for thermoelectric power generation.

  20. Chemical composition tuning in quaternary p-type Pb-chalcogenides--a promising strategy for enhanced thermoelectric performance.

    PubMed

    Yamini, Sima Aminorroaya; Wang, Heng; Gibbs, Zachary M; Pei, Yanzhong; Dou, Shi Xue; Snyder, G Jeffrey

    2014-02-07

    Recently a significant improvement in the thermoelectric performance of p-type ternary PbTe-PbSe and PbTe-PbS systems has been realized through alternating the electronic band structure and introducing nano-scale precipitates to bulk materials respectively. However, the quaternary system of PbTe-PbSe-PbS has received less attention. In the current work, we have excluded phase complexity by fabricating single phase sodium doped PbTe, alloyed with PbS up to its solubility limit which is extended to larger concentrations than in the ternary system of PbTe-PbS due to the presence of PbSe. We have presented a thermoelectric efficiency of approximately 1.6 which is superior to ternary PbTe-PbSe and PbTe-PbS at similar carrier concentrations and the binary PbTe, PbSe and PbS alloys. The quaternary system shows a larger Seebeck coefficient than the ternary PbTe-PbSe alloy, indicative of a wider band gap, valence band energy offset and heavier carriers effective mass. In addition, the existence of PbS in the alloy further reduces the lattice thermal conductivity originated from phonon scattering on solute atoms with high contrast atomic mass. Single phase quaternary PbTe-PbSe-PbS alloys are promising thermoelectric materials that provide high performance through adjusting the electronic band structure by regulating chemical composition.

  1. Optimizing the thermoelectric performance of zigzag and chiral carbon nanotubes

    PubMed Central

    2012-01-01

    Using nonequilibrium molecular dynamics simulations and nonequilibrium Green's function method, we investigate the thermoelectric properties of a series of zigzag and chiral carbon nanotubes which exhibit interesting diameter and chirality dependence. Our calculated results indicate that these carbon nanotubes could have higher ZT values at appropriate carrier concentration and operating temperature. Moreover, their thermoelectric performance can be significantly enhanced via isotope substitution, isoelectronic impurities, and hydrogen adsorption. It is thus reasonable to expect that carbon nanotubes may be promising candidates for high-performance thermoelectric materials. PMID:22325623

  2. The role of nanoscale defect features in enhancing the thermoelectric performance of p-type nanostructured SiGe alloys.

    PubMed

    Bathula, Sivaiah; Jayasimhadri, M; Gahtori, Bhasker; Singh, Niraj Kumar; Tyagi, Kriti; Srivastava, A K; Dhar, Ajay

    2015-08-07

    Despite SiGe being one of the most widely studied thermoelectric materials owing to its application in radioisotope thermoelectric generators (RTG), the thermoelectric figure-of merit (ZT) of p-type SiGe is still quite low, resulting in poor device efficiencies. In the present study, we report a substantial enhancement in ZT∼ 1.2 at 900 °C for p-type nanostructured Si80Ge20 alloys by creating several types of defect features within the Si80Ge20 nanostructured matrix in a spectrum of nano to meso-scale dimensions during its nanostructuring, by employing mechanical alloying followed by spark plasma sintering. This enhancement in ZT, which is ∼25% over the existing state-of-the-art value for a p-type nanostructured Si80Ge20 alloy, is primarily due to its ultralow thermal conductivity of ∼2.04 W m(-1) K(-1) at 900 °C, resulting from the scattering of low-to-high wavelength heat-carrying phonons by different types of defect features in a range of nano to meso-scale dimensions in the Si80Ge20 nanostructured matrix. These include point defects, dislocations, isolated amorphous regions, nano-scale grain boundaries and more importantly, the nano to meso-scale residual porosity distributed throughout the Si80Ge20 matrix. These nanoscale multi-dimensional defect features have been characterized by employing scanning and transmission electron microscopy and correlated with the electrical and thermal transport properties, based on which the enhancement of ZT has been discussed.

  3. Intriguing substitution of conducting layer triggered enhancement of thermoelectric performance in misfit-layered (SnS)1.2(TiS2)2

    NASA Astrophysics Data System (ADS)

    Yin, Cong; Hu, Qing; Wang, Guoyu; Huang, Tianyu; Zhou, Xiaoyuan; Zhang, Xiong; Dou, Yunwei; Kang, Bin; Tang, Jun; Liu, Ning; Ang, Ran

    2017-01-01

    We have systematically investigated the thermoelectric properties of misfit-layered chalcogenide (SnS)1.2(TiS2)2. Surprisingly, an unexpected Cu and Co substitution in the conducting TiS2 layer, acceptor dopant, can induce an exotic enhancement of thermoelectric performance. In particular, the value of dimensionless figure of merit ZT has increased by 33.3% and up to 0.42 at 720 K for Cu-substituted (SnS)1.2(Cu0.02Ti0.98S2)2. The present findings demonstrate that large effective mass and low carrier concentration are responsible for the emergence of large Seebeck coefficient and high power factor. Furthermore, the enhanced disorder effect due to the substitution accounts for the decrease of electronic thermal conductivity, while the increased phonon scattering of interlayer between SnS and TiS2 layers leads to the reduction of phononic thermal conductivity. Consequently, the Cu- and Co-substituted (SnS)1.2(TiS2)2 could be considered as a promising candidate of thermoelectric materials.

  4. Molybdenum, Tungsten, and Aluminium Substitution for Enhancement of the Thermoelectric Performance of Higher Manganese Silicides

    NASA Astrophysics Data System (ADS)

    Nhi Truong, D. Y.; Berthebaud, David; Gascoin, Franck; Kleinke, Holger

    2015-10-01

    An easy and efficient process involving ball milling under soft conditions and spark plasma sintering was used to synthesize higher manganese silicide (HMS)-based compounds, for example MnSi1.75Ge0.02, with different molybdenum, tungsten, and aluminium substitution. The x-ray diffraction patterns of the samples after sintering showed the main phase to be HMS with the presence of some side products. Molybdenum substitution enlarges the unit cells more than tungsten substitution, owing to its greater solubility in the HMS structure, whereas substitution with aluminium did not substantially alter the cell parameters. The electrical resistivity of HMS-based compounds was reduced by <10% by this substitution, because of increased carrier concentrations. Changes of the Seebeck coefficient were insignificant after molybdenum and aluminium substitution whereas tungsten substitution slightly reduced the thermopower of the base material by approximately 8% over the whole temperature range; this was ascribed to reduced carrier mobility as a result of enhanced scattering. Substitution with any combination of two of these elements resulted in no crucial modification of the electrical properties of the base material. Large decreases of lattice thermal conductivity were observed, because of enhanced phonon scattering, with the highest reduction up to 25% for molybdenum substitution; this resulted in a 20% decrease of total thermal conductivity, which contributed to improvement of the figure of merit ZT of the HMS-based materials. The maximum ZT value was approximately 0.40 for the material with 2 at.% molybdenum substitution at the Mn sites.

  5. High performance thermoelectrics from earth-abundant materials: enhanced figure of merit in PbS by second phase nanostructures.

    PubMed

    Zhao, Li-Dong; Lo, Shih-Han; He, Jiaqing; Li, Hao; Biswas, Kanishka; Androulakis, John; Wu, Chun-I; Hogan, Timothy P; Chung, Duck-Young; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2011-12-21

    Lead sulfide, a compound consisting of elements with high natural abundance, can be converted into an excellent thermoelectric material. We report extensive doping studies, which show that the power factor maximum for pure n-type PbS can be raised substantially to ~12 μW cm(-1) K(-2) at >723 K using 1.0 mol % PbCl(2) as the electron donor dopant. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding selected metal sulfide phases. The thermal conductivity at 723 K can be reduced by ~50%, 52%, 30%, and 42% through introduction of up to 5.0 mol % Bi(2)S(3), Sb(2)S(3), SrS, and CaS, respectively. These phases form as nanoscale precipitates in the PbS matrix, as confirmed by transmission electron microscopy (TEM), and the experimental results show that they cause huge phonon scattering. As a consequence of this nanostructuring, ZT values as high as 0.8 and 0.78 at 723 K can be obtained for nominal bulk PbS material. When processed with spark plasma sintering, PbS samples with 1.0 mol % Bi(2)S(3) dispersion phase and doped with 1.0 mol % PbCl(2) show even lower levels of lattice thermal conductivity and further enhanced ZT values of 1.1 at 923 K. The promising thermoelectric properties promote PbS as a robust alternative to PbTe and other thermoelectric materials.

  6. Enhanced low temperature thermoelectric performance of Ag-doped BiCuSeO

    NASA Astrophysics Data System (ADS)

    Tan, S. G.; Lei, Hechang; Shao, D. F.; Lv, H. Y.; Lu, W. J.; Huang, Y. N.; Liu, Y.; Yuan, B.; Zu, L.; Kan, X. C.; Song, W. H.; Sun, Y. P.

    2014-08-01

    We investigated the physical properties of the silver doped layered oxyselenides BiCu1-xAgxSeO (x = 0-0.4), which crystallize in an unusual intergrowth structure with [Cu2Se2]2- and [Bi2O2]2+ layers. The total thermal conductivity is decreased because the heavier Ag doping in BiCuSeO lattice decreased the lattice thermal conductivity. The undoped BiCuSeO exhibits a semiconducting behavior, and the Ag-doped BiCuSeO performs much improved electrical conductivity. Although Ag-doping causes a decreasing Seebeck coefficient, the significant increase of the electrical conductivity compensates the moderate decrease of the Seebeck coefficient, which leads to the strongly improved power factor values. Finally, the figure of merit is improved and reaches a maximum ˜0.07 at 300 K for the sample BiCu0.7Ag0.3SeO.

  7. High performance thermoelectric nanocomposite device

    DOEpatents

    Yang, Jihui; Snyder, Dexter D.

    2011-10-25

    A thermoelectric device includes a nanocomposite material with nanowires of at least one thermoelectric material having a predetermined figure of merit, the nanowires being formed in a porous substrate having a low thermal conductivity and having an average pore diameter ranging from about 4 nm to about 300 nm.

  8. Power factor enhancement in solution-processed organic n-type thermoelectrics through molecular design.

    PubMed

    Russ, Boris; Robb, Maxwell J; Brunetti, Fulvio G; Miller, P Levi; Perry, Erin E; Patel, Shrayesh N; Ho, Victor; Chang, William B; Urban, Jeffrey J; Chabinyc, Michael L; Hawker, Craig J; Segalman, Rachel A

    2014-06-04

    A new class of high-performance n-type organic thermoelectric materials, self-doping perylene diimide derivatives with modified side chains, is reported. These materials achieve the highest n-type thermoelectric performance of solution-processed organic materials reported to date, with power factors as high as 1.4 μW/mK(2). These results demonstrate that molecular design is a promising strategy for enhancing organic thermoelectric performance.

  9. Enhanced thermoelectric performance of a chalcopyrite compound CuIn3Se5−xTex (x = 0~0.5) through crystal structure engineering

    PubMed Central

    Lu, Yufu; Chen, Shaoping; Wu, Wenchang; Du, Zhengliang; Chao, Yimin; Cui, Jiaolin

    2017-01-01

    In this work the chalcopyrite CuIn3Se5−xTex (x = 0~0.5) with space group through isoelectronic substitution of Te for Se have been prepared, and the crystal structure dilation has been observed with increasing Te content. This substitution allows the anion position displacement ∆u = 0.25-u to be zero at x ≈ 0.15. However, the material at x = 0.1 (∆u = 0.15 × 10−3), which is the critical Te content, presents the best thermoelectric (TE) performance with dimensionless figure of merit ZT = 0.4 at 930 K. As x value increases from 0.1, the quality factor B, which informs about how large a ZT can be expected for any given material, decreases, and the TE performance degrades gradually due to the reduction in nH and enhancement in κL. Combining with the ZTs from several chalcopyrite compounds, it is believable that the best thermoelectric performance can be achieved at a certain ∆u value (∆u ≠ 0) for a specific space group if their crystal structures can be engineered. PMID:28057940

  10. Enhanced thermoelectric performance of a chalcopyrite compound CuIn3Se5‑xTex (x = 0~0.5) through crystal structure engineering

    NASA Astrophysics Data System (ADS)

    Lu, Yufu; Chen, Shaoping; Wu, Wenchang; Du, Zhengliang; Chao, Yimin; Cui, Jiaolin

    2017-01-01

    In this work the chalcopyrite CuIn3Se5‑xTex (x = 0~0.5) with space group through isoelectronic substitution of Te for Se have been prepared, and the crystal structure dilation has been observed with increasing Te content. This substitution allows the anion position displacement ∆u = 0.25-u to be zero at x ≈ 0.15. However, the material at x = 0.1 (∆u = 0.15 × 10‑3), which is the critical Te content, presents the best thermoelectric (TE) performance with dimensionless figure of merit ZT = 0.4 at 930 K. As x value increases from 0.1, the quality factor B, which informs about how large a ZT can be expected for any given material, decreases, and the TE performance degrades gradually due to the reduction in nH and enhancement in κL. Combining with the ZTs from several chalcopyrite compounds, it is believable that the best thermoelectric performance can be achieved at a certain ∆u value (∆u ≠ 0) for a specific space group if their crystal structures can be engineered.

  11. Enhanced thermoelectric properties of graphene oxide patterned by nanoroads.

    PubMed

    Zhou, Si; Guo, Yu; Zhao, Jijun

    2016-04-21

    The thermoelectric properties of two-dimensional (2D) materials are of great interest for both fundamental science and device applications. Graphene oxide (GO), whose physical properties are highly tailorable by chemical and structural modifications, is a potential 2D thermoelectric material. In this report, we pattern nanoroads on GO sheets with epoxide functionalization, and investigate their ballistic thermoelectric transport properties based on density functional theory and the nonequilibrium Green's function method. These graphene oxide nanoroads (GONRDs) are all semiconductors with their band gaps tunable by the road width, edge orientation, and the structure of the GO matrix. These nanostructures show appreciable electrical conductance at certain doping levels and enhanced thermopower of 127-287 μV K(-1), yielding a power factor 4-22 times of the graphene value; meanwhile, the lattice thermal conductance is remarkably reduced to 15-22% of the graphene value; consequently, attaining the figure of merit of 0.05-0.75. Our theoretical results are not only helpful for understanding the thermoelectric properties of graphene and its derivatives, but also would guide the theoretical design and experimental fabrication of graphene-based thermoelectric devices of high performance.

  12. Enhanced thermoelectric performance of β-Zn4Sb3 based nanocomposites through combined effects of density of states resonance and carrier energy filtering

    PubMed Central

    Zou, Tianhua; Qin, Xiaoying; Zhang, Yongsheng; Li, Xiaoguang; Zeng, Zhi; Li, Di; Zhang, Jian; Xin, Hongxing; Xie, Wenjie; Weidenkaff, Anke

    2015-01-01

    It is a major challenge to elevate the thermoelectric figure of merit ZT of materials through enhancing their power factor (PF) and reducing the thermal conductivity at the same time. Experience has shown that engineering of the electronic density of states (eDOS) and the energy filtering mechanism (EFM) are two different effective approaches to improve the PF. However, the successful combination of these two methods is elusive. Here we show that the PF of β-Zn4Sb3 can greatly benefit from both effects. Simultaneous resonant distortion in eDOS via Pb-doping and energy filtering via introduction of interface potentials result in a ~40% increase of PF and an approximately twofold reduction of the lattice thermal conductivity due to interface scattering. Accordingly, the ZT of β-Pb0.02Zn3.98Sb3 with 3 vol.% of Cu3SbSe4 nanoinclusions reaches a value of 1.4 at 648 K. The combination of eDOS engineering and EFM would potentially facilitate the development of high-performance thermoelectric materials. PMID:26666813

  13. Decoupling interrelated parameters for designing high performance thermoelectric materials.

    PubMed

    Xiao, Chong; Li, Zhou; Li, Kun; Huang, Pengcheng; Xie, Yi

    2014-04-15

    synergistically enhanced thermoelectric properties. This occurs through a significant reduction of thermal conductivity, without the deterioration of thermopower and electrical conductivity. In addition, we introduce the concept of spin entropy in wide band gap semiconductor nanocrystals, which acts to fully disentangle the otherwise interconnected quantities for synergistically optimized thermoelectric performance. Finally, we discuss a new concept we developed that is based on an ultrathin-nanosheet composite that we fabricated from ultrathin nanosheets of atomic thickness. These retain the original strong two-dimensional electron gas (2DEG) and allow for decoupled optimization of the three thermoelectric parameters, which improves thermoelectric performance.

  14. Heavily Doped PBSE with High Thermoelectric Performance

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey (Inventor); Wang, Heng (Inventor); Pei, Yanzhong (Inventor)

    2015-01-01

    The present invention discloses heavily doped PbSe with high thermoelectric performance. Thermoelectric property measurements disclosed herein indicated that PbSe is high zT material for mid-to-high temperature thermoelectric applications. At 850 K a peak zT (is) greater than 1.3 was observed when n(sub H) approximately 1.0 X 10(exp 20) cm(exp -3). The present invention also discloses that a number of strategies used to improve zT of PbTe, such as alloying with other elements, nanostructuring and band modification may also be used to further improve zT in PbSe.

  15. Enhanced thermoelectric performance driven by high-temperature phase transition in the phase change material Ge4SbTe5

    DOE PAGES

    Williams, Jared B.; Lara-Curzio, Edgar; Cakmak, Ercan; ...

    2015-05-15

    Phase change materials are identified for their ability to rapidly alternate between amorphous and crystalline phases and have large contrast in the optical/electrical properties of the respective phases. The materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase change materials researched today can be found on the pseudo-binary (GeTe)1-x(Sb2Te3)x tie-line. While many compounds on this tie-line have been recognized as thermoelectric materials, here we focus on Ge4SbTe5, a single phase compound just off of the (GeTe)1-x(Sb2Te3)x tie-line, that forms in a stable rocksalt crystal structure atmore » room temperature. We find that stoichiometric and undoped Ge4SbTe5 exhibits a thermal conductivity of ~1.2 W/m-K at high temperature and a large Seebeck coefficient of ~250 μV/K. The resistivity decreases dramatically at 623 K due to a structural phase transition which lends to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. In a more general sense the research presents evidence that phase change materials can potentially provide a new route to highly efficient thermoelectric materials for power generation at high temperature.« less

  16. High three dimensional thermoelectric performance from low dimensional bands

    SciTech Connect

    Singh, David J; Chen, Xin; Parker, David S

    2013-01-01

    Reduced dimensionality has long been regarded as an important strategy for increasing thermoelectric performance, for example in superlattices and other engineered structures. Here we point out and illustrate by examples that three dimensional bulk materials can be made to behave as if they were two dimensional from the point of view of thermoelectric performance. Implications for the discovery of new practical thermoelectrics are discussed.

  17. Optimal performance of a thermoelectric refrigerator

    SciTech Connect

    Goektun, S.

    1996-07-01

    By employing an externally and internally irreversible Carnot-like reversed heat engine model, the coefficient of performance and maximum cooling rate have been determined for a thermoelectric refrigerator. The irreversibilities can be characterized by a single parameter called the device-design parameter. The coefficient of performance and the cooling rate increase with an increase of the device-design parameter, which appears in the equations for maximum cooling rate and coefficient of performance.

  18. Enhanced Thermoelectric Power in Dual-Gated Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Wang, Chang-Ran; Lu, Wen-Sen; Hao, Lei; Lee, Wei-Li; Lee, Ting-Kuo; Lin, Feng; Cheng, I.-Chun; Chen, Jian-Zhang

    2011-10-01

    The thermoelectric power of a material, typically governed by its band structure and carrier density, can be varied by chemical doping that is often restricted by solubility of the dopant. Materials showing large thermoelectric power are useful for many industrial applications, such as the heat-to-electricity conversion and the thermoelectric cooling device. Here we show a full electric-field tuning of thermoelectric power in a dual-gated bilayer graphene device resulting from the opening of a band gap by applying a perpendicular electric field on bilayer graphene. We uncover a large enhancement in thermoelectric power at a low temperature, which may open up a new possibility in low temperature thermoelectric application using graphene-based device.

  19. Enhanced thermoelectric power in dual-gated bilayer graphene.

    PubMed

    Wang, Chang-Ran; Lu, Wen-Sen; Hao, Lei; Lee, Wei-Li; Lee, Ting-Kuo; Lin, Feng; Cheng, I-Chun; Chen, Jian-Zhang

    2011-10-28

    The thermoelectric power of a material, typically governed by its band structure and carrier density, can be varied by chemical doping that is often restricted by solubility of the dopant. Materials showing large thermoelectric power are useful for many industrial applications, such as the heat-to-electricity conversion and the thermoelectric cooling device. Here we show a full electric-field tuning of thermoelectric power in a dual-gated bilayer graphene device resulting from the opening of a band gap by applying a perpendicular electric field on bilayer graphene. We uncover a large enhancement in thermoelectric power at a low temperature, which may open up a new possibility in low temperature thermoelectric application using graphene-based device.

  20. Enhanced thermoelectric performance of In-substituted GeSb{sub 6}Te{sub 10} with homologous structure

    SciTech Connect

    Kosuga, Atsuko Matsuzawa, Mie; Fujii, Yousuke; Nakai, Kazuki; Funahashi, Ryoji; Tachizawa, Takuya; Kubota, Yoshiki; Kifune, Kouichi

    2014-08-01

    We studied the crystal structure and thermoelectric properties of polycrystalline GeIn{sub x}Sb{sub 6−x}Te{sub 10} (x = 0, 0.18, 0.3, and 0.6). Rietveld and Le Bail analyses showed that all compositions crystallized in trigonal structures with a 51-layer period. Substituting In decreased both the lattice and electronic thermal conductivity, as well as markedly increased the Seebeck coefficient. We ascribed this increase to increases in the effective mass of the carriers, likely caused by the formation of additional energy states near the Fermi level. In GeIn{sub 0.6}Sb{sub 5.4}Te{sub 10}, we found a maximum ZT of 0.75 at 710 K, 1.9 times higher than that of GeSb{sub 6}Te{sub 10}.

  1. Enhanced thermoelectric performance driven by high-temperature phase transition in the phase change material Ge4SbTe5

    SciTech Connect

    Williams, Jared B.; Lara-Curzio, Edgar; Cakmak, Ercan; Watkins, Thomas R.; Morelli, Donald T.

    2015-05-15

    Phase change materials are identified for their ability to rapidly alternate between amorphous and crystalline phases and have large contrast in the optical/electrical properties of the respective phases. The materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase change materials researched today can be found on the pseudo-binary (GeTe)1-x(Sb2Te3)x tie-line. While many compounds on this tie-line have been recognized as thermoelectric materials, here we focus on Ge4SbTe5, a single phase compound just off of the (GeTe)1-x(Sb2Te3)x tie-line, that forms in a stable rocksalt crystal structure at room temperature. We find that stoichiometric and undoped Ge4SbTe5 exhibits a thermal conductivity of ~1.2 W/m-K at high temperature and a large Seebeck coefficient of ~250 μV/K. The resistivity decreases dramatically at 623 K due to a structural phase transition which lends to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. In a more general sense the research presents evidence that phase change materials can potentially provide a new route to highly efficient thermoelectric materials for power generation at high temperature.

  2. Performance evaluation of an automotive thermoelectric generator

    NASA Astrophysics Data System (ADS)

    Dubitsky, Andrei O.

    Around 40% of the total fuel energy in typical internal combustion engines (ICEs) is rejected to the environment in the form of exhaust gas waste heat. Efficient recovery of this waste heat in automobiles can promise a fuel economy improvement of 5%. The thermal energy can be harvested through thermoelectric generators (TEGs) utilizing the Seebeck effect. In the present work, a versatile test bench has been designed and built in order to simulate conditions found on test vehicles. This allows experimental performance evaluation and model validation of automotive thermoelectric generators. An electrically heated exhaust gas circuit and a circulator based coolant loop enable integrated system testing of hot and cold side heat exchangers, thermoelectric modules (TEMs), and thermal interface materials at various scales. A transient thermal model of the coolant loop was created in order to design a system which can maintain constant coolant temperature under variable heat input. Additionally, as electrical heaters cannot match the transient response of an ICE, modelling was completed in order to design a relaxed exhaust flow and temperature history utilizing the system thermal lag. This profile reduced required heating power and gas flow rates by over 50%. The test bench was used to evaluate a DOE/GM initial prototype automotive TEG and validate analytical performance models. The maximum electrical power generation was found to be 54 W with a thermal conversion efficiency of 1.8%. It has been found that thermal interface management is critical for achieving maximum system performance, with novel designs being considered for further improvement.

  3. High Power Factor and Enhanced Thermoelectric Performance of SnTe-AgInTe2: Synergistic Effect of Resonance Level and Valence Band Convergence.

    PubMed

    Banik, Ananya; Shenoy, U Sandhya; Saha, Sujoy; Waghmare, Umesh V; Biswas, Kanishka

    2016-10-05

    Understanding the basis of electronic transport and developing ideas to improve thermoelectric power factor are essential for production of efficient thermoelectric materials. Here, we report a significantly large thermoelectric power factor of ∼31.4 μW/cm·K(2) at 856 K in Ag and In co-doped SnTe (i.e., SnAgxInxTe1+2x). This is the highest power factor so far reported for SnTe-based material, which arises from the synergistic effects of Ag and In on the electronic structure and the improved electrical transport properties of SnTe. In and Ag play different but complementary roles in modifying the valence band structure of SnTe. In-doping introduces resonance levels inside the valence bands, leading to a significant improvement in the Seebeck coefficient at room temperature. On the other hand, Ag-doping reduces the energy separation between light- and heavy-hole valence bands by widening the principal band gap, which also results in an improved Seebeck coefficient. Additionally, Ag-doping in SnTe enhances the p-type carrier mobility. Co-doping of In and Ag in SnTe yields synergistically enhanced Seebeck coefficient and power factor over a broad temperature range because of the synergy of the introduction of resonance states and convergence of valence bands, which have been confirmed by first-principles density functional theory-based electronic structure calculations. As a consequence, we have achieved an improved thermoelectric figure of merit, zT ≈ 1, in SnAg0.025In0.025Te1.05 at 856 K.

  4. Boundary Engineering for the Thermoelectric Performance of Bulk Alloys Based on Bismuth Telluride.

    PubMed

    Mun, Hyeona; Choi, Soon-Mok; Lee, Kyu Hyoung; Kim, Sung Wng

    2015-07-20

    Thermoelectrics, which transports heat for refrigeration or converts heat into electricity directly, is a key technology for renewable energy harvesting and solid-state refrigeration. Despite its importance, the widespread use of thermoelectric devices is constrained because of the low efficiency of thermoelectric bulk alloys. However, boundary engineering has been demonstrated as one of the most effective ways to enhance the thermoelectric performance of conventional thermoelectric materials such as Bi2 Te3 , PbTe, and SiGe alloys because their thermal and electronic transport properties can be manipulated separately by this approach. We review our recent progress on the enhancement of the thermoelectric figure of merit through boundary engineering together with the processing technologies for boundary engineering developed most recently using Bi2 Te3 -based bulk alloys. A brief discussion of the principles and current status of boundary-engineered bulk alloys for the enhancement of the thermoelectric figure of merit is presented. We focus mainly on (1) the reduction of the thermal conductivity by grain boundary engineering and (2) the reduction of thermal conductivity without deterioration of the electrical conductivity by phase boundary engineering. We also discuss the next potential approach using two boundary engineering strategies for a breakthrough in the area of bulk thermoelectric alloys.

  5. High performance p-type thermoelectric materials and methods of preparation

    NASA Technical Reports Server (NTRS)

    Caillat, Thierry (Inventor); Borshchevsky, Alexander (Inventor); Fleurial, Jean-Pierre (Inventor)

    2005-01-01

    The present invention is embodied in high performance p-type thermoelectric materials having enhanced thermoelectric properties and the methods of preparing such materials. In one aspect of the invention, p-type semiconductors of formula Zn4-xAxSb3-yBy wherein 0?x?4, A is a transition metal, B is a pnicogen, and 0?y?3 are formed for use in manufacturing thermoelectric devices with substantially enhanced operating characteristics and improved efficiency. Two methods of preparing p-type Zn4Sb3 and related alloys of the present invention include a crystal growth method and a powder metallurgy method.

  6. Designing high-performance layered thermoelectric materials through orbital engineering

    PubMed Central

    Zhang, Jiawei; Song, Lirong; Madsen, Georg K. H.; Fischer, Karl F. F.; Zhang, Wenqing; Shi, Xun; Iversen, Bo B.

    2016-01-01

    Thermoelectric technology, which possesses potential application in recycling industrial waste heat as energy, calls for novel high-performance materials. The systematic exploration of novel thermoelectric materials with excellent electronic transport properties is severely hindered by limited insight into the underlying bonding orbitals of atomic structures. Here we propose a simple yet successful strategy to discover and design high-performance layered thermoelectric materials through minimizing the crystal field splitting energy of orbitals to realize high orbital degeneracy. The approach naturally leads to design maps for optimizing the thermoelectric power factor through forming solid solutions and biaxial strain. Using this approach, we predict a series of potential thermoelectric candidates from layered CaAl2Si2-type Zintl compounds. Several of them contain nontoxic, low-cost and earth-abundant elements. Moreover, the approach can be extended to several other non-cubic materials, thereby substantially accelerating the screening and design of new thermoelectric materials. PMID:26948043

  7. Performance of Novel Thermoelectric Cooling Module Depending on Geometrical Factors

    NASA Astrophysics Data System (ADS)

    Derebasi, Naim; Eltez, Muhammed; Guldiken, Fikret; Sever, Aziz; Kallis, Klaus; Kilic, Halil; Ozmutlu, Emin N.

    2015-06-01

    A geometrical shape factor was investigated for optimum thermoelectric performance of a thermoelectric module using finite element analysis. The cooling power, electrical energy consumption, and coefficient of performance were analyzed using simulation with different current values passing through the thermoelectric elements for varying temperature differences between the two sides. A dramatic increase in cooling power density was obtained, since it was inversely proportional to the length of the thermoelectric legs. An artificial neural network model for each thermoelectric property was also developed using input-output relations. The models including the shape factor showed good predictive capability and agreement with simulation results. The correlation of the models was found to be 99%, and the overall prediction error was in the range of 1.5% and 1.0%, which is within acceptable limits. A thermoelectric module was produced based on the numerical results and was shown to be a promising device for use in cooling systems.

  8. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    SciTech Connect

    Avery, Azure D.; Zhou, Ben H.; Lee, Jounghee; Lee, Eui -Sup; Miller, Elisa M.; Ihly, Rachelle; Wesenberg, Devin; Mistry, Kevin S.; Guillot, Sarah L.; Zink, Barry L.; Kim, Yong -Hyun; Blackburn, Jeffrey L.; Ferguson, Andrew J.

    2016-04-04

    Thermoelectric power generation, allowing recovery of part of the energy wasted as heat, is emerging as an important component of renewable energy and energy efficiency portfolios. Although inorganic semiconductors have traditionally been employed in thermoelectric applications, organic semiconductors garner increasing attention as versatile thermoelectric materials. Here we present a combined theoretical and experimental study suggesting that semiconducting single-walled carbon nanotubes with carefully controlled chirality distribution and carrier density are capable of large thermoelectric power factors, higher than 340 μW m-1 K-2, comparable to the best-performing conducting polymers and larger than previously observed for carbon nanotube films. Furthermore, we demonstrate that phonons are the dominant source of thermal conductivity in the networks, and that our carrier doping process significantly reduces the thermal conductivity relative to undoped networks. As a result, these findings provide the scientific underpinning for improved functional organic thermoelectric composites with carbon nanotube inclusions.

  9. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    DOE PAGES

    Avery, Azure D.; Zhou, Ben H.; Lee, Jounghee; ...

    2016-04-04

    Thermoelectric power generation, allowing recovery of part of the energy wasted as heat, is emerging as an important component of renewable energy and energy efficiency portfolios. Although inorganic semiconductors have traditionally been employed in thermoelectric applications, organic semiconductors garner increasing attention as versatile thermoelectric materials. Here we present a combined theoretical and experimental study suggesting that semiconducting single-walled carbon nanotubes with carefully controlled chirality distribution and carrier density are capable of large thermoelectric power factors, higher than 340 μW m-1 K-2, comparable to the best-performing conducting polymers and larger than previously observed for carbon nanotube films. Furthermore, we demonstrate thatmore » phonons are the dominant source of thermal conductivity in the networks, and that our carrier doping process significantly reduces the thermal conductivity relative to undoped networks. As a result, these findings provide the scientific underpinning for improved functional organic thermoelectric composites with carbon nanotube inclusions.« less

  10. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Avery, Azure D.; Zhou, Ben H.; Lee, Jounghee; Lee, Eui-Sup; Miller, Elisa M.; Ihly, Rachelle; Wesenberg, Devin; Mistry, Kevin S.; Guillot, Sarah L.; Zink, Barry L.; Kim, Yong-Hyun; Blackburn, Jeffrey L.; Ferguson, Andrew J.

    2016-04-01

    Thermoelectric power generation, allowing recovery of part of the energy wasted as heat, is emerging as an important component of renewable energy and energy efficiency portfolios. Although inorganic semiconductors have traditionally been employed in thermoelectric applications, organic semiconductors garner increasing attention as versatile thermoelectric materials. Here we present a combined theoretical and experimental study suggesting that semiconducting single-walled carbon nanotubes with carefully controlled chirality distribution and carrier density are capable of large thermoelectric power factors, higher than 340 μW m-1 K-2, comparable to the best-performing conducting polymers and larger than previously observed for carbon nanotube films. Furthermore, we demonstrate that phonons are the dominant source of thermal conductivity in the networks, and that our carrier doping process significantly reduces the thermal conductivity relative to undoped networks. These findings provide the scientific underpinning for improved functional organic thermoelectric composites with carbon nanotube inclusions.

  11. Enhancing the thermoelectric figure of merit in engineered graphene nanoribbons

    PubMed Central

    Sangtarash, Sara; Lambert, Colin J

    2015-01-01

    Summary We demonstrate that thermoelectric properties of graphene nanoribbons can be dramatically improved by introducing nanopores. In monolayer graphene, this increases the electronic thermoelectric figure of merit ZT e from 0.01 to 0.5. The largest values of ZT e are found when a nanopore is introduced into bilayer graphene, such that the current flows from one layer to the other via the inner surface of the pore, for which values as high as ZT e = 2.45 are obtained. All thermoelectric properties can be further enhanced by tuning the Fermi energy of the leads. PMID:26171293

  12. Enhanced thermoelectric performance of Cu2Se/Bi0.4Sb1.6Te3 nanocomposites at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Li, Y. Y.; Qin, X. Y.; Li, D.; Zhang, J.; Li, C.; Liu, Y. F.; Song, C. J.; Xin, H. X.; Guo, H. F.

    2016-02-01

    Bi2Te3-based thermoelectric materials with large thermoelectric figure of merit, ZT, at elevated temperatures are advantageous in power generation by using the low-grade waste heat. Here, we show that incorporation of small proportion (0.3 vol. %) of nanophase Cu2Se into BiSbTe matrix causes an enhanced high-temperature thermopower due to elevated energy filtering of carriers and inhibition of minority transport besides enhanced phonon blocking from scattering at interfaces, which concurrently result in an ˜20% increase in the power factor and an ˜60% reduction in the lattice thermal conductivity at 488 K. As a result, ZT = 1.6 is achieved at 488 K in the composite system with 0.3 vol. % of Cu2Se. Significantly, its ZT is larger than unit in broad high-temperature range (e.g., ZT = 1.3 at 400 K and ZT = 1.6 at 488 K), which makes this material to be attractive for applications in energy harvesting from the low-grade waste heat.

  13. Wearable and flexible thermoelectric generator with enhanced package

    NASA Astrophysics Data System (ADS)

    Francioso, L.; De Pascali, C.; Taurino, A.; Siciliano, P.; De Risi, A.

    2013-05-01

    Present work shows recent progresses in thin film-based flexible and wearable thermoelectric generator (TEG), finalized to support energy scavenging and local storage for low consumption electronics in Ambient Assisted Living (AAL) applications and buildings integration. The proposed TEG is able to recover energy from heat dispersed into the environment converting a thermal gradient to an effective electrical energy available to power ultra-low consumption devices. A low cost fabrication process based on planar thin-film technology was optimized to scale down the TEG dimensions to micrometer range. The prototype integrates 2778 thermocouples of sputtered Sb2Te3 and Bi2Te3 thin films (1 μm thick) on an area of 25 cm2. The electrical properties of thermoelectric materials were investigated by Van der Pauw measurements. Transfer Length Method (TLM) analysis was performed on three different multi-layer contact schemes in order to select the best solution to use for the definition of the contact pads realized on each section of the thermoelectric array configuration to allow electrical testing of single production areas. Kapton polyimide film was used as flexible substrate in order to add comfortable lightweight and better wearability to the device. The realized TEG is able to autonomously recover the thermal gradient useful to thermoelectric generation thanks to an appropriate package designed and optimized by a thermal analysis based on finite element method (FEM). The proposed package solution consists in coupling the module realized onto Kapton foil to a PDMS layer opportunely molded to thermally insulate TEG cold junctions and enhance the thermal gradient useful for the energy scavenging. Simulations results were compared to experimental tests performed by a thermal infrared camera, in order to evaluate the real performance of the designed package. First tests conducted on the realized TEG indicate that the prototype is able to recover about 5°C between hot and

  14. Enhanced thermoelectric performance in zinc substituted p-type filled skutterudites CeFe{sub 4-x}Zn{sub x}Sb{sub 12}

    SciTech Connect

    Tan Gangjian; Wang Shanyu; Li Han; Yan Yonggao; Tang Xinfeng

    2012-03-15

    In this study, Zn-substituted polycrystalline skutterudites CeFe{sub 4-x}Zn{sub x}Sb{sub 12} (x=0, 0.05, 0.1, 0.2, 0.3) were successfully prepared by a traditional melting-annealing method. The solubility of Zn in Fe site is {approx}1.2%, exceeding which trace amount of ZnSb phase can be detected in the XRD. This ZnSb impurity phase, with size of several hundred nanometers for the sample with x=0.2 but showing surprisingly small size of {approx}10 nm for the sample with x=0.3, selectively distributes on the grain boundaries. In particular, the introduction of Zn in Fe site effectively improves the Seebeck coefficient in a manner of enhancement in hole effective mass, but it has negligible influence on both electrical and thermal conductivities though the hole concentration is increased. Consequently the corresponding improvement in power factor leads to an improved thermoelectric figure of merit (ZT) of 0.9 at 800 K for the sample with x=0.1, which is {approx}15% higher than that of Zn-free sample. This study demonstrates a favorable effect of Zn iso-substitution and opens a new strategy to improve the thermoelectric properties of p-type Fe-based skutterudites beyond the sole phonon engineering. - Graphical abstract: (a)-(c) ZnSb nanoinclusions emerge when Zn exceeds its solubility limit. (d), (e) The introduction of Zn boosts the Seebeck coefficient and thus enhances the ZT value. Highlights: Black-Right-Pointing-Pointer Zn is successfully employed to substitute Fe atom for the first time. Black-Right-Pointing-Pointer ZnSb nanoinclusions emerge when Zn exceeds its solubility limit {approx}0.12. Black-Right-Pointing-Pointer The introduction of Zn boosts the Seebeck coefficient and enhances the ZT value.

  15. Tellurium as a high-performance elemental thermoelectric

    PubMed Central

    Lin, Siqi; Li, Wen; Chen, Zhiwei; Shen, Jiawen; Ge, Binghui; Pei, Yanzhong

    2016-01-01

    High-efficiency thermoelectric materials require a high conductivity. It is known that a large number of degenerate band valleys offers many conducting channels for improving the conductivity without detrimental effects on the other properties explicitly, and therefore, increases thermoelectric performance. In addition to the strategy of converging different bands, many semiconductors provide an inherent band nestification, equally enabling a large number of effective band valley degeneracy. Here we show as an example that a simple elemental semiconductor, tellurium, exhibits a high thermoelectric figure of merit of unity, not only demonstrating the concept but also filling up the high performance gap from 300 to 700 K for elemental thermoelectrics. The concept used here should be applicable in general for thermoelectrics with similar band features. PMID:26751919

  16. Tellurium as a high-performance elemental thermoelectric.

    PubMed

    Lin, Siqi; Li, Wen; Chen, Zhiwei; Shen, Jiawen; Ge, Binghui; Pei, Yanzhong

    2016-01-11

    High-efficiency thermoelectric materials require a high conductivity. It is known that a large number of degenerate band valleys offers many conducting channels for improving the conductivity without detrimental effects on the other properties explicitly, and therefore, increases thermoelectric performance. In addition to the strategy of converging different bands, many semiconductors provide an inherent band nestification, equally enabling a large number of effective band valley degeneracy. Here we show as an example that a simple elemental semiconductor, tellurium, exhibits a high thermoelectric figure of merit of unity, not only demonstrating the concept but also filling up the high performance gap from 300 to 700 K for elemental thermoelectrics. The concept used here should be applicable in general for thermoelectrics with similar band features.

  17. Enhancement of automotive exhaust heat recovery by thermoelectric devices

    SciTech Connect

    Ibrahim, Essam; Szybist, James P; Parks, II, James E

    2010-01-01

    In an effort to improve automobile fuel economy, an experimental study is undertaken to explore practical aspects of implementing thermoelectric devices for exhaust gas energy recovery. A highly instrumented apparatus consisting of a hot (exhaust gas) and a cold (coolant liquid) side rectangular ducts enclosing the thermoelectric elements has been built. Measurements of thermoelectric voltage output and flow and surface temperatures were acquired and analyzed to investigate the power generation and heat transfer properties of the apparatus. Effects of inserting aluminum wool packing material inside the hot side duct on augmentation of heat transfer from the gas stream to duct walls were studied. Data were collected for both the unpacked and packed cases to allow for detection of packing influence on flow and surface temperatures. Effects of gas and coolant inlet temperatures as well as gas flow rate on the thermoelectric power output were examined. The results indicate that thermoelectric power production is increased at higher gas inlet temperature or flow rate. However, thermoelectric power generation decreases with a higher coolant temperature as a consequence of the reduced hot-cold side temperature differential. For the hot-side duct, a large temperature gradient exists between the gas and solid surface temperature due to poor heat transfer through the gaseous medium. Adding the packing material inside the exhaust duct enhanced heat transfer and hence raised hot-side duct surface temperatures and thermoelectric power compared to the unpacked duct, particularly where the gas-to-surface temperature differential is highest. Therefore it is recommended that packing of exhaust duct becomes common practice in thermoelectric waste energy harvesting applications.

  18. Nanostructures having high performance thermoelectric properties

    DOEpatents

    Yang, Peidong; Majumdar, Arunava; Hochbaum, Allon I; Chen, Renkun; Delgado, Raul Diaz

    2014-05-20

    The invention provides for a nanostructure, or an array of such nanostructures, each comprising a rough surface, and a doped or undoped semiconductor. The nanostructure is an one-dimensional (1-D) nanostructure, such a nanowire, or a two-dimensional (2-D) nanostructure. The nanostructure can be placed between two electrodes and used for thermoelectric power generation or thermoelectric cooling.

  19. Nanostructures having high performance thermoelectric properties

    DOEpatents

    Yang, Peidong; Majumdar, Arunava; Hochbaum, Allon I.; Chen, Renkun; Delgado, Raul Diaz

    2015-12-22

    The invention provides for a nanostructure, or an array of such nanostructures, each comprising a rough surface, and a doped or undoped semiconductor. The nanostructure is an one-dimensional (1-D) nanostructure, such a nanowire, or a two-dimensional (2-D) nanostructure. The nanostructure can be placed between two electrodes and used for thermoelectric power generation or thermoelectric cooling.

  20. Interference enhanced thermoelectricity in quinoid type structures

    SciTech Connect

    Strange, M. Solomon, G. C.; Seldenthuis, J. S.; Verzijl, C. J. O.; Thijssen, J. M.

    2015-02-28

    Quantum interference (QI) effects in molecular junctions may be used to obtain large thermoelectric responses. We study the electrical conductance G and the thermoelectric response of a series of molecules featuring a quinoid core using density functional theory, as well as a semi-empirical interacting model Hamiltonian describing the π-system of the molecule which we treat in the GW approximation. Molecules with a quinoid type structure are shown to have two distinct destructive QI features close to the frontier orbital energies. These manifest themselves as two dips in the transmission, that remain separated, even when either electron donating or withdrawing side groups are added. We find that the position of the dips in the transmission and the frontier molecular levels can be chemically controlled by varying the electron donating or withdrawing character of the side groups as well as the conjugation length inside the molecule. This feature results in a very high thermoelectric power factor S{sup 2}G and figure of merit ZT, where S is the Seebeck coefficient, making quinoid type molecules potential candidates for efficient thermoelectric devices.

  1. Interference enhanced thermoelectricity in quinoid type structures.

    PubMed

    Strange, M; Seldenthuis, J S; Verzijl, C J O; Thijssen, J M; Solomon, G C

    2015-02-28

    Quantum interference (QI) effects in molecular junctions may be used to obtain large thermoelectric responses. We study the electrical conductance G and the thermoelectric response of a series of molecules featuring a quinoid core using density functional theory, as well as a semi-empirical interacting model Hamiltonian describing the π-system of the molecule which we treat in the GW approximation. Molecules with a quinoid type structure are shown to have two distinct destructive QI features close to the frontier orbital energies. These manifest themselves as two dips in the transmission, that remain separated, even when either electron donating or withdrawing side groups are added. We find that the position of the dips in the transmission and the frontier molecular levels can be chemically controlled by varying the electron donating or withdrawing character of the side groups as well as the conjugation length inside the molecule. This feature results in a very high thermoelectric power factor S(2)G and figure of merit ZT, where S is the Seebeck coefficient, making quinoid type molecules potential candidates for efficient thermoelectric devices.

  2. Band structure engineering through orbital interaction for enhanced thermoelectric power factor

    SciTech Connect

    Zhu, Hong; Sun, Wenhao; Ceder, Gerbrand; Armiento, Rickard; Lazic, Predrag

    2014-02-24

    Band structure engineering for specific electronic or optical properties is essential for the further development of many important technologies including thermoelectrics, optoelectronics, and microelectronics. In this work, we report orbital interaction as a powerful tool to finetune the band structure and the transport properties of charge carriers in bulk crystalline semiconductors. The proposed mechanism of orbital interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we find that the convergence of multiple carrier pockets not only displays a strong correlation with the s-p and spin-orbit coupling but also coincides with the enhancement of power factor. Our results suggest a useful path to engineer the band structure and an enticing solid-solution design principle to enhance thermoelectric performance.

  3. Quantum-interference-enhanced thermoelectricity in single molecules and molecular films

    NASA Astrophysics Data System (ADS)

    Lambert, Colin J.; Sadeghi, Hatef; Al-Galiby, Qusiy H.

    2016-12-01

    We provide a brief overview of recent measurements and predictions of thermoelectric properties of single-molecules and porous nanoribbons and discuss some principles underpinning strategies for enhancing their thermoelectric performance. The latter include (a) taking advantage of steep slopes in the electron transmission coefficient T (E), (b) creating structures with delta-function-like transmission coefficients and (c) utilising step-like features in T (E). To achieve high performance, we suggest that the latter may be the most fruitful, since it is less susceptible to inhomogeneous broadening. For the purpose of extrapolating thermoelectric properties of single or few molecules to monolayer molecular films, we also discuss the relevance of the conductance-weighted average Seebeck coefficient. xml:lang="fr"

  4. Enhancing efficiency and power of quantum-dots resonant tunneling thermoelectrics in three-terminal geometry by cooperative effects

    SciTech Connect

    Jiang, Jian-Hua

    2014-11-21

    We propose a scheme of multilayer thermoelectric engine where one electric current is coupled to two temperature gradients in three-terminal geometry. This is realized by resonant tunneling through quantum dots embedded in two thermal and electrical resisting polymer matrix layers between highly conducting semiconductor layers. There are two thermoelectric effects, one of which is pertaining to inelastic transport processes (if energies of quantum dots in the two layers are different), while the other exists also for elastic transport processes. These two correspond to the transverse and longitudinal thermoelectric effects, respectively, and are associated with different temperature gradients. We show that cooperation between the two thermoelectric effects leads to markedly improved figure of merit and power factor, which is confirmed by numerical calculation using material parameters. Such enhancement is robust against phonon heat conduction and energy level broadening. Therefore, we demonstrated cooperative effect as an additional way to effectively improve performance of thermoelectrics in three-terminal geometry.

  5. High Performance Graphene Nano-ribbon Thermoelectric Devices by Incorporation and Dimensional Tuning of Nanopores

    PubMed Central

    Sharafat Hossain, Md; Al-Dirini, Feras; Hossain, Faruque M.; Skafidas, Efstratios

    2015-01-01

    Thermoelectric properties of Graphene nano-ribbons (GNRs) with nanopores (NPs) are explored for a range of pore dimensions in order to achieve a high performance two-dimensional nano-scale thermoelectric device. We reduce thermal conductivity of GNRs by introducing pores in them in order to enhance their thermoelectric performance. The electrical properties (Seebeck coefficient and conductivity) of the device usually degrade with pore inclusion; however, we tune the pore to its optimal dimension in order to minimize this degradation, enhancing the overall thermoelectric performance (high ZT value) of our device. We observe that the side channel width plays an important role to achieve optimal performance while the effect of pore length is less pronounced. This result is consistent with the fact that electronic conduction in GNRs is dominated along its edges. Ballistic transport regime is assumed and a semi-empirical method using Huckel basis set is used to obtain the electrical properties, while the phononic system is characterized by Tersoff empirical potential model. The proposed device structure has potential applications as a nanoscale local cooler and as a thermoelectric power generator. PMID:26083450

  6. Spinodal decomposition and nucleation and growth as a means to bulk nanostructured thermoelectrics: enhanced performance in Pb(1-x)Sn(x)Te-PbS.

    PubMed

    Androulakis, John; Lin, Chia-Her; Kong, Hun-Jin; Uher, Ctirad; Wu, Chun-I; Hogan, Timothy; Cook, Bruce A; Caillat, Thierry; Paraskevopoulos, Konstantinos M; Kanatzidis, Mercouri G

    2007-08-08

    The solid-state transformation phenomena of spinodal decomposition and nucleation and growth are presented as tools to create nanostructured thermoelectric materials with very low thermal conductivity and greatly enhanced figure of merit. The systems (PbTe)(1-x)(PbS)(x) and (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) are not solid solutions but phase separate into PbTe-rich and PbS-rich regions to produce coherent nanoscale heterogeneities that severely depress the lattice thermal conductivity. For x > approximately 0.03 the materials are ordered on three submicrometer length scales. Transmission electron microscopy reveals both spinodal decomposition and nucleation and growth phenomena the relative magnitude of which varies with x. We show that the (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) system, despite its nanostructured nature, maintains a high electron mobility (>100 cm(2)/V x s at 700 K). At x approximately 0.08 the material achieves a very low room-temperature lattice thermal conductivity of approximately 0.4 W/m x K. This value is only 28% of the PbTe lattice thermal conductivity at room temperature. The inhibition of heat flow in this system is caused by nanostructure-induced acoustic impedance mismatch between the PbTe-rich and PbS-rich regions. As a result the thermoelectric properties of (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) at x = 0.04, 0.08, and 0.16 were found to be superior to those of PbTe by almost a factor of 2. The relative importance of the two observed modes of nanostructuring, spinodal decomposition and nucleation and growth, in suppressing the thermal conductivity was assessed in this work, and we can conclude that the latter mode seems more effective in doing so. The promise of such a system for high efficiency is highlighted by a ZT approximately 1.50 at 642 K for x approximately 0.08.

  7. Theoretical Approach to Predict the Performance of Thermoelectric Generator Modules

    NASA Astrophysics Data System (ADS)

    Elarusi, Abdulmunaem H.; Fagehi, Hassan; Lee, Hosung; Attar, Alaa

    2017-02-01

    The aim of this work was to examine the validity of the thermoelectric modules' performance predicted by formulating the effective thermoelectric material properties. The three maximum parameters (output power, current, and efficiency) are defined in terms of the average temperature of the thermoelectric generator (TEG). These three maximum parameters, which are either taken from commercial TEG modules or measurements for particular operating conditions, are used to define the effective material properties (Seebeck coefficient, thermal conductivity, and electrical resistivity). The commercial performance curves provided by the manufacturer were compared with the results obtained here by the effective material properties with the simple standard thermoelectric equations. It has been found that this technique predicts the performance of four commercial thermoelectric modules with fair to good accuracy. The characteristics of the TEGs were represented using the normalized charts constructed by formulating the parameters as a fraction of over the maximum parameters. The normalized charts would be universal for any given TEG module once the thermoelectric material is known.

  8. Enhancement of Thermoelectric Properties of Lead Selenide by Doping

    NASA Astrophysics Data System (ADS)

    Peng, Haowei; Song, Jung-Hwan; Freeman, A. J.

    2010-03-01

    Lead chalcogenide materials are very important in thermoelectric investigations. Recently, it is reported that Tl doping in PbTe can greatly enhance the figure of merit (ZT) of PbTe,footnotetextJ. P. Heremans, et al, Science, 321, 554 (2008) which can be mainly attributed to resonance states near the Fermi level. PbSe is also a good candidate as a thermoelectric material since it has a high melting temperature and low thermal conductivity (1.6 W/mK).footnotetextS. Ahmad, et al., Phys. Rev. B 74, 155205 (2006) Here we present a theoretical study of the electronic structures, formation energies, and transport properties of PbSe doped with various impurities such as Ga, In, Tl, As, Sb, and Cd using the highly precise FLAPW method.footnotetextWimmer, Krakauer, Weinert, Freeman, Phys. Rev. B, 24, 864 (1981) Our calculated formation energies indicate that As prefers Se sites rather than Pb sites due to atom size mismatch, but Sb has no apparent preferable sites. Based on the analysis of the densities of states, PbSe with Tl and Cd doped on the cation sites are good candidates for thermoelectric applications as p-, and n-type materials. We also discuss the possible enhancement of thermoelectric properties in terms of optimal carrier concentrations.

  9. Enhancement of figure of merit of thermoelectric materials: a new theoretical approach

    NASA Astrophysics Data System (ADS)

    Sofi, A. H.; Abubakr, B.; Shah, M. A.

    2016-03-01

    Thermoelectric materials have attained importance because of the gargantuan energy crisis the world faces today. A thermoelectric material can be used efficiently and frequently, provided, its figure of merit ZT is increased. Also, easy availability, manufacturing, and low cost are the other factors to be considered for a novel thermoelectric material. A theoretical model is proposed in this paper for the enhancement of the figure of merit of thermoelectric materials.

  10. Experimental Investigation on Effect of Adhesives on Thermoelectric Generator Performance

    NASA Astrophysics Data System (ADS)

    Singh, Baljit; Remeli, Muhammad Fairuz; Chet, Ding Lai; Oberoi, Amandeep; Date, Abhijit; Akbarzadeh, Aliakbar

    2015-06-01

    Thermoelectric generators (TEGs) convert heat energy into electricity. Currently, these devices are attached to heat exchangers by means of mechanical devices such as clamps or fixtures with nuts and bolts. These mechanical devices are not suitable for use in harsh environments due to problems with rusting and maintenance. To eliminate the need for such mechanical devices, various kinds of adhesives used to attach thermoelectric generators to heat exchangers are investigated experimentally in this work. These adhesives have been selected based on their thermal properties and also their stability to work in harsh environments to avoid damage to the integrity of the attachment over long periods of time. Stainless-steel plates were attached to a thermoelectric generator using the adhesives. The introduction of the adhesive as a means of attachment for thermoelectric generators contributes to increase the thermal resistance to heat transfer across the TEG. The adhesive layers increased the thermal resistance of the thermoelectric generator by 16% to 109%. This work examines the effect of the adhesives on the thermal performance and power output of a single thermoelectric generator for various heat inputs.

  11. Thermoelectric pump performance analysis computer code

    NASA Technical Reports Server (NTRS)

    Johnson, J. L.

    1973-01-01

    A computer program is presented that was used to analyze and design dual-throat electromagnetic dc conduction pumps for the 5-kwe ZrH reactor thermoelectric system. In addition to a listing of the code and corresponding identification of symbols, the bases for this analytical model are provided.

  12. High performance P-type thermoelectric materials and methods of preparation

    NASA Technical Reports Server (NTRS)

    Caillat, Thierry (Inventor); Borshchevsky, Alexander (Inventor); Fleurial, Jean-Pierre (Inventor)

    2002-01-01

    The present invention is embodied in high performance p-type thermoelectric materials having enhanced thermoelectric properties and the methods of preparing such materials. In one aspect of the invention, p-type semiconductors of formula Zn.sub.4-x A.sub.x Sb.sub.3-y B.sub.y wherein 0.ltoreq.x.ltoreq.4, A is a transition metal, B is a pnicogen, and 0.ltoreq.y.ltoreq.3 are formed for use in manufacturing thermoelectric devices with substantially enhanced operating characteristics and improved efficiency. Two methods of preparing p-type Zn.sub.4 Sb.sub.3 and related alloys of the present invention include a crystal growth method and a powder metallurgy method.

  13. Enhancing thermoelectric properties of organic composites through hierarchical nanostructures

    PubMed Central

    Zhang, Kun; Zhang, Yue; Wang, Shiren

    2013-01-01

    Organic thermoelectric (TE) materials are very attractive due to easy processing, material abundance, and environmentally-benign characteristics, but their potential is significantly restricted by the inferior thermoelectric properties. In this work, noncovalently functionalized graphene with fullerene by π-π stacking in a liquid-liquid interface was integrated into poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate). Graphene helps to improve electrical conductivity while fullerene enhances the Seebeck coefficient and hinders thermal conductivity, resulting in the synergistic effect on enhancing thermoelectric properties. With the integration of nanohybrids, the electrical conductivity increased from ~10000 to ~70000 S/m, the thermal conductivity changed from 0.2 to 2 W·K−1m−1 while the Seebeck coefficient was enhanced by around 4-fold. As a result, nanohybrids-based polymer composites demonstrated the figure of merit (ZT) as high as 6.7 × 10−2, indicating an enhancement of more than one order of magnitude in comparison to single-phase filler-based polymer composites with ZT at the level of 10−3. PMID:24336319

  14. Enhancement of Thermoelectric Properties of PEDOT:PSS and Tellurium-PEDOT:PSS Hybrid Composites by Simple Chemical Treatment

    NASA Astrophysics Data System (ADS)

    Jin Bae, Eun; Hun Kang, Young; Jang, Kwang-Suk; Yun Cho, Song

    2016-01-01

    The thermoelectric properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and tellurium-PEDOT:PSS (Te-PEDOT:PSS) hybrid composites were enhanced via simple chemical treatment. The performance of thermoelectric materials is determined by their electrical conductivity, thermal conductivity, and Seebeck coefficient. Significant enhancement of the electrical conductivity of PEDOT:PSS and Te-PEDOT:PSS hybrid composites from 787.99 and 11.01 to 4839.92 and 334.68 S cm‑1, respectively was achieved by simple chemical treatment with H2SO4. The power factor of the developed materials could be effectively tuned over a very wide range depending on the concentration of the H2SO4 solution used in the chemical treatment. The power factors of the developed thermoelectric materials were optimized to 51.85 and 284 μW m‑1 K‑2, respectively, which represent an increase of four orders of magnitude relative to the corresponding parameters of the untreated thermoelectric materials. Using the Te-PEDOT:PSS hybrid composites, a flexible thermoelectric generator that could be embedded in textiles was fabricated by a printing process. This thermoelectric array generates a thermoelectric voltage of 2 mV using human body heat.

  15. Molten gallium flux synthesis of known thermoelectric and novel magnetic inorganic clathrate compounds: Improving thermoelectric performance

    NASA Astrophysics Data System (ADS)

    Bryan, John Daniel

    Molten gallium metal has been used as a solvent to grow large single crystals of known inorganic thermoelectric clathrates Sr8Ga 16Ge30, Ba8Ga16Ge30, and Ba8Ga16Si30. X-ray diffraction, thermal analysis, electron microprobe, Glow Discharge Mass Spectrometry, temperature dependent electrical conductivity and Seebeck coefficient measurements characterized the single crystals. The Thermoelectric performance was shown to be heavily dependent on the synthetic conditions including container choice, thermal history and impurity concentration. Inorganic Clathrates have attracted intense interest in last several years as potential new materials for thermoelectric devices. If a small to moderate increase in thermoelectric performance over the currently used materials is realized, substantial environmental and technological gains could be achieved. Since thermoelectric refrigeration modules require no moving parts or heat exchange gas (freon) they offer significant advantages over conventional refrigeration technology that tends to fail due to the finite lifetime of the pumping equipment. High temperature devices are also extremely useful for power generation in harsh unforgiving environments where excess heat is available. The thermoelectric performance, primarily at room temperature, of these compounds was found to be heavily dependent on the synthetic procedures used to obtain them. A flux growth procedure was developed to overcome the problems of the traditional melt-quench-anneal solid-state chemical approach. This procedure yielded large single crystals of the Sr8Ga16Ge 30, Ba8Ga16Ge30 and Ba8Ga 16Si30 compounds which ready facilitated their chemical and electronic study. Finally, an outlook on the application of these compounds as thermoelectric devices is given. Application of the flux method to other systems was also successful in the discovery of two new inorganic clathrate compounds: type IV Eu4Ga 8Ge16 and type V Yb8Ga16Ge14. The Eu4Ga8Ge16 compound was found to

  16. High performance thermoelectric materials and methods of preparation

    NASA Technical Reports Server (NTRS)

    Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

    1997-01-01

    Transition metals (T) of Group VIII (Co, Rh and Ir) have been prepared as semiconductor alloys with Sb having the general formula TSb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor alloys and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor alloys having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using vertical gradient freeze techniques, liquid-solid phase sintering techniques, low temperature powder sintering and/or hot-pressing. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities (up to 8000 cm.sup.2.V.sup.-1.s.sup.-1), good Seebeck coefficients (up to 400 .mu.VK.sup.-1 between 300.degree. C. and 700.degree. C.), and low thermal conductivities (as low as 15 mW/cmK). Optimizing the transport properties of semiconductor materials prepared from elemental mixtures Co, Rh, Ir and Sb resulted in a two fold increase in the thermoelectric figure of merit (ZT) at temperatures as high as 400.degree. C. for thermoelectric elements fabricated from such semiconductor materials.

  17. Optimization of thermoelectric performance in semiconducting polymers for understanding charge transport and flexible thermoelectric applications

    NASA Astrophysics Data System (ADS)

    Glaudell, Anne; Chabinyc, Michael

    2014-03-01

    Organic electronic materials have been widely considered for a variety of energy conversion applications, from photovoltaics to LEDs. Only very recently have organic materials been considered for thermoelectric applications - converting between temperature gradients and electrical potential. The intrinsic disorder in semiconducting polymers leads to an inherently low thermal conductivity, a key parameter in thermoelectric performance. The ability to solution deposit on flexible substrates opens up niche applications including personal cooling and conformal devices. Here work is presented on the electrical conductivity and thermopower of thin film semiconducting polymers, including P3HT and PBTTT-C14. Thermoelectric properties are explored over a wide range of conductivities, from nearly insulating to beyond 100 S/cm, enabled by employing different doping mechanisms, including molecular charge-transfer doping with F4TCNQ and vapor doping with a fluoroalkyl trichlorosilane (FTS). Temperature-dependent measurements suggest competing charge transport mechanisms, likely due to the mixed ordered/disordered character of these polymers. These results show promise for organic materials for thermoelectric applications, and recent results on thin film devices will also be presented.

  18. Potential thermoelectric performance of hole-doped Cu2O

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Parker, David; Du, Mao-Hua; Singh, David J.

    2013-04-01

    High thermoelectric performance in oxides requires stable conductive materials that have suitable band structures. Here we show, based on an analysis of the thermopower and related properties using first-principles calculations and Boltzmann transport theory in the relaxation time approximation, that hole-doped Cu2O may be such a material. We find that hole-doped Cu2O has a high thermopower of above 200 μV K-1 even with doping levels as high as 5.2 × 1020 cm-3 at 500 K, mainly attributed to the heavy valence bands of Cu2O. This is reminiscent of the cobaltate family of high-performance oxide thermoelectrics and implies that hole-doped Cu2O could be an excellent thermoelectric material if suitably doped.

  19. Thermoelectric effect enhanced by resonant states in graphene

    NASA Astrophysics Data System (ADS)

    Inglot, M.; Dyrdał, A.; Dugaev, V. K.; Barnaś, J.

    2015-03-01

    Thermoelectric effects in graphene are considered theoretically with particular attention paid to the role of resonant scattering on impurities. Using the T -matrix method we calculate the impurity resonant states and the momentum relaxation time due to scattering on impurities. The Boltzmann kinetic equation is used to determine the thermoelectric coefficients. It is shown that the resonant impurity states near the Fermi level give rise to a resonant enhancement of the Seebeck coefficient and figure of merit Z T . The Wiedemann-Franz ratio deviates from that known for ordinary metals, where this ratio is constant and equal to the Lorentz number. This deviation appears for small chemical potentials and in the vicinity of the resonant states. In the limit of a constant relaxation time, this ratio has been calculated analytically for μ =0 .

  20. Critical Role of Processing on the Thermoelectric Performance of Doped Semiconducting Polymers

    NASA Astrophysics Data System (ADS)

    Patel, Shrayesh; Glaudell, Anne; Chabinyc, Michael

    The ability to convert excess waste heat into useable energy can significantly help meet the global energy demands. One may capture this waste heat through thermoelectrics devices. In a thermoelectric material, the charge carriers transport both electrical current and heat. Consequently, under a temperature difference (ΔT), a carrier concentration gradient results in a voltage (ΔV), which is related to the Seebeck coefficient, α = - Δ V/ ΔT. One of the challenges lies in finding materials that simultaneously have low thermal conductivity (κ) , high electrical conductivity (σ) , and high Seebeck coefficient (α) . Conjugated semiconducting polymers can potentially meet this demand due to their inherent low thermal conductivity and high electrical conductivity through sufficient doping. Here, we report on the critical role of thermal processing on the enhancement of thermoelectric properties of conjugated polymer thin films. These films were doping using three different mechanisms: acid (toluene sulfonic acid), charge transfer (F4TCNQ), and vapor (fluorinated-alkyl trichlorosilane). These thermoelectrics properties will be correlated to the structural and morphological properties of the doped thin-films through various synchrotron X-ray scattering techniques. Lastly, to further elucidate the charge transport mechanism driving the thermoelectric performance, we report on the temperature-dependent measurements of both the Seebeck coefficient and electrical conductivity.

  1. Thermoelectric ZT enhanced by asymmetric configuration in single-molecule-magnet junctions

    NASA Astrophysics Data System (ADS)

    Niu, Pengbin; Shi, Yunlong; Sun, Zhu; Nie, Yi-Hang; Luo, Hong-Gang

    2016-02-01

    In mesoscopic devices, many factors like the Coulomb and spin interactions can enhance the thermoelectric figure of merit ZT. Here we use a system consisting of a single-molecule magnet (SMM) connected to two ferromagnetic electrodes to consider the possible enhancement effects of thermoelectric efficiency. By introducing an asymmetric configuration to the transport junction, we find that this configuration can significantly enhance the thermoelectric ZT. The optimized asymmetric thermoelectric ZT is five times that of the ZT with a symmetric configuration or non-magnetic case. Due to this asymmetry, a non-zero charge thermopower at the electron-hole symmetry point is also found. These results demonstrate that the asymmetry of the transport junction helps to enhance thermoelectric efficiency and is useful for fabricating SMM-based thermoelectric devices.

  2. Terbium Ion Doping in Ca3Co4O9: A Step towards High-Performance Thermoelectric Materials

    PubMed Central

    Saini, Shrikant; Yaddanapudi, Haritha Sree; Tian, Kun; Yin, Yinong; Magginetti, David; Tiwari, Ashutosh

    2017-01-01

    The potential of thermoelectric materials to generate electricity from the waste heat can play a key role in achieving a global sustainable energy future. In order to proceed in this direction, it is essential to have thermoelectric materials that are environmentally friendly and exhibit high figure of merit, ZT. Oxide thermoelectric materials are considered ideal for such applications. High thermoelectric performance has been reported in single crystals of Ca3Co4O9. However, for large scale applications single crystals are not suitable and it is essential to develop high-performance polycrystalline thermoelectric materials. In polycrystalline form, Ca3Co4O9 is known to exhibit much weaker thermoelectric response than in single crystal form. Here, we report the observation of enhanced thermoelectric response in polycrystalline Ca3Co4O9 on doping Tb ions in the material. Polycrystalline Ca3−xTbxCo4O9 (x = 0.0–0.7) samples were prepared by a solid-state reaction technique. Samples were thoroughly characterized using several state of the art techniques including XRD, TEM, SEM and XPS. Temperature dependent Seebeck coefficient, electrical resistivity and thermal conductivity measurements were performed. A record ZT of 0.74 at 800 K was observed for Tb doped Ca3Co4O9 which is the highest value observed till date in any polycrystalline sample of this system. PMID:28317853

  3. Terbium Ion Doping in Ca3Co4O9: A Step towards High-Performance Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Saini, Shrikant; Yaddanapudi, Haritha Sree; Tian, Kun; Yin, Yinong; Magginetti, David; Tiwari, Ashutosh

    2017-03-01

    The potential of thermoelectric materials to generate electricity from the waste heat can play a key role in achieving a global sustainable energy future. In order to proceed in this direction, it is essential to have thermoelectric materials that are environmentally friendly and exhibit high figure of merit, ZT. Oxide thermoelectric materials are considered ideal for such applications. High thermoelectric performance has been reported in single crystals of Ca3Co4O9. However, for large scale applications single crystals are not suitable and it is essential to develop high-performance polycrystalline thermoelectric materials. In polycrystalline form, Ca3Co4O9 is known to exhibit much weaker thermoelectric response than in single crystal form. Here, we report the observation of enhanced thermoelectric response in polycrystalline Ca3Co4O9 on doping Tb ions in the material. Polycrystalline Ca3‑xTbxCo4O9 (x = 0.0–0.7) samples were prepared by a solid-state reaction technique. Samples were thoroughly characterized using several state of the art techniques including XRD, TEM, SEM and XPS. Temperature dependent Seebeck coefficient, electrical resistivity and thermal conductivity measurements were performed. A record ZT of 0.74 at 800 K was observed for Tb doped Ca3Co4O9 which is the highest value observed till date in any polycrystalline sample of this system.

  4. Nanocrystalline silicon: lattice dynamics and enhanced thermoelectric properties.

    PubMed

    Claudio, Tania; Stein, Niklas; Stroppa, Daniel G; Klobes, Benedikt; Koza, Michael Marek; Kudejova, Petra; Petermann, Nils; Wiggers, Hartmut; Schierning, Gabi; Hermann, Raphaël P

    2014-12-21

    Silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K(-1) m(-1) at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K(-1) m(-1), which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.

  5. Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties

    DOE PAGES

    Claudio, Tania; Stein, Niklas; Stroppa, Daniel G.; ...

    2014-12-21

    In this study, silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K-1 m-1 at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured,more » which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K-1 m-1, which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT ≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.« less

  6. Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties

    SciTech Connect

    Claudio, Tania; Stein, Niklas; Stroppa, Daniel G.; Klobes, Benedikt; Koza, Michael Marek; Kudejova, Petra; Petermann, Nils; Wiggers, Hartmut; Schierning, Gabi; Hermann, Raphaël P.

    2014-12-21

    In this study, silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K-1 m-1 at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K-1 m-1, which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT ≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.

  7. Thermoelectrics. Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics.

    PubMed

    Kim, Sang Il; Lee, Kyu Hyoung; Mun, Hyeon A; Kim, Hyun Sik; Hwang, Sung Woo; Roh, Jong Wook; Yang, Dae Jin; Shin, Weon Ho; Li, Xiang Shu; Lee, Young Hee; Snyder, G Jeffrey; Kim, Sung Wng

    2015-04-03

    The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi(0.5)Sb(1.5)Te3 (bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved the zT to 1.86 ± 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices.

  8. Nanostructures boost the thermoelectric performance of PbS

    SciTech Connect

    Johnsen, Simon; He, Jiaqing; Androulakis, John; Dravid, Vinayak; Todorov, Iliya; Chung, Duck Young; Kanatzidis, Mercouri G.

    2011-02-18

    In situ nanostructuring in bulk thermoelectric materials through thermo-dynamic phase segregation has established itself as an effective paradigm for optimizing the performance of thermoelectric materials. In bulk PbTe small compositional variations create coherent and semicoherent nanometer sized precipitates embedded in a PbTe matrix, where they can impede phonon propagation at little or no expense to the electronic properties. In this paper the nanostructuring paradigm is for the first time extended to a bulk PbS based system, which despite obvious advantages of price and abundancy, so far has been largely disregarded in thermoelectric research due to inferior room temperature thermoelectric properties relative to the pristine fellow chalcogenides, PbSe and PbTe. Herein we report on the synthesis, microstructural morphology and thermoelectric properties of two phase (PbS)1-x(PbTe)xx = 0–0.16 samples. We have found that the addition of only a few percent PbTe to PbS results in a highly nanostructured material, where PbTe precipitates are coherently and semicoherently embedded in a PbS matrix. The present (PbS)1-x(PbTe)x nanostructured samples show substantial decreases in lattice thermal conductivity relative to pristine PbS, while the electronic properties are left largely unaltered. This in turn leads to a marked increase in the thermoelectric figure of merit. This study underlines the efficiency of the nanostructuring approach and strongly supports its generality and applicability to other material systems. We demonstrate that these PbS-based materials, which are made primarily from abundant Pb and S, outperform optimally n-type doped pristine PbTe above 770 K.

  9. Thermoelectric-figure-of-merit enhancement of silicon-germanium through nanocomposite concept

    NASA Astrophysics Data System (ADS)

    Wang, Dezhi

    SiGe alloy has been the thermoelectric material element of RTGs (Radioisotope thermoelectric power generators) for more than 20 years because of its good performance at high temperature. It also has a very high potential application in converting exhaust heat into useful electricity, which currently attracts a lot of research interest in the automotive industry where 40% of the energy was rejected as exhaust heat. However, its low conversion efficiency (8%) is a major concern although it is the best in practice. A new concept, namely Si-Ge nanocomposite, was proposed to enhance thermoelectric figure-of-merit. Fast heating pressure sintering was found to be an appropriate synthesizing method and a lab-made direct current-induced hot press system was established. It can reach l200°C within several minutes and many parameters can be controlled. The uniquely designed graphite die assembly can stand l60MPa pressure which is better than the best commercial products (127MPa). Numerous Si-Ge nanocomposite samples were pressed using our DC hot press. Fully dense n-type Si-Ge nanocomposite samples of nanoSi80nanoGe20P were finally obtained. The nanocomposite structure was characterized via XRD, SEM, EDS, and TEM. The proposed nanocomposite structure, dots in a matrix, was observed. Most importantly, the thermoelectric property measurements showed that the Si-Ge nanocomposite of n-type nanoSi80nanoGe20 possessed higher electrical conductivity but lower thermal conductivity, thus a higher ZT than that of n-type nanoSi80microGe20. This result proved that thermoelectric-figure-of-merit enhancement through the nanocomposite concept was the right direction.

  10. Size effect in thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Mao, Jun; Liu, Zihang; Ren, Zhifeng

    2016-12-01

    Thermoelectric applications have attracted increasing interest recently due to its capability of converting waste heat into electricity without hazardous emissions. Materials with enhanced thermoelectric performance have been reported in recent two decades. The revival of research for thermoelectric materials began in early 1990s when the size effect is considered. Low-dimensional materials with exceptionally high thermoelectric figure of merit (ZT) have been presented, which broke the limit of ZT around unity. The idea of size effect in thermoelectric materials even inspired the later nanostructuring and band engineering strategies, which effectively enhanced the thermoelectric performance of bulk materials. In this overview, the size effect in low-dimensional thermoelectric materials is reviewed. We first discuss the quantum confinement effect on carriers, including the enhancement of electronic density of states, semimetal to semiconductor transition and carrier pocket engineering. Then, the effect of assumptions on theoretical calculations is presented. Finally, the effect of phonon confinement and interface scattering on lattice thermal conductivity is discussed.

  11. Enhanced thermoelectric performance in the p-type half-Heusler (Ti/Zr/Hf)CoSb0.8Sn0.2 system via phase separation.

    PubMed

    Rausch, Elisabeth; Balke, Benjamin; Ouardi, Siham; Felser, Claudia

    2014-12-14

    A novel approach for optimization of the thermoelectric properties of p-type Heusler compounds with a C1b structure was investigated. A successful recipe for achieving intrinsic phase separation in the n-type material based on the TiNiSn system is isoelectronic partial substitution of Ti with its heavier homologues Zr and Hf. We applied this concept to the p-type system MCoSb0.8Sn0.2 by a systematic investigation of samples with different compositions at the Ti position (M = Ti, Zr, Hf, Ti0.5Zr0.5, Zr0.5Hf0.5, and Ti0.5Hf0.5). We thus achieved an approximately 40% reduction of the thermal conductivity and a maximum figure of merit ZT of 0.9 at 700 °C. This is a 80% improvement in peak ZT from 0.5 to 0.9 at 700 °C compared to the best published value of an ingot p-type half-Heusler compound. Thus far, comparable good thermoelectric p-type materials of this structure type have only been realized by a nanostructuring process via ball milling of premelted ingot samples followed by a rapid consolidation method, like hot pressing. The herein-presented simple arc-melting fabrication method reduces the fabrication time as compared to this multi-step nanostructuring process. The high mechanical stability of the Heusler compounds is favorable for the construction of thermoelectric modules. The Vickers hardness values are close to those of the n-type material, leading to good co-processability of both materials.

  12. High-performance bulk thermoelectrics with all-scale hierarchical architectures.

    PubMed

    Biswas, Kanishka; He, Jiaqing; Blum, Ivan D; Wu, Chun-I; Hogan, Timothy P; Seidman, David N; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2012-09-20

    With about two-thirds of all used energy being lost as waste heat, there is a compelling need for high-performance thermoelectric materials that can directly and reversibly convert heat to electrical energy. However, the practical realization of thermoelectric materials is limited by their hitherto low figure of merit, ZT, which governs the Carnot efficiency according to the second law of thermodynamics. The recent successful strategy of nanostructuring to reduce thermal conductivity has achieved record-high ZT values in the range 1.5-1.8 at 750-900 kelvin, but still falls short of the generally desired threshold value of 2. Nanostructures in bulk thermoelectrics allow effective phonon scattering of a significant portion of the phonon spectrum, but phonons with long mean free paths remain largely unaffected. Here we show that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials. Thus, by considering sources of scattering on all relevant length scales in a hierarchical fashion--from atomic-scale lattice disorder and nanoscale endotaxial precipitates to mesoscale grain boundaries--we achieve the maximum reduction in lattice thermal conductivity and a large enhancement in the thermoelectric performance of PbTe. By taking such a panoscopic approach to the scattering of heat-carrying phonons across integrated length scales, we go beyond nanostructuring and demonstrate a ZT value of ∼2.2 at 915 kelvin in p-type PbTe endotaxially nanostructured with SrTe at a concentration of 4 mole per cent and mesostructured with powder processing and spark plasma sintering. This increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoelectrics, and offers a realistic prospect of the recovery of a significant portion of waste heat.

  13. Enhanced Thermoelectricity in High-Temperature β-Phase Copper(I) Selenides Embedded with Cu2Te Nanoclusters.

    PubMed

    Butt, Sajid; Xu, Wei; Farooq, Muhammad U; Ren, Guang K; Zhang, Qinghua; Zhu, Yingcai; Khan, Sajid U; Liu, Lijuan; Yu, Meijuan; Mohmed, Fida; Lin, Yuanhua; Nan, Ce-Wen

    2016-06-22

    We report remarkably enhanced thermoelectric performance of Te doped Cu2Se in midtemperature range. Through ball-milling process followed by spark plasma sintering (SPS), nanoscale Cu2Te clusters were embeded in the matrix of Cu2Se, inducing a drastic enhancement of thermoelectric performance by reducing the thermal conductivity without degrading the power factor. A large ZT value of 1.9 was achieved at 873 K for Cu2Se1.9Te0.1, which is about 2 times larger than that of the pure Cu2Se. The nanoscale heat management by Cu2Te nanoclusters in superionic conductors opens up an avenue for thermoelectric materials research.

  14. Enhanced thermoelectric properties in bulk nanowire heterostructure-based nanocomposites through minority carrier blocking.

    PubMed

    Yang, Haoran; Bahk, Je-Hyeong; Day, Tristan; Mohammed, Amr M S; Snyder, G Jeffrey; Shakouri, Ali; Wu, Yue

    2015-02-11

    To design superior thermoelectric materials the minority carrier blocking effect in which the unwanted bipolar transport is prevented by the interfacial energy barriers in the heterogeneous nanostructures has been theoretically proposed recently. The theory predicts an enhanced power factor and a reduced bipolar thermal conductivity for materials with a relatively low doping level, which could lead to an improvement in the thermoelectric figure of merit (ZT). Here we show the first experimental demonstration of the minority carrier blocking in lead telluride-silver telluride (PbTe-Ag2Te) nanowire heterostructure-based nanocomposites. The nanocomposites are made by sintering PbTe-Ag2Te nanowire heterostructures produced in a highly scalable solution-phase synthesis. Compared with Ag2Te nanowire-based nanocomposite produced in similar method, the PbTe-Ag2Te nanocomposite containing ∼5 atomic % PbTe exhibits enhanced Seebeck coefficient, reduced thermal conductivity, and ∼40% improved ZT, which can be well explained by the theoretical modeling based on the Boltzmann transport equations when energy barriers for both electrons and holes at the heterostructure interfaces are considered in the calculations. For this p-type PbTe-Ag2Te nanocomposite, the barriers for electrons, that is, minority carriers, are primarily responsible for the ZT enhancement. By extending this approach to other nanostructured systems, it represents a key step toward low-cost solution-processable nanomaterials without heavy doping level for high-performance thermoelectric energy harvesting.

  15. Development of a prototype thermoelectric space cooling system using phase change material to improve the performance

    NASA Astrophysics Data System (ADS)

    Zhao, Dongliang

    The thermoelectric cooling system has advantages over conventional vapor compression cooling devices, including compact in size, light in weight, high reliability, no mechanical moving parts, no refrigerant, being powered by direct current, and easily switching between cooling and heating modes. However, it has been long suffering from its relatively high cost and low energy efficiency, which has restricted its usage to niche applications, such as space missions, portable cooling devices, scientific and medical equipment, where coefficient of performance (COP) is not as important as reliability, energy availability, and quiet operation environment. Enhancement of thermoelectric cooling system performance generally relies on two methods: improving thermoelectric material efficiency and through thermoelectric cooling system thermal design. This research has been focused on the latter one. A prototype thermoelectric cooling system integrated with phase change material (PCM) thermal energy storage unit for space cooling has been developed. The PCM thermal storage unit used for cold storage at night, functions as the thermoelectric cooling system's heat sink during daytime's cooling period and provides relatively lower hot side temperature for the thermoelectric cooling system. The experimental test of the prototype system in a reduced-scale chamber has realized an average cooling COP of 0.87, with the maximum value of 1.22. Another comparison test for efficacy of PCM thermal storage unit shows that 35.3% electrical energy has been saved from using PCM for the thermoelectric cooling system. In general, PCM faces difficulty of poor thermal conductivity at both solid and liquid phases. This system implemented a finned inner tube to increase heat transfer during PCM charging (melting) process that directly impacts thermoelectric system's performance. A simulation tool for the entire system has been developed including mathematical models for a single thermoelectric module

  16. Precise measurement of the performance of thermoelectric modules

    NASA Astrophysics Data System (ADS)

    Díaz-Chao, Pablo; Muñiz-Piniella, Andrés; Selezneva, Ekaterina; Cuenat, Alexandre

    2016-08-01

    The potential exploitation of thermoelectric modules into mass market applications such as exhaust gas heat recovery in combustion engines requires an accurate knowledge of their performance. Further expansion of the market will also require confidence on the results provided by suppliers to end-users. However, large variation in performance and maximum operating point is observed for identical modules when tested by different laboratories. Here, we present the first metrological study of the impact of mounting and testing procedures on the precision of thermoelectric modules measurement. Variability in the electrical output due to mechanical pressure or type of thermal interface materials is quantified for the first time. The respective contribution of the temperature difference and the mean temperature to the variation in the output performance is quantified. The contribution of these factors to the total uncertainties in module characterisation is detailed.

  17. Thermoelectric Enhancement in Polyaniline Composites with Polypyrrole-Functionalized Multiwall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Jie; Yu, Hui-Qun

    2014-04-01

    This work suggests a facile method to improve the thermoelectric properties of polyaniline (PANi) composites. Carbon multiwall nanotubes (MWNTs) were noncovalently functionalized with polypyrrole (PPy-MWNTs) based on in situ polymerization, and these PPy-MWNTs were used to synthesize PPy-MWNT/PANi composites. The surface-functionalized PPy nanolayer on the MWNTs was found to yield a homogeneous dispersion of MWNTs and strong interfacial adhesion. The resulting composites demonstrated a remarkable enhancement in both electrical conductivity and Seebeck coefficient, and exhibited a high power factor of 3.1 μW/m K2 compared with the values of 0.006 μW/m K2 for PANi and 0.1 μW/m K2 for MWNT/PANi composite at 28.6 wt.% MWNT loading. The obtained results indicate that this method is useful for synthesizing conductive polymer composites with improved thermoelectric performance.

  18. Enhanced power factor and high-pressure effects in (Bi,Sb){sub 2}(Te,Se){sub 3} thermoelectrics

    SciTech Connect

    Ovsyannikov, Sergey V. E-mail: sergey2503@gmail.com; Morozova, Natalia V.; Korobeinikov, Igor V.; Vokhmyanin, Alexander P.; Shchennikov, Vladimir V.; Lukyanova, Lidia N.; Usov, Oleg A.; Kutasov, Vsevolod A.; Manakov, Andrey Y.; Likhacheva, Anna Y.; Ancharov, Alexey I.; Berger, Ivan F.; Kulbachinskii, Vladimir A.; Okada, Taku

    2015-04-06

    We investigated the effects of applied high pressure on thermoelectric, electric, structural, and optical properties of single-crystalline thermoelectrics, Bi{sub 2}Te{sub 3}, Bi{sub x}Sb{sub 2−x}Te{sub 3} (x = 0.4, 0.5, 0.6), and Bi{sub 2}Te{sub 2.73}Se{sub 0.27} with the high thermoelectric performance. We established that moderate pressure of about 2–4 GPa can greatly enhance the thermoelectric power factor of all of them. X-ray diffraction and Raman studies on Bi{sub 2}Te{sub 3} and Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} found anomalies at similar pressures, indicating a link between crystal structure deformation and physical properties. We speculate about possible mechanisms of the power factor enhancement and suppose that pressure/stress tuning can be an effective tool for the optimization of the thermoelectric performance.

  19. High Thermoelectric Performance in Copper Telluride

    SciTech Connect

    He, Ying; Zhang, Tiansong; Shi, Xun; Wei, Su-Huai; Chen, Lidong

    2015-06-21

    Recently, Cu 2-δ S and Cu 2-δ Se were reported to have an ultralow thermal conductivity and high thermoelectric figure of merit zT. Thus, as a member of the copper chalcogenide group, Cu 2-δ Te is expected to possess superior zTs because Te is less ionic and heavy. However, the zT value is low in the Cu2Te sintered using spark plasma sintering, which is typically used to fabricate high-density bulk samples. In addition, the extra sintering processes may change the samples’ compositions as well as their physical properties, especially for Cu2Te, which has many stable and meta-stable phases as well as weaker ionic bonding between Cu and Te as compared with Cu2S and Cu2Se. In this study, high-density Cu2Te samples were obtained using direct annealing without a sintering process. In the absence of sintering processes, the samples’ compositions could be well controlled, leading to substantially reduced carrier concentrations that are close to the optimal value. The electrical transports were optimized, and the thermal conductivity was considerably reduced. The zT values were significantly improved—to 1.1 at 1000 K—which is nearly 100% improvement. Furthermore, this method saves substantial time and cost during the sample’s growth. The study demonstrates that Cu 2-δ X (X=S, Se and Te) is the only existing system to show high zTs in the series of compounds composed of three sequential primary group elements.

  20. High Thermoelectric Performance in Copper Telluride

    DOE PAGES

    He, Ying; Zhang, Tiansong; Shi, Xun; ...

    2015-06-21

    Recently, Cu 2-δ S and Cu 2-δ Se were reported to have an ultralow thermal conductivity and high thermoelectric figure of merit zT. Thus, as a member of the copper chalcogenide group, Cu 2-δ Te is expected to possess superior zTs because Te is less ionic and heavy. However, the zT value is low in the Cu2Te sintered using spark plasma sintering, which is typically used to fabricate high-density bulk samples. In addition, the extra sintering processes may change the samples’ compositions as well as their physical properties, especially for Cu2Te, which has many stable and meta-stable phasesmore » as well as weaker ionic bonding between Cu and Te as compared with Cu2S and Cu2Se. In this study, high-density Cu2Te samples were obtained using direct annealing without a sintering process. In the absence of sintering processes, the samples’ compositions could be well controlled, leading to substantially reduced carrier concentrations that are close to the optimal value. The electrical transports were optimized, and the thermal conductivity was considerably reduced. The zT values were significantly improved—to 1.1 at 1000 K—which is nearly 100% improvement. Furthermore, this method saves substantial time and cost during the sample’s growth. The study demonstrates that Cu 2-δ X (X=S, Se and Te) is the only existing system to show high zTs in the series of compounds composed of three sequential primary group elements.« less

  1. Impact of thermoelectric phenomena on phase-change memory performance metrics and scaling.

    PubMed

    Lee, Jaeho; Asheghi, Mehdi; Goodson, Kenneth E

    2012-05-25

    The coupled transport of heat and electrical current, or thermoelectric phenomena, can strongly influence the temperature distribution and figures of merit for phase-change memory (PCM). This paper simulates PCM devices with careful attention to thermoelectric transport and the resulting impact on programming current during the reset operation. The electrothermal simulations consider Thomson heating within the phase-change material and Peltier heating at the electrode interface. Using representative values for the Thomson and Seebeck coefficients extracted from our past measurements of these properties, we predict a cell temperature increase of 44% and a decrease in the programming current of 16%. Scaling arguments indicate that the impact of thermoelectric phenomena becomes greater with smaller dimensions due to enhanced thermal confinement. This work estimates the scaling of this reduction in programming current as electrode contact areas are reduced down to 10 nm × 10 nm. Precise understanding of thermoelectric phenomena and their impact on device performance is a critical part of PCM design strategies.

  2. Al-doped zinc oxide nanocomposites with enhanced thermoelectric properties.

    PubMed

    Jood, Priyanka; Mehta, Rutvik J; Zhang, Yanliang; Peleckis, Germanas; Wang, Xiaolin; Siegel, Richard W; Borca-Tasciuc, Theo; Dou, Shi Xue; Ramanath, Ganpati

    2011-10-12

    ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κ(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κ(L) than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl(2)O(4) nanoprecipitates presages ultralow κ ∼ 2 Wm( -1) K(-1) at 1000 K. The high α∼ -300 μV K(-1) and high σ ∼ 1-10(4) Ω(-1 )m(-1) result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ∼ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.

  3. High thermoelectric performance of the distorted bismuth(110) layer.

    PubMed

    Cheng, L; Liu, H J; Zhang, J; Wei, J; Liang, J H; Jiang, P H; Fan, D D; Sun, L; Shi, J

    2016-07-14

    The thermoelectric properties of the distorted bismuth(110) layer are investigated using first-principles calculations combined with the Boltzmann transport equation for both electrons and phonons. To accurately predict the electronic and transport properties, the quasiparticle corrections with the GW approximation of many-body effects have been explicitly included. It is found that a maximum ZT value of 6.4 can be achieved for n-type systems, which essentially stemmed from the weak scattering of electrons. Moreover, we demonstrate that the distorted Bi layer retains high ZT values in relatively broad regions of both temperature and carrier concentration. Our theoretical work emphasizes that the deformation potential constant characterizing the electron-phonon scattering strength is an important paradigm for searching high thermoelectric performance materials.

  4. Copper Selenide Nanocrystals as a High Performance, Solution Processed Thermoelectric Material

    NASA Astrophysics Data System (ADS)

    Forster, Jason; Lynch, Jared; Coates, Nelson; Sahu, Ayaskanta; Liu, Jun; Cahill, David; Urban, Jeff

    Nano-structuring a thermoelectric material often results in enhanced performance due to a decrease in the materials' thermal conductivity. Traditional nano-structuring techniques involve ball milling a bulk material followed by spark plasma sintering, a very energy intensive process. In this talk, we will describe the development of a self-assembled, high-performing, nano-structured thin film based on copper selenide nanocrystals. Mild thermal annealing of these films results in concurrent increases in the Seebeck coefficient and electrical conductivity. We are able to achieve power factors at room temperature that are as high as the best spark plasma sintered materials. These solution-processed films have potential applications as conformal, flexible materials for thermoelectric power generation.

  5. Compositional disorder and its effect on the thermoelectric performance of Zn₃P₂ nanowire-copper nanoparticle composites.

    PubMed

    Brockway, Lance; Vasiraju, Venkata; Vaddiraju, Sreeram

    2014-03-28

    Recent studies indicated that nanowire format of materials is ideal for enhancing the thermoelectric performance of materials. Most of these studies were performed using individual nanowires as the test elements. It is not currently clear whether bulk assemblies of nanowires replicate this enhanced thermoelectric performance of individual nanowires. Therefore, it is imperative to understand whether enhanced thermoelectric performance exhibited by individual nanowires can be extended to bulk assemblies of nanowires. It is also imperative to know whether the addition of metal nanoparticle to semiconductor nanowires can be employed for enhancing their thermoelectric performance further. Specifically, it is important to understand the effect of microstructure and composition on the thermoelectric performance on bulk compound semiconductor nanowire-metal nanoparticle composites. In this study, bulk composites composed of mixtures of copper nanoparticles with either unfunctionalized or 1,4-benzenedithiol (BDT) functionalized Zn₃P₂ nanowires were fabricated and analyzed for their thermoelectric performance. The results indicated that use of BDT functionalized nanowires for the fabrication of composites leads to interface-engineered composites that have uniform composition all across their cross-section. The interface engineering allows for increasing their Seebeck coefficients and electrical conductivities, relative to the Zn₃P₂ nanowire pellets. In contrast, the use of unfunctionalized Zn₃P₂ nanowires for the fabrication of composite leads to the formation of composites that are non-uniform in composition across their cross-section. Ultimately, the composites were found to have Zn₃P₂ nanowires interspersed with metal alloy nanoparticles. Such non-uniform composites exhibited very high electrical conductivities, but slightly lower Seebeck coefficients, relative to Zn₃P₂ nanowire pellets. These composites were found to show a very high zT of 0.23 at 770

  6. Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

    NASA Astrophysics Data System (ADS)

    Ramos, R.; Anadón, A.; Lucas, I.; Uchida, K.; Algarabel, P. A.; Morellón, L.; Aguirre, M. H.; Saitoh, E.; Ibarra, M. R.

    2016-10-01

    We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect.

  7. Enhanced thermoelectric power and electronic correlations in RuSe₂

    SciTech Connect

    Wang, Kefeng; Wang, Aifeng; Tomic, A.; Wang, Limin; Abeykoon, A. M. Milinda; Dooryhee, E.; Billinge, S. J.L.; Petrovic, C.

    2015-03-03

    We report the electronic structure, electric and thermal transport properties of Ru₁₋xIrxSe₂ (x ≤ 0.2). RuSe₂ is a semiconductor that crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe₂ exceeds -200 µV/K around 730 K. Ir substitution results in the suppression of the resistivity and the Seebeck coefficient, suggesting the removal of the peaks in density of states near the Fermi level. Ru₀.₈Ir₀.₂Se₂ shows a semiconductor-metal crossover at about 30 K. The magnetic field restores the semiconducting behavior. Our results indicate the importance of the electronic correlations in enhanced thermoelectricity of RuSb₂.

  8. Enhanced thermoelectric power and electronic correlations in RuSe₂

    DOE PAGES

    Wang, Kefeng; Wang, Aifeng; Tomic, A.; ...

    2015-03-03

    We report the electronic structure, electric and thermal transport properties of Ru₁₋xIrxSe₂ (x ≤ 0.2). RuSe₂ is a semiconductor that crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe₂ exceeds -200 µV/K around 730 K. Ir substitution results in the suppression of the resistivity and the Seebeck coefficient, suggesting the removal of the peaks in density of states near the Fermi level. Ru₀.₈Ir₀.₂Se₂ shows a semiconductor-metal crossover at about 30 K. The magnetic field restores the semiconducting behavior. Our results indicate the importance of the electronic correlations in enhanced thermoelectricity of RuSb₂.

  9. Thermoelectric property enhancement by Cu nanoparticles in nanostructured FeSb2

    NASA Astrophysics Data System (ADS)

    Koirala, Machhindra; Zhao, Huaizhou; Pokharel, Mani; Chen, Shuo; Dahal, Tulashi; Opeil, Cyril; Chen, Gang; Ren, Zhifeng

    2013-05-01

    We present the thermoelectric figure-of-merit (ZT) improvement in nanostructured FeSb2 by Cu nanoparticles of ˜5 nm as a modulation dopant. Because of the similar work functions between FeSb2 and Cu and the high electrical conductivity of Cu, the Kondo insulator-like electrical resistivity of FeSb2 at low temperatures was dramatically reduced. Both carrier concentration and mobility of the nanocomposites were improved over pure FeSb2 without degrading the Seebeck coefficient. Overall, an improvement of ˜90% in power factor was achieved for the optimized nanocomposite FeSb2Cu0.045. Combined with the reduced thermal conductivity by Cu/FeSb2 interfaces, ZT was improved by ˜110%. These results clearly demonstrate the potential of modulation doping to enhance the thermoelectric performance of FeSb2. A similar approach could be applied to other Kondo insulators or previously known thermoelectric materials to improve ZT.

  10. ZnTe Alloying Effect on Enhanced Thermoelectric Properties of p-Type PbTe.

    PubMed

    Ahn, Kyunghan; Shin, Hocheol; Im, Jino; Park, Sang Hyun; Chung, In

    2017-02-01

    We investigate the effect of ZnTe incorporation on PbTe to enhance thermoelectric performance. We report structural, microscopic, and spectroscopic characterizations, ab initio theoretical calculations, and thermoelectric transport properties of Pb0.985Na0.015Te-x% ZnTe (x = 0, 1, 2, 4). We find that the solid solubility limit of ZnTe in PbTe is less than 1 mol %. The introduction of 2% ZnTe in p-type Pb0.985Na0.015Te reduces the lattice thermal conductivity through the ZnTe precipitates at the microscale. Consequently, a maximum thermoelectric figure of merit (ZT) of 1.73 at 700 K is achieved for the spark plasma-sintered Pb0.985Na0.015Te-2% ZnTe, which arises from a decreased lattice thermal conductivity of ∼0.69 W m(-1) K(-1) at ∼700 K in comparison with Pb0.985Na0.015Te.

  11. Modeling and theoretical efficiency of a silicon nanowire based thermoelectric junction with area enhancement

    SciTech Connect

    Seong, M; Sadhu, JS; Ma, J; Ghossoub, MG; Sinha, S

    2012-06-15

    Recent experimental work suggests that individual silicon nanowires with rough surfaces possess a thermoelectric figure of merit as high as 0.6 near room temperature. This paper addresses the possibility of using an array of such nanowires in a thermoelectric junction for generation. Employing a model of frequency dependent phonon boundary scattering, we estimate the effective thermal conductivity of the array and investigate heat flow through the junction. We show that charge transport is largely unaffected by the roughness scales considered. Enhancing the area for heat exchange at an individual 200 mu m x 200 mu m p-n junction yields significant temperature differences across the junction leading to power >0.6 mW and efficiency >1.5% for a junction with effective thermal conductivity <5 W/mK, when the source and sink are at 450 K and 300 K, respectively. We show that relatively short nanowires of similar to 50 mu m length are sufficient for obtaining peak power and reasonable efficiency. This substantially reduces the challenge of engineering low resistivity electrical contacts that critically affect power and efficiency. This paper provides insight into how fundamental transport in relation to bulk heat transfer and charge transport, affects the performance of thermoelectric junctions based on nanostructured materials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4728189

  12. Spectacular enhancement of thermoelectric phenomena in chemically synthesized graphene nanoribbons with substitution atoms.

    PubMed

    Zberecki, K; Swirkowicz, R; Wierzbicki, M; Barnaś, J

    2016-07-21

    We analyze theoretically the transport and thermoelectric properties of graphene nanoribbons of a specific geometry, which have been synthesized recently from polymers [Cai, et al., Nature, 2011, 466, 470]. When such nanoribbons are modified at one of the two edges by Al or N substitutions, they acquire a ferromagnetic moment localized at the modified edge. We present numerical results on the electronic structure and thermoelectric properties (including also spin thermoelectricity) of the modified nanoribbons. The results show that such nanoribbons can display large thermoelectric efficiency in certain regions of chemical potential, where the corresponding electric and spin figures of merit achieve unusually large values. The enhancement of thermoelectric efficiency follows from a reduced phonon heat conductance of the nanoribbons and from their peculiar electronic band structure. Thus, such nanoribbons are promising for practical applications in nanoelectronic and spintronic devices.

  13. Effect of microstructure on the thermoelectric performance of La1-xSrxCoO3

    NASA Astrophysics Data System (ADS)

    Viskadourakis, Z.; Athanasopoulos, G. I.; Kasotakis, E.; Giapintzakis, J.

    2016-11-01

    We present a case where the microstructure has a profound effect on the thermoelectric properties of oxide compounds. Specifically, we have investigated the effect of different sintering treatments on La1-xSrxCoO3 samples synthesized using the Pechini method. We found that the samples, which are dense and consist of inhomogeneously-mixed grains of different size, exhibit both higher Seebeck coefficient and thermoelectric figure of merit than the samples, which are porous and consist of grains with almost identical size. The enhancement of Seebeck coefficient in the dense samples is attributed to the so-called "energy-filtering" mechanism that is related to the energy barrier of the grain boundary. On the other hand, the thermal conductivity for the porous compounds is significantly reduced in comparison to the dense compounds. It is suggested that a fine-manipulation of grain size ratio combined with a fine-tuning of porosity could considerably enhance the thermoelectric performance of oxides.

  14. Performance Model and Sensitivity Analysis for a Solar Thermoelectric Generator

    NASA Astrophysics Data System (ADS)

    Rehman, Naveed Ur; Siddiqui, Mubashir Ali

    2017-01-01

    In this paper, a regression model for evaluating the performance of solar concentrated thermoelectric generators (SCTEGs) is established and the significance of contributing parameters is discussed in detail. The model is based on several natural, design and operational parameters of the system, including the thermoelectric generator (TEG) module and its intrinsic material properties, the connected electrical load, concentrator attributes, heat transfer coefficients, solar flux, and ambient temperature. The model is developed by fitting a response curve, using the least-squares method, to the results. The sample points for the model were obtained by simulating a thermodynamic model, also developed in this paper, over a range of values of input variables. These samples were generated employing the Latin hypercube sampling (LHS) technique using a realistic distribution of parameters. The coefficient of determination was found to be 99.2%. The proposed model is validated by comparing the predicted results with those in the published literature. In addition, based on the elasticity for parameters in the model, sensitivity analysis was performed and the effects of parameters on the performance of SCTEGs are discussed in detail. This research will contribute to the design and performance evaluation of any SCTEG system for a variety of applications.

  15. Performance Model and Sensitivity Analysis for a Solar Thermoelectric Generator

    NASA Astrophysics Data System (ADS)

    Rehman, Naveed Ur; Siddiqui, Mubashir Ali

    2017-03-01

    In this paper, a regression model for evaluating the performance of solar concentrated thermoelectric generators (SCTEGs) is established and the significance of contributing parameters is discussed in detail. The model is based on several natural, design and operational parameters of the system, including the thermoelectric generator (TEG) module and its intrinsic material properties, the connected electrical load, concentrator attributes, heat transfer coefficients, solar flux, and ambient temperature. The model is developed by fitting a response curve, using the least-squares method, to the results. The sample points for the model were obtained by simulating a thermodynamic model, also developed in this paper, over a range of values of input variables. These samples were generated employing the Latin hypercube sampling (LHS) technique using a realistic distribution of parameters. The coefficient of determination was found to be 99.2%. The proposed model is validated by comparing the predicted results with those in the published literature. In addition, based on the elasticity for parameters in the model, sensitivity analysis was performed and the effects of parameters on the performance of SCTEGs are discussed in detail. This research will contribute to the design and performance evaluation of any SCTEG system for a variety of applications.

  16. Cross-plane enhanced thermoelectricity and phonon suppression in graphene/MoS2 van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Sadeghi, Hatef; Sangtarash, Sara; Lambert, Colin J.

    2017-03-01

    The thermoelectric figures of merit of pristine two-dimensional materials are predicted to be significantly less than unity, making them uncompetitive as thermoelectric materials. Here we elucidate a new strategy that overcomes this limitation by creating multi-layer nanoribbons of two different materials and allowing thermal and electrical currents to flow perpendicular to their planes. To demonstrate this enhancement of thermoelectric efficiency ZT, we analyse the thermoelectric performance of monolayer molybdenum disulphide (MoS2) sandwiched between two graphene monolayers and demonstrate that the cross-plane (CP) ZT is significantly enhanced compared with the pristine parent materials. For the parent monolayer of MoS2, we find that ZT can be as high as approximately 0.3, whereas monolayer graphene has a negligibly small ZT. In contrast for the graphene/MoS2/graphene heterostructure, we find that the CP ZT can be as large as 2.8. One contribution to this enhancement is a reduction of the thermal conductance of the van der Waals heterostructure compared with the parent materials, caused by a combination of boundary scattering at the MoS2/graphene interface which suppresses the phonons transmission and the lower Debye frequency of monolayer MoS2, which filters phonons from the monolayer graphene. A second contribution is an increase in the electrical conductance and Seebeck coefficient associated with molybdenum atoms at the edges of the nanoribbons.

  17. Thermoelectric Property Dependence on Performance of Peltier Current Leads Under Overcurrent Conditions

    NASA Astrophysics Data System (ADS)

    Kawahara, Toshio; Emoto, Masahiko; Hamabe, Makoto; Watanabe, Hirofumi; Ivanov, Yury; Sun, Jian; Yamaguchi, Satarou

    2012-06-01

    Superconductivity can potentially provide a solution to the world's energy needs because superconducting transmission and distribution (T&D) systems can decrease losses and are also capable of integrating renewables into the power grid. At Chubu University we have built a 200-m-class superconducting direct-current T&D system (CASER-2). To minimize heat leakage from the current leads, we investigated thermoelectric materials. The Peltier current lead (PCL) is one of the key technologies that will enhance the performance of superconducting systems: as direct current (DC) flows through the current lead, thermoelectric elements on opposite terminations of the superconducting line can be used to decrease the heat ingress to the cryogenic environment ( n-type on one end, p-type on the opposite end). The heat leakage to the cryogenic environment depends on the properties of the thermoelectric materials. In this paper, we estimate the performance of PCLs in cryogenic operations, including the potential for overcurrent operation, through both modeling and experiments at CASER-2.

  18. Thermoelectric power enhancement by way of flow impedance for fixed thermal input conditions

    NASA Astrophysics Data System (ADS)

    Amaral, Calil; Brandão, Caio; Sempels, Éric V.; Lesage, Frédéric J.

    2014-12-01

    Liquid-to-liquid thermoelectric generators are now being considered for the purpose of converting low cost heat to electricity for local energy uses. The importance in investigating their system efficiency lies in the fact that the generator's purpose is to maintain a heat source and a heat sink for its embedded thermoelectric modules. Of particular importance is the generator's ability to maintain an asymmetric thermal field across its embedded modules since this mechanism partially dictates the devices' thermal to electric conversion efficiency. Indeed, since the modules' semiconductor materials' ability to generate an electromotive force is dependent on the quality of the thermal dipole across the material, gains in thermoelectric generator energy conversion efficiency are made possible with thermal system management. In an effort to improve the system conversion efficiency of a liquid-to-liquid thermoelectric generator (TEG), the present work builds upon recent advancements in TEG inner pipe flow optimisation by investigating the thermoelectric power enhancement brought upon by flow impeding panel inserts in a thermoelectric generator's flow channels for fixed thermal input conditions and with respect to varying insert panel densities. The pumping penalty associated with the flow impedance is measured in order to present and to discuss the net thermoelectric power enhancement.

  19. Multi-role of Sodium Doping in BiCuSeO on High Thermoelectric Performance

    NASA Astrophysics Data System (ADS)

    Zhang, Mingyang; Yang, Junyou; Jiang, Qinghui; Fu, Liangwei; Xiao, Ye; Luo, Yubo; Zhang, Dan; Cheng, Yudong; Zhou, Zhiwei

    2015-08-01

    In this work, Na-doped BiCuSeO thermoelectric materials have been prepared and the effect of Na doping on their microstructure and thermoelectric properties has been studied. When the doping content is less than 6%, all Na+ can dissolve into the matrix and substitute for Bi3+ sites and play a role of acceptor; when the content is above 6%, the substitution saturates and excessive doping results in the formation of Na2CO3 and Na2SeO3 secondary phases. On the one hand, the doping of Na+ for Bi3+ can significantly improve the electrical properties due to the significant increase of carrier concentration. Furthermore, the phonon and total thermal conductivity also decrease with Na doping because of the dual phonon scattering by the point defects and secondary phases both resulting from Na+ doping. As a result, the thermoelectric performance is enhanced, and a maximum ZT value of 0.97, which is approximately triple that of the undoped BiCuSeO, is achieved at 873 K for the Bi0.92Na0.08CuSeO sample.

  20. High Thermoelectric Performance by Convergence of Bands in IV-VI Semiconductors, Heavily Doped PbTe, and Alloys/Nanocomposites

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey (Inventor); Pei, Yanzhong (Inventor)

    2015-01-01

    The present invention teaches an effective mechanism for enhancing thermoelectric performance through additional conductive bands. Using heavily doped p-PbTe materials as an example, a quantitative explanation is disclosed, as to why and how these additional bands affect the figure of merit. A high zT of approaching 2 at high temperatures makes these simple, likely more stable (than nanostructured materials) and Tl-free materials excellent for thermoelectric applications.

  1. Thermochemically evolved nanoplatelets of bismuth selenide with enhanced thermoelectric figure of merit

    SciTech Connect

    Ali, Zulfiqar; Cao, Chuanbao Butt, Faheem K.; Tahir, Muhammad; Tanveer, M.; Aslam, Imran; Rizwan, Muhammad; Idrees, Faryal; Khalid, Syed; Butt, Sajid

    2014-11-15

    We firstly present a simple thermochemical method to fabricate high-quality Bi{sub 2}Se{sub 3} nanoplatelets with enhanced figure of merit using elemental bismuth and selenium powders as precursors. The crystal structure of as synthesized products is characterized via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) measurements. Morphological and chemical synthetic parameters are investigated through a series of experiments; thickness and composition of the platelets are well controlled in large scale production. Subsequently spark plasma sintering (SPS) is performed to fabricate n-type nanostructured bulk thermoelectric materials. Raman Spectroscopy of the two selected samples with approximately of 50 and 100 nm thicknesses shows three vibrational modes. The lower thickness sample exhibits the maximum red shift of about 2.17 cm{sup -1} and maximum broadening of about 10 cm{sup -1} by in-plane vibrational mode E{sup 2}{sub g}. The enhanced value of figure of merit ∼0.41 is obtained for pure phase bismuth selenide to the best of our knowledge. We observe metallic conduction behavior while semiconducting behavior for nanostructured bismuth selenide is reported elsewhere which could be due to different synthetic techniques adopted. These results clearly suggest that our adopted synthetic technique has profound effect on the electronic and thermoelectric transport properties of this material.

  2. Numerical Examination of the Performance of a Thermoelectric Cooler with Peltier Heating and Cooling

    NASA Astrophysics Data System (ADS)

    Kim, Chang Nyung; Kim, Jeongho

    2015-10-01

    There has recently been much progress in the development of materials with higher thermoelectric performance, leading to the design of thermoelectric devices for generation of electricity and for heating or cooling. Local heating can be achieved by current flow through an electric resistance, and local heating and cooling can be performed by Peltier heating and cooling. In this study, we developed computer software that can be used to predict the Seebeck and Peltier effects for thermoelectric devices. The temperature, electric potential, heat flow, electric current, and coefficient of performance were determined, with the objective of investigating the Peltier effect in a thermoelectric device. In addition to Peltier heating and cooling, Joule and Thomson heating were quantitatively evaluated for the thermoelectric device.

  3. Enhanced thermoelectric power in two-dimensional transition metal dichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Pu, Jiang; Kanahashi, Kaito; Cuong, Nguyen Thanh; Chen, Chang-Hsiao; Li, Lain-Jong; Okada, Susumu; Ohta, Hiromichi; Takenobu, Taishi

    2016-07-01

    The carrier-density-dependent conductance and thermoelectric properties of large-area Mo S2 and WS e2 monolayers are simultaneously investigated using the electrolyte gating method. The sign of the thermoelectric power changes across the transistor off-state in the ambipolar WS e2 transistor as the majority carrier density switches from electron to hole. The thermopower and thermoelectric power factor of monolayer samples are one order of magnitude larger than that of bulk materials, and their carrier-density dependences exhibit a quantitative agreement with the semiclassical Mott relation based on the two-dimensional energy band structure, concluding the thermoelectric properties are enhanced by the low-dimensional effect.

  4. High-performance and flexible thermoelectric films by screen printing solution-processed nanoplate crystals

    PubMed Central

    Varghese, Tony; Hollar, Courtney; Richardson, Joseph; Kempf, Nicholas; Han, Chao; Gamarachchi, Pasindu; Estrada, David; Mehta, Rutvik J.; Zhang, Yanliang

    2016-01-01

    Screen printing allows for direct conversion of thermoelectric nanocrystals into flexible energy harvesters and coolers. However, obtaining flexible thermoelectric materials with high figure of merit ZT through printing is an exacting challenge due to the difficulties to synthesize high-performance thermoelectric inks and the poor density and electrical conductivity of the printed films. Here, we demonstrate high-performance flexible films and devices by screen printing bismuth telluride based nanocrystal inks synthesized using a microwave-stimulated wet-chemical method. Thermoelectric films of several tens of microns thickness were screen printed onto a flexible polyimide substrate followed by cold compaction and sintering. The n-type films demonstrate a peak ZT of 0.43 along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density of 4.1 mW/cm2 with 60 °C temperature difference between the hot side and cold side. The highly scalable and low cost process to fabricate flexible thermoelectric materials and devices demonstrated here opens up many opportunities to transform thermoelectric energy harvesting and cooling applications. PMID:27615036

  5. High-performance and flexible thermoelectric films by screen printing solution-processed nanoplate crystals

    NASA Astrophysics Data System (ADS)

    Varghese, Tony; Hollar, Courtney; Richardson, Joseph; Kempf, Nicholas; Han, Chao; Gamarachchi, Pasindu; Estrada, David; Mehta, Rutvik J.; Zhang, Yanliang

    2016-09-01

    Screen printing allows for direct conversion of thermoelectric nanocrystals into flexible energy harvesters and coolers. However, obtaining flexible thermoelectric materials with high figure of merit ZT through printing is an exacting challenge due to the difficulties to synthesize high-performance thermoelectric inks and the poor density and electrical conductivity of the printed films. Here, we demonstrate high-performance flexible films and devices by screen printing bismuth telluride based nanocrystal inks synthesized using a microwave-stimulated wet-chemical method. Thermoelectric films of several tens of microns thickness were screen printed onto a flexible polyimide substrate followed by cold compaction and sintering. The n-type films demonstrate a peak ZT of 0.43 along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density of 4.1 mW/cm2 with 60 °C temperature difference between the hot side and cold side. The highly scalable and low cost process to fabricate flexible thermoelectric materials and devices demonstrated here opens up many opportunities to transform thermoelectric energy harvesting and cooling applications.

  6. Discovery of high-performance low-cost n-type Mg3Sb2-based thermoelectric materials with multi-valley conduction bands

    NASA Astrophysics Data System (ADS)

    Zhang, Jiawei; Song, Lirong; Pedersen, Steffen Hindborg; Yin, Hao; Hung, Le Thanh; Iversen, Bo Brummerstedt

    2017-01-01

    Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg3Sb1.5Bi0.5, that exhibits a very high figure of merit zT ranging from 0.56 to 1.65 at 300-725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg3Sb1.5Bi0.5 a promising candidate for the low- and intermediate-temperature thermoelectric applications.

  7. Advanced thermoelectric materials with enhanced crystal lattice structure and methods of preparation

    NASA Technical Reports Server (NTRS)

    Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

    1998-01-01

    New skutterudite phases including Ru.sub.0.5 Pd.sub.0.5 Sb.sub.3, RuSb.sub.2 Te, and FeSb.sub.2 Te, have been prepared having desirable thermoelectric properties. In addition, a novel thermoelectric device has been prepared using skutterudite phase Fe.sub.0.5 Ni.sub.0.5 Sb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using powder metallurgy techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities and good Seebeck coefficients. These materials have low thermal conductivity and relatively low electrical resistivity, and are good candidates for low temperature thermoelectric applications.

  8. Enhancement of thermoelectric efficiency by quantum interference effects in trilayer silicene flakes

    NASA Astrophysics Data System (ADS)

    Cortés, Natalia; Rosales, L.; Chico, Leonor; Pacheco, M.; Orellana, P. A.

    2017-01-01

    In recent years, the enhancement of thermoelectric efficiencies has been accomplished in nanoscale systems by making use of quantum effects. We exploit the presence of quantum interference phenomena such as bound states in the continuum and Fano antiresonances in trilayer silicene flakes to produce sharp changes in the electronic transmission of the system. By applying symmetric gate voltages the thermoelectric properties can be tuned and, for particular flake lengths, a great enhancement of the figure of merit can be achieved. We show that the most favorable configurations are those in which the electronic transmission is dominated by the coupling of bound states to the continuum, tuned by an external gate.

  9. Numerical and Experimental Investigation for Heat Transfer Enhancement by Dimpled Surface Heat Exchanger in Thermoelectric Generator

    NASA Astrophysics Data System (ADS)

    Wang, Yiping; Li, Shuai; Yang, Xue; Deng, Yadong; Su, Chuqi

    2016-03-01

    For vehicle thermoelectric exhaust energy recovery, the temperature difference between the heat exchanger and the coolant has a strong influence on the electric power generation, and ribs are often employed to enhance the heat transfer of the heat exchanger. However, the introduction of ribs will result in a large unwanted pressure drop in the exhaust system which is unfavorable for the engine's efficiency. Therefore, how to enhance the heat transfer and control the pressure drop in the exhaust system is quite important for thermoelectric generators (TEG). In the current study, a symmetrical arrangement of dimpled surfaces staggered in the upper and lower surfaces of the heat exchanger was proposed to augment heat transfer rates with minimal pressure drop penalties. The turbulent flow characteristics and heat transfer performance of turbulent flow over the dimpled surface in a flat heat exchanger was investigated by numerical simulation and temperature measurements. The heat transfer capacity in terms of Nusselt number and the pressure loss in terms of Fanning friction factors of the exchanger were compared with those of the flat plate. The pressure loss and heat transfer characteristics of dimples with a depth-to-diameter ratio ( h/D) at 0.2 were investigated. Finally, a quite good heat transfer performance with minimal pressure drop heat exchanger in a vehicle TEG was obtained. And based on the area-averaged surface temperature of the heat exchanger and the Seeback effect, the power generation can be improved by about 15% at Re = 25,000 compared to a heat exchanger with a flat surface.

  10. Phase transition enhanced thermoelectric figure-of-merit in copper chalcogenides

    NASA Astrophysics Data System (ADS)

    Brown, David R.; Day, Tristan; Borup, Kasper A.; Christensen, Sebastian; Iversen, Bo B.; Snyder, G. Jeffrey

    2013-11-01

    While thermoelectric materials can be used for solid state cooling, waste heat recovery, and solar electricity generation, low values of the thermoelectric figure of merit, zT, have led to an efficiency too low for widespread use. Thermoelectric effects are characterized by the Seebeck coefficient or thermopower, which is related to the entropy associated with charge transport. For example, coupling spin entropy with the presence of charge carriers has enabled the enhancement of zT in cobalt oxides. We demonstrate that the coupling of a continuous phase transition to carrier transport in Cu2Se over a broad (360-410 K) temperature range results in a dramatic peak in thermopower, an increase in phonon and electron scattering, and a corresponding doubling of zT (to 0.7 at 406 K), and a similar but larger increase over a wider temperature range in the zT of Cu1.97Ag.03Se (almost 1.0 at 400 K). The use of structural entropy for enhanced thermopower could lead to new engineering approaches for thermoelectric materials with high zT and new green applications for thermoelectrics.

  11. Phase transition enhanced thermoelectric figure-of-merit in copper chalcogenides

    SciTech Connect

    Brown, David R.; Day, Tristan; Snyder, G. Jeffrey; Borup, Kasper A.; Christensen, Sebastian; Iversen, Bo B.

    2013-11-01

    While thermoelectric materials can be used for solid state cooling, waste heat recovery, and solar electricity generation, low values of the thermoelectric figure of merit, zT, have led to an efficiency too low for widespread use. Thermoelectric effects are characterized by the Seebeck coefficient or thermopower, which is related to the entropy associated with charge transport. For example, coupling spin entropy with the presence of charge carriers has enabled the enhancement of zT in cobalt oxides. We demonstrate that the coupling of a continuous phase transition to carrier transport in Cu{sub 2}Se over a broad (360–410 K) temperature range results in a dramatic peak in thermopower, an increase in phonon and electron scattering, and a corresponding doubling of zT (to 0.7 at 406 K), and a similar but larger increase over a wider temperature range in the zT of Cu{sub 1.97}Ag{sub .03}Se (almost 1.0 at 400 K). The use of structural entropy for enhanced thermopower could lead to new engineering approaches for thermoelectric materials with high zT and new green applications for thermoelectrics.

  12. High-performance thermoelectric nanocomposites from nanocrystal building blocks

    NASA Astrophysics Data System (ADS)

    Ibáñez, Maria; Luo, Zhishan; Genç, Aziz; Piveteau, Laura; Ortega, Silvia; Cadavid, Doris; Dobrozhan, Oleksandr; Liu, Yu; Nachtegaal, Maarten; Zebarjadi, Mona; Arbiol, Jordi; Kovalenko, Maksym V.; Cabot, Andreu

    2016-03-01

    The efficient conversion between thermal and electrical energy by means of durable, silent and scalable solid-state thermoelectric devices has been a long standing goal. While nanocrystalline materials have already led to substantially higher thermoelectric efficiencies, further improvements are expected to arise from precise chemical engineering of nanoscale building blocks and interfaces. Here we present a simple and versatile bottom-up strategy based on the assembly of colloidal nanocrystals to produce consolidated yet nanostructured thermoelectric materials. In the case study on the PbS-Ag system, Ag nanodomains not only contribute to block phonon propagation, but also provide electrons to the PbS host semiconductor and reduce the PbS intergrain energy barriers for charge transport. Thus, PbS-Ag nanocomposites exhibit reduced thermal conductivities and higher charge carrier concentrations and mobilities than PbS nanomaterial. Such improvements of the material transport properties provide thermoelectric figures of merit up to 1.7 at 850 K.

  13. Investigation of the photovoltaic cell/ thermoelectric element hybrid system performance

    NASA Astrophysics Data System (ADS)

    Cotfas, D. T.; Cotfas, P. A.; Machidon, O. M.; Ciobanu, D.

    2016-06-01

    The PV/TEG hybrid system, consisting of the photovoltaic cells and thermoelectric element, is presented in the paper. The dependence of the PV/TEG hybrid system parameters on the illumination levels and the temperature is analysed. The maxim power values of the photovoltaic cell, of the thermoelectric element and of the PV/TEG system are calculated and a comparison between them is presented and analysed. An economic analysis is also presented.

  14. Enhanced thermoelectric figure of merit in strained Tl-doped Bi{sub 2}Se{sub 3}

    SciTech Connect

    Saeed, Y.; Singh, N.; Schwingenschlögl, U.

    2014-07-21

    We explain recent experimental findings on Tl-doped Bi{sub 2}Se{sub 3} by determining the electronic and transport properties by first-principles calculations and semi-classical Boltzmann theory. Though Tl-doping introduces a momentum-dependent spin-orbit splitting, the effective mass of the carriers is essentially not modified, while the band gap is reduced. Tl is found to be exceptional in this respect as other dopants modify the dispersion, which compromises thermoelectricity. Moreover, we demonstrate that only after Tl-doping strain becomes an efficient tool for enhancing the thermoelectric performance. A high figure of merit of 0.86 is obtained for strong p-doping (7 × 10{sup 20} cm{sup −3}, maximal power factor) at 500 K under 2% tensile strain.

  15. Evaluation of Thermoelectric Performance and Durability of Functionalized Skutterudite Legs

    NASA Astrophysics Data System (ADS)

    Skomedal, Gunstein; Kristiansen, Nils R.; Sottong, Reinhard; Middleton, Hugh

    2017-04-01

    Thermoelectric generators are a promising technology for waste heat recovery. As new materials and devices enter a market penetration stage, it is of interest to employ fast and efficient measurement methods to evaluate the long-term stability of thermoelectric materials in combination with metallization and coating (functionalized thermoelectric legs). We have investigated a method for measuring several thermoelectric legs simultaneously. The legs are put under a common temperature gradient, and the electrical characteristics of each leg are measured individually during thermal cycling. Using this method, one can test different types of metallization and coating applied to skutterudite thermoelectric legs and look at the relative changes over time. Postcharacterization of these initial tests with skutterudite legs using a potential Seebeck microprobe and an electron microscope showed that oxidation and interlayer diffusion are the main reasons for the gradual increase in internal resistance and the decrease in open-circuit voltage. Although we only tested skutterudite material in this work, the method is fully capable of testing all kinds of material, metallization, and coating. It is thus a promising method for studying the relationship between failure modes and mechanisms of functionalized thermoelectric legs.

  16. Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers

    PubMed Central

    Lee, Kyeong-Dong; Kim, Dong-Jun; Yeon Lee, Hae; Kim, Seung-Hyun; Lee, Jong-Hyun; Lee, Kyung-Min; Jeong, Jong-Ryul; Lee, Ki-Suk; Song, Hyon-Seok; Sohn, Jeong-Woo; Shin, Sung-Chul; Park, Byong-Guk

    2015-01-01

    The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices. PMID:26020492

  17. Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers.

    PubMed

    Lee, Kyeong-Dong; Kim, Dong-Jun; Yeon Lee, Hae; Kim, Seung-Hyun; Lee, Jong-Hyun; Lee, Kyung-Min; Jeong, Jong-Ryul; Lee, Ki-Suk; Song, Hyon-Seok; Sohn, Jeong-Woo; Shin, Sung-Chul; Park, Byong-Guk

    2015-05-28

    The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices.

  18. Semimetal/Semiconductor Nanocomposites for Thermoelectrics

    SciTech Connect

    Lu, Hong; Burke, Peter G.; Gossard, Arthur C.; Zeng, Gehong; Ramu, Ashok T.; Bahk, Je-Hyeong; Bowers, John E.

    2011-04-15

    In this work, we present research on semimetal-semiconductor nanocomposites grown by molecular beam epitaxy (MBE) for thermoelectric applications. We study several different III-V semiconductors embedded with semimetallic rare earth-group V (RE-V) compounds, but focus is given here to ErSb:InxGa1-xSb as a promising p-type thermoelectric material. Nano­structures of RE-V compounds are formed and embedded within the III-V semiconductor matrix. By codoping the nanocomposites with the appropriate dopants, both n-type and p-type materials have been made for thermoelectric applications. The thermoelectric properties have been engineered for enhanced thermoelectric device performance. Segmented thermoelectric power generator modules using 50 μm thick Er-containing nanocomposites have been fabricated and measured. Research on different rare earth elements for thermoelectrics is discussed.

  19. Semimetal/semiconductor nanocomposites for thermoelectrics.

    PubMed

    Lu, Hong; Burke, Peter G; Gossard, Arthur C; Zeng, Gehong; Ramu, Ashok T; Bahk, Je-Hyeong; Bowers, John E

    2011-05-24

    In this work, we present research on semimetal-semiconductor nanocomposites grown by molecular beam epitaxy (MBE) for thermoelectric applications. We study several different III-V semiconductors embedded with semimetallic rare earth-group V (RE-V) compounds, but focus is given here to ErSb:In(x)Ga(1−x)Sb as a promising p-type thermoelectric material. Nanostructures of RE-V compounds are formed and embedded within the III-V semiconductor matrix. By co-doping the nanocomposites with the appropriate dopants, both n-type and p-type materials have been made for thermoelectric applications. The thermoelectric properties have been engineered for enhanced thermoelectric device performance. Segmented thermoelectric power generator modules using 50 μ m thick Er-containing nanocomposites have been fabricated and measured. Research on different rare earth elements for thermoelectrics is discussed.

  20. Thermoelectric efficiency of (1 - x)(GeTe) x(Bi2Se0.2Te2.8) and implementation into highly performing thermoelectric power generators.

    PubMed

    Koenig, J; Winkler, M; Dankwort, T; Hansen, A-L; Pernau, H-F; Duppel, V; Jaegle, M; Bartholomé, K; Kienle, L; Bensch, W

    2015-02-14

    Here we report for the first time on a complete simulation assisted "material to module" development of a high performance thermoelectric generator (TEG) based on the combination of a phase change material and established thermoelectrics yielding the compositions (1 - x)(GeTe) x(Bi(2)Se(0.2)Te(2.8)). For the generator design our approach for benchmarking thermoelectric materials is demonstrated which is not restricted to the determination of the intrinsically imprecise ZT value but includes the implementation of the material into a TEG. This approach is enabling a much more reliable benchmarking of thermoelectric materials for TEG application. Furthermore we analyzed the microstructure and performance close to in-operandi conditions for two different compositions in order to demonstrate the sensitivity of the material against processing and thermal cycling. For x = 0.038 the microstructure of the as-prepared material remains unchanged, consequently, excellent and stable thermoelectric performance as prerequisites for TEG production was obtained. For x = 0.063 we observed strain phenomena for the pristine state which are released by the formation of planar defects after thermal cycling. Consequently the thermoelectric performance degrades significantly. These findings highlight a complication for deriving the correlation of microstructure and properties of thermoelectric materials in general.

  1. Carbon nanotube bundles/polystyrene composites as high-performance flexible thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Suemori, Kouji; Watanabe, Yuichi; Hoshino, Satoshi

    2015-03-01

    Lightweight and flexible thermoelectric devices consisting of carbon nanotube (CNT)-based materials have the potential to be used for the various applications, such as energy harvesting from the low-temperature waste heat that exists ubiquitously in living areas. Because high-performance CNT-based materials are crucial for the broad-ranging employment of CNT-based thermoelectric devices, considerable efforts are being made to improve the power-generation capability of CNT-based thermoelectric materials. Here, we report high-performance thermoelectric composites consisting of CNT bundles and polystyrene fabricated by a planetary ball milling-based dispersion technique, which allows for the direct dispersion of the CNT bundles within the polystyrene matrix without causing the disaggregation of the bundled CNTs into individual ones. The CNT-bundles/polystyrene composites reported here exhibit a power factor of 413 μW/K2.m.

  2. Nanograin-enhanced in-plane thermoelectric figure of merit in n-type SiGe thin films

    NASA Astrophysics Data System (ADS)

    Lu, Jianbiao; Guo, Ruiqiang; Huang, Baoling

    2016-04-01

    SiGe thin films are desirable candidates for many thermoelectric applications because of their low cost, low toxicity, and high compatibility with microelectronics fabrications. Currently, their applications are limited by their very poor thermoelectric performance. In this study, phosphorus-doped SiGe thin films with improved thermoelectric properties were grown using low pressure chemical vapor deposition, and the effects of different annealing treatments, doping concentration, composition, and temperature on their thermoelectric properties were explored. It is found that the segregation of phosphorus dopants plays an important role in grain growth and thermoelectric transport properties. The improved thermoelectric performance is mainly attributed to the significantly reduced in-plane thermal conductivity by the naturally formed nanograins. By adjusting the growth conditions, doping and post treatments, an in-plane ZT ˜ 0.16 at 300 K was obtained for the optimized n-type samples, which is even ˜50% higher than the record of bulk SiGe.

  3. Enhancement of thermoelectric performance in n-type PbTe1-ySey by doping Cr and tuning Te:Se ratio

    SciTech Connect

    Chere, Eyob K.; Zhang, Qian; McEnaney, Kenneth; Yao, Mengliang; Cao, Feng; Sun, Jingying; Chen, Shuo; Opeil, Cyril; Chen, Gang; Ren, Zhifeng

    2015-04-01

    Lead telluride and its alloys have been extensively studied for medium temperature thermoelectric applications due to decent figure-of-merit (ZT) at temperature close to 900 K. However, little emphasis has been given to improve the ZT near room temperature. In this investigation, we report a systematic study of Cr doping in PbTe1-ySey with y=0, 0.25, 0.5, 0.75, 0.85, and 1. We found the peak ZT temperature increased with increasing concentration of Se. The highest ZT of ~0.6 at room temperature in Te-rich Cr0.015Pb0.985Te0.75Se0.25 was obtained due to a lowered thermal conductivity and enhanced power factor resulted from high Seebeck coefficient of about -220 µV K-1 and high Hall mobility ~1120 cm2 V-1 s-1 at room temperature. A room temperature ZT of ~0.5 and peak ZT of ~1 at about 573–673 K is shown by Se-rich sample Cr0.01Pb0.99Te0.25Se0.75. This improvement of the room temperature ZTimproved the average ZT over a wide temperature range and could potentially lead to a single leg efficiency of thermoelectric conversion for Te-rich Cr0.015Pb0.985Te0.75Se0.25 up to ~11% and Se-rich Cr0.01Pb0.99Te0.25Se0.75 up to ~13% with cold side and hot side temperature at 300 K and 873 K, respectively, if matched with appropriate p-type legs.

  4. Synergistic Strategy to Enhance the Thermoelectric Properties of CoSbS1-xSex Compounds via Solid Solution.

    PubMed

    Yao, Wei; Yang, Dingfeng; Yan, Yanci; Peng, Kunling; Zhan, Heng; Liu, Anping; Lu, Xu; Wang, Guoyu; Zhou, Xiaoyuan

    2017-03-17

    High thermal conductivity of CoSbS-based limited its own prospect application in thermoelectric energy conversion. Solid solution is an effective approach to optimize the performance of thermoelectric materials with high lattice thermal conductivity because of the enhanced phonons scattering from disorder atoms. In this paper, we have synthesized and measured the thermoelectric properties of solid solution CoSbS1-xSex (x = 0, 0.05, 0.10, 0.15, 0.20, 0.30) series samples. The collaborative optimization (enhancing the power factors and reducing the thermal conductivities) to add zT values were realized via substitution of S atoms with the isoelectronic Se atoms in the matrix. Meanwhile, the lowest room temperature lattice thermal conductivity in CoSbS-based materials is obtained (4.72 W m(-1) K(-1)) at present. Benefiting from the results of synergistic strategy, a zT of 0.35 was achieved at 923 K for sample CoSbS0.85Se0.15, a 59% improvement as compared with that of the pristine CoSbS. Band calculation demonstrated that CoSbS0.85Se0.15 present a similar band dispersion with CoSbS. The mechanism of point defect scattering for reducing the lattice thermal conductivity at room temperature, was also analyzed by the Callaway model. The contributions to decrease the room temperature lattice thermal conductivity from the mass and the strain fluctuation in the crystal are comparable. These results can also be extended to other high-efficiency thermoelectric materials with stiff bond and smaller Gruneisen parameters.

  5. Heterogeneous in-situ nanostructure contributes to the thermoelectric performance of Zn{sub 4}Sb{sub 3}

    SciTech Connect

    Lin, Jianping; Ma, Lingzhi; Yang, Baifeng; Fei, Youjian; Lei, Lei; Qiao, Guanjun; Ren, Yang

    2013-04-22

    Single-phase Zn{sub 4}Sb{sub 3} and ZnSb-containing samples were prepared by Plasma Activated Sintering. An abrupt decrease of thermal conductivity was found at about 400 K, which is attributed to the microstructure change of Zn{sub 4}Sb{sub 3}. Nanoscale inclusions and compositional inhomogeneities were found in Zn{sub 4}Sb{sub 3} sample at 473 K by high-resolution transmission electron microscopy. The phonon scattering is enhanced by increasing grain boundaries and chaotic structure, which reduces the thermal conductivity and increases the thermoelectric performance of Zn{sub 4}Sb{sub 3} at elevated temperature. The Rietveld refinement results show that large ZnSb grains in ZnSb-containing samples will accommodate excess Zn atoms, and then reduce thermoelectric performance.

  6. Characterization of Thermoelectric Materials and Contacts by an Enhanced Harman Method

    NASA Astrophysics Data System (ADS)

    Castillo, Eduardo

    This work develops a strategy for thermoelectric characterization by transient Harman method under non-ideal contact and boundary conditions. A thermoelectric transport model is presented that accounts for the effects of thermal and electrical contact resistances and heat transport through electrodes and supporting substrate. Parasitic effects play a large role in controlling the temperature difference across thin thermoelectric films on substrate. Analytical expressions for the temperature difference across the thermoelectric sample are provided to aid in the separate determination of the Seebeck coefficient, and thermal conductivity of the sample, and to quantify the parasitic effects. An electrical scanning probe technique was used to extract the intrinsic electrical resistivity of the sample as well as to study the electrical contact resistance between the sample and its electrodes and copper pad. A thermal characterization experimental setup employs the Harman method under bipolar current excitation over a wide range of currents, to allow Peltier only, and combined Peltier and Joule heating effects to control the temperature difference across the sample. Proof of concept experiments were performed on commercial thermoelectric pellets mounted on the original ceramic substrate. Excellent results were obtained for the thermoelectric properties of the samples with higher thickness, compared with the manufacturer values. On another hand, assuming these properties for the smaller samples, the thermal and electrical contact resistivities calculated with this technique were very consistent, in the order of 10 -7 m2 K/W and 10-10 m2 O, respectively. Additionally, a comparable theoretical approach was employed to predict the cooling power or to design a thermoelectric nanowire heat pump for cooling hot spots in thermal management applications.

  7. Convergence of electronic bands for high performance bulk thermoelectrics.

    PubMed

    Pei, Yanzhong; Shi, Xiaoya; LaLonde, Aaron; Wang, Heng; Chen, Lidong; Snyder, G Jeffrey

    2011-05-05

    Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems-such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe(1-x)Se(x) alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.

  8. Enhancing the Figure of Merit of Heavy-Band Thermoelectric Materials Through Hierarchical Phonon Scattering.

    PubMed

    Fu, Chenguang; Wu, Haijun; Liu, Yintu; He, Jiaqing; Zhao, Xinbing; Zhu, Tiejun

    2016-08-01

    Hierarchical scattering is suggested as an effective strategy to enhance the figure of merit zT of heavy-band thermoelectric materials. Heavy-band FeNbSb half-Heusler system with intrinsically low carrier mean free path is demonstrated as a paradigm. An enhanced zT of 1.34 is obtained at 1150 K for the Fe1.05Nb0.75Ti0.25Sb compound with intentionally designed hierarchical scattering centers.

  9. Low Sound Velocity Contributing to the High Thermoelectric Performance of Ag8SnSe6

    PubMed Central

    Li, Wen; Lin, Siqi; Ge, Binghui; Yang, Jiong; Zhang, Wenqing

    2016-01-01

    Conventional strategies for advancing thermoelectrics by minimizing the lattice thermal conductivity focus on phonon scattering for a short mean free path. Here, a design of slow phonon propagation as an effective approach for high‐performance thermoelectrics is shown. Taking Ag8SnSe6 as an example, which shows one of the lowest sound velocities among known thermoelectric semiconductors, the lattice thermal conductivity is found to be as low as 0.2 W m−1 K−1 in the entire temperature range. As a result, a peak thermoelectric figure of merit zT > 1.2 and an average zT as high as ≈0.8 are achieved in Nb‐doped materials, without relying on a high thermoelectric power factor. This work demonstrates not only a guiding principle of low sound velocity for minimal lattice thermal conductivity and therefore high zT, but also argyrodite compounds as promising thermoelectric materials with weak chemical bonds and heavy constituent elements. PMID:27980995

  10. Low Sound Velocity Contributing to the High Thermoelectric Performance of Ag8SnSe6.

    PubMed

    Li, Wen; Lin, Siqi; Ge, Binghui; Yang, Jiong; Zhang, Wenqing; Pei, Yanzhong

    2016-11-01

    Conventional strategies for advancing thermoelectrics by minimizing the lattice thermal conductivity focus on phonon scattering for a short mean free path. Here, a design of slow phonon propagation as an effective approach for high-performance thermoelectrics is shown. Taking Ag8SnSe6 as an example, which shows one of the lowest sound velocities among known thermoelectric semiconductors, the lattice thermal conductivity is found to be as low as 0.2 W m(-1) K(-1) in the entire temperature range. As a result, a peak thermoelectric figure of merit zT > 1.2 and an average zT as high as ≈0.8 are achieved in Nb-doped materials, without relying on a high thermoelectric power factor. This work demonstrates not only a guiding principle of low sound velocity for minimal lattice thermal conductivity and therefore high zT, but also argyrodite compounds as promising thermoelectric materials with weak chemical bonds and heavy constituent elements.

  11. Improved Thermoelectric Performances of SrTiO3 Ceramic Doped with Nb by Surface Modification of Nanosized Titania

    NASA Astrophysics Data System (ADS)

    Li, Enzhu; Wang, Ning; He, Hongcai; Chen, Haijun

    2016-04-01

    Nb-doped SrTiO3 ceramics doped with the surface modification of nanosized titania was prepared via liquid phase deposition approach and subsequent sintered in an Ar atmosphere. The surface modification of nanosized titania significantly improved the ratio of the electrical conductivity to thermal conductivity of SrTiO3 ceramic doped with Nb, and has little impact on the Seebeck coefficient, thus obviously improving the dimensionless thermoelectric figure of merit ( ZT value). The surface modification of nanosized titania is a much better method to lower the thermal conductivity and to enhance the electrical conductivity than the mechanical mixing process of nanosized titania. The highest ZT value of 0.33 at 900 K was obtained. The reason for the improved thermoelectric performances by the surface modification of nano-sized titania was preliminary investigated.

  12. Improved Thermoelectric Performances of SrTiO3 Ceramic Doped with Nb by Surface Modification of Nanosized Titania.

    PubMed

    Li, Enzhu; Wang, Ning; He, Hongcai; Chen, Haijun

    2016-12-01

    Nb-doped SrTiO3 ceramics doped with the surface modification of nanosized titania was prepared via liquid phase deposition approach and subsequent sintered in an Ar atmosphere. The surface modification of nanosized titania significantly improved the ratio of the electrical conductivity to thermal conductivity of SrTiO3 ceramic doped with Nb, and has little impact on the Seebeck coefficient, thus obviously improving the dimensionless thermoelectric figure of merit (ZT value). The surface modification of nanosized titania is a much better method to lower the thermal conductivity and to enhance the electrical conductivity than the mechanical mixing process of nanosized titania. The highest ZT value of 0.33 at 900 K was obtained. The reason for the improved thermoelectric performances by the surface modification of nano-sized titania was preliminary investigated.

  13. Tuning the carrier concentration to improve the thermoelectric performance of CuInTe{sub 2} compound

    SciTech Connect

    Wei, J.; Liu, H. J. Cheng, L.; Zhang, J.; Liang, J. H.; Jiang, P. H.; Fan, D. D.; Shi, J.

    2015-10-15

    The electronic and transport properties of CuInTe{sub 2} chalcopyrite are investigated using density functional calculations combined with Boltzmann theory. The band gap predicted from hybrid functional is 0.92 eV, which agrees well with experimental data and leads to relatively larger Seebeck coefficient compared with those of narrow-gap thermoelectric materials. By fine tuning the carrier concentration, the electrical conductivity and power factor of the system can be significantly optimized. Together with the inherent low thermal conductivity, the ZT values of CuInTe{sub 2} compound can be enhanced to as high as 1.72 at 850 K, which is obviously larger than those measured experimentally and suggests there is still room to improve the thermoelectric performance of this chalcopyrite compound.

  14. High-performance thermoelectric nanocomposites from nanocrystal building blocks

    PubMed Central

    Ibáñez, Maria; Luo, Zhishan; Genç, Aziz; Piveteau, Laura; Ortega, Silvia; Cadavid, Doris; Dobrozhan, Oleksandr; Liu, Yu; Nachtegaal, Maarten; Zebarjadi, Mona; Arbiol, Jordi; Kovalenko, Maksym V.; Cabot, Andreu

    2016-01-01

    The efficient conversion between thermal and electrical energy by means of durable, silent and scalable solid-state thermoelectric devices has been a long standing goal. While nanocrystalline materials have already led to substantially higher thermoelectric efficiencies, further improvements are expected to arise from precise chemical engineering of nanoscale building blocks and interfaces. Here we present a simple and versatile bottom–up strategy based on the assembly of colloidal nanocrystals to produce consolidated yet nanostructured thermoelectric materials. In the case study on the PbS–Ag system, Ag nanodomains not only contribute to block phonon propagation, but also provide electrons to the PbS host semiconductor and reduce the PbS intergrain energy barriers for charge transport. Thus, PbS–Ag nanocomposites exhibit reduced thermal conductivities and higher charge carrier concentrations and mobilities than PbS nanomaterial. Such improvements of the material transport properties provide thermoelectric figures of merit up to 1.7 at 850 K. PMID:26948987

  15. Structurally-driven Enhancement of Thermoelectric Properties within Poly(3,4-ethylenedioxythiophene) thin Films

    PubMed Central

    Petsagkourakis, Ioannis; Pavlopoulou, Eleni; Portale, Giuseppe; Kuropatwa, Bryan A.; Dilhaire, Stefan; Fleury, Guillaume; Hadziioannou, Georges

    2016-01-01

    Due to the rising need for clean energy, thermoelectricity has raised as a potential alternative to reduce dependence on fossil fuels. Specifically, thermoelectric devices based on polymers could offer an efficient path for near-room temperature energy harvesters. Thus, control over thermoelectric properties of conducting polymers is crucial and, herein, the structural, electrical and thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films doped with p-toluenesulfonate (Tos) molecules were investigated with regards to thin film processing. PEDOT:Tos thin films were prepared by in-situ polymerization of (3,4-ethylenedioxythiophene) monomers in presence of iron(III) p-toluenesulfonate with different co-solvents in order to tune the film structure. While the Seebeck coefficient remained constant, a large improvement in the electrical conductivity was observed for thin films processed with high boiling point additives. The increase of electrical conductivity was found to be solely in-plane mobility-driven. Probing the thin film structure by Grazing Incidence Wide Angle X-ray Scattering has shown that this behavior is dictated by the structural properties of the PEDOT:Tos films; specifically by the thin film crystallinity combined to the preferential edge-on orientation of the PEDOT crystallites. Consequentially enhancement of the power factor from 25 to 78.5 μW/mK2 has been readily obtained for PEDOT:Tos thin films following this methodology. PMID:27470637

  16. Structurally-driven Enhancement of Thermoelectric Properties within Poly(3,4-ethylenedioxythiophene) thin Films

    NASA Astrophysics Data System (ADS)

    Petsagkourakis, Ioannis; Pavlopoulou, Eleni; Portale, Giuseppe; Kuropatwa, Bryan A.; Dilhaire, Stefan; Fleury, Guillaume; Hadziioannou, Georges

    2016-07-01

    Due to the rising need for clean energy, thermoelectricity has raised as a potential alternative to reduce dependence on fossil fuels. Specifically, thermoelectric devices based on polymers could offer an efficient path for near-room temperature energy harvesters. Thus, control over thermoelectric properties of conducting polymers is crucial and, herein, the structural, electrical and thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films doped with p-toluenesulfonate (Tos) molecules were investigated with regards to thin film processing. PEDOT:Tos thin films were prepared by in-situ polymerization of (3,4-ethylenedioxythiophene) monomers in presence of iron(III) p-toluenesulfonate with different co-solvents in order to tune the film structure. While the Seebeck coefficient remained constant, a large improvement in the electrical conductivity was observed for thin films processed with high boiling point additives. The increase of electrical conductivity was found to be solely in-plane mobility-driven. Probing the thin film structure by Grazing Incidence Wide Angle X-ray Scattering has shown that this behavior is dictated by the structural properties of the PEDOT:Tos films; specifically by the thin film crystallinity combined to the preferential edge-on orientation of the PEDOT crystallites. Consequentially enhancement of the power factor from 25 to 78.5 μW/mK2 has been readily obtained for PEDOT:Tos thin films following this methodology.

  17. High-performance shape-engineerable thermoelectric painting

    PubMed Central

    Park, Sung Hoon; Jo, Seungki; Kwon, Beomjin; Kim, Fredrick; Ban, Hyeong Woo; Lee, Ji Eun; Gu, Da Hwi; Lee, Se Hwa; Hwang, Younghun; Kim, Jin-Sang; Hyun, Dow-Bin; Lee, Sukbin; Choi, Kyoung Jin; Jo, Wook; Son, Jae Sung

    2016-01-01

    Output power of thermoelectric generators depends on device engineering minimizing heat loss as well as inherent material properties. However, the device engineering has been largely neglected due to the limited flat or angular shape of devices. Considering that the surface of most heat sources where these planar devices are attached is curved, a considerable amount of heat loss is inevitable. To address this issue, here, we present the shape-engineerable thermoelectric painting, geometrically compatible to surfaces of any shape. We prepared Bi2Te3-based inorganic paints using the molecular Sb2Te3 chalcogenidometalate as a sintering aid for thermoelectric particles, with ZT values of 0.67 for n-type and 1.21 for p-type painted materials that compete the bulk values. Devices directly brush-painted onto curved surfaces produced the high output power of 4.0 mW cm−2. This approach paves the way to designing materials and devices that can be easily transferred to other applications. PMID:27834369

  18. High-performance shape-engineerable thermoelectric painting

    NASA Astrophysics Data System (ADS)

    Park, Sung Hoon; Jo, Seungki; Kwon, Beomjin; Kim, Fredrick; Ban, Hyeong Woo; Lee, Ji Eun; Gu, Da Hwi; Lee, Se Hwa; Hwang, Younghun; Kim, Jin-Sang; Hyun, Dow-Bin; Lee, Sukbin; Choi, Kyoung Jin; Jo, Wook; Son, Jae Sung

    2016-11-01

    Output power of thermoelectric generators depends on device engineering minimizing heat loss as well as inherent material properties. However, the device engineering has been largely neglected due to the limited flat or angular shape of devices. Considering that the surface of most heat sources where these planar devices are attached is curved, a considerable amount of heat loss is inevitable. To address this issue, here, we present the shape-engineerable thermoelectric painting, geometrically compatible to surfaces of any shape. We prepared Bi2Te3-based inorganic paints using the molecular Sb2Te3 chalcogenidometalate as a sintering aid for thermoelectric particles, with ZT values of 0.67 for n-type and 1.21 for p-type painted materials that compete the bulk values. Devices directly brush-painted onto curved surfaces produced the high output power of 4.0 mW cm-2. This approach paves the way to designing materials and devices that can be easily transferred to other applications.

  19. Experimental Performance of a Solar Thermoelectric Cogenerator Comprising Thermoelectric Modules and Parabolic Trough Concentrator without Evacuated Tube

    NASA Astrophysics Data System (ADS)

    Miao, L.; Kang, Y. P.; Li, C.; Tanemura, S.; Wan, C. L.; Iwamoto, Y.; Shen, Y.; Lin, H.

    2015-06-01

    A prototype practical solar-thermoelectric cogenerator composed of (1) a primary component of a pile of solar-selective absorber (SSA) slab, thermoelectric (TE) modules, and a depressed water flow tube (multichannel cooling heat sink, MCS), and (2) a parabolic trough concentrator with aperture area of 2m × 2m and east-west focal axis was constructed. Its cogeneration performance under the best climatic and solar insolation conditions in Guangzhou, China was tested. For simplicity, the evacuated glass tube to cover the primary component was eliminated from the system. Six Bi2Te3 TE modules were arranged in series, directly bonded to the rear surface of the solar absorber slab. The hot-side temperature of the TE module reached up to 152°C. The experimentally obtained instantaneous results for the solar to electrical conversion efficiency, heat exchange coefficient of the MCS, and overall system efficiency under the best environmental and solar insolation conditions were about 1.14%, 56.1%, and 49.5%, respectively. To justify these values, an equivalent thermal network diagram based on a single-temperature-node heat transfer model representing the respective system components was used to analyze the thermal transfer and losses of the system. Finally, electrical power of 18° W was generated, with 2 L/min of hot water at 37°C being produced and stored in the insulated container.

  20. A Solution Processable High-Performance Thermoelectric Copper Selenide Thin Film.

    PubMed

    Lin, Zhaoyang; Hollar, Courtney; Kang, Joon Sang; Yin, Anxiang; Wang, Yiliu; Shiu, Hui-Ying; Huang, Yu; Hu, Yongjie; Zhang, Yanliang; Duan, Xiangfeng

    2017-03-29

    A solid-state thermoelectric device is attractive for diverse technological areas such as cooling, power generation and waste heat recovery with unique advantages of quiet operation, zero hazardous emissions, and long lifetime. With the rapid growth of flexible electronics and miniature sensors, the low-cost flexible thermoelectric energy harvester is highly desired as a potential power supply. Herein, a flexible thermoelectric copper selenide (Cu2 Se) thin film, consisting of earth-abundant elements, is reported. The thin film is fabricated by a low-cost and scalable spin coating process using ink solution with a truly soluble precursor. The Cu2 Se thin film exhibits a power factor of 0.62 mW/(m K(2) ) at 684 K on rigid Al2 O3 substrate and 0.46 mW/(m K(2) ) at 664 K on flexible polyimide substrate, which is much higher than the values obtained from other solution processed Cu2 Se thin films (<0.1 mW/(m K(2) )) and among the highest values reported in all flexible thermoelectric films to date (≈0.5 mW/(m K(2) )). Additionally, the fabricated thin film shows great promise to be integrated with the flexible electronic devices, with negligible performance change after 1000 bending cycles. Together, the study demonstrates a low-cost and scalable pathway to high-performance flexible thin film thermoelectric devices from relatively earth-abundant elements.

  1. Fabrication of Advanced Thermoelectric Materials by Hierarchical Nanovoid Generation

    NASA Technical Reports Server (NTRS)

    Choi, Sang Hyouk (Inventor); Park, Yeonjoon (Inventor); Chu, Sang-Hyon (Inventor); Elliott, James R. (Inventor); King, Glen C. (Inventor); Kim, Jae-Woo (Inventor); Lillehei, Peter T. (Inventor); Stoakley, Diane M. (Inventor)

    2011-01-01

    A novel method to prepare an advanced thermoelectric material has hierarchical structures embedded with nanometer-sized voids which are key to enhancement of the thermoelectric performance. Solution-based thin film deposition technique enables preparation of stable film of thermoelectric material and void generator (voigen). A subsequent thermal process creates hierarchical nanovoid structure inside the thermoelectric material. Potential application areas of this advanced thermoelectric material with nanovoid structure are commercial applications (electronics cooling), medical and scientific applications (biological analysis device, medical imaging systems), telecommunications, and defense and military applications (night vision equipments).

  2. New Insights into High-Performance Thermoelectric Tellurides from ^125Te NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Hu, Y.-Y.; Cook, B. A.; Harringa, J. L.; Schmidt-Rohr, K.; Kanatzidis, M. G.

    2009-11-01

    Thermoelectric materials are widely used for direct transformation of heat to electricity (Seebeck effect) and for solid state refrigeration (Peltier effect). Efforts to increase the efficiency of high-performance thermoelectrics, which include narrow-gap, doped tellurium-based semiconductors, require detailed knowledge of their local structure and bonding. We have used ^125Te nuclear magnetic resonance (NMR) as a local probe for obtaining better understanding of these high-performance thermoelectric tellurides, specifically PbTe doped with Ag and Sb (LAST materials) and GeTe doped with Ag and Sb (TAGS materials). The resonance frequencies and line shapes of the NMR spectra, as well as spin-lattice relaxation times and chemical shift anisotropies are highly sensitive to the composition and synthesis conditions of LAST and TAGS materials, enabling studies of the local composition, distortion, bonding, and carrier concentration. Several intriguing phenomena including electronic inhomogeneity and local distortions of the crystal lattice have been observed by NMR.

  3. a Study on Performance Evaluation of Thermoelectric Cooling System Using Piezoelectric Bending Actuator

    NASA Astrophysics Data System (ADS)

    Yoon, Hee-Sung; Yang, Ho-Dong; Oh, Yool-Kwon

    This study investigated the performance of thermoelectric cooling system using the piezoelectric bending actuator. The temperatures in the cooling region of thermoelectric cooling system were measured with and without operation of piezoelectric bending actuator at the frequencies of 90 Hz and 120 Hz. The cooling coefficients were calculated by the temperature measurement results, and the thermo-flow phenomenon in the cooling region was visualized under the same condition. The coefficient of performance of the thermoelectric cooling system was improved by the piezoelectric bending actuator when the results of temperature measurement and thermo-flow visualization were compared, because that the vibration from the piezoelectric bending actuator generated compulsive convection and the cold air in the cooling region was actively circulated by the compulsive convection.

  4. Fabrication of Bi2Te3-x Se x nanowires with tunable chemical compositions and enhanced thermoelectric properties.

    PubMed

    Liu, Shuai; Peng, Nan; Zhou, Chongjian; Bai, Yu; Tang, Shuang; Ma, Dayan; Ma, Fei; Xu, Kewei

    2017-02-24

    Uniform Bi2Te3-x Se x nanowires (NWs) with tunable components are synthesized by a modified solution method free of any template, and inter-diffusion mechanism is proposed for the growth and transformation of ternary nanowires. Spark plasma sintering is adopted to fabricate the pellets of Bi2Te3-x Se x NWs and thermoelectric transport properties are measured. As compared to Bi2Te3 pellets, Se doping results in lowered electrical conductivity because of the reduced carrier concentration, both the Seebeck coefficient and the power factor are enhanced substantially. The Bi2Te2.7Se0.3 pellet exhibits the highest power factor at room temperature as a result of optimized carrier concentration (4.37 × 10(19) cm(-3)) and mobility (60.22 cm(2) V(-1) s(-1)). As compared to Bi2Te3, the thermal conductivity of Bi2Te3-x Se x is lowered owing to the enhanced phonon scattering by dopants and grain boundaries. As a result, the ZT value at 300 K is substantially improved from 0.045 of Bi2Te3 to 0.42 of Bi2Te2.7Se0.3. It is suggested that Se doping is an effective way to enhance the thermoelectric performance of Bi2Te3 based materials.

  5. Fabrication of Bi2Te3-x Se x nanowires with tunable chemical compositions and enhanced thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Liu, Shuai; Peng, Nan; Zhou, Chongjian; Bai, Yu; Tang, Shuang; Ma, Dayan; Ma, Fei; Xu, Kewei

    2017-02-01

    Uniform Bi2Te3-x Se x nanowires (NWs) with tunable components are synthesized by a modified solution method free of any template, and inter-diffusion mechanism is proposed for the growth and transformation of ternary nanowires. Spark plasma sintering is adopted to fabricate the pellets of Bi2Te3-x Se x NWs and thermoelectric transport properties are measured. As compared to Bi2Te3 pellets, Se doping results in lowered electrical conductivity because of the reduced carrier concentration, both the Seebeck coefficient and the power factor are enhanced substantially. The Bi2Te2.7Se0.3 pellet exhibits the highest power factor at room temperature as a result of optimized carrier concentration (4.37 × 1019 cm-3) and mobility (60.22 cm2 V-1 s-1). As compared to Bi2Te3, the thermal conductivity of Bi2Te3-x Se x is lowered owing to the enhanced phonon scattering by dopants and grain boundaries. As a result, the ZT value at 300 K is substantially improved from 0.045 of Bi2Te3 to 0.42 of Bi2Te2.7Se0.3. It is suggested that Se doping is an effective way to enhance the thermoelectric performance of Bi2Te3 based materials.

  6. Enhanced Flexible Thermoelectric Generators Based on Oxide-Metal Composite Materials

    NASA Astrophysics Data System (ADS)

    Geppert, Benjamin; Brittner, Artur; Helmich, Lailah; Bittner, Michael; Feldhoff, Armin

    2017-04-01

    The thermoelectric performance of flexible thermoelectric generator stripes was investigated in terms of different material combinations. The thermoelectric generators were constructed using Cu-Ni-Mn alloy as n-type legs while varying the p-type leg material by including a metallic silver phase and an oxidic copper phase. For the synthesis of Ca_3Co_4O9/CuO/Ag ceramic-based composite materials, silver and the copper were added to the sol-gel batches in the form of nitrates. For both additional elements, the isothermal specific electronic conductivity increases with increasing amounts of Ag and CuO in the samples. The amounts for Ag and Cu were 0 mol.%, 2 mol.%, 5 mol.%, 10 mol.%, and 20 mol.%. The phases were confirmed by x-ray diffraction. Furthermore, secondary electron microscopy including energy dispersive x-ray spectroscopy were processed in the scanning electron microscope and the transmission electron microscope. For each p-type material, the data for the thermoelectric parameters, isothermal specific electronic conductivity σ and the Seebeck coefficient α, were determined. The p-type material with a content of 5 mol.% Ag and Cu exhibited a local maximum of the power factor and led to the generator with the highest electric power output P_el.

  7. Thermoelectric efficiency of molecular junctions.

    PubMed

    Perroni, C A; Ninno, D; Cataudella, V

    2016-09-21

    Focus of the review is on experimental set-ups and theoretical proposals aimed to enhance thermoelectric performances of molecular junctions. In addition to charge conductance, the thermoelectric parameter commonly measured in these systems is the thermopower, which is typically rather low. We review recent experimental outcomes relative to several junction configurations used to optimize the thermopower. On the other hand, theoretical calculations provide estimations of all the thermoelectric parameters in the linear and non-linear regime, in particular of the thermoelectric figure of merit and efficiency, completing our knowledge of molecular thermoelectricity. For this reason, the review will mainly focus on theoretical studies analyzing the role of not only electronic, but also of the vibrational degrees of freedom. Theoretical results about thermoelectric phenomena in the coherent regime are reviewed focusing on interference effects which play a significant role in enhancing the figure of merit. Moreover, we review theoretical studies including the effects of molecular many-body interactions, such as electron-vibration couplings, which typically tend to reduce the efficiency. Since a fine tuning of many parameters and coupling strengths is required to optimize the thermoelectric conversion in molecular junctions, new theoretically proposed set-ups are discussed in the conclusions.

  8. Peierls distortion as a route to high thermoelectric performance in In(4)Se(3-delta) crystals.

    PubMed

    Rhyee, Jong-Soo; Lee, Kyu Hyoung; Lee, Sang Mock; Cho, Eunseog; Kim, Sang Il; Lee, Eunsung; Kwon, Yong Seung; Shim, Ji Hoon; Kotliar, Gabriel

    2009-06-18

    Thermoelectric energy harvesting-the transformation of waste heat into useful electricity-is of great interest for energy sustainability. The main obstacle is the low thermoelectric efficiency of materials for converting heat to electricity, quantified by the thermoelectric figure of merit, ZT. The best available n-type materials for use in mid-temperature (500-900 K) thermoelectric generators have a relatively low ZT of 1 or less, and so there is much interest in finding avenues for increasing this figure of merit. Here we report a binary crystalline n-type material, In(4)Se(3-delta), which achieves the ZT value of 1.48 at 705 K-very high for a bulk material. Using high-resolution transmission electron microscopy, electron diffraction, and first-principles calculations, we demonstrate that this material supports a charge density wave instability which is responsible for the large anisotropy observed in the electric and thermal transport. The high ZT value is the result of the high Seebeck coefficient and the low thermal conductivity in the plane of the charge density wave. Our results suggest a new direction in the search for high-performance thermoelectric materials, exploiting intrinsic nanostructural bulk properties induced by charge density waves.

  9. Evaluation of Temperature-Dependent Effective Material Properties and Performance of a Thermoelectric Module

    NASA Astrophysics Data System (ADS)

    Chien, Heng-Chieh; Chu, En-Ting; Hsieh, Huey-Lin; Huang, Jing-Yi; Wu, Sheng-Tsai; Dai, Ming-Ji; Liu, Chun-Kai; Yao, Da-Jeng

    2013-07-01

    We devised a novel method to evaluate the temperature-dependent effective properties of a thermoelectric module (TEM): Seebeck coefficient ( S m), internal electrical resistance ( R m), and thermal conductance ( K m). After calculation, the effective properties of the module are converted to the average material properties of a p- n thermoelectric pillar pair inside the module: Seebeck coefficient ( S TE), electrical resistivity ( ρ TE), and thermal conductivity ( k TE). For a commercial thermoelectric module (Altec 1091) chosen to verify the novel method, the measured S TE has a maximum value at bath temperature of 110°C; ρ TE shows a positive linear trend dependent on the bath temperature, and k TE increases slightly with increasing bath temperature. The results show the method to have satisfactory measurement performance in terms of practicability and reliability; the data for tests near 23°C agree with published values.

  10. Narrow band gap and enhanced thermoelectricity in FeSb2.

    PubMed

    Sun, Peijie; Oeschler, Niels; Johnsen, Simon; Iversen, Bo B; Steglich, Frank

    2010-01-28

    FeSb(2) was recently identified as a narrow-gap semiconductor with indications of strong electron-electron correlations. In this manuscript, we report on systematic thermoelectric investigation of a number of FeSb(2) single crystals with varying carrier concentrations, together with two isoelectronically substituted FeSb(2-x)As(x) samples (x = 0.01 and 0.03) and two reference compounds FeAs(2) and RuSb(2). Typical behaviour associated with narrow bands and narrow gaps is only confirmed for the FeSb(2) and the FeSb(2-x)As(x) samples. The maximum absolute thermopower of FeSb(2) spans from 10 to 45 mV/K at around 10 K, greatly exceeding that of both FeAs(2) and RuSb(2). The relation between the carrier concentration and the maximum thermopower value is in approximate agreement with theoretical predictions of the electron-diffusion contribution which, however, requires an enhancement factor larger than 30. The isoelectronic substitution leads to a reduction of the thermal conductivity, but the charge-carrier mobility is also largely reduced due to doping-induced crystallographic defects or impurities. In combination with the high charge-carrier mobility and the enhanced thermoelectricity, FeSb(2) represents a promising candidate for thermoelectric cooling applications at cryogenic temperatures.

  11. Thermoelectric performance of various benzo-difuran wires

    SciTech Connect

    Péterfalvi, Csaba G.; Grace, Iain; Manrique, Dávid Zs.; Lambert, Colin J.

    2014-05-07

    Using a first principles approach to electron transport, we calculate the electrical and thermoelectrical transport properties of a series of molecular wires containing benzo-difuran subunits. We demonstrate that the side groups introduce Fano resonances, the energy of which is changing with the electronegativity of selected atoms in it. We also study the relative effect of single, double, or triple bonds along the molecular backbone and find that single bonds yield the highest thermopower, approximately 22 μV/K at room temperature, which is comparable with the highest measured values for single-molecule thermopower reported to date.

  12. Thermoelectric Performance for SnSe Hot-Pressed at Different Temperature

    NASA Astrophysics Data System (ADS)

    Li, D.; Li, J. C.; Qin, X. Y.; Zhang, J.; Song, C. J.; Wang, L.; Xin, H. X.

    2017-01-01

    Herein, nanoparticles SnSe are prepared by fusion method together with ball-milling technique and the effect of hot-pressing temperatures on the thermoelectric properties of the dense materials is explored. Due to the optimization of carrier concentration, the peak figure of merit (ZT) value of the compacted material reaches 0.73 for SnSe sample hot-pressed at 400°C and 450°C. The present investigation indicates that the thermoelectric performance of the SnSe compound can be significantly improved by sintering with suitable temperature.

  13. Ultrahigh thermoelectric performance by electron and phonon critical scattering in Cu2 Se1-x Ix.

    PubMed

    Liu, Huili; Yuan, Xun; Lu, Ping; Shi, Xun; Xu, Fangfang; He, Ying; Tang, Yunshan; Bai, Shengqiang; Zhang, Wenqing; Chen, Lidong; Lin, Yue; Shi, Lei; Lin, He; Gao, Xingyu; Zhang, Xingmin; Chi, Hang; Uher, Ctirad

    2013-12-03

    Iodine-doped Cu2 Se shows a significantly improved thermoelectric performance during phase transitions by electron and phonon critical scattering, leading to a dramatic increase in zT by a factor of 3-7 times culminating in zT values of 2.3 at 400 K.

  14. Thermoelectrically cooled cloud physics expansion chamber. [systems engineering and performance prediction

    NASA Technical Reports Server (NTRS)

    Buist, R. J.

    1977-01-01

    The design and fabrication of a thermoelectric chiller for use in chilling a liquid reservoir is described. Acceptance test results establish the accuracy of the thermal model and predict the unit performance under various conditions required by the overall spacelab program.

  15. Modeling of thermal conductivity in high performing thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Hatzikraniotis, E.; Kyratsi, Th.; Paraskevopoulos, K. M.

    2017-01-01

    The enhanced TE-performance in Mg2Si-Mg2Sn based pseudo-binaries is presented, which is attributed to low thermal conductivity. Sn-Si alloying, reduces the lattice thermal conductivity due to mass fluctuation. Furthermore, miscibility gap in the Sn-Si substitution causes the formation of composites, with Si-rich and Sn-rich phases, which span from mm to nm scale, and these nano-inclusions reduce further lattice thermal conductivity.

  16. First-principles calculations of thermoelectric properties of TiN/MgO superlattices: The route for an enhancement of thermoelectric effects in artificial nanostructures

    SciTech Connect

    Takaki, Hirokazu; Kobayashi, Kazuaki; Shimono, Masato; Kobayashi, Nobuhiko; Hirose, Kenji

    2016-01-07

    We present the thermoelectric properties of TiN/MgO superlattices employing first-principles calculation techniques. The Seebeck coefficients, the electrical conductances, the thermal conductances, and the figure of merit are investigated employing electrical and thermal transport calculations based on density functional theory combined with the nonequilibrium Green's function and nonequilibrium molecular dynamics simulation methods. The TiN/MgO superlattices with a small lattice mismatch at the interfaces are ideal systems to study the way for an enhancement of thermoelectric properties in artificial nanostructures. We find that the interfacial scattering between the two materials in the metal/insulator superlattices causes the electrical conductance to change rapidly, which enhances the Seebeck coefficient significantly. We show that the figure of merit for the artificial superlattice nanostructures has a much larger value compared with that of the bulk material and changes drastically with the superlattice configurations at the atomistic level.

  17. Exploring the Thermoelectric Performance of BaGd2NiO5 Haldane Gap Materials.

    PubMed

    Nasani, Narendar; Oliveira Rocha, Carlos Miguel; Kovalevsky, Andrei V; Otero Irurueta, Gonzalo; Populoh, Sascha; Thiel, Philipp; Weidenkaff, Anke; Neto da Silva, Fernando; Fagg, Duncan P

    2017-02-20

    One-dimensional Haldane gap materials, such as the rare earth barium chain nickelates, have received great interest due to their vibrant one-dimensional spin antiferromagnetic character and unique structure. Herein we report how these 1D structural features can also be highly beneficial for thermoelectric applications by analysis of the system CaxBaGd2-xNiO5 0 ≤ x ≤ 0.25. Attractive Seebeck coefficients of 140-280 μV K(-1) at 350-1300 K are retained even at high acceptor-substitution levels, provided by the interplay of low dimensionality and electronic correlations. Furthermore, the highly anisotropic crystal structure of Haldane gap materials allows very low thermal conductivities, reaching only 1.5 W m(-1) K(-1) at temperatures above 1000 K, one of the lowest values currently documented for prospective oxide thermoelectrics. Although calcium substitution in BaGd2NiO5 increases the electrical conductivity up to 5-6 S cm(-1) at 1150 K < T < 1300 K, this level remains insufficient for thermoelectric applications. Hence, the combination of highly promising Seebeck coefficients and low thermal conductivities offered by this 1D material type underscores a potential new structure type for thermoelectric materials, where the main challenge will be to engineer the electronic band structure and, probably, microstructural features to further enhance the mobility of the charge carriers.

  18. Rare earth-doped materials with enhanced thermoelectric figure of merit

    DOEpatents

    Venkatasubramanian, Rama; Cook, Bruce Allen; Levin, Evgenii M.; Harringa, Joel Lee

    2016-09-06

    A thermoelectric material and a thermoelectric converter using this material. The thermoelectric material has a first component including a semiconductor material and a second component including a rare earth material included in the first component to thereby increase a figure of merit of a composite of the semiconductor material and the rare earth material relative to a figure of merit of the semiconductor material. The thermoelectric converter has a p-type thermoelectric material and a n-type thermoelectric material. At least one of the p-type thermoelectric material and the n-type thermoelectric material includes a rare earth material in at least one of the p-type thermoelectric material or the n-type thermoelectric material.

  19. Thermoelectric Properties of Silicon Germanium: An Investigation of the Reduction of Lattice Thermal Conductivity and Enhancement of Power Factor

    NASA Astrophysics Data System (ADS)

    Lahwal, Ali Sadek

    Thermoelectric materials are of technological interest owing to their ability of direct thermal-to-electrical energy conversion. In thermoelectricity, thermal gradients can be used to generate an electrical power output. Recent efforts in thermoelectrics are focused on developing higher efficient power generation materials. In this dissertation, the overall goal is to investigate both the n-type and p-type of the state of the art thermoelectric material, silicon germanium (SiGe), for high temperature power generation. Further improvement of thermoelectric performance of Si-Ge alloys hinges upon how to significantly reduce the as yet large lattice thermal conductivity, and optimizing the thermoelectric power factor PF. Our methods, in this thesis, will be into two different approaches as follow: The first approach is manipulating the lattice thermal conductivity of n and p-type SiGe alloys via direct nanoparticle inclusion into the n-type SiGe matrix and, in a different process, using a core shell method for the p-type SiGe. This approach is in line with the process of in-situ nanocomposites. Nanocomposites have become a new paradigm for thermoelectric research in recent years and have resulted in the reduction of thermal conductivity via the nano-inclusion and grain boundary scattering of heat-carrying phonons. To this end, a promising choice of nano-particle to include by direct mixing into a SiGe matrix would be Yttria Stabilized Zirconia ( YSZ). In this work we report the preparation and thermoelectric study of n-type SiGe + YSZ nanocomposites prepared by direct mechanical mixing followed by Spark Plasma Sintering (SPS) processing. Specifically, we experimentally investigated the reduction of lattice thermal conductivity (kappaL) in the temperature range (30--800K) of n-type Si 80Ge20P2 alloys with the incorporation of YSZ nanoparticles (20 ˜ 40 nm diameter) into the Si-Ge matrix. These samples synthesized by SPS were found to have densities > 95% of the

  20. Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Okuhata, Ryo; Ishibe, Takafumi; Watanabe, Kentaro; Suzuki, Takeyuki; Fujita, Takeshi; Sawano, Kentarou; Nakamura, Yoshiaki

    2016-10-01

    We have investigated the intrinsic thermoelectric properties of epitaxial β-FeSi2 thin films and the impact of phosphorus (P) doping. Epitaxial β-FeSi2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β-FeSi2 thin films on Si(111) substrates, and MBE of β-FeSi2 thin films on epitaxial β-FeSi2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β-FeSi2/Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β-FeSi2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β-FeSi2. We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β-FeSi2. A route to enhance the thermoelectric performance of β-FeSi2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.

  1. Methods of thermoelectric enhancement in silicon-germanium alloy type I clathrates and in nanostructured lead chalcogenides

    NASA Astrophysics Data System (ADS)

    Martin, Joshua

    The rapid increase in thermoelectric (TE) materials R&D is a consequence of the growing need to increase energy efficiency and independence through waste heat recovery. TE materials enable the direct solid-state conversion of heat into electricity, with little maintenance, noise, or cost. In addition, these compact devices can be incorporated into existing technologies to increase the overall operating efficiency. High efficiency TE materials would enable the practical solid-state conversion of thermal to electrical energy. Optimizing the interdependent physical parameters to achieve acceptable efficiencies requires materials exhibiting a unique combination of properties. This research reports two methods of thermoelectric enhancement: lattice strain effects in silicon-germanium alloy type I clathrates and the nanostructured enhancement of lead chalcogenides. The synthesis and chemical, structural, and transport properties characterization of Ba8Ga16SixGe30-x type I clathrates with similar Ga-to-group IV element ratios but with increasing Si substitution (4 < x < 14) is reported. Substitution of Si within the Ga-Ge lattice framework of the type I clathrate Ba8Ga16Ge30 results in thermoelectric performance enhancement. The unique dependences of carrier concentration, electrical resistivity, Seebeck coefficient, and carrier effective mass on Si substitution level, may imply a modified band structure with Si substitution. These materials were then further optimized by adjusting the Ga-to-group IV element ratios. Recent progress in a number of higher efficiency TE materials can be attributed to nanoscale enhancement. Many of these materials demonstrate increased Seebeck coefficient and decreased thermal conductivity due to the phenomenological properties of nanometer length scales. To satisfy the demands of bulk industrial applications requires additional synthesis techniques to incorporate nanostructure directly within a bulk matrix. This research investigates, for

  2. Thermoelectric properties of correlated materials

    NASA Astrophysics Data System (ADS)

    Tomczak, Jan; Haule, Kristjan; Miyake, Takashi; Georges, Antoine; Kotliar, Gabriel

    2011-03-01

    The discovery of large Seebeck coefficients in transition metal compounds such as FeSi, FeSb2, or the iron pnictides, has stirred renewed interest in the potential merits of electronic correlation effects for thermoelectric properties. The notorious sensitivity in this class of materials to small changes in composition (doping, chemical pressure) and external stimuli (temperature, pressure), makes a reliable and, possibly, predictive description cumbersome, while at the same time providing an arena of possibilities in the search for high performance thermoelectrics. Based on state-of-the-art electronic structure methods (density functional theory with the dynamical mean field theory) we here compute the thermoelectric response for several of the above mentioned exemplary materials from first principles. With the ultimate goal to understand the origin of a large thermoelectricity in these systems, we discuss various many-body renormalizations, and identify correlation controlled ingredients that are pivotal for thermopower enhancements.

  3. Thermoelectric materials and devices

    NASA Technical Reports Server (NTRS)

    Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor); Talcott, Noel A. (Inventor)

    2011-01-01

    New thermoelectric materials comprise highly [111]-oriented twinned group IV alloys on the basal plane of trigonal substrates, which exhibit a high thermoelectric figure of merit and good material performance, and devices made with these materials.

  4. Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics

    DOE PAGES

    Chen, Zhiwei; Ge, Binghui; Li, Wen; ...

    2017-01-04

    To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb1$-$xSb2x/3Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains. This leadsmore » to a lattice thermal conductivity as low as 0.4Wm-1 K-1 and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. As a result, the vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT.« less

  5. RAPID COMMUNICATION: Novel high performance small-scale thermoelectric power generation employing regenerative combustion systems

    NASA Astrophysics Data System (ADS)

    Weinberg, F. J.; Rowe, D. M.; Min, G.

    2002-07-01

    Hydrocarbon fuels have specific energy contents some two orders of magnitude greater than any electrical storage device. They therefore proffer an ideal source in the universal quest for compact, lightweight, long-lasting alternatives for batteries to power the ever-proliferating electronic devices. The motivation lies in the need to power, for example, equipment for infantry troops, for weather stations and buoys in polar regions which need to signal their readings intermittently to passing satellites, unattended over long periods, and many others. Fuel cells, converters based on miniaturized gas turbines, and other systems under intensive study, give rise to diverse practical difficulties. Thermoelectric devices are robust, durable and have no moving parts, but tend to be exceedingly inefficient. We propose regenerative combustion systems which mitigate this impediment and are likely to make high performance small-scale thermoelectric power generation applicable in practice. The efficiency of a thermoelectric generating system using preheat when operated between ambient and 1200 K is calculated to exceed the efficiency of the best present day thermoelectric conversion system by more than 20%.

  6. Thermal diffusivity measurement using thermographic method and performance evaluation by impedance spectroscopy for thermoelectric module

    NASA Astrophysics Data System (ADS)

    Otsuka, Mioko; Terakado, Hiroki; Homma, Ryoei; Hasegawa, Yasuhiro; Zahidul Islam, Md.; Bastian, Georg; Stuck, Alexander

    2016-12-01

    The thermal diffusivity of two bulk thermoelectric elements and a thermoelectric module was measured by an infrared camera using a thermographic method without any contact in air at room temperature. The estimated values for the elements (3.45 × 10-6 m2/s for a BiSb sample and 1.60 × 10-6 m2/s for a BiTe sample) were slightly larger than those measured in vacuum. The difference was explained as the effect of heat convection on the surface of the samples by solving the one-dimensional heat conduction equation numerically. The thermal diffusivity of thermoelectric elements in a thermoelectric module was also estimated using the thermographic method, and values of (1.1-1.7) × 10-6 m2/s in air were obtained, depending on the element. On the basis of the measurement results, the performance of the module was estimated using impedance spectroscopy, which can estimate not only the dimensionless figure of merit but also the thermal loss and response. The thermal response and thermal loss in air were similar to those in vacuum; however, the dimensionless figure of merit was 0.82 in vacuum and 0.70 in air.

  7. Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics

    NASA Astrophysics Data System (ADS)

    Chen, Zhiwei; Ge, Binghui; Li, Wen; Lin, Siqi; Shen, Jiawen; Chang, Yunjie; Hanus, Riley; Snyder, G. Jeffrey; Pei, Yanzhong

    2017-01-01

    To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb1-xSb2x/3Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains. This leads to a lattice thermal conductivity as low as 0.4 Wm-1 K-1 and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. The vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT.

  8. Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics

    PubMed Central

    Chen, Zhiwei; Ge, Binghui; Li, Wen; Lin, Siqi; Shen, Jiawen; Chang, Yunjie; Hanus, Riley; Snyder, G. Jeffrey; Pei, Yanzhong

    2017-01-01

    To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb1−xSb2x/3Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains. This leads to a lattice thermal conductivity as low as 0.4 Wm−1 K−1 and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. The vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT. PMID:28051063

  9. Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics.

    PubMed

    Chen, Zhiwei; Ge, Binghui; Li, Wen; Lin, Siqi; Shen, Jiawen; Chang, Yunjie; Hanus, Riley; Snyder, G Jeffrey; Pei, Yanzhong

    2017-01-04

    To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb1-xSb2x/3Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains. This leads to a lattice thermal conductivity as low as 0.4 Wm(-1) K(-1) and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. The vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT.

  10. Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation by Inelastic Scattering

    NASA Astrophysics Data System (ADS)

    Ghahari, Fereshte; Xie, Hong-Yi; Taniguchi, Takashi; Watanabe, Kenji; Foster, Matthew S.; Kim, Philip

    2016-04-01

    We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons.

  11. Enhanced valley-resolved thermoelectric transport in a magnetic silicene superlattice

    NASA Astrophysics Data System (ADS)

    Niu, Zhi Ping; Zhang, Yong Mei; Dong, Shihao

    2015-07-01

    Electrons in two-dimensional crystals with a honeycomb lattice structure possess a valley degree of freedom in addition to charge and spin, which has revived the field of valleytronics. In this work we investigate the valley-resolved thermoelectric transport through a magnetic silicene superlattice. Since spin is coupled to the valley, this device allows a coexistence of the insulating transmission gap of one valley and the metallic resonant band of the other, resulting in a strong valley polarization Pv. Pv oscillates with the barrier strength V with its magnitude greatly enhanced by the superlattice structure. In addition, a controllable fully valley polarized transport and an on/off switching effect in the conductance spectra are obtained. Furthermore, the spin- and valley-dependent thermopowers can be controlled by V, the on-site potential difference between A and B sublattices and Fermi energy, and enhanced by the superlattice structure. Enhanced valley-resolved thermoelectric transport and its control by means of gate voltages make the magnetic silicene superlattice attractive in valleytronics applications.

  12. Discovery of high-performance low-cost n-type Mg3Sb2-based thermoelectric materials with multi-valley conduction bands

    PubMed Central

    Zhang, Jiawei; Song, Lirong; Pedersen, Steffen Hindborg; Yin, Hao; Hung, Le Thanh; Iversen, Bo Brummerstedt

    2017-01-01

    Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg3Sb1.5Bi0.5, that exhibits a very high figure of merit zT ranging from 0.56 to 1.65 at 300−725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg3Sb1.5Bi0.5 a promising candidate for the low- and intermediate-temperature thermoelectric applications. PMID:28059069

  13. Enhancement of thermoelectric figure of merit of nanostructured FeSb2 by adding Cu nanoparticles

    NASA Astrophysics Data System (ADS)

    Koirala, Machhindra; Zhao, Huaizhou; Pokharel, Mani; Chen, Shuo; Opeil, Cyril; Chen, Gang; Ren, Zhifeng

    2014-03-01

    We present the enhancement of thermoelectric properties of FeSb2 through modulation doping by Cu nanoparticles. Since, FeSb2 and Cu have matched work function, the electrical conductivity of this Kondo-like system can be increased dramatically without affecting Seebeck coefficient. The optimized nanocomposite FeSb2Cu0.045 has enhancement of power factor by 90% compared to pure nanostructured FeSb2. The further reduction of thermal conductivity from FeSb2/Cu interface gives the total enhancement of figure of merit (ZT) by 110%. This strategy has been widely used on other semiconductors to improve ZT. Our result demonstrates that the potential of the modulation doping technique can also be extended to Kondo insulator systems.

  14. Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n-Type Thermoelectric Power Factor.

    PubMed

    Park, Kunsu; Ahn, Kyunghan; Cha, Joonil; Lee, Sanghwa; Chae, Sue In; Cho, Sung-Pyo; Ryee, Siheon; Im, Jino; Lee, Jaeki; Park, Su-Dong; Han, Myung Joon; Chung, In; Hyeon, Taeghwan

    2016-11-02

    Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (ZT) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi2Te3) that violates phase equilibrium, namely, phase-pure n-type K0.06Bi2Te3.18. Incorporated potassium and tellurium in Bi2Te3 far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of ∼43 μW cm(-1) K(-2) and a high ZT > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications.

  15. Benefits of Carrier-Pocket Anisotropy to Thermoelectric Performance: The Case of p -Type AgBiSe2

    DOE PAGES

    Parker, David S.; May, Andrew F.; Singh, David J.

    2015-06-05

    Here we study theoretically the effects of anisotropy on the thermoelectric performance of p-type AgBiSe2. We present an apparent realization of the thermoelectric benefits of one-dimensional plate-like carrier pocket anisotropy in the valence band of this material. Based on first principles calculations we find a substantial anisotropy in the electronic structure, likely favorable for thermoelectric performance, in the valence bands of the hexagonal phase of the silver chalcogenide thermoelectric AgBiSe2, while the conduction bands are more isotropic, and in our experiments do not attain high performance. AgBiSe2 has already exhibited a ZT value of 1.5 in a high-temperature disordered fccmore » phase, but room-temperature performance has not been demonstrated. We develop a theory for the ability of anisotropy to decouple the density-of-states and conductivity effective masses, pointing out the influence of this effect in the high performance thermoelectrics Bi2Te3 and PbTe. From our first principles and Boltzmann transport calculations we find that p-type AgBiSe2 has substantial promise as a room temperature thermoelectric, and estimate its performance.« less

  16. Mechanochemical synthesis of high thermoelectric performance bulk Cu2X (X = S, Se) materials

    NASA Astrophysics Data System (ADS)

    Yang, Dongwang; Su, Xianli; Yan, Yonggao; He, Jian; Uher, Ctirad; Tang, Xinfeng

    2016-11-01

    We devised a single-step mechanochemical synthesis/densification procedure for Cu2X (X = S, Se) thermoelectric materials via applying a pressure of 3 GPa to a stoichiometric admixture of elemental Cu and X for 3 min at room temperature. The obtained bulk materials were single-phase, nearly stoichiometric structures with a relative packing density of 97% or higher. The structures contained high concentration of atomic scale defects and pores of 20-200 nm diameter. The above attributes gave rise to a high thermoelectric performance: at 873 K, the ZT value of Cu2S reached 1.07, about 2.1 times the value typical of samples grown from the melt. The ZT value of Cu2Se samples reached in excess of 1.2, close to the state-of-the-art value.

  17. Performance of four-stage thermoelectric cooler for extended wavelength InGaAs detectors

    NASA Astrophysics Data System (ADS)

    Mo, De-feng; Yang, Li-yi; Liu, Da-fu; Xu, Qin-fei; Li, Tao; Li, Xue

    2015-04-01

    Experimental setup for evaluating four-stage thermoelectric cooler's performance was designed. Effects of input power, heat dissipation condition and heat load on the temperature difference (ΔT) of four-stage thermoelectric coolers' hot and cold faces were obtained experimentally. The result shows that, the ΔT increases as the input power increases. A linear relationship exists between input current and feedback voltage. In different cooling conditions, the ΔT of thermoelectric cooler (TEC) increases with the temperature of hot face. As the temperature increasing on hot face is 1K, the ΔT increasing of TEC can be about 0.5K. Meanwhile, the power consumption of TEC also increases slightly. Water condensation can be prevented in either dry nitrogen environment or vacuum environment, but the vacuum level has great influence to the ΔT, especially in low operation temperature. The better the vacuum level is, the smaller the convection heat loss has. When the operation temperature of focal plane array (FPA) is lower than 220K, it is prior to use vacuum packaging. Considering the Joule-heat of readout circuit and the heat loss of wire conduction, the minimum working temperature of FPA can reach below 200 K when the temperature of the hot face is 285K. And the coefficient of performance (COP) of TEC can increase sharply from 0.8% to 4% when the controlled operation temperature is 220K rather than 200K.

  18. Enhancing Workgroup Performance.

    ERIC Educational Resources Information Center

    1998

    This document contains four papers from a symposium on enhancing workgroup performance in human resource development (HRD). "Formation of Cross-Cultural Global Teams: Making Informed Choices on Team Composition" (Robert L. Dilworth) describes how a mixed class of U.S. and international students identified their cultural and learning…

  19. Enhanced thermoelectric properties of phase-separating bismuth selenium telluride thin films via a two-step method

    NASA Astrophysics Data System (ADS)

    Takashiri, Masayuki; Kurita, Kensuke; Hagino, Harutoshi; Tanaka, Saburo; Miyazaki, Koji

    2015-08-01

    A two-step method that combines homogeneous electron beam (EB) irradiation and thermal annealing has been developed to enhance the thermoelectric properties of nanocrystalline bismuth selenium telluride thin films. The thin films, prepared using a flash evaporation method, were treated with EB irradiation in a N2 atmosphere at room temperature and an acceleration voltage of 0.17 MeV. Thermal annealing was performed under Ar/H2 (5%) at 300 °C for 60 min. X-ray diffraction was used to determine that compositional phase separation between bismuth telluride and bismuth selenium telluride developed in the thin films exposed to higher EB doses and thermal annealing. We propose that the phase separation was induced by fluctuations in the distribution of selenium atoms after EB irradiation, followed by the migration of selenium atoms to more stable sites during thermal annealing. As a result, thin film crystallinity improved and mobility was significantly enhanced. This indicates that the phase separation resulting from the two-step method enhanced, rather than disturbed, the electron transport. Both the electrical conductivity and the Seebeck coefficient were improved following the two-step method. Consequently, the power factor of thin films that underwent the two-step method was enhanced to 20 times (from 0.96 to 21.0 μW/(cm K2) that of the thin films treated with EB irradiation alone.

  20. Enhanced thermoelectric properties of phase-separating bismuth selenium telluride thin films via a two-step method

    SciTech Connect

    Takashiri, Masayuki Kurita, Kensuke; Hagino, Harutoshi; Miyazaki, Koji; Tanaka, Saburo

    2015-08-14

    A two-step method that combines homogeneous electron beam (EB) irradiation and thermal annealing has been developed to enhance the thermoelectric properties of nanocrystalline bismuth selenium telluride thin films. The thin films, prepared using a flash evaporation method, were treated with EB irradiation in a N{sub 2} atmosphere at room temperature and an acceleration voltage of 0.17 MeV. Thermal annealing was performed under Ar/H{sub 2} (5%) at 300 °C for 60 min. X-ray diffraction was used to determine that compositional phase separation between bismuth telluride and bismuth selenium telluride developed in the thin films exposed to higher EB doses and thermal annealing. We propose that the phase separation was induced by fluctuations in the distribution of selenium atoms after EB irradiation, followed by the migration of selenium atoms to more stable sites during thermal annealing. As a result, thin film crystallinity improved and mobility was significantly enhanced. This indicates that the phase separation resulting from the two-step method enhanced, rather than disturbed, the electron transport. Both the electrical conductivity and the Seebeck coefficient were improved following the two-step method. Consequently, the power factor of thin films that underwent the two-step method was enhanced to 20 times (from 0.96 to 21.0 μW/(cm K{sup 2}) that of the thin films treated with EB irradiation alone.

  1. Nanowire Thermoelectric Devices

    NASA Technical Reports Server (NTRS)

    Borshchevsky, Alexander; Fleurial, Jean-Pierre; Herman, Jennifer; Ryan, Margaret

    2005-01-01

    Nanowire thermoelectric devices, now under development, are intended to take miniaturization a step beyond the prior state of the art to exploit the potential advantages afforded by shrinking some device features to approximately molecular dimensions (of the order of 10 nm). The development of nanowire-based thermoelectric devices could lead to novel power-generating, cooling, and sensing devices that operate at relatively low currents and high voltages. Recent work on the theory of thermoelectric devices has led to the expectation that the performance of such a device could be enhanced if the diameter of the wires could be reduced to a point where quantum confinement effects increase charge-carrier mobility (thereby increasing the Seebeck coefficient) and reduce thermal conductivity. In addition, even in the absence of these effects, the large aspect ratios (length of the order of tens of microns diameter of the order of tens of nanometers) of nanowires would be conducive to the maintenance of large temperature differences at small heat fluxes. The predicted net effect of reducing diameters to the order of tens of nanometers would be to increase its efficiency by a factor of .3. Nanowires made of thermoelectric materials and devices that comprise arrays of such nanowires can be fabricated by electrochemical growth of the thermoelectric materials in templates that contain suitably dimensioned pores (10 to 100 nm in diameter and 1 to 100 microns long). The nanowires can then be contacted in bundles to form devices that look similar to conventional thermoelectric devices, except that a production version may contain nearly a billion elements (wires) per square centimeter, instead of fewer than a hundred as in a conventional bulk thermoelectric device or fewer than 100,000 as in a microdevice. It is not yet possible to form contacts with individual nanowires. Therefore, in fabricating a nanowire thermoelectric device, one forms contacts on nanowires in bundles of the

  2. Performance Analysis of a Thermoelectric Solar Collector Integrated with a Heat Pump

    NASA Astrophysics Data System (ADS)

    Lertsatitthanakorn, C.; Jamradloedluk, J.; Rungsiyopas, M.; Therdyothin, A.; Soponronnarit, S.

    2013-07-01

    A novel heat pump system is proposed. A thermoelectric solar collector was coupled to a solar-assisted heat pump (TESC-HP) to work as an evaporator. The cooling effect of the system's refrigerant allowed the cold side of the system's thermoelectric modules to work at lower temperature, improving the conversion efficiency. The TESC-HP system mainly consisted of transparent glass, an air gap, an absorber plate that acted as a direct expansion-type collector/evaporator, an R-134a piston-type hermetic compressor, a water-cooled plate-type condenser, thermoelectric modules, and a water storage tank. Test results indicated that the TESC-HP has better coefficient of performance (COP) and conversion efficiency than the separate units. For the meteorological conditions in Mahasarakham, the COP of the TESC-HP system can reach 5.48 when the average temperature of 100 L of water is increased from 28°C to 40°C in 60 min with average ambient temperature of 32.5°C and average solar intensity of 815 W/m2, whereas the conversion efficiency of the TE power generator was around 2.03%.

  3. Synthetic thermoelectric materials comprising phononic crystals

    DOEpatents

    El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang

    2013-08-13

    Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.

  4. Enhanced thermoelectric power and electronic correlations in RuSe{sub 2}

    SciTech Connect

    Wang, Kefeng Wang, Aifeng; Tomic, A.; Wang, Limin; Petrovic, C.; Abeykoon, A. M. Milinda; Dooryhee, E.; Billinge, S. J. L.

    2015-04-01

    We report the electronic structure, electric and thermal transport properties of Ru{sub 1−x}Ir{sub x}Se{sub 2} (x ≤ 0.2). RuSe{sub 2} is a semiconductor that crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe{sub 2} exceeds −200 μV/K around 730 K. Ir substitution results in the suppression of the resistivity and the Seebeck coefficient, suggesting the removal of the peaks in density of states near the Fermi level. Ru{sub 0.8}Ir{sub 0.2}Se{sub 2} shows a semiconductor-metal crossover at about 30 K. The magnetic field restores the semiconducting behavior. Our results indicate the importance of the electronic correlations in enhanced thermoelectricity of RuSb{sub 2}.

  5. Toward enhanced thermoelectric effects in Bi2Te3/Sb2Te3 heterostructures

    NASA Astrophysics Data System (ADS)

    Narendra, Namita; Kim, Ki Wook

    2017-03-01

    The possibility of enhanced thermoelectric properties through nanostructuring is investigated theoretically in a p-type Bi2Te3/Sb2Te3 heterostructure. A multi-scale modeling approach is adopted to account for the atomistic characteristics of the interface as well as the carrier/phonon transport properties in the larger scales. The calculations clearly illustrate the desired impact of carrier energy filtering at the potential barrier by locally boosting the power factor over a sizable distance in the well region. Further, the phonon transport analysis illustrates a considerable reduction in the thermal conductivity at the heterointerface. Both effects are expected to provide an effective means to engineer higher zT in this material system.

  6. A Comprehensive 3D Finite Element Model of a Thermoelectric Module Used in a Power Generator: A Transient Performance Perspective

    NASA Astrophysics Data System (ADS)

    Wu, Guangxi; Yu, Xiong

    2015-06-01

    Thermoelectric power generator has potential for small-scale and distributed power generation because of its high durability and scalability. It is very important to realize that the transient behavior of thermoelectric modules (TEM) affects a thermoelectric generator's response to dynamic working environments. Traditionally, researchers have used simplified models to describe the behavior of thermoelectric modules. In this paper we propose a comprehensive mathematical model that considers the effect of variations of chemical potential and carrier density, which are ignored by traditional models. Finite element models based on this new model are used to simulate the transient behavior of a thermoelectric module subjected to rapid changes in boundary temperature or working load. Simulation results show that transition times of thermoelectric modules affected by temperature change are much longer than those of modules affected by changes in electrical load resistance. Sudden changes in working temperature cause voltage overshoot of the TEM output, which, however, is not observed in responses to sudden changes of load resistance. Comparisons also show there are significant differences between the behavior of TEM predicted by use of this new comprehensive model and that predicted by use of traditional models, particularly for the high-temperature intrinsic ionization region and the low-temperature weak ionization region. This implies that chemical potential and carrier density variations, which are taken into account by this new model but ignored by traditional models, have major effects on the performance of TEM.

  7. Thermoelectric performance of co-doped SnTe with resonant levels

    NASA Astrophysics Data System (ADS)

    Zhou, Min; Gibbs, Zachary M.; Wang, Heng; Han, Yemao; Li, Laifeng; Snyder, G. Jeffrey

    2016-07-01

    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 (nH) and extrinsic dopant concentration (NI, NAg) in the stabilization region, where a linear increase of dopant concentration does not lead to linear response in the measured nH. Upon substituting extrinsic dopants beyond a certain amount, the nH 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.

  8. Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics.

    PubMed

    Wang, Hongchao; Bahk, Je-Hyeong; Kang, Chanyoung; Hwang, Junphil; Kim, Kangmin; Kim, Jungwon; Burke, Peter; Bowers, John E; Gossard, Arthur C; Shakouri, Ali; Kim, Woochul

    2014-07-29

    In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to ∼ 2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities; the smallest sizes (2 ∼ 6 nm) of nanostructures in the QH sample are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to ∼ 0.5 W/m K. The reduced electronic thermal conductivity associated with the suppressed electrical conductivity by nanostructures also helped reduce the total thermal conductivity. In addition to the high zT of the QH sample, the mechanical hardness is higher than the other samples by a factor of around 2 due to the smaller grain sizes. Overall, this paper suggests a guideline on how to achieve high zT and mechanical strength of a thermoelectric material by controlling nano- and microstructures of the material.

  9. AgI alloying in SnTe boosts the thermoelectric performance via simultaneous valence band convergence and carrier concentration optimization

    NASA Astrophysics Data System (ADS)

    Banik, Ananya; Biswas, Kanishka

    2016-10-01

    SnTe, a Pb-free analogue of PbTe, was earlier assumed to be a poor thermoelectric material due to excess p-type carrier concentration and large energy separation between light and heavy hole valence bands. Here, we report the enhancement of the thermoelectric performance of p-type SnTe by Ag and I co-doping. AgI (1-6 mol%) alloying in SnTe modulates its electronic structure by increasing the band gap of SnTe, which results in decrease in the energy separation between its light and heavy hole valence bands, thereby giving rise to valence band convergence. Additionally, iodine doping in the Te sublattice of SnTe decreases the excess p-type carrier concentration. Due to significant decrease in hole concentration and reduction of the energy separation between light and heavy hole valence bands, significant enhancement in Seebeck coefficient was achieved at the temperature range of 600-900 K for Sn1-xAgxTe1-xIx samples. A maximum thermoelectric figure of merit, zT, of ~1.05 was achieved at 860 K in high quality crystalline ingot of p-type Sn0.95Ag0.05Te0.95I0.05.

  10. Potential improvements in SiGe radioisotope thermoelectric generator performance

    SciTech Connect

    Mowery, A.L.

    1999-01-01

    In accordance with NASA{close_quote}s slogan: {open_quotes}Better, Cheaper, Faster,{close_quotes} this paper will address potential improvements to SiGe RTG technology to make them Better. RTGs are doubtless cheaper than {open_quotes}paper designs{close_quotes} which are better and cheaper until development, performance and safety test costs are considered. RTGs have the advantage of being fully developed and tested in the rigors of space for over twenty years. Further, unless a new system can be accelerated tested, as were the RTGs, they cannot be deployed reliably unless a number of systems have succeeded for test periods exceeding the mission lifetime. Two potential developments are discussed that can improve the basic RTG performance by 10 to 40{sup +}{percent} depending on the mission profile. These improvements could be demonstrated in years. Accelerated testing could also be performed in this period to preserve existing RTG reliability. Data from a qualification tested RTG will be displayed, while not definitive, to support the conclusions. Finally, it is anticipated that other investigators will be encouraged to suggest further modifications to the basic RTG design to improve its performance. {copyright} {ital 1999 American Institute of Physics.}

  11. LaPtSb: a half-Heusler compound with high thermoelectric performance.

    PubMed

    Xue, Q Y; Liu, H J; Fan, D D; Cheng, L; Zhao, B Y; Shi, J

    2016-07-21

    The electronic and transport properties of the half-Heusler compound LaPtSb are investigated by performing first-principles calculations combined with semi-classical Boltzmann theory and deformation potential theory. Compared with many typical half-Heusler compounds, LaPtSb exhibits an obviously larger power factor at room temperature, especially for the n-type system. Together with the very low lattice thermal conductivity, the thermoelectric figure of merit (ZT) of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the carrier concentration.

  12. LaPtSb: a half-Heusler compound with high thermoelectric performance

    NASA Astrophysics Data System (ADS)

    Xue, Q. Y.; Liu, H. J.; Fan, D. D.; Cheng, L.; Zhao, B. Y.; Shi, J.

    The electronic and transport properties of the half-Heusler compound LaPtSb are investigated by performing first-principles calculations combined with semi-classical Boltzmann theory and deformation potential theory. Compared with many typical half-Heusler compounds, the LaPtSb exhibits obviously larger power factor at room temperature, especially for the n-type system. Together with the very low lattice thermal conductivity, the thermoelectric figure of merit (ZT) of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the carrier concentration.

  13. High power density performance of WPt and WRh electrodes in the alkali metal thermoelectric converter

    NASA Technical Reports Server (NTRS)

    Williams, R. M.; Jeffries-Nakamura, B.; Underwood, M. L.; Wheeler, B. L.; Loveland, M. E.; Kikkert, S. J.; Lamb, J. L.; Cole, T.; Kummer, J. T.; Bankston, C. P.

    1989-01-01

    The properties of the alkali metal thermoelectric converter (AMTEC) are discussed together with those of an efficient AMTEC electrode. Three groups of electrodes were prepared and tested for their performance as AMTEC electrodes, including WPt-T3, WRh-B1, and WRh-B2. The best electrodes of both WPt and WRh types typically exhibited low porosity, and thickness greater than 0.8 micron, which indicated that transport in these electrodes does not occur by a purely free-molecular flow mode. The observed values of the exchange current were found to be within the range of those observed for oxide-free Mo electrodes under similar conditions.

  14. 100 WATT THERMOELECTRIC GENERATOR.

    DTIC Science & Technology

    GENERATORS , THERMOELECTRICITY, THERMOCOUPLES, HEATERS, HEAT TRANSFER, ENERGY CONVERSION, GASOLINE, VOLTAGE REGULATORS, HEAT EXCHANGERS, LIFE EXPECTANCY(SERVICE LIFE), STARTING, PERFORMANCE(ENGINEERING).

  15. An ab initio study of the thermoelectric enhancement potential in nano-grained TiNiSn.

    PubMed

    Kirievsky, K; Shlimovich, M; Fuks, D; Gelbstein, Y

    2014-10-07

    Novel approaches for the development of highly efficient thermoelectric materials capable of a direct conversion of heat into electricity, are being constantly investigated. TiNiSn based half-Heusler alloys exhibit a high thermoelectric potential for practical, renewable power generation applications. The main challenge of further enhancement of the thermoelectric efficiency of these alloys lies in the reduction of the associated high lattice thermal conductivity values without adversely affecting the electronic transport properties. The current manuscript theoretically investigates two possible routes for overcoming this limitation in TiNiSn alloys. On the one hand, the influence of nano-grained structure of TiNiSn on the electronic structure of the material is theoretically demonstrated. On the other hand, the potential for thermal conductivity reduction upon increasing the Ni fraction in the intermetallic TiNiSn compound via the formation of metallic TiNi2Sn nanoparticles is also shown. Using the applied approach, a useful route for optimizing both the electronic and thermal properties of half-Heusler TiNiSn, for practical thermoelectric applications, is demonstrated.

  16. A quick and efficient measurement technique for performance evaluation of thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Rao, Ashwin; Banjade, Pawan; Bosak, Gregg; Joshi, Binay; Keane, Jennifer; Nally, Luke; Peng, Adam; Perera, Susanthri; Waring, Alfred; Joshi, Giri; Poudel, Bed

    2016-10-01

    Evaluating the performance of thermoelectric (TE) materials is critical for developing an efficient long lasting thermoelectric generator. Various parameters like resistance, TE power, TE efficiency as a function of temperature and time play an important role in developing and optimizing TE materials and legs. If one needs to evaluate the TE legs for performance or contact metallization optimization, study of a brazed or packaged device everytime could prove to be an expensive, time consuming process especially as a quick intermediate qualification. In this work, a simple approach that uses eutectic Gallium Indium (Ga-In) paste as a metallizing substitute with good electrical/thermal contact is employed which also avoids the need for brazing/welding (or any permanent joining) and provides a reliable platform for a quick leg qualification. Using open circuit voltage (V oc) and device voltage (V d), one can evaluate important TE quantities like peak power, material resistance changes, peak current and power versus current characteristics to understand the leg performance. The proposed approach is successfully demonstrated with three different TE material systems namely Bismuth Telluride, Skutterudite and Half Heusler systems.

  17. Control system for thermoelectric refrigerator

    NASA Technical Reports Server (NTRS)

    Nelson, John L. (Inventor); Criscuolo, Lance (Inventor); Gilley, Michael D. (Inventor); Park, Brian V. (Inventor)

    1996-01-01

    Apparatus including a power supply (202) and control system is provided for maintaining the temperature within an enclosed structure (40) using thermoelectric devices (92). The apparatus may be particularly beneficial for use with a refrigerator (20) having superinsulation materials (46) and phase change materials (112) which cooperate with the thermoelectric device (92) to substantially enhance the overall operating efficiency of the refrigerator (20). The electrical power supply (202) and control system allows increasing the maximum power capability of the thermoelectric device (92) in response to increased heat loads within the refrigerator (20). The electrical power supply (202) and control system may also be used to monitor the performance of the cooling system (70) associated with the refrigerator (20).

  18. High thermoelectric performance by resonant dopant indium in nanostructured SnTe.

    PubMed

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-08-13

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

  19. High thermoelectric performance by resonant dopant indium in nanostructured SnTe

    PubMed Central

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-01-01

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K. PMID:23901106

  20. High-performance and compact-designed flexible thermoelectric modules enabled by a reticulate carbon nanotube architecture

    NASA Astrophysics Data System (ADS)

    Zhou, Wenbin; Fan, Qingxia; Zhang, Qiang; Cai, Le; Li, Kewei; Gu, Xiaogang; Yang, Feng; Zhang, Nan; Wang, Yanchun; Liu, Huaping; Zhou, Weiya; Xie, Sishen

    2017-03-01

    It is a great challenge to substantially improve the practical performance of flexible thermoelectric modules due to the absence of air-stable n-type thermoelectric materials with high-power factor. Here an excellent flexible n-type thermoelectric film is developed, which can be conveniently and rapidly prepared based on the as-grown carbon nanotube continuous networks with high conductivity. The optimum n-type film exhibits ultrahigh power factor of ~1,500 μW m-1 K-2 and outstanding stability in air without encapsulation. Inspired by the findings, we design and successfully fabricate the compact-configuration flexible TE modules, which own great advantages compared with the conventional π-type configuration modules and well integrate the superior thermoelectric properties of p-type and n-type carbon nanotube films resulting in a markedly high performance. Moreover, the research results are highly scalable and also open opportunities for the large-scale production of flexible thermoelectric modules.

  1. High-performance and compact-designed flexible thermoelectric modules enabled by a reticulate carbon nanotube architecture.

    PubMed

    Zhou, Wenbin; Fan, Qingxia; Zhang, Qiang; Cai, Le; Li, Kewei; Gu, Xiaogang; Yang, Feng; Zhang, Nan; Wang, Yanchun; Liu, Huaping; Zhou, Weiya; Xie, Sishen

    2017-03-24

    It is a great challenge to substantially improve the practical performance of flexible thermoelectric modules due to the absence of air-stable n-type thermoelectric materials with high-power factor. Here an excellent flexible n-type thermoelectric film is developed, which can be conveniently and rapidly prepared based on the as-grown carbon nanotube continuous networks with high conductivity. The optimum n-type film exhibits ultrahigh power factor of ∼1,500 μW m(-1) K(-2) and outstanding stability in air without encapsulation. Inspired by the findings, we design and successfully fabricate the compact-configuration flexible TE modules, which own great advantages compared with the conventional π-type configuration modules and well integrate the superior thermoelectric properties of p-type and n-type carbon nanotube films resulting in a markedly high performance. Moreover, the research results are highly scalable and also open opportunities for the large-scale production of flexible thermoelectric modules.

  2. A study of hear sink performance in air and soil for use in a thermoelectric energy harvesting device

    NASA Technical Reports Server (NTRS)

    Snyder, J.; Lawrence, E. E.

    2002-01-01

    A suggested application of a thermoelectric generator is to exploit the natural temperature difference between the air and the soil to generate small amounts of electrical energy. Since the conversion efficiency of even the best thermoelectric generators available is very low, the performance of the heat sinks providing the heat flow is critical. By providing a constant heat input to various heat sinks, field tests of their thermal conductances in soil and in air were performed. Aprototype device without a thermoelectric generator was constructed, buried, and monitored to experimentally measure the heat flow achievable in such a system. Theoretical considerations for design and selection of improved heat sinks are also presented. In particular, the method of shape factoranalysis is used to give rough estimates and upper bounds for the thermal conductance of a passive heat sink buried in soil.

  3. Embedded-ZnO Nanowire Structure for High-Performance Transparent Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Ishibe, Takafumi; Tomeda, Atsuki; Watanabe, Kentaro; Kikkawa, Jun; Fujita, Takeshi; Nakamura, Yoshiaki

    2016-11-01

    We present the structure of ZnO nanowires (NWs) embedded in ZnO films for high-performance transparent thermoelectric materials. The design concept is that the ZnO NWs exhibit high power factor and work as phonon scatterers to reduce the thermal conductivity. Here, we form an embedded-ZnO NWs structure on Si(111) substrates using physical vapor transport for ZnO NW formation and pulsed laser deposition for embedding NWs with ZnO. The NWs grew along the c-axis orientation vertically on the ZnO buffer/Si(111) substrates. Nanoscale voids near NWs were also observed in filling ZnO. The electrical measurements of films including NWs exhibited the reduction of electrical conductivity from that of bulk ZnO to a similar extent to the reduction in the case of ZnO films without NWs. This indicates that there was small electron scattering by ZnO NWs and the voids. However, considering that the mean free path of electron becomes lower by increasing carrier concentration, the electron scattering effect by nanostructuring can be found to be even weaker under the high doping condition compared with phonon scattering with large mean free path. Therefore, our study develops embedded-ZnO NWs structures promising for high-performance thermoelectric material with high electrical conductivity and low thermal conductivity.

  4. Enhanced thermoelectric properties of bismuth sulfide polycrystals prepared by mechanical alloying and spark plasma sintering

    SciTech Connect

    Zhao Lidong; Zhang Boping Liu Weishu; Zhang Hailong; Li Jingfeng

    2008-12-15

    Bismuth sulfide powders were synthesized by mechanical alloying (MA) and then consolidated by spark plasma sintering (SPS) technique. In order to improve the electrical transport properties of bismuth sulfides, the carrier concentration was optimized by modifying chemical composition of sulfur through producing sulfur vacancies, and the carrier mobility was enhanced by a two-step SPS as a hot-forging process through increasing grain orientation. The electrical resistivity of bismuth sulfides was reduced to 10{sup -4} from 10{sup -2} {omega} m by optimizing sulfur content, and further lowered by hot-forging, whereby the power factor was significantly increased from 91 to 254 {mu}W/mK{sup 2}. The hot-forged Bi{sub 2}S{sub 2.90} sample showed the highest ZT=0.11 (at 523 K), which is higher than the reported value. The present work revealed that bismuth sulfide compounds as a promising candidate of thermoelectric materials can be synthesized by a simple process. - Abstract: Electrical properties of bismuth sulfides were improved by optimizing carrier concentration through modifying compositions of sulfur and enhancing carrier mobility through SPSed hot-forging. The ZT value of 0.11 was obtained, which is the maximum reported so far . Display Omitted.

  5. High Thermoelectric Performance Lead Selenide Materials through All-scale Hierarchical Structuring

    NASA Astrophysics Data System (ADS)

    Lee, Yeseul

    Industries have paid increasing attention to power generation using waste heat through thermoelectrics, which convert heat to electric energy. This method can be used in renewable applications because of its environmentally friendly process. Large-scale production of bulk materials with high thermoelectric figure of merit (ZT) is the key to practical applications. PbTe-based materials have been mostly studied, but are facing a challenge regarding scarcity of Te. PbSe is a more abundant analog of PbTe that has been less frequently studied. This work presents a synthesis and characterization of bulk thermoelectric materials based on both n- and p-type PbSe with atomic-, nano-, meso-scale architectures. When PbSe is doped with Ga and In they efficiently generate electron carriers that are sufficient for high ZT. Thus, higher ZT of n-type PbSe can be achieved than that of optimized n-type PbTe at high temperatures. The study of the thermoelectric properties of p-type PbSe with Li, Na, and K indicates that the efficiency of Na in doping PbSe is found to be the highest. The additional spark plasma sintering (SPS) process allows samples to have increased carrier density and produce mesoscale grains that reduce lattice thermal conductivity, increasing ZT. Additional studies for reducing lattice thermal conductivity through nanostructuring were conducted. Adding (Ca/Sr/Ba)Se and EuSe to Na doped SPS PbSe generates nanoprecipitates. This study shows that the hierarchical architecture on the atomic scale (Na and Ca/Sr/Ba/Eu solid solution), nanoscale (MSe/EuSe nanoprecipitates), and mesoscale (grains) effectively increases ZT. MSe samples show no appreciable change in charge transport, while EuSe samples show decreased charge carriers. However, adding more Na optimizes properties. Continued investigating n-type dopants with Sb and Bi shows that Sb not only plays the role as a dopant but also is unexpectedly effective in generating nanostructuring. The Sb-rich precipitates

  6. Higher thermoelectric performance of Zintl phases (Eu0.5Yb0.5)1-xCaxMg2Bi2 by band engineering and strain fluctuation

    NASA Astrophysics Data System (ADS)

    Shuai, Jing; Geng, Huiyuan; Lan, Yucheng; Zhu, Zhuan; Wang, Chao; Liu, Zihang; Bao, Jiming; Chu, Ching-Wu; Sui, Jiehe; Ren, Zhifeng

    2016-07-01

    Complex Zintl phases, especially antimony (Sb)-based YbZn0.4Cd1.6Sb2 with figure-of-merit (ZT) of ˜1.2 at 700 K, are good candidates as thermoelectric materials because of their intrinsic “electron-crystal, phonon-glass” nature. Here, we report the rarely studied p-type bismuth (Bi)-based Zintl phases (Ca,Yb,Eu)Mg2Bi2 with a record thermoelectric performance. Phase-pure EuMg2Bi2 is successfully prepared with suppressed bipolar effect to reach ZT ˜ 1. Further partial substitution of Eu by Ca and Yb enhanced ZT to ˜1.3 for Eu0.2Yb0.2Ca0.6Mg2Bi2 at 873 K. Density-functional theory (DFT) simulation indicates the alloying has no effect on the valence band, but does affect the conduction band. Such band engineering results in good p-type thermoelectric properties with high carrier mobility. Using transmission electron microscopy, various types of strains are observed and are believed to be due to atomic mass and size fluctuations. Point defects, strain, dislocations, and nanostructures jointly contribute to phonon scattering, confirmed by the semiclassical theoretical calculations based on a modified Debye-Callaway model of lattice thermal conductivity. This work indicates Bi-based (Ca,Yb,Eu)Mg2Bi2 is better than the Sb-based Zintl phases.

  7. An impurity intermediate band due to Pb doping induced promising thermoelectric performance of Ca5In2Sb6.

    PubMed

    Feng, Zhenzhen; Wang, Yuanxu; Yan, Yuli; Zhang, Guangbiao; Yang, Jueming; Zhang, Jihua; Wang, Chao

    2015-06-21

    Band engineering is one of the effective approaches for designing ideal thermoelectric materials. Introducing an intermediate band in the band gap of semiconducting thermoelectric compounds may largely increase the carrier concentration and improve the electrical conductivity of these compounds. We test this hypothesis by Pb doping in Zintl Ca5In2Sb6. In the current work, we have systematically investigated the electronic structure and thermoelectric performances of substitutional doping with Pb on In sites at a doping level of 5% (0.2 e per cell) for Ca5In2Sb6 by using density functional theory combined with semi-classical Boltzmann theory. It is found that in contrast to Zn doping, Pb doping introduces a partially filled intermediate band in the band gap of Ca5In2Sb6, which originates from the Pb s states by weakly hybridizing with the Sb p states. Such an intermediate band dramatically increases the electrical conductivity of Ca5In2Sb6 and has little detrimental effect on its Seebeck coefficient, which may increase its thermoelectric figure of merit, ZT. Interestingly, a maximum ZT value of 2.46 may be achieved at 900 K for crystalline Pb-doped Ca5In2Sb6 when the carrier concentration is optimized. Therefore, Pb-doped Ca5In2Sb6 may be a promising thermoelectric material.

  8. Universal thermoelectric unit

    SciTech Connect

    Fedorov, M.I.; Engalychev, A.E.; Zaitsev, V.K.; Kaliazin, A.E.; Solomkin, F.Y.

    1994-08-10

    The problems of energy supply of low power electric devices very often can be solved with thermoelectric generator even with low coefficient of performance, when other electric energy sources are not convenient. The problems of thermoelectric and construction choice for such generators are discussed in the paper. A series of domestic thermoelectric generators was designed by the authors. The work is based on designing an universal thermoelectric unit---a battery which consist of ten thermoelements. The coefficient of performance of the unit is about 4%. Any thermoelectric generator can be made as a combination of these units. Principal opportunity of production such thermoelectric generators on industrial scale was proved. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  9. Enhancement of thermoelectric properties in benzene molecule junction by the magnetic flux

    NASA Astrophysics Data System (ADS)

    Li, Haidong; Wang, Yuan; kang, Xiubao; Liu, Shaohui; Li, Ruixue

    2017-02-01

    The thermoelectric properties through a benzene molecule with two metal leads are theoretically studied. The results reveal that the thermoelectric properties are strongly influenced by the magnetic flux. The reason for such a behavior is that the quantum interference caused by the magnetic field leads to the anti-resonance effect, which results in obvious thermoelectric effects. The value of Z T with a period of 1 for the magnetic flux and the magnitude of Z T may exceed 2 under some specific magnetic flux and onsite Coulomb interaction.

  10. What are the Historical and Future Impacts of Temperature Variability on Thermoelectric Power Plant Performance?

    NASA Astrophysics Data System (ADS)

    Henry, C.; Pratson, L.

    2015-12-01

    Current literature hypothesize that climate change-driven temperature increases will negatively affect the power production capacity of thermoelectric power plants, which currently produce ~88% of electricity used in the United States. This impact can occur through 1) warm cooling water that reduces the quantity of heat removed from the once-through (open-loop) steam system, 2) increased air temperature and/or humidity that decrease the amount of heat absorption in cooling towers/ponds of wet-recirculating (closed-loop) plants, and 3) environmental protection regulations that impose restrictions on both cooling water withdrawal volume and temperature of discharge. However, despite the widespread consensus that temperature and power generation are negatively related, different models yield a range of results and the magnitude of effects is uncertain. In this study, we test current literature's model predictions using historical data by assembling and analyzing a database of relevant parameters from distinct sources. We examine how daily and seasonal changes in cooling water, ambient air, and wet bulb temperatures have historically impacted coal and natural gas power plants in the U.S., focusing on 39 plants over a period up to 14 years. This allows us to assess how future changes in temperatures may affect generation. Our results suggest that water and ambient air temperatures have a lower impact on thermoelectric plant performance than previously predicted. Moreover, we find that recirculating power plants are more resilient to temperature variability than are once-through plants.

  11. Contrasting role of antimony and bismuth dopants on the thermoelectric performance of lead selenide.

    PubMed

    Lee, Yeseul; Lo, Shih-Han; Chen, Changqiang; Sun, Hui; Chung, Duck-Young; Chasapis, Thomas C; Uher, Ctirad; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2014-05-02

    Increasing the conversion efficiency of thermoelectric materials is a key scientific driver behind a worldwide effort to enable heat to electricity power generation at competitive cost. Here we report an increased performance for antimony-doped lead selenide with a thermoelectric figure of merit of ~1.5 at 800 K. This is in sharp contrast to bismuth doped lead selenide, which reaches a figure of merit of <1. Substituting antimony or bismuth for lead achieves maximum power factors between ~23-27 μW cm(-1) K(-2) at temperatures above 400 K. The addition of small amounts (~0.25 mol%) of antimony generates extensive nanoscale precipitates, whereas comparable amounts of bismuth results in very few or no precipitates. The antimony-rich precipitates are endotaxial in lead selenide, and appear remarkably effective in reducing the lattice thermal conductivity. The corresponding bismuth-containing samples exhibit smaller reduction in lattice thermal conductivity.

  12. High-performance flat-panel solar thermoelectric generators with high thermal concentration.

    PubMed

    Kraemer, Daniel; Poudel, Bed; Feng, Hsien-Ping; Caylor, J Christopher; Yu, Bo; Yan, Xiao; Ma, Yi; Wang, Xiaowei; Wang, Dezhi; Muto, Andrew; McEnaney, Kenneth; Chiesa, Matteo; Ren, Zhifeng; Chen, Gang

    2011-05-01

    The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. Photovoltaic cells are deployed widely, mostly as flat panels, whereas solar thermal electricity generation relying on optical concentrators and mechanical heat engines is only seen in large-scale power plants. Here we demonstrate a promising flat-panel solar thermal to electric power conversion technology based on the Seebeck effect and high thermal concentration, thus enabling wider applications. The developed solar thermoelectric generators (STEGs) achieved a peak efficiency of 4.6% under AM1.5G (1 kW m(-2)) conditions. The efficiency is 7-8 times higher than the previously reported best value for a flat-panel STEG, and is enabled by the use of high-performance nanostructured thermoelectric materials and spectrally-selective solar absorbers in an innovative design that exploits high thermal concentration in an evacuated environment. Our work opens up a promising new approach which has the potential to achieve cost-effective conversion of solar energy into electricity.

  13. Lattice thermal conductivities and thermoelectric performances of binary tin-based sheets: A computational study

    NASA Astrophysics Data System (ADS)

    Ding, Yi; Wang, Yanli

    2017-02-01

    Thermal transport properties of nanomaterials are essential for their nanodevices and nano-energy applications. Here, utilizing first-principles calculation with the Boltzmann transport equation, we investigate the lattice thermal conductivities and thermoelectric performances of SnSi and SnGe sheets. Their room-temperature lattice thermal conductivities (κlat) are found in the magnitude of 5-12 W/mK, which are smaller than the values in elemental silicene, germanene, and stanene sheets. A long phonon mean free path limitation is found for the SnSi system, which causes a ballistic thermal transport in its finite micro-scale samples, while for the SnGe one, it will still exhibit a diffusive feature instead. Accompanied with the low κlat, their figures of merit are estimated to exceed one in the wide temperature range of 350-800 K, where the peak value can arrive at 1.47 and 1.64 for SnSi and SnGe sheets, respectively. Those merits of thermal transport properties will enable intriguing thermoelectric and other sustain-energy applications for binary SnSi and SnGe systems.

  14. High-Performance Silicon-Germanium-Based Thermoelectric Modules for Gas Exhaust Energy Scavenging

    NASA Astrophysics Data System (ADS)

    Romanjek, K.; Vesin, S.; Aixala, L.; Baffie, T.; Bernard-Granger, G.; Dufourcq, J.

    2015-06-01

    Some of the energy used in transportation and industry is lost as heat, often at high-temperatures, during conversion processes. Thermoelectricity enables direct conversion of heat into electricity, and is an alternative to the waste-heat-recovery technology currently used, for example turbines and other types of thermodynamic cycling. The performance of thermoelectric (TE) materials and modules has improved continuously in recent decades. In the high-temperature range ( T hot side > 500°C), silicon-germanium (SiGe) alloys are among the best TE materials reported in the literature. These materials are based on non-toxic elements. The Thermoelectrics Laboratory at CEA (Commissariat à l'Energie Atomique et aux Energies Alternatives) has synthesized n and p-type SiGe pellets, manufactured TE modules, and integrated these into thermoelectric generators (TEG) which were tested on a dedicated bench with hot air as the source of heat. SiGe TE samples of diameter 60 mm were created by spark-plasma sintering. For n-type SiGe doped with phosphorus the peak thermoelectric figure of merit reached ZT = 1.0 at 700°C whereas for p-type SiGe doped with boron the peak was ZT = 0.75 at 700°C. Thus, state-of-the-art conversion efficiency was obtained while also achieving higher production throughput capacity than for competing processes. A standard deviation <4% in the electrical resistance of batches of ten pellets of both types was indicative of high reproducibility. A silver-paste-based brazing technique was used to assemble the TE elements into modules. This assembly technique afforded low and repeatable electrical contact resistance (<3 nΩ m2). A test bench was developed for measuring the performance of TE modules at high temperatures (up to 600°C), and thirty 20 mm × 20 mm TE modules were produced and tested. The results revealed the performance was reproducible, with power output reaching 1.9 ± 0.2 W for a 370 degree temperature difference. When the temperature

  15. Performance parameters and numerical model of thermoelectric generator dedicated for energy harvesting from flue gases

    NASA Astrophysics Data System (ADS)

    Borcuch, M.; Musiał, M.; Gumuła, S.; Wojciechowski, K. T.

    2016-09-01

    The paper presents results of preliminary studies of thermoelectric generator (TEG) dedicated for waste heat harvesting from flue gases. Investigation includes numerical analysis for estimating power losses due to pressure drop in the installation with the TEG and experimental tests for obtaining electrical parameters and operation conditions, such as casing temperatures and the temperature difference between the inlet and the outlet. Proposed prototype has been equipped with the pin fins for increase the heat transfer. Results indicates that power losses are negligible in comparison with generated electrical power. The heat exchanger's interior demands to be modified to enhance the efficiency by increasing temperatures on the external surfaces of the hot-side heat exchanger (HHX). Further research will focus on numerical analysis of the influence of geometry modifications on the thermal and flow parameters of the TEG resulting in the increase of generated power and efficiency.

  16. Enhanced Thermoelectric Properties of Cu2ZnSnSe4 with Ga-doping

    DOE PAGES

    Wei, Kaya; Beauchemin, Laura; Wang, Hsin; ...

    2015-08-10

    Gallium doped Cu2ZnSnSe4 quaternary chalcogenides with and without excess Cu were synthesized by elemental reaction and densified using hot pressing in order to investigate their high temperature thermoelectric properties. The resistivity, , and Seebeck coefficient, S, for these materials decrease with increased Ga-doping while both mobility and effective mass increase with Ga doping. The power factor (S2/ρ) therefore increases with Ga-doping. The highest thermoelectric figure of merit (ZT = 0.39 at 700 K) was obtained for the composition that had the lowest thermal conductivity. Our results suggest an approach to achieving optimized thermoelectric properties and are part of the continuingmore » effort to explore different quaternary chalcogenide compositions and structure types, as this class of materials continues to be of interest for thermoelectrics applications.« less

  17. Enhanced thermoelectric properties of Co1- x- y Ni x+ y Sb3- x Sn x materials

    NASA Astrophysics Data System (ADS)

    Liu, Hong-Quan; Zhang, Sheng-Nan; Zhu, Tie-Jun; Zhao, Xin-Bing; Gu, Yi-Jie; Cui, Hong-Zhi

    2012-03-01

    Co1- x- y Nix+ y Sb3- x Sn x polycrystals were fabricated by vacuum melting combined with hot-press sintering. The effect of alloying on the thermoelectric properties of unfilled skutterudite Co1- x Ni x Sb3- x Sn x was investigated. A leap of electrical conductivity from the Co0.93Ni0.07Sb2.93Sn0.07 sample to the Co0.88Ni0.12Sb2.88Sn0.12 sample occurs during the measurement of electrical conductivity, indicating the adjustment of band structure by proper alloying. The results show that alloying enhances the power factor of the materials. On the basis of alloying, the thermoelectric properties of Co0.88Ni0.12Sb2.88Sn0.12 are improved by Ni-doping. The thermal conductivities of Ni-doping samples have no reduction, but their power factors have obvious enhancement. The power factor of Co0.81Ni0.19Sb2.88Sn0.12 reaches 3.0 mW·m-1·K-2 by Ni doping. The dimensionless thermoelectric figure of merit reaches 0.55 at 773 K for the unfilled Co0.81Ni0.19 Sb2.88Sn0.12.

  18. Enhanced magneto-thermoelectric power factor of a 70 nm Ni-nanowire

    NASA Astrophysics Data System (ADS)

    Mitdank, R.; Handwerg, M.; Steinweg, C.; Töllner, W.; Daub, M.; Nielsch, K.; Fischer, S. F.

    2012-05-01

    Thermoelectric (TE) properties of a single nanowire (NW) are investigated in a microlab which allows the determination of the Seebeck coefficient S, the electrical conductivity σ, and a full ZT-characterization in the validity limit of the Wiedemann-Franz-law (ZT—figure of merit). A significant influence of the magnetization of a 70 nm diameter ferromagnetic Ni-NW on its power factor S2σ is observed. We detected a strong magnetothermopower effect (MTP) of about 10% and an anisotropic magnetoresistance (AMR) as a function of an external magnetic field B in the order of 1%. At T = 295 K and B = 0 T, we determined the absolute value of S = -(19 ± 2) μV/K. The thermopower S increases considerably as a function of B up to 10% at B = 0.5 T, and with a magnetothermopower of ∂S/∂B ≈ -(3.8 ± 0.5) μV/(KT). The AMR and MTP are related by ∂s/∂r ≈ -11 ± 1 (∂s = ∂S/S). Hence, the TE efficiency increases in a transversal magnetic field (B = 0.5 T) due to an enhanced power factor by nearly 20%.

  19. Great enhancements in the thermoelectric power factor of BiSbTe nanostructured films with well-ordered interfaces.

    PubMed

    Chang, Hsiu-Cheng; Chen, Chun-Hua; Kuo, Yung-Kang

    2013-08-07

    An innovative concept of twin-enhanced thermoelectricity was proposed to fundamentally resolve the high electrical resistance while not degrading the phonon scattering of the thermoelectric nanoassemblies. Under this frame, a variety of highly oriented and twinned bismuth antimony telluride (BixSb2-xTe3) nanocrystals were successfully fabricated by a large-area pulsed-laser deposition (PLD) technique on insulated silicon substrates at various deposition temperatures. The significant presence of the nonbasal- and basal-plane twins across the hexagonal BiSbTe nanocrystals, which were experimentally and systematically observed for the first time, evidently contributes to the unusually high electrical conductivity of ~2700 S cm(-1) and the power factor of ~25 μW cm(-1) K(-2) as well as the relatively low thermal conductivity of ~1.1 W m(-1) K(-1) found in these nanostructured films.

  20. Great thermoelectric power factor enhancement of CoSb{sub 3} through the lightest metal element filling

    SciTech Connect

    Zhang Jianjun; Xu Bo; Wang Limin; Yu Dongli; Liu Zhongyuan; He Julong; Tian Yongjun

    2011-02-14

    Lithium, the lightest metal element with a small ionic radius, is successfully filled into the voids of CoSb{sub 3} by utilizing the high pressure synthesis technique. The synthesized Li{sub 0.4}Co{sub 4}Sb{sub 12} shows the largest thermoelectric power factor of 6000 {mu}W m{sup -1} K{sup -2} among all elemental filled CoSb{sub 3} materials. This significantly enhanced thermoelectric power factor is attributed to the large carrier mobility of Li{sub 0.4}Co{sub 4}Sb{sub 12}, 61 cm{sup 2} V{sup -1} s{sup -1}, featuring a good electron crystal property for the Li-filled CoSb{sub 3} samples.

  1. YbCu2Si2-LaCu2Si2 Solid Solutions with Enhanced Thermoelectric Power Factors

    NASA Astrophysics Data System (ADS)

    Lehr, Gloria J.; Morelli, Donald T.; Jin, Hyungyu; Heremans, Joseph P.

    2015-06-01

    Cryogenic Peltier coolers are ideal for cooling infrared sensors on satellites. To make these thermoelectric devices a realistic option for this application, the efficiency of thermoelectric materials at cryogenic temperatures must be substantially enhanced. Intermediate valence Yb-based compounds have large peaks in the Seebeck coefficient at low temperatures; to optimize these materials this must be understood. We created solid solutions between the intermediate valence compound YbCu2Si2 and an isostructural compound LaCu2Si2 to manipulate the temperature at which the Seebeck coefficient peaks and to maximize zT by reduction of lattice thermal conductivity. An enormous power factor of 110 μW/cm K2 at 100 K and a maximum zT of 0.14 at 125 K were achieved for one of these solid solutions.

  2. A theoretical study on the performances of thermoelectric heat engine and refrigerator with two-dimensional electron reservoirs

    SciTech Connect

    Luo, Xiaoguang Long, Kailin; Wang, Jun; Qiu, Teng; He, Jizhou; Liu, Nian

    2014-06-28

    Theoretical thermoelectric nanophysics models of low-dimensional electronic heat engine and refrigerator devices, comprising two-dimensional hot and cold reservoirs and an interconnecting filtered electron transport mechanism have been established. The models were used to numerically simulate and evaluate the thermoelectric performance and energy conversion efficiencies of these low-dimensional devices, based on three different types of electron transport momentum-dependent filters, referred to herein as k{sub x}, k{sub y}, and k{sub r} filters. Assuming the Fermi-Dirac distribution of electrons, expressions for key thermoelectric performance parameters were derived for the resonant transport processes, in which the transmission of electrons has been approximated as a Lorentzian resonance function. Optimizations were carried out and the corresponding optimized design parameters have been determined, including but not limited to the universal theoretical upper bound of the efficiency at maximum power for heat engines, and the maximum coefficient of performance for refrigerators. From the results, it was determined that k{sub r} filter delivers the best thermoelectric performance, followed by the k{sub x} filter, and then the k{sub y} filter. For refrigerators with any one of three filters, an optimum range for the full width at half maximum of the transport resonance was found to be <2k{sub B}T.

  3. Thermoelectric Enhancement by Compositing Carbon Nanotubes into Iodine-Doped Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene].

    PubMed

    Tonga, Murat; Wei, Lang; Taylor, Patrick S; Wilusz, Eugene; Korugic-Karasz, Ljiljana; Karasz, Frank E; Lahti, Paul M

    2017-03-15

    Free-standing iodine-doped composite samples of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with carbon nanotubes (NTs) showed thermoelectric (TE) power factors (PFs) up to 33 μW·m(-1)·K(-2) after optimizing multiple factors, including: (1) sample fabrication solvent, (2) doping time, (3) average MEH-PPV molecular weight, (4) NT fraction in the composite, and (5) use of single-wall versus multi-wall nanotubes (SWNT and MWNT, respectively). Composite fabrication from halogenated solvents gave the best TE performance after iodine doping times of 2-4 h; performance drops substantially in ∼20 h doped samples. TE performance dropped after at least 24 h of removal from iodine vapor but was fully restored upon re-exposure to the dopant. Longer-chain MEH-PPV gave not only mechanically stronger films but also higher PFs in doped SWNT composites. MWNT composites gave low PFs, attributed to poor NT dispersion. Scanning electron microscopy showed increasingly extensive network formation as NT fraction increased in the composites; this phase separation provides charge transport pathways that improve thermoelectric PFs. The results support a strategy of producing phase-separated materials having both electrical conduction enhanced regions and Seebeck thermopower retaining regions to maximize organic TE response.

  4. Improved thermoelectric performance of (Fe,Co)Sb{sub 3}-type skutterudites from first-principles

    SciTech Connect

    Williamson, Izaak; Her, Logan Ju-Yee; Su, Xianli; Yan, Yonggao; Wong-Ng, Winnie; Li, Lan

    2016-02-07

    Skutterudite materials have been considered as promising thermoelectric candidates due to intrinsically good electrical conductivity and tailorable thermal conductivity. Options for improving thermal-to-electrical conversion efficiency include identifying novel materials, adding filler atoms, and substitutional dopants. Incorporating filler or substitutional dopant atoms in the skutterudite compounds can enhance phonon scattering, resulting in reduction of thermal conductivity, as well as improving electrical conductivity. The structures, electronic properties, and thermal properties of double-filled Ca{sub 0.5}Ce{sub 0.5}Fe{sub 4}Sb{sub 12} and Co{sub 4}Sb{sub 12−2x}Te{sub x}Ge{sub x} compounds (x = 0, 0.5, 1, 2, 3, and 6) have been studied using density functional theory-based calculations. Both Ca/Ce filler atoms in FeSb{sub 3} and Te/Ge substitution in CoSb{sub 3} cause a decrease in lattice constant for the compounds. As Te/Ge substitution concentration increases, lattice constant decreases and structural distortion of pnictogen rings in the compounds occurs. This indicates a break in cubic symmetry of the structure. The presence of fillers and substitutions cause an increase in electrical conductivity and a gradual decrease in electronic band gap. A transition from direct to indirect band-gap semiconducting behavior is found at x = 3. Phonon density of states for both compounds indicate phonon band broadening by the incorporation of fillers and substitutional atoms. Both systems are also assumed to have acoustic-mode-dominated lattice thermal conductivity. For the Co{sub 4}Sb{sub 12−2x}Te{sub x}Ge{sub x} compounds, x = 3 has the lowest phonon dispersion gradient and lattice thermal conductivity, agreeing well with experimental measurements. Our results exhibit the improvement of thermoelectric properties of skutterudite compounds through fillers and substitutional doping.

  5. Hinge-like structure induced unusual properties of black phosphorus and new strategies to improve the thermoelectric performance

    PubMed Central

    Qin, Guangzhao; Yan, Qing-Bo; Qin, Zhenzhen; Yue, Sheng-Ying; Cui, Hui-Juan; Zheng, Qing-Rong; Su, Gang

    2014-01-01

    We systematically investigated the geometric, electronic and thermoelectric (TE) properties of bulk black phosphorus (BP) under strain. The hinge-like structure of BP brings unusual mechanical responses such as anisotropic Young's modulus and negative Poisson's ratio. A sensitive electronic structure of BP makes it transform among metal, direct and indirect semiconductors under strain. The maximal figure of merit ZT of BP is found to be 0.72 at 800 K that could be enhanced to 0.87 by exerting an appropriate strain, revealing BP could be a potential medium-high temperature TE material. Such strain-induced enhancements of TE performance are often observed to occur at the boundary of the direct-indirect band gap transition, which can be attributed to the increase of degeneracy of energy valleys at the transition point. By comparing the structure of BP with SnSe, a family of potential TE materials with hinge-like structure are suggested. This study not only exposes various novel properties of BP under strain, but also proposes effective strategies to seek for better TE materials. PMID:25374306

  6. Half-Heusler thermoelectrics: a complex class of materials.

    PubMed

    Bos, Jan-Willem G; Downie, Ruth A

    2014-10-29

    Half-Heusler thermoelectrics first attracted interest in the late-1990s and are currently undergoing a renaissance. This has been driven by improved synthesis, processing and characterisation methods, leading to increases in the thermoelectric figure of merit and the observation of novel phenomena such as carrier filtering in nanocomposite samples. The difficulty in extracting good thermoelectric performance is at first glance surprising given the relative simplicity of the ideal crystal structure with only site occupancies and lattice parameter as crystallographic variables. However, the observed thermoelectric properties are found to depend sensitively on sample processing. Recent work has shown that prepared ingots can contain a range of inhomogeneities, including interstitials, nano- and micron sized Heusler inclusions and multiple half-Heusler phases. For this reason, the prepared materials are far more complex than initially appreciated and this may offer opportunities to enhance the thermoelectric figure of merit.

  7. Experimental Performance of a Thermoelectric Heat-Pump Drying System for Drying Herbs

    NASA Astrophysics Data System (ADS)

    Wongsim, K.; Jamradloedluk, J.; Lertsatitthanakorn, C.; Siriamornpun, S.; Rungsiyopas, M.; Soponronnarit, S.

    2015-06-01

    In this study we investigated thermoelectric (TE) heat-pump drying of laurel clock vine leaves, and the effect of drying-air temperature on the characteristics of the leaves. The TE drying system comprised four TE modules each with its own rectangular fin heat sink. The hot side of each TE module was fixed to its own heat sink; the cold sides were fixed to heat-pipe heat sinks and a drying chamber. The drying time depended on drying-air temperature. The heating capacity and coefficient of performance (COP) increased as the current supplied to the TE modules was increased. Calculated COP for the entire TE heat-pump drying system were 1.28 and 0.81 for drying-air temperatures of 50 and 40°C, respectively.

  8. Thermoelectric converter

    DOEpatents

    Kim, C.K.

    1974-02-26

    This invention relates in general to thermoelectric units and more particularly to a tubular thermoelectric unit which includes an array of tandemly arranged radially tapered annular thermoelectric pellets having insulation material of a lower density than the thermoelectric pellets positioned between each pellet. (Official Gazette)

  9. Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

    SciTech Connect

    Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T.; Martinez, Julio A.

    2015-11-25

    The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

  10. Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

    DOE PAGES

    Song, Erdong; Li, Qiming; Swartzentruber, Brian; ...

    2015-11-25

    The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN coremore » of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.« less

  11. Modelling of segmented high-performance thermoelectric generators with effects of thermal radiation, electrical and thermal contact resistances

    PubMed Central

    Ouyang, Zhongliang; Li, Dawen

    2016-01-01

    In this study, segmented thermoelectric generators (TEGs) have been simulated with various state-of-the-art TE materials spanning a wide temperature range, from 300 K up to 1000 K. The results reveal that by combining the current best p-type TE materials, BiSbTe, MgAgSb, K-doped PbTeS and SnSe with the strongest n-type TE materials, Cu-Doped BiTeSe, AgPbSbTe and SiGe to build segmented legs, TE modules could achieve efficiencies of up to 17.0% and 20.9% at ΔT = 500 K and ΔT = 700 K, respectively, and a high output power densities of over 2.1 Watt cm−2 at the temperature difference of 700 K. Moreover, we demonstrate that successful segmentation requires a smooth change of compatibility factor s from one end of the TEG leg to the other, even if s values of two ends differ by more than a factor of 2. The influence of the thermal radiation, electrical and thermal contact effects have also been studied. Although considered potentially detrimental to the TEG performance, these effects, if well-regulated, do not prevent segmentation of the current best TE materials from being a prospective way to construct high performance TEGs with greatly enhanced efficiency and output power density. PMID:27052592

  12. Modelling of segmented high-performance thermoelectric generators with effects of thermal radiation, electrical and thermal contact resistances.

    PubMed

    Ouyang, Zhongliang; Li, Dawen

    2016-04-07

    In this study, segmented thermoelectric generators (TEGs) have been simulated with various state-of-the-art TE materials spanning a wide temperature range, from 300 K up to 1000 K. The results reveal that by combining the current best p-type TE materials, BiSbTe, MgAgSb, K-doped PbTeS and SnSe with the strongest n-type TE materials, Cu-Doped BiTeSe, AgPbSbTe and SiGe to build segmented legs, TE modules could achieve efficiencies of up to 17.0% and 20.9% at ΔT = 500 K and ΔT = 700 K, respectively, and a high output power densities of over 2.1 Watt cm(-2) at the temperature difference of 700 K. Moreover, we demonstrate that successful segmentation requires a smooth change of compatibility factor s from one end of the TEG leg to the other, even if s values of two ends differ by more than a factor of 2. The influence of the thermal radiation, electrical and thermal contact effects have also been studied. Although considered potentially detrimental to the TEG performance, these effects, if well-regulated, do not prevent segmentation of the current best TE materials from being a prospective way to construct high performance TEGs with greatly enhanced efficiency and output power density.

  13. Optimization of thermoelectric performance of SrSi2-based alloys via the modification in band structure and phonon-point-defect scattering.

    PubMed

    Kuo, Yung-Kang; Ramachandran, Balakrishnan; Lue, Chin-Shan

    2014-01-01

    Thermoelectric properties of alkaline-earth-metal disilicides are strongly dependent on their electronic band structure in the vicinity of the Fermi level. In particular, the strontium disilicide, SrSi2 with a narrow band gap of about few tens of meV is composed of non-toxic, naturally abundant elements, and its thermoelectric properties are very sensitive to the substitution/alloying with third elements. In this article, we summarize the thermoelectric performance of substituted and Sr-deficient/Sr-rich SrSi2 alloys to realize the high thermoelectric figure-of-merit (ZT) for practical applications in the electronic and thermoelectric aspects, and also to explore the alternative routes to further improve its ZT value.

  14. Optimization of thermoelectric performance of SrSi2-based alloys via the modification in band structure and phonon-point-defect scattering

    PubMed Central

    Kuo, Yung-Kang; Ramachandran, Balakrishnan; Lue, Chin-Shan

    2014-01-01

    Thermoelectric properties of alkaline-earth-metal disilicides are strongly dependent on their electronic band structure in the vicinity of the Fermi level. In particular, the strontium disilicide, SrSi2 with a narrow band gap of about few tens of meV is composed of non-toxic, naturally abundant elements, and its thermoelectric properties are very sensitive to the substitution/alloying with third elements. In this article, we summarize the thermoelectric performance of substituted and Sr-deficient/Sr-rich SrSi2 alloys to realize the high thermoelectric figure-of-merit (ZT) for practical applications in the electronic and thermoelectric aspects, and also to explore the alternative routes to further improve its ZT value. PMID:25505784

  15. Great enhancements in the thermoelectric power factor of BiSbTe nanostructured films with well-ordered interfaces

    NASA Astrophysics Data System (ADS)

    Chang, Hsiu-Cheng; Chen, Chun-Hua; Kuo, Yung-Kang

    2013-07-01

    An innovative concept of twin-enhanced thermoelectricity was proposed to fundamentally resolve the high electrical resistance while not degrading the phonon scattering of the thermoelectric nanoassemblies. Under this frame, a variety of highly oriented and twinned bismuth antimony telluride (BixSb2-xTe3) nanocrystals were successfully fabricated by a large-area pulsed-laser deposition (PLD) technique on insulated silicon substrates at various deposition temperatures. The significant presence of the nonbasal- and basal-plane twins across the hexagonal BiSbTe nanocrystals, which were experimentally and systematically observed for the first time, evidently contributes to the unusually high electrical conductivity of ~2700 S cm-1 and the power factor of ~25 μW cm-1 K-2 as well as the relatively low thermal conductivity of ~1.1 W m-1 K-1 found in these nanostructured films.An innovative concept of twin-enhanced thermoelectricity was proposed to fundamentally resolve the high electrical resistance while not degrading the phonon scattering of the thermoelectric nanoassemblies. Under this frame, a variety of highly oriented and twinned bismuth antimony telluride (BixSb2-xTe3) nanocrystals were successfully fabricated by a large-area pulsed-laser deposition (PLD) technique on insulated silicon substrates at various deposition temperatures. The significant presence of the nonbasal- and basal-plane twins across the hexagonal BiSbTe nanocrystals, which were experimentally and systematically observed for the first time, evidently contributes to the unusually high electrical conductivity of ~2700 S cm-1 and the power factor of ~25 μW cm-1 K-2 as well as the relatively low thermal conductivity of ~1.1 W m-1 K-1 found in these nanostructured films. Electronic supplementary information (ESI) available: Morphologies, XRD patterns, SEM compositions and room-temperature thermoelectric properties of the series of (015) oriented Bi0.4Sb1.6Te3 nanocolumns (Fig. S1-S3), (00l) oriented

  16. Low thermal conductivity and improved thermoelectric performance of nanocrystalline silicon germanium films by sputtering.

    PubMed

    Taborda, J A Perez; Romero, J J; Abad, B; Muñoz-Rojo, M; Mello, A; Briones, F; Gonzalez, M S Martin

    2016-04-29

    Si x Ge1-x alloys are well-known thermoelectric materials with a high figure of merit at high temperatures. In this work, metal-induced crystallization (MIC) has been used to grow Si0.8Ge0.2 films that present improved thermoelectric performance (zT = 5.6 × 10(-4) at room temperature)--according to previously reported values on films--with a relatively large power factor (σ · S (2) = 16 μW · m(-1) · K(-2)). More importantly, a reduction in the thermal conductivity at room temperature (κ = 1.13 ± 0.12 W · m(-1) · K(-1)) compared to other Si-Ge films (∼3 W · m(-1) · K(-1)) has been found. Whereas the usual crystallization of amorphous SiGe (a-SiGe) is achieved at high temperatures and for long times, which triggers dopant loss, MIC reduces the crystallization temperature and the heating time. The associated dopant loss is thus avoided, resulting in a nanostructuration of the film. Using this method, we obtained Si0.8Ge0.2 films (grown by DC plasma sputtering) with appropriate compositional and structural properties. Different thermal treatments were tested in situ (by heating the sample inside the deposition chamber) and ex situ (annealed in an external furnace with controlled conditions). From the studies of the films by: x-ray diffraction (XRD), synchrotron radiation grazing incidence x-ray diffraction (SR-GIXRD), micro Raman, scanning electron microscopy (SEM), x-ray photoemission spectroscopy (XPS), Hall effect, Seebeck coefficient, electrical and thermal conductivity measurements, we observed that the in situ films at 500 °C presented the best zT values with no gold contamination.

  17. Low thermal conductivity and improved thermoelectric performance of nanocrystalline silicon germanium films by sputtering

    NASA Astrophysics Data System (ADS)

    Perez Taborda, J. A.; Romero, J. J.; Abad, B.; Muñoz-Rojo, M.; Mello, A.; Briones, F.; Gonzalez, M. S. Martin

    2016-04-01

    Si x Ge1-x alloys are well-known thermoelectric materials with a high figure of merit at high temperatures. In this work, metal-induced crystallization (MIC) has been used to grow Si0.8Ge0.2 films that present improved thermoelectric performance (zT = 5.6 × 10-4 at room temperature)—according to previously reported values on films—with a relatively large power factor (σ · S 2 = 16 μW · m-1 · K-2). More importantly, a reduction in the thermal conductivity at room temperature (κ = 1.13 ± 0.12 W · m-1 · K-1) compared to other Si-Ge films (˜3 W · m-1 · K-1) has been found. Whereas the usual crystallization of amorphous SiGe (a-SiGe) is achieved at high temperatures and for long times, which triggers dopant loss, MIC reduces the crystallization temperature and the heating time. The associated dopant loss is thus avoided, resulting in a nanostructuration of the film. Using this method, we obtained Si0.8Ge0.2 films (grown by DC plasma sputtering) with appropriate compositional and structural properties. Different thermal treatments were tested in situ (by heating the sample inside the deposition chamber) and ex situ (annealed in an external furnace with controlled conditions). From the studies of the films by: x-ray diffraction (XRD), synchrotron radiation grazing incidence x-ray diffraction (SR-GIXRD), micro Raman, scanning electron microscopy (SEM), x-ray photoemission spectroscopy (XPS), Hall effect, Seebeck coefficient, electrical and thermal conductivity measurements, we observed that the in situ films at 500 °C presented the best zT values with no gold contamination.

  18. The influence of Thomson effect in the performance optimization of a two stage thermoelectric cooler

    NASA Astrophysics Data System (ADS)

    Kaushik, S. C.; Manikandan, S.

    2015-12-01

    The exoreversible and irreversible thermodynamic models of a two stage thermoelectric cooler (TTEC) considering Thomson effect in conjunction with Peltier, Joule and Fourier heat conduction effects have been investigated using exergy analysis. New expressions for the interstage temperature, optimum current for the maximum cooling power, energy and exergy efficiency conditions, energy efficiency and exergy efficiency of a TTEC are derived as well. The number of thermocouples in the first and second stages of a TTEC for the maximum cooling power, energy and exergy efficiency conditions are optimized. The results show that the exergy efficiency is lower than the energy efficiency e.g., in an irreversible TTEC with total 30 thermocouples, heat sink temperature (TH) of 300 K and heat source temperature (TC) of 280 K, the obtained maximum cooling power, maximum energy and exergy efficiency are 20.37 W, 0.7147 and 5.10% respectively. It has been found that the Thomson effect increases the cooling power and energy efficiency of the TTEC system e.g., in the exoreversible TTEC the cooling power and energy efficiency increased from 14.87 W to 16.36 W and from 0.4079 to 0.4998 respectively for ΔTC of 40 K when Thomson effect is considered. It has also been found that the heat transfer area at the hot side of an irreversible TTEC should be higher than the cold side for maximum performance operation. This study will help in the designing of the actual multistage thermoelectric cooling systems.

  19. Origin of high thermoelectric performance of FeNb1‑xZr/HfxSb1‑ySny alloys: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, Xiwen; Wang, Yuanxu; Yan, Yuli; Wang, Chao; Zhang, Guangbiao; Cheng, Zhenxiang; Ren, Fengzhu; Deng, Hao; Zhang, Jihua

    2016-09-01

    The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds.

  20. Origin of high thermoelectric performance of FeNb1-xZr/HfxSb1-ySny alloys: A first-principles study.

    PubMed

    Zhang, Xiwen; Wang, Yuanxu; Yan, Yuli; Wang, Chao; Zhang, Guangbiao; Cheng, Zhenxiang; Ren, Fengzhu; Deng, Hao; Zhang, Jihua

    2016-09-08

    The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds.

  1. Origin of high thermoelectric performance of FeNb1−xZr/HfxSb1−ySny alloys: A first-principles study

    PubMed Central

    Zhang, Xiwen; Wang, Yuanxu; Yan, Yuli; Wang, Chao; Zhang, Guangbiao; Cheng, Zhenxiang; Ren, Fengzhu; Deng, Hao; Zhang, Jihua

    2016-01-01

    The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds. PMID:27604826

  2. Advanced Thermoelectric Materials for Radioisotope Thermoelectric Generators

    NASA Technical Reports Server (NTRS)

    Caillat, Thierry; Hunag, C.-K.; Cheng, S.; Chi, S. C.; Gogna, P.; Paik, J.; Ravi, V.; Firdosy, S.; Ewell, R.

    2008-01-01

    This slide presentation reviews the progress and processes involved in creating new and advanced thermoelectric materials to be used in the design of new radioiootope thermoelectric generators (RTGs). In a program with Department of Energy, NASA is working to develop the next generation of RTGs, that will provide significant benefits for deep space missions that NASA will perform. These RTG's are planned to be capable of delivering up to 17% system efficiency and over 12 W/kg specific power. The thermoelectric materials being developed are an important step in this process.

  3. Dopant's chemical coordination: a path for engineering high performance thermoelectric sodium cobaltate

    NASA Astrophysics Data System (ADS)

    Assadi, M. Hussein N.; Katayama-Yoshida, Hiroshi

    2014-03-01

    Engineered Na0.75CoO2 is considered a prime candidate to achieve high efficiency thermoelectric systems to generate electricity from waste heat. Our recent experiments on Mg doped Na0.75CoO2 demonstrated 50% enhancement in power factor at ambient. This motivated us to theoretically analyze the mechanisms behind simultaneous improvement of interdependent Seebeck coefficient and electrical conductivity. For this, we comprehensively studied the electronic and crystallographic structure of Na0.75CoO2 doped with 5 elements Mg, Sb, Zn, Ni and Eu. These elements represent wide variety of electronic configurations such as open d and f shells, closed d and s shells, combined with great variation in atomic mass. Systematic density functional calculations showed that the Ni and Zn were more stable when substituting Co with formation energy 2.35 eV, 2.08 eV. While Eu and Mg and Sb are more stable when it substitutes Na. In the case of Mg these results are consistent with Raman scattering measurement. This suggests that the doped Mg ions immobilize Na ions, reducing the resistivity by improving the mobility of carriers and thus enhancing the thermo-power. This work was supported by JSPS and Intersect.

  4. Enhanced thermoelectric properties of bismuth telluride-organic hybrid films via graphene doping

    NASA Astrophysics Data System (ADS)

    Rahman, Airul Azha Abd; Umar, Akrajas Ali; Chen, Xiaomei; Salleh, Muhamad Mat; Oyama, Munetaka

    2016-02-01

    The thermoelectric properties of graphene-doped bismuth telluride-PEDOT:PSS-glycerol (hybrid) films were investigated. Prior to the study, p-type and n-type hybrid films were prepared by doping the PEDOT:PSS-glycerol with the p- and n-type bismuth telluride. Graphene-doped hybrid films were prepared by adding graphene particles of concentration ranging from 0.02 to 0.1 wt% into the hybrid films. Films of graphene-doped hybrid system were then prepared on a glass substrate using a spin-coating technique. It was found that the electrical conductivity of the hybrid films increases with the increasing of the graphene-dopant concentration and optimum at 0.08 wt% for both p- and n-type films, namely 400 and 195 S/cm, respectively. Further increasing in the concentration caused a decreasing in the electrical conductivity. Analysis of the thermoelectric properties of the films obtained that the p-type film exhibited significant improvement in its thermoelectric properties, where the thermoelectric properties increased with the increasing of the doping concentration. Meanwhile, for the case of n-type film, graphene doping showed a negative effect to the thermoelectrical properties, where the thermoelectric properties decreased with the increasing of doping concentration. Seebeck coefficient (and power factor) for optimum p-type and n-type hybrid thin films, i.e., doped with 0.08 wt% of graphene, is 20 μV/K (and 160 μW m-1 K-2) and 10 μV/K (and 19.5 μW m-1 K-2), respectively. The obtained electrical conductivity and thermoelectric properties of graphene-doped hybrid film are interestingly several orders higher than the pristine hybrid films. A thermocouple device fabricated utilizing the p- and n-type graphene-doped hybrid films can generate an electric voltage as high as 2.2 mV under a temperature difference between the hot-side and the cold-side terminal as only low as 55 K. This is equivalent to the output power as high as 24.2 nW (for output load as high as 50

  5. Enhanced room temperature electronic and thermoelectric properties of the dilute bismuthide InGaBiAs

    SciTech Connect

    Dongmo, Pernell; Zhong Yujun; Bomberger, Cory; Zide, Joshua; Attia, Peter; Cheaito, Ramez; Hopkins, Patrick E.; Ihlefeld, Jon F.

    2012-11-01

    We report room temperature electronic and thermoelectric properties of Si-doped In{sub 0.52}Ga{sub 0.48}Bi{sub y}As{sub 1-y} with varying Bi concentrations. These films were grown epitaxially on a semi-insulating InP substrate by molecular beam epitaxy. We show that low Bi concentrations are optimal in improving the conductivity, Seebeck coefficient, and thermoelectric power factor, possibly due to the surfactant effects of bismuth. We observed a reduction in thermal conductivity with increasing Bi concentration, which is expected because of alloy scattering. We report a peak ZT of 0.23 at 300 K.

  6. Enhancing the Thermoelectric Characteristics of PEDOT:PSS Through the Incorporation of a Redox-Active Small Molecule

    NASA Astrophysics Data System (ADS)

    Tomlinson, Edward; Willmore, Matthew; Zhu, Xiaoqin; Boudouris, Bryan

    2015-03-01

    The polymer blend composed of poly(3,4-ethylene dioxythiophene) and poly(styrene sulfonate) (PEDOT:PSS) is a leading organic thermoelectric material due to its high-performing properties. Here, we establish the effect of incorporating the redox-active small molecule4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH) on the structural and thermoelectric properties of PEDOT:PSS. Specifically, the thermoelectric power factor (PF) was monitored as a function of TEMPO-OH loading, elucidating a clear trend in the PF. Importantly, at loadings as low as 5% TEMPO-OH, by mass, the thermopower of the sample was increased by a factor of two. Furthermore, the role of the TEMPO-OH on the thin film morphology of the composite material is examined through the use of grazing incidence-wide angle x-ray scattering (GI-WAXS) and atomic force microscopy (AFM). Despite the acidic conditions associated with the presence of PSS, the existence of radical functionality is confirmed through electron paramagnetic resonance (EPR) spectroscopy. Through careful tuning, the optimized conditions outlined within this work results in PF gains in excess of 40%.

  7. Camel-back band-induced power factor enhancement of thermoelectric lead-tellurium from Boltzmann transport calculations

    SciTech Connect

    Wang, X. G. Wang, L. Liu, J. Peng, L. M.

    2014-03-31

    Band structures of PbTe can be abnormally bended via dual-doping on both the cationic and anionic sites to form camel-back multivalley energy band structures near the band edge. As a result, additional carrier pockets and strong intervalley scattering of carriers are introduced. Boltzmann transport calculations indicate that their contradictory effects yield remarkably enhanced power factor due to the improved thermopower and almost unchanged electrical conductivity in low temperature and high carrier concentration ranges. These findings prove dual-doping-induced band bending as an effective approach to improve the thermoelectric properties of PbTe and other similar materials.

  8. Research Update: Oxide thermoelectrics: Beyond the conventional design rules

    NASA Astrophysics Data System (ADS)

    Terasaki, Ichiro

    2016-10-01

    Materials' design for high-performance thermoelectric oxides is discussed. Since chemical stability at high temperature in air is a considerable advantage in oxides, we evaluate thermoelectric power factor in the high temperature limit. We show that highly disordered materials can be good thermoelectric materials at high temperatures, and the effects of strong correlation can further enhance the figure of merit by adding thermopower arising from the spin and orbital degrees of freedom. We also discuss the Kelvin formula as a promising expression for strongly correlated materials and show that the calculation based on the Kelvin formula can be directly compared with the cross-layer thermopower of layered materials.

  9. BiSb and spin-related thermoelectric phenomena

    NASA Astrophysics Data System (ADS)

    Heremans, Joseph P.; Jin, Hyungyu; Zheng, Yuanhua; Watzman, Sarah J.; Prakash, Arati

    2016-05-01

    This article reviews the factors limiting the figure of merit zT of conventional thermoelectrics especially at cryogenic temperatures and then highlights modern approaches used to increase zT below 200 K. Two type of materials are discussed. The first are BiSb alloys, relatively conventional thermoelectrics in which the zT is enhanced by using resonant levels. The second is the spin- Seebeck effect (SSE), a new solid-state energy conversion technology. Classical thermoelectric and SSE physics are combined to provide new concepts, like magnon-drag, in which we hope to increase the performance of solid-state coolers by exploiting the spin degree of freedom.

  10. Optimization of the Mechanical and Electrical Performance of a Thermoelectric Module

    NASA Astrophysics Data System (ADS)

    Sarhadi, Ali; Bjørk, Rasmus; Pryds, Nini

    2015-11-01

    Finite-element simulation of a thermoelectric (TE) module was conducted to optimize its geometrical dimensions in terms of mechanical reliability and performance. The TE module consisted of bismuth telluride n- and p-type legs. The geometrical dimensions of the module, i.e., leg length and leg cross-sectional area, were varied, and the corresponding maximum thermal stress, output power, and efficiency of the module obtained. An optimal design for the module was then suggested based on minimizing the thermal stresses and maximizing the performance, i.e., power and efficiency. The optimal dimensions at maximum von Mises stress of 75 MPa were leg length of 2 mm to 2.5 mm and leg width of 1.5 mm to 2 mm, resulting in efficiency of 7.2%. Finally, the influence of solders, i.e., solder material between the leg, the interconnector, and the top ceramic layer, on the induced thermal stresses and module performance was investigated. The results revealed that the transition from elastic to plastic deformation in the solder decreased the induced thermal stresses significantly. Moreover, beyond the elastic limit, the stress magnitude was highly dependent on the magnitude and mechanism of plastic deformation in the module. The present study provides a basis for a unique and new optimization scheme for TE modules in terms of endurance and performance.

  11. Three novel electrochemical electrodes for the fabrication of conducting polymer/SWCNTs layered nanostructures and their thermoelectric performance

    NASA Astrophysics Data System (ADS)

    Shi, Hui; Liu, Congcong; Jiang, Qinglin; Xu, Jingkun; Lu, Baoyang; Jiang, Fengxing; Zhu, Zhengyou

    2015-06-01

    Single-walled carbon nanotubes (SWCNTs), PEDOT:PSS/SWCNTs, and SWCNTs/PEDOT:PSS nanofilms were used as working electrodes to electrodeposit polyaniline (PANI) in a mixed alcohol solution of isopropyl alcohol (IPA), boron trifluoride ethyl ether (BFEE), and polyethylene glycol (PEG). The thermoelectric (TE) performances of the resulting nanofilms were systematically investigated. SWCNTs/PEDOT:PSS/PANI nanofilms showed a relatively high electrical conductivity value of 232.0 S cm-1. The Seebeck coefficient was enhanced and exhibited the values of 33.8, 25.6, and 23.0 μV K-1 for the SWCNTs/PANI, PEDOT:PSS/SWCNTs/PANI, and SWCNTs/PEDOT:PSS/PANI films, respectively. The maximum power factor achieved was 12.3 μW m-1 K-2. This technique offers a facile and versatile approach to a class of layered nanostructures, and it may provide a general strategy for fabricating a new generation of conducting polymer/SWCNTs materials for further practical applications.

  12. Thermoelectric power factor enhancement with gate-all-around silicon nanowires

    SciTech Connect

    Curtin, Benjamin M.; Bowers, John E.

    2014-04-14

    The thermoelectric properties of gate-all-around silicon nanowires (Si NWs) are calculated to determine the potential for significant power factor enhancement. The Boltzmann transport equation and relaxation time approximation are employed to develop an electron transport model used to determine the field-effect mobility, electrical conductivity, Seebeck coefficient, and power factor for Si NWs with cross-sectional areas between 4 nm × 4 nm and 12 nm × 12 nm and a range of gate biases. Electrical conductivity for the gated Si NWs was much higher than that of doped Si due to the lack of ionized impurities and correspondingly greater carrier mobility. A significant increase in electrical conductivity with decreasing Si NW cross-sectional area was also observed due to a large increase in the average carrier density. For all Si NWs, the Seebeck coefficient was lower than that of doped bulk Si due to the different energy dependence between ionized impurity and phonon-mediated scattering processes. This decrease was also confirmed with Seebeck coefficient measurements of multigated Si NWs and n-type Si thin-films. Quantum confinement was also found to increase the Seebeck coefficient for <8 nm × 8 nm Si NWs and also at high charge densities. A maximum power factor of 6.8 × 10{sup −3} W m{sup −1} K{sup −2} was calculated for the 6 nm × 6 nm Si NWs with typical Si/SiO{sub 2} interface roughness, which is 2–3 × those obtained experimentally for bulk Si. The power factor was also found to greatly depend on surface roughness, with a root-mean-square roughness of <0.8 nm necessary for power factor enhancement. An increase in ZT may also be possible if a low thermal conductivity can be obtained with minimal surface roughness.

  13. Low Thermal Conductivity and High Thermoelectric Performance in In4Se3- x with Phase-Separated Indium Inclusions

    NASA Astrophysics Data System (ADS)

    Rawat, Pankaj Kumar; Park, Hwanjoo; Hwang, Junphil; Kim, Woochul

    2017-03-01

    We report the thermoelectric properties of undoped hot-pressed In4Se3- x ( x = 0.05). Stoichiometric imbalance due to selenium deficiency in In4Se3 was found to create a secondary phase of elemental indium in the host material. Heat treatment drove grain growth and increased the indium solubility in In4Se3. Indium-rich domains at grain surfaces/boundaries in untreated samples were found to redistribute inside the grains and their junctions after heat treatment. Due to enhanced phonon scattering by secondary phase of indium, very low values of thermal conductivity were observed for all samples, leading to a maximum thermoelectric figure of merit ( zT) of 1.13 at 723 K along the hot-pressing direction for the heat-treated sample.

  14. Enhancing Decision Performance

    DTIC Science & Technology

    2002-07-09

    The first is temporary storage of information, as proposed by Atkinson and Shiffrin (1968) in their model of short term memory . The second demand...Reference: Atkinson , R.C., & Shiffrin , R.M. (1968). Human memory : A proposed system and its control processes. In K.W. Spence (Ed.), The psychology of...Flexiablity in Performance Study 2: Use and Memory of Configural and Holistic Information Study 3: Time Pressure REPORT DOCUMENTATION PAGE Form Approved

  15. Thermoelectrics with earth abundant elements: high performance p-type PbS nanostructured with SrS and CaS.

    PubMed

    Zhao, Li-Dong; He, Jiaqing; Wu, Chun-I; Hogan, Timothy P; Zhou, Xiaoyuan; Uher, Ctirad; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2012-05-09

    We report high thermoelectric performance in nanostructured p-type PbS, a material consisting of highly earth abundant and inexpensive elements. The high level of Na doping switched intrinsic n-type PbS to p-type and substantially raised the power factor maximum for pure PbS to ~9.0 μW cm(-1) K(-2) at >723 K using 2.5 at. % Na as the hole dopant. Contrary to that of PbTe, no enhancement in the Hall coefficient occurs at high temperature for heavily doped p-type PbS, indicating a single band model and no heavy hole band. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding SrS or CaS, which form a combination of a nanostructured/solid solution material as determined by transmission electron microscopy. We find that both nanoscale precipitates and point defects play an important role in reducing the lattice thermal conductivity, but the contribution from nanoscale precipitates of SrS is greater than that of CaS, whereas the contribution from point defects in the case of CaS is greater than that of SrS. Theoretical calculations of the lattice thermal conductivity based on the modified Callaway model reveal that both nanostructures and point defects (solid solution) effectively scatter phonons in this system. The lattice thermal conductivity at 723 K can be reduced by ~50% by introducing up to 4.0 at. % of either SrS or CaS. As a consequence, ZT values as high as 1.22 and 1.12 at 923 K can be achieved for nominal Pb(0.975)Na(0.025)S with 3.0 at. % SrS and CaS, respectively. No deterioration was observed after a 15 d annealing treatment of the samples, indicating the excellent thermal stability for these high performance thermoelectrics. The promising thermoelectric properties of nanostructured PbS point to a robust low cost alternative to other high performance thermoelectric materials.

  16. High-Performance Three-Stage Cascade Thermoelectric Devices with 20% Efficiency

    NASA Astrophysics Data System (ADS)

    Cook, B. A.; Chan, T. E.; Dezsi, G.; Thomas, P.; Koch, C. C.; Poon, J.; Tritt, T.; Venkatasubramanian, R.

    2015-06-01

    The use of advanced materials has resulted in a significant improvement in thermoelectric device conversion efficiency. Three-stage cascade devices were assembled, consisting of nano-bulk Bi2Te3-based materials on the cold side, PbTe and enhanced TAGS-85 [(AgSbTe2)15(GeTe)85] for the mid-stage, and half-Heusler alloys for the high-temperature top stage. In addition, an area aspect ratio optimization process was applied in order to account for asymmetric thermal transport down the individual n- and p-legs. The n- and p-type chalcogenide alloy materials were prepared by high-energy mechanical ball-milling and/or cryogenic ball-milling of elementary powders, with subsequent consolidation by high-pressure uniaxial hot-pressing. The low-temperature stage materials, nano-bulk Bi2Te3- x Sb x and Bi2Te3- x Se x , exhibit a unique mixture of nanoscale features that leads to an enhanced Seebeck coefficient and reduced lattice thermal conductivity, thereby achieving an average ZT of ~1.26 and ~1.7 in the 27°C to 100°C range for the n-type and p-type materials, respectively. Also, the addition of small amounts of selected rare earth elements has been shown to improve the ZT of TAGS-85 by 25%, compared with conventional or neat TAGS-85, resulting in a ZT = 1.5 at 400°C. The incorporation of these improved materials resulted in a peak device conversion efficiency of ~20% at a temperature difference of 750°C when corrected for radiation heat losses and thermal conduction losses through the lead wires. These high-efficiency results were shown to be reproducible across multiple cascade devices.

  17. High-Temperature Performance of Stacked Silicon Nanowires for Thermoelectric Power Generation

    NASA Astrophysics Data System (ADS)

    Stranz, Andrej; Waag, Andreas; Peiner, Erwin

    2013-07-01

    Deep reactive-ion etching at cryogenic temperatures (cryo-DRIE) has been used to produce arrays of silicon nanowires (NWs) for thermoelectric (TE) power generation devices. Using cryo-DRIE, we were able to fabricate NWs of large aspect ratios (up to 32) using a photoresist mask. Roughening of the NW sidewalls occurred, which has been recognized as beneficial for low thermal conductivity. Generated NWs, which were 7 μm in length and 220 nm to 270 nm in diameter, were robust enough to be stacked with a bulk silicon chip as a common top contact to the NWs. Mechanical support of the NW array, which can be created by filling the free space between the NWs using silicon oxide or polyimide, was not required. The Seebeck voltage, measured across multiple stacks of up to 16 bulk silicon dies, revealed negligible thermal interface resistance. With stacked silicon NWs, we observed Seebeck voltages that were an order of magnitude higher than those observed for bulk silicon. Degradation of the TE performance of silicon NWs was not observed for temperatures up to 470°C and temperature gradients up to 170 K.

  18. Performance Study of Thermoelectric Solar-Assisted Heat Pump with Reflectors

    NASA Astrophysics Data System (ADS)

    Lertsatitthanakorn, C.; Soponronnarit, S.; Jamradloedluk, J.; Rungsiyopas, M.; Sarachitti, R.

    2014-06-01

    The simultaneous conversion of solar radiation into thermal and electrical energy in a thermoelectric (TE) solar-assisted heat pump is, for the purposes of this study, referred to as hybrid conversion. To capture more thermal and electrical energy, flat-plate reflectors have been mounted on a TE solar collector. To obtain higher solar radiation intensity on the TE solar collector, the position of the reflectors has been changed and the optimal position of the reflectors determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with measured ones. Improvements to the thermal energy and electrical power outputs of the system can be achieved by the use of the TE solar-assisted heat pump with reflectors. For the optimum position of the reflectors, the coefficient of performance (COP) of the system formed from a TE solar collector integrated with a heat pump (TESC-HP) was 5.60. The power output and conversion efficiency of the TE modules can reach 10.09 W and 2.40%, respectively, being improved by 34.5% and 18.2%, respectively, compared with the TESC-HP without reflectors.

  19. Performance Study of a Double-Pass Thermoelectric Solar Air Collector with Flat-Plate Reflectors

    NASA Astrophysics Data System (ADS)

    Lertsatitthanakorn, C.; Rungsiyopas, M.; Therdyothin, A.; Soponronnarit, S.

    2012-06-01

    In this paper the results of the influence of flat-plate reflectors made of aluminum foil on the performance of a double-pass thermoelectric (TE) solar air collector are presented. The proposed TE solar collector with reflectors was composed of transparent glass, an air gap, an absorber plate, TE modules, a rectangular fin heat sink, and two flat-plate reflectors. The flat-plate reflectors were placed on two sides of the TE solar collector (east and west directions). The TE solar collector was installed on a one-axis sun-tracking system to obtain high solar radiation. Direct and reflected incident solar radiation heats up the absorber plate so that a temperature difference is created across the TE modules to generate a direct current. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the absorber plate. Ambient air flows through the heat sink located in the lower channel to gain heat. The heated air then flows to the upper channel, where it receives additional heating from the absorber plate. Improvements to the thermal energy and electrical power outputs of the system can be achieved by the use of the double-pass collector system with reflectors and TE technology. It was found that the optimum position of the reflectors is 60°, which gave significantly higher thermal energy and electrical power outputs compared with the TE solar collector without reflectors.

  20. Superior thermoelectric performance in PbTe-PbS pseudo-binary. Extremely low thermal conductivity and modulated carrier concentration

    DOE PAGES

    Wu, D.; Zhao, L. -D.; Tong, X.; ...

    2015-05-19

    Lead chalcogenides have exhibited their irreplaceable role as thermoelectric materials at the medium temperature range, owing to highly degenerate electronic bands and intrinsically low thermal conductivities. PbTe-PbS pseudo-binary has been paid extensive attentions due to the even lower thermal conductivity which originates largely from the coexistence of both alloying and phase-separated precipitations. To investigate the competition between alloying and phase separation and its pronounced effect on the thermoelectric performance in PbTe-PbS, we systematically studied Spark Plasma Sintered (SPSed), 3 at% Na- doped (PbTe)1-x(PbS)x samples with x=10%, 15%, 20%, 25%, 30% and 35% by means of transmission electron microscopy (TEM) observationsmore » and theoretical calculations. Corresponding to the lowest lattice thermal conductivity as a result of the balance between point defect- and precipitates- scattering, the highest figure of merit ZT~2.3 was obtained at 923 K when PbS phase fraction x is at 20%. The consistently lower lattice thermal conductivities in SPSed samples compared with corresponding ingots, resulting from the powdering and follow-up consolidation processes, also contribute to the observed superior ZT. Notably, the onset of carrier concentration modulation ~600 K due to excessive Na’s diffusion and re-dissolution leads to the observed saturations of electrical transport properties, which is believed equally crucial to the outstanding thermoelectric performance of SPSed PbTe-PbS samples.« less

  1. Boost in room temperature thermoelectric performance of PbSe:Alx through band modification and low densification

    NASA Astrophysics Data System (ADS)

    Gayner, Chhatrasal; Sharma, Raghunandan; Das, Malay K.; Kar, Kamal K.

    2016-10-01

    Optimization of the transport properties of PbSe to maximize its thermoelectric performance at room temperature has been achieved through a combination of elemental doping and low densification. Al doped PbSe (PbSe:Alx; 0 ≤ x ≤ 0.06) with both lattice substitutional (Pb site) and interstitial occupation has been synthesized through solid state reaction. High Seebeck coefficient of ˜300 to 400 μV/K is noticed at 300 to 500 K. This, combined with the lower thermal conductivity of ˜1.20 W/m K, provides an improved ZT value as high as ˜0.67 at 300 K to the PbSe:Alx Also, by substituting Al in PbSe, maximum power factors of ˜20 to 26.6 μW/cm K2 at 310 K are produced. The high room temperature thermoelectric performance of PbSe:Alx has been attributed to the mix contribution of the Al impurity states and the low densification. The strategy may be utilized to cost effective development of the low working temperature thermoelectric devices.

  2. Superior thermoelectric performance in PbTe-PbS pseudo-binary. Extremely low thermal conductivity and modulated carrier concentration

    SciTech Connect

    Wu, D.; Zhao, L. -D.; Tong, X.; Li, W.; Wu, L.; Tan, Q.; Pei, Y.; Huang, L.; Li, J. -F.; Zhu, Y.; Kanatzidis, M. G.; He, J.

    2015-05-19

    Lead chalcogenides have exhibited their irreplaceable role as thermoelectric materials at the medium temperature range, owing to highly degenerate electronic bands and intrinsically low thermal conductivities. PbTe-PbS pseudo-binary has been paid extensive attentions due to the even lower thermal conductivity which originates largely from the coexistence of both alloying and phase-separated precipitations. To investigate the competition between alloying and phase separation and its pronounced effect on the thermoelectric performance in PbTe-PbS, we systematically studied Spark Plasma Sintered (SPSed), 3 at% Na- doped (PbTe)1-x(PbS)x samples with x=10%, 15%, 20%, 25%, 30% and 35% by means of transmission electron microscopy (TEM) observations and theoretical calculations. Corresponding to the lowest lattice thermal conductivity as a result of the balance between point defect- and precipitates- scattering, the highest figure of merit ZT~2.3 was obtained at 923 K when PbS phase fraction x is at 20%. The consistently lower lattice thermal conductivities in SPSed samples compared with corresponding ingots, resulting from the powdering and follow-up consolidation processes, also contribute to the observed superior ZT. Notably, the onset of carrier concentration modulation ~600 K due to excessive Na’s diffusion and re-dissolution leads to the observed saturations of electrical transport properties, which is believed equally crucial to the outstanding thermoelectric performance of SPSed PbTe-PbS samples.

  3. Reduction of Specimen Size for the Full Simultaneous Characterization of Thermoelectric Performance

    NASA Astrophysics Data System (ADS)

    Vasilevskiy, D.; Simard, J.-M.; Masut, R. A.; Turenne, S.

    2016-11-01

    The successful implementation of thermoelectric (TE) materials for waste heat recovery depends strongly on our ability to increase their performance. This challenge continues to generate a renewed interest in novel high TE performance compounds. The technological difficulties in producing homogeneous ingots of new compounds or alloys with regular shape and a size sufficiently large to prepare several samples that are usually needed for a separate measurement of all TE parameters are well known. It creates a situation whereby material performance could be critically over- or under-evaluated at the first stages of the research process of a new material. Both cases would equally lead to negative consequences. Thus, minimizing the specimen size yet keeping it adequate for accurate material characterization becomes extremely important. In this work we report the experimental validation of reliable simultaneous measurements of the four most relevant TE parameters on a single bismuth telluride alloy based specimen of 4 mm × 4 mm × 1.4 mm in size. This translates in roughly 140 mg in weight for one of the heaviest TE materials, as was used in this study, and <100 mg for most others. Our validation is based on comparative measurements performed by a Harman apparatus (ZT-Scanner) on a series of differently sized specimens of hot extruded bismuth telluride based alloys. The Seebeck coefficient, electrical resistivity, thermal conductivity and the figure of merit were simultaneously assessed from 300 K to 440 K with increments of 20 K, 15 K, 10 K, 5 K, and 1 K. Our choice of a well-known homogeneous material has been made to increase measurement reliability and accuracy, but the results are expected to be valid for the full TE characterization of any unknown material. These results show a way to significantly decrease specimen sizes which has the potential to accelerate investigation of novel TE materials for large scale waste heat recovery.

  4. Enhanced phonon scattering by nanovoids in high thermoelectric power factor polysilicon thin films

    NASA Astrophysics Data System (ADS)

    Dunham, Marc T.; Lorenzi, Bruno; Andrews, Sean C.; Sood, Aditya; Asheghi, Mehdi; Narducci, Dario; Goodson, Kenneth E.

    2016-12-01

    The ability to tune the thermal conductivity of semiconductor materials is of interest for thermoelectric applications, in particular, for doped silicon, which can be readily integrated in electronic microstructures and have a high thermoelectric power factor. Here, we examine the impact of nanovoids on the thermal conductivity of highly doped, high-power factor polysilicon thin films using time-domain thermoreflectance. Voids are formed through ion implantation and annealing, evolving from many small (˜4 nm mean diameter) voids after 500 °C anneal to fewer, larger (˜29 nm mean diameter) voids with a constant total volume fraction after staged thermal annealing to 1000 °C. The thermal conductivity is reduced to 65% of the non-implanted reference film conductivity after implantation and 500 °C anneal, increasing with anneal temperature until fully restored after 800 °C anneal. The void size distributions are determined experimentally using small-angle and wide-angle X-ray scattering. While we believe multiple physical mechanisms are at play, we are able to corroborate the positive correlation between measurements of thermal conductivity and void size with Monte Carlo calculations and a scattering probability based on Matthiessen's rule. The data suggest an opportunity for thermal conductivity suppression combined with the high power factor for increased material zT and efficiency of nanostructured polysilicon as a thermoelectric material.

  5. Improved thermoelectric performance of n-type Ca and Ca-Ce filled skutterudites

    SciTech Connect

    Thompson, Daniel R.; Liu, Chang; Ellison, Nicole D.; Salvador, James R.; Meyer, Martin S.; Haddad, Daad B.; Wang, Hsin; Cai, W.

    2014-12-28

    Thermoelectric (TE) technology for use in automotive waste heat recovery is being advanced by General Motors with support from the US Department of Energy. Skutterudites are a very promising material for this application of TE technology due to their superior mechanical properties and good TE performance. Double-filled YbxBayCo4Sb12 with ZT values around 1.1 at 750K are the best performing n-type skutterudites produced on a large scale using an economically viable approach of melt spinning (MS) in conjunction with spark plasma sintering (SPS). Another economical production method on the tons scale, the melt quench annealing (MQA) technique, has been recently claimed by Treibacher Industrie AG, further information is available [G. Rogl et al., Acta Mater. 76, 434-448 (2014)]. A possible hurdle to commercial implementation of these materials is the use of rare earths as the fillers to reduce thermal conductivity and improve the electrical transport properties. It will be shown herein that skutterudites double-filled with Ca and Ce, both of which are lower-cost fillers, display markedly different TE properties depending on whether they are produced by MQA or MS + SPS synthesis techniques. Finally, Ca and Ce double-filled skutterudites prepared by MS + SPS have TE properties that are superior to the same compositions prepared by MQA and that are comparable to the best performing Yb and Ba filled materials. Furthermore, the results of this study suggest that the unusually poor transport properties of MQA Ca-filled skutterudites can be ascribed to deleterious secondary phases, which is contrary to reports in the literature attempting to explain these irregularities via band structure features.

  6. Improved thermoelectric performance of n-type Ca and Ca-Ce filled skutterudites

    SciTech Connect

    Thompson, Daniel R.; Liu, Chang; Ellison, Nicole D.; Salvador, James R.; Meyer, Martin S.; Haddad, Daad B.; Wang, Hsin; Cai, W.

    2014-12-28

    Thermoelectric (TE) technology for use in automotive waste heat recovery is being advanced by General Motors with support from the US Department of Energy. Skutterudites are a very promising material for this application of TE technology due to their superior mechanical properties and good TE performance. Double-filled Yb{sub x}Ba{sub y}Co{sub 4}Sb{sub 12} with ZT values around 1.1 at 750 K are the best performing n-type skutterudites produced on a large scale using an economically viable approach of melt spinning (MS) in conjunction with spark plasma sintering (SPS). Another economical production method on the tons scale, the melt quench annealing (MQA) technique, has been recently claimed by Treibacher Industrie AG, further information is available [G. Rogl et al., Acta Mater. 76, 434–448 (2014)]. A possible hurdle to commercial implementation of these materials is the use of rare earths as the fillers to reduce thermal conductivity and improve the electrical transport properties. It will be shown herein that skutterudites double-filled with Ca and Ce, both of which are lower-cost fillers, display markedly different TE properties depending on whether they are produced by MQA or MS + SPS synthesis techniques. Ca and Ce double-filled skutterudites prepared by MS + SPS have TE properties that are superior to the same compositions prepared by MQA and that are comparable to the best performing Yb and Ba filled materials. Furthermore, the results of this study suggest that the unusually poor transport properties of MQA Ca-filled skutterudites can be ascribed to deleterious secondary phases, which is contrary to reports in the literature attempting to explain these irregularities via band structure features.

  7. Improved thermoelectric performance of n-type Ca and Ca-Ce filled skutterudites

    DOE PAGES

    Thompson, Daniel R.; Liu, Chang; Ellison, Nicole D.; ...

    2014-12-28

    Thermoelectric (TE) technology for use in automotive waste heat recovery is being advanced by General Motors with support from the US Department of Energy. Skutterudites are a very promising material for this application of TE technology due to their superior mechanical properties and good TE performance. Double-filled YbxBayCo4Sb12 with ZT values around 1.1 at 750K are the best performing n-type skutterudites produced on a large scale using an economically viable approach of melt spinning (MS) in conjunction with spark plasma sintering (SPS). Another economical production method on the tons scale, the melt quench annealing (MQA) technique, has been recently claimedmore » by Treibacher Industrie AG, further information is available [G. Rogl et al., Acta Mater. 76, 434-448 (2014)]. A possible hurdle to commercial implementation of these materials is the use of rare earths as the fillers to reduce thermal conductivity and improve the electrical transport properties. It will be shown herein that skutterudites double-filled with Ca and Ce, both of which are lower-cost fillers, display markedly different TE properties depending on whether they are produced by MQA or MS + SPS synthesis techniques. Finally, Ca and Ce double-filled skutterudites prepared by MS + SPS have TE properties that are superior to the same compositions prepared by MQA and that are comparable to the best performing Yb and Ba filled materials. Furthermore, the results of this study suggest that the unusually poor transport properties of MQA Ca-filled skutterudites can be ascribed to deleterious secondary phases, which is contrary to reports in the literature attempting to explain these irregularities via band structure features.« less

  8. Enhanced in-plane thermoelectric figure of merit in p-type SiGe thin films by nanograin boundaries

    NASA Astrophysics Data System (ADS)

    Lu, Jianbiao; Guo, Ruiqiang; Dai, Weijing; Huang, Baoling

    2015-04-01

    P-Type polycrystalline silicon-germanium (SiGe) thin films are grown by low-pressure chemical vapor deposition (LPCVD) and their thermoelectric properties are characterized from 120 K to 300 K for potential application in integrated microscale cooling. The naturally formed grain boundaries are found to play a crucial role in determining both the charge and thermal transport properties of the films. Particularly, the grain boundaries create energy barriers for charge transport which lead to different dependences of charge mobility on doping concentration and temperature from the bulk counterparts. Meanwhile, the unique columnar grain structures result in remarkable thermal conductivity anisotropy with the in-plane thermal conductivities of SiGe films about 50% lower than the cross-plane values. By optimizing the growth conditions and doping level, a high in-plane figure of merit (ZT) of 0.2 for SiGe films is achieved at 300 K, which is about 100% higher than the previous record for p-type SiGe alloys, mainly due to the significant reduction in the in-plane thermal conductivity caused by nanograin boundaries. The low cost and excellent scalability of LPCVD render these high-performance SiGe films ideal candidates for thin-film thermoelectric applications.P-Type polycrystalline silicon-germanium (SiGe) thin films are grown by low-pressure chemical vapor deposition (LPCVD) and their thermoelectric properties are characterized from 120 K to 300 K for potential application in integrated microscale cooling. The naturally formed grain boundaries are found to play a crucial role in determining both the charge and thermal transport properties of the films. Particularly, the grain boundaries create energy barriers for charge transport which lead to different dependences of charge mobility on doping concentration and temperature from the bulk counterparts. Meanwhile, the unique columnar grain structures result in remarkable thermal conductivity anisotropy with the in

  9. Solar thermoelectric generators

    NASA Technical Reports Server (NTRS)

    1977-01-01

    The methods, the findings and the conclusions of a study for the design of a Solar Thermoelectric Generator (STG) intended for use as a power source for a spacecraft orbiting the planet Mercury are discussed. Several state-of-the-art thermoelectric technologies in the intended application were considered. The design of various STG configurations based on the thermoelectric technology selected from among the various technologies was examined in detail and a recommended STG design was derived. The performance characteristics of the selected STG technology and associated design were studied in detail as a function of the orbital characteristics of the STG in Mercury and throughout the orbit of Mercury around the sun.

  10. Hybridization of electronic band structure and enhancement of thermoelectric properties of ZnSb thin film by In doping

    NASA Astrophysics Data System (ADS)

    Zheng, Zhuang-hao; Fan, Ping; Luo, Jing-ting; Liang, Guang-xing

    2017-04-01

    Here we report the In doped ZnSb thermoelectric thin films which were deposited by direct current magnetron co-sputtering with prefabricate layer doping method. The X-ray diffraction result indicates that the peaks of the In doped ZnSb thin films are related to ZnSb phase and are slightly shifted to smaller angle. The calculations of In occupy one of the Sb or Zn location in normal site were performed based on the first-principles and it has lower total energy when the In substitutes the Zn. The thermo-electrical testing experimental results indicate that the Seebeck coefficient increases greatly after In doped due to increase of the total density of states and the complicate of the electronic band structure. The Fermi surface moves to the valence band after In doped that will reduce the electrical conductivity and it corresponds to the testing result. It can be observed that the power factor of the In doped ZnSb is approach two times than that of the thin film without doping.

  11. Enhanced thermoelectric properties of n-type NbCoSn half-Heusler by improving phase purity

    NASA Astrophysics Data System (ADS)

    He, Ran; Huang, Lihong; Wang, Yumei; Samsonidze, Georgy; Kozinsky, Boris; Zhang, Qinyong; Ren, Zhifeng

    2016-10-01

    Here we report the thermoelectric properties of NbCoSn-based n-type half-Heuslers (HHs) that were obtained through arc melting, ball milling, and hot pressing process. With 10% Sb substitution at the Sn site, we obtained enhanced n-type properties with a maximum power factor reaching ˜35 μW cm-1 K-2 and figure of merit (ZT) value ˜0.6 in NbCoSn0.9Sb0.1. The ZT is doubled compared to the previous report. In addition, the specific power cost ( W-1) is decreased by ˜68% comparing to HfNiSn-based n-type HH because of the elimination of Hf.

  12. Thermoelectricity Generation and Electron-Magnon Scattering in a Natural Chalcopyrite Mineral from a Deep-Sea Hydrothermal Vent.

    PubMed

    Ang, Ran; Khan, Atta Ullah; Tsujii, Naohito; Takai, Ken; Nakamura, Ryuhei; Mori, Takao

    2015-10-26

    Current high-performance thermoelectric materials require elaborate doping and synthesis procedures, particularly in regard to the artificial structure, and the underlying thermoelectric mechanisms are still poorly understood. Here, we report that a natural chalcopyrite mineral, Cu1+x Fe1-x S2 , obtained from a deep-sea hydrothermal vent can directly generate thermoelectricity. The resistivity displayed an excellent semiconducting character, and a large thermoelectric power and high power factor were found in the low x region. Notably, electron-magnon scattering and a large effective mass was detected in this region, thus suggesting that the strong coupling of doped carriers and antiferromagnetic spins resulted in the natural enhancement of thermoelectric properties during mineralization reactions. The present findings demonstrate the feasibility of thermoelectric energy generation and electron/hole carrier modulation with natural materials that are abundant in the Earth's crust.

  13. Analysis of Phase Separation in High Performance PbTe–PbS Thermoelectric Materials

    SciTech Connect

    Girard, Steven N.; Schmidt-Rohr, Klaus; Chasapis, Thomas C.; Hatzikraniotis, Euripides; Njegic, B.; Levin, E. M.; Rawal, A.; Paraskevopoulos, Konstantios M.; Kanatzidis, Mercouri G.

    2013-02-11

    Phase immiscibility in PbTe–based thermoelectric materials is an effective means of top-down synthesis of nanostructured composites exhibiting low lattice thermal conductivities. PbTe1-x Sx thermoelectric materials can be synthesized as metastable solid solution alloys through rapid quenching. Subsequent post-annealing induces phase separation at the nanometer scale, producing nanostructures that increase phonon scattering and reduce lattice thermal conductivity. However, there has yet to be any study investigating in detail the local chemical structure of both the solid solution and nanostructured variants of this material system. Herein, quenched and annealed (i.e., solid solution and phase-separated) samples of PbTe–PbS are analyzed by in situ high-resolution synchrotron powder X-ray diffraction, solid-state 125Te nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy analysis. For high concentrations of PbS in PbTe, e.g., x >16%, NMR and IR analyses reveal that rapidly quenched samples exhibit incipient phase separation that is not detected by state-of-the-art synchrotron X-ray diffraction, providing an example of a PbTe thermoelectric “alloy” that is in fact phase inhomogeneous. Thermally-induced PbS phase separation in PbTe–PbS occurs close to 200 °C for all compositions studied, and the solubility of the PbS phase in PbTe at elevated temperatures >500 °C is reported. The findings of this study suggest that there may be a large number of thermoelectric alloy systems that are phase inhomogeneous or nanostructured despite adherence to Vegard's Law of alloys, highlighting the importance of careful chemical characterization to differentiate between thermoelectric alloys and composites.

  14. Photo-induced enhancement of the power factor of Cu2S thermoelectric films

    PubMed Central

    Lv, Yanhong; Chen, Jikun; Zheng, Ren-Kui; Song, Junqiang; Zhang, Tiansong; Li, Xiaomin; Shi, Xun; Chen, Lidong

    2015-01-01

    Element doping is commonly used to adjust the carrier concentrations in semiconductors such as thermoelectric materials. However, the doping process unavoidably brings in defects or distortions in crystal lattices, which further strongly affects the physical properties of the materials. In this work, high energy photons have been used to activate the carriers in Cu2S thermoelectric films. As a result, the carrier concentrations, and the respective electrical conductivity as well as Seebeck coefficient are further changed. The photon-induced electrical transport properties are further analyzed utilizing a Parallel circuit model. Due to the realization of optimized carrier concentrations by photon activation, the power factor of Cu2S film is improved more than 900 times as compared with the dark data. As compared to the traditional doping process, the approach using photon activation can realize the tuning of carrier concentrations without affecting crystal lattice. This method provides an opportunity to investigate the intrinsic physical properties of semiconductor materials without involving traditional element doping process that usually brings in additional lattice defects or distortions. PMID:26573407

  15. Enhanced thermoelectric figure of merit of p-type half-Heuslers.

    PubMed

    Yan, Xiao; Joshi, Giri; Liu, Weishu; Lan, Yucheng; Wang, Hui; Lee, Sangyeop; Simonson, J W; Poon, S J; Tritt, T M; Chen, Gang; Ren, Z F

    2011-02-09

    Half-Heuslers would be important thermoelectric materials due to their high temperature stability and abundance if their dimensionless thermoelectric figure of merit (ZT) could be made high enough. The highest peak ZT of a p-type half-Heusler has been so far reported about 0.5 due to the high thermal conductivity. Through a nanocomposite approach using ball milling and hot pressing, we have achieved a peak ZT of 0.8 at 700 °C, which is about 60% higher than the best reported 0.5 and might be good enough for consideration for waste heat recovery in car exhaust systems. The improvement comes from a simultaneous increase in Seebeck coefficient and a significant decrease in thermal conductivity due to nanostructures. The samples were made by first forming alloyed ingots using arc melting and then creating nanopowders by ball milling the ingots and finally obtaining dense bulk by hot pressing. Further improvement in ZT is expected when average grain sizes are made smaller than 100 nm.

  16. Thermoelectric module

    DOEpatents

    Kortier, William E.; Mueller, John J.; Eggers, Philip E.

    1980-07-08

    A thermoelectric module containing lead telluride as the thermoelectric mrial is encapsulated as tightly as possible in a stainless steel canister to provide minimum void volume in the canister. The lead telluride thermoelectric elements are pressure-contacted to a tungsten hot strap and metallurgically bonded at the cold junction to iron shoes with a barrier layer of tin telluride between the iron shoe and the p-type lead telluride element.

  17. Thermal Performance of a Multi-Evaporator Loop Heat Pipe with Thermal Masses and Thermoelectric Coolers

    NASA Technical Reports Server (NTRS)

    Ku, Jen-Tung; Ottenstein, Laura; Birur, Gajanana

    2004-01-01

    This paper describes thermal performance of a loop heat pipe (LHP) with two evaporators and two condensers in ambient testing. Each evaporator has an outer diameter of 15mm and a length of 76mm, and has an integral compensation chamber (CC). An aluminum mass of 500 grams is attached to each evaporator to simulate the instrument mass. A thermoelectric cooler (TEC) is installed on each CC to provide heating as well as cooling for CC temperature control. A flow regulator is installed in the condenser section to prevent vapor from going back to the evaporators in the event that one of the condensers is fully utilized. Ammonia was used as the working fluid. Tests conducted included start-up, power cycle, heat load sharing, sink temperature cycle, operating temperature control with TECs, and capillary limit tests. Experimental data showed that the loop could start with a heat load of less than 10W even with added thermal masses. The loop operated stably with even and uneven evaporator heat loads, and even and uneven condenser sink temperatures. The operating temperature could be controlled within +/- 0.5K of the set point temperature using either or both TECs, and the required TEC control heater power was less than 2W under most test conditions. Heat load sharing between the two evaporators was also successfully demonstrated. The loop had a heat transport capability of 120W to 140W, and could recover from a dry-out when the heat load was reduced. The 500-gram aluminum mass on each evaporator had a negligible effect on the loop operation. Existing LHPs servicing orbiting spacecraft have a single evaporator with an outer diameter of about 25mm. Important performance characteristics demonstrated by this LHP included: 1) Operation of an LHP with 15mm diameter evaporators; 2) Robustness and reliability of an LHP with multiple evaporators and multiple condensers under various test conditions; 3) Heat load sharing among LHP evaporators; 4) Effectiveness of TECs in controlling

  18. Enhanced Thermoelectric Properties of In-Doped ZnSb Thin Film with Surface Nanocrystallization

    NASA Astrophysics Data System (ADS)

    Zheng, Zhuang-hao; Fan, Ping; Luo, Jing-ting; Liang, Guang-xing

    2017-02-01

    This work establishes the high-temperature properties of In-doped ZnSb thin films prepared by a multistep cosputtering method on flexible substrates. The microstructure and thermoelectric properties of the In-doped ZnSb thin films were investigated. X-Ray diffraction results indicated that the main peaks of the In-doped ZnSb thin films were related to ZnSb phase, with some nanocrystallization on the surface after In doping. All samples exhibited p-type conduction behavior, with increased Seebeck coefficient after In doping. The thermal conductivity decreased sharply for the In-doped samples with nanocrystallization, resulting in a ZT value almost six times higher than for undoped ZnSb thin film.

  19. Enhanced Thermoelectric Properties of W- and Fe-Substituted MnSi γ

    NASA Astrophysics Data System (ADS)

    Ghodke, Swapnil; Hiroishi, Naoya; Yamamoto, Akio; Ikuta, Hiroshi; Matsunami, Masaharu; Takeuchi, Tsunehiro

    2016-10-01

    We have investigated the effect of heavy-element (W) substitution on the thermoelectric properties of higher manganese silicide (HMS). Samples were prepared by arc melting followed by liquid quenching, where the latter assisted in achieving higher solubility for tungsten. We observed that Mn34.6W1.8Si63.6 was a p-type material, whereas simultaneous substitution of 12 at.% Fe made the higher manganese silicide an n-type material. The optimal carrier concentration was obtained by simultaneous substitution of Fe and W for Mn atoms. Although the samples were metastable, we successfully obtained bulk samples by a low-temperature (970 K), high-pressure (>100 MPa), long-duration sintering process. The lattice thermal conductivity was effectively reduced by W substitution, and the ZT value was improved to above 0.5 for both n- and p-type samples.

  20. Thermoelectric-enhanced, liquid-based cooling of a multi-component electronic system

    DOEpatents

    Chainer, Timothy J; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Steinke, Mark E

    2015-11-10

    Methods are provided for facilitating cooling of an electronic component. The methods include providing: a liquid-cooled structure, a thermal conduction path coupling the electronic component and the liquid-cooled structure, a coolant loop in fluid communication with a coolant-carrying channel of the liquid-cooled structure, and an outdoor-air-cooled heat exchange unit coupled to facilitate heat transfer from the liquid-cooled structure via, at least in part, the coolant loop. The thermoelectric array facilitates transfer of heat from the electronic component to the liquid-cooled structure, and the heat exchange unit cools coolant passing through the coolant loop by dissipating heat from the coolant to outdoor ambient air. In one implementation, temperature of coolant entering the liquid-cooled structure is greater than temperature of the outdoor ambient air to which heat is dissipated.

  1. Thermoelectric-enhanced, liquid-based cooling of a multi-component electronic system

    DOEpatents

    Chainer, Timothy J; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Steinke, Mark E

    2015-05-12

    Apparatus and method are provided for facilitating cooling of an electronic component. The apparatus includes a liquid-cooled structure, a thermal conduction path coupling the electronic component and the liquid-cooled structure, a coolant loop in fluid communication with a coolant-carrying channel of the liquid-cooled structure, and an outdoor-air-cooled heat exchange unit coupled to facilitate heat transfer from the liquid-cooled structure via, at least in part, the coolant loop. The thermoelectric array facilitates transfer of heat from the electronic component to the liquid-cooled structure, and the heat exchange unit cools coolant passing through the coolant loop by dissipating heat from the coolant to outdoor ambient air. In one implementation, temperature of coolant entering the liquid-cooled structure is greater than temperature of the outdoor ambient air to which heat is dissipated.

  2. Thermal Conductivity Measurement of Thermoelectric Thin Films by a Versatility-Enhanced 2ω Method

    NASA Astrophysics Data System (ADS)

    Okuhata, Ryo; Watanabe, Kentaro; Ikeuchi, Satoaki; Ishida, Akihiro; Nakamura, Yoshiaki

    2016-12-01

    The 2ω method is a technique to measure the cross-plane thermal conductivity, κ, of a film sample based on sinusoidal Joule-heating of a metal film deposited on the sample surface and its thermoreflectance (TR) measurement of surface temperature cooling due to the heat dissipation. The 2ω method is being paid attention because it is more cost-effective and easier to use than the conventional time domain thermoreflectance (TDTR) method or the 3ω method. In some cases, however, it is difficult to apply the conventional 2ω method to the κ measurement of high thermal resistance films such as general thermoelectric films due to its non-linear TR signal response to (2ω)-0.5. Here, we present a 2ω method based on a versatile TR signal analysis which enables the κ measurement of high thermal resistance film more explicitly than the conventional analysis based on a linear TR signal response. This method determines explicitly the thermal conductivities of PbTe films and PbTe/GeS superlattices grown on BaF2(111) substrates by hot wall epitaxy: κ = 2.1 ± 0.13 Wm-1 K-1 and κ = 0.71 ± 0.05 Wm-1 K-1, respectively. Furthermore, a significant impact of PbTe film crystallinity on thermal conductivity is demonstrated by comparative measurements between polycrystalline PbTe film and epitaxial PbTe film grown on the BaF2(111) substrates. These results demonstrate that our method can be a powerful tool to measure the thermal conductivity of thermoelectric films.

  3. Improved Thermoelectric Performance in Flexible Tellurium Nanowires/Reduced Graphene Oxide Sandwich Structure Hybrid Films

    NASA Astrophysics Data System (ADS)

    Gao, Jie; Liu, Chengyan; Miao, Lei; Wang, Xiaoyang; Peng, Ying; Chen, Yu

    2016-11-01

    With a high flexibility and an adjustable electronic structure, reduced graphene oxide (RGO) is a potential candidate for flexible thermoelectric materials. Here, we report that flexible RGO/tellurium nanowires (Te NWs)/RGO sandwich structure hybrid films are prepared on glass fabrics through the drop-cast method. The addition of 20 wt.% Te NWs into a RGO matrix remarkably improves the Seebeck coefficient from 15.2 μV/K to 89.7 μV/K while maintaining relatively high electrical conductivity, thus resulting in a one order of magnitude higher power factor value compared with the Te NWs. According to the values of carrier mobility and concentration of hybrid films, the improved thermoelectric properties are presented because of the energy filtering effect on the interfaces in hybrid films. This article suggests that RGO/Te NWs/RGO hybrid films would be promising for fabricating flexible energy sources.

  4. Elemental Diffusion and Service Performance of Bi2Te3-Based Thermoelectric Generation Modules with Flexible Connection Electrodes

    NASA Astrophysics Data System (ADS)

    Jiang, Chengpeng; Fan, Xi'an; Rong, Zhenzhou; Zhang, Chengcheng; Li, Guangqiang; Feng, Bo; Hu, Jie; Xiang, Qiusheng

    2017-02-01

    In this work, the elemental diffusion and service performance of Bi2Te3-based thermoelectric generation (TEG) modules with flexible Al electrodes were evaluated at a temperature difference of 240°C and a cold junction temperature of 50°C. The results indicated that while the maximum output power ( P max) and open circuit voltage ( U 0) first increased rapidly and then decreased gradually with service time, the dynamic inner-resistance ( R i) showed the opposite trend. Obvious defects and elemental diffusion across the interfaces were observed and resulted in the performance degradation of the TEG modules. The Ni barrier layer with a thickness of 8-10 μm could not effectively restrain the elemental diffusion for the TEG applications at the high operating temperatures. Al was not suitable as the electrode material for the Bi2Te3-based TEG modules due to its ready absorption of Se from the n-type thermoelectric legs. Encouragingly, we found that the Al electrode could restrain the diffusion of the other elements such as Bi, Te, Sb, Cu, Ni, and I. These results provided insight into the improvement of the service performance of the TEG modules.

  5. Nonequilibrium Thermoelectrics: Low-Cost, High-Performance Materials for Cooling and Power Generation

    SciTech Connect

    Li, Q.

    2011-05-18

    Thermoelectric materials can be made into coolers (TECs) that use electricity to develop a temperature difference, cooling something, or generators (TEGs) that convert heat directly to electricity. One application of TEGs is to place them in a waste heat stream to recuperate some of the power being lost and putting it to use more profitably. To be effective thermoelectrics, however, materials must have both high electrical conductivity and low thermal conductivity, a combination rarely found in nature. Materials selection and processing has led to the development of several systems with a figure of merit, ZT, of nearly unity. By using non-equilibrium techniques, we have fabricated higher efficiency thermoelectric materials. The process involves creating an amorphous material through melt spinning and then sintering it with either spark plasma or a hot press for as little as two minutes. This results in a 100% dense material with an extremely fine grain structure. The grain boundaries appear to retard phonons resulting in a reduced thermal conductivity while the electrons move through the material relatively unchecked. The techniques used are low-cost and scaleable to support industrial manufacturing.

  6. Enhancement of thermoelectric properties in the Nb-Co-Sn half-Heusler/Heusler system through spontaneous inclusion of a coherent second phase

    NASA Astrophysics Data System (ADS)

    Buffon, Malinda L. C.; Laurita, Geneva; Verma, Nisha; Lamontagne, Leo; Ghadbeigi, Leila; Lloyd, Demetrious L.; Sparks, Taylor D.; Pollock, Tresa M.; Seshadri, Ram

    2016-08-01

    Half-Heusler XYZ compounds with an 18 valence electron count are promising thermoelectric materials, being thermally and chemically stable, deriving from relatively earth-abundant components, and possessing appropriate electrical transport properties. The typical drawback with this family of compounds is their high thermal conductivity. A strategy for reducing thermal conductivity is through the inclusion of secondary phases designed to minimize negative impact on other properties. Here, we achieve this through the addition of excess Co to half-Heusler NbCoSn, which introduces precipitates of a semi-coherent NbCo2Sn Heusler phase. A series of NbCo1+xSn materials are characterized here using X-ray and neutron diffraction studies and electron microscopy. Electrical and thermal transport measurements and electronic structure calculations are used to understand property evolution. We find that annealing has an important role to play in determining antisite ordering and properties. Antisite disorder in the as-prepared samples improves thermoelectric performance through the reduction of thermal conductivity, but annealing during the measurement degrades properties to resemble those of the annealed samples. Similar to the more widely studied TiNi1+xSn system, Co addition to the NbCoSn phase results in improved thermoelectric performance through a decrease in thermal conductivity which results in a 20% improvement in the thermoelectric figure of merit, zT.

  7. Thermoelectric Enhancement in PbTe with K or Na codoping from tuning the interaction of the light- and heavy-hole valence bands

    SciTech Connect

    Androulakis, John; Todorov, Iliya; Chung, Duck Young; Ballikaya, Sedat; Wang, Guoyu Y; Uher, Ctirad; Kanatzidis, Mercouri G.

    2010-09-16

    The effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high-temperature Hall-effect, electrical conductivity, and thermal conductivity measurements to show that K-Na codoping do not form resonance states but can control the energy difference of the maxima of the two primary valence subbands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p -type PbTe. The experimental data can be explained by a combination of a single- and two-band models for the valence band of PbTe depending on hole density that varies in the range of 1–15x1019 cm-3 .

  8. Higher thermoelectric performance of Zintl phases (Eu0.5Yb0.5)1−xCaxMg2Bi2 by band engineering and strain fluctuation

    PubMed Central

    Shuai, Jing; Geng, Huiyuan; Lan, Yucheng; Zhu, Zhuan; Wang, Chao; Liu, Zihang; Bao, Jiming; Chu, Ching-Wu; Sui, Jiehe; Ren, Zhifeng

    2016-01-01

    Complex Zintl phases, especially antimony (Sb)-based YbZn0.4Cd1.6Sb2 with figure-of-merit (ZT) of ∼1.2 at 700 K, are good candidates as thermoelectric materials because of their intrinsic “electron–crystal, phonon–glass” nature. Here, we report the rarely studied p-type bismuth (Bi)-based Zintl phases (Ca,Yb,Eu)Mg2Bi2 with a record thermoelectric performance. Phase-pure EuMg2Bi2 is successfully prepared with suppressed bipolar effect to reach ZT ∼ 1. Further partial substitution of Eu by Ca and Yb enhanced ZT to ∼1.3 for Eu0.2Yb0.2Ca0.6Mg2Bi2 at 873 K. Density-functional theory (DFT) simulation indicates the alloying has no effect on the valence band, but does affect the conduction band. Such band engineering results in good p-type thermoelectric properties with high carrier mobility. Using transmission electron microscopy, various types of strains are observed and are believed to be due to atomic mass and size fluctuations. Point defects, strain, dislocations, and nanostructures jointly contribute to phonon scattering, confirmed by the semiclassical theoretical calculations based on a modified Debye–Callaway model of lattice thermal conductivity. This work indicates Bi-based (Ca,Yb,Eu)Mg2Bi2 is better than the Sb-based Zintl phases. PMID:27385824

  9. Enhanced Thermoelectric Properties of Melt-Spun p-Type Yb0.9Fe3CoSb12

    NASA Astrophysics Data System (ADS)

    Son, Geonsik; Lee, Kyu Hyoung; Choi, Soon-Mok

    2016-10-01

    We herein report an enhancement of the thermoelectric properties of p-type Yb0.9Fe3CoSb12 skutterudite by melt spinning combined with spark plasma sintering (SPS). By thermal aging (873 K for 120 h) of the starting Yb0.9Fe3 CoSb12 compound for melt spinning, fabricated by conventional melting and quenching, highly dense single phase bulks with reduced grain sizes of ~300 nm are successfully fabricated after SPS. The power factor value of the sample (~3.6 mW m-1 K-2 at 723 K) is increased, benefiting from an enhancement of the electrical conductivity due to the elimination of the secondary phase CoSb2 during the thermal aging process. In addition, lattice thermal conductivity is significantly decreased due to the reduced grain size, thus intensifying the grain boundary phonon scattering. Through these synergetic effects, the maximum dimensionless figure of merit ZT increases by 25% (0.70 at 723 K) compared to a pristine sample with microscale grains.

  10. Enhanced thermoelectric properties of PEDOT/PSS/Te composite films treated with H2SO4

    NASA Astrophysics Data System (ADS)

    Song, Haijun; Cai, Kefeng; Shen, Shirley

    2016-12-01

    Firstly, tellurium (Te) nanorods with a high Seebeck coefficient have been integrated into a conducting polymer PEDOT/PSS to form PEDOT/PSS/Te composite films. The Seebeck coefficient of the PEDOT/PSS/Te (90 wt.%) composite films is 191 μV/K, which is about 13 times greater than that of pristine PEDOT/PSS. Then, H2SO4 treatment has been used to further tune the thermoelectric properties of the composite films by adjusting the doping level and increasing the carrier concentration. After the acid treatment, the electrical conductivity of the composite films has increased from 0.22 to 1613 S/cm due to the removal of insulating PSS and the structural rearrangement of PEDOT. An optimized power factor of 42.1 μW/mK2 has been obtained at room temperature for a PEDOT/PSS/Te (80 wt.%) sample, which is about ten times larger than that of the untreated PEDOT/PSS/Te composite film.

  11. Nanoscale thermal and thermoelectric transport in silicon

    NASA Astrophysics Data System (ADS)

    Ryu, Hyuk Ju

    Hotspots on microchips are a major challenge for the semiconductor industry. To understand heat conduction from hotspots on silicon, measurements of the thermal resistance and transfer function have been performed using patterned nanoheater/sensor pairs with width from 100 nm up to 5000 nm at temperature range of 30 ˜ 300 K. Calculations of the thermal resistance based on a simple thermal model, considering resistances by spreading, interface, and localized heating match with the measurements. The results reveal several important trends indicating the prevalence of localized heating or sub-continuum transport phenomena in the vicinity of a nanoscale hotspot. Thermoelectric cooling is a possible solution to cope with the hotspot issue. Silicon, in a nanostructured form, is an interesting thermoelectric material, because of significantly reduced thermal conductivity. However, further improvement in thermoelectric efficiency is highly desirable. Thermopower measurements of silicon nanoribbons with an integrated gate have been performed. The gate in the device is used to provide strong carrier confinement and enable tunability of the carrier density over a wide range, which is fully compatible with conventional silicon processing and microelectronics. It therefore offers a promising alternative to doping when considering the thermoelectric engineering of nanostructures. An enhancement of thermoelectric power factor has been observed in silicon nanoribbons. This enhancement can be understood by considering its behavior as a function of carrier density. We identify the underlying mechanisms for the power factor in the nanoribbon, which include quantum confinement, low scattering due to the absence of dopants, and, at low temperatures, a significant phonon drag contribution.

  12. Superatom Thermoelectric Materials

    DTIC Science & Technology

    2012-07-30

    147 C, NaCl Structure Becomes Fast Ion Conductor (the silver sub-lattice melts) Ag + 1.15 A (115 pm) I- 2.20 A (220 pm) Enhanced Thermoelectric...nanostructured thermoelectric materials can increase ZT>1, the materials (Bi, Te, Pb, Sb and Ag ) and processes used are not often easy to scale to practically...500 1000 1500 Raman shift / cm-1 0 5000 10000 15000 C ou nt s Raman Modes in Neutral C60 Hg(7) Ag (2) Ag (1) Hg(2) Raman Spectroscopy of ZnxC60

  13. Performance Pressure Enhances Speech Learning

    PubMed Central

    Maddox, W. Todd; Koslov, Seth; Yi, Han-Gyol; Chandrasekaran, Bharath

    2015-01-01

    Real-world speech learning often occurs in high pressure situations such as trying to communicate in a foreign country. However, the impact of pressure on speech learning success is largely unexplored. In this study, adult, native speakers of English learned non-native speech categories under pressure or no-pressure conditions. In the pressure conditions, participants were informed that they were paired with a (fictitious) partner, and that each had to independently exceed a performance criterion for both to receive a monetary bonus. They were then informed that their partner had exceeded the bonus and the fate of both bonuses depended upon the participant’s performance. Our results demonstrate that pressure significantly enhanced speech learning success. In addition, neurobiologically-inspired computational modeling revealed that the performance advantage was due to faster and more frequent use of procedural learning strategies. These results integrate two well-studied research domains and suggest a facilitatory role of motivational factors in speech learning performance that may not be captured in traditional training paradigms. PMID:28077883

  14. p × n-type transverse thermoelectrics: an alternative Peltier refrigerator with cryogenic promise

    NASA Astrophysics Data System (ADS)

    Zhou, Chuanle; Tang, Y.; Grayson, M.

    2014-02-01

    This work describes a band-engineered transverse thermoelectric with p-type Seebeck in one direction and ntype orthogonal, with off-diagonal terms that drive heat flow transverse to electrical current. Such materials are named p × n type transverse thermoelectrics. Whereas thermoelectric performance is normally limited by the figure of merit ZT, p × n type materials can be more easily geometrically shaped and integrated for devices, leading to more compact, longer lifetime, enhanced efficiency coolers for infrared detectors or photovoltaic generators.

  15. Improvement of thermoelectric performance of single-wall carbon nanotubes by heavy doping: Effect of one-dimensional band multiplicity

    NASA Astrophysics Data System (ADS)

    Hayashi, Daisuke; Nakai, Yusuke; Kyakuno, Haruka; Yamamoto, Takahiro; Miyata, Yasumitsu; Yanagi, Kazuhiro; Maniwa, Yutaka

    2016-12-01

    Doped single-wall carbon nanotube (SWCNT) films were prepared and their Seebeck coefficient (S) and electrical resistivity (ρ) were investigated as functions of carrier density. For heavy doping, a second maximum of S (S = 35 µV/K) was discovered, with its corresponding power factor, P = 85 µW/(m·K2), 6 times that of the first maximum for lightly doped films. Calculations for zigzag SWCNTs suggest that the thermoelectric performance can be effectively improved by controlling the multiplicity of the one-dimensional band and tuning the carrier density. This provides a new strategy for achieving higher performance at a lower cost than using high-purity semiconducting SWCNTs.

  16. Thermoelectric system

    DOEpatents

    Reiners, Eric A.; Taher, Mahmoud A.; Fei, Dong; McGilvray, Andrew N.

    2007-10-30

    In one particular embodiment, an internal combustion engine is provided. The engine comprises a block, a head, a piston, a combustion chamber defined by the block, the piston, and the head, and at least one thermoelectric device positioned between the combustion chamber and the head. In this particular embodiment, the thermoelectric device is in direct contact with the combustion chamber. In another particular embodiment, a cylinder head configured to sit atop a cylinder bank of an internal combustion engine is provided. The cylinder head comprises a cooling channel configured to receive cooling fluid, valve seats configured for receiving intake and exhaust valves, and thermoelectric devices positioned around the valve seats.

  17. 300 WATT PORTABLE THERMOELECTRIC GENERATOR.

    DTIC Science & Technology

    THERMOELECTRICITY, POWER SUPPLIES), (* GENERATORS , THERMOELECTRICITY), (*ELECTRIC POWER PRODUCTION, THERMOELECTRICITY), PORTABLE EQUIPMENT, THERMOCOUPLES, ENERGY CONVERSION, HEAT EXCHANGERS, WIRING DIAGRAMS

  18. Improved thermoelectric performance of p-type polycrystalline bismuth telluride via hydrothermal treatment with alkali metal salts

    NASA Astrophysics Data System (ADS)

    Su, Zhe

    amorphous phase. Once Na- and Rb-treatments with various molar ratios were applied to the same sample, a similar grain boundary layer formed with a compositional gradient along the depth direction. The Hall effect measurements showed that the grain boundary phase introduced new carriers into the system and thereby compensated the loss in mobility. With alpha almost untouched, the rho to kappa ratio has been optimized by varying the Na:Rb ratio in the starting solution. As a result, the Na:Rb = 1:2 ratio yielded the best ZT value of ˜ 0.92 at 350K, comparable with that of the state-of-the-art p-Bi2Te3 commercial ingot. Besides ZT, the hydrothermal treatment lessened the temperature dependence of compatibility factor S of as-treated polycrystalline samples, helping a thermoelectric device have overall better performance even if it did not work under its optimal condition.

  19. Enhanced Thermoelectric Properties of Cu2ZnSnSe4 with Ga-doping

    SciTech Connect

    Wei, Kaya; Beauchemin, Laura; Wang, Hsin; Porter, Wallace D.; Martin, Joshua; Nolas, George S.

    2015-08-10

    Gallium doped Cu2ZnSnSe4 quaternary chalcogenides with and without excess Cu were synthesized by elemental reaction and densified using hot pressing in order to investigate their high temperature thermoelectric properties. The resistivity, , and Seebeck coefficient, S, for these materials decrease with increased Ga-doping while both mobility and effective mass increase with Ga doping. The power factor (S2/ρ) therefore increases with Ga-doping. The highest thermoelectric figure of merit (ZT = 0.39 at 700 K) was obtained for the composition that had the lowest thermal conductivity. Our results suggest an approach to achieving optimized thermoelectric properties and are part of the continuing effort to explore different quaternary chalcogenide compositions and structure types, as this class of materials continues to be of interest for thermoelectrics applications.

  20. Variations of thermoelectric performance by electric fields in bilayer MX2 (M = W, Mo; X = S, Se).

    PubMed

    Wang, Rui-Ning; Dong, Guo-Yi; Wang, Shu-Fang; Fu, Guang-Sheng; Wang, Jiang-Long

    2017-02-22

    A gate electrode is usually used to controllably tune the carrier concentrations, further modulating the electrical conductivity and the Seebeck coefficient to obtain the optimum thermoelectric figure of merit (ZT) in two-dimensional materials. On the other hand, it is necessary to investigate how an electric field induced by a gate voltage affects the electronic structures, further determining the thermoelectric properties. Therefore, by using density functional calculations in combination with Boltzmann theory, the thermoelectric properties of bilayer MX2 (M = W, Mo; X = S, Se) with or without a 1 V nm(-1) perpendicular electric field are comparatively investigated. First of all, the variations of the electrical conductivity (σ), electron thermal conductivity and Seebeck coefficient (S) with the carrier concentration are studied. Due to the trade-off relationship between S and σ, there is an optimum concentration to obtain the maximum ZT, which increases with the temperature due to the enhancement of the Seebeck coefficient. Moreover, N-type bilayers have larger optimum ZTs than P-type bilayers. In addition, the electric field results in the increase of the Seebeck coefficient in low hole-doped MS2 bilayers and high hole-doped MSe2 bilayers, thus leading to similar variations in ZT. The optimum ZTs are reduced from 2.11 × 10(-2), 3.19 × 10(-2), 2.47 × 10(-2), and 2.58 × 10(-2) to 1.57 × 10(-2), 1.51 × 10(-2), 2.08 × 10(-2), and 1.43 × 10(-2) for the hole-doped MoS2, MoSe2, and WSe2 bilayers, respectively. For N-type bilayers, the electric field shows a destructive effect, resulting in the obvious reduction of the Seebeck coefficient in the MSe2 layers and the low electron-doped MS2 bilayers. In electron-doped bilayers, the optimum ZTs will decrease from 3.03 × 10(-2), 6.64 × 10(-2), and 6.69 × 10(-2) to 2.81 × 10(-2), 3.59 × 10(-2), and 4.39 × 10(-2) for the MoS2, MoSe2, and WSe2 bilayers, respectively.

  1. Enhancement of thermoelectric properties of CoSb3-based skutterudites by double filling of Tl and In

    NASA Astrophysics Data System (ADS)

    Harnwunggmoung, Adul; Kurosaki, Ken; Kosuga, Atsuko; Ishimaru, Manabu; Plirdpring, Theerayuth; Yimnirun, Rattikorn; Jutimoosik, Jaru; Rujirawat, Saroj; Ohishi, Yuji; Muta, Hiroaki; Yamanaka, Shinsuke

    2012-08-01

    Thermoelectric (TE) generators can directly generate electrical power from waste heat, and thus could be an important part of the solution to future power supply and sustainable energy management. The main obstacle to the widespread use of TE materials in diverse industries, e.g., for exhaust heat recovery in automobiles, is their low efficiency in converting heat to electricity. The conversion efficiency of TE materials is quantified by the dimensionless figure of merit, ZT, and the way to enhance ZT is to decrease the lattice thermal conductivity (κlat) of the material, while maintaining a high electrical conductivity, i.e., to create a situation in which phonons are scattered but electrons are unaffected. Here, we report skutterudites filled by Tl and In, Tl0.1InxCo4Sb12, which allow a dramatic reduction of κlat, yielding a ZT of 1.2 at 700 K. We demonstrate that the reduction of κlat is due to the effective phonon scattering induced both by the rattling of Tl and In and by the naturally formed In2O3 nanoparticles (<50 nm). The combined approach of double filling and self-formed nanostructures might be applicable to various clathrate compounds. Thus, our results point to a new strategy in the improvement of bulk TE materials.

  2. Thermoelectric Products

    NASA Technical Reports Server (NTRS)

    1988-01-01

    Instead of bulky coils and compressors used in conventional refrigeration systems, UST design engineers drew on thermo-electric technology. UST's precision temperature chambers (PTC's) feature small thermoelectric modules that measure not much more than 1 square inch and operate on unique phenomenon of heat exchange. When electric current flows through specialized metallic crystals, heat is produced; when current direction is reversed cooling is produced.

  3. Bandgap reduction responsible for the improved thermoelectric performance of bulk polycrystalline In2-xCuxSe3 (x = 0-0.2)

    NASA Astrophysics Data System (ADS)

    Cui, Jiaolin; Liu, Xianglian; Zhang, Xiaojun; Li, Yiyun; Deng, Yuan

    2011-07-01

    α-In2Se3 is of large bandgap (˜1.4 eV) semiconductor and its structure is based on two-layer hexagonally packed arrays of selenium atoms with 1/3 of the sites of indium atoms being empty. Here we report a bandgap Eg reduction due mainly to the formation of a Cu2Se slab in the host In2Se3, which is responsible for the remarkable improvement of thermoelectric performance of bulk polycrystalline In2-xCuxSe3 (x = 0.1-0.2). When x = 0.2 the dimensionless figure of merit ZT and power factor were increased by a factor of 2 and 3, respectively, at 846 K if compared to those of Cu-free In2Se3. Interestingly, an incorporation of Cu into the lattice of In2Se3 results in a change in morphology from amorphouslike structure represented by In2Se3 to a visible polycrystalline form attributed to partial crystallization of the structure. This change enhances lattice thermal conductivities κL over the very low values of In2Se3. However, the enhancement is only moderate because of the effective scattering of phonons in the polycrystalline nanostructure.

  4. Thermoelectric performance of electron and hole doped PtSb2

    SciTech Connect

    Saeed, Yasir; Singh, Nirprenda; Schwingenschlogl, Udo; Parker, David S

    2013-01-01

    We investigate the thermoelectric properties of electron and hole doped PtSb2. Our results show that for doping of 0.04 holes per unit cell (1:5 1020 cm 3) PtSb2 shows a high Seebeck coefficient at room temperature, which can also be achieved at other temperatures by controlling the carrier concentration (both electron and hole). The electrical conductivity becomes temperature independent when the doping exceeds some 0.2 electrons/holes per unit cell. The figure of merit at 800 K in electron and hole doped PtSb2 is comparatively low at 0.13 and 0.21, respectively, but may increase significantly with As alloying due to the likely opening of a band gap and reduction of the lattice thermal conductivity

  5. A T-type method for characterization of the thermoelectric performance of an individual free-standing single crystal Bi2S3 nanowire

    NASA Astrophysics Data System (ADS)

    Ma, Weigang; Miao, Tingting; Zhang, Xing; Takahashi, Koji; Ikuta, Tatsuya; Zhang, Boping; Ge, Zhenhua

    2016-01-01

    A comprehensive method to evaluate the thermoelectric performance of one-dimensional nanostructures, called the T-type method, has been first developed. The thermoelectric properties, including the Seebeck coefficient, thermal conductivity and electrical conductivity, of an individual free-standing single crystal Bi2S3 nanowire have been first characterized by applying the T-type method. The determined figure of merit is far less than the reported values of nanostructured bulk Bi2S3 samples, and the mechanism is that the Seebeck coefficient is nearly zero in the temperature range of 300-420 K and changes its sign at 320 K.A comprehensive method to evaluate the thermoelectric performance of one-dimensional nanostructures, called the T-type method, has been first developed. The thermoelectric properties, including the Seebeck coefficient, thermal conductivity and electrical conductivity, of an individual free-standing single crystal Bi2S3 nanowire have been first characterized by applying the T-type method. The determined figure of merit is far less than the reported values of nanostructured bulk Bi2S3 samples, and the mechanism is that the Seebeck coefficient is nearly zero in the temperature range of 300-420 K and changes its sign at 320 K. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05946a

  6. Nanostructured Bulk Thermoelectric Generator for Efficient Power Harvesting for Self-powered Sensor Networks

    SciTech Connect

    Zhang, Yanliang; Butt, Darryl; Agarwal, Vivek

    2015-07-01

    The objective of this Nuclear Energy Enabling Technology research project is to develop high-efficiency and reliable thermoelectric generators for self-powered wireless sensors nodes utilizing thermal energy from nuclear plant or fuel cycle. The power harvesting technology has crosscutting significance to address critical technology gaps in monitoring nuclear plants and fuel cycle. The outcomes of the project will lead to significant advancement in sensors and instrumentation technology, reducing cost, improving monitoring reliability and therefore enhancing safety. The self-powered wireless sensor networks could support the long-term safe and economical operation of all the reactor designs and fuel cycle concepts, as well as spent fuel storage and many other nuclear science and engineering applications. The research is based on recent breakthroughs in high-performance nanostructured bulk (nanobulk) thermoelectric materials that enable high-efficiency direct heat-to-electricity conversion over a wide temperature range. The nanobulk thermoelectric materials that the research team at Boise State University and University of Houston has developed yield up to a 50% increase in the thermoelectric figure of merit, ZT, compared with state-of-the-art bulk counterparts. This report focuses on the selection of optimal thermoelectric materials for this project. The team has performed extensive study on two thermoelectric materials systems, i.e. the half-Heusler materials, and the Bismuth-Telluride materials. The report contains our recent research results on the fabrication, characterization and thermoelectric property measurements of these two materials.

  7. Thermoelectric refrigerator having improved temperature stabilization means

    DOEpatents

    Falco, Charles M.

    1982-01-01

    A control system for thermoelectric refrigerators is disclosed. The thermoelectric refrigerator includes at least one thermoelectric element that undergoes a first order change at a predetermined critical temperature. The element functions as a thermoelectric refrigerator element above the critical temperature, but discontinuously ceases to function as a thermoelectric refrigerator element below the critical temperature. One example of such an arrangement includes thermoelectric refrigerator elements which are superconductors. The transition temperature of one of the superconductor elements is selected as the temperature control point of the refrigerator. When the refrigerator attempts to cool below the point, the metals become superconductors losing their ability to perform as a thermoelectric refrigerator. An extremely accurate, first-order control is realized.

  8. Potential for high thermoelectric performance in n-type Zintl compounds: a case study of Ba doped KAlSb 4

    SciTech Connect

    Ortiz, Brenden R.; Gorai, Prashun; Krishna, Lakshmi; Mow, Rachel; Lopez, Armando; McKinney, Robert; Stevanović, Vladan; Toberer, Eric S.

    2017-01-01

    High-throughput calculations (first-principles density functional theory and semi-empirical transport models) have the potential to guide the discovery of new thermoelectric materials. Herein we have computationally assessed the potential for thermoelectric performance of 145 complex Zintl pnictides. Of the 145 Zintl compounds assessed, 17% show promising n-type transport properties, compared with only 6% showing promising p-type transport. We predict that n-type Zintl compounds should exhibit high mobility un while maintaining the low thermal conductivity KL typical of Zintl phases. Thus, not only do candidate n-type Zintls outnumber their p-type counterparts, but they may also exhibit improved thermoelectric performance. From the computational search, we have selected n-type KAlSb4 as a promising thermoelectric material. Synthesis and characterization of polycrystalline KAlSb4 reveals non-degenerate n-type transport. With Ba substitution, the carrier concentration is tuned between 1018 and 1019 e- cm-3 with a maximum Ba solubility of 0.7% on the K site. High temperature transport measurements confirm a high un (50 cm2 V-1 s-1) coupled with a near minimum KL (0.5 W m-1 K-1) at 370 degrees C. Together, these properties yield a zT of 0.7 at 370 degrees C for the composition K0.99Ba0.01AlSb4. Based on the theoretical predictions and subsequent experimental validation, we find significant motivation for the exploration of n-type thermoelectric performance in other Zintl pnictides.

  9. Thermoelectric Cooler Design

    DTIC Science & Technology

    1992-12-01

    coefficient of performance which is the term to the left of the brackets in equation (36) Egli (Ref. 4: p. 31] and Tipler [Ref. 5:pp 575-576]. H. CASCADED...Thermoelectricity, John Wiley and Sons Inc., 1960. 5. Tipler , P. A., Physics for Scientists and Engineers, 3rd ed., Worth Publishers, 1991. 70 BIBLIOGRAPHY 1

  10. Simulations for the Development of Thermoelectric Measurements

    NASA Astrophysics Data System (ADS)

    Zabrocki, Knud; Ziolkowski, Pawel; Dasgupta, Titas; de Boor, Johannes; Müller, Eckhard

    2013-07-01

    In thermoelectricity, continuum theoretical equations are usually used for the calculation of the characteristics and performance of thermoelectric elements, modules or devices as a function of external parameters (material, geometry, temperatures, current, flow, load, etc.). An increasing number of commercial software packages aimed at applications, such as COMSOL and ANSYS, contain vkernels using direct thermoelectric coupling. Application of these numerical tools also allows analysis of physical measurement conditions and can lead to specifically adapted methods for developing special test equipment required for the determination of TE material and module properties. System-theoretical and simulation-based considerations of favorable geometries are taken into account to create draft sketches in the development of such measurement systems. Particular consideration is given to the development of transient measurement methods, which have great advantages compared with the conventional static methods in terms of the measurement duration required. In this paper the benefits of using numerical tools in designing measurement facilities are shown using two examples. The first is the determination of geometric correction factors in four-point probe measurement of electrical conductivity, whereas the second example is focused on the so-called combined thermoelectric measurement (CTEM) system, where all thermoelectric material properties (Seebeck coefficient, electrical and thermal conductivity, and Harman measurement of zT) are measured in a combined way. Here, we want to highlight especially the measurement of thermal conductivity in a transient mode. Factors influencing the measurement results such as coupling to the environment due to radiation, heat losses via the mounting of the probe head, as well as contact resistance between the sample and sample holder are illustrated, analyzed, and discussed. By employing the results of the simulations, we have developed an

  11. Enhanced Thermoelectric Properties of p-type Bi0.5Sb1.5Te3 Thermoelectric Materials by Mechanical Alloying and Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Madavali, Babu; Hong, Soon-Jik

    2016-12-01

    In this research, the microstructure and transport properties of p-type Bi0.5Sb1.5Te3 thermoelectric materials were investigated as a function of milling time. The p-type Bi0.5Sb1.5Te3 alloys were fabricated by mechanical alloying of elemental chunks of bismuth, antimony, and tellurium. This was followed by plasma spark sintering at 673 K. The micro-Vickers hardness (98.7 Hv) was considerably improved in the 90-min sample due to the presence of fine grains in the matrix that prevented crack propagation via grain-boundary hardening. The lowest lattice thermal conductivity (0.63 W/mK) was obtained for the 90-min sample, a value slightly lower than the minimum total thermal conductivity (0.872 ± 0.5 W/mK at 300 K) due to strong scattering of phonons and carriers owing to the completely randomness of the distribution of the fine-grain structure in the bulk samples. The maximum figure-of-merit ( ZT = 0.98 ± 0.5 at 300 K) was obtained for the 90-min sample due to its superior power factor values.

  12. Large enhancement in thermoelectric efficiency of quantum dot junctions due to increase of level degeneracy

    NASA Astrophysics Data System (ADS)

    Kuo, David M. T.; Chen, Chih-Chieh; Chang, Yia-Chung

    2017-02-01

    It is theoretically demonstrated that the figure of merit (Z T ) of quantum dot (QD) junctions can be significantly enhanced when the degree of degeneracy of the energy levels involved in electron transport is increased. The theory is based on the the Green-function approach in the Coulomb blockade regime by including all correlation functions resulting from electron-electron interactions associated with the degenerate levels (L ). We found that electrical conductance (Ge) as well as electron thermal conductance (κe) are highly dependent on the level degeneracy (L ), whereas the Seebeck coefficient (S ) is not. Therefore, the large enhancement of Z T is mainly attributed to the increase of Ge when the phonon thermal conductance (κp h) dominates the heat transport of the QD junction system. In the serially coupled double-QD case, we also obtain a large enhancement of Z T arising from higher L . Unlike Ge and κe, S is found almost independent on electron interdot hopping strength.

  13. A Novel Optimization Method for the Electric Topology of Thermoelectric Modules Used in an Automobile Exhaust Thermoelectric Generator

    NASA Astrophysics Data System (ADS)

    Quan, Rui; Tang, Xinfeng; Quan, Shuhai; Huang, Liang

    2013-07-01

    Based on Bi2Te3 thermoelectric modules, a kind of automobile exhaust thermoelectric generator (AETEG) with a single-column cold-source structure was designed. To enhance its net power and efficiency, the output performance of all the thermoelectric modules was tested with a temperature monitoring unit and voltage monitoring unit, and modeled using a back-propagation (BP) neural network based on various hot-source temperatures, cold-source temperatures, load currents, and contact pressures according to the temperature distribution of the designed heat exchanger and cooling system. Then, their electric topology (series or parallel hybrid) was optimized using a genetic algorithm to achieve the maximum peak power of the AETEG. From the experimental results, compared with when all the thermoelectric modules were connected only in series or parallel at random, it is concluded that the AETEG performance is evidently affected by the electric topology of all the single thermoelectric modules. The optimized AETEG output power is greatly superior to the other two investigated designs, validating the proposed optimized electric topology as both feasible and practical.

  14. Enhanced Thermoelectric Properties of Sn0.8Pb0.2Te Alloy by Mn Substitution

    NASA Astrophysics Data System (ADS)

    Li, J. Q.; Lu, Z. W.; Wang, C. Y.; Li, Y.; Liu, F. S.; Ao, W. Q.

    2016-06-01

    A series of (Sn0.8Pb0.2)1- x Mn x Te alloys with x = 0, 0.03, 0.06, 0.09, 0.12 and 0.15 were prepared by melting, quenching and spark plasma sintering (SPS) techniques to investigate their phases and thermoelectric properties. Mn was used as doped element in Sn0.8Pb0.2Te solid solution to reduce the carrier concentration, enhance the Seebeck coefficient and reduce the thermal conductivity of the material. Experimental results show that the SnTe-based solid solution single phase was formed in the alloys with x = 0 and 0.03. The minor irregular-shaped MnTe2 phase presents in the alloys with x ≥ 0.06, while the minor needle-like MnTe phase appears in the alloys with x ≥ 0.12, together with the SnTe-based solid solution matrix. The lattice parameter a of SnTe-based solid solution decreases nearly linearly as Mn content x increases up to 0.12, but keeps constant as x further increases. All the samples show p-type conduction. Mn doping in Sn0.8Pb0.2Te decreases its carrier concentration and thus increases its Seebeck coefficient. The solute Mn and Pb atoms in the SnTe-based solid solution, and the minor phases MnTe2 and MnTe, enhance the phonon scattering and thus reduce the thermal conductivity. As a result, the figure-of-merit ZT of the (Sn0.8Pb0.2)1- x Mn x Te composites can be enhanced with proper Mn substitution. The maximum ZT of 0.65 was obtained in the sample (Sn0.8Pb0.2)0.88Mn0.12Te at 723 K, which is higher than the 0.29 of its parent alloy Sn0.8Pb0.2Te.

  15. Study of thermal stability of Cu2Se thermoelectric material

    NASA Astrophysics Data System (ADS)

    Bohra, Anil; Bhatt, Ranu; Bhattacharya, Shovit; Basu, Ranita; Ahmad, Sajid; Singh, Ajay; Aswal, D. K.; Gupta, S. K.

    2016-05-01

    Sustainability of thermoelectric parameter in operating temperature range is a key consideration factor for fabricating thermoelectric generator or cooler. In present work, we have studied the stability of thermoelectric parameter of Cu2Se within the temperature range of 50-800°C. Temperature dependent Seebeck coefficients and electrical resistivity measurement are performed under three continuous thermal cycles. X-ray diffraction pattern shows the presence of mixed cubic-monoclinic Cu2Se phase in bare pellet which transforms to pure α-Cu2Se phase with repeating thermal cycle. Significant enhancement in Seebeck coefficient and electrical resistivity is observed which may be attributed to (i) Se loss observed in EDS and (ii) the phase transformation from mixed cubic-monoclinic structure to pure monoclinic α-Cu2Se phase.

  16. Electronic Inhomogeneity in PbTe-based High Performance Thermoelectric Materials Observed by NMR

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Schmidt-Rohr, K.; Cook, B. A.; Kanatzidis, M. G.

    2009-03-01

    Effects of composition and synthesis conditions on the local structure and charge carrier concentration in AgxSbyPb18Te20 (LAST-18) thermoelectric (TE) materials have been studied by ^125Te and ^207Pb nuclear magnetic resonance (NMR) with magic-angle spinning. The high-resolution ^125Te NMR spectra show that most Sb and Ag is not part of Sb2Te3, AgSbTe2, or Ag2Te inclusions. Biexponential NMR spin-lattice (T1) relaxation as well as Knight shifts of ^125Te and ^207Pb NMR signals show that many LAST-18 materials contain two phases of similar composition but with free electron concentrations that differ by more than an order of magnitude, i.e. these materials are electronically inhomogeneous. The NMR data were calibrated against Hall- and Seebeck-effect measurements to give the charge carrier concentrations in the two phases. This electronic inhomogeneity may result in the appearance of potential barriers inside TE materials, similar to those observed for semiconductor-semiconductor or metal-semiconductor junctions. Such barriers may affect thermopower, electrical, and thermal conductivity of TE materials.

  17. Thermoelectrics from abundant chemical elements: high-performance nanostructured PbSe-PbS.

    PubMed

    Androulakis, John; Todorov, Iliya; He, Jiaqing; Chung, Duck-Young; Dravid, Vinayak; Kanatzidis, Mercouri

    2011-07-20

    We report promising thermoelectric properties of the rock salt PbSe-PbS system which consists of chemical elements with high natural abundance. Doping with PbCl(2), excess Pb, and Bi gives n-type behavior without significantly perturbing the cation sublattice. Thus, despite the great extent of dissolution of PbS in PbSe, the transport properties in this system, such as carrier mobilities and power factors, are remarkably similar to those of pristine n-type PbSe in fractions as high as 16%. The unexpected finding is the presence of precipitates ~2-5 nm in size, revealed by transmission electron microscopy, that increase in density with increasing PbS concentration, in contrast to previous reports of the occurrence of a complete solid solution in this system. We report a marked impact of the observed nanostructuring on the lattice thermal conductivity, as highlighted by contrasting the experimental values (~1.3 W/mK) to those predicted by Klemens-Drabble theory at room temperature (~1.6 W/mK). Our thermal conductivity results show that, unlike in PbTe, optical phonon excitations in PbSe-PbS systems contribute to heat transport at all temperatures. We show that figures of merit reaching as high as ~1.2-1.3 at 900 K can be obtained, suggesting that large-scale applications with good conversion efficiencies are possible from systems based on abundant, inexpensive chemical elements.

  18. Heterovalent substitution to Enrich electrical conductivity in Cu2CdSn(1-x)GaxSe4 series for high thermoelectric performances.

    PubMed

    Wang, Bo; Li, Yu; Zheng, Jiaxin; Xu, Ming; Liu, Fusheng; Ao, Weiqing; Li, Junqing; Pan, Feng

    2015-03-20

    Serials of Ga doping on Sn sites as heterovalent substitution in Cu2CdSnSe4 are prepared by the melting method and the spark plasma sintering (SPS) technique to form Cu2CdSn(1-x)GaxSe4 (x = 0, 0.025, 0.05, 0.075, 0.01, and 0.125). Massive atomic vacancies are found at x = 0.10 by the heterovalent substitution, which contributes significantly to the increase of electrical conductivity and the decrease of lattice thermal conductivity. The electrical conductivity is increased by about ten times at 300 K after Ga doping. Moreover, the seebeck coefficient only decreases slightly from 310 to 226 μV/K at 723 K, and a significant increase of the power factor is obtained. As a result, a maximum value of 0.27 for the figure of merit (ZT) is obtained at x = 0.10 and at 723 K. Through an ab initio study of the Ga doping effect, we find that the Fermi level of Cu2CdSnSe4 is shifted downward to the valence band, thus improving the hole concentration and enhancing the electrical conductivity at low doping levels. Our experimental and theoretical studies show that a moderate Ga doping on Sn sites is an effective method to improve the thermoelectric performance of Cu2CdSnSe4.

  19. Heterovalent Substitution to Enrich Electrical Conductivity in Cu2CdSn1-xGaxSe4 Series for High Thermoelectric Performances

    PubMed Central

    Wang, Bo; Li, Yu; Zheng, Jiaxin; Xu, Ming; Liu, Fusheng; Ao, Weiqing; Li, Junqing; Pan, Feng

    2015-01-01

    Serials of Ga doping on Sn sites as heterovalent substitution in Cu2CdSnSe4 are prepared by the melting method and the spark plasma sintering (SPS) technique to form Cu2CdSn1-xGaxSe4 (x = 0, 0.025, 0.05, 0.075, 0.01, and 0.125). Massive atomic vacancies are found at x = 0.10 by the heterovalent substitution, which contributes significantly to the increase of electrical conductivity and the decrease of lattice thermal conductivity. The electrical conductivity is increased by about ten times at 300 K after Ga doping. Moreover, the seebeck coefficient only decreases slightly from 310 to 226 μV/K at 723 K, and a significant increase of the power factor is obtained. As a result, a maxium value of 0.27 for the figure of merit (ZT) is obtained at x = 0.10 and at 723 K. Through an ab initio study of the Ga doping effect, we find that the Fermi level of Cu2CdSnSe4 is shifted downward to the valence band, thus improving the hole concentration and enhancing the electrical conductivity at low doping levels. Our experimental and theoretical studies show that a moderate Ga doping on Sn sites is an effective method to improve the thermoelectric performance of Cu2CdSnSe4. PMID:25791823

  20. ATAMM enhancement and multiprocessor performance evaluation

    NASA Technical Reports Server (NTRS)

    Stoughton, John W.; Mielke, Roland R.; Som, Sukhamoy; Obando, Rodrigo; Malekpour, Mahyar R.; Jones, Robert L., III; Mandala, Brij Mohan V.

    1991-01-01

    ATAMM (Algorithm To Architecture Mapping Model) enhancement and multiprocessor performance evaluation is discussed. The following topics are included: the ATAMM model; ATAMM enhancement; ADM (Advanced Development Model) implementation of ATAMM; and ATAMM support tools.

  1. Thermoelectric generators incorporating phase-change materials for waste heat recovery from engine exhaust

    SciTech Connect

    Meisner, Gregory P; Yang, Jihui

    2014-02-11

    Thermoelectric devices, intended for placement in the exhaust of a hydrocarbon fuelled combustion device and particularly suited for use in the exhaust gas stream of an internal combustion engine propelling a vehicle, are described. Exhaust gas passing through the device is in thermal communication with one side of a thermoelectric module while the other side of the thermoelectric module is in thermal communication with a lower temperature environment. The heat extracted from the exhaust gasses is converted to electrical energy by the thermoelectric module. The performance of the generator is enhanced by thermally coupling the hot and cold junctions of the thermoelectric modules to phase-change materials which transform at a temperature compatible with the preferred operating temperatures of the thermoelectric modules. In a second embodiment, a plurality of thermoelectric modules, each with a preferred operating temperature and each with a uniquely-matched phase-change material may be used to compensate for the progressive lowering of the exhaust gas temperature as it traverses the length of the exhaust pipe.

  2. Electric-Field Guided Synthesis of Standalone Nanowire Arrays for Thermoelectric Applications

    NASA Astrophysics Data System (ADS)

    San Hor, Yew

    2012-02-01

    Theoretical studies have suggested that figure of merits of thermoelectric materials can be improved through fabrications of nanoscaled thermoelectric materials. Thin films are expected to result in up to a seven fold improvement in efficiency over bulk materials; even greater enhancement, up to 15 times in efficiency, is expected for very thin wires. Researchers have already succeeded in increasing the efficiency by making thin-layered materials and nanowires of a non-thermoelectric material, i.e. silicone. For practical applications, however, arrays of standalone nanowires or isolated thermoelectric nanowire devices without any template will be required. Here I present an electromagnetic field guided nanostructured synthesis of an array of standalone thermoelectric nanowires. This technique utilizing electric field as a guide in building highly ordered nanostructures will be an elegant, ``bottom-up'' method for nanofabrication without the need of a template. An array of quasi-one dimensional chalcogenide nanowires has been successfully grown in between two conducting plates. Thermoelectric transport measurements including thermalconductivity, thermoelectric power and figure of merit can be easily performed in the device, without any need of complicated electron beam lithography technique.

  3. Band engineering of thermoelectric materials.

    PubMed

    Pei, Yanzhong; Wang, Heng; Snyder, G J

    2012-12-04

    Lead chalcogenides have long been used for space-based and thermoelectric remote power generation applications, but recent discoveries have revealed a much greater potential for these materials. This renaissance of interest combined with the need for increased energy efficiency has led to active consideration of thermoelectrics for practical waste heat recovery systems-such as the conversion of car exhaust heat into electricity. The simple high symmetry NaCl-type cubic structure, leads to several properties desirable for thermoelectricity, such as high valley degeneracy for high electrical conductivity and phonon anharmonicity for low thermal conductivity. The rich capabilities for both band structure and microstructure engineering enable a variety of approaches for achieving high thermoelectric performance in lead chalcogenides. This Review focuses on manipulation of the electronic and atomic structural features which makes up the thermoelectric quality factor. While these strategies are well demonstrated in lead chalcogenides, the principles used are equally applicable to most good thermoelectric materials that could enable improvement of thermoelectric devices from niche applications into the mainstream of energy technologies.

  4. Development of High-efficiency Thermoelectric Materials for Vehicle Waste Heat Utililization

    SciTech Connect

    Li, Qiang

    2009-04-30

    The goals of this . CRADA are: 1) Investigation of atomistic structure and nucleation of nanoprecipitates in (PbTe){sub I-x}(AgSbTe2){sub x} (LAST) system; and 2) Development of non-equilibrium synthesis of thermoelectric materials for waste heat recovery. We have made significant accomplishment in both areas. We studied the structure of LAST materials using high resolution imaging, nanoelectron diffraction, energy dispersive spectrum, arid electron energy loss spectrum, and observed a range of nanoparticles The results, published in J. of Applied Physics, provide quantitative structure information about nanoparticles, that is essential for the understanding of the origin of the high thermoelectric performance in this class of materials. We coordinated non-equilibrium synthesis and characterization of thermoelectric materials for waste heat recovery application. Our results, published in J. of Electronic Materials, show enhanced thermoelectric figure of merit and robust mechanical properties in bulk . filled skutterudites.

  5. Origins of enhanced thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films

    SciTech Connect

    Liu, Wei; Chi, Hang; Walrath, J. C.; Chang, A. S.; Stoica, Vladimir A.; Endicott, Lynn; Uher, Ctirad; Tang, Xinfeng; Goldman, R. S.

    2016-01-25

    In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materials with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m{sup −1} K{sup −2} is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films.

  6. Thermoelectric refrigerator

    NASA Technical Reports Server (NTRS)

    Park, Brian V. (Inventor); Smith, Jr., Malcolm C. (Inventor); McGrath, Ralph D. (Inventor); Gilley, Michael D. (Inventor); Criscuolo, Lance (Inventor); Nelson, John L. (Inventor)

    1996-01-01

    A refrigerator is provided which combines the benefits of superinsulation materials with thermoelectric devices and phase change materials to provide an environmentally benign system that is energy efficient and can maintain relatively uniform temperatures for extended periods of time with relatively low electrical power requirements. The refrigerator includes a thermoelectric assembly having a thermoelectric device with a hot sink and a cold sink. The superinsulation materials include a plurality of vacuum panels. The refrigerator is formed from an enclosed structure having a door. The vacuum panels may be contained within the walls of the enclosed structure and the door. By mounting the thermoelectric assembly on the door, the manufacturer of the enclosed structure is simplified and the overall R rating of the refrigerator increased. Also an electrical motor and propellers may be mounted on the door to assist in the circulation of air to improve the efficiency of the cold sink and the hot sink. A propeller and/or impeller is preferably mounted within the refrigerator to assist in establishing the desired air circulation flow path.

  7. A theoretical prediction of super high-performance thermoelectric materials based on MoS2/WS2 hybrid nanoribbons

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongwei; Xie, Yuee; Peng, Qing; Chen, Yuanping

    2016-02-01

    Modern society is hungry for electrical power. To improve the efficiency of energy harvesting from heat, extensive efforts seek high-performance thermoelectric materials that possess large differences between electronic and thermal conductance. Here we report a super high-performance material of consisting of MoS2/WS2 hybrid nanoribbons discovered from a theoretical investigation using nonequilibrium Green’s function methods combined with first-principles calculations and molecular dynamics simulations. The hybrid nanoribbons show higher efficiency of energy conversion than the MoS2 and WS2 nanoribbons due to the fact that the MoS2/WS2 interface reduces lattice thermal conductivity more than the electron transport. By tuning the number of the MoS2/WS2 interfaces, a figure of merit ZT as high as 5.5 is achieved at a temperature of 600 K. Our results imply that the MoS2/WS2 hybrid nanoribbons have promising applications in thermal energy harvesting.

  8. A theoretical prediction of super high-performance thermoelectric materials based on MoS2/WS2 hybrid nanoribbons

    PubMed Central

    Zhang, Zhongwei; Xie, Yuee; Peng, Qing; Chen, Yuanping

    2016-01-01

    Modern society is hungry for electrical power. To improve the efficiency of energy harvesting from heat, extensive efforts seek high-performance thermoelectric materials that possess large differences between electronic and thermal conductance. Here we report a super high-performance material of consisting of MoS2/WS2 hybrid nanoribbons discovered from a theoretical investigation using nonequilibrium Green’s function methods combined with first-principles calculations and molecular dynamics simulations. The hybrid nanoribbons show higher efficiency of energy conversion than the MoS2 and WS2 nanoribbons due to the fact that the MoS2/WS2 interface reduces lattice thermal conductivity more than the electron transport. By tuning the number of the MoS2/WS2 interfaces, a figure of merit ZT as high as 5.5 is achieved at a temperature of 600 K. Our results imply that the MoS2/WS2 hybrid nanoribbons have promising applications in thermal energy harvesting. PMID:26884123

  9. Zintl Phases for Thermoelectric Applications

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey (Inventor); Toberer, Eric (Inventor); Zevalkink, Alex (Inventor)

    2014-01-01

    The inventors demonstrate herein that various Zintl compounds can be useful as thermoelectric materials for a variety of applications. Specifically, the utility of Ca3AlSb3, Ca5Al2Sb6, Ca5In2Sb6, Ca5Ga2Sb6, is described herein. Carrier concentration control via doping has also been demonstrated, resulting in considerably improved thermoelectric performance in the various systems described herein.

  10. High temperature thermoelectrics

    SciTech Connect

    Moczygemba, Joshua E.; Biershcenk, James L.; Sharp, Jeffrey W.

    2014-09-23

    In accordance with one embodiment of the present disclosure, a thermoelectric device includes a plurality of thermoelectric elements that each include a diffusion barrier. The diffusion barrier includes a refractory metal. The thermoelectric device also includes a plurality of conductors coupled to the plurality of thermoelectric elements. The plurality of conductors include aluminum. In addition, the thermoelectric device includes at least one plate coupled to the plurality of thermoelectric elements using a braze. The braze includes aluminum.

  11. Performance-Enhancing Drugs: Know the Risks

    MedlinePlus

    ... and most of what is known about the drugs' effects on athletes comes from observing users. It is ... lead to a positive test for performance-enhancing drugs. Possible side effects of creatine that can decrease athletic performance include: ...

  12. SHI induced enhancement in conductivity of PbTe thin film for thermoelectric applications

    SciTech Connect

    Gupta, Srashti; Agarwal, D. C.; Singh, J. P.; Tripathi, S. K.; Neeleshwar, S.; Asokan, K.; Panigrahi, B. K.; Avasthi, D. K.

    2012-06-05

    PbTe thin film were synthesized using thermal evaporation and irradiated by 100 MeV Ag ions at different fluences ranging from 3x10{sup 13} and 1x10{sup 14} ions/cm{sup 2}. Pristine films annealed under Ar atm at 250 deg. C for 1 hr. X-ray Diffraction (XRD) of pristine and irradiated films reveals the improvement of PbTe phase with increasing fluence. The thickness of the film is decreased from 195 nm to 150 nm after ion irradiation as indicated by Rutherford backscattering spectrometry (RBS) analysis due to the sputtering. Resistivity measurement using four probe techniques of these films shows the conductivity enhancement with ion fluence. The conductivity is found to be {approx} 6 fold at fluence 3x10{sup 13} ions/cm{sup 2} whereas it decreases to 3 fold after annealing in comparison to pristine sample. On further increasing the fluence from 3x10{sup 13} ions/cm{sup 2}, the properties of the film begin to deteriorate. SHI induced modification may be explained on the basis of oxygen desorption and change in stochiometry of film during irradiation.

  13. Thermoelectric effects and topological insulators

    NASA Astrophysics Data System (ADS)

    Xu, Yong

    2016-11-01

    The recent discovery of topological insulators (TIs) offers new opportunities for the development of thermoelectrics, because many TIs (like Bi2Te3) are excellent thermoelectric (TE) materials. In this review, we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties, including strong size effects and an anomalous Seebeck effect. Importantly, the TE figure of merit zT of TIs is no longer an intrinsic property, but depends strongly on the geometric size. The geometric parameters of two-dimensional TIs can be tuned to enhance zT to be significantly greater than 1. Then a few proof-of-principle experiments on three-dimensional TIs will be discussed, which observed unconventional TE phenomena that are closely related to the topological nature of the materials. However, current experiments indicate that the metallic surface states, if their advantage of high mobility is not fully utilized, would be detrimental to TE performance. Finally, we provide an outlook for future work on topological materials, which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving zT. Project supported by the National Thousand-Young-Talents Program, China and Tsinghua University Initiative Scientific Research Program, China.

  14. Se Vacancy Effect on the Thermoelectric Performance of Pb-Doped In4Pb0.01Se3-x Polycrystalline

    NASA Astrophysics Data System (ADS)

    Alsharafi, Rashed; Zhan, Heng; Shaheen, Nusrat; Lu, Xu; Wang, Guoyu; Sun, Xiaonan; Zhou, Xiaoyuan

    2017-01-01

    Indium selenides have been considered as highly efficient thermoelectric materials due to their excellent electrical and thermal properties. Herein, we report the effect of Se vacancy on the thermoelectric performance of Pb-doped In4Pb0.01Se3-x polycrystalline (x = 0, 0.03, 0.07, and 0.1) synthesized by solid state reaction followed by spark plasma sintering. The obtained products are characterized by x-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Owing to the increase of Se vacancy in Pb-doped compounds, the electrical resistivity is reduced by increasing carrier concentration along with the reduction of the lattice thermal conductivity. Ultimately, the In4Pb0.01Se3-x (x = 0.07) exhibits a high ZT value of 0.95 at 690 K.

  15. Optimization of Heat Exchangers with Dimpled Surfaces to Improve the Performance in Thermoelectric Generators Using a Kriging Model

    NASA Astrophysics Data System (ADS)

    Li, Shuai; Wang, Yiping; Wang, Tao; Yang, Xue; Deng, Yadong; Su, Chuqi

    2016-11-01

    Thermoelectric generators (TEGs) have become a topic of interest for vehicle exhaust energy recovery. Electrical power generation is deeply influenced by temperature differences, temperature uniformity and topological structures of TEGs. When the dimpled surfaces are adopted in heat exchangers, the heat transfer rates can be augmented with a minimal pressure drop. However, the temperature distribution shows a large gradient along the flow direction which has adverse effects on the power generation. In the current study, the heat exchanger performance was studied in a computational fluid dynamics (CFD) model. The dimple depth, dimple print diameter, and channel height were chosen as design variables. The objective function was defined as a combination of average temperature, temperature uniformity and pressure loss. The optimal Latin hypercube method was used to determine the experiment points as a method of design of the experiment in order to analyze the sensitivity of the design variables. A Kriging surrogate model was built and verified according to the database resulting from the CFD simulation. A multi-island genetic algorithm was used to optimize the structure in the heat exchanger based on the surrogate model. The results showed that the average temperature of the heat exchanger was most sensitive to the dimple depth. The pressure loss and temperature uniformity were most sensitive to the parameter of channel rear height, h 2. With an optimal design of channel structure, the temperature uniformity can be greatly improved compared with the initial exchanger, and the additional pressure loss also increased.

  16. Performance and impedance studies of thin, porous molybdenum and tungsten electrodes for the alkali metal thermoelectric converter

    NASA Technical Reports Server (NTRS)

    Wheeler, B. L.; Williams, R. M.; Jeffries-Nakamura, B.; Lamb, J. L.; Loveland, M. E.; Bankston, C. P.; Cole, T.

    1988-01-01

    Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optimum performance as alkali metal thermoelectric converter electrodes at thicknesses less than 1.0 micron when used with molybdenum or nickel current collector grids. Power densities of 0.40 W/sq cm for 0.5-micron molybdenum films at 1200 K and 0.35 W/sq cm for 0.5-micron tungsten films at 1180 K were obtained at electrode maturity after 40-90 h. Sheet resistances of magnetron sputter deposited films on sodium beta-double-prime-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3-double-prime 0.4-micron. The ac impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness less than 2.0 microns, is not utilized efficiently unless a fairly fine (about 1 x 1 mm) current collector grid is employed.

  17. TCP Performance Enhancement Over Iridium

    NASA Technical Reports Server (NTRS)

    Torgerson, Leigh; Hutcherson, Joseph; McKelvey, James

    2007-01-01

    In support of iNET maturation, NASA-JPL has collaborated with NASA-Dryden to develop, test and demonstrate an over-the-horizon vehicle-to-ground networking capability, using Iridium as the vehicle-to-ground communications link for relaying critical vehicle telemetry. To ensure reliability concerns are met, the Space Communications Protocol Standards (SCPS) transport protocol was investigated for its performance characteristics in this environment. In particular, the SCPS-TP software performance was compared to that of the standard Transmission Control Protocol (TCP) over the Internet Protocol (IP). This paper will report on the results of this work.

  18. Perform or Else: The Performative Enhancement of Teacher Professionalism

    ERIC Educational Resources Information Center

    Liew, Warren Mark

    2012-01-01

    The Singapore Ministry of Education's Enhanced Performance Management System (EPMS) was instituted in 2005 as a system of professional accountability to enhance the standards and stakes of teacher professionalism in schools. This essay explores how the EPMS, with its underlying paradigm of performance management, functions as a "technology of…

  19. Enhancement of thermoelectric figure of merit in β-Zn4Sb3 by indium doping control

    NASA Astrophysics Data System (ADS)

    Wei, Pai-Chun; Yang, Chun-Chuen; Chen, Jeng-Lung; Sankar, Raman; Chen, Chi-Liang; Hsu, Chia-Hao; Chang, Chung-Chieh; Chen, Cheng-Lung; Dong, Chung-Li; Chou, Fang-Cheng; Chen, Kuei-Hsien; Wu, Maw-Kuen; Chen, Yang-Yuan

    2015-09-01

    We demonstrate the control of phase composition in Bridgman-grown β-Zn4Sb3 crystals by indium doping, an effective way to overcome the difficulty of growing very pure β-Zn4Sb3 thermoelectric material. The crystal structures are characterized by Rietveld refinement with synchrotron X-ray diffraction data. The results show an anisotropic lattice expansion in In-doped β-Zn4Sb3 wherein the zinc atoms are partially substituted by indium ones at 36f site of R-3c symmetry. Through the elimination of ZnSb phase, all the three individual thermoelectric properties are simultaneously improved, i.e., increasing electrical conductivity and Seebeck coefficient while reducing thermal conductivity. Under an optimal In concentration (x = 0.05), pure phase β-Zn4Sb3 crystal can be obtained, which possesses a high figure of merit (ZT) of 1.4 at 700 K.

  20. Thermionic Energy Conversion (TEC) topping thermoelectrics

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1981-01-01

    Performance expectations for thermionic and thermoelectric energy conversion systems are reviewed. It is noted that internal radiation effects diminish thermoelectric figures of merit significantly at 1000 K and substantially at 2000 K; the effective thermal conductivity contribution of intrathermoelectric radiative dissipation increases with the third power of temperature. It is argued that a consideration of thermoelectric power generation with high temperature heat sources should include utilization of thermionic energy conversion (TEC) topping thermoelectrics. However TEC alone or TEC topping more efficient conversion systems like steam or gas turbines, combined cycles, or Stirling engines would be more desirable generally.

  1. CFB sorbent selection enhances performance

    SciTech Connect

    Buecker, B.; Wofford, J.; DuBose, R.; Ray, D.

    1997-07-01

    The quality and particle size of the sorbent has a direct influence on the efficiency of sulfur dioxide (SO{sub 2}) removal in a circulating fluidized bed (CFB) boiler. This report outlines tests and subsequent operation of a CFB unit at the University of North Carolina at Chapel Hill Cogeneration Facility (UNC-CH) that proved how dramatically a change in sorbent can change the efficiency of performance.

  2. Significant enhancement of thermoelectric properties and metallization of Al-doped Mg{sub 2}Si under pressure

    SciTech Connect

    Morozova, Natalia V.; Korobeinikov, Igor V.; Karkin, Alexander E.; Shchennikov, Vladimir V.; Ovsyannikov, Sergey V. E-mail: sergey2503@gmail.com; Takarabe, Ken-ichi; Mori, Yoshihisa; Nakamura, Shigeyuki

    2014-06-07

    We report results of investigations of electronic transport properties and lattice dynamics of Al-doped magnesium silicide (Mg{sub 2}Si) thermoelectrics at ambient and high pressures to and beyond 15 GPa. High-quality samples of Mg{sub 2}Si doped with 1 at. % of Al were prepared by spark plasma sintering technique. The samples were extensively examined at ambient pressure conditions by X-ray diffraction studies, Raman spectroscopy, electrical resistivity, magnetoresistance, Hall effect, thermoelectric power (Seebeck effect), and thermal conductivity. A Kondo-like feature in the electrical resistivity curves at low temperatures indicates a possible magnetism in the samples. The absolute values of the thermopower and electrical resistivity, and Raman spectra intensity of Mg{sub 2}Si:Al dramatically diminished upon room-temperature compression. The calculated thermoelectric power factor of Mg{sub 2}Si:Al raised with pressure to 2–3 GPa peaking in the maximum the values as high as about 8 × 10{sup −3} W/(K{sup 2}m) and then gradually decreased with further compression. Raman spectroscopy studies indicated the crossovers near ∼5–7 and ∼11–12 GPa that are likely related to phase transitions. The data gathered suggest that Mg{sub 2}Si:Al is metallized under moderate pressures between ∼5 and 12 GPa.

  3. Thermoelectric generator

    DOEpatents

    Pryslak, N.E.

    1974-02-26

    A thermoelectric generator having a rigid coupling or stack'' between the heat source and the hot strap joining the thermoelements is described. The stack includes a member of an insulating material, such as ceramic, for electrically isolating the thermoelements from the heat source, and a pair of members of a ductile material, such as gold, one each on each side of the insulating member, to absorb thermal differential expansion stresses in the stack. (Official Gazette)

  4. A strategy to optimize the thermoelectric performance in a spark plasma sintering process

    PubMed Central

    Chiu, Wan-Ting; Chen, Cheng-Lung; Chen, Yang-Yuan

    2016-01-01

    Spark plasma sintering (SPS) is currently widely applied to existing alloys as a means of further enhancing the alloys’ figure of merit. However, the determination of the optimal sintering condition is challenging in the SPS process. This report demonstrates a systematic way to independently optimize the Seebeck coefficient S and the ratio of electrical to thermal conductivity (σ/κ) and thus achieve the maximum figure of merit zT = S2(σ/κ)T. Sb2−xInxTe3 (x = 0–0.2) were chosen as examples to validate the method. Although high sintering temperature and pressure are helpful in enhancing the compactness and electrical conductivity of pressed samples, the resultant deteriorated Seebeck coefficient and increasing thermal conductivity eventually offset the benefit. We found that the optimal sintering temperature coincides with temperatures at which the maximum Seebeck coefficient begins to degrade, whereas the optimal sintering pressure coincided with the pressure at which the σ/κ ratio reaches a maximum. Based on this principle, the optimized sintering conditions were determined, and the zT of Sb1.9In0.1Te3 is raised to 0.92 at 600 K, showing an approximately 84% enhancement. This work develops a facile strategy for selecting the optimal SPS sintering condition to further enhance the zT of bulk specimens. PMID:26975209

  5. A strategy to optimize the thermoelectric performance in a spark plasma sintering process.

    PubMed

    Chiu, Wan-Ting; Chen, Cheng-Lung; Chen, Yang-Yuan

    2016-03-15

    Spark plasma sintering (SPS) is currently widely applied to existing alloys as a means of further enhancing the alloys' figure of merit. However, the determination of the optimal sintering condition is challenging in the SPS process. This report demonstrates a systematic way to independently optimize the Seebeck coefficient S and the ratio of electrical to thermal conductivity (σ/κ) and thus achieve the maximum figure of merit zT = S(2)(σ/κ)T. Sb2-xInxTe3 (x = 0-0.2) were chosen as examples to validate the method. Although high sintering temperature and pressure are helpful in enhancing the compactness and electrical conductivity of pressed samples, the resultant deteriorated Seebeck coefficient and increasing thermal conductivity eventually offset the benefit. We found that the optimal sintering temperature coincides with temperatures at which the maximum Seebeck coefficient begins to degrade, whereas the optimal sintering pressure coincided with the pressure at which the σ/κ ratio reaches a maximum. Based on this principle, the optimized sintering conditions were determined, and the zT of Sb1.9In0.1Te3 is raised to 0.92 at 600 K, showing an approximately 84% enhancement. This work develops a facile strategy for selecting the optimal SPS sintering condition to further enhance the zT of bulk specimens.

  6. Modular Isotopic Thermoelectric Generator

    SciTech Connect

    Schock, Alfred

    1981-04-03

    Advanced RTG concepts utilizing improved thermoelectric materials and converter concepts are under study at Fairchild for DOE. The design described here is based on DOE's newly developed radioisotope heat source, and on an improved silicon-germanium material and a multicouple converter module under development at Syncal. Fairchild's assignment was to combine the above into an attractive power system for use in space, and to assess the specific power and other attributes of that design. The resultant design is highly modular, consisting of standard RTG slices, each producing ~24 watts at the desired output voltage of 28 volt. Thus, the design could be adapted to various space missions over a wide range of power levels, with little or no redesign. Each RTG slice consists of a 250-watt heat source module, eight multicouple thermoelectric modules, and standard sections of insulator, housing, radiator fins, and electrical circuit. The design makes it possible to check each thermoelectric module for electrical performance, thermal contact, leaktightness, and performance stability, after the generator is fully assembled; and to replace any deficient modules without disassembling the generator or perturbing the others. The RTG end sections provide the spring-loaded supports required to hold the free-standing heat source stack together during launch vibration. Details analysis indicates that the design offers a substantial improvement in specific power over the present generator of RTGs, using the same heat source modules. There are three copies in the file.

  7. Flexible n-Type High-Performance Thermoelectric Thin Films of Poly(nickel-ethylenetetrathiolate) Prepared by an Electrochemical Method.

    PubMed

    Sun, Yuanhui; Qiu, Lin; Tang, Liangpo; Geng, Hua; Wang, Hanfu; Zhang, Fengjiao; Huang, Dazhen; Xu, Wei; Yue, Peng; Guan, Ying-Shi; Jiao, Fei; Sun, Yimeng; Tang, Dawei; Di, Chong-An; Yi, Yuanping; Zhu, Daoben

    2016-05-01

    Flexible thin films of poly(nickel-ethylenetetrathiolate) prepared by an electrochemical method display promising n-type thermoelectric properties with the highest ZT value up to 0.3 at room temperature. Coexistence of high electrical conductivity and high Seebeck coefficient in this coordination polymer is attributed to its degenerate narrow-bandgap semiconductor behavior.

  8. Superlattice Thermoelectric Materials and Devices

    NASA Astrophysics Data System (ADS)

    Venkatasubramanian, Rama

    2002-03-01

    We have recently demonstrated a significant enhancement in thermoelectric figure-of-merit (ZT) at 300K, of about 2.4 in p-type Bi2Te3/Sb2Te3 superlattices, using the concept of phonon-blocking electron-transmitting superlattice structures [1]. The phonon blocking arises from a complex localization-like behavior for phonons in nano-structured superlattices and the electron transmission is facilitated by optimal choice of band-offsets in these semiconductor hetero-structures. We will also discuss the ZT 1.2 results in n-type Bi2Te3/Bi2Te3-xSex superlattices and our initial understanding on the reasons behind the less-than-dramatic performance of these materials compared to the p-type superlattices. Due to the high ZT of the material, devices potentially offer high coefficient of performance (COP) in solid-state refrigeration. The thin-film devices, resulting from rather simple microelectronic processing, allow high cooling power densities to be achieved for a variety of high-power electronic applications. We have obtained 32K and 40K sub-ambient cooling at 298K and 353K, respectively, in these superlattice micro-thermoelements with potential localized active-cooling power densities approaching 700 W/cm2. In addition to high-performance (in terms of COP) and power densities, these thin-film microdevices are also extremely fast-acting, within 10 microsec and about a factor of 23,000 better than bulk thermoelectric technology. Thus, these are of significance for preventing thermal run-away in high-power electronics. We will present results to demonstrate this concept with infrared imaging of cooling/heating with superlattice micro-devices. We will also discuss outstanding issues such as heat removal from the heat sink towards the full exploitation of this technology. In addition, we will compare the state-of-the-art with other thin-film superlattice materials and device concepts. [1] R. Venkatasubramanian, E. Siivola, T. Colpitts, and B.C. O’Quinn, Thin

  9. Enhancement of redox- and phase-stability of thermoelectric CaMnO{sub 3−δ} by substitution

    SciTech Connect

    Thiel, Philipp; Populoh, Sascha; Yoon, Songhak; Weidenkaff, Anke

    2015-09-15

    Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric CaMnO{sub 3−δ}. In this study series of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} (0≤x,y≤0.8) compounds, each with A-site (Dy{sup 3+}, Yb{sup 3+}) or B-site (Nb{sup 5+}, Ta{sup 5+} and Mo{sup 6+}, W{sup 6+}) substitution, were synthesized and crystallographically analyzed. It was found that the high-temperature oxygen content is widely independent from the substituent. Subsequently, with increasing temperature the differences in the Seebeck coefficient vanish above 1200 K. With increasing substitution the orthorhombic distortion of the perovskite-like phase increases. The orthorhombic distortion and the upper temperature limit of the stability of the orthorhombic crystal structure show an almost linear dependency. Accordingly, the mechanical stability of all-oxides thermoelectric converters at temperatures exceeding 1000 K will be increased employing materials with high substitution level and substituents inducing a high orthorhombic distortion. - Graphical abstract: Thermoelectric n-type CaMn{sub 0.98}W{sub 0.02}O{sub 3−δ}—Transport properties and expansion coefficient of: Oxygen loss (green region) and upper stability limit of the orthorhombic phase (yellow region) strongly affect the transport properties. Both features also cause lattice expansion, which leads to cracking of thermoelectric all-oxide converters. We report how the upper limit for application can be shifted to even higher temperatures. - Highlights: • Level of Mn{sup 3+} at RT determines reduction behavior of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} at HT. • Differences in Seebeck coefficient vanish at T>1200 K independent from substitution. • Substitution increases orthorhombicity of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ}. • Linear dependence of orthorhombicity and phase stability. • Design guidelines for

  10. Improved thermoelectric behavior of nanotube-filled polymer composites with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate).

    PubMed

    Kim, Dasaroyong; Kim, Yeonseok; Choi, Kyungwho; Grunlan, Jaime C; Yu, Choongho

    2010-01-26

    The thermoelectric properties of carbon nanotube (CNT)-filled polymer composites can be enhanced by modifying junctions between CNTs using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), yielding high electrical conductivities (up to approximately 40000 S/m) without significantly altering thermopower (or Seebeck coefficient). This is because PEDOT:PSS particles are decorated on the surface of CNTs, electrically connecting junctions between CNTs. On the other hand, thermal transport remains comparable to typical polymeric materials due to the dissimilar bonding and vibrational spectra between CNT and PEDOT:PSS. This behavior is very different from that of typical semiconductors whose thermoelectric properties are strongly correlated. The decoupled thermoelectric properties, which is ideal for developing better thermoelectric materials, are believed to be due to thermally disconnected and electrically connected contact junctions between CNTs. Carrier transport at the junction is found to be strongly dependent on the type and concentration of stabilizers. The crucial role of stabilizers was revealed by characterizing transport characteristics of composites synthesized by electrically conducting PEDOT:PSS and insulating gum Arabic (GA) with 1:1-1:4 weight ratios of CNT to stabilizers. The influence of composite synthesis temperature and CNT-type and concentration on thermoelectric properties has also been studied. Single-walled (SW) CNT-filled composites dried at room temperature followed by 80 degrees C exhibited the best thermoelectric performance in this study. The highest thermoelectric figure of merit (ZT) in this study is estimated to be approximately 0.02 at room temperature, which is at least one order of magnitude higher than most polymers and higher than that of bulk Si. Further studies with various polymers and nanoparticles with high thermoelectric performance may result in economical, lightweight, and efficient polymer thermoelectric

  11. Sensorimotor Rhythm Neurofeedback Enhances Golf Putting Performance.

    PubMed

    Cheng, Ming-Yang; Huang, Chung-Ju; Chang, Yu-Kai; Koester, Dirk; Schack, Thomas; Hung, Tsung-Min

    2015-12-01

    Sensorimotor rhythm (SMR) activity has been related to automaticity during skilled action execution. However, few studies have bridged the causal link between SMR activity and sports performance. This study investigated the effect of SMR neurofeedback training (SMR NFT) on golf putting performance. We hypothesized that preelite golfers would exhibit enhanced putting performance after SMR NFT. Sixteen preelite golfers were recruited and randomly assigned into either an SMR or a control group. Participants were asked to perform putting while electroencephalogram (EEG) was recorded, both before and after intervention. Our results showed that the SMR group performed more accurately when putting and exhibited greater SMR power than the control group after 8 intervention sessions. This study concludes that SMR NFT is effective for increasing SMR during action preparation and for enhancing golf putting performance. Moreover, greater SMR activity might be an EEG signature of improved attention processing, which induces superior putting performance.

  12. Oxide Thermoelectrics

    SciTech Connect

    Singh, David J

    2008-01-01

    Thermoelectricity in oxides, especially NaxCoO2 and related materials, is discussed from the point of view of first principles calculations and Boltzmann transport theory. The electronic structure of this material is exceptional in that it has a combination of very narrow bands and strong hybridization between metal d states and ligand p states. As shown within the framework of conventional Boltzmann transport theory, this leads to high Seebeck coefficients even at metallic carrier densities. This suggests a strategy of searching for other narrow band oxides that can be doped metallic with mobile carriers. Some possible avenues for finding such materials are suggested.

  13. Learning, Remembering, Believing. Enhancing Human Performance.

    ERIC Educational Resources Information Center

    Druckman, Daniel, Ed.; Bjork, Robert A., Ed.

    This book is the third report of the Committee on Techniques for the Enhancement of Human Performance. Based on hundreds of research studies of learning and human performance as reported in the literature, the book consists of 11 chapters organized in five parts. The two chapters of the first part provide the background and summary of the…

  14. Enhanced thermoelectricity of three-dimensionally mesostructured BixSb2-xTe3 nanoassemblies: from micro-scaled open gaps to isolated sealed mesopores.

    PubMed

    Chen, Tsung-Han; Lin, Ping-Yu; Chang, Hsiu-Cheng; Chen, Chun-Hua

    2017-03-02

    We describe an innovative interfacial design concept and nanostructuring of novel BixSb2-xTe3 (BST) nanoassembled films comprising unique air-solid interfaces from micro-scaled open gaps to isolated sealed mesopores, and high-quality solid-solid ones including the coherent grain boundaries and specific twins, utilizing pulsed laser deposition (PLD), for potentially activating multiple thermoelectric enhancing mechanisms. The unusual mesopore embedded BST films exhibit the highest power factor of ∼33 μW cm(-1) K(-2), which is comparable to or higher than the previously reported values for BST, and the corresponding relatively low thermal diffusivity in contrast to that for dense pore-less BST films evidently reveals the crucial role of the three-dimensionally and densely arranged air-solid interfaces in significantly arising the phonon scattering.

  15. Caffeine and taurine enhance endurance performance.

    PubMed

    Imagawa, T F; Hirano, I; Utsuki, K; Horie, M; Naka, A; Matsumoto, K; Imagawa, S

    2009-07-01

    Caffeine enhances endurance performance; however, its effect on accumulated lactate remains unclear. Conversely, taurine, which also enhances endurance performance, decreases accumulated lactate. In this study, the effect of combination of caffeine and taurine on endurance performance was assessed. Mice ran on a treadmill, and the accumulated lactate was measured. In addition, muscle fibers from the gastrocnemius muscle of the mice were stained with ATPase and analyzed. The use of caffeine and taurine over a 2 week period enhanced endurance performance. Moreover, taurine significantly decreased the accumulated concentration of lactate over long running distances. However, the diameter of the cross-sections and ratios of Types I, IIA, and IIB muscle fibers were not affected.

  16. A Revisit to High Thermoelectric Performance of Single-layer MoS2

    PubMed Central

    Jin, Zelin; Liao, Quanwen; Fang, Haisheng; Liu, Zhichun; Liu, Wei; Ding, Zhidong; Luo, Tengfei; Yang, Nuo

    2015-01-01

    Both electron and phonon transport properties of single layer MoS2 (SLMoS2) are studied. Based on first-principles calculations, the electrical conductivity of SLMoS2 is calculated by Boltzmann equations. The thermal conductivity of SLMoS2 is calculated to be as high as 116.8 Wm−1K−1 by equilibrium molecular dynamics simulations. The predicted value of ZT is as high as 0.11 at 500 K. As the thermal conductivity could be reduced largely by phonon engineering, there should be a high possibility to enhance ZT in the SLMoS2-based materials. PMID:26677953

  17. Enhanced Expectancies Improve Performance Under Pressure

    PubMed Central

    McKay, Brad; Lewthwaite, Rebecca; Wulf, Gabriele

    2012-01-01

    Beyond skill, beliefs in requisite abilities and expectations can affect performance. This experiment examined effects of induced perceptions of ability to perform well under generic situations of challenge. Participants (N = 31) first completed one block of 20 trials on a throwing accuracy task. They then completed questionnaires ostensibly measuring individual differences in the ability to perform under pressure. Enhanced-expectancy group participants were told that they were well-suited to perform under pressure, while the control group received neutral information. Subsequently, all participants completed another block of 20 trials on the throwing task, with their performance videotaped and under the assumption that they could secure a prize for themselves and a paired participant with successful performance. Both groups had similar accuracy scores on the first trial block. The enhanced-expectancy group significantly increased their throwing accuracy in the higher-pressure situation (second block), whereas the control group showed no change in performance. Furthermore, beliefs regarding performance under challenge predicted throwing accuracy on the second block. The present findings provide evidence that enhancing individuals’ generic expectancies regarding performance under pressure can affect their motor performance. PMID:22291680

  18. Classification of Valleytronics in Thermoelectricity.

    PubMed

    Norouzzadeh, Payam; Vashaee, Daryoosh

    2016-03-14

    The theory of valleytronics as a material design tool for engineering both thermal and electrical transport properties is presented. It is shown that the interplay among the valleytronics parameters such as the degeneracy of the band, intervalley transitions, effective mass, scattering exponent, and the Fermi energy may deteriorate or ameliorate any or all of the main thermoelectric properties. A flowchart classifying the different paths through which the valleytronics can influence the thermoelectric figure-of-merit ZT is derived and discussed in detail. To exemplify the application of the flowchart, valleytronics in four different semiconductors, Mg2Si, Si0.8Ge0.2, Al(x)Ga(1-x)As and clathrate Si46-VIII were studied, which showed different trends. Therefore, a degenerate multivalley bandstructure, which is typically anticipated for a good thermoelectric material, cannot be a general design rule for ZT enhancement and a detailed transport study is required to engineer the optimum bandstructure.

  19. Nanostructured materials for thermoelectric applications.

    PubMed

    Bux, Sabah K; Fleurial, Jean-Pierre; Kaner, Richard B

    2010-11-28

    Recent studies indicate that nanostructuring can be an effective method for increasing the dimensionless thermoelectric figure of merit (ZT) in materials. Most of the enhancement in ZT can be attributed to large reductions in the lattice thermal conductivity due to increased phonon scattering at interfaces. Although significant gains have been reported, much higher ZTs in practical, cost-effective and environmentally benign materials are needed in order for thermoelectrics to become effective for large-scale, wide-spread power and thermal management applications. This review discusses the various synthetic techniques that can be used in the production of bulk scale nanostructured materials. The advantages and disadvantages of each synthetic method are evaluated along with guidelines and goals presented for an ideal thermoelectric material. With proper optimization, some of these techniques hold promise for producing high efficiency devices.

  20. Classification of Valleytronics in Thermoelectricity

    PubMed Central

    Norouzzadeh, Payam; Vashaee, Daryoosh

    2016-01-01

    The theory of valleytronics as a material design tool for engineering both thermal and electrical transport properties is presented. It is shown that the interplay among the valleytronics parameters such as the degeneracy of the band, intervalley transitions, effective mass, scattering exponent, and the Fermi energy may deteriorate or ameliorate any or all of the main thermoelectric properties. A flowchart classifying the different paths through which the valleytronics can influence the thermoelectric figure-of-merit ZT is derived and discussed in detail. To exemplify the application of the flowchart, valleytronics in four different semiconductors, Mg2Si, Si0.8Ge0.2, AlxGa1−xAs and clathrate Si46-VIII were studied, which showed different trends. Therefore, a degenerate multivalley bandstructure, which is typically anticipated for a good thermoelectric material, cannot be a general design rule for ZT enhancement and a detailed transport study is required to engineer the optimum bandstructure. PMID:26972331

  1. Embedded Ag-rich nanodots in PbTe: Enhancement of thermoelectric properties through energy filtering of the carriers

    NASA Astrophysics Data System (ADS)

    Paul, Biplab; V, Ajay Kumar; Banerji, P.

    2010-09-01

    The concept of energy filtering of the carriers to control the thermoelectric properties of PbTe is experimentally applied in this present work. The energy barriers at the grain interfaces of the nanocomposites and the embedded Ag-rich nanodots within the grains are supposed to control the energy dependency of carrier scattering: that is what we mean by energy filtering of carriers. As a case study, vertical Bridgman grown bulk PbTe:undoped, PbTe:Ag crystals and nanocomposites of PbTe:Ag are used as samples. Thermoelectric properties of all the samples have been evaluated through temperature dependent electrical conductivity, Seebeck coefficient and room temperature Hall and thermal conductivity measurements. It is found that the PbTe:Ag nanocomposites has the highest power factor of 18.78×10-4 W m-1 K-2 with a room temperature thermal conductivity of 1.69 W m-1 K-1. The crystal structures of these samples show the effective potential barrier at the grain boundaries and embedded nanodots within the grains to facilitate the energy filtering of the carriers.

  2. Enhancement of thermoelectric figure of merit in β-Zn{sub 4}Sb{sub 3} by indium doping control

    SciTech Connect

    Wei, Pai-Chun E-mail: cheny2@phys.sinica.edu.tw; Hsu, Chia-Hao; Chang, Chung-Chieh; Chen, Cheng-Lung; Wu, Maw-Kuen; Chen, Yang-Yuan E-mail: cheny2@phys.sinica.edu.tw; Yang, Chun-Chuen; Chen, Jeng-Lung; Sankar, Raman; Chou, Fang-Cheng; Chen, Chi-Liang; Dong, Chung-Li; Chen, Kuei-Hsien

    2015-09-21

    We demonstrate the control of phase composition in Bridgman-grown β-Zn{sub 4}Sb{sub 3} crystals by indium doping, an effective way to overcome the difficulty of growing very pure β-Zn{sub 4}Sb{sub 3} thermoelectric material. The crystal structures are characterized by Rietveld refinement with synchrotron X-ray diffraction data. The results show an anisotropic lattice expansion in In-doped β-Zn{sub 4}Sb{sub 3} wherein the zinc atoms are partially substituted by indium ones at 36f site of R-3c symmetry. Through the elimination of ZnSb phase, all the three individual thermoelectric properties are simultaneously improved, i.e., increasing electrical conductivity and Seebeck coefficient while reducing thermal conductivity. Under an optimal In concentration (x = 0.05), pure phase β-Zn{sub 4}Sb{sub 3} crystal can be obtained, which possesses a high figure of merit (ZT) of 1.4 at 700 K.

  3. Mg{sub 2}Si nanocomposite converted from diatomaceous earth as a potential thermoelectric nanomaterial

    SciTech Connect

    Szczech, Jeannine R.; Jin Song

    2008-07-15

    With recent literature demonstrating enhancement of the thermoelectric performance of nanoscale materials relative to their corresponding bulk materials, methods to synthesize low-dimensional nanomaterials in large scale at low cost are needed. We demonstrate a method for preparing nanostructured dimagnesium silicide (Mg{sub 2}Si) thermoelectric materials that are nanocomposites with MgO by the reduction of diatomaceous earth (diatoms) using a gas-displacement solid state reaction with magnesium vapor. The resulting semiconducting Mg{sub 2}Si preserves the general morphology of the original diatoms and their nanosized grains at least down to the size of 30 nm. This reaction represents a possible method for the production of large quantities of low-cost nanoscale thermoelectric materials with potential for enhanced thermoelectric performance. - Graphical abstract: A nanostructured Mg{sub 2}Si and MgO nanocomposite thermoelectric material is synthesized in the Mg gas-displacement solid state reduction of SiO{sub 2} from diatomaceous earth. The resulting semiconducting Mg{sub 2}Si nanostructures preserve the original diatom morphology, with nanosized grains at least down to the size of 30 nm.

  4. Connecting thermoelectric performance and topological-insulator behavior: Bi2Te3 and Bi2Te2Se from first principles

    DOE PAGES

    Shi, Hongliang; Parker, David S.; Du, Mao-Hua; ...

    2015-01-20

    Thermoelectric performance is of interest for numerous applications such as waste-heat recovery and solid-state energy conversion and will be seen to be closely connected to topological-insulator behavior. In this paper, we here report first-principles transport and defect calculations for Bi2Te2Se in relation to Bi2Te3. The two compounds are found to contain remarkably different electronic structures in spite of being isostructural and isoelectronic. We also discuss these results in terms of the topological-insulator characteristics of these compounds.

  5. Superlattices in thermoelectric applications

    SciTech Connect

    Sofo, J.O.; Mahan, G.D. |

    1994-08-01

    The electrical conductivity, thermopower and the electronic contribution to the thermal conductivity of a superlattice, are calculated with the electric field and the thermal gradient applied parallel to the interfaces. Tunneling between quantum wells is included. The broadening of the lowest subband when the period of the superlattice is decreased produces a reduction of the thermoelectric figure of merit. However, we found that a moderate increase of the figure of merit may be expected for intermediate values of the period, due to the enhancement of the density of states produced by the superlattice structure.

  6. Transient thermoelectric supercooling: Isosceles current pulses from a response surface perspective and the performance effects of pulse cooling a heat generating mass

    NASA Astrophysics Data System (ADS)

    Piggott, Alfred J., III

    With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials

  7. Sports medicine: performance-enhancing drugs.

    PubMed

    Gregory, Andrew J M; Fitch, Robert W

    2007-08-01

    Performance-enhancing drugs, ergogenic aids, or sports supplements have been a part of sports since sporting competition began and likely always will be. Considered cheating by purists and necessary by some athletes, we must accept the fact that they are used, understand why they are used, and study how to prevent their use to institute change. This article summarizes current information regarding the use of performance-enhancing drugs in young athletes and provides proven prevention strategies for instituting a program in your local schools.

  8. Performance of a flight qualified, thermoelectrically temperature controlled QCM sensor with power supply, thermal controller and signal processor

    NASA Technical Reports Server (NTRS)

    Wallace, D. A.

    1980-01-01

    A thermoelectrically temperature controlled quartz crystal microbalance (QCM) system was developed for the measurement of ion thrustor generated mercury contamination on spacecraft. Meaningful flux rate measurements dictated an accurately held sensing crystal temperature despite spacecraft surface temperature variations from -35 C to +60 C over the flight temperature range. An electronic control unit was developed with magentic amplifier transformer secondary power supply, thermal control electronics, crystal temperature analog conditioning and a multiplexed 16 bit frequency encoder.

  9. Improved Thermoelectric Devices: Advanced Semiconductor Materials for Thermoelectric Devices

    SciTech Connect

    2009-12-11

    Broad Funding Opportunity Announcement Project: Phononic Devices is working to recapture waste heat and convert it into usable electric power. To do this, the company is using thermoelectric devices, which are made from advanced semiconductor materials that convert heat into electricity or actively remove heat for refrigeration and cooling purposes. Thermoelectric devices resemble computer chips, and they manage heat by manipulating the direction of electrons at the nanoscale. These devices aren’t new, but they are currently too inefficient and expensive for widespread use. Phononic Devices is using a high-performance, cost-effective thermoelectric design that will improve the device’s efficiency and enable electronics manufacturers to more easily integrate them into their products.

  10. Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3}

    SciTech Connect

    Bhame, Shekhar D.; Noudem, Jacques G.; Pravarthana, Dhanapal; Prellier, Wilfrid

    2013-05-27

    Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications.

  11. Concerted Rattling in CsAg5 Te3 Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance.

    PubMed

    Lin, Hua; Tan, Gangjian; Shen, Jin-Ni; Hao, Shiqiang; Wu, Li-Ming; Calta, Nicholas; Malliakas, Christos; Wang, Si; Uher, Ctirad; Wolverton, Christopher; Kanatzidis, Mercouri G

    2016-09-12

    Thermoelectric (TE) materials convert heat energy directly into electricity, and introducing new materials with high conversion efficiency is a great challenge because of the rare combination of interdependent electrical and thermal transport properties required to be present in a single material. The TE efficiency is defined by the figure of merit ZT=(S(2) σ) T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity, and T is the absolute temperature. A new p-type thermoelectric material, CsAg5 Te3 , is presented that exhibits ultralow lattice thermal conductivity (ca. 0.18 Wm(-1)  K(-1) ) and a high figure of merit of about 1.5 at 727 K. The lattice thermal conductivity is the lowest among state-of-the-art thermoelectrics; it is attributed to a previously unrecognized phonon scattering mechanism that involves the concerted rattling of a group of Ag ions that strongly raises the Grüneisen parameters of the material.

  12. Photoresponse in arrays of thermoelectric nanowire junctions

    NASA Astrophysics Data System (ADS)

    Huber, T. E.; Scott, R.; Johnson, S.; Brower, T.; Belk, J. H.; Hunt, J. H.

    2013-07-01

    We report the first demonstration of optical detection by thermoelectric nanowire junctions. We employed devices composed of bismuth nanowire arrays which are capped with a transparent indium tin oxide electrode. The incident surface features very low optical reflectivity and enhanced light trapping. The unique attributes of the thermoelectric arrays are the combination of strong temporal and optical wavelength dependences of the photocurrent. Under infrared illumination, the signal can be completely described by thermoelectric effects considering cooling rates given by heat diffusion through the array. In addition, under visible illumination, we observe a photovoltaic response.

  13. Highly enhanced thermoelectric figure of merit of a β-SiC nanowire with a nanoelectromechanical measurement approach

    NASA Astrophysics Data System (ADS)

    Lee, Kyung-Min; Lee, Sang-Kwon; Choi, Tae-Youl

    2012-03-01

    We developed a reliable and highly reproducible way of fabricating a one-stop measurement platform for characterizing the thermoelectric properties of individual nanowires (NWs) using a focused ion beam and a nanomanipulator. 3- ω and 1- ω signals obtained by the four-point-probe method were used in measuring the thermal and electrical conductivities of the NW. Subsequently, the Seebeck coefficient was measured by using additional nanoelectrodes including a nanoheater. The thermal conductivity of the single β-SiC NW was obtained at 86.5±3.5 W/mK. The Seebeck coefficient was obtained to be -1.21 mV/K by using the same measurement platform. Thus, the dimensionless figure of merit, ZT= σS 2 T/ k, was measured to be ˜0.12. This value is around 120 times higher than the reported maximum value of bulk β-SiC.

  14. Exploring Resonance Levels and Nanostructuring in the PbTe-CdTe System and Enhancement of the Thermoelectric Figure of Merit

    SciTech Connect

    Ahn, Kyunghan; Han, Mi-Kyung; He, Jiaqing; Androulakis, John; Ballikaya, Sedat; Uher, Ctirad; Dravid, Vinayak; Kanatzidis, Mercouri G.

    2010-04-14

    We explored the effect of Cd substitution on the thermoelectric properties of PbTe in an effort to test a theoretical hypothesis that Cd atoms on Pb sites of the rock salt lattice can increase the Seebeck coefficient via the formation of a resonance level in the density of states near the Fermi energy. We find that the solubility of Cd is less than previously reported, and CdTe precipitation occurs to create nanostructuring, which strongly suppresses the lattice thermal conductivity. We present detailed characterization including structural and spectroscopic data, transmission electron microscopy, and thermoelectric transport properties of samples of PbTe-x% CdTe-0.055% PbI2 (x = 1, 3, 5, 7, 10), PbTe-1% CdTe-y% PbI2 (y = 0.03, 0.045, 0.055, 0.08, 0.1, 0.2), PbTe-5% CdTe-y% PbI2 (y = 0.01, 0.03, 0.055, 0.08), and PbTe-1% CdTe-z% Sb (z = 0.3, 0.5, 1, 1.5, 2, 3, 4, 5, 6). All samples follow the Pisarenko relationship, and no enhancement of the Seebeck coefficient was observed that could be attributed to a resonance level or a distortion in the density of states. A maximum ZT of 1.2 at 720 K was achieved for the PbTe-1% CdTe-0.055% PbI2 sample arising from a high power factor of 17 μW/(cm K2) and a very low lattice thermal conductivity of 0.5 W/(m K) at 720 K.

  15. Enhancement of Thermoelectric Behavior of La0.5Co4Sb12-x Te x Skutterudite Materials

    NASA Astrophysics Data System (ADS)

    Said, Suhana Mohd; Bashir, Mohamed Bashir Ali; Sabri, Mohd Faizul Mohd; Miyazaki, Yuzuru; Shnawah, Dhafer Abdul Ameer; Hakeem, Abbas Saeed; Shimada, Masanori; Bakare, Akolade Idris; Ghazali, Nik Nazri Nik; Elsheikh, Mohamed Hamid

    2017-03-01

    In this work, the effects of Te doping on the microstructure and thermoelectric properties of the partially filled skutterudite La0.5Co4Sb12 compounds have been examined. La0.5Co4Sb12-x Te x skutterudite compounds were synthesized by a combination of the mechanical alloying technique and spark plasma sintering processing, which resulted in partial substitution of Te atoms in Sb sites. The XRD results showed that all the Te-doped bulk samples were composed of a major phase of the Co4Sb12 skutterudite with a small amount of CoSb2 and Sb as the secondary phases. Thermoelectric measurements of the consolidated samples were examined in a temperature range of 300 K to 800 K (27 °C to 527 °C). With the La0.5Co4Sb11.7Te0.3 sample, the highest absolute Seebeck coefficient of 300 μV/K was obtained at 404 K (131 °C) and the lowest lattice thermal conductivity of 2 W/mK was achieved at 501 K (228 °C). Moreover, the minimum electrical resistivity of 19.7 μΩm was recorded at 501 K (228 °C) for La0.5Co4Sb11.5Te0.5 sample. The effect of the secondary phases was negligible for the electrical resistivity, and between 0.5 to 1.6 pct for the thermal conductivity. Thus, the highest figure of merit, ZT = 0.47, was obtained at 792 K (519 °C) for La0.5Co4Sb11.5Te0.5 sample due to a significant reduction in electrical resistivity and a moderate increase in the absolute Seebeck coefficient.

  16. Semiconducting glasses: A new class of thermoelectric materials?

    SciTech Connect

    Goncalves, A.P.; Vaney, J.B.; Lenoir, B.; Piarristeguy, A.; Pradel, A.; Monnier, J.; Ochin, P.; Godart, C.

    2012-09-15

    The deeper understanding of the factors that affect the dimensionless figure of merit, ZT, and the use of new synthetic methods has recently led to the development of novel systems with improved thermoelectric performances. Albeit up to now with ZT values lower than the conventional bulk materials, semiconducting glasses have also emerged as a new family of potential thermoelectric materials. This paper reviews the latest advances on semiconducting glasses for thermoelectric applications. Key examples of tellurium-based glasses, with high Seebeck coefficients, very low thermal conductivities and tunable electrical conductivities, are presented. ZT values as high as 0.2 were obtained at room temperature for several tellurium-based glasses with high copper concentrations, confirming chalcogenide semiconducting glasses as good candidates for high-performance thermoelectric materials. However, the temperature stability and electrical conductivity of the reported glasses are still not good enough for practical applications and further studies are still needed to enhance them. - Graphical abstract: Power factor as a function of the temperature for the Cu{sub 27.5}Ge{sub 2.5}Te{sub 70} and Cu{sub 30}As{sub 15}Te{sub 55} seniconducting glasses. Highlights: Black-Right-Pointing-Pointer A review of semiconducting glasses for thermoelectrics applications is presented. Black-Right-Pointing-Pointer The studied semiconducting glasses present very low thermal conductivities. Black-Right-Pointing-Pointer Composition can tune electrical conductivity and Seebeck coefficient. Black-Right-Pointing-Pointer ZT=0.2 is obtained at 300 K for different semiconducting glasses.

  17. Performance management system enhancement and maintenance

    NASA Technical Reports Server (NTRS)

    Cleaver, T. G.; Ahour, R.; Johnson, B. R.

    1984-01-01

    The research described in this report concludes a two-year effort to develop a Performance Management System (PMS) for the NCC computers. PMS provides semi-automated monthly reports to NASA and contractor management on the status and performance of the NCC computers in the TDRSS program. Throughout 1984, PMS was tested, debugged, extended, and enhanced. Regular PMS monthly reports were produced and distributed. PMS continues to operate at the NCC under control of Bendix Corp. personnel.

  18. Peripheral visual performance enhancement by neurofeedback training.

    PubMed

    Nan, Wenya; Wan, Feng; Lou, Chin Ian; Vai, Mang I; Rosa, Agostinho

    2013-12-01

    Peripheral visual performance is an important ability for everyone, and a positive inter-individual correlation is found between the peripheral visual performance and the alpha amplitude during the performance test. This study investigated the effect of alpha neurofeedback training on the peripheral visual performance. A neurofeedback group of 13 subjects finished 20 sessions of alpha enhancement feedback within 20 days. The peripheral visual performance was assessed by a new dynamic peripheral visual test on the first and last training day. The results revealed that the neurofeedback group showed significant enhancement of the peripheral visual performance as well as the relative alpha amplitude during the peripheral visual test. It was not the case in the non-neurofeedback control group, which performed the tests within the same time frame as the neurofeedback group but without any training sessions. These findings suggest that alpha neurofeedback training was effective in improving peripheral visual performance. To the best of our knowledge, this is the first study to show evidence for performance improvement in peripheral vision via alpha neurofeedback training.

  19. Practice Enhancement: Optimising Teaching Performance in Schools

    ERIC Educational Resources Information Center

    Perillo, Suzanne

    2006-01-01

    Purpose: The purpose of this paper is to show that in comparison to performance appraisal, "practice enhancement" is offered as a conceptual tool that can be used to develop strategies for reflecting on, communicating changes in and planning for excellence in teaching practice. Design/methodology/approach: The conceptual notion of…

  20. Thermoelectric effects in graphene nanostructures

    NASA Astrophysics Data System (ADS)

    Dollfus, Philippe; Nguyen, Viet Hung; Saint-Martin, Jérôme

    2015-04-01

    The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very useful in elucidating some details of the electronic band structure of graphene that cannot be probed by conductance measurements alone, due in particular to the ambipolar nature of this gapless material. For applications in thermoelectric energy conversion, graphene has two major disadvantages. It is gapless, which leads to a small Seebeck coefficient due to the opposite contributions of electrons and holes, and it is an excellent thermal conductor. The thermoelectric figure of merit ZT of a two-dimensional (2D) graphene sheet is thus very limited. However, many works have demonstrated recently that appropriate nanostructuring and bandgap engineering of graphene can concomitantly strongly reduce the lattice thermal conductance and enhance the Seebeck coefficient without dramatically degrading the electronic conductance. Hence, in various graphene nanostructures, ZT has been predicted to be high enough to make them attractive for energy conversion. In this article, we review the main results obtained experimentally and theoretically on the thermoelectric properties of graphene and its nanostructures, emphasizing the physical effects that govern these properties. Beyond pure graphene structures, we discuss also the thermoelectric properties of some hybrid graphene structures, as graphane, layered carbon allotropes such as graphynes and graphdiynes, and graphene/hexagonal boron nitride heterostructures which offer new opportunities. Finally, we briefly review the recent activities on other atomically thin 2D semiconductors with finite bandgap, i.e. dichalcogenides and phosphorene, which have attracted great attention for various kinds of applications, including thermoelectrics.

  1. Thermoelectric performance of n-type (PbTe)0.75(PbS)0.15(PbSe)0.1 composites.

    PubMed

    Yamini, Sima Aminorroaya; Wang, Heng; Ginting, Dianta; Mitchell, David R G; Dou, Shi Xue; Snyder, G Jeffrey

    2014-07-23

    Lead chalcogenides (PbQ, Q = Te, Se, S) have proved to possess high thermoelectric efficiency for both n-type and p-type compounds. Recent success in tuning of electronic band structure, including manipulating the band gap, multiple bands, or introducing resonant states, has led to a significant improvement in the thermoelectric performance of p-type lead chalcogenides compared to the n-type ones. Here, the n-type quaternary composites of (PbTe)0.75(PbS)0.15(PbSe)0.1 are studied to evaluate the effects of nanostructuring on lattice thermal conductivity, carrier mobility, and effective mass variation. The results are compared with the similar ternary systems of (PbTe)(1-x)(PbSe)x, (PbSe)(1-x)(PbS)x, and (PbS)(1-x)(PbTe)x. The reduction in the lattice thermal conductivity owing to phonon scattering at the defects and interfaces was found to be compensated by reduced carrier mobility. This results in a maximum figure of merit, zT, of ∼1.1 at 800 K similar to the performance of the single phase alloys of PbTe, PbSe, and (PbTe)(1-x)(PbSe)x.

  2. Component for thermoelectric generator

    DOEpatents

    Purdy, David L.

    1977-01-01

    In a thermoelectric generator, a component comprises a ceramic insulator, having over limited areas thereof, each area corresponding to a terminal end of thermoelectric wires, a coating of a first metal which adheres to the insulator, and an electrical thermoelectric junction including a second metal which wets said first metal and adheres to said terminal ends but does not wet said insulator, and a cloth composed of electrically insulating threads interlaced with thermoelectric wires.

  3. On the tuning of electrical and thermal transport in thermoelectrics: an integrated theory-experiment perspective

    NASA Astrophysics Data System (ADS)

    Yang, Jiong; Xi, Lili; Qiu, Wujie; Wu, Lihua; Shi, Xun; Chen, Lidong; Yang, Jihui; Zhang, Wenqing; Uher, Ctirad; Singh, David J.

    2016-02-01

    During the last two decades, we have witnessed great progress in research on thermoelectrics. There are two primary focuses. One is the fundamental understanding of electrical and thermal transport, enabled by the interplay of theory and experiment; the other is the substantial enhancement of the performance of various thermoelectric materials, through synergistic optimisation of those intercorrelated transport parameters. Here we review some of the successful strategies for tuning electrical and thermal transport. For electrical transport, we start from the classical but still very active strategy of tuning band degeneracy (or band convergence), then discuss the engineering of carrier scattering, and finally address the concept of conduction channels and conductive networks that emerge in complex thermoelectric materials. For thermal transport, we summarise the approaches for studying thermal transport based on phonon-phonon interactions valid for conventional solids, as well as some quantitative efforts for nanostructures. We also discuss the thermal transport in complex materials with chemical-bond hierarchy, in which a portion of the atoms (or subunits) are weakly bonded to the rest of the structure, leading to an intrinsic manifestation of part-crystalline part-liquid state at elevated temperatures. In this review, we provide a summary of achievements made in recent studies of thermoelectric transport properties, and demonstrate how they have led to improvements in thermoelectric performance by the integration of modern theory and experiment, and point out some challenges and possible directions.

  4. Enhanced performance for the manned maneuvering unit

    NASA Astrophysics Data System (ADS)

    Bingham, Paul E.

    We have all seen the Manned Maneuvering Unit (MMU) on television, in the newspaper, magazines and any number of other places. It is probably one of the most widely recognized articles ever put into orbit. This paper briefly describes the MMU. The description includes an overview of the controls and physical features and a discussion of the propulsion and electrical systems. Operational experience to date is briefly covered. The MMU was first used on STS 41-B for the first untethered space walk on February 7, 1984. Next usage was for the Solar Max mission on STS 41-C, followed by the retrieval of the Westar and Palapa communication satellites on mission STS 51-A in November, 1984. One of the "lessons learned" during these space operations was the need for enhanced performance by the MMU, and leads into a discussion of how that increased performance capability will be provided. Current work on a Propellant Tank Kit (PTK), which will provide enhanced performance, is shown. The PTK will provide sufficient propellant storage capability such that the MMU with PTK will have twice the previous delta velocity capability; i.e., double the MMU's maneuvering ability. Results of development testing in the NASA/JSC Weightless Environment Test Facility are included. Current status of PTK development is presented. This paper ends with a brief discussion of proposed space operations using the enhanced MMU performance in erecting space structures from the Space Shuttle, assembling and maintaining Space Station, rescue-transfer of astronauts and other space operations.

  5. Towards a high thermoelectric performance in rare-earth substituted SrTiO3: effects provided by strongly-reducing sintering conditions.

    PubMed

    Kovalevsky, A V; Yaremchenko, A A; Populoh, S; Thiel, P; Fagg, D P; Weidenkaff, A; Frade, J R

    2014-12-28

    Donor-substituted strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth substituted titanates Sr0.9R0.1TiO3±δ (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H2-90%N2, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350-1550 μW m(-1) K(-2) at 400-550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic SrTiO3-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics.

  6. Improved thermoelectric performance of Bi2Te3-xSex bulk materials produced by the preparation of high-pressure

    NASA Astrophysics Data System (ADS)

    Guo, Xin; Jia, Xiaopeng; Jiang, Yiping; Sun, Hairui; Zhang, Yuewen; Sun, Bing; Liu, Binwu; Ma, Hongan

    2014-05-01

    The purpose of this research is to study the effect of Se doping content on the improvement in thermoelectric properties of Bi2Te3-xSex bulk materials produced by high-pressure role. The Bi2Te3-xSex bulk materials can be successfully synthesized within 30 min due to high-pressure role, which significantly shortened the synthesis time. The typical textures of the reaction products exhibit abundant cracked crystal planes and special layer structures with increasing Se content, which can coordinate electrical and thermal transport in the Bi2Te3-xSex samples to achieve an optimal thermoelectric performance. As a result, a Bi2Te2.73Se0.27 bulk material obtained a maximum ZT value of 1.03 at 344 K. These results suggest that the low Se doping content with high-pressure can improve the figure of merit of Bi2Te3-xSex materials.

  7. Prediction of reliability on thermoelectric module through accelerated life test and Physics-of-failure

    NASA Astrophysics Data System (ADS)

    Choi, Hyoung-Seuk; Seo, Won-Seon; Choi, Duck-Kyun

    2011-09-01

    Thermoelectric cooling module (TEM) which is electric device has a mechanical stress because of temperature gradient in itself. It means that structure of TEM is vulnerable in an aspect of reliability but research on reliability of TEM was not performed a lot. Recently, the more the utilization of thermoelectric cooling devices grows, the more the needs for life prediction and improvement are increasing. In this paper, we investigated life distribution, shape parameter of the TEM through accelerated life test (ALT). And we discussed about how to enhance life of TEM through the Physics-of-failure. Experimental results of ALT showed that the thermoelectric cooling module follows the Weibull distribution, shape parameter of which is 3.6. The acceleration model is coffin Coffin-Manson and material constant is 1.8.

  8. High Temperature Thermoelectric Oxides Engineered At Multiple Length Scales For Energy Harvesting

    SciTech Connect

    Ohuchi, Fumio; Bordia, Rajendra

    2014-12-20

    Thermoelectric aspects of the processing parameters the n-type relaxors, including SrxBa1-xNb2O6 (SBN100x), Sr2Nb2O7 (SN) and SrBi2Nb2O9 (SBiN), were investigated. A solution combustion synthesis (SCS) route was devised to fabricate SBN, SN and SBiN nanoparticles with excellent phase purity. X-ray photoelectron spectroscopy (XPS) was used to deduce the local cation site occupancy, and detailed thermoelectric transport processes were investigated. Based on the identified behavior, effectiveness of pore formers on the thermoelectric performance was investigated with the goal of decreasing κ through enhanced phonon scattering while preserving the electron transport characteristics.

  9. Thermoelectric properties of WS2 nanotube networks

    NASA Astrophysics Data System (ADS)

    Kawai, Hideki; Sugahara, Mitsunari; Okada, Ryotaro; Maniwa, Yutaka; Yomogida, Yohei; Yanagi, Kazuhiro

    2017-01-01

    We report the thermoelectric properties of WS2 nanotube networks. By using electrolyte-gating techniques, we turned on a conducting channel in the macroscopic networks of WS2 nanotubes in both the hole and electron regions and evaluated the thermoelectric properties of the networks. We manipulated the P- and N-type Seebeck coefficients in the WS2 nanotube networks by changing the shifts in the gate voltage potentials. The power factor of the WS2 nanotube networks increased as the gate voltage shifted and exhibited a high thermoelectric performance approaching that of single-crystalline WS2 flakes.

  10. Encapsulated Thermoelectric Modules for Advanced Thermoelectric Systems

    NASA Astrophysics Data System (ADS)

    Kambe, Mitsuru; Jinushi, Takahiro; Ishijima, Zenzo

    2014-06-01

    An encapsulated thermoelectric (TE) module consists of a vacuum-tight stainless-steel container in which an SiGe or BiTe TE module is encapsulated. This construction enables maximum performance and durability because: the thermal expansion mismatch between the hot and cold sides of the container can be accommodated by a sliding sheet in the container; the TE module inside is always kept in a vacuum environment, therefore no oxidation can occur; and the pressure difference between the inside and outside of the container reduces thermal contact resistance inside the container. Our encapsulated SiGe module features higher operating temperature—up to 650°C for both hot and cold sides. Other high-temperature modules and conventional BiTe modules, including both-sides and one-side skeleton types, have been encapsulated. Several variants of the encapsulated module are available. Encapsulated thermoelectric modules with integrated coolers contain cooling panels through which water can pass. If the module hot side is heated by a radiating heat source (radiation coupling) or convection of a hot gas or fluid (convection coupling), no pressing force on the module is necessary. It therefore features minimum contact resistance with the cooling duct, because no pressure is applied, maximum TE power, and minimum installation cost. Another, larger, variant is a quadruple flexible container in which four modules (each of maximum size 40 mm × 40 mm) are encapsulated. These encapsulated modules were used in a powder metallurgy furnace and were in use for more than 3000 h. Application to cryogenic temperatures simulating the liquid nitrogen gas vaporizer has been also attempted.

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

    SciTech Connect

    Cho, Jung Y; Ye, Zuxin; Tessema, Misle; Salvador, James R.; Waldo, Richard; Yang, Jiong; Zhang, Weiqing; Yang, Jihui; Cai, Wei; Wang, Hsin

    2013-01-01

    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.

  12. Thermoelectricity in fullerene-metal heterojunctions.

    PubMed

    Yee, Shannon K; Malen, Jonathan A; Majumdar, Arun; Segalman, Rachel A

    2011-10-12

    Thermoelectricty in heterojunctions, where a single-molecule is trapped between metal electrodes, has been used to understand transport properties at organic-inorganic interfaces. (1) The transport in these systems is highly dependent on the energy level alignment between the molecular orbitals and the Fermi level (or work function) of the metal contacts. To date, the majority of single-molecule measurements have focused on simple small molecules where transport is dominated through the highest occupied molecular orbital. (2, 3) In these systems, energy level alignment is limited by the absence of electrode materials with low Fermi levels (i.e., large work functions). Alternatively, more controllable alignment between molecular orbitals and the Fermi level can be achieved with molecules whose transport is dominated by the lowest unoccupied molecular orbital (LUMO) because of readily available metals with lower work functions. Herein, we report molecular junction thermoelectric measurements of fullerene molecules (i.e., C(60), PCBM, and C(70)) trapped between metallic electrodes (i.e., Pt, Au, Ag). Fullerene junctions demonstrate the first strongly n-type molecular thermopower corresponding to transport through the LUMO, and the highest measured magnitude of molecular thermopower to date. While the electronic conductance of fullerenes is highly variable, due to fullerene's variable bonding geometries with the electrodes, the thermopower shows predictable trends based on the alignment of the LUMO with the work function of the electrodes. Both the magnitude and trend of the thermopower suggest that heterostructuring organic and inorganic materials at the nanoscale can further enhance thermoelectric performance, therein providing a new pathway for designing thermoelectric materials.

  13. Thermoelectricity in atom-sized junctions at room temperatures

    PubMed Central

    Tsutsui, Makusu; Morikawa, Takanori; Arima, Akihide; Taniguchi, Masateru

    2013-01-01

    Atomic and molecular junctions are an emerging class of thermoelectric materials that exploit quantum confinement effects to obtain an enhanced figure of merit. An important feature in such nanoscale systems is that the electron and heat transport become highly sensitive to the atomic configurations. Here we report the characterization of geometry-sensitive thermoelectricity in atom-sized junctions at room temperatures. We measured the electrical conductance and thermoelectric power of gold nanocontacts simultaneously down to the single atom size. We found junction conductance dependent thermoelectric voltage oscillations with period 2e2/h. We also observed quantum suppression of thermovoltage fluctuations in fully-transparent contacts. These quantum confinement effects appeared only statistically due to the geometry-sensitive nature of thermoelectricity in the atom-sized junctions. The present method can be applied to various nanomaterials including single-molecules or nanoparticles and thus may be used as a useful platform for developing low-dimensional thermoelectric building blocks. PMID:24270238

  14. Thermoelectricity in atom-sized junctions at room temperatures.

    PubMed

    Tsutsui, Makusu; Morikawa, Takanori; Arima, Akihide; Taniguchi, Masateru

    2013-11-25

    Atomic and molecular junctions are an emerging class of thermoelectric materials that exploit quantum confinement effects to obtain an enhanced figure of merit. An important feature in such nanoscale systems is that the electron and heat transport become highly sensitive to the atomic configurations. Here we report the characterization of geometry-sensitive thermoelectricity in atom-sized junctions at room temperatures. We measured the electrical conductance and thermoelectric power of gold nanocontacts simultaneously down to the single atom size. We found junction conductance dependent thermoelectric voltage oscillations with period 2e(2)/h. We also observed quantum suppression of thermovoltage fluctuations in fully-transparent contacts. These quantum confinement effects appeared only statistically due to the geometry-sensitive nature of thermoelectricity in the atom-sized junctions. The present method can be applied to various nanomaterials including single-molecules or nanoparticles and thus may be used as a useful platform for developing low-dimensional thermoelectric building blocks.

  15. Direct evidence of strong local ferroelectric ordering in a thermoelectric semiconductor

    SciTech Connect

    Aggarwal, Leena; Sekhon, Jagmeet S.; Arora, Ashima; Sheet, Goutam; Guin, Satya N.; Negi, Devendra S.; Datta, Ranjan; Biswas, Kanishka

    2014-09-15

    It is thought that the proposed new family of multi-functional materials, namely, the ferroelectric thermoelectrics may exhibit enhanced functionalities due to the coupling of the thermoelectric parameters with ferroelectric polarization in solids. Therefore, the ferroelectric thermoelectrics are expected to be of immense technological and fundamental significance. As a first step towards this direction, it is most important to identify the existing high performance thermoelectric materials exhibiting ferroelectricity. Herein, through the direct measurement of local polarization switching, we show that the recently discovered thermoelectric semiconductor AgSbSe{sub 2} has local ferroelectric ordering. Using piezo-response force microscopy, we demonstrate the existence of nanometer scale ferroelectric domains that can be switched by external electric field. These observations are intriguing as AgSbSe{sub 2} crystalizes in cubic rock-salt structure with centro-symmetric space group (Fm–3m), and therefore, no ferroelectricity is expected. However, from high resolution transmission electron microscopy measurement, we found the evidence of local superstructure formation which, we believe, leads to local distortion of the centro-symmetric arrangement in AgSbSe{sub 2} and gives rise to the observed ferroelectricity. Stereochemically active 5S{sup 2} lone-pair of Sb may also give rise to local structural distortion thereby creating ferroelectricity in AgSbSe{sub 2}.

  16. Facile Preparation of Highly Conductive Metal Oxides by Self-Combustion for Solution-Processed Thermoelectric Generators.

    PubMed

    Kang, Young Hun; Jang, Kwang-Suk; Lee, Changjin; Cho, Song Yun

    2016-03-02

    Highly conductive indium zinc oxide (IZO) thin films were successfully fabricated via a self-combustion reaction for application in solution-processed thermoelectric devices. Self-combustion efficiently facilitates the conversion of soluble precursors into metal oxides by lowering the required annealing temperature of oxide films, which leads to considerable enhancement of the electrical conductivity of IZO thin films. Such enhanced electrical conductivity induced by exothermic heat from a combustion reaction consequently yields high performance IZO thermoelectric films. In addition, the effect of the composition ratio of In to Zn precursors on the electrical and thermoelectric properties of the IZO thin films was investigated. IZO thin films with a composition ratio of In:Zn = 6:2 at the low annealing temperature of 350 °C showed an enhanced electrical conductivity, Seebeck coefficient, and power factor of 327 S cm(-1), 50.6 μV K(-1), and 83.8 μW m(-1) K(-2), respectively. Moreover, the IZO thin film prepared at an even lower temperature of 300 °C retained a large power factor of 78.7 μW m(-1) K(-2) with an electrical conductivity of 168 S cm(-1). Using the combustive IZO precursor, a thermoelectric generator consisting of 15 legs was fabricated by a printing process. The thermoelectric array generated a thermoelectric voltage of 4.95 mV at a low temperature difference (5 °C). We suggest that the highly conductive IZO thin films by self-combustion may be utilized for fabricating n-type flexible printed thermoelectric devices.

  17. Thermoelectric characterization of individual bismuth selenide topological insulator nanoribbons

    NASA Astrophysics Data System (ADS)

    Tang, Hao; Wang, Xiaomeng; Xiong, Yucheng; Zhao, Yang; Zhang, Yin; Zhang, Yan; Yang, Juekuan; Xu, Dongyan

    2015-04-01

    Bismuth selenide (Bi2Se3) nanoribbons have attracted tremendous research interest recently to study the properties of topologically protected surface states that enable new opportunities to enhance the thermoelectric performance. However, the thermoelectric characterization of individual Bi2Se3 nanoribbons is rare due to the technological challenges in the measurements. One challenge is to ensure good contacts between the nanoribbon and electrodes in order to determine the thermal and electrical properties accurately. In this work, we report the thermoelectric characterization of individual Bi2Se3 nanoribbons via a suspended microdevice method. Through careful measurements, we have demonstrated that contact thermal resistance is negligible after the electron-beam-induced deposition (EBID) of platinum/carbon (Pt/C) composites at the contacts between the nanoribbon and electrodes. It is shown that the thermal conductivity of the Bi2Se3 nanoribbons is less than 50% of the bulk value over the whole measurement temperature range, which can be attributed to enhanced phonon boundary scattering. Our results indicate that intrinsic Bi2Se3 nanoribbons prepared in this work are highly doped n-type semiconductors, and therefore the Fermi level should be in the conduction band and no topological transport behavior can be observed in the intrinsic system.

  18. Heat Management in Thermoelectric Power Generators

    PubMed Central

    Zebarjadi, M.

    2016-01-01

    Thermoelectric power generators are used to convert heat into electricity. Like any other heat engine, the performance of a thermoelectric generator increases as the temperature difference on the sides increases. It is generally assumed that as more heat is forced through the thermoelectric legs, their performance increases. Therefore, insulations are typically used to minimize the heat losses and to confine the heat transport through the thermoelectric legs. In this paper we show that to some extend it is beneficial to purposely open heat loss channels in order to establish a larger temperature gradient and therefore to increase the overall efficiency and achieve larger electric power output. We define a modified Biot number (Bi) as an indicator of requirements for sidewall insulation. We show cooling from sidewalls increases the efficiency for Bi values less than one, and decreases the efficiency for Bi values larger than one. PMID:27033717

  19. Heat Management in Thermoelectric Power Generators

    NASA Astrophysics Data System (ADS)

    Zebarjadi, M.

    2016-04-01

    Thermoelectric power generators are used to convert heat into electricity. Like any other heat engine, the performance of a thermoelectric generator increases as the temperature difference on the sides increases. It is generally assumed that as more heat is forced through the thermoelectric legs, their performance increases. Therefore, insulations are typically used to minimize the heat losses and to confine the heat transport through the thermoelectric legs. In this paper we show that to some extend it is beneficial to purposely open heat loss channels in order to establish a larger temperature gradient and therefore to increase the overall efficiency and achieve larger electric power output. We define a modified Biot number (Bi) as an indicator of requirements for sidewall insulation. We show cooling from sidewalls increases the efficiency for Bi values less than one, and decreases the efficiency for Bi values larger than one.

  20. Enhanced thermoelectric properties and development of nanotwins in Na-doped Bi0.5Sb1.5Te3 alloy

    NASA Astrophysics Data System (ADS)

    Kim, Hyun; Lee, Jae Ki; Park, Su-Dong; Ryu, Byungki; Lee, Ji Eun; Kim, Bong-Seo; Min, Bok-Ki; Joo, Sung-Jae; Lee, Hee-Woong; Cho, Young-Rae

    2016-03-01

    We found that Na is a good source to develop twin structures in the Bi-Te system, such as Ag as noted in a previous study. The twin boundaries had a considerable influence on reductions of the lattice thermal conductivity due to phonon scattering by the nano-ordered layers and on reductions of the electrical resistivity owing to the defects generated by the substitution of Na into the cation sites. Here, we report the enhanced thermoelectric properties of a Na-doped p-type Bi0.5Sb1.5Te3 alloy. Measurements show that the electrical resistivity and the Seebeck coefficient decrease with Na doping due to an increase in the free carrier (hole) concentration and that the lattice thermal conductivity decreases with Na doping. The achieved maximum ZT value was 1.20 at 423 K, which is approximately 20% higher than that of Bi0.5Sb1.5Te3 under the same fabrication conditions. These results were achievable by controlling the morphology of the twin structure and the carrier concentration by means of Na doping. [Figure not available: see fulltext.

  1. Dynamic thermoelectricity in uniform bipolar semiconductor

    NASA Astrophysics Data System (ADS)

    Volovichev, I. N.

    2016-07-01

    The theory of the dynamic thermoelectric effect has been developed. The effect lies in an electric current flowing in a closed circuit that consists of a uniform bipolar semiconductor, in which a non-uniform temperature distribution in the form of the traveling wave is created. The calculations are performed for the one-dimensional model in the quasi-neutrality approximation. It was shown that the direct thermoelectric current prevails, despite the periodicity of the thermal excitation, the circuit homogeneity and the lack of rectifier properties of the semiconductor system. Several physical reasons underlining the dynamic thermoelectric effect are found. One of them is similar to the Dember photoelectric effect, its contribution to the current flowing is determined by the difference in the electron and hole mobilities, and is completely independent of the carrier Seebeck coefficients. The dependence of the thermoelectric short circuit current magnitude on the semiconductor parameters, as well as on the temperature wave amplitude, length and velocity is studied. It is shown that the magnitude of the thermoelectric current is proportional to the square of the temperature wave amplitude. The dependence of the thermoelectric short circuit current on the temperature wave length and velocity is the nonmonotonic function. The optimum values for the temperature wave length and velocity, at which the dynamic thermoelectric effect is the greatest, have been deduced. It is found that the thermoelectric short circuit current changes its direction with decreasing the temperature wave length under certain conditions. The prospects for the possible applications of the dynamic thermoelectric effect are also discussed.

  2. Anomalous enhancement of the thermoelectric power in gallium-doped p-(Bi{sub 1-x}Sb{sub x}){sub 2}Te{sub 3} single crystals

    SciTech Connect

    Kulbachinskii, V. A. Kytin, V. G.; Tarasov, P. M.

    2010-04-15

    The effect of gallium on the temperature dependences (5 K {<=} T {<=} 300 K) of Seebeck coefficient {alpha}, electrical conductivity {sigma}, thermal conductivity k, and thermoelectric efficiency Z of mixed p-(Bi{sub 0.5}Sb{sub 0.5}){sub 2}Te{sub 3} semiconductor single crystals is studied. The hole concentration decreases upon gallium doping; that is, gallium causes a donor effect. The Seebeck coefficient increases anomalously, i.e., much higher than it should be at the detected decrease in the hole concentration. This leads to an enhancement of the thermoelectric power. The observed changes in the Seebeck coefficient indicate a noticeable gallium-induced change in the density of states in the valence band.

  3. Development of a High Efficiency Thermoelectric Unicouple for Power Generation Applications

    NASA Technical Reports Server (NTRS)

    Caillat, T.; Fleurial, J-P.; Synder, G.; Zoltan, A.; Zoltan, D.; Borshchevsky, A.

    1999-01-01

    To achieve high thermal-to-electric energy conversion efficiency, it is desirable to operate thermoelectric generator devices over large temperature gradients and also to maximize the performance of the thermoelectric materials used to build the devices.

  4. Enhancing neural-network performance via assortativity

    SciTech Connect

    Franciscis, Sebastiano de; Johnson, Samuel; Torres, Joaquin J.

    2011-03-15

    The performance of attractor neural networks has been shown to depend crucially on the heterogeneity of the underlying topology. We take this analysis a step further by examining the effect of degree-degree correlations - assortativity - on neural-network behavior. We make use of a method recently put forward for studying correlated networks and dynamics thereon, both analytically and computationally, which is independent of how the topology may have evolved. We show how the robustness to noise is greatly enhanced in assortative (positively correlated) neural networks, especially if it is the hub neurons that store the information.

  5. Enhancing neural-network performance via assortativity.

    PubMed

    de Franciscis, Sebastiano; Johnson, Samuel; Torres, Joaquín J

    2011-03-01

    The performance of attractor neural networks has been shown to depend crucially on the heterogeneity of the underlying topology. We take this analysis a step further by examining the effect of degree-degree correlations--assortativity--on neural-network behavior. We make use of a method recently put forward for studying correlated networks and dynamics thereon, both analytically and computationally, which is independent of how the topology may have evolved. We show how the robustness to noise is greatly enhanced in assortative (positively correlated) neural networks, especially if it is the hub neurons that store the information.

  6. Manipulation of the crystal structure defects: An alternative route to the reduction in lattice thermal conductivity and improvement in thermoelectric performance of CuGaTe2

    NASA Astrophysics Data System (ADS)

    Wu, Wenchang; Li, Yapeng; Du, Zhengliang; Meng, Qingsen; Sun, Zheng; Ren, Wei; Cui, Jiaolin

    2013-07-01

    Here, we present the manipulation of the crystal structure defects: an alternative route to reduce the lattice thermal conductivity (κL) on an atomic scale and improve the thermoelectric performance of CuGaTe2. This semiconductor with defects, represented by anion position displacement (u) and tetragonal deformation (η), generally gives low κL values when u and η distinctly deviate from 0.25 and 1 in the ideal zinc-blende structure, respectively. However, this semiconductor will show high Seebeck coefficients and low electrical conductivities when u and η are close to 0.25 and 1, respectively, due to the electrical inactivity caused by an attractive interaction between donor-acceptor defect pairs (GaCu2+ + 2VCu-).

  7. Marine Thermoelectric Devices and Installations,

    DTIC Science & Technology

    thermoelectric devices and units as marine sources of electric power, Prospects for the use of thermoelectric generators in main ship propulsion plants, Electric propulsion complexes for marine thermoelectric plants).

  8. Thermoelectric materials having porosity

    DOEpatents

    Heremans, Joseph P.; Jaworski, Christopher M.; Jovovic, Vladimir; Harris, Fred

    2014-08-05

    A thermoelectric material and a method of making a thermoelectric material are provided. In certain embodiments, the thermoelectric material comprises at least 10 volume percent porosity. In some embodiments, the thermoelectric material has a zT greater than about 1.2 at a temperature of about 375 K. In some embodiments, the thermoelectric material comprises a topological thermoelectric material. In some embodiments, the thermoelectric material comprises a general composition of (Bi.sub.1-xSb.sub.x).sub.u(Te.sub.1-ySe.sub.y).sub.w, wherein 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 1.8.ltoreq.u.ltoreq.2.2, 2.8.ltoreq.w.ltoreq.3.2. In further embodiments, the thermoelectric material includes a compound having at least one group IV element and at least one group VI element. In certain embodiments, the method includes providing a powder comprising a thermoelectric composition, pressing the powder, and sintering the powder to form the thermoelectric material.

  9. The 5-kwe reactor thermoelectric system summary

    NASA Technical Reports Server (NTRS)

    Vanosdol, J. H. (Editor)

    1973-01-01

    Design of the 5-kwe reactor thermoelectric system was initiated in February 1972 and extended through the conceptual design phase into the preliminary design phase. Design effort was terminated in January, 1973. This report documents the system and component requirements, design approaches, and performance and design characteristics for the 5-kwe system. Included is summary information on the reactor, radiation shields, power conversion systems, thermoelectric pump, radiator/structure, liquid metal components, and the control system.

  10. Computational prediction of high thermoelectric performance in p-type half-Heusler compounds with low band effective mass.

    PubMed

    Fang, Teng; Zheng, Shuqi; Zhou, Tian; Yan, Lei; Zhang, Peng

    2017-02-08

    Half-Heusler (HH) compounds are important high temperature thermoelectric (TE) materials and have gained ever-increasing popularity. In recent years, p-type FeNbSb-based heavy-band HH compounds have attracted considerable attention with the record-high zT value of 1.5. Here, we use first-principles based methods to predict a very high zT value of 1.54 at 1200 K in p-type RuTaSb alloys. The high band degeneracy and low band effective mass contribute to a high power factor. Although the electrical thermal conductivity is high due to the high carrier mobility and hence electrical conductivity, the total thermal conductivity is moderate because of the low lattice thermal conductivity. The predicted high zT demonstrates that the p-type RuTaSb HH alloys are promising as TE materials for high temperature power generation.

  11. Novel Transition Metal Compounds with Promising Thermoelectric Properties

    NASA Technical Reports Server (NTRS)

    Caillat, T.; Borshchevsky, A.; Fleurial, J. -P.

    1993-01-01

    Progress in the search for new high temperature thermoelectric materials at the Jet Propulsion Laboratory is reviewed. Novel transition metal compounds were selected as potential new high performance thermoelectric materials and criteria of selection are presented and discussed. Samples of these new compounds were prepared at JPL by a variety of techniques. Encouraging experimental results obtained on several of these compounds are reported and show that they have the potential to be the next generation of thermoelectric materials.

  12. Magnetoelectric interaction and transport behaviours in magnetic nanocomposite thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Zhao, Wenyu; Liu, Zhiyuan; Wei, Ping; Zhang, Qingjie; Zhu, Wanting; Su, Xianli; Tang, Xinfeng; Yang, Jihui; Liu, Yong; Shi, Jing; Chao, Yimin; Lin, Siqi; Pei, Yanzhong

    2017-01-01

    How to suppress the performance deterioration of thermoelectric materials in the intrinsic excitation region remains a key challenge. The magnetic transition of permanent magnet nanoparticles from ferromagnetism to paramagnetism provides an effective approach to finding the solution to this challenge. Here, we have designed and prepared magnetic nanocomposite thermoelectric materials consisting of BaFe12O19 nanoparticles and Ba0.3In0.3Co4Sb12 matrix. It was found that the electrical transport behaviours of the nanocomposites are controlled by the magnetic transition of BaFe12O19 nanoparticles from ferromagnetism to paramagnetism. BaFe12O19 nanoparticles trap electrons below the Curie temperature (TC) and release the trapped electrons above the TC, playing an 'electron repository' role in maintaining high figure of merit ZT. BaFe12O19 nanoparticles produce two types of magnetoelectric effect—electron spiral motion and magnon-drag thermopower—as well as enhancing phonon scattering. Our work demonstrates that the performance deterioration of thermoelectric materials in the intrinsic excitation region can be suppressed through the magnetic transition of permanent magnet nanoparticles.

  13. Electrodeposition of bismuth:tellurium nanowire arrays into porous alumina templates for thermoelectric applications

    NASA Astrophysics Data System (ADS)

    Trahey, Lynn

    Bismuth telluride is a well-known thermoelectric material for refrigeration applications. Thermoelectrics possess several advantages over conventional refrigeration and power generation devices, yet are not widely-used due to low efficiencies. It has been predicted and shown experimentally that the efficiency of thermoelectric devices increases when the semiconducting materials have reduced dimensions. Therefore, the aim of this research was to show enhanced thermoelectric efficiency in one-dimensional nanowires. The nanowires were synthesized via electrochemical deposition into porous alumina templates. Electrodeposition is a versatile technique that ensures electrical continuity in the deposited material. The nanowire templates, porous alumina, were made by the double anodization of high-purity aluminum foil in oxalic acid solutions. This technique produces parallel, hexagonally packed, and nanometer-range diameter pores that can reach high aspect ratios (greater than 2000:1). The main anodization variables (electrolyte concentration, applied potential, 2nd anodization time, and temperature) were studied systematically in order to deconvolute their effects on the resulting pores and to obtain high aspect ratio pores. The porous alumina is of great importance because the pore dimensions determine the dimensions of the electrodeposited nanowires, which influence the thermoelectric performance of the nanowire arrays. Nanowire arrays were characterized in several ways. Powder X-ray diffraction was used to assess crystallinity and preferred orientation of the nanowires, revealing that the nanowires are highly crystalline and grow with strong preferred orientation such that the material is suited for optimal thermoelectric performance. Scanning electron microscopy was used to evaluate the nanowire nucleation percentage and growth-front uniformity, both of which were enhanced by pulsed-potential electrodeposition. Compositional analysis via electron microprobe indicates

  14. Thermoelectric Materials at 300k.

    DTIC Science & Technology

    Thermoelectric power generation, *Peltier effect, *Semiconductors, Thermoelectricity, Seebeck effect , Tellurides, Selenides, Antimonides, Thermal conductivity, Air conditioning equipment, Bismuth compounds, Band theory of solids

  15. 300 WATT PORTABLE THERMOELECTRIC GENERATOR.

    DTIC Science & Technology

    GENERATORS , *ELECTRIC POWER PRODUCTION, POWER SUPPLIES, THERMOELECTRICITY, THERMOELECTRICITY, PORTABLE EQUIPMENT, THERMOCOUPLES, ENERGY CONVERSION, LIFE EXPECTANCY(SERVICE LIFE), HEAT TRANSFER, VOLTAGE REGULATORS.

  16. Excess vibrational modes and high thermoelectric performance of the quenched and slow-cooled two-phase alloy Cu0.2Ag2.8SbSeTe2.

    PubMed

    Drymiotis, F R; Lindsey, S; Capps, J; Lashley, J C; Rhodes, D; Zhang, Q R; Nucklos, C; Drye, T B

    2011-04-06

    In this article we examine the low-temperature specific heat of slow-cooled Cu(0.2)Ag(2.8)SbSeTe(2) and the thermoelectric performance of quenched samples. We find that the low-temperature specific heat is dominated by two Einstein terms of approximate energies of 2.5 and 5 meV. The specific-heat behavior is consistent with the amorphous low-temperature thermal conductivity behavior and validates the glassy nature of the structure. We performed the synthesis of quenched samples in an attempt to eliminate the presence of micro-cracks, whose existence presumably enhances electronic scattering. We find that quenching eliminates the presence of micro-cracks but does not result in an improvement of the figure of merit. Specifically, the highest ZT obtained in the quenched samples (ZT = 1.5), though very competitive, is still significantly less that the ZT obtained in the slow-cooled samples (ZT = 1.75).

  17. Reach preparation enhances visual performance and appearance.

    PubMed

    Rolfs, Martin; Lawrence, Bonnie M; Carrasco, Marisa

    2013-10-19

    We investigated the impact of the preparation of reach movements on visual perception by simultaneously quantifying both an objective measure of visual sensitivity and the subjective experience of apparent contrast. Using a two-by-two alternative forced choice task, observers compared the orientation (clockwise or counterclockwise) and the contrast (higher or lower) of a Standard Gabor and a Test Gabor, the latter of which was presented during reach preparation, at the reach target location or the opposite location. Discrimination performance was better overall at the reach target than at the opposite location. Perceived contrast increased continuously at the target relative to the opposite location during reach preparation, that is, after the onset of the cue indicating the reach target. The finding that performance and appearance do not evolve in parallel during reach preparation points to a distinction with saccade preparation, for which we have shown previously there is a parallel temporal evolution of performance and appearance. Yet akin to saccade preparation, this study reveals that overall reach preparation enhances both visual performance and appearance.

  18. Electrostatic control of thermoelectricity in molecular junctions.

    PubMed

    Kim, Youngsang; Jeong, Wonho; Kim, Kyeongtae; Lee, Woochul; Reddy, Pramod

    2014-11-01

    Molecular junctions hold significant promise for efficient and high-power-output thermoelectric energy conversion. Recent experiments have probed the thermoelectric properties of molecular junctions. However, electrostatic control of thermoelectric properties via a gate electrode has not been possible due to technical challenges in creating temperature differentials in three-terminal devices. Here, we show that extremely large temperature gradients (exceeding 1 × 10(9) K m(-1)) can be established in nanoscale gaps bridged by molecules, while simultaneously controlling their electronic structure via a gate electrode. Using this platform, we study prototypical Au-biphenyl-4,4'-dithiol-Au and Au-fullerene-Au junctions to demonstrate that the Seebeck coefficient and the electrical conductance of molecular junctions can be simultaneously increased by electrostatic control. Moreover, from our studies of fullerene junctions, we show that thermoelectric properties can be significantly enhanced when the dominant transport orbital is located close to the chemical potential (Fermi level) of the electrodes. These results illustrate the intimate relationship between the thermoelectric properties and charge transmission characteristics of molecular junctions and should enable systematic exploration of the recent computational predictions that promise extremely efficient thermoelectric energy conversion in molecular junctions.

  19. Thermoelectric Outer Planets Spacecraft (TOPS)

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The research and advanced development work is reported on a ballistic-mode, outer planet spacecraft using radioisotope thermoelectric generator (RTG) power. The Thermoelectric Outer Planet Spacecraft (TOPS) project was established to provide the advanced systems technology that would allow the realistic estimates of performance, cost, reliability, and scheduling that are required for an actual flight mission. A system design of the complete RTG-powered outer planet spacecraft was made; major technical innovations of certain hardware elements were designed, developed, and tested; and reliability and quality assurance concepts were developed for long-life requirements. At the conclusion of its active phase, the TOPS Project reached its principal objectives: a development and experience base was established for project definition, and for estimating cost, performance, and reliability; an understanding of system and subsystem capabilities for successful outer planets missions was achieved. The system design answered long-life requirements with massive redundancy, controlled by on-board analysis of spacecraft performance data.

  20. 100 WATT THERMOELECTRIC GENERATOR.

    DTIC Science & Technology

    GENERATORS , *ENERGY CONVERSION, HEAT EXCHANGERS, THERMOELECTRICITY, THERMOCOUPLES, BLOWERS, MODULES(ELECTRONICS), SILICON ALLOYS, GERMANIUM ALLOYS, COMBUSTION, GASOLINE, VAPORIZATION, FUELS, LEAD COMPOUNDS.

  1. Symmetry-enhanced performance of dynamical decoupling

    SciTech Connect

    Pasini, S.; Uhrig, G. S.

    2011-10-15

    We consider a system with general decoherence and a quadratic dynamical decoupling sequence (QDD) for the coherence control of a qubit coupled to a bath of spins. We investigate the influence of the geometry and of the initial conditions of the bath on the performance of the sequence. The overall performance is quantified by a distance norm d. It is expected that d scales with {tau}, the total duration of the sequence, as {tau}{sup min{l_brace}N{sub x},N{sub z}{r_brace}+1}, where N{sub x} and N{sub z} are the number of pulses of the outer and of the inner sequence, respectively. We show both numerically and analytically that the state of the bath can boost the performance of QDD under certain conditions: The scaling of QDD for a given number of pulses can be enhanced by a factor of 2 if the bath is prepared in a highly symmetric state and if the system Hamiltonian is SU(2) invariant.

  2. Enhancement of Perfluoropolyether Boundary Lubrication Performance

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Ajayi, O. O.; Wedeven, L. D.

    1996-01-01

    A ball bearing simulator operating under starved conditions was used to perform screening tests to evaluate the boundary lubrication performance of a branched perfluoropolyether (PFPE), K-143 AB. Several approaches to enhance boundary lubrication were studied. These included: (1) soluble boundary additives, (2) bearing surface modifications, (3) 'run-in' surface films, and (4) ceramic bearing components. In addition, results were compared with two non-perfluorinated liquid lubricant formulations. Based on these tests, the following tentative conclusions can be made: (1) Substantial improvements in boundary lubrication performance were observed with a beta-diketone boundary additive and a tricresyl phosphate (TCP) liquid surface pretreatment, (2) the use of rough Si3N4 balls (R(sub a) = 40 micro-inch) also provided increases in test duration, but with concomitant abrasive wear, (3) moderate improvements were seen with two boundary additives (a phosphine and a phosphatriazine) and a neat (100%) fluid (a carboxylic acid terminated PFPE); and small improvements with surface pretreatments with synthetic hydrocarbons, a polytetrafluoroethylene (PTFE) coating, and TiC coated 440 C and smooth Si3N4 balls (R(sub a) = 1 micro-inch), and (4) two non-PFPE lubricant formulations (a polyalphaolefin (PAO) and synthetic hydrocarbon) yielded substantial improvements.

  3. Enhanced piezoelectric performance from carbon fluoropolymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Baur, Cary; DiMaio, Jeffrey R.; McAllister, Elliot; Hossini, Reza; Wagener, Earl; Ballato, John; Priya, Shashank; Ballato, Arthur; Smith, Dennis W.

    2012-12-01

    The piezoelectric performance of polyvinylidene fluoride (PVDF) is shown to double through the controlled incorporation of carbon nanomaterial. Specifically, PVDF composites containing carbon fullerenes (C60) and single-walled carbon nanotubes (SWNT) are fabricated over a range of compositions and optimized for their Young's modulus, dielectric constant, and d31 piezoelectric coefficient. Thermally stimulated current measurements show a large increase in internal charge and polarization in the composites over pure PVDF. The electromechanical coupling coefficients (k31) at optimal loading levels are found to be 1.84 and 2 times greater than pure PVDF for the PVDF-C60 and PVDF-SWNT composites, respectively. Such property-enhanced nanocomposites could have significant benefit to electromechanical systems employed for structural sensing, energy scavenging, sonar, and biomedical imaging.

  4. Understanding performance-enhancing drug use.

    PubMed

    Wang, David

    2012-09-01

    Performance-enhancing drug use is a prevalent problem in sports. It is a problem that has captured the world's attention as the media highlights story after story of athletes who have transformed their bodies over a short period of time, those who have simply defied the aging process in an attempt to prolong a career and those whose careers have been tarnished because of drug use. The baseball investigations and the Mitchell Report of 2007 opened our eyes and gave us a glimpse of a secretive underground world. This "world" is much more intelligent and sophisticated than it is given credit for. It is the goal of this article to increase the awareness of the medical provider about the types of steroids and other medications used, the influence these substances have on the athletes, and how and why they use them.

  5. Printable Graphene-based Thermoelectric Device with High Temperature Capability

    NASA Astrophysics Data System (ADS)

    Li, Tian; Chen, Yanan; Drew, Dennis; Hu, Liangbing; NanomaterialsEmerging Devices Collaboration

    Thermoelectric devices are of particular interest due to their capability to convert heat into electrical power. We demonstrate the use of a Graphene-based thermoelectric device that can generate output voltages of hundreds of millivolts with an illuminating Graphene strip as the blackbody source. Our proposed device is superior for thermoelectric conversion mainly due to its high temperature capability that yields a maximum Carnot efficiency limit of 90% (referenced to room temperature) and a high Seebeck coefficient. Our device is also macroscopic with good mechanical strength and stabilized performance, making it attractive for large scale and reliable thermoelectric devices.

  6. Optimal Number of Thermoelectric Couples in a Heat Pipe Assisted Thermoelectric Generator for Waste Heat Recovery

    NASA Astrophysics Data System (ADS)

    Liu, Tongjun; Wang, Tongcai; Luan, Weiling; Cao, Qimin

    2017-01-01

    Waste heat recovery through thermoelectric generators is a promising way to improve energy conversion efficiency. This paper proposes a type of heat pipe assisted thermoelectric generator (HP-TEG) system. The expandable evaporator and condenser surface of the heat pipe facilitates the intensive assembly of thermoelectric (TE) modules to compose a compact device. Compared with a conventional layer structure thermoelectric generator, this system is feasible for the installment of more TE couples, thus increasing power output. To investigate the performance of the HP-TEG and the optimal number of TE couples, a theoretical model was presented and verified by experiment results. Further theoretical analysis results showed the performance of the HP-TEG could be further improved by optimizing the parameters, including the inlet air temperature, the thermal resistance of the heating section, and thermal resistance of the cooling structure. Moreover, applying a proper number of TE couples is important to acquire the best power output performance.

  7. Silicon Germanium Quantum Well Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Davidson, Anthony Lee, III

    Today's growing energy demands require new technologies to provide high efficiency clean energy. Thermoelectrics that convert heat to electrical energy directly can provide a method for the automobile industry to recover waste heat to power vehicle electronics, hence improving fuel economy. If large enough efficiencies can be obtained then the internal combustion engine could even be replaced. Exhaust temperature for automotive application range from 400 to 800 K. In this temperature range the current state of the art materials are bulk Si1-xGex alloys. By alternating layers of Si and Si1-xGex alloy device performance may be enhanced through quantum well effects and variations in material thermal properties. In this study, superlattices designed for in-plane operation with varying period and crystallinity are examined to determine the effect on electrical and thermal properties. In-plane electrical resistivity of these materials was found to be below the bulk material at a similar doping at room temperature, confirming the role of quantum wells in electron transport. As period is reduced in the structures boundary scattering limits electron propagation leading to increased resistivity. The Seebeck coefficient measured at room temperature is higher than the bulk material, additionally lending proof to the effects of quantum wells. When examining cross-plane operation the low doping in the Si layers of the device produce high resistivity resulting from boundary scattering. Thermal conductivity was measured from 77 K up to 674 K and shows little variation due to periodicity and temperature, however an order of magnitude reduction over bulk Si1-xGex is shown in all samples. A model is developed that suggests a combination of phonon dispersion effects and strong boundary scattering. Further study of the phonon dispersion effects was achieved through the examination of the heat capacity by combining thermal diffusivity with thermal conductivity. All superlattices show a

  8. Synthesis & Properties of Nano-Composite Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Tritt, Terry

    2007-03-01

    PbTe nanocrystals have been grown in our labs by chemical vapor deposition. These materials grow in size selective regions exhibiting very high yield and have size distributions of around 100 nm to 1000 nm. These nano-materials are incorporated into a bulk matrix, making a composite material in hopes of achieving a higher thermoelectric performance due to the increased phonon scattering that the nano-materials are expected to exhibit, as well as potential for enhancement of their Seebeck coefficient. Some of the advantages as well as the challenges will be discussed. These nanocomposites give a new level of potential control as a tuning parameter with which to vary the materials' thermoelectric properties. In addition, Bi2Te3, another state of the art thermoelectric material and skutterudites (CoSb3) have been synthesized as nanomaterials using hydrothermal techniques. A brief discussion of the synthesis techniques, the characterization techniques and highlights of several systems of materials will be presented. In collaboration with Xiaohua Ji, Jian He, Bo Zhang, Nick Gothard, and Paola Alboni, Dept. of Physics, Clemson University.

  9. Electrochemically deposited BiTe-based nanowires for thermoelectric applications

    SciTech Connect

    Ng, Inn-Khuan; Kok, Kuan-Ying; Rahman, Che Zuraini Che Ab; Saidin, Nur Ubaidah; Ilias, Suhaila Hani; Choo, Thye-Foo

    2014-02-12

    Nanostructured materials systems such as thin-films and nanowires (NWs) are promising for thermoelectric power generation and refrigeration compared to traditional counterparts in bulk, due to their enhanced thermoelectric figures-of-merit. BiTe and its derivative compounds, in particular, are well-known for their near-room temperature thermoelectric performance. In this work, both the binary and ternary BiTe-based nanowires namely, BiTe and BiSbTe, were synthesized using template-assisted electrodeposition. Diameters of the nanowires were controlled by the pore sizes of the anodised alumina (AAO) templates used. Systematic study on the compositional change as a function of applied potential was carried out via Linear Sweep Voltanmetry (LSV). Chemical compositions of the nanowires were studied using Energy Dispersive X-ray Spectrometry (EDXS) and their microstructures evaluated using diffraction and imaging techniques. Results from chemical analysis on the nanowires indicated that while the Sb content in BiSbTe nanowires increased with more negative deposition potentials, the formation of Te{sup 0} and Bi{sub 2}Te{sub 3} were favorable at more positive potentials.

  10. Improved Performance of an Air Cooled Condenser (ACC) Using SPX Wind Guide Technology at Coal-Based Thermoelectric Power Plants

    SciTech Connect

    Ken Mortensen

    2010-12-31

    This project added a new airflow enhancement technology to an existing ACC cooling process at a selected coal power plant. Airflow parameters and efficiency improvement for the main plant cooling process using the applied technology were determined and compared with the capabilities of existing systems. The project required significant planning and pre-test execution in order to reach the required Air Cooled Condenser system configuration for evaluation. A host Power Plant ACC system had to be identified, agreement finalized, and addition of the SPX ACC Wind Guide Technology completed on that site. Design of the modification, along with procurement, fabrication, instrumentation, and installation of the new airflow enhancement technology were executed. Baseline and post-modification cooling system data was collected and evaluated. The improvement of ACC thermal performance after SPX wind guide installation was clear. Testing of the improvement indicates there is a 5% improvement in heat transfer coefficient in high wind conditions and 1% improvement at low wind speed. The benefit increased with increasing wind speed. This project was completed on schedule and within budget.

  11. Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure.

    PubMed

    Berry, T; Ouardi, S; Fecher, G H; Balke, B; Kreiner, G; Auffermann, G; Schnelle, W; Felser, C

    2017-01-04

    The thermoelectric properties of the n-type semiconductor TiNiSn were optimized by partial substitution with metallic MnNiSb in the half Heusler structure. Herein, we study the transport properties and intrinsic phase separation in the Ti1-xMnxNiSn1-xSbx system. The alloys were prepared by arc-melting and annealed at temperatures obtained from differential thermal analysis and differential scanning calorimetry results. The phases were characterized using powder X-ray diffraction patterns, energy-dispersive X-ray spectroscopy, and differential scanning calorimetry. After annealing, the majority phase was TiNiSn with some Ni-rich sites, and the minority phases were primarily Ti6Sn5, Sn and MnSn2. The Ni-rich sites were caused by Frenkel defects; this led to metal-like behavior in the semiconductor specimens at low temperature. For x ≤ 0.05 the samples showed an activated conduction, whereas for x > 0.05 they showed metallic character. The figure of merit for x = 0.05 was increased by 61% (zT = 0.45) in comparison with the pure TiNiSn.

  12. Note: extraction of temperature-dependent interfacial resistance of thermoelectric modules.

    PubMed

    Chen, Min

    2011-11-01

    This article discusses an approach for extracting the temperature dependency of the electrical interfacial resistance associated with thermoelectric devices. The method combines a traditional module-level test rig and a nonlinear numerical model of thermoelectricity to minimize measurement errors on the interfacial resistance. The extracted results represent useful data to investigating the characteristics of thermoelectric module resistance and comparing performance of various modules.

  13. Thermoelectric Properties of Pristine and Doped Graphene Nanosheets and Graphene Nanoribbons: Part II

    NASA Astrophysics Data System (ADS)

    Muley, Sarang V.; Ravindra, N. M.

    2016-06-01

    In Part II of this study, approaches to improve the thermoelectric figure of merit ( ZT) of graphene nanosheets and nanoribbons is discussed. The presence of vacancies in graphene is found to increase the ZT of zigzag graphene nanoribbons significantly. Graphene can be a promising material with much better thermoelectric performance than conventional thermoelectrics.

  14. Thermoelectric Properties of Complex Oxide Heterostructures

    NASA Astrophysics Data System (ADS)

    Cain, Tyler Andrew

    Thermoelectrics are a promising energy conversion technology for power generation and cooling systems. The thermal and electrical properties of the materials at the heart of thermoelectric devices dictate conversion efficiency and technological viability. Studying the fundamental properties of potentially new thermoelectric materials is of great importance for improving device performance and understanding the electronic structure of materials systems. In this dissertation, investigations on the thermoelectric properties of a prototypical complex oxide, SrTiO3, are discussed. Hybrid molecular beam epitaxy (MBE) is used to synthesize La-doped SrTiO3 thin films, which exhibit high electron mobilities and large Seebeck coefficients resulting in large thermoelectric power factors at low temperatures. Large interfacial electron densities have been observed in SrTiO3/RTiO 3 (R=Gd,Sm) heterostructures. The thermoelectric properties of such heterostructures are investigated, including the use of a modulation doping approach to control interfacial electron densities. Low-temperature Seebeck coefficients of extreme electron-density SrTiO3 quantum wells are shown to provide insight into their electronic structure.

  15. POTENTIAL THERMOELECTRIC APPLICATIONS IN DIESEL VEHICLES

    SciTech Connect

    Crane, D

    2003-08-24

    Novel thermodynamic cycles developed by BSST provide improvements by factors of approximately 2 in cooling, heating and power generation efficiency of solid-state thermoelectric systems. The currently available BSST technology is being evaluated in automotive development programs for important new applications. Thermoelectric materials are likely to become available that further increase performance by a comparable factor. These major advancements should allow the use of thermoelectric systems in new applications that have the prospect of contributing to emissions reduction, fuel economy, and improved user comfort. Potential applications of thermoelectrics in diesel vehicles are identified and discussed. As a case in point, the history and status of the Climate Controlled Seat (CCS) system from Amerigon, the parent of BSST, is presented. CCS is the most successful and highest production volume thermoelectric system in vehicles today. As a second example, the results of recent analyses on electric power generation from vehicle waste heat are discussed. Conclusions are drawn as to the practicality of waste power generation systems that incorporate BSST's thermodynamic cycle and advanced thermoelectric materials.

  16. Squad Overmatch Study: Training Human Dimension to Enhance Performance

    DTIC Science & Technology

    2014-09-30

    Program. This provides an introduction to the common language associated with Enhance Performance Mental Skills Training and Sustainment. (50 students ... students can attend the one-week course at one time. d. Five-day Enhance Performance Training for Warrior Transition Battalion Soldiers. This course...Squad Overmatch Study Training Human Dimension to Enhance Performance FY14 Final Report 30 September 2014

  17. Optimization of Bulk Thermoelectrics: Influence of Cu Insertion in Ag3.6Mo9Se11

    NASA Astrophysics Data System (ADS)

    Colin, Malika; Zhou, Tong; Lenoir, Bertrand; Dauscher, Anne; Al Rahal Al Orabi, Rabih; Gougeon, Patrick; Potel, Michel; Baranek, Philippe; Semprimoschnig, Christopher

    2012-06-01

    Currently, there is a resurgence of interest in thermoelectric materials with enhanced efficiency. Among investigated classes of bulk thermoelectrics such as partially filled skutterudites, Zn4Sb3-based materials, and clathrates, novel polycrystalline Mo9 cluster-based chalcogenides were reported recently. Among those, Chevrel phase-derived Ag y Mo9Se11 (with 3.4 ≤ y ≤ 3.9) compounds have shown interesting thermoelectric properties, in particular extremely low thermal conductivity allowing improved thermoelectric efficiency compared with reported Chevrel phases. They also possess a complex crystallographic structure where stacked Mo9Se11 units leave channels occupied by Ag atoms. Analysis of the structural determinants of the thermoelectric properties of Ag y Mo9Se11 suggested that performance improvements could result from further Cu insertion. In this paper, we describe the synthesis route we used for preparing quaternary Ag-Cu-Mo-Se compositions by a combination of powder metallurgy and spark plasma sintering techniques. Characterization by x-ray diffraction, scanning electron microscopy, and electrical and thermal measurements has been performed. The results obtained for two compounds (Ag3.6Cu0.2Mo9Se11 and Ag3.6Cu0.4Mo9Se11) are discussed and compared with those of the parent ternary compound Ag3.6Mo9Se11.

  18. Effects of Sn Substitution on Thermoelectric Properties of Ge4SbTe5

    NASA Astrophysics Data System (ADS)

    Williams, Jared B.; Mather, Spencer; Morelli, Donald T.

    2016-02-01

    Phase-change materials are identified by their ability to rapidly alternate between amorphous and crystalline phases upon heating, exhibiting large contrast in the optical/electrical properties of the respective phases. Such materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase-change materials studied today can be found on the pseudobinary (GeTe)1- x (Sb2Te3) x tie-line. Ge4SbTe5, a single-phase compound just off of the (GeTe)1- x (Sb2Te3) x tie-line, forms in a metastable rocksalt crystal structure at room temperature. It has been found that stoichiometric and undoped Ge4SbTe5 exhibits thermal conductivity of ~1.2 W/m-K at high temperature and a dramatic decrease in electrical resistivity at 623 K due to a structural phase transition, which leads to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. Introducing point defects via isoelectronic substitutions can be an effective means of reducing thermal conductivity and enhancing thermoelectric performance. We present a study of the effects of Sn substitution for Ge on the electrical and thermal transport properties of Ge4SbTe5.

  19. Improved Thermal Behavior of Multiple Linked Arrays of Silicon Nanowires Integrated into Planar Thermoelectric Microgenerators

    NASA Astrophysics Data System (ADS)

    Dávila, Diana; Tarancón, Albert; Calaza, Carlos; Salleras, Marc; Fernández-Regúlez, Marta; Paulo, Alvaro San; Fonseca, Luis

    2013-07-01

    Low-dimensional structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductors, paving the way for integration of thermoelectric generators into silicon microtechnology. With this aim, dense arrays of well-oriented and size-controlled silicon nanowires (Si NWs) obtained by the chemical vapor deposition (CVD)-vapor-liquid-solid (VLS) mechanism have been implemented into microfabricated structures to develop planar unileg thermoelectric microgenerators ( μTEGs). Different low-thermal-mass suspended structures have been designed and microfabricated on silicon-on-insulator (SOI) substrates to operate as microthermoelements using p-type Si NW arrays as the thermoelectric material. To obtain nanowire arrays with effective lengths larger than normally attained by the VLS technique, structures composed of multiple ordered arrays consecutively bridged by transversal microspacers have been fabricated. The successive linkage of multiple Si NW arrays enabled the development of larger temperature differences while preserving good electrical contact. This gives rise to small internal thermoelement resistances, enhancing the performance of the devices as energy harvesters.

  20. Thermoelectrics: Better half found

    NASA Astrophysics Data System (ADS)

    Weidenkaff, Anke

    2017-02-01

    Thermoelectric converters built with high thermoelectric activity p-type and n-type materials have the potential to replace mechanical heat-to-electricity converters. Now, efficient n-type SnSe has been prepared, ready to complement its previously reported p-type counterpart.

  1. Heat Transfer Enhancement in High Performance Heat Sink Channels by Autonomous, Aero-Elastic Reed Fluttering

    NASA Astrophysics Data System (ADS)

    Jha, Sourabh; Crittenden, Thomas; Glezer, Ari

    2016-11-01

    Heat transport within high aspect ratio, rectangular mm-scale channels that model segments of a high-performance, air-cooled heat sink is enhanced by the formation of unsteady small-scale vortical motions induced by autonomous, aeroelastic fluttering of cantilevered planar thin-film reeds. The flow mechanisms and scaling of the interactions between the reed and the channel flow are explored to overcome the limits of forced convection heat transport from air-side heat exchangers. High-resolution PIV measurements in a testbed model show that undulations of the reed's surface lead to formation and advection of vorticity concentrations, and to alternate shedding of spanwise CW and CCW vortices. These vortices scale with the reed motion amplitude, and ultimately result in motions of decreasing scales and enhanced dissipation that are reminiscent of a turbulent flow. The vorticity shedding lead to strong enhancement in heat transfer that increases with the Reynolds number of the base flow (e.g., the channel's thermal coefficient of performance is enhanced by 2.4-fold and 9-fold for base flow Re = 4,000 and 17,400, respectively, with corresponding decreases of 50 and 77% in the required channel flow rates). This is demonstrated in heat sinks for improving the thermal performance of low-Re thermoelectric power plant air-cooled condensers, where the global air-side pressure losses can be significantly reduced by lowering the required air volume flow rate at a given heat flux and surface temperature. AFOSR and NSF-EPRI.

  2. Thermoelectric transport properties of high mobility organic semiconductors

    NASA Astrophysics Data System (ADS)

    Venkateshvaran, Deepak; Broch, Katharina; Warwick, Chris N.; Sirringhaus, Henning

    2016-09-01

    Transport in organic semiconductors has traditionally been investigated using measurements of the temperature and gate voltage dependent mobility of charge carriers within the channel of organic field-effect transistors (OFETs). In such measurements, the behavior of charge carrier mobility with temperature and gate voltage, studied together with carrier activation energies, provide a metric to quantify the extent of disorder within these van der Waals bonded materials. In addition to the mobility and activation energy, another potent but often-overlooked transport coefficient useful in understanding disorder is the Seebeck coefficient (also known as thermoelectric power). Fundamentally, the Seebeck coefficient represents the entropy per charge carrier in the solid state, and thus proves powerful in distinguishing materials in which charge carriers move freely from those where a high degree of disorder causes the induced carriers to remain trapped. This paper briefly covers the recent highlights in the field of organic thermoelectrics, showing how significant strides have been made both from an applied standpoint as well as from a viewpoint of fundamental thermoelectric transport physics. It shall be illustrated how thermoelectric transport parameters in organic semiconductors can be tuned over a significant range, and how this tunability facilitates an enhanced performance for heat-to-electricity conversion as well as quantifies energetic disorder and the nature of the density of states (DOS). The work of the authors shall be spotlighted in this context, illustrating how Seebeck coefficient measurements in the polymer indacenodithiophene-co-benzothiadiazole (IDTBT) known for its ultra-low degree of torsion within the polymer backbone, has a trend consistent with low disorder. 1 Finally, using examples of the small molecules C8-BTBT and C10-DNTT, it shall be discussed how the Seebeck coefficient can aid the estimation of the density and distribution of trap states

  3. Misfit layer compounds and ferecrystals: Model systems for thermoelectric nanocomposites

    DOE PAGES

    Merrill, Devin R.; Moore, Daniel B.; Bauers, Sage R.; ...

    2015-04-22

    A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit layer compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their layered structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class ofmore » metastable, turbostratically-disordered misfit layer compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and layering schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe₂)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor.« less

  4. Misfit layer compounds and ferecrystals: Model systems for thermoelectric nanocomposites

    SciTech Connect

    Merrill, Devin R.; Moore, Daniel B.; Bauers, Sage R.; Falmbigl, Matthias; Johnson, David C.

    2015-04-22

    A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit layer compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their layered structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class of metastable, turbostratically-disordered misfit layer compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and layering schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe₂)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor.

  5. A review on the fabrication of polymer-based thermoelectric materials and fabrication methods.

    PubMed

    Kamarudin, Muhammad Akmal; Sahamir, Shahrir Razey; Datta, Robi Shankar; Long, Bui Duc; Mohd Sabri, Mohd Faizul; Mohd Said, Suhana

    2013-11-12

    Thermoelectricity, by converting heat energy directly into useable electricity, offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts. In recent years, most of the efforts have been done on improving the thermoelectric efficiency using different approaches, that is, nanostructuring, doping, molecular rattling, and nanocomposite formation. The applications of thermoelectric polymers at low temperatures, especially conducting polymers, have shown various advantages such as easy and low cost of fabrication, light weight, and flexibility. In this review, we will focus on exploring new types of polymers and the effects of different structures, concentrations, and molecular weight on thermoelectric properties. Various strategies to improve the performance of thermoelectric materials will be discussed. In addition, a discussion on the fabrication of thermoelectric devices, especially suited to polymers, will also be given. Finally, we provide the challenge and the future of thermoelectric polymers, especially thermoelectric hybrid model.

  6. A Review on the Fabrication of Polymer-Based Thermoelectric Materials and Fabrication Methods

    PubMed Central

    Kamarudin, Muhammad Akmal; Sahamir, Shahrir Razey; Datta, Robi Shankar; Long, Bui Duc; Mohd Sabri, Mohd Faizul; Mohd Said, Suhana

    2013-01-01

    Thermoelectricity, by converting heat energy directly into useable electricity, offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts. In recent years, most of the efforts have been done on improving the thermoelectric efficiency using different approaches, that is, nanostructuring, doping, molecular rattling, and nanocomposite formation. The applications of thermoelectric polymers at low temperatures, especially conducting polymers, have shown various advantages such as easy and low cost of fabrication, light weight, and flexibility. In this review, we will focus on exploring new types of polymers and the effects of different structures, concentrations, and molecular weight on thermoelectric properties. Various strategies to improve the performance of thermoelectric materials will be discussed. In addition, a discussion on the fabrication of thermoelectric devices, especially suited to polymers, will also be given. Finally, we provide the challenge and the future of thermoelectric polymers, especially thermoelectric hybrid model. PMID:24324378

  7. Enhanced-performance active fiber composites

    NASA Astrophysics Data System (ADS)

    Gentilman, Richard L.; McNeal, Kelley; Schmidt, Gerald E.; Pizzochero, Alessandro E.; Rossetti, George A., Jr.

    2003-08-01

    Active fiber composites (AFCs) find applications in a variety of industrial, commercial, and aerospace markets as both actuators and sensors. Among the key attributes of AFCs relative to conventional monolithic piezoceramic actuators are high strain energy density, unidirectional response, conformability, and robustness. Recently, performance enhancements in AFCs have been demonstrated through the use of a modified injection molding process to produce piezoceramic modules with multiple identical fibers of a uniform rectangular cross section. AFC actuators made from Type II PZT fiber modules exhibit free micro-strains of 1830 +/- 30 ppm at a peak-peak E-field drive of 26.1 kV/cm, and show exceptional part-to-part uniformity. In addition, AFCs made from injection molded PMN-PT fiber modules show a low-field d33 of 650 pm/V. The successful incorporation of PMN-PT materials into AFCs also demonstrates the viability of using highly textured ceramic PMN-PT piezofibers, for which even larger increases in strain response are expected.

  8. Electronic structure and thermoelectric properties of (PbSe)m/(SnSe)n superlattice: A first principles study

    NASA Astrophysics Data System (ADS)

    Do, Duc Cuong; Rhim, S. H.; Hong, Soon Cheol

    2015-03-01

    Figure of merit (ZT) of thermoelectric materials can be enhanced by lowering thermal conductivity or/and increasing electrical conductivity. The extremely high ZT of layered structure SnSe opened up a new direction in study of thermoelectricity due to its low thermal conductivity, which, however, is limited to high temperature. Here, we performed first principles density functional calculations to explore room-temperature thermoelectricity. We consider (PbSe)m/(SnSe)n superlattices with different period, whose quantum well structure is expected to increase electrical conductivity by modulation of charge doping at interface. Calculations of Seebeck coefficients for the superlattices are presented. Supported by the Ministry of Trade, Industry & Energy, Korea (20132020000110) and Priority Research Centers Program (2009-0093818) through National Research Foundation of Korea.

  9. On the effects of substitution, intercalation, non-stoichiometry and block layer concept in TiS2 based thermoelectrics.

    PubMed

    Guilmeau, E; Maignan, A; Wan, C; Koumoto, K

    2015-10-14

    TiS2 based layered sulfides have recently received increasing interest from the thermoelectric community. Due to its layered structure, the TiS2 compound with its enormous capacity for chemical substitution and intercalation offers different means to optimize the thermoelectric response through concomitant tuning of carrier concentration and decrease of the lattice thermal conductivity. In this review, we first discuss and summarize the crystal structures and physical/chemical properties of TiS2 based layered sulfides. Then, the approaches that successfully enhanced the thermoelectric performances in the TiS2 ceramic samples densified by Spark Plasma sintering are outlined, which include intercalation, non-stoichiometry, cationic substitution, and the block layer concept.

  10. Thermoelectric Properties of Poly(selenophene-co-3, 4-ethylenedioxythiophene) via Electropolymerization

    NASA Astrophysics Data System (ADS)

    Gu, Hua; Ming, Shouli; Lin, Kaiwen; Liu, Hongtao; Chen, Shuai; Lu, Baoyang; Xu, Jingkun

    2016-12-01

    Conducting polymers as thermoelectric (TE) materials have drawn extensive attention most recently because they are intrinsically light weight, flexible, highly processable, abundant in nature, and have especially low thermal conductivity. Relative studies have been focused on several typical structures such as polyacetylene, polyaniline, polythiophenes. However, TE performance of polyselenophenes have drawn very little attention because of its unstability and difficulty in synthesis. Previously, our group demonstrated that polyselenophene revealed high Seebeck coefficient (>180 μV K-1), but their electrical conductivity was very low (typically 10-5-10-2 S cm-1). For the sake of improving the thermoelectric performance of polyselenophene, the simplest and most effective method is to copolymerize with other high-performance thermoelectric materials. Herein, 3,4-ethylenedioxythiophene (EDOT), the monomer precursor of poly(3,4-ethylenedioxythiophene) (probably the best organic thermoelectric materials so far) was chosen to copolymerize with selenophene (SE) under different feeding ratios via electropolymerization to improve the thermoelectric performance. It is found that the electrical conductivity of all the copolymer films was obviously enhanced with the highest value of 0.91 S cm-1 by inserting EDOT in the conjugated block, whereas their Seebeck coefficient was brought down to 12 μV K-1. In this work, We obtained four different feeding ratios copolymers of SE and EDOT, 2:1 (PA), 1:1 (PB), 1:2 (PC), and 1:5 (PD). The copolymers had improved electrical conductivity and environmental stability compared with polyselenophene. Furthermore, with increasing the feeding ratio of EDOT, the TE performance of the copolymers was significantly improved.

  11. Thermoelectric Devices Advance Thermal Management

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Thermoelectric (TE) devices heat, cool, and generate electricity when a temperature differential is provided between the two module faces. In cooperation with NASA, Chico, California-based United States Thermoelectric Consortium Inc. (USTC) built a gas emissions analyzer (GEA) for combustion research. The GEA precipitated hydrocarbon particles, preventing contamination that would hinder precise rocket fuel analysis. The USTC research and design team uses patent-pending dimple, pin-fin, microchannel and microjet structures to develop and design heat dissipation devices on the mini-scale level, which not only guarantee high performance of products, but also scale device size from 1 centimeter to 10 centimeters. USTC continues to integrate the benefits of TE devices in its current line of thermal management solutions and has found the accessibility of NASA technical research to be a valuable, sustainable resource that has continued to positively influence its product design and manufacturing

  12. Production Well Performance Enhancement using Sonication Technology

    SciTech Connect

    Adewumi, Michael A; Ityokumbul, M Thaddeus; Watson, Robert W; Eltohami, Eltohami; Farias, Mario; Heckman, Glenn; Houlihan, Brendan; Karoor, Samata Prakash; Miller, Bruce G; Mohammed, Nazia; Olanrewaju, Johnson; Ozdemir, Mine; Rejepov, Dautmamed; Sadegh, Abdallah A; Quammie, Kevin E; Zaghloul, Jose; Hughes, W Jack; Montgomery, Thomas C

    2005-12-31

    The objective of this project was to develop a sonic well performance enhancement technology that focused on near wellbore formation damage. In order to successfully achieve this objective, a three-year project was defined. The entire project was broken into four tasks. The overall objective of all this was to foster a better understanding of the mechanisms involved in sonic energy interactions with fluid flow in porous media and adapt such knowledge for field applications. The fours tasks are: • Laboratory studies • Mathematical modeling • Sonic tool design and development • Field demonstration The project was designed to be completed in three years; however, due to budget cuts, support was only provided for the first year, and hence the full objective of the project could not be accomplished. This report summarizes what was accomplished with the support provided by the US Department of Energy. Experiments performed focused on determining the inception of cavitation, studying thermal dissipation under cavitation conditions, investigating sonic energy interactions with glass beads and oil, and studying the effects of sonication on crude oil properties. Our findings show that the voltage threshold for onset of cavitation is independent of transducer-hydrophone separation distance. In addition, thermal dissipation under cavitation conditions contributed to the mobilization of deposited paraffins and waxes. Our preliminary laboratory experiments suggest that waxes are mobilized when the fluid temperature approaches 40°C. Experiments were conducted that provided insights into the interactions between sonic wave and the fluid contained in the porous media. Most of these studies were carried out in a slim-tube apparatus. A numerical model was developed for simulating the effect of sonication in the nearwellbore region. The numerical model developed was validated using a number of standard testbed problems. However, actual application of the model for scale

  13. Benefits of Carrier-Pocket Anisotropy to Thermoelectric Performance: The Case of p -Type AgBiSe2

    SciTech Connect

    Parker, David S.; May, Andrew F.; Singh, David J.

    2015-06-05

    Here we study theoretically the effects of anisotropy on the thermoelectric performance of p-type AgBiSe2. We present an apparent realization of the thermoelectric benefits of one-dimensional plate-like carrier pocket anisotropy in the valence band of this material. Based on first principles calculations we find a substantial anisotropy in the electronic structure, likely favorable for thermoelectric performance, in the valence bands of the hexagonal phase of the silver chalcogenide thermoelectric AgBiSe2, while the conduction bands are more isotropic, and in our experiments do not attain high performance. AgBiSe2 has already exhibited a ZT value of 1.5 in a high-temperature disordered fcc phase, but room-temperature performance has not been demonstrated. We develop a theory for the ability of anisotropy to decouple the density-of-states and conductivity effective masses, pointing out the influence of this effect in the high performance thermoelectrics Bi2Te3 and PbTe. From our first principles and Boltzmann transport calculations we find that p-type AgBiSe2 has substantial promise as a room temperature thermoelectric, and estimate its performance.

  14. Semiconducting quaternary chalcogenide glasses as new potential thermoelectric materials: an As-Ge-Se-Sb case.

    PubMed

    Dahshan, A; Sharma, Pankaj; Aly, K A

    2015-09-07

    The performance of thermoelectric materials may be improved via complex structures, impurities, disorder etc. Chalcogenide glasses possess such properties. In the present paper, we report the electrical and thermoelectric properties of As14Ge14Se72-xSbx (where x = 3, 6, 9, 12, 15 at%) chalcogenide glasses in the temperature range of 300 K-450 K. The electrical conductivity has been observed to increase from 1.46 × 10(-9) Ω(-1) cm(-1) to 1.80 × 10(-6) Ω(-1) cm(-1) for x = 3 at% to x = 15 at%. The addition of Sb increases the Seebeck coefficient to a large value of 1124 μV K(-1) for x = 15 at% at 333 K. As a result of increased electrical conductivity and Seebeck coefficient for enhanced values of Sb, the power factor (a measure of the performance of the thermoelectric energy converters) has been observed to increase strongly. Results indicate that the investigated chalcogenide glassy compositions may be potential candidates for incurring high action thermoelectric materials.

  15. Design, manufacturing and testing of a portable vaccine carrier box employing thermoelectric module and heat pipe.

    PubMed

    Putra, N

    2009-01-01

    Vaccination is a highly effective method and a cheap tool for preventing certain infectious diseases. Routine immunization programs protect most of the world's children from diseases that claim millions of lives each year. There are many practical problems impeding vaccine delivery, especially to maintain the cold chain system, which is the means for storing and transporting vaccines in a potent state from the manufacturer to the person being immunized at a temperature of 2-8 degrees C. The development of the solid state thermoelectric cooling system has permitted newly developed packages that are capable of meeting many requirements and applications where environmental concern, size, weight, performance and noise are an issue. This paper describes the development of a vaccine carrier box. A combination of a thermoelectric module and a heat pipe is used for the cooling system. The position of the heat pipe as a heat sink on the hot side of the thermoelectric module will enhance the thermoelectric performance. The minimum temperature in the cabin of the vaccine carrier box reached -10 degrees C, which indicates that the design of the vaccine carrier box can maintain the vaccine at desired temperatures.

  16. Adopting Emerging Technology to Enhance Organizational Performance

    DTIC Science & Technology

    2009-06-01

    Center, Pacific with open-source, competitive intelligence to enhance their situational awareness and fulfill the external information needs of the...Group – An Overview To provide and enhance the situational awareness of its parent organization, the CSG has employed a competitive intelligence infrastructure...in 2001 by senior leadership to address SA imperative • Why: Provide open-source competitive intelligence to enhance situational awareness of SSC

  17. Thermal Optimization of the Heat Exchanger in an Automotive Exhaust-Based Thermoelectric Generator

    NASA Astrophysics Data System (ADS)

    Deng, Y. D.; Liu, X.; Chen, S.; Tong, N. Q.

    2013-07-01

    Recent advances in thermoelectric technologies have made exhaust-based thermoelectric generators (TEGs) promising to recover waste heat. The thermal performance of the heat exchanger in exhaust-based TEGs is studied in this work. In terms of interface temperature and thermal uniformity, the thermal characteristics of heat exchangers with different internal structures, lengths, and materials are discussed. Following computational fluid dynamics simulations, infrared experiments are carried out on a high-performance production engine with a dynamometer. Simulation and experimental results show that a plate-shaped heat exchanger made of brass with fishbone-shaped internal structure and length of 600 mm achieves a relatively ideal thermal performance, which is practically helpful to enhance the thermal performance of the TEG.

  18. High Temperature Integrated Thermoelectric Ststem and Materials

    SciTech Connect

    Mike S. H. Chu

    2011-06-06

    . Two composition systems, specifically 1.0 SrO - 0.8 x 1.03 TiO2 - 0.2 x 1.03 NbO2.5 and 0.97 TiO2 - 0.03 NbO2.5, have been identified as good base line compositions for n-type thermoelectric compositions in future module design. Tests of these materials at an outside company were promising using that company's processing and material expertise. There was no unique p-type thermoelectric compositions identified in phase I work other than several current cobaltite materials. Ca3Co4O9 will be the primary p-type material for the future module design until alternative materials are developed. BaTiO3 and rare earth titanate based dielectric compositions show both p-type and n-type behavior even though their electrical conductivities were very low. Further research and development of these materials for thermoelectric applications is planned in the future. A preliminary modeling and optimization of a thermoelectric generator (TEG) that uses the n-type 1.0 SrO - 1.03 x 0.8 TiO2 - 1.03 x 0.2 NbO2.5 was performed. Future work will combine development of ceramic powders and manufacturing expertise at TAM, development of SPS at TAM or a partner organization, and thermoelectric material/module testing, modeling, optimization, production at several partner organizations.

  19. Conducting Polymers and Their Hybrids as Organic Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Toshima, Naoki; Ichikawa, Shoko

    2015-01-01

    Conducting polymers have received much attention recently as organic thermoelectric materials, because of such advantages as plentiful resources, easy synthesis, easy processing, low cost, low thermal conductivity, and easy fabrication of flexible, light, and printable devices with large area. Many reports on organic thermoelectric materials have recently been published. We have studied conducting polymers as organic thermoelectric materials since 1999. During these investigations, we found that the thermal conductivity of conducting polymers did not increase even though electrical conductivity increased; this was a major advantage of conducting polymers as organic thermoelectric materials. We also observed that molecular alignment was one of the most important factors for improvement of the thermoelectric performance of conducting polymers. Stretching of conducting polymers or their precursors was one of the most common techniques used to achieve good molecular alignment. Recently, alignment of the clusters of conducting polymers by treatment with solvents has been proposed as a means of achieving high electrical conductivity. Hybridization of conducting polymers with inorganic nanoparticles has also been found to improve thermoelectric performance. Here we present a brief history and discuss recent progress of research on conducting polymers as organic thermoelectric materials, and describe the techniques used to improve thermoelectric performance by treatment of conducting polymers with solvents and hybridization of conducting polymers with Bi2Te3 and gold nanoparticles.

  20. Complex oxides useful for thermoelectric energy conversion

    DOEpatents

    Majumdar, Arunava [Orinda, CA; Ramesh, Ramamoorthy [Moraga, CA; Yu, Choongho [College Station, TX; Scullin, Matthew L [Berkeley, CA; Huijben, Mark [Enschede, NL

    2012-07-17

    The invention provides for a thermoelectric system comprising a substrate comprising a first complex oxide, wherein the substrate is optionally embedded with a second complex oxide. The thermoelectric system can be used for thermoelectric power generation or thermoelectric cooling.