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Sample records for low-temperature thermoelectric properties

  1. Design, crystal growth, and physical properties of low-temperature thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Fuccillo, Michael K.

    Thermoelectric materials serve as the foundation for two important modern technologies, namely 1) solid-state cooling, which enables small-area refrigeration without vibrations or moving parts, and 2) thermoelectric power generation, which has important implications for waste heat recovery and improved sources of alternative energy. Although the overall field of thermoelectrics research has been active for decades, and several consumer and industrial products have already been commercialized, the design and synthesis of new thermoelectrics that outperform long-standing state of the art materials has proven extremely challenging. This is particularly true for low-temperature refrigeration applications, which is the focus of this work; however, scientific advances in this area generally support power generation as well. In order to achieve more efficient materials for virtually all thermoelectric applications, improved materials design principles must be developed and synthetic procedures must be better understood. We aim to contribute to these goals by studying two classes of materials, namely 1) the tetradymites Bi2TeSe 2 and Bi2Te2Se, which are close relatives of state of the art thermoelectric cooling materials, and 2) Kondo insulating (-like) FeSb2 and FeSi, which possess anomalously enhanced low-temperature thermoelectric properties that arise from exotic electronic and magnetic properties. The organization of this dissertation is as follows: Chapter 1 is a brief perspective on solid-state chemistry. Chapter 2 presents experimental methods for synthesizing and characterizing thermoelectric materials. In Chapter 3, two original research projects are discussed: first, work on the tetradymite Bi2TeSe2 doped with Sb to achieve an n- to p-type transition, and second, the tetradymite Bi2Te2Se with chemical defects through two different methods. Chapter 4 gives the magnetic and transport properties of FeSb 2--RuSb2 alloys, a family of compounds exemplifying what we

  2. Transport properties of cubic crystalline Ge2Sb2Te5: A potential low-temperature thermoelectric material

    NASA Astrophysics Data System (ADS)

    Sun, Jifeng; Mukhopadhyay, Saikat; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2015-03-01

    Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200-300 μV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of ˜1 × 1019-6 × 1019 cm-3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 μV/K for a doping range of 1 × 1019-3.5 × 1019 cm-3. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low (˜0.7 W/m-K at 300 K) [K. S. Siegert et al., Rep. Prog. Phys. 78, 013001 (2015)], our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.

  3. Transport properties of cubic crystalline Ge2Sb2Te5: a potential low-temperature thermoelectric material.

    DOE PAGESBeta

    Sun, Jifeng; Mukhopadhyay, Saikat; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2015-03-26

    Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coe cients 200 - 300 μV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of 1 1019 - 6 1019 cm-3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coe cient was found to exceed 200 μV/K for a doping range 1 1019 - 3.5 1019 cm-3. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low ( 0.7 W/m-K atmore » 300 K), our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.« less

  4. Electronic structure and low temperature thermoelectric properties of In₂₄M₈O₄₈ (M = Ge(4+), Sn(4+), Ti(4+), and Zr(4+)).

    PubMed

    Yan, Yu Li; Wang, Yuan Xu

    2012-01-01

    The electronic structure and transport properties of In₂₄M₈O₄₈ (M = Ge(4+), Sn(4+), Ti(4+), and Zr(4+)) have been studied by using the full-potential linearized augmented plane-wave method and the semiclassical Boltzmann theory, respectively. It is found that the magnitude of powerfactor with respect to relation time follows the order of In₂₄Sn₈O₄₈ > In₂₄Zr₈O₄₈ > In₂₄Ge₈O₄₈ > In₂₄Ti₈O₄₈. The largest powerfactor is 2.7 × 10¹² W/K² ms for In₂₄Sn₈O₄₈ at 60 K, which is nearly thirty times larger than those of conventional n-type thermoelectric materials. The origin of the different thermoelectric behavior for these compounds is discussed from the electronic structure level. It is found that, at low temperature, the dopant strongly affect the bands near the Fermi level, which consequently leads to their different thermoelectric properties. The electronic configuration and the difference in atomic number between the dopant and the host atom also play an important role on the thermoelectric properties of In₂₄M₈O₄₈. Our calculations give a valuable insight on how to enhance the thermoelectric performance of In₃₂O₄₈. PMID:21952977

  5. Influence of ZnO Inclusions on the Low-Temperature Thermoelectric Properties of CoSb3

    NASA Astrophysics Data System (ADS)

    Chubilleau, C.; Lenoir, B.; Masschelein, P.; Dauscher, A.; Godart, C.

    2012-06-01

    CoSb3 composites with different amounts of ZnO nanoparticles (2 wt.% to 12 wt.%) were prepared from nanosized ZnO (commercial) and micron-sized CoSb3 (obtained via solid-state reaction) particles mixed in solution and freeze dried. The resulting powders were densified by spark plasma sintering. The samples were characterized by x-ray diffraction and scanning electron microscopy. It was found that ZnO forms micron-sized clusters at the grain boundaries of the matrix material. The thermoelectric properties (electrical resistivity, thermopower, and thermal conductivity) were measured in the 2 K to 300 K temperature range. Both the electrical and thermal conductivities were observed to decrease with increasing ZnO content. The dimensionless figure of merit ZT was improved by up to 30% at 300 K for the sample containing 2 wt.% ZnO.

  6. Low-temperature magnetic, galvanomagnetic, and thermoelectric properties of the type-I clathrates Ba8NixSi46-x

    NASA Astrophysics Data System (ADS)

    Candolfi, C.; Aydemir, U.; Ormeci, A.; Baitinger, M.; Oeschler, N.; Steglich, F.; Grin, Yu.

    2011-05-01

    Galvanomagnetic and thermoelectric properties including Hall effect, electrical resistivity, thermopower, and thermal conductivity of polycrystalline type-I clathrates Ba8NixSi46-x (2.6 ⩽ x ⩽ 3.8) have been studied in the 2- to 350-K temperature range. Further characterization of the electronic properties of these compounds has been performed via low-temperature specific heat and magnetic susceptibility measurements (2-300 K). The electronic band structure, density of states, dispersion curves, and Fermi surface were calculated within the full-potential local-orbital method (FPLO). These calculations have not only revealed that the electronic band structure evolves in a nonrigid manner but have also shown that the density of states at the Fermi level strongly varies with x. The variations in the band structure have been experimentally confirmed by transport properties and specific heat measurements. Regardless of the Ni content, the Fermi surface shows disconnected electron and hole sections that appear consistent with thermopower data indicating that both types of carriers contribute to the electrical conduction in these materials. Magnetic susceptibility measurements have indicated that the Ni atoms do not carry any magnetic moment in these compounds. All the investigated samples exhibit metallic-like behavior resulting in moderate thermopower values and thus, in low dimensionless thermoelectric figures of merit ZT.

  7. Thermoelectric harvesting of low temperature natural/waste heat

    NASA Astrophysics Data System (ADS)

    Rowe, David Michael

    2012-06-01

    Apart from specialized space requirements current development in applications of thermoelectric generation mainly relate to reducing harmful carbon emissions and decreasing costly fuel consumption through the recovery of exhaust heat from fossil fuel powered engines and emissions from industrial utilities. Focus on these applications is to the detriment of the wider exploitations of thermoelectrics with other sources of heat energy, and in particular natural occurring and waste low temperature heat, receiving little, if any, attention. In this presentation thermoelectric generation applications, both potential and real in harvesting low temperature waste/natural heat are reviewed. The use of thermoelectrics to harvest solar energy, ocean thermal energy, geothermal heat and waste heat are discussed and their credibility as future large-scale sources of electrical power assessed.

  8. Thermoelectric Materials Development for Low Temperature Geothermal Power Generation

    DOE Data Explorer

    Tim Hansen

    2016-01-29

    Data includes characterization results for novel thermoelectric materials developed specifically for power generation from low temperature geothermal brines. Materials characterization data includes material density, thickness, resistance, Seebeck coefficient. This research was carried out by Novus Energy Partners in Cooperation with Southern Research Institute for a Department of Energy Sponsored Project.

  9. Low Temperature Thermoelectric Characterization of Ag2Se

    NASA Astrophysics Data System (ADS)

    Drymiotis, Fivos; Neff, David; Coney, Michael; Bux, Sabah; Fleurial, Jean-Pierre

    Previous work on Ag2Se showed that this n-type material could have a dimensionless thermoelectric figure of merit (zT) ~1 at room temperature, due to its high mobility and low thermal conductivity. However, the results from the initial reports have not yet been reproduced. In this talk, I will summarize our efforts to replicate the aforementioned thermoelectric performance, and also discuss the experimental setup that we utilized in order to perform the low-temperature thermoelectric characterization of this material. This work was performed at the California Institute of Technology/Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration. This work was supported by JPL's Research and Technology Development Program.

  10. Low-temperature thermoelectric, galvanomagnetic, and thermodynamic properties of the type-I clathrate Ba8AuxSi46-x

    NASA Astrophysics Data System (ADS)

    Aydemir, U.; Candolfi, C.; Ormeci, A.; Oztan, Y.; Baitinger, M.; Oeschler, N.; Steglich, F.; Grin, Yu.

    2011-11-01

    Polycrystalline samples of the clathrate Ba8AuxSi46-x were synthesized for 0.2 ⩽ x ⩽ 10. The homogeneity range of the type-I clathrate phase was determined to be 3.63 ⩽ x ⩽ 6.10 after annealing at 900 °C, while a lower Au concentration (x ≈ 2.2) was obtained by steel-quenching. Quasisingle phase materials were obtained for 4.10 ⩽ x ⩽ 6.10. In this composition range, thermoelectric properties, including electrical resistivity, thermopower, and thermal conductivity, were investigated between 2 and 350 K. These experiments were complemented by low-temperature specific heat and Hall-effect measurements (2-300 K). First-principles calculations were carried out to determine the evolution of the electronic structure as a function of x. Both theoretical and experimental results evidence a progressive evolution, with the Au content, from a metallic-like behavior towards a highly doped semiconducting state which develops around x = 5.43. At this concentration, a crossover from n- to p-type conduction occurs, suggesting that the present system satisfies the Zintl-Klemm concept, which predicts a transition at x = 5.33. This crossover is traced by Hall-effect data indicating a dominant electronlike response for x ⩽ 5.43, which turns into a holelike signal at higher x values. Analysis of the data based on a single-parabolic-band model under the assumption of a single scattering mechanism of the charge carriers proved to adequately describe the transport properties in the compositional range investigated. Interestingly, the temperature dependence of the lattice thermal conductivity is strongly influenced by the Au concentration: the typical behavior of crystalline insulators in the n-type compounds evolves into a glasslike dependence in the p-type samples. The series Ba8AuxSi46-x thus provides an excellent testing ground for the interplay between crystal structure, electronic properties, and lattice thermal conductivity in type-I clathrates.

  11. Transport properties of cubic crystalline Ge2Sb2Te5: a potential low-temperature thermoelectric material.

    SciTech Connect

    Sun, Jifeng; Mukhopadhyay, Saikat; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2015-03-26

    Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coe cients 200 - 300 μV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of 1 1019 - 6 1019 cm-3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coe cient was found to exceed 200 μV/K for a doping range 1 1019 - 3.5 1019 cm-3. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low ( 0.7 W/m-K at 300 K), our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.

  12. Low-temperature solid state reaction synthesis and thermoelectric properties of high-performance and low-cost Sb-doped Mg2Si0.6Sn0.4

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Tang, Xinfeng; Sharp, Jeff

    2010-03-01

    Mg2Si1-xSnx compounds are a type of low-price, environment-friendly medium temperature thermoelectric materials with very important prospects for practical application, and the exploration of high performance Mg2Si1-xSnx compounds is currently attracting worldwide interest. In this study, Sb-doped Mg2Si0.6Sn0.4 compounds were prepared through a two-step, low-temperature solid state reaction method combined with the spark plasma sintering technique for rapid densification. The influence of Sb doping amount on the thermoelectric properties of Mg2Si0.6-ySn0.4Sby (0 <= y <= 0.015) compounds was investigated. The solid solubility limit of Sb in Mg2Si0.6Sn0.4 compounds was estimated around y = 0.0125. As y increased, the electrical conductivity of Mg2Si0.6-ySn0.4Sby (0 <= y <= 0.0125) compounds increased considerably, while the absolute value of the Seebeck coefficient and the lattice thermal conductivity decreased. The sample with y = 0.0125 had the highest ZT, reaching 1.11 at 860 K, and the samples with 0.005 <= y <= 0.015 all attained ZTmax > 0.95. The adopted synthesis process also showed very good repeatability and regularity in obtaining thermoelectric properties, together with the capability of precise composition control of Mg2Si0.6-ySn0.4Sby, making it promising for the practical application of Mg2Si based thermoelectric materials.

  13. p -type Bi2Se3 for topological insulator and low-temperature thermoelectric applications

    NASA Astrophysics Data System (ADS)

    Hor, Y. S.; Richardella, A.; Roushan, P.; Xia, Y.; Checkelsky, J. G.; Yazdani, A.; Hasan, M. Z.; Ong, N. P.; Cava, R. J.

    2009-05-01

    The growth and elementary properties of p -type Bi2Se3 single crystals are reported. Based on a hypothesis about the defect chemistry of Bi2Se3 , the p -type behavior has been induced through low-level substitutions (1% or less) of Ca for Bi. Scanning tunneling microscopy is employed to image the defects and establish their charge. Tunneling and angle-resolved photoemission spectra show that the Fermi level has been lowered into the valence band by about 400 meV in Bi1.98Ca0.02Se3 relative to the n -type material. p -type single crystals with ab -plane Seebeck coefficients of +180μV/K at room temperature are reported. These crystals show an anomalous peak in the Seebeck coefficient at low temperatures, reaching +120μVK-1 at 7 K, giving them a high thermoelectric power factor at low temperatures. In addition to its interesting thermoelectric properties, p -type Bi2Se3 is of substantial interest for studies of technologies and phenomena proposed for topological insulators.

  14. High thermoelectric figure of merit in nanocrystalline polyaniline at low temperatures

    SciTech Connect

    Nath, Chandrani; Kumar, Ashok E-mail: okram@csr.res.in; Kuo, Yung-Kang; Okram, Gunadhor Singh E-mail: okram@csr.res.in

    2014-09-29

    Thermoelectric coolers with figure of merit (ZT) close to unity at low temperatures are the need of the hour with new advances in high temperature superconductors, superconducting microelectronic circuits, quantum computers, and photonics. Here, we demonstrate that the conducting polymer polyaniline (Pani) doped with camphor sulfonic acid synthesized in semi-crystalline nanostructures, possesses a giant Seebeck effect at low temperatures. The resulting enormously large Seebeck coefficient (up to 0.6 V/K) combined with an intrinsically low electrical conductivity and thermal conductivity give rise to a ZT = 0.77 at 45 K and ZT = 2.17 at 17 K.

  15. High thermoelectric figure of merit in nanocrystalline polyaniline at low temperatures

    NASA Astrophysics Data System (ADS)

    Nath, Chandrani; Kumar, Ashok; Kuo, Yung-Kang; Okram, Gunadhor Singh

    2014-09-01

    Thermoelectric coolers with figure of merit (ZT) close to unity at low temperatures are the need of the hour with new advances in high temperature superconductors, superconducting microelectronic circuits, quantum computers, and photonics. Here, we demonstrate that the conducting polymer polyaniline (Pani) doped with camphor sulfonic acid synthesized in semi-crystalline nanostructures, possesses a giant Seebeck effect at low temperatures. The resulting enormously large Seebeck coefficient (up to 0.6 V/K) combined with an intrinsically low electrical conductivity and thermal conductivity give rise to a ZT = 0.77 at 45 K and ZT = 2.17 at 17 K.

  16. Intermediate Valence Tuning and Seebeck Coefficient Optimization in Yb-based Low-Temperature Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Lehr, Gloria; Morelli, Donald; Jin, Hyungyu; Heremans, Joseph

    2014-03-01

    Several Yb-based intermediate valence compounds have unique thermoelectric properties at low temperatures. These materials are interesting to study for niche applications such as cryogenic Peltier cooling of infrared sensors on satellites. Elements of different sizes, which form isostructural compounds, are used to form solid solutions creating a chemical pressure (smaller atoms - Sc) or relaxation (larger atoms - La) to alter the volume of the unit cell and thereby manipulate the average Yb valence. Magnetic susceptibility measurements show a strong correlation between the Seebeck coefficient and the ratio of trivalent to divalent Yb in these compounds. Two different Yb-based solid solution systems, Yb1-xScxAl2 and Yb1-xLaxCu2Si2, demonstrate that the concentration of Yb can be used to tune both the magnitude of the Seebeck coefficient as well as the temperature at which its absolute maximum occurs. This work is supported by Michigan State University and AFOSR-MURI ``Cryogenic Peltier Cooling'' Contract #FA9550-10-1-0533.

  17. Low temperature thermophysical properties of lunar soil

    NASA Technical Reports Server (NTRS)

    Cremers, C. J.

    1973-01-01

    The thermal conductivity and thermal diffusivity of lunar fines samples from the Apollo 11 and Apollo 12 missions, determined at low temperatures as a function of temperature and various densities, are reviewed. It is shown that the thermal conductivity of lunar soil is nearly the same as that of terrestrial basaltic rock under the same temperature and pressure conditions.

  18. Thermoelectric Properties of Selenides Spinels

    NASA Technical Reports Server (NTRS)

    Snyder, G.; Caillat, T.; Fleurial, J-P.

    2000-01-01

    Many compounds with the spinel structure type have been analyzed for their thermoelectric properties. Published data was used to augment experimental results presented here to select promising thermoelectric spinels.

  19. Bottom-up processing and low temperature transport properties of polycrystalline SnSe

    SciTech Connect

    Ge, Zhen-Hua; Wei, Kaya; Lewis, Hutton; Martin, Joshua; Nolas, George S.

    2015-05-15

    A hydrothermal approach was employed to efficiently synthesize SnSe nanorods. The nanorods were consolidated into polycrystalline SnSe by spark plasma sintering for low temperature electrical and thermal properties characterization. The low temperature transport properties indicate semiconducting behavior with a typical dielectric temperature dependence of the thermal conductivity. The transport properties are discussed in light of the recent interest in this material for thermoelectric applications. The nanorod growth mechanism is also discussed in detail. - Graphical abstract: SnSe nanorods were synthesized by a simple hydrothermal method through a bottom-up approach. Micron sized flower-like crystals changed to nanorods with increasing hydrothermal temperature. Low temperature transport properties of polycrystalline SnSe, after SPS densification, were reported for the first time. This bottom-up synthetic approach can be used to produce phase-pure dense polycrystalline materials for thermoelectrics applications. - Highlights: • SnSe nanorods were synthesized by a simple and efficient hydrothermal approach. • The role of temperature, time and NaOH content was investigated. • SPS densification allowed for low temperature transport properties measurements. • Transport measurements indicate semiconducting behavior.

  20. Optoelectronic and low temperature thermoelectric studies on nanostructured thin films of silver gallium selenide

    SciTech Connect

    Jacob, Rajani Philip, Rachel Reena Nazer, Sheeba Abraham, Anitha Nair, Sinitha B.; Pradeep, B.; Urmila, K. S.; Okram, G. S.

    2014-01-28

    Polycrystalline thin films of silver gallium selenide were deposited on ultrasonically cleaned soda lime glass substrates by multi-source vacuum co-evaporation technique. The structural analysis done by X-ray diffraction ascertained the formation of nano structured tetragonal chalcopyrite thin films. The compound formation was confirmed by X-ray photo-electron spectroscopy. Atomic force microscopic technique has been used for surface morphological analysis. Direct allowed band gap ∼1.78eV with high absorption coefficient ∼10{sup 6}/m was estimated from absorbance spectra. Low temperature thermoelectric effects has been investigated in the temperature range 80–330K which manifested an unusual increase in Seebeck coefficient with negligible phonon drag toward the very low and room temperature regime. The electrical resistivity of these n-type films was assessed to be ∼2.6Ωm and the films showed good photo response.

  1. Optoelectronic and low temperature thermoelectric studies on nanostructured thin films of silver gallium selenide

    NASA Astrophysics Data System (ADS)

    Jacob, Rajani; Philip, Rachel Reena; Nazer, Sheeba; Abraham, Anitha; Nair, Sinitha B.; Pradeep, B.; Urmila, K. S.; Okram, G. S.

    2014-01-01

    Polycrystalline thin films of silver gallium selenide were deposited on ultrasonically cleaned soda lime glass substrates by multi-source vacuum co-evaporation technique. The structural analysis done by X-ray diffraction ascertained the formation of nano structured tetragonal chalcopyrite thin films. The compound formation was confirmed by X-ray photo-electron spectroscopy. Atomic force microscopic technique has been used for surface morphological analysis. Direct allowed band gap ˜1.78eV with high absorption coefficient ˜106/m was estimated from absorbance spectra. Low temperature thermoelectric effects has been investigated in the temperature range 80-330K which manifested an unusual increase in Seebeck coefficient with negligible phonon drag toward the very low and room temperature regime. The electrical resistivity of these n-type films was assessed to be ˜2.6Ωm and the films showed good photo response.

  2. Low Temperature Properties and Thermal Stability of Oligomerized Soybean Oil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soybean oil polymers with lower molecular weight prepared in supercritical carbon dioxide (scCO2) by cationic polymerization were investigated for their applications as lubricants and hydraulic fluids. The low-temperature properties were studied by measuring their cloud and pour points; while therm...

  3. Thermoelectric Properties of Nanostructured CeAl3

    NASA Astrophysics Data System (ADS)

    Pokharel, Mani; Dahal, Tulashi; Ren, Zhifeng; Opeil, Cyril; Opeil Group Team; Ren Group Team

    2014-03-01

    Past investigations into the heavy fermion compound CeAl3 reveal a complex low-temperature physics resulting from the strong hybridization of localized 4f states with delocalized conduction electrons. This phenomenon gives rise to unusual electronic, thermal, and magnetic properties. We investigate the low-temperature thermoelectric properties of this strongly correlated system for its potential application as a p-type Peltier cooling element. In our work, nanostructured samples of CeAl3 have been prepared using dc hot-press method and evaluated for their thermoelectric properties. Effects of different hot-pressing temperatures on the nanostructure and the thermoelectric properties will be discussed. Our results on CeAl3 will be compared with our previous work on CeCu6. Funding for this work was provided by the DOD, USAF-OSR, MURI Program under Contract FA9550-10-1-0533.

  4. and Their Thermoelectric Properties

    NASA Astrophysics Data System (ADS)

    Wagner-Reetz, M.; Cardoso-Gil, R.; Grin, Yu.

    2014-06-01

    In this study we performed substitution experiments on the gallium site of the intermetallic semiconductor FeGa3, to adjust the charge carrier concentration, and determined the thermoelectric (TE) properties of the resulting products. Isoelectronic species aluminium and indium, hole-doping zinc, and electron-doping germanium were chosen to find suitable substituent elements. The samples FeGa3- x E x ( E = Al, In, Zn, Ge; x = 0.03, 0.05, 0.06, 0.10, 0.20) were prepared by liquid-solid-reaction with subsequent spark plasma sintering treatment. X-ray diffraction, metallographic, and microstructure analysis were used to determine chemical composition and to evaluate the suitability of the substitution element. For solid solutions FeGa3- x Al x and FeGa3- x In x the substitution concentrations were very low ( x ≤ 0.02) and did not improve the TE properties of FeGa3. The samples FeGa3- x Zn x had the expected p-type behaviour and slightly lower thermal conductivity than the binary compound. A substantial increase in the TE figure of merit was achieved for the solid solution FeGa3- x Ge x for which transition from semiconducting to metal-like behaviour was observed, with an additional decrease of thermal conductivity. The maximum ZT value of 0.21 was achieved for the composition FeGa2.80Ge0.20.

  5. Evaluation of low temperature properties of warm mix asphalt

    NASA Astrophysics Data System (ADS)

    Wen, Jin; Liu, Zhifei; Wu, Shaopeng

    2010-03-01

    Warm mix asphalt (WMA), which reduces the mixing and compaction temperature of conventional hot mix asphalt (HMA), is becoming an attractive paving material. It is critical to identify the low temperature properties of warm mix asphalt. In this study, the three-point bending, bending creep tests and indirect tensile tests were conducted to test the low-temperature properties of warm mix asphalt as well as the conventional hot mix asphalt, which was used as the control mixture. Sasobit and Aspha-min were used as additives for warm mix asphalt, which was mixed and compacted lower than the traditional hot mix asphalt about 25°C dosages accounted for 3% of asphalt, and 0.3% of mixture, respectively. The results of bending strength, bending modulus, and creep rate indicate that warm mix asphalt using Sasobit and Aspha-min slightly affects the resistance property to cracking compared with the conventional hot mix asphalt. The results suggest that the warm mix asphalt can maintain the low temperature properties of hot mix asphalt.

  6. Evaluation of low temperature properties of warm mix asphalt

    NASA Astrophysics Data System (ADS)

    Wen, Jin; Liu, Zhifei; Wu, Shaopeng

    2009-12-01

    Warm mix asphalt (WMA), which reduces the mixing and compaction temperature of conventional hot mix asphalt (HMA), is becoming an attractive paving material. It is critical to identify the low temperature properties of warm mix asphalt. In this study, the three-point bending, bending creep tests and indirect tensile tests were conducted to test the low-temperature properties of warm mix asphalt as well as the conventional hot mix asphalt, which was used as the control mixture. Sasobit and Aspha-min were used as additives for warm mix asphalt, which was mixed and compacted lower than the traditional hot mix asphalt about 25°C dosages accounted for 3% of asphalt, and 0.3% of mixture, respectively. The results of bending strength, bending modulus, and creep rate indicate that warm mix asphalt using Sasobit and Aspha-min slightly affects the resistance property to cracking compared with the conventional hot mix asphalt. The results suggest that the warm mix asphalt can maintain the low temperature properties of hot mix asphalt.

  7. Low temperature transport properties of Ce-Al metallic glasses

    SciTech Connect

    Zeng, Q. S.; Rotundu, C. R.; Mao, W. L.; Dai, J. H.; Xiao, Y. M.; Chow, P.; Chen, X. J.; Qin, C. L.; Mao, H.-k.; Jiang, J. Z.

    2011-01-01

    The low temperature transport properties of Ce75- x Al25+ x (x = 0, 10, and 15 at. %) metallic glasses were investigated. Magnetic field and composition tuned magnetoresistances changing from negative to positive values were observed at low temperature. It was suggested that these peculiar phenomena were caused by the tunable competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida interaction in Ce-Al metallic glass with the variation in Ce content and magnetic field. Further magnetization and Ce-2p3d resonant inelastic x-ray scattering spectroscopy measurements supported this scenario. These Ce-Al metallic glasses could provide an interesting model system for the investigation of 4f electron behaviors in complex condensed matter with tunable transport properties.

  8. Promising thermoelectric properties of phosphorenes.

    PubMed

    Sevik, Cem; Sevinçli, Hâldun

    2016-09-01

    Electronic, phononic, and thermoelectric transport properties of single layer black- and blue-phosphorene structures are investigated with first-principles based ballistic electron and phonon transport calculations employing hybrid functionals. The maximum values of room temperature thermoelectric figure of merit, ZT corresponding to armchair and zigzag directions of black-phosphorene, ∼0.5 and ∼0.25, are calculated as rather smaller than those obtained with first-principles based semiclassical Boltzmann transport theory calculations. On the other hand, the maximum value of room temperature ZT of blue-phosphorene is predicted to be substantially high and remarkable values as high as 2.5 are obtained for elevated temperatures. Besides the fact that these figures are obtained at the ballistic limit, our findings mark the strong possibility of high thermoelectric performance of blue-phosphorene in new generation thermoelectric applications. PMID:27455173

  9. Promising thermoelectric properties of phosphorenes

    NASA Astrophysics Data System (ADS)

    Sevik, Cem; Sevinçli, Hâldun

    2016-09-01

    Electronic, phononic, and thermoelectric transport properties of single layer black- and blue-phosphorene structures are investigated with first-principles based ballistic electron and phonon transport calculations employing hybrid functionals. The maximum values of room temperature thermoelectric figure of merit, ZT corresponding to armchair and zigzag directions of black-phosphorene, ∼0.5 and ∼0.25, are calculated as rather smaller than those obtained with first-principles based semiclassical Boltzmann transport theory calculations. On the other hand, the maximum value of room temperature ZT of blue-phosphorene is predicted to be substantially high and remarkable values as high as 2.5 are obtained for elevated temperatures. Besides the fact that these figures are obtained at the ballistic limit, our findings mark the strong possibility of high thermoelectric performance of blue-phosphorene in new generation thermoelectric applications.

  10. Interplay of chemical expansion, Yb valence, and low temperature thermoelectricity in the YbCu2Si2-xGex solid solution

    NASA Astrophysics Data System (ADS)

    Lehr, Gloria J.; Morelli, Donald T.

    2015-04-01

    YbCu2Si2 is a promising low temperature thermoelectric material because of the large broad peak in the Seebeck coefficient near 100 K combined with a low electrical resistivity. This behavior is thought to arise from fluctuating, or intermediate, valence effects due to partial occupation of Yb 4f energy states near the Fermi level. Previous studies of the magnetic properties under pressure have demonstrated that the average Yb valence is sensitive to the contraction of unit cell volume. By forming a solid solution of YbCu2Si2 with YbCu2Ge2, an isostructural compound with a larger unit cell volume, here we examine the subtle effects of lattice expansion on the transport properties and average Yb valence. We observe a shift in the peak of the Seebeck coefficient towards higher temperatures, as well as an enhanced power factor in the solid solutions. At the same time, a reduction in thermal conductivity due to alloy scattering enhances the thermoelectric figure of merit. Chemical pressure effects may thus be utilized to control and optimize the thermoelectric properties of these alloys in the cryogenic temperature range.

  11. Measuring Thermoelectric Properties Automatically

    NASA Technical Reports Server (NTRS)

    Chmielewski, A.; Wood, C.

    1986-01-01

    Microcomputer-controlled system speeds up measurements of Hall voltage, Seebeck coefficient, and thermal diffusivity in semiconductor compounds for thermoelectric-generator applications. With microcomputer system, large data base of these parameters gathered over wide temperature range. Microcomputer increases measurement accuracy, improves operator productivity, and reduces test time.

  12. Challenges in Characterizing Low-Temperature Regolith Properties

    NASA Technical Reports Server (NTRS)

    Swanger, Adam Michael; Mantovani, James G.

    2014-01-01

    The success or failure of in-situ resource utilization for planetary surface exploration--be it for scientific, colonization or commercialization purposes--relies heavily on the ability to design and implement systems which effectively process the associated regolith and exploit its benefits. In most cases this challenge necessarily includes the characterization of low-temperature (cryogenic) properties; as many celestial destinations of interest, such as the moon, Mars and asteroids, have little or no atmosphere to help sustain the consistently "high" surface temperatures seen on planets such as Earth, and therefore can experience permanent cryogenic temperatures or dramatic cyclical changes. Characterization of physical properties (such as specific heat, thermal and electrical conductivity, etc.) over the entire temperature profile is undoubtedly an important piece of the puzzle; however, the impact on mechanical properties due to the introduction of icy deposit must also be explored in order to devise effective and robust excavation technologies. Currently the Granular Mechanics and Regolith Operations Lab and the Cryogenics Test Lab at NASA Kennedy Space Center are developing technologies and experimental methods to address these challenges and aid in the characterization of physical and mechanical properties of regolith at cryogenic temperatures. This presentation will review the current state of knowledge concerning lunar regolith at low temperature including that of icy regolith.

  13. The anomalous thermal properties of glasses at low temperatures

    NASA Technical Reports Server (NTRS)

    Pohl, R. O.; Salinger, G. L.

    1976-01-01

    While experimentally there is great regularity below 1 deg K in the behavior of a particular thermal property for all amorphous dielectrics it is not understood why these properties should differ from those of crystalline dielectrics, since it would seem that at low temperatures long-wavelength elastic waves, similar in both cases, would determine the thermal properties. A model involving systems having very few levels is used in the present study, although the relation between the model's systems and the nature of the glassy state is not known. It is shown, among other effects, that: specific heat measurements above 0.1 K indicate a distribution of local modes independent of energy; ultrasonic velocity measurements give information about phonon-local mode coupling parameters; and thermal expansion and far infrared experiments indicate a phonon-assisted tunneling model.

  14. Shape memory polymers with high and low temperature resistant properties

    PubMed Central

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-01-01

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to −150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed. PMID:26382318

  15. Shape memory polymers with high and low temperature resistant properties

    NASA Astrophysics Data System (ADS)

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-09-01

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to -150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed.

  16. Low temperature resistivity, thermoelectricity, and power factor of Nb doped anatase TiO2

    NASA Astrophysics Data System (ADS)

    Jaćimović, J.; Gaál, R.; Magrez, A.; Piatek, J.; Forró, L.; Nakao, S.; Hirose, Y.; Hasegawa, T.

    2013-01-01

    The resistivity of a very high quality anatase TiO2 doped with 6% of Nb was measured from 300 K down to 40 mK. No sign of superconductivity was detected. Instead, a minute quantity of cation vacancies resulted in a Kondo scattering. Measurements of thermo-electric power and resistivity were extended up to 600 K. The calculated power factor has a peak value of 14 μW/(K2cm) at 350 K, which is comparable to that of Bi2Te3 [Venkatasubramanian et al., Nature 413, 597 (2001)], the archetype thermolectrics. Taking the literature value for the thermal conductivity of Nb doped TiO2 thin films, the calculated figure of merit (ZT) is in the range of 0.1 above 300 K. This value is encouraging for further engineering of the material in order to reach ZT of 1 suitable for high temperature thermoelectrics.

  17. Low-Temperature Seebeck Coefficients for Polaron-Driven Thermoelectric Effect in Organic Polymers.

    PubMed

    de Oliveira Neto, Pedro Henrique; da Silva Filho, Demétrio A; Roncaratti, Luiz F; Acioli, Paulo H; E Silva, Geraldo Magela

    2016-07-14

    We report the results of electronic structure coupled to molecular dynamics simulations on organic polymers subject to a temperature gradient at low-temperature regimes. The temperature gradient is introduced using a Langevin-type dynamics corrected for quantum effects, which are very important in these systems. Under this condition we were able to determine that in these no-impurity systems the Seebeck coefficient is in the range of 1-3 μV/K. These results are in good agreement with reported experimental results under the same low-temperature conditions. PMID:26886243

  18. Low temperature carrier transport properties in isotopically controlled germanium

    SciTech Connect

    Itoh, K.

    1994-12-01

    Investigations of electronic and optical properties of semiconductors often require specimens with extremely homogeneous dopant distributions and precisely controlled net-carrier concentrations and compensation ratios. The previous difficulties in fabricating such samples are overcome as reported in this thesis by growing high-purity Ge single crystals of controlled {sup 75}Ge and {sup 70}Ge isotopic compositions, and doping these crystals by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios are precisely determined by the thermal neutron fluence and the [{sup 74}Ge]/[{sup 70}Ge] ratios of the starting Ge materials, respectively. This method also guarantees unprecedented doping uniformity. Using such samples the authors have conducted four types of electron (hole) transport studies probing the nature of (1) free carrier scattering by neutral impurities, (2) free carrier scattering by ionized impurities, (3) low temperature hopping conduction, and (4) free carrier transport in samples close to the metal-insulator transition.

  19. Investigating Low Temperature Properties of Rubber Seals - 13020

    SciTech Connect

    Jaunich, M.; Wolff, D.; Stark, W.

    2013-07-01

    To achieve the required tightness levels of containers for low and intermediate level radioactive wastes rubbers are widely applied as main sealing materials. The save encapsulation of the radioactive container contents has to be guaranteed according to legislation and appropriate guidelines for long storage periods as well as down to temperatures of -40 deg. C during transportation. Therefore the understanding of failure mechanisms that lead to leakage at low temperatures is of high importance. It is known that the material properties of rubbers are strongly influenced by temperature. At low temperatures this is caused by the rubber-glass transition (abbr. glass transition). During continuous cooling the material changes from rubber-like entropy-elastic to stiff energy-elastic behaviour, that allows nearly no strain or retraction. Therefore, rubbers are normally used above their glass transition but the minimum working temperature limit is not defined precisely, what can cause problems during application. The temperature range where full functionality is possible is strongly dependent on the application conditions and the material. For this investigation mainly ethylene propylene diene (EPDM) and fluorocarbon rubbers (FKM) were selected as they are often used for radioactive waste containers. Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) are typically used for the determination of the temperature range of the glass transition process. The standardized compression set measurement according to ISO 815 is common for investigation of rubber sealing materials as the test simulates the seal behaviour after release. To reduce the test time of the standard tests a faster technique giving the same information was developed. Additionally, the breakdown temperature of the sealing function of complete O-ring seals is measured in a component test setup to compare it with the results of the other tests. The experimental setup is capable of

  20. Low temperature self-cleaning properties of superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Wang, Fajun; Shen, Taohua; Li, Changquan; Li, Wen; Yan, Guilong

    2014-10-01

    Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of -10 °C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of -12 °C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.

  1. Thermoelectric Properties of Complex Zintl Phases

    NASA Astrophysics Data System (ADS)

    Snyder, G. Jeffrey

    2008-03-01

    Complex Zintl phases make ideal thermoelectric materials because they can exhibit the necessary ``electron-crystal, phonon-glass'' properties required for high thermoelectric efficiency. Complex crystal structures can lead to high thermoelectric figure of merit (zT) by having extraordinarily low lattice thermal conductivity. A recent example is the discovery that Yb14MnSb11, a complex Zintl compound, has twice the zT as the SiGe based material currently in use at NASA. The high temperature (300K - 1300K) electronic properties of Yb14MnSb11 can be understood using models for heavily doped semiconductors. The free hole concentration, confirmed by Hall effect measurements, is set by the electron counting rules of Zintl and the valence of the transition metal (Mn^+2). Substitution of nonmagnetic Zn^+2 for the magnetic Mn^+2 reduces the spin-disorder scattering and leads to increased zT (10%). The reduction of spin-disorder scattering is consistent with the picture of Yb14MnSb11 as an underscreened Kondo lattice as derived from low temperature measurements. The hole concentration can be reduced by the substitution of Al^+3 for Mn^+2, which leads to an increase in the Seebeck coefficient and electrical resistivity consistent with models for degenerate semiconductors. This leads to further improvements (about 25%) in zT and a reduction in the temperature where the zT peaks. The peak in zT is due to the onset of minority carrier conduction and can be correlated with reduction in Seebeck coefficient, increase in electrical conductivity and increase in thermal conductivity due to bipolar thermal conduction.

  2. Correlation between low temperature properties and fragility of glasses

    NASA Astrophysics Data System (ADS)

    Zhu, Da-Ming

    1997-03-01

    The nature of glass transition and the nature of low energy excitations that govern the low temperature properties of glasses are the two fundamental problems remain unsolved in the study of glasses. It was recently suggested that several properties governed by the low energy excitations in glasses are correlated to the glass fragility,[1] a parameter used to characterize the temperature variation of relaxation time near glass transitions.[2] A previous examination of the specific heats at T < 1 K and the fragility of a dozen different glasses found a correlation seems to exist.[3] The correlation is also consistent with an interpretation of fragility of glasses in terms of difference in potential energy landscape in configuration space.[2] We recently compared the specific heats and thermal conductivity of several glasses at 1K < T < 20 K and their fragility. We found that a general trend appears to exist that more fragile glasses have lower specific heat bump in the plot of C/T3 versus T or lower step in the plot of C/T versus T. The implication of the correlation and the possible interpretation in terms of potential energy landscape will be discussed. [1] A. P. Sokolov et al, Phys. Rev. Lett. 71, 2062 (1993). [2] C. A. Angell, J. Non-Cryst. Solids 131-133, 13 (1993). [3] Da-Ming Zhu, Phys. Rev. B 54, 6287 (1996).

  3. InAs/GaSb Type II Superlattices as Low-Temperature Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Birner, S.; Norko, M.; Tang, Y.; Grayson, M.

    2011-12-01

    Leo Esaki originally proposed that by increasing the layer thickness, InAs/GaSb superlattices can be tuned from a semiconducting to a semimetallic state, where electron and hole wavefunctions are spatially localized to InAs and GaSb layers, respectively. Because of the tunably small spatially indirect gap of InAs/GaSb and the anisotropy of the superlattice structure, this material might have interesting thermoelectric applications at cryogenic temperatures. We measured the thermal conductivity of such Type II superlattices using the 3ω method and observe a reduction by two orders of magnitude from the average GaSb and InAs bulk thermal conductivities. We also use 8×8 band kṡp envelope-function approach to simulate the dispersion function of different period InAs/GaSb superlattices, and we find the InAs and GaSb layer thicknesses can be adjusted to engineer anisotropic band structures.

  4. Low temperature property of Metaphosphatecopper(II/I) salt

    NASA Astrophysics Data System (ADS)

    Swain, Trilochan; Brahma, Gouri Sankhar

    2016-04-01

    An inorganically template metaphosphoric acid containing copper salt, nanomaterial, has been synthesized and characterized with different measurement techniques such as Differential Scanning Calorimeter (DSC), UV-Vis-NIR, HRTEM, VSM, PPMS and X-RD. The thermal property of this salt has been studied at a low temperature up to 223 K from 298 K with DSC. The specific heat capacity of this complex has been measured in atmospheric O2 at a rate of 10 K min-1 from 298 K to 223 K and vice versa in two thermal cycles. The net specific heat capacity of this salt is found -88.28 J/gm.K and - 86.56 J/gm.K in first and second thermal cycles, respectively. There is a discontinuity in the specific heat at 106 s while measuring the specific heat capacity of the above nanomaterial at constant temperature 283 K. This particle size of this nanomaterial is ˜ 10 nm. The paramagnetic Curie temperature (θP) and Curie constant (C) are 18.29 K and 1.35x10-3 respectively. This material founds insulator from PPMS and UV-Vis-NIR measurements. So, it can be used as thermal interface material as a composite component with some organic polymers such as paraffin wax, ethylene-vinyl acetate etc.

  5. Ulta-Low Temperature Properties of Amorphous and Glassy Materials

    SciTech Connect

    Douglas D. Osheroff

    2013-01-10

    During the grant period we made detailed studies of the dynamics of two level tunneling systems in glasses at very low temperature and by the application of AC and DC electric fields. Models have been developed that now account for both the formation and subsequent breaking of resonant tunneling pairs, and strongly bound pairs in a swept electric field. Perhaps most importantly, we saw a critical field in the polymeric glass Mylar, beyond which recovery following the application of a strong electric field is substantially modified from the predictions of current models. It was essential during the final grant period to see how general these new properties were by testing for them in a new and broader set of glasses. At the same time, the discovery that tunneling systems with nuclei possessing electric quadrupole moments that couple the TS behavior to magnetic fields was studied in this laboratory, using some of the probes that we alone employ. Finally, we were developing our own dielectric pulsed echo system, operating for the first time at the low energy splittings and hence temperatures at which interactions between TS are important. We combined this technique with the sudden application of both electric and strain fields to better understand the dynamics of the response of TS in glasses on a much shorter time scale than is possible with our established probes.

  6. Low temperature properties of some Er-rich intermetallic compounds

    SciTech Connect

    K.A. Gshneidner,jr; A.O. Pecharsky; L.Hale; V.K. Pecharsky

    2004-09-30

    The low temperature volumetric heat capacity ({approx}3.5 to 350 K) and magnetic susceptibility ({approx}4 to 320 K) of Er{sub 3}Rh, Er{sub 3}Ir, Er{sub 3}Pt, Er{sub 2}Al, and Er{sub 2}Sn have been measured. All of the compounds order antiferromagnetically (or ferrimagnetically), and most exhibit more than one magnetic ordering transition. The volumetric heat capacities in general are smaller than those of the prototype magnetic regenerator materials, except for Er{sub 3}Ir in the 12 to 14 K temperature range.

  7. Thermal Properties of Double-Aluminized Kapton at Low Temperatures

    NASA Technical Reports Server (NTRS)

    Tuttle, J.; DiPirro, M.; Canavan, E.; Hait, T.

    2007-01-01

    Double-aluminized kapton (DAK) is commonly used in multi-layer insulation blankets in cryogenic systems. NASA plans to use individual DAK sheets in lightweight deployable shields for satellites carrying instruments. A set of these shields will reflect away thermal radiation from the sun, the earth, and the instrument's warm side and allow the instrument's cold side to radiate its own heat to deep space. In order to optimally design such a shield system, it is important to understand the thermal characteristics of DAK down to low temperatures. We describe experiments which measured the thermal conductivity and electrical resistivity down to 4 Kelvin and the emissivity down to 10 Kelvin.

  8. Thermal Properties of Double-Aluminized Kapton at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Tuttle, J.; DiPirro, M.; Canavan, E.; Hait, T.

    2008-03-01

    Double-aluminized kapton (DAK) is commonly used in multi-layer insulation blankets in cryogenic systems. NASA plans to use individual DAK sheets in lightweight deployable shields for satellites carrying instruments. A set of these shields will reflect away thermal radiation from the sun, the earth, and the instrument's warm side and allow the instrument's cold side to radiate its own heat to deep space. In order to optimally design such a shield system, it is important to understand the thermal characteristics of DAK down to low temperatures. We describe experiments which measured the thermal conductivity and electrical resistivity down to 4 Kelvin and the emissivity down to 10 Kelvin.

  9. Low-Temperature Transport Properties of Bi-Substituted β-As2Te3 Compounds

    NASA Astrophysics Data System (ADS)

    Vaney, J.-B.; Carreaud, J.; Delaizir, G.; Morin, C.; Monnier, J.; Alleno, E.; Piarristeguy, A.; Pradel, A.; Gonçalves, A. P.; Lopes, E. B.; Candolfi, C.; Dauscher, A.; Lenoir, B.

    2016-03-01

    β-As2Te3 belongs to the family of Bi2Te3-based alloys, a well-known class of efficient thermoelectric materials around room temperature. As2Te3 exists in two allotropic configurations: α- and β-As2Te3, of which only the latter crystallizes in the same rhombohedral structure as Bi2Te3. Herein, we report on substitution of Bi for As in the As2- x Bi x Te3 system with x = 0.0, 0.015, 0.025, and 0.035. These samples have been characterized by x-ray diffraction and scanning electron microscopy. The transport properties have been measured at low temperatures (5 K to 300 K) in both directions, parallel and perpendicular to the pressing direction. The results are compared with those obtained in previous study on samples substituted by Sn. Compared with Sn, Bi allows for a clear decrease in electrical resistivity while maintaining the thermal conductivity below 1 W/(m K) over the whole temperature range. As a result, a comparable peak ZT value near 0.2 was obtained at room temperature.

  10. semiconducting nanostructures: morphology and thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Culebras, Mario; Torán, Raquel; Gómez, Clara M.; Cantarero, Andrés

    2014-08-01

    Semiconducting metallic oxides, especially perosvkite materials, are great candidates for thermoelectric applications due to several advantages over traditionally metallic alloys such as low production costs and high chemical stability at high temperatures. Nanostructuration can be the key to develop highly efficient thermoelectric materials. In this work, La 1- x Ca x MnO 3 perosvkite nanostructures with Ca as a dopant have been synthesized by the hydrothermal method to be used in thermoelectric applications at room temperature. Several heat treatments have been made in all samples, leading to a change in their morphology and thermoelectric properties. The best thermoelectric efficiency has been obtained for a Ca content of x=0.5. The electrical conductivity and Seebeck coefficient are strongly related to the calcium content.

  11. Low-temperature mechanical properties of glass/epoxy laminates

    SciTech Connect

    Reed, R. P.; Madhukar, M.; Thaicharoenporn, B.; Martovetsky, N. N.

    2014-01-27

    Selected mechanical properties of glass/epoxy laminate candidates for use in the electrical turn and ground insulation of the ITER Central solenoid (CS) modules were measured. Short-beam shear and flexural tests have been conducted on various E-glass cloth weaves/epoxy laminates at 295 and 77 K. Types of glass weave include 1581, 7500, 7781, and 38050, which represent both satin and plain weaves. The epoxy, planned for use for vacuum-pressure impregnation of the CS module, consists of an anhydride-cured bisphenol F resin system. Inter-laminar shear strength, flexural elastic modulus, and flexural strength have been measured. The data indicate that these properties are dependent on the volume percent of glass. Short-beam shear strength was measured as a function of the span-to-thickness ratio for all laminates at 77 K. Comprehensive fractography was conducted to obtain the failure mode of each short-beam shear test sample.

  12. Low-temperature mechanical properties of glass/epoxy laminates

    NASA Astrophysics Data System (ADS)

    Reed, R. P.; Madhukar, M.; Thaicharoenporn, B.; Martovetsky, N. N.

    2014-01-01

    Selected mechanical properties of glass/epoxy laminate candidates for use in the electrical turn and ground insulation of the ITER Central solenoid (CS) modules were measured. Short-beam shear and flexural tests have been conducted on various E-glass cloth weaves/epoxy laminates at 295 and 77 K. Types of glass weave include 1581, 7500, 7781, and 38050, which represent both satin and plain weaves. The epoxy, planned for use for vacuum-pressure impregnation of the CS module, consists of an anhydride-cured bisphenol F resin system. Inter-laminar shear strength, flexural elastic modulus, and flexural strength have been measured. The data indicate that these properties are dependent on the volume percent of glass. Short-beam shear strength was measured as a function of the span-to-thickness ratio for all laminates at 77 K. Comprehensive fractography was conducted to obtain the failure mode of each short-beam shear test sample.

  13. Thermoelectric properties of granular metals.

    SciTech Connect

    Glatz, A.; Beloborodov, I. S.; Materials Science Division; California State Univ. Northridge

    2009-01-01

    We investigate the thermopower and thermoelectric coefficient of nanogranular materials at large tunneling conductance between the grains, g{sub T} >> 1. We show that at intermediate temperatures, T>g{sub T}{delta}, where {delta} is the mean energy-level spacing for a single grain, electron-electron interaction leads to an increase in the thermopower with decreasing grain size. We discuss our results in light of the next generation of thermoelectric materials and present the behavior of the figure of merit depending on the system parameters.

  14. The thermal properties and thermoelectric performance of γ-graphyne nanoribbons

    NASA Astrophysics Data System (ADS)

    Yang, Zhi; Ji, Yu-Long; Lan, Guoqiang; Xu, Li-Chun; Wang, Hua; Liu, Xuguang; Xu, Bingshe

    2016-04-01

    The thermal properties and thermoelectric performance of one-dimensional armchair and zigzag γ-graphyne nanoribbons (γ-GYNRs) are theoretically investigated in the present study. We found that the pristine γ-GYNRs hold lower phononic thermal conductance and better figure of merit (ZT) than graphene nanorribons. The maximal ZT values for the armchair and zigzag γ-GYNRs are 0.93 and 0.61, respectively. By introducing 14C atoms, the thermoelectric conversion efficiencies of γ-GYNRs are greatly enhanced, thus the isotope effect can significantly improve the thermoelectric properties of the systems. More importantly, under a relatively low temperature, the maximal ZT of a defective zigzag γ-GYNR is as high as 2.12, indicating that γ-GYNRs are promising materials for constructing excellent thermoelectric nanodevices.

  15. Lattice dynamics and thermoelectric properties of nanocrystalline silicon-germanium alloys

    SciTech Connect

    Claudio, Tania; Stein, Niklas; Peterman, Nils; Stroppa, Daniel; Koza, Michael M.; Wiggers, Hartmut; Klobes, B.; Schierning, Gabi; Hermann, Raphael P.

    2015-10-26

    The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon- germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low- temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000C. A peak figure of merit zT = 0:88 at 900C is observed and comparatively insensitive to the aforementioned param- eter variations.

  16. Thermoelectric Properties of Lanthanum Sulfide

    NASA Technical Reports Server (NTRS)

    Wood, C.; Lockwood, R.; Parker, J. B.; Zoltan, A.; Zoltan, L. D.; Danielson, L.; Raag, V.

    1987-01-01

    Report describes measurement of Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect in gamma-phase lanthanum sulfide with composition of La3-x S4. Results of study, part of search for high-temperature thermoelectric energy-conversion materials, indicate this sulfide behaves like extrinsic semiconductor over temperature range of 300 to 1,400 K, with degenerate carrier concentration controlled by stoichiometric ratio of La to S.

  17. Optimizing Thermoelectric Properties in Composites

    NASA Astrophysics Data System (ADS)

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

    Here we consider semiconductor composites as a way to yield high thermoelectric figure of merit. Effective medium theory limits the figure of merit of a composite made from two non-interacting materials, A and B, to the larger of the two. In previous work, we describe a mechanism that can lift this limitation by treating charge and heat flux separately. Silica beads coated with a conducting shell are inserted into a thermoelectric host. Thermal conductivity decreases with insulating material added, but electrical conductivity is maintained via locally conducting surfaces. We apply the theory to p-type (Bi,Sb)2Te3 host material. Several permutations are possible: Te-coated beads in Sb-rich material, or Sb-coated beads in Te-rich material. First, we review data for varying bead coatings and heat treatments, followed by varying stoichiometry in the host. New data considers an additional parameter of varying bead diameter, as well as optimizing these parameters simultaneously to enhance thermoelectric performance.

  18. Thermoelectric property of a new silicon crystal

    NASA Astrophysics Data System (ADS)

    Chae, Kisung; Choi, Seon-Myeong; Kim, Duck Young; Son, Young-Woo

    We present ab initio calculations on thermoelectric properties of a recently synthesised allotrope of silicon crystal. A new silicon crystal with 24 Si atoms per unit cell has open channels along the specific crystallographic direction and shows a quasidirect energy gap of 1.3 eV. Using various first-principles calculation techniques for electrical and thermal conductivity as well as Seebeck coefficient, we find large suppression of thermal conductivity and relatively large Seebeck coefficient in the new silicon crystal, thus demonstrating a competitive thermoelectric figure of merit.

  19. Thermoelectric properties of -FeSi2

    SciTech Connect

    Parker, David S; Singh, David J; Pandey, Tribhuwan; Singh, Abhishek

    2013-01-01

    We investigate the thermoelectric properties of -FeSi2 using first principles electronic structure and Boltzmann trans- port calculations. We report a high thermopower for both p- and n-type -FeSi2 over a wide range of carrier concentra- tion and in addition find the performance for n-type to be higher than for the p-type. Our results indicate that, depending upon temperature, a doping level of 3 1020 - 2 1021 cm 3 may optimize the thermoelectric performance.

  20. The thermoelectric properties of strongly correlated systems

    NASA Astrophysics Data System (ADS)

    Cai, Jianwei

    Strongly correlated systems are among the most interesting and complicated systems in physics. Large Seebeck coefficients are found in some of these systems, which highlight the possibility for thermoelectric applications. In this thesis, we study the thermoelectric properties of these strongly correlated systems with various methods. We derived analytic formulas for the resistivity and Seebeck coefficient of the periodic Anderson model based on the dynamic mean field theory. These formulas were possible as the self energy of the single impurity Anderson model could be given by an analytic ansatz derived from experiments and numerical calculations instead of complicated numerical calculations. The results show good agreement with the experimental data of rare-earth compound in a restricted temperature range. These formulas help to understand the properties of periodic Anderson model. Based on the study of rare-earth compounds, we proposed a design for the thermoelectric meta-material. This manmade material is made of quantum dots linked by conducting linkers. The quantum dots act as the rare-earth atoms with heavier mass. We set up a model similar to the periodic Anderson model for this new material. The new model was studied with the perturbation theory for energy bands. The dynamic mean field theory with numerical renormalization group as the impurity solver was used to study the transport properties. With these studies, we confirmed the improved thermoelectric properties of the designed material.

  1. Enhanced thermoelectric properties in silicon nanowires

    NASA Astrophysics Data System (ADS)

    Mitrovic, Slobodan; Yu, Jen-Kan; Boukai, Akram; Tahir-Kheli, Jamil; Goddard, William A., III; Heath, James R.

    2008-03-01

    Recently, we demonstrated that silicon nanowires can be designed and fabricated to achieve an approximately 100-fold enhancement in thermoelectric efficiency compared to bulk silicon. Independent measurements of thermoelectric power, and thermal and electrical conductivities suggest that this improvement is due to phonon effects rather than quantum confinement. Here, we present the study of the scaling laws (i.e. nanowire length/width dependence) for the phonon dynamics and transport. We investigate the influence of the phonon drag, carrier mobility and doping on the thermoelectric properties, and the universality of these findings. This work is supported by the Office of Naval Research, the Department of Energy, the National Science Foundation, and the Defense Advanced Research Projects Agency.

  2. Thermoelectric properties of cerium monopnictides

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Alexander, M. N.; Wood, C.; Lockwood, R. A.; Vandersande, J. W.

    1987-01-01

    Several cerium pnictides have been synthesized from the pure elements and hot pressed into test samples. Measurements of Seebeck coefficients and electrical resistivities were performed on these samples from room temperature to 1000 C. Cerium arsenide and cerium antimonide are n-type; cerium nitride changes from p-type to n-type conduction at 800 C. The materials are semimetals with resistivities below 1 mohm/cm. Cerium arsenide is the most favorable of the pnictides studied for high-temperature thermoelectric energy conversion, with an average power factor of 15 microW/cm K sq from 500 to 1000 C.

  3. Thermoelectric properties of inverse opals

    NASA Astrophysics Data System (ADS)

    Mahan, G. D.; Poilvert, N.; Crespi, V. H.

    2016-02-01

    Rayleigh's method [Philos. Mag. Ser. 5 34, 481 (1892)] is used to solve for the classical thermoelectric equations in inverse opals. His theory predicts that in an inverse opal, with periodic holes, the Seebeck coefficient and the figure of merit are identical to that of the bulk material. We also provide a major revision to Rayleigh's method, in using the electrochemical potential as an important variable, instead of the electrostatic potential. We also show that in some cases, the thermal boundary resistance is important in the effective thermal conductivity.

  4. Oxidation, Low Temperature, and Lubricating Properties of Chemically-modified Methyl Oleates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The inherent problems of vegetable oils, such as poor oxidation and low temperature properties, can be improved by attaching functional groups at the sites of unsaturation through chemical modification. In this study, we have shown how functionalization helps overcome these disadvantages. Five bra...

  5. Glycerol Tri-Ester Derivatives as Diluents to Improve Low Temperature Properties of Vegetable Oils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Large-scale production of biodiesel has led to a surplus of glycerol, so new commercial uses of this co-product are being sought. Twenty four vegetable oils were screened using glycerol tris (2-ethylhexanoate) [GTEH] as a diluent to improve the low temperature properties. Epoxidized soybean oil (E...

  6. Thermoelectric properties of lanthanum sulfide

    NASA Technical Reports Server (NTRS)

    Wood, C.; Lockwood, A.; Parker, J.; Zoltan, A.; Zoltan, D.

    1985-01-01

    The Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect have been studied in gamma-phase La(3-x)S4(LaS/y/) for compositions with x in the range from 0.04 to 0.3 (y in the range from 1.35 to 1.48) in order to ascertain its suitability for high-temperature (300 to 1400 K) thermoelectric energy conversion. In this temperature and composition range the material behaves as an extrinsic semiconductor whose degenerate carrier concentration is controlled by the stoichiometric ratio of La to S. A maximum figure-of-merit (Z) of approximately 0.0005 per K at a composition x = 0.3, y = 1.48 (LaS/1.48/) was obtained.

  7. Low-Temperature Thermodynamic Properties of a One-Dimensional Generalized Wigner Crystal

    NASA Astrophysics Data System (ADS)

    Slavin, V.

    The low-temperature thermodynamic properties of a one-dimensional generalized Wigner crystal at arbitrary values of electron density and arbitrary number of interacting electrons are studied. The modified transfer-matrixes method is applied. It is shown that increasing the number of interacting electrons leads to the appearance of more and more fine "stairs" in low-temperature dependence of chemical potential against electron density. An influence of the disorder in host-lattice site positions on thermodynamic characteristics of the system is considered. It is established that the disorder destroys the "stairs".

  8. Thermoelectric properties of zinc based pnictide semiconductors

    NASA Astrophysics Data System (ADS)

    Sreeparvathy, P. C.; Kanchana, V.; Vaitheeswaran, G.

    2016-02-01

    We report a detailed first principles density functional calculations to understand the electronic structure and transport properties of Zn-based pnictides ZnXPn2 (X: Si, Ge, and Sn; Pn: P and As) and ZnSiSb2. The electronic properties calculated using Tran-Blaha modified Becke-Johnson functional reveals the semi-conducting nature, and the resulting band gaps are in good agreement with experimental and other theoretical reports. We find a mixture of heavy and light bands in the band structure which is an advantage for good thermoelectric (TE) properties. The calculated transport properties unveils the favour p-type conduction in ZnXP2 (X: Si, Ge, and Sn) and n-type conduction in ZnGeP2 and ZnSiAs2. Comparison of transport properties of Zn-based pnictides with the prototype chalcopyrite thermoelectric materials implies that the thermopower values of the investigated compounds to be higher when compared with the prototype chalcopyrite thermoelectric materials, together with the comparable values for electrical conductivity scaled by relaxation time. In addition to this, Zn-based pnictides are found to possess higher thermopower than well known traditional TE materials at room temperature and above which motivates further research in these compounds.

  9. Thermoelectric Properties of Non-Metallic Topological Insulator Bi2 Te 3 at High Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Qu, Dong-Xia; Hor, Yew San; Cava, Robert J.; Ong, N. Phuan; Princeton University Team

    2011-03-01

    Three-dimensional topological insulators are a new class of electronic systems characterized by a bulk insulating state and conducting surface states with Dirac-like energy-momentum dispersion [1, 2]. One of the interesting aspects of this material is how the surface states affect thermoelectric properties of the whole electronic system, given that the bismuth based topological insulators are also excellent thermoelectric materials. We studied the low-temperature thermoelectric transport properties of high-mobility bulk topological insulator Bi 2 Te 3 at high magnetic fields up to 35 T. We found remarkably large quantum oscillations in the thermopower of the surface states over a field range of 14 to 35 T. The existence of a non-zero Berry's phase in surface electrons is confirmed from the magneto-oscillations of both thermopower and magnetoresistance. Supported by NSF-MRSEC under Grant DMR 08-19860.

  10. Thermoelectric properties of magnesium silicide fabricated using vacuum plasma thermal spray

    NASA Astrophysics Data System (ADS)

    Fu, Gaosheng; Zuo, Lei; Longtin, Jon; Nie, Chao; Gambino, Richard

    2013-10-01

    The thermoelectric properties of magnesium silicide samples prepared by Vacuum Plasma Spray (VPS) are compared with those made from the conventional hot press method using the same feedstock powder. Thermal conductivity, electrical conductivity, Seebeck coefficient, and figure of merit are characterized from room temperature to 700 K. X-ray diffraction and scanning electron microscopy of the samples are obtained to assess how phase and microstructure influence the thermoelectric properties. Carrier concentration and Hall mobility are obtained from Hall Effect measurements, which provide further insight into the electrical conductivity and Seebeck coefficient mechanisms. Low-temperature electrical conductivity measurements suggest a 3D variable range hopping effect in the samples. VPS samples achieved a maximum ZT = 0.16 at 700 K, which is around 30% of the hot press sample ZT = 0.55 at 700 K using the same raw powder. The results suggest that thermal spray is a potential deposition technique for thermoelectric materials.

  11. Joining of Silver Nanomaterials at Low Temperatures: Processes, Properties, and Applications.

    PubMed

    Peng, Peng; Hu, Anming; Gerlich, Adrian P; Zou, Guisheng; Liu, Lei; Zhou, Y Norman

    2015-06-17

    A review is provided, which first considers low-temperature diffusion bonding with silver nanomaterials as filler materials via thermal sintering for microelectronic applications, and then other recent innovations in low-temperature joining are discussed. The theoretical background and transition of applications from micro to nanoparticle (NP) pastes based on joining using silver filler materials and nanojoining mechanisms are elucidated. The mechanical and electrical properties of sintered silver nanomaterial joints at low temperatures are discussed in terms of the key influencing factors, such as porosity and coverage of substrates, parameters for the sintering processes, and the size and shape of nanomaterials. Further, the use of sintered silver nanomaterials for printable electronics and as robust surface-enhanced Raman spectroscopy substrates by exploiting their optical properties is also considered. Other low-temperature nanojoining strategies such as optical welding of silver nanowires (NWs) through a plasmonic heating effect by visible light irradiation, ultrafast laser nanojoining, and ion-activated joining of silver NPs using ionic solvents are also summarized. In addition, pressure-driven joining of silver NWs with large plastic deformation and self-joining of gold or silver NWs via oriented attachment of clean and activated surfaces are summarized. Finally, at the end of this review, the future outlook for joining applications with silver nanomaterials is explored. PMID:26005792

  12. Ferrous sulfate based low temperature synthesis and magnetic properties of nickel ferrite nanostructures

    SciTech Connect

    Tejabhiram, Y.; Pradeep, R.; Helen, A.T.; Gopalakrishnan, C.; Ramasamy, C.

    2014-12-15

    Highlights: • Novel low temperature synthesis of nickel ferrite nanoparticles. • Comparison with two conventional synthesis techniques including hydrothermal method. • XRD results confirm the formation of crystalline nickel ferrites at 110 °C. • Superparamagnetic particles with applications in drug delivery and hyperthermia. • Magnetic properties superior to conventional methods found in new process. - Abstract: We report a simple, low temperature and surfactant free co-precipitation method for the preparation of nickel ferrite nanostructures using ferrous sulfate as the iron precursor. The products obtained from this method were compared for their physical properties with nickel ferrites produced through conventional co-precipitation and hydrothermal methods which used ferric nitrate as the iron precursor. X-ray diffraction analysis confirmed the synthesis of single phase inverse spinel nanocrystalline nickel ferrites at temperature as low as 110 °C in the low temperature method. Electron microscopy analysis on the samples revealed the formation of nearly spherical nanostructures in the size range of 20–30 nm which are comparable to other conventional methods. Vibrating sample magnetometer measurements showed the formation of superparamagnetic particles with high magnetic saturation 41.3 emu/g which corresponds well with conventional synthesis methods. The spontaneous synthesis of the nickel ferrite nanoparticles by the low temperature synthesis method was attributed to the presence of 0.808 kJ mol{sup −1} of excess Gibbs free energy due to ferrous sulfate precursor.

  13. Low-Temperature Bonding of Bi0.5Sb1.5Te3 Thermoelectric Material with Cu Electrodes Using a Thin-Film In Interlayer

    NASA Astrophysics Data System (ADS)

    Lin, Yan-Cheng; Yang, Chung-Lin; Huang, Jing-Yi; Jain, Chao-Chi; Hwang, Jen-Dong; Chu, Hsu-Shen; Chen, Sheng-Chi; Chuang, Tung-Han

    2016-09-01

    A Bi0.5Sb1.5Te3 thermoelectric material electroplated with a Ni barrier layer and a Ag reaction layer was bonded with a Ag-coated Cu electrode at low temperatures of 448 K (175 °C) to 523 K (250 °C) using a 4- μm-thick In interlayer under an external pressure of 3 MPa. During the bonding process, the In thin film reacted with the Ag layer to form a double layer of Ag3In and Ag2In intermetallic compounds. No reaction occurred at the Bi0.5Sb1.5Te3/Ni interface, which resulted in low bonding strengths of about 3.2 MPa. The adhesion of the Bi0.5Sb1.5Te3/Ni interface was improved by precoating a 1- μm Sn film on the surface of the thermoelectric element and preheating it at 523 K (250 °C) for 3 minutes. In this case, the bonding strengths increased to a range of 9.1 to 11.5 MPa after bonding at 473 K (200 °C) for 5 to 60 minutes, and the shear-tested specimens fractured with cleavage characteristics in the interior of the thermoelectric material. The bonding at 448 K (175 °C) led to shear strengths ranging from 7.1 to 8.5 MPa for various bonding times between 5 and 60 minutes, which were further increased to the values of 10.4 to 11.7 MPa by increasing the bonding pressure to 9.8 MPa. The shear strengths of Bi0.5Sb1.5Te3/Cu joints bonded with the optimized conditions of the modified solid-liquid interdiffusion bonding process changed only slightly after long-term exposure at 473 K (200 °C) for 1000 hours.

  14. Low-Temperature Bonding of Bi0.5Sb1.5Te3 Thermoelectric Material with Cu Electrodes Using a Thin-Film In Interlayer

    NASA Astrophysics Data System (ADS)

    Lin, Yan-Cheng; Yang, Chung-Lin; Huang, Jing-Yi; Jain, Chao-Chi; Hwang, Jen-Dong; Chu, Hsu-Shen; Chen, Sheng-Chi; Chuang, Tung-Han

    2016-07-01

    A Bi0.5Sb1.5Te3 thermoelectric material electroplated with a Ni barrier layer and a Ag reaction layer was bonded with a Ag-coated Cu electrode at low temperatures of 448 K (175 °C) to 523 K (250 °C) using a 4-μm-thick In interlayer under an external pressure of 3 MPa. During the bonding process, the In thin film reacted with the Ag layer to form a double layer of Ag3In and Ag2In intermetallic compounds. No reaction occurred at the Bi0.5Sb1.5Te3/Ni interface, which resulted in low bonding strengths of about 3.2 MPa. The adhesion of the Bi0.5Sb1.5Te3/Ni interface was improved by precoating a 1-μm Sn film on the surface of the thermoelectric element and preheating it at 523 K (250 °C) for 3 minutes. In this case, the bonding strengths increased to a range of 9.1 to 11.5 MPa after bonding at 473 K (200 °C) for 5 to 60 minutes, and the shear-tested specimens fractured with cleavage characteristics in the interior of the thermoelectric material. The bonding at 448 K (175 °C) led to shear strengths ranging from 7.1 to 8.5 MPa for various bonding times between 5 and 60 minutes, which were further increased to the values of 10.4 to 11.7 MPa by increasing the bonding pressure to 9.8 MPa. The shear strengths of Bi0.5Sb1.5Te3/Cu joints bonded with the optimized conditions of the modified solid-liquid interdiffusion bonding process changed only slightly after long-term exposure at 473 K (200 °C) for 1000 hours.

  15. The influence of the nanostructure geometry on the thermoelectric properties

    NASA Astrophysics Data System (ADS)

    AL-Badry, Lafy F.

    2016-09-01

    We discuss the influence of nanostructure geometry on the thermoelectric properties in quantum ring consists of one QD in each arm, each QD connects with side QD. The calculations are based on the time-dependent Hamiltonian model, the steady state is considered to obtain an analytical expression for the transmission probability as a function of system energies. We employed the transmission probability to calculate the thermoelectric properties. We investigate thermoelectric properties through three configurations of this nanostructure. Figure of merit enhanced in configuration (II) when side QD connected to upper arm of quantum ring. The magnetic flux threads quantum ring. The effect of magnetic flux on the thermoelectric properties is examined.

  16. Effect of metal doping on the low-temperature structural behavior of thermoelectric {beta}-Zn{sub 4}Sb{sub 3}

    SciTech Connect

    Nylen, Johanna; Lidin, Sven; Andersson, Magnus; Liu Hongxue; Newman, Nate; Haeussermann, Ulrich

    2007-09-15

    The low-temperature structural phase transitions of Bi, Pb, In and Sn-doped samples of thermoelectric Zn{sub 4}Sb{sub 3} have been characterized on crystals grown from molten metal fluxes, using electrical resistance and single crystal X-ray diffraction measurements. Room temperature stable, disordered, {beta}-Zn{sub 4}Sb{sub 3} undergoes two phase transitions at 254 and 235 K to the consecutively higher ordered phases {alpha} and {alpha}', respectively. The ideal crystallographic composition of {alpha}-Zn{sub 4}Sb{sub 3} is Zn{sub 13}Sb{sub 10}. The {alpha}-{alpha}' transformation is triggered by a slight and homogenous Zn deficiency with respect to this composition and introduces a compositional modulation in the {alpha}-Zn{sub 4}Sb{sub 3} structure. When preparing {beta}-Zn{sub 4}Sb{sub 3} in the presence of metals with low melting points (Bi, Sn, In, Pb) the additional metal atoms are unavoidably incorporated in small concentrations (0.04-1.3 at%) and act as dopants. This incorporation alters the subtle balance between Zn disorder and Zn deficiency in Zn{sub 4}Sb{sub 3} and has dramatic consequences for its low-temperature structural behavior. From molten metal flux synthesis it is possible to obtain (doped) Zn{sub 4}Sb{sub 3} samples which (1) only display a {beta}-{alpha} transition, (2) only display a {beta}-{alpha}' transition, or (3) do not display any low-temperature phase transition at all. Case (2) provided diffraction data with a sufficient quality to obtain a structural model for highly complex, compositionally modulated, {alpha}'-Zn{sub 4}Sb{sub 3}. The crystallographic composition of this phase is Zn{sub 84}Sb{sub 65}. - Graphical abstract: The thermoelectric material Zn{sub 4}Sb{sub 3} displays complex temperature polymorphism. Room temperature stable, disordered, {beta}-Zn{sub 4}Sb{sub 3} undergoes two phase transitions at 254 and 235 K to the consecutively higher ordered phases {alpha} and {alpha}', respectively. The {alpha

  17. Thermal and thermoelectric properties of graphene.

    PubMed

    Xu, Yong; Li, Zuanyi; Duan, Wenhui

    2014-06-12

    The subject of thermal transport at the mesoscopic scale and in low-dimensional systems is interesting for both fundamental research and practical applications. As the first example of truly two-dimensional materials, graphene has exceptionally high thermal conductivity, and thus provides an ideal platform for the research. Here we review recent studies on thermal and thermoelectric properties of graphene, with an emphasis on experimental progresses. A general physical picture based on the Landauer transport formalism is introduced to understand underlying mechanisms. We show that the superior thermal conductivity of graphene is contributed not only by large ballistic thermal conductance but also by very long phonon mean free path (MFP). The long phonon MFP, explained by the low-dimensional nature and high sample purity of graphene, results in important isotope effects and size effects on thermal conduction. In terms of various scattering mechanisms in graphene, several approaches are suggested to control thermal conductivity. Among them, introducing rough boundaries and weakly-coupled interfaces are promising ways to suppress thermal conduction effectively. We also discuss the Seebeck effect of graphene. Graphene itself might not be a good thermoelectric material. However, the concepts developed by graphene research might be applied to improve thermoelectric performance of other materials. PMID:24610791

  18. Tunable thermoelectric properties in bended graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Chang-Ning, Pan; Jun, He; Mao-Fa, Fang

    2016-07-01

    The ballistic thermoelectric properties in bended graphene nanoribbons (GNRs) are systematically investigated by using atomistic simulation of electron and phonon transport. We find that the electron resonant tunneling effect occurs in the metallic–semiconducting linked ZZ-GNRs (the bended GNRs with zigzag edge leads). The electron-wave quantum interference effect occurs in the metallic–metallic linked AA-GNRs (the bended GNRs with armchair edge leads). These different physical mechanisms lead to the large Seebeck coefficient S and high electron conductance in bended ZZ-GNRs/AA-GNRs. Combined with the reduced lattice thermal conduction, the significant enhancement of the figure of merit ZT is predicted. Moreover, we find that the ZTmax (the maximum peak of ZT) is sensitive to the structural parameters. It can be conveniently tuned by changing the interbend length of bended GNRs. The magnitude of ZT ranges from the 0.15 to 0.72. Geometry-controlled ballistic thermoelectric effect offers an effective way to design thermoelectric devices such as thermocouples based on graphene. Project supported by the National Natural Science Foundation of China (Grant No. 61401153) and the Natural Science Foundation of Hunan Province, China (Grant Nos. 2015JJ2050 and 14JJ3126).

  19. Ballistic thermal transport properties at low temperatures in semiconductor nanowires-based heterojunctions

    NASA Astrophysics Data System (ADS)

    Yu, Xia; Xie, Zhong-Xiang; Liu, Jun-Hun; Chen, Qiao; Li, Ke-Min; Zhang, Yong

    2016-04-01

    In this paper, we study ballistic thermal transport properties at low temperatures in semiconductor nanowires-based heterojunctions under hard-wall boundary conditions (HWBCs) and stress-free boundary conditions (SFBCs). Here, the numerical calculations for the asymmetric heterojunction (ASHJ) and symmetric heterojunction (SHJ) are done. When SFBCs are employed, the transmission coefficient exhibits different behaviors between ASHJ and SHJ especially at low frequency, but when HWBCs are employed, the transmission coefficient displays similar smooth platforms in both heterojunctions. In low temperature limit, the quantized thermal conductance can be observed in SHJ under SFBCs regardless of the structural details. However, this quantization cannot be observed in ASHJ under SFBCs, and the thermal conductance is strongly sensitive to the transverse width ratio rather than the slant angle. With increasing the transverse width ratio, the thermal conductance in both heterojunctions gradually increases especially, and such the increasing degree is more evident at higher temperatures. A brief analysis of these results is given.

  20. Low temperature transport properties of the quadrupolar Kondo lattice system PrTi2Al20

    NASA Astrophysics Data System (ADS)

    Sakai, Akito; Nakatsuji, Satoru

    2013-08-01

    We have investigated the low temperature transport properties of the cubic Γ3 compound PrTi2Al20. This is a quadrupolar Kondo lattice system where the nongmagnetic quadrupoles, which form a long-range order at low temperatures, have strong hybridization with the conduction electrons. A sharp drop of the resistivity due to a ferroquadrupole ordering is observed at T Q = 2.0 K. The T 2 dependence of the resistivity and the large Sommerfeld coefficient γ above T Q suggest the formation of a heavy-fermion state. The temperature dependence of the resistivity below T Q does not show a power law but exponential law behavior, indicating the emergence of an anisotropy gap Δ in the collective mode associated with the ferroquadrupole order below T Q. The Fisher-Langer relation holds around T Q, suggesting the higher order scattering processes than those in Born approximation are not dominant for this ferroquadrupole ordering.

  1. Ballistic thermoelectric properties in boron nitride nanoribbons

    NASA Astrophysics Data System (ADS)

    Xie, Zhong-Xiang; Tang, Li-Ming; Pan, Chang-Ning; Chen, Qiao; Chen, Ke-Qiu

    2013-10-01

    Ballistic thermoelectric properties (TPs) in boron nitride nanoribbons (BNNRs) are studied using the nonequilibrium Green's function atomistic simulation of electron and phonon transport. A comparative analysis for TPs between BNNRs and graphene nanoribbons (GNRs) is made. Results show that the TPs of BNNRs are better than those of GNRs stemming from the higher power factor and smaller thermal conductance of BNNRs. With increasing the ribbon width, the maximum value of ZT (ZTmax) of BNNRs exhibits a transformation from the monotonic decrease to nonlinear increase. We also show that the lattice defect can enhance the ZTmax of these nanoribbons strongly depending on its positions and the edge shape.

  2. Temperature dependent phonon properties of thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Hellman, Olle; Broido, David; Fultz, Brent

    2015-03-01

    We present recent developments using the temperature dependent effective potential technique (TDEP) to model thermoelectric materials. We use ab initio molecular dynamics to generate an effective Hamiltonian that reproduce neutron scattering spectra, thermal conductivity, phonon self energies, and heat capacities. Results are presented for (among others) SnSe, Bi2Te3, and Cu2Se proving the necessity of careful modelling of finite temperature properties for strongly anharmonic materials. Supported by the Swedish Research Council (VR) Project Number 637-2013-7296.

  3. Effect of low temperature plasma on the functional properties of basmati rice flour.

    PubMed

    Thirumdas, Rohit; Deshmukh, R R; Annapure, U S

    2016-06-01

    The present study deals with the application of low temperature plasma on basmati rice flour and its effect on functional properties such as gel hydrations properties, flour hydration properties, gelatinization temperatures and antioxidant properties. The water holding capacity and water binding capacity were observed to be increased with increase in plasma power and time of treatment as the air plasma is known to make the surface more hydrophilic. XRD analysis revealed there is no significance difference in the crystalline structure after the plasma treatment. DSC shows a decrease in peak temperatures (Tp) after the treatment. Hot paste viscosities were observed to be decease from 692 to 591 BU was corresponded to decrease in peak temperature. The total polyphenolic content and reducing power was observed to be increased. The effects of plasma treatment on functional groups of polyphenols were observed by changes in absorption intensities using FTIR. This study demonstrates that the low temperature plasma treatmentis capable of improving the functional properties of basmati rice. PMID:27478230

  4. Photoluminescence, electrical and structural properties of ZnO films, grown by ALD at low temperature

    NASA Astrophysics Data System (ADS)

    Przeździecka, E.; Wachnicki, Ł.; Paszkowicz, W.; Łusakowska, E.; Krajewski, T.; Łuka, G.; Guziewicz, E.; Godlewski, M.

    2009-10-01

    We report the first results of the low-temperature photoluminescence study on polycrystal zinc oxide (ZnO) films obtained by atomic layer deposition at 100 °C, 130 °C and 200 °C. These ZnO films, when studied 'as-grown', show a strong excitonic emission even at room temperature. Low-temperature (T = 9 K) photoluminescence reveals lack of defect-related bands and a sharp photoluminescence peak at 3.36 eV with full width at half maximum of 6 meV which is comparable with the value reported for good quality bulk ZnO crystals. The energy position of the excitonic peak scales with temperature according to standard formulas and give the Debye temperature of 963 ± 26 K. We show that optical properties of low-temperature 'as-grown' ZnO films are correlated with structural and electrical ones and that optical study can be a valuable tool for evaluation of quality of ZnO films for novel electronic applications.

  5. Low temperature physical properties of a Ni-Mo-Cr alloy Haynes® 242™

    NASA Astrophysics Data System (ADS)

    Lu, J.; Han, K.; Choi, E. S.; Jo, Y.; Balicas, L.; Xin, Y.

    2007-06-01

    Haynes 242 is a Ni-Mo-Cr based superalloy. High strength and high fracture toughness at low temperatures make Haynes 242 an attractive choice for cryogenic applications such as the conduit material for the cable-in-conduit conductor of superconducting magnets. In this work, its low temperature physical properties including magnetization, specific heat, electrical resistivity, thermal conductivity, and Seebeck coefficient are measured from 2to300K. Haynes 242 shows Curie paramagnetism with a Curie constant C =0.0289K. The electrical resistivity has a minimum at ˜12K and shows weakly linear T dependence at high temperatures as expected. The specific heat Cp between 10 and 40K can be fitted by Cp=γT+AT3 with γ =9.43×10-5J/gK2 and A =5.91×10-7J/gK4. Below 10K, an upturn in Cp/T with decreasing T is interpreted by the existence of very small ferromagnetic clusters which is supported by our magnetization data. The thermal conductivity is analyzed by separating the electronic and phonon contributions. The relatively strong phonon thermal conduction at temperatures <100K results in effective Lorenz number a few times larger than the ideal Lorenz number. Our results suggest that Haynes 242 is suitable for many cryogenic applications including conduit for large superconducting magnet and low temperature probe.

  6. Effect of low temperatures on tensile properties of ultrathin copper films

    NASA Astrophysics Data System (ADS)

    Guo, Qiao-Neng; Pan, Ernie; Yang, Shi-E.; Wang, Mingxing; Sun, Qiang; Wang, Jie-Fang; Jia, Yu

    2014-03-01

    The recent developments in MEMS have created a requirement for comprehending the mechanical properties of copper thin films. Moreover, the serviceability temperature of the films used for space research, superconductivity and so on is mainly low temperature. Thus, the molecular dynamics is employed to simulate the mechanical responses of single-crystal copper thin films under uniaxial tensile loading in different low temperature environments. With varying applied temperatures to the thin films, the variation of the maximum stress, Young's modulus and maximal potential energy is characterized and three different deformation mechanisms in the low temperature range from 40 to 250 K are identified. These different mechanisms of copper films in different temperature ranges are then explained via the continuum damage mechanics based on the evolutionary features of the slip and twin in the thin film. It is concluded that at temperatures above 200 K normal slip process occurs; whereas at temperatures below 70 K, twin nucleation process appears. However, when the temperature is between 70 K and 200 K, both twin and slip processes happen. Project supported by the National Natural Science Foundation of China (Grant No. 11372283) and the Foundation of Henan Educational Committee, China (Grant No.13A140674).

  7. Characterizing the Physical and Thermal Properties of Planetary Regolith at Low Temperatures

    NASA Technical Reports Server (NTRS)

    Mantovani, James G.; Swanger, Adam; Townsend, Ivan I., III; Sibille, Laurent; Galloway, Gregory

    2014-01-01

    The success or failure of in-situ resource utilization for planetary surface exploration-whether for science, colonization, or commercialization-relies heavily on the design and implementation of systems that can effectively process planetary regolith and exploit its potential benefits. In most cases, this challenge necessarily includes the characterization of regolith properties at low temperatures (cryogenic). None of the nearby solar system destinations of interest, such as the moon, Mars and asteroids, possess a sufficient atmosphere to sustain the consistently "high" surface temperatures found on Earth. Therefore, they can experience permanent cryogenic temperatures or dramatic cyclical changes in surface temperature. Characterization of physical properties (e.g., specific heat, thermal and electrical conductivity) over the entire temperature profile is important when planning a mission to a planetary surface; however, the impact on mechanical properties due to the introduction of icy deposits must also be explored in order to devise effective and robust excavation technologies. The Granular Mechanics and Regolith Operations Laboratory and the Cryogenics Test Laboratory at NASA Kennedy Space Center are developing technologies and experimental methods to address these challenges and to aid in the characterization of the physical and mechanical properties of regolith at cryogenic temperatures. This paper will review the current state of knowledge concerning planetary regolith at low temperature, including that of icy regolith, and describe efforts to manipulate icy regolith through novel penetration and excavation techniques.

  8. Experiments with proteins at low temperature: What do we learn on properties in their functional state?

    NASA Astrophysics Data System (ADS)

    Ponkratov, V. V.; Wiedersich, J.; Friedrich, J.; Vanderkooi, J. M.

    2007-04-01

    The authors compared the spectral response of Zn-substituted horseradish peroxidase in a glycerol/water solvent to hydrostatic pressure at 2K and ambient temperature. The low temperature experiments clearly demonstrate the presence of at least three different conformations with drastically different elastic properties. However, the main conformation, which determines the fluorescence spectrum at ambient temperature, did not show any significant difference between low and high temperature and pressure. The authors conclude that the local compressibility of the heme pocket of the protein depends only very weakly on temperature.

  9. Nondestructive Methods to Characterize Rock Mechanical Properties at Low-Temperature: Applications for Asteroid Capture Technologies

    NASA Astrophysics Data System (ADS)

    Savage, Kara A.

    Recent government initiatives and commercial activities have targeted asteroids for in situ material characterization, manipulation, and possible resource extraction. Most of these activities and missions have proposed significant robotic components, given the risks and costs associated with manned missions. To successfully execute these robotic activities, detailed mechanical characteristics of the target space bodies must be known prior to contact, in order to appropriately plan and direct the autonomous robotic protocols. Unfortunately, current estimates of asteroid mechanical properties are based on limited direct information, and significant uncertainty remains specifically concerning internal structures, strengths, and elastic properties of asteroids. One proposed method to elucidate this information is through in situ, nondestructive testing of asteroid material immediately after contact, but prior to any manipulation or resource extraction activities. While numerous nondestructive rock characterization techniques have been widely deployed for terrestrial applications, these methods must be adapted to account for unique properties of asteroid material and environmental conditions of space. For example, asteroid surface temperatures may range from -100°C to 30°C due to diurnal cycling, and these low temperatures are especially noteworthy due to their deleterious influence on non-destructive testing. As a result, this thesis investigates the effect of low temperature on the mechanical characteristics and nondestructive technique responses of rock material. Initially, a novel method to produce low temperature rock samples was developed. Dry ice and methanol cooling baths of specific formulations were used to decrease rock to temperatures ranging from -60°C to 0°C. At these temperatures, shale, chalk, and limestone rock samples were exposed to several nondestructive and conventional mechanical tests, including Schmidt hammer, ultrasonic pulse velocity, point

  10. Low-temperature Mechanical Properties of Bulk MgB2 Fabricated by Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Murakami, A.; Teshima, H.; Naito, T.; Fujishiro, H.; Kudo, T.; Iwamoto, A.

    Mechanical properties ina MgB2superconducting bulk sample,whose packing ratio is 92%,fabricated by hot isostatic pressing (HIP)areevaluated at 77 K through bending tests.The fracture strength at 77 K is higher than at room temperature. From the bending test result at 77 K, the fracture strength of ideal bulk MgB2,whose packing ratio is 100%,is estimated. The fracture strength at very low temperature of the HIP bulk MgB2is also estimated from the bending test results at 77 K and room temperature.

  11. Multifunctional fuel additives derived from aminodiols to improve the low-temperature properties of distillate fuels

    SciTech Connect

    Baillargeon, D.J.; Cardis, A.B.; Heck, D.B.

    1991-03-19

    This patent describes a liquid hydrocarbyl fuel composition comprising a major amount of a combustible liquid hydrocarbon fuel and a minor low-temperature properties improving amount of from about 0.001% to about 10 wt % based on the total weight of the composition of an additive comprising a product of reaction made by reacting comonomers. It comprises: an aminodiol or combination or mixture of aminodiols with a reactive acid/anhydride product alone or in combination with other monomers derived from the reaction of benzophenone tetracarboxylic dianhydride or its acid equivalent.

  12. Experimental investigation of thermal properties and Grueneisen parameter of aligned polycarbonate at low temperatures

    NASA Astrophysics Data System (ADS)

    Escher, U.; v. Schoenebeck, F.; Jäckel, M.; Gladun, A.

    Thermal expansion α, specific heat capacity c and thermal conductivity λ of untreated and stretched polycarbonate (PC) have been measured at temperatures above 4.2 K and the Grueneisen parameter γ has been calculated from α and c. All properties exhibit typical low-temperature features of amorphous solids. The specific heat c is not influenced by stretching, α, γ and λ, however, get very anisotropic. The temperature dependence of α, λ and γ changes distinctly when mechanically loaded or oriented. The Grueneisen parameter γ( T) shows a maximum at 10 K for untreated PC and at 20 K for stretched PC.

  13. Properties of silicon dioxide films deposited at low temperatures by microwave plasma enhanced decomposition of tetraethylorthosilicate

    SciTech Connect

    Ray, S.K.; Maiti, C.K.; Lahiri, S.K.; Chakrabarti, N.B.

    1992-05-01

    Silicon dioxide films have been deposited at low temperatures (200-250{degrees}C) by microwave plasma enhanced decomposition of tetraethylorthosilicate (TEOS). The effects of the presence of oxygen in the discharge in film deposition rate, mechanism, and the physical properties of the films have been investigated. Structural characterization of the deposited films has been carried out by etch rate measurements, infrared transmission spectra, x-ray photoelectron spectroscopy, Auger, and secondary ion mass spectrometry analyses. Films deposited using TEOS and oxygen have confirmed a density comparable to standard silane-based low-pressure chemical vapor deposited and plasma enhanced chemical vapor deposited oxides, nearly perfect stoichiometry, extremely low sodium and carbon content, and the absence of many undesirable hydrogen related bonds. Various electrical properties, viz., resistivity, breakdown strength, fixed oxide charge density, interface state density, and trapping behavior have been evaluated by the characterization of metal-oxide-semiconductor capacitors fabricated using deposited oxides. Deposited films on thin native oxides grown by either in situ plasma oxidation or a low temperature thermal oxidation exhibited excellent electrical properties. 32 refs., 16 figs., 2 tabs.

  14. Thermally cascaded thermoelectric generator

    NASA Technical Reports Server (NTRS)

    Flaherty, R.

    1970-01-01

    High efficiency thermoelectric generator utilizes a high-temperature thermoelectric material in thermal series with a low-temperature material. A thermally cascaded generator increases system efficiency.

  15. Electrical properties of the YSZ/STO/YSZ-STO superlattice electrolyte film at low temperatures

    NASA Astrophysics Data System (ADS)

    Xu, Yan-Bin; Kang, Zhen-Feng; Fan, Yue; Xiao, Ling-Ling; Bo, Qing-Rui; Ding, Tie-Zhu

    2016-02-01

    This study is focused on characterization of the low temperature properties of the YSZ/STO/YSZ superlattice film deposited onto unilateral polished SrTiO3 (STO) monocrystalline substrates using pulsed laser deposition (PLD). The phase composition, structure, surface morphology and electrical properties of the oxygen ion conducting electrolyte YSZ/STO/YSZ multilayers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The minimum conductivity activation energy of YSZ/STO/YSZ is 0.76 eV at 300-500°C. The YSZ/STO/YSZ superlattice film shows an enhancement in conductivity by three orders of magnitude compared to bulk YSZ at a temperature of 300°C.

  16. Endurance and Other Properties at Low Temperatures of Some Alloys for Aircraft Use

    NASA Technical Reports Server (NTRS)

    Russell, H W; Welcker, W A , Jr

    1931-01-01

    The low temperature endurance properties of materials for aircraft construction are not well known. In order to determine them, apparatus for testing endurance at -40 C has been devised. The endurance properties of monel metal, low-carbon stainless steel, "18 and *, " 3 1/2% Ni steel and chromium-molybdenum steel have been determined at -40 C and at room temperature about +20 C. Tensile, impact and hardness tests of these materials have also been made at various temperatures. The results show an increase in endurance limit, tensile strength, and hardness with decreased temperature. Impact strength is, in general, decreased, but of all the alloys tested, only one, low-carbon stainless steel, gives less than 15 ft. lb. Chrpay impact test at -40 C.

  17. Thermoelectric properties of an ultra-thin topological insulator.

    PubMed

    Islam, S K Firoz; Ghosh, T K

    2014-04-23

    Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In the absence of a magnetic field, the thermopower increases and thermal conductivity decreases with an increase in the hybridization energy. In the presence of a magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and whose phase factor is governed by the product of the Landé g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results for the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, at a frequency that depends on the Landé g-factor. PMID:24694878

  18. Lattice dynamics and thermoelectric properties of nanocrystalline silicon-germanium alloys

    DOE PAGESBeta

    Claudio, Tania; Stein, Niklas; Peterman, Nils; Stroppa, Daniel; Koza, Michael M.; Wiggers, Hartmut; Klobes, B.; Schierning, Gabi; Hermann, Raphael P.

    2015-10-26

    The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon- germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low- temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000C. A peak figure of merit zT = 0:88 at 900C is observed and comparatively insensitive to the aforementioned param-more » eter variations.« less

  19. Low-temperature dielectric properties of SrTiO3 glass-ceramics

    NASA Astrophysics Data System (ADS)

    Swartz, S. L.; Bhalla, A. S.; Cross, L. E.; Clark, C. F.; Lawless, W. N.

    1986-09-01

    The low-temperature dielectric properties of strontium titanate aluminosilicate glass-ceramics, in which perovskite SrTiO3 is the primary crystalline phase, have been investigated. These glass-ceramics exhibited dielectric constant peaks at temperatures below 100 K; the magnitude of these peaks, along with their frequency and temperature dependencies, were strongly dependent on the crystallization conditions. In heavily crystallized glass-ceramics, two low-temperature, relaxation-type loss mechanisms were identified, at temperature ranges near 50 and 100 K. The magnitude of the dielectric loss peak increased with increasing frequency for the lower temperature (50 K) mechanism and the magnitude of the loss peak decreased with increasing frequency for the higher temperature (100 K) mechanism. Arrhenius activation energies were calculated to be 0.054 and 0.17 eV for the lower and higher temperature loss mechanisms, respectively. The higher temperature loss mechanism was further analyzed by the Cole-Cole method, and a relaxation strength of 41 was calculated. It was proposed that the dielectric constant and loss peaks were related to ferroic phenomena occurring in the SrTiO3 phase, caused by interactions of the SrTiO3 with the glass-ceramic matrix.

  20. Revisiting the low-temperature dielectric properties of ZnO

    NASA Astrophysics Data System (ADS)

    Wang, Chunchang; Liu, Lina; Li, Qiuju; Huang, Shouguo; Zhang, Jian; Zheng, Jun; Cheng, Chao

    2014-09-01

    Electric modulus spectroscopy and impedance analysis were used to investigate the low-temperature (˜100-333 K) dielectric properties of ZnO crystals. Two relaxations were observed. The low-temperature relaxation (R1) features a thermally activated behavior resulting from the bulk response. Our results convincingly demonstrate that this relaxation is a polaronic relaxation. The relaxing species for R1 are localized holes created by zinc vacancies instead of the commonly agreed oxygen vacancies. The high-temperature relaxation (R2) is a Maxwell-Wagner relaxation due to skin-layer effect as it can be eliminated by grinding off the sample surface. The inhomogeneous distribution of zinc interstitials leads to the formation of the skin layer. Interestingly, an abnormal dielectric behavior contrary to the thermally activated behavior was found for the R2 relaxation. This abnormal behavior was confirmed to be related to the positive temperature coefficient of resistance due to the metal-insulator transition occurring within the skin layer.

  1. Thermoelectric properties of TlPSe

    SciTech Connect

    Karimov, S.K.; Sitamov, S.S.; Umarov, A.

    1988-08-01

    This investigation was conducted to study the thermoelectric properties of thallium selenium phosphide (TlPSe) over a broad temperature range, including the liquid state. The electrical conductivity and Hall constant were determined by contact and noncontact techniques. The coefficient of thermo-emf was measured in a horizontal boat with a temperature drop of 40-50 K along the specimen. As the temperature was raised, the conductivity of the TlPSe increased monotonically at first; it dropped sharply at the melting point (666 K) and again rose monotonically when the temperature of the TlPSe melt was further increased, i.e, TlPSe exhibits semiconductor-semiconductor type melting.

  2. Thermoelectric properties by high temperature annealing

    NASA Technical Reports Server (NTRS)

    Ren, Zhifeng (Inventor); Chen, Gang (Inventor); Kumar, Shankar (Inventor); Lee, Hohyun (Inventor)

    2009-01-01

    The present invention generally provides methods of improving thermoelectric properties of alloys by subjecting them to one or more high temperature annealing steps, performed at temperatures at which the alloys exhibit a mixed solid/liquid phase, followed by cooling steps. For example, in one aspect, such a method of the invention can include subjecting an alloy sample to a temperature that is sufficiently elevated to cause partial melting of at least some of the grains. The sample can then be cooled so as to solidify the melted grain portions such that each solidified grain portion exhibits an average chemical composition, characterized by a relative concentration of elements forming the alloy, that is different than that of the remainder of the grain.

  3. Optical and electrical properties and phonon drag effect in low temperature TEP measurements of AgSbSe2 thin films

    NASA Astrophysics Data System (ADS)

    Namitha Asokan, T.; Urmila, K. S.; Jacob, Rajani; Reena Philip, Rachel; Okram, G. S.; Ganesan, V.; Pradeep, B.

    2014-05-01

    Polycrystalline thin films of silver antimony selenide have been deposited using a reactive evaporation technique onto an ultrasonically cleaned glass substrate at a vacuum of 10-5 torr. The preparative parameters, like substrate temperature and incident fluxes, have been properly controlled in order to get stoichiometric, good quality and reproducible thin film samples. The samples are characterized by XRD, SEM, AFM and a UV—vis—NIR spectrophotometer. The prepared sample is found to be polycrystalline in nature. From the XRD pattern, the average particle size and lattice constant are calculated. The dislocation density, strain and number of crystallites per unit area are evaluated using the average particle size. The dependence of the electrical conductivity on the temperature has also been studied and the prepared AgSbSe2 samples are semiconducting in nature. The AgSbSe2 thin films exhibited an indirect allowed optical transition with a band gap of 0.64 eV. The compound exhibits promising thermoelectric properties, a large Seebeck coefficient of 30 mV/K at 48 K due to strong phonon electron interaction. It shows a strong temperature dependence on thermoelectric properties, including the inversion of a dominant carrier type from p to n over a low temperature range 9-300 K, which is explained on the basis of a phonon drag effect.

  4. On the thermoelectric transport properties of graphyne by the first-principles method.

    PubMed

    Wang, Xiao-Ming; Mo, Dong-Chuan; Lu, Shu-Shen

    2013-05-28

    Graphyne, another two-dimensional carbon allotrope, has received increased attentions in recent years. By using the first-principles density functional calculations combined with the non-equilibrium Green's function formalism, we investigated the electronic, thermal, and thermoelectric transport properties of graphyne systematically and comparatively. It is found that the phonon thermal conductance of graphyne is greatly reduced compared to that of graphene in most temperature regions while larger than that of graphene at low temperatures, which is attributed to the different bond strengths and phonon spectra of graphyne and graphene. Due to the semiconductor property of graphyne, the thermoelectric power (TEP) is found to be one magnitude larger than that of graphene. Besides, distinct peak value regions of TEP in the contour of chemical potential and temperature are displayed for graphyne and graphene. Finally, the thermoelectric figure of merit (ZT) of graphyne is found to be much larger than that of graphene as a result of large TEP and greatly reduced thermal conductance in graphyne, which indicates preferred thermoelectric applications for graphyne. PMID:23742497

  5. On the thermoelectric transport properties of graphyne by the first-principles method

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Ming; Mo, Dong-Chuan; Lu, Shu-Shen

    2013-05-01

    Graphyne, another two-dimensional carbon allotrope, has received increased attentions in recent years. By using the first-principles density functional calculations combined with the non-equilibrium Green's function formalism, we investigated the electronic, thermal, and thermoelectric transport properties of graphyne systematically and comparatively. It is found that the phonon thermal conductance of graphyne is greatly reduced compared to that of graphene in most temperature regions while larger than that of graphene at low temperatures, which is attributed to the different bond strengths and phonon spectra of graphyne and graphene. Due to the semiconductor property of graphyne, the thermoelectric power (TEP) is found to be one magnitude larger than that of graphene. Besides, distinct peak value regions of TEP in the contour of chemical potential and temperature are displayed for graphyne and graphene. Finally, the thermoelectric figure of merit (ZT) of graphyne is found to be much larger than that of graphene as a result of large TEP and greatly reduced thermal conductance in graphyne, which indicates preferred thermoelectric applications for graphyne.

  6. Low-temperature ferromagnetic properties in Co-doped Ag{sub 2}Se nanoparticles

    SciTech Connect

    Yang, Fengxia E-mail: xia9020@hust.edu.cn; Yu, Gen; Han, Chong; Liu, Tingting; Zhang, Duanming; Xia, Zhengcai E-mail: xia9020@hust.edu.cn

    2014-01-06

    β-Ag{sub 2}Se is a topologically nontrivial insulator. The magnetic properties of Co-doped Ag{sub 2}Se nanoparticles with Co concentrations up to 40% were investigated. The cusp of zero-field-cooling magnetization curves and the low-temperature hysteresis loops were observed. With increasing concentration of Co{sup 2+} ions mainly substituting Ag{sub I} sites in the Ag{sub 2}Se structure, the resistivity, Curie temperature T{sub c}, and magnetization increased. At 10 T, a sharp drop of resistance near T{sub c} was detected due to Co dopants. The ferromagnetic behavior in Co-doped Ag{sub 2}Se might result from the intra-layer ferromagnetic coupling and surface spin. This magnetic semiconductor is a promising candidate in electronics and spintronics.

  7. Low temperature magnetic properties of magnesium substituted YbMnO{sub 3}

    SciTech Connect

    Sattibabu, Bhumireddi Bhatnagar, Anil K. Mohan, Dasari Das, Dibakar Sundararaman, Mahadevan; Siruguri, Vasudeva; Rayaprol, Sudhindra

    2014-04-24

    Structural and magnetic properties of polycrystalline Yb{sub 1−x}Mg{sub x}MnO{sub 3} (x = 0, 0.05 and 0.10) hexagonal compounds prepared by solid state method, have been studied. The structural analyses of the samples were carried out by Rietveld analysis of neutron diffraction data. With increasing Mg content, we find that the lattice parameter a decreases and c increases whereas the overall Mn-O bond length decreases. Magnetization measured as a function of magnetic field at 2.5 K exhibits hysteresis, which is attributed to ferromagnetic like ordering of Yb{sup 3+} sublattice. Temperature dependence of ac magnetic susceptibility, χ{sub ac}(T), shows no signature of spin-glass behavior. χ”(T) exhibits a sudden increase at low temperatures which is due to ordering of Yb{sup 3+} sublattice.

  8. Optical properties of single wurtzite/zinc-blende ZnSe nanowires grown at low temperature

    SciTech Connect

    Zannier, V.; Cremel, T.; Kheng, K.; Artioli, A.; Ferrand, D.; Grillo, V.

    2015-09-07

    ZnSe nanowires with a dominant wurtzite structure have been grown at low temperature (300 °C) by molecular beam epitaxy assisted by solid Au nanoparticles. The nanowires emission is polarized perpendicularly to their axis in agreement with the wurtzite selection rules. Alternations of wurtzite and zinc-blende regions have been observed by transmission electron microscopy, and their impact on the nanowires optical properties has been studied by microphotoluminescence. The nanowires show a dominant intense near-band-edge emission as well as the ZnSe wurtzite free exciton line. A type II band alignment between zinc-blende and wurtzite ZnSe is evidenced by time-resolved photoluminescence. From this measurement, we deduce values for the conduction and valence band offsets of 98 and 50 meV, respectively.

  9. Low-temperature synthesis and electrical transport properties of W 18O 49 nanowires

    NASA Astrophysics Data System (ADS)

    Shi, Songlin; Xue, Xinyu; Feng, Ping; Liu, Yonggang; Zhao, Heng; Wang, Taihong

    2008-01-01

    W 18O 49 nanowires are simply synthesized by the reaction between water vapor and tungsten powders in tube furnace at a low temperature of 600 °C. The nanowires have diameters of 20-50 nm, lengths several micrometers. XRD, TEM and SAED results show that the nanowires are of single crystalline monoclinic W 18O 49 structures with the growth direction [0 1 0]. The growth mechanism is analyzed. We investigate the temperature dependence electrical transport properties of individual W 18O 49 nanowires. The conductivity is 2.58 Ω -1 cm -1 at 290 K and 42.35 Ω -1 cm -1 at 500 K, respectively. And the electron activation energy is calculated to be about 0.26 eV.

  10. Low-temperature mechanical and magnetic properties of the reduced activation martensitic steel

    NASA Astrophysics Data System (ADS)

    Ding, Hui-Li; Zhang, Tao; Gao, Rui; Wang, Xian-Ping; Fang, Qian-Feng; Liu, Chang-Song; Suo, Jin-Ping

    2015-09-01

    Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic (RAM) steel were investigated in the temperature range from -90°C to 20°C. Charpy impact tests show that the ductile-to-brittle transition temperature (DBTT) of the RAM steel is about -60°C. Low-temperature tensile tests show that the yield strength, ultimate tensile strength and total elongation values increase as temperature decreases, indicating that the strength and plasticity below the DBTT are higher than those above the DBTT. The coercive field ( H C) in the scale of logarithm decreases linearly with the increasing temperature and the absolute value of the slope of ln H C versus temperature above the DBTT is obviously larger than that below the DBTT, also confirmed in the T91 steel. The results indicate that the non-destructive magnetic measurement is a promising candidate method for the DBTT detection of ferromagnetic steels.

  11. Hysteresis, thermomagnetic, and low-temperature magnetic properties of Southwestern U.S. obsidians

    NASA Astrophysics Data System (ADS)

    Sternberg, R. S.; Jackson, M. J.; Shackley, M. S.

    2011-12-01

    Geochemical signatures of Southwestern U.S. obsidians have been intensively studied, in part to use as a provenance method for archaeological obsidians (Shackley, 2005). We reported (Sternberg et al. 2010) examined magnetic properties of 50 unoriented samples from 10 geologic obsidian sources in Arizona, Nevada, and New Mexico; here we provide additional results measured at the Institute for Rock magnetism. Room-temperature hysteresis curves were measured using a vibrating sample magnetometer on 58 specimens from all 50 samples. The Quantum Designs Magnetic Properties Measurement System was used to measure low temperature cycling of the natural remanence and/or of a room-temperature saturation isothermal remanence for 10 specimens, and frequency dependence of susceptibility for 7 specimens. A Princeton VSM was used to measure hysteresis curves and thermomagnetic curves for 19 specimens from 17 samples. Eleven of the thermomagnetic curves show Curie temperatures close to that for magnetite, and most of them are almost perfectly reversible. Many of the specimens also show a less well-defined Curie point around 150-200°C; for a few specimens the thermomagnetic behavior is dominated by paramagnetic iron and no ferromagnetic phases can be identified. The low-temperature remanence and susceptibility measurements show the magnetite Verwey transition in almost all specimens, and a significant superparamagnetic presence in only a few cases. Hysteresis parameters plot mainly in the lower half of the PSD domain on a Day plot, and saturation magnetization values indicate magnetite concentrations of about 0.2% to 0.5% for most specimens. The coercivity of remanence decreased considerably for one specimen after surface cleaning, although for 5 other comparisons there was no change.

  12. Polyesters Based on Linoleic Acid for Biolubricant Basestocks: Low-Temperature, Tribological and Rheological Properties

    PubMed Central

    Abdullah, Bashar Mudhaffar; Zubairi, Saiful Irwan; Huri, Hasniza Zaman; Hairunisa, Nany; Yousif, Emad; Basu, Roma Choudhury

    2016-01-01

    Presently, plant oils which contain high percentage of linoleic acid 1 are perceived to be a viable alternative to mineral oil for biolubricant applications due to their biodegradability and technical properties. In order to get biodegradable lubricant, triester derivatives compounds (1–5) were synthesized and characterized. The processes involved were monoepoxidation of linoleic acid 2, oxirane ring opening 3, esterification 4 and acylation 5. The structures of the products were confirmed by FTIR, 1H and 13C-NMR and LC-MS. The results that showed lowest temperature properties were obtained for triester 5, with a pour point value (PP) of -73°C, highest onset temperature (260°C) and lowest volatility at 0.30%. Viscosity index (VI) increased for the ester’s synthetic compounds (2, 3, 4, 5), while the PP decreased. This behavior is the result of the increase of the chain length of the branching agents. Triester based linoleic acid has improved properties such as low-temperature and tribological properties. These results will make it feasible for plant oil to be used for biolubricants, fuels in chain saws, transmission oil and brake fluid. PMID:27008312

  13. Polyesters Based on Linoleic Acid for Biolubricant Basestocks: Low-Temperature, Tribological and Rheological Properties.

    PubMed

    Abdullah, Bashar Mudhaffar; Zubairi, Saiful Irwan; Huri, Hasniza Zaman; Hairunisa, Nany; Yousif, Emad; Basu, Roma Choudhury

    2016-01-01

    Presently, plant oils which contain high percentage of linoleic acid 1 are perceived to be a viable alternative to mineral oil for biolubricant applications due to their biodegradability and technical properties. In order to get biodegradable lubricant, triester derivatives compounds (1-5) were synthesized and characterized. The processes involved were monoepoxidation of linoleic acid 2, oxirane ring opening 3, esterification 4 and acylation 5. The structures of the products were confirmed by FTIR, 1H and 13C-NMR and LC-MS. The results that showed lowest temperature properties were obtained for triester 5, with a pour point value (PP) of -73°C, highest onset temperature (260°C) and lowest volatility at 0.30%. Viscosity index (VI) increased for the ester's synthetic compounds (2, 3, 4, 5), while the PP decreased. This behavior is the result of the increase of the chain length of the branching agents. Triester based linoleic acid has improved properties such as low-temperature and tribological properties. These results will make it feasible for plant oil to be used for biolubricants, fuels in chain saws, transmission oil and brake fluid. PMID:27008312

  14. Thermal transport and thermoelectric properties of beta-graphyne nanostructures.

    PubMed

    Ouyang, Tao; Hu, Ming

    2014-06-20

    Graphyne, an allotrope of graphene, is currently a hot topic in the carbon-based nanomaterials research community. Taking beta-graphyne as an example, we performed a comprehensive study of thermal transport and related thermoelectric properties by means of nonequilibrium Green's function (NEGF). Our simulation demonstrated that thermal conductance of beta-graphyne is only approximately 26% of that of the graphene counterpart and also shows evident anisotropy. Meanwhile, thermal conductance of armchair beta-graphyne nanoribbons (A-BGYNRs) presents abnormal stepwise width dependence. As for the thermoelectric property, we found that zigzag beta-graphyne nanoribbons (Z-BGYNRs) possess superior thermoelectric performance with figure of merit value achieving 0.5 at room temperature, as compared with graphene nanoribbons (~0.05). Aiming at obtaining a better thermoelectric coefficient, we also investigated Z-BGYNRs with geometric modulations. The results show that the thermoelectric performance can be enhanced dramatically (figure of merit exceeding 1.5 at room temperature), and such enhancement strongly depends on the width of the nanoribbons and location and quantity of geometric modulation. Our findings shed light on transport properties of beta-graphyne as high efficiency thermoelectrics. We anticipate that our simulation results could offer useful guidance for the design and fabrication of future thermoelectric devices. PMID:24859889

  15. 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.

  16. 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.

  17. Thermoelectric properties of heavily boron- and phosphorus-doped silicon

    NASA Astrophysics Data System (ADS)

    Ohishi, Yuji; Xie, Jun; Miyazaki, Yoshinobu; Aikebaier, Yusufu; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke; Uchida, Noriyuki; Tada, Tetsuya

    2015-07-01

    In recent years, nanostructured thermoelectric materials have attracted much attention. However, despite this increasing attention, available information on the thermoelectric properties of single-crystal Si is quite limited, especially for high doping concentrations at high temperatures. In this study, the thermoelectric properties of heavily doped (1018-1020 cm-3) n- and p-type single-crystal Si were studied from room temperature to above 1000 K. The figures of merit, ZT, were calculated from the measured data of electrical conductivity, Seebeck coefficient, and thermal conductivity. The maximum ZT values were 0.015 for n-type and 0.008 for p-type Si at room temperature. To better understand the carrier and phonon transport and to predict the thermoelectric properties of Si, we have developed a simple theoretical model based on the Boltzmann transport equation with the relaxation-time approximation.

  18. Low-temperature aluminum reduction of graphene oxide, electrical properties, surface wettability, and energy storage applications.

    PubMed

    Wan, Dongyun; Yang, Chongyin; Lin, Tianquan; Tang, Yufeng; Zhou, Mi; Zhong, Yajuan; Huang, Fuqiang; Lin, Jianhua

    2012-10-23

    Low-temperature aluminum (Al) reduction is first introduced to reduce graphene oxide (GO) at 100-200 °C in a two-zone furnace. The melted Al metal exhibits an excellent deoxygen ability to produce well-crystallized reduced graphene oxide (RGO) papers with a low O/C ratio of 0.058 (Al-RGO), compared with 0.201 in the thermally reduced one (T-RGO). The Al-RGO papers possess outstanding mechanical flexibility and extremely high electrical conductivities (sheet resistance R(s) ~ 1.75 Ω/sq), compared with 20.12 Ω/sq of T-RGO. More interestingly, very nice hydrophobic nature (90.5°) was observed, significantly superior to the reported chemically or thermally reduced papers. These enhanced properties are attributed to the low oxygen content in the RGO papers. During the aluminum reduction, highly active H atoms from H(2)O reacted with melted Al promise an efficient oxygen removal. This method was also applicable to reduce graphene oxide foams, which were used in the GO/SA (stearic acid) composite as a highly thermally conductive reservoir to hold the phase change material for thermal energy storage. The Al-reduced RGO/SnS(2) composites were further used in an anode material of lithium ion batteries possessing a higher specific capacity. Overall, low-temperature Al reduction is an effective method to prepare highly conductive RGO papers and related composites for flexible energy conversion and storage device applications. PMID:22984901

  19. Novel low temperature synthesis of ZnO nanostructures and its efficient field emission property

    SciTech Connect

    Maiti, U.N.; Ahmed, Sk.F.; Mitra, M.K.; Chattopadhyay, K.K.

    2009-01-08

    We have developed a novel, simple and cost effective wet chemical synthetic route for the production of ZnO nanoneedles and nanoflowers at low temperature. The synthesis process does not require any surfactant, template or pre-seeding. The synthesized ZnO nanoneedles have very sharp tips with their lengths in the range 2-3 {mu}m, while for the case of nanoflowers, the nanoneedles were bunched together. X-ray diffraction study and X-ray photoelectron spectroscopic studies confirmed the formation of pure ZnO phase. Studies on the electron field emission property of the grown nanostructures showed that they are very efficient field emitter. The turn-on fields and the threshold fields are 3.6 V/{mu}m, 4.4 V/{mu}m and 5.4 V/{mu}m, 6.8 V/{mu}m for the ZnO nanoneedles and ZnO nanoflowers, respectively. The enhanced field emission property was attributed to the presence of sharp tips of the nanostructures.

  20. Mechanical and electrical properties of low temperature phase MnBi

    NASA Astrophysics Data System (ADS)

    Jiang, Xiujuan; Roosendaal, Timothy; Lu, Xiaochuan; Palasyuk, Olena; Dennis, Kevin W.; Dahl, Michael; Choi, Jung-Pyung; Polikarpov, Evgueni; Marinescu, Melania; Cui, Jun

    2016-01-01

    Low temperature phase (LTP) manganese bismuth (MnBi) is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have begun considering MnBi magnets for motor applications. Physical properties other than magnetic ones could significantly affect motor design. Here, we report results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their temperature dependence. A MnBi ingot was prepared using an arc melting technique and subsequently underwent grinding, sieving, heat treatment, and cryomilling. The resultant powders with a particle size of ˜5 μm were magnetically aligned, cold pressed, and sintered at a predefined temperature. Micro-hardness testing was performed on a part of original ingot and we found that the hardness of MnBi was 109 ± 15 HV. The sintered magnets were subjected to compressive testing at different temperatures and it was observed that a sintered MnBi magnet fractured when the compressive stress exceeded 193 MPa at room temperature. Impedance spectra were obtained using electrochemical impedance spectroscopy at various temperatures and we found that the electrical resistance of MnBi at room temperature was about 6.85 μΩ m.

  1. Thermoelectric properties of gallium-doped p-type germanium

    NASA Astrophysics Data System (ADS)

    Ohishi, Yuji; Takarada, Sho; Aikebaier, Yusufu; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke; Miyazaki, Yoshinobu; Uchida, Noriyuki; Tada, Tetsuya

    2016-05-01

    In this study, the temperature-dependent thermoelectric properties of p-type single-crystal Ge, which is a useful material for thermoelectric applications owing to its significantly high carrier mobility, were investigated. The thermoelectric properties of Ga-doped (5.7 × 1016, 3.4 × 1018, and 1.0 × 1019 cm-3) p-type single-crystal Ge were measured from room temperature to 770 K. The sample with a carrier concentration of 1.0 × 1019 cm-3 showed the highest thermoelectric figure of merit, ZT, over the entire measured temperature range. The maximum ZT value was 0.06 at 650 K. A theoretical model based on the Boltzmann transport equation with relaxation-time approximation was developed and quantitatively reproduced the experimentally observed data. The optimal impurity concentration predicted by this model was 3 × 1019 cm-3 at 300 K and increased with temperature.

  2. Thermoelectric properties of semiconductor nanowire networks

    DOE PAGESBeta

    Roslyak, Oleksiy; Piryatinski, Andrei

    2016-03-28

    To examine the thermoelectric (TE) properties of a semiconductor nanowire (NW) network, we propose a theoretical approach mapping the TE network on a two-port network. In contrast to a conventional single-port (i.e., resistor)network model, our model allows for large scale calculations showing convergence of TE figure of merit, ZT, with an increasing number of junctions. Using this model, numerical simulations are performed for the Bi2Te3 branched nanowire (BNW) and Cayley tree NW (CTNW) network. We find that the phonon scattering at the network junctions plays a dominant role in enhancing the network ZT. Specifically, disordered BNW and CTNW demonstrate anmore » order of magnitude higher ZT enhancement compared to their ordered counterparts. Formation of preferential TE pathways in CTNW makes the network effectively behave as its BNW counterpart. In conclusion, we provide formalism for simulating large scale nanowire networks hinged upon experimentally measurable TE parameters of a single T-junction.« less

  3. Determining factors of thermoelectric properties of semiconductor nanowires

    PubMed Central

    2011-01-01

    It is widely accepted that low dimensionality of semiconductor heterostructures and nanostructures can significantly improve their thermoelectric efficiency. However, what is less well understood is the precise role of electronic and lattice transport coefficients in the improvement. We differentiate and analyze the electronic and lattice contributions to the enhancement by using a nearly parameter-free theory of the thermoelectric properties of semiconductor nanowires. By combining molecular dynamics, density functional theory, and Boltzmann transport theory methods, we provide a complete picture for the competing factors of thermoelectric figure of merit. As an example, we study the thermoelectric properties of ZnO and Si nanowires. We find that the figure of merit can be increased as much as 30 times in 8-Å-diameter ZnO nanowires and 20 times in 12-Å-diameter Si nanowires, compared with the bulk. Decoupling of thermoelectric contributions reveals that the reduction of lattice thermal conductivity is the predominant factor in the improvement of thermoelectric properties in nanowires. While the lattice contribution to the efficiency enhancement consistently becomes larger with decreasing size of nanowires, the electronic contribution is relatively small in ZnO and disadvantageous in Si. PMID:21854613

  4. Mechanical properties of 1950's vintage 304 stainless steel weldment components after low temperature neutron irradiation

    SciTech Connect

    Sindelar, R.L.; Caskey, G.R. Jr.; Thomas, J.K. ); Hawthorne, J.R.; Hiser, A.L. ); Lott, R.A.; Begley, J.A.; Shogan, R.P. . Science and Technology Center)

    1991-01-01

    The reactor vessels of the nuclear production reactors at the Savannah River Site (SRS) were constructed in the 1950's from Type 304 stainless steel plates welded with Type 308 stainless steel filler using the multipass metal inert gas process. An irradiated mechanical properties database has been developed for the vessel with materials from archival primary coolant system piping irradiated at low temperatures (75 to 150{degrees}C) in the State University of New York at Buffalo reactor (UBR) and the High Flux Isotope Reactor (HFIR) to doses of 0.065 to 2.1 dpa. Fracture toughness, tensile, and Charpy-V impact properties of the weldment components (base, weld, and weld heat-affected-zone (HAZ)) have been measured at temperatures of 25{degrees}C and 125{degrees}C in the L-C and C-L orientations for materials in both the irradiated and unirradiated conditions for companion specimens. Fracture toughness and tensile properties of specimens cut from an SRS reactor vessel sidewall with doses of 0.1 and 0.5 dpa were also measured at temperatures of 25 and 125{degrees}C. The irradiated materials exhibit hardening with loss of work hardenability and a reduction in toughness relative to the unirradiated materials. The HFIR-irradiated materials show an increase in yield strength between about 20% and 190% with a concomitant tensile strength increase between about 15% to 30%. The elastic-plastic fracture toughness parameters and Charpy-V energy absorption both decrease and show only a slight sensitivity to dose. The irradiation-induced decrease in the elastic-plastic fracture toughness (J{sub def} at 1 mm crack extension) is between 20% to 65%; the range of J{sub 1C} values are 72.8 to 366 kJ/m{sup 2} for the irradiated materials. Similarly, Charpy V-notch results show a 40% to 60% decrease in impact energies.

  5. Mechanical properties of 1950`s vintage 304 stainless steel weldment components after low temperature neutron irradiation

    SciTech Connect

    Sindelar, R.L.; Caskey, G.R. Jr.; Thomas, J.K.; Hawthorne, J.R.; Hiser, A.L.; Lott, R.A.; Begley, J.A.; Shogan, R.P.

    1991-12-31

    The reactor vessels of the nuclear production reactors at the Savannah River Site (SRS) were constructed in the 1950`s from Type 304 stainless steel plates welded with Type 308 stainless steel filler using the multipass metal inert gas process. An irradiated mechanical properties database has been developed for the vessel with materials from archival primary coolant system piping irradiated at low temperatures (75 to 150{degrees}C) in the State University of New York at Buffalo reactor (UBR) and the High Flux Isotope Reactor (HFIR) to doses of 0.065 to 2.1 dpa. Fracture toughness, tensile, and Charpy-V impact properties of the weldment components (base, weld, and weld heat-affected-zone (HAZ)) have been measured at temperatures of 25{degrees}C and 125{degrees}C in the L-C and C-L orientations for materials in both the irradiated and unirradiated conditions for companion specimens. Fracture toughness and tensile properties of specimens cut from an SRS reactor vessel sidewall with doses of 0.1 and 0.5 dpa were also measured at temperatures of 25 and 125{degrees}C. The irradiated materials exhibit hardening with loss of work hardenability and a reduction in toughness relative to the unirradiated materials. The HFIR-irradiated materials show an increase in yield strength between about 20% and 190% with a concomitant tensile strength increase between about 15% to 30%. The elastic-plastic fracture toughness parameters and Charpy-V energy absorption both decrease and show only a slight sensitivity to dose. The irradiation-induced decrease in the elastic-plastic fracture toughness (J{sub def} at 1 mm crack extension) is between 20% to 65%; the range of J{sub 1C} values are 72.8 to 366 kJ/m{sup 2} for the irradiated materials. Similarly, Charpy V-notch results show a 40% to 60% decrease in impact energies.

  6. Effects of the low-temperature thermo-alkaline method on the rheological properties of sludge.

    PubMed

    Wang, Ruikun; Zhao, Zhenghui; Yin, Qianqian; Liu, Jianzhong

    2016-07-15

    Municipal sewage sludge (hereafter referred to as sludge) in increasing amounts is a serious threat to the environment and human health. Sludge is difficult to dispose because of its complex properties, such as high water content, viscosity, and hazardous compound concentration. The rheological properties of sludge also significantly influence treatment processes, including stirring, mixing, pumping, and conveying. Improving the rheological properties and reducing the apparent viscosity of sludge are conducive to economic and safe sludge treatment. In this study, the low-temperature thermo-alkaline (LTTA) method was used to modify sludge. Compared with the original sludge with an apparent viscosity at 100 s(-1) (η100) of 979.3 mPa s, the sludge modified under 90 °C-Ca(OH)2-1 h and 90 °C-NaOH-1 h conditions exhibited lower η100 values of 208.7 and 110.8 mPa s respectively. The original sludge exhibited a pseudoplastic behavior. After modification, the pseudoplastic behavior was weakened, and the sludge gradually tended to behave as Newton fluids. The hysteresis loop observed during the shear rate cycle was mainly caused by the viscoelasticity of the sludge. The hysteresis loop area (Hla) reflected to a certain extent the energy required to break the elastic solid structure of the sludge. The larger the Hla, the more energy was needed. However, this result should be evaluated comprehensively by considering other sludge parameters, such as yield stress and apparent viscosity. Hla may also reflect the damage degree of the sludge structure after shearing action. The irreversible destruction of the structure during shearing may also increase Hla. PMID:27082259

  7. Low temperature crystal structure and magnetic properties of RAl{sub 2}

    SciTech Connect

    Pathak, Arjun K. Paudyal, D.; Gschneidner, K. A.; Pecharsky, V. K.

    2014-05-07

    Low temperature crystal structure and magnetic properties of RAl{sub 2} (R = Pr and Nd) have been studied using temperature dependent powder x-ray diffraction, magnetization, and heat capacity measurements. Unlike PrAl{sub 2}, NdAl{sub 2} retains cubic MgCu{sub 2}-type structure from room temperature down to 5 K, which is also confirmed from first principles electronic structure calculations. The magnetization measurements show both PrAl{sub 2} and NdAl{sub 2} order ferromagnetically at T{sub C} = 32 K and 77 K, respectively. However, the magnetization measurements show the former is a hard ferromagnet compared to the latter which is a soft ferromagnetic material. The magnetic entropy change obtained from heat capacity measurements at ΔH = 30 kOe for PrAl{sub 2} and NdAl{sub 2} are 3.15 J mol{sup −1} K{sup −1} and 1.18 J mol{sup −1} K{sup −1}, respectively.

  8. Effect of low temperature annealing on the wear properties of NITINOL

    NASA Astrophysics Data System (ADS)

    Mukunda, Sriram; Nath. S, Narendra; Herbert, Mervin A.; Mukunda, P. G.

    2016-02-01

    NiTi shape memory alloy is a wonder material that is a solution looking for problems. The material finds wide biomedical applications like endodontic files for root canal treatment and cardiovascular stents. This material has rendered the surgical procedure simple compared to that with the existing Stainless Steel (SS) or titanium ones. NiTi as an endodontic file would cause less discomfort to the patients in comparison to that with far stiffer SS or titanium ones. Here nearly equi-atomic 50:50 commercial NiTi rods were subjected to low temperature aging at 300 to 450°C. The wear resistance of the as-received and the heat-treated samples was studied using adhesive wear tests on hardened steel counter face. Abrasive wear tests were run against Alumina disc to simulate the working of endodontic drills and files against dental hard and soft tissues. The abrasive wear resistance is expected to be proportional to the Vickers Hardness of the material and is high for the 450°C heat-treated sample. A correlation between the mechanical properties and microstructures of this material is attempted

  9. Effect of low temperature and calcium on survival and membrane properties of isolated winter wheat cells.

    PubMed

    Pomeroy, M K; Andrews, C J

    1985-07-01

    Isolated cells obtained by enzymic digestion of young primary leaves of cold-hardened, dark-grown Kharkov winter wheat (Triticum aestivum L.) were exposed to various low temperature stresses. The initial uptake of (86)Rb was generally decreased by increasing concentrations of Ca(2+), but after longer periods of incubation, the inhibiting effect of high Ca(2+) levels diminished. Viability of isolated cells suspended in water declined rapidly when ice encased at -1 degrees C, while in the presence of 10 millimolar Ca(2+) viability declined only gradually over a 5-week period. Ice encasement markedly reduced (86)Rb uptake prior to a significant decline in cell viability or increased ion efflux. Cell damage increased progressively when the icing temperature was reduced from -1 to -2 and -3 degrees C, but the presence of Ca(2+) in the suspending medium reduced injury. Cell viability and ion uptake were reduced to a greater extent following slow cooling than after rapid cooling to subfreezing temperatures ranging from -10 to -30 degrees C. The results from this study support the view that an early change in cellular properties due to prolonged ice encasement at -1 degrees C involves the ion transport system, whereas cooling to lower subfreezing temperatures for only a few hours results in more general membrane damage, including loss of semipermeability of the plasma membrane. PMID:16664270

  10. Mechanical properties and fracture toughness of rail steels and thermite welds at low temperature

    NASA Astrophysics Data System (ADS)

    Wang, Yuan-qing; Zhou, Hui; Shi, Yong-jiu; Feng, Bao-rui

    2012-05-01

    Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway service. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fracture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation after fracture and percentage reduction of area) and the toughness indices (Charpy impact energy A k and plane-strain fracture toughness K IC) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger A k and K IC values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.

  11. Low-temperature mechanical properties of superconducting radio frequency cavity materials

    SciTech Connect

    Byun, Thak Sang; Kim, Sang-Ho; Mammosser, John

    2009-01-01

    Low temperature mechanical behaviors have been investigated for the constituent materials of superconducting radio frequency cavities. Test materials consist of small grain Nb, single crystal Nb, large grain Nb (bicrystal), Ti45Nb-Nb weld joint (e-beam welded), and Ti-316L bimetal joint (explosion welded). The strength of all test metals displayed strong temperature dependence and the Ti-316L bimetal showed the highest strength and lowest ductility among the test materials. The fracture toughness of the small grain Nb metals decreased with decreasing test temperature and reached the lower shelf values (30 40 MPa m) at or above 173 K. The Ti45Nb base and Ti45Nb-Nb weld metals showed much higher fracture toughness than the small grain Nb. An extrapolation and comparison with existing data showed that the fracture toughness of the small grain Nb metals at 4 K was expected to be similar to those at 173 K and 77 K. The results from optical photography at a low magnification and fractography by a scanning electron microscope were consistent with corresponding mechanical properties.

  12. Electronic, phononic, and thermoelectric properties of graphyne sheets

    SciTech Connect

    Sevinçli, Hâldun; Sevik, Cem

    2014-12-01

    Electron, phonon, and thermoelectric transport properties of α-, β-, γ-, and 6,6,12-graphyne sheets are compared and contrasted with those of graphene. α-, β-, and 6,6,12-graphynes, with direction dependent Dirac dispersions, have higher electronic transmittance than graphene. γ-graphyne also attains better electrical conduction than graphene except at its band gap. Vibrationally, graphene conducts heat much more efficiently than graphynes, a behavior beyond an atomic density differences explanation. Seebeck coefficients of the considered Dirac materials are similar but thermoelectric power factors decrease with increasing effective speeds of light. γ-graphyne yields the highest thermoelectric efficiency with a thermoelectric figure of merit as high as ZT = 0.45, almost an order of magnitude higher than that of graphene.

  13. Efficient Visible-Light Photocatalytic Properties in Low-Temperature Bi-Nb-O System Photocatalysts.

    PubMed

    Zhai, Haifa; Shang, Shuying; Zheng, Liuyang; Li, Panpan; Li, Haiqin; Luo, Hongying; Kong, Jizhou

    2016-12-01

    Low-temperature Bi-Nb-O system photocatalysts were prepared by a citrate method using homemade water-soluble niobium precursors. The structures, morphologies, and optical properties of Bi-Nb-O system photocatalysts with different compositions were investigated deeply. All the Bi-Nb-O powders exhibit appreciably much higher photocatalytic efficiency of photo-degradation of methyl violet (MV), especially for Bi-Nb-O photocatalysts sintered at 750 °C (BNO750), only 1.5 h to completely decompose MV, and the obtained first-order rate constant (k) is 1.94/h. A larger degradation rate of Bi-Nb-O photocatalysts sintered at 550 °C (BNO550) can be attributed to the synergistic effect between β-BiNbO4 and Bi5Nb3O15. Bi5Nb3O15 with small particle size on β-BiNbO4 surface can effectively short the diffuse length of electron. BNO750 exhibits the best photocatalytic properties under visible-light irradiation, which can be attributed to its better crystallinity and the synergistic effect between β-BiNbO4 and α-BiNbO4. The small amount of α-BiNbO4 loading on surface of β-BiNbO4 can effectively improve the electron and hole segregation and migration. Holes are the main active species of Bi-Nb-O system photocatalysts in aqueous solution under visible-light irradiation. PMID:27576523

  14. Improving low temperature properties of synthetic diesel fuels derived from oil shale. Alternative fuels utilization program

    SciTech Connect

    Frankenfeld, J.W.; Taylor, W.F.

    1980-11-01

    The ability of additives to improve the cold flow properties of shale oil derived fuels boiling in the diesel fuel range was evaluated. Because a commercial shale oil industry did not exist to provide actual samples of finished fuels, a representative range of hydroprocessed shale oil fractions was prepared for use in the additive testing work. Crude oil shale from Occidental Shale Company was fractionated to give three liquids in the diesel fuel boiling range. The initial boiling point in each case was 325/sup 0/F (163/sup 0/C). The final boiling points were 640/sup 0/F (338/sup 0/C), 670/sup 0/F (354/sup 0/C) and 700/sup 0/F (371/sup 0/F). Each fraction was hydrotreated to three different severities (800, 1200 and 1500 psi total pressure) over a Shell 324 nickel molybdate on alumina catalyst at 710 to 750/sup 0/F to afford 9 different model fuels. A variety of commercial and experimental additives were evaluated as cold flow improvers in the model fuels at treat levels of 0.04 to 0.4 wt %. Both the standard pour point test (ASTM D97) and a more severe low temperature flow test (LTFT) were employed. Reductions in pour points of up to 70/sup 0/F and improvements in LTFT temperatures up to 16/sup 0/F were achieved. It is concluded that flow improver additives can play an important role in improving the cold flow properties of future synthetic fuels of the diesel type derived from oil shale.

  15. Tuning Thermoelectric Properties of Chirality Selected Single Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Yanagi, Kazuhiro; Oshima, Yuki; Kitamura, Yoshimasa; Maniwa, Yutaka

    Thermoelectrics are a very important technology for efficiently converting waste heat into electric power. Hicks and Dresselhaus proposed an important approach to innovate the performance of thermoelectric devices, which involves using one-dimensional materials and properly tuning their Fermi level (PRB 1993). Therefore, understanding the relationship between the thermoelectric performance and the Fermi level of one-dimensional materials is of great importance to maximize their thermoelectric performance. Single wall carbon nanotube (SWCNT) is an ideal model for one-dimensional materials. Previously we reported continuous p-type and n-type control over the Seebeck coefficients of semiconducting SWCNT networks with diameter of 1.4 nm through an electric double layer transistor setup using an ionic liquid as the electrolyte (Yanagi et al., Nano Lett. 14, 6437 2014). We clarified the thermoelectric properties of semiconducting SWCNTs with diameter of 1.4 nm as a function of Fermi level. In this study, we investigated how the chiralities or electronic structures of SWCNTs influence on the thermoelectric properties. We found the significant difference in the line-shape of Seebeck coefficient as a function of gate voltage between the different electronic structures of SWCNTs.

  16. Thermoelectric Properties of Bi Doped Tetrahedrite

    NASA Astrophysics Data System (ADS)

    Prem Kumar, D. S.; Chetty, R.; Femi, O. E.; Chattopadhyay, K.; Malar, P.; Mallik, R. C.

    2016-08-01

    Bi doped tetrahedrites with nominal compositions of Cu12Sb4-x Bi x S13 (x = 0, 0.2, 0.4, 0.6, 0.8) were synthesized by the solid state reaction method. Powder x-ray diffraction patterns confirmed that Cu12Sb4S13 (tetrahedrite structure) was the main phase, along with Cu3SbS4 and Cu3SbS3 as the secondary phases. Electron probe microanalysis provided the elemental composition of all the samples. It was confirmed that the main phase is the tetrahedrite phase with slight deviations in the stoichiometry. All the transport properties were measured between 423 K and 673 K. The electrical resistivity increased with an increase in Bi content for all the samples, possibly induced by the variation in the carrier concentration, which may be due to the influence of impurity phases. The increase in electrical resistivity with an increase in temperature indicates the degenerate semiconducting nature of the samples. The absolute Seebeck coefficient is positive throughout the temperature range indicating the p-type nature of the samples. The Seebeck coefficient for all the samples increased with an increase in Bi content as electrical resistivity. The variation of electrical resistivity and the Seebeck coefficient with doping can be attributed to the changes in the carrier concentration of the samples. The total thermal conductivity increases with an increase in temperature and decreases with an increase in the Bi content that could be due to the reduction in carrier thermal conductivity. The highest thermoelectric figure of merit (zT) ~0.84 at 673 K was obtained for the sample with x = 0.2 due to lower thermal conductivity (1.17 W/m K).

  17. Dose dependence of mechanical properties in tantalum and tantalum alloys after low temperature irradiation

    SciTech Connect

    Byun, Thak Sang

    2008-01-01

    The dose dependence of mechanical properties was investigated for tantalum and tantalum alloys after low temperature irradiation. Miniature tensile specimens of three pure tantalum metals, ISIS Ta, Aesar Ta1, Aesar Ta2, and one tantalum alloy, Ta-1W, were irradiated by neutrons in the High Flux Isotope Reactor (HFIR) at ORNL to doses ranging from 0.00004 to 0.14 displacements per atom (dpa) in the temperature range 60 C 100 oC. Also, two tantalum-tungsten alloys, Ta-1W and Ta-10W, were irradiated by protons and spallation neutrons in the LANSCE facility at LANL to doses ranging from 0.7 to 7.5 dpa and from 0.7 to 25.2 dpa, respectively, in the temperature range 50 C 160 oC. Tensile tests were performed at room temperature and at 250oC at nominal strain rates of about 10-3 s-1. All neutron-irradiated materials underwent progressive irradiation hardening and loss of ductility with increasing dose. The ISIS Ta experienced embrittlement at 0.14 dpa, while the other metals retained significant necking ductility. Such a premature embrittlement in ISIS Ta is believed to be because of high initial oxygen concentrations picked up during a pre-irradiation anneal. The Ta-1W and Ta-10W specimens irradiated in spallation condition experienced prompt necking at yield since irradiation doses for those specimens were high ( 0.7 dpa). At the highest dose, 25.2 dpa, the Ta-10W alloy specimen broke with little necking strain. Among the test materials, the Ta-1W alloy displayed the best combination of strength and ductility. The plastic instability stress and true fracture stress were nearly independent of dose. Increasing test temperature decreased strength and delayed the onset of necking at yield.

  18. 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. PMID:27035740

  19. Low-temperature properties of crankcase motor oils: A fundamental approach to pumpability phenomena

    SciTech Connect

    Riga, A.T.; Roby, S.H.

    1994-05-01

    Pumpability-related engine failures have resulted from an inadequate understanding of the time-dependent rheology of motor oils at low temperatures. The current work elucidates the nature of the wax-oil structure formed at temperatures below the cloud points for a series of mineral oils and formulated lubricants having documented field and bench test performance. Low-temperature field performance of motor oils was differentiated by slow-cool, low-shear rate methods. The solidification of each motor oil was characterized by a viscosity-temperature profile. The activation energies for crystallization and fusion were higher for the problem oils. The creep moduli of wax-oil gels were determined from low-temperature isothermal thermomechanical (TMA) experiments. The engine-pass oils had lower moduli at -65{degrees}C.

  20. Thermoelectric Properties of Nanowires with a Graphitic Shell.

    PubMed

    Lee, Jong Woon; Lee, Eun Kyung; Kim, Byung Sung; Lee, Jae Hyun; Kim, Hee Goo; Jang, Hyeon Sik; Hwang, Sung Woo; Choi, Byoung Lyong; Whang, Dongmok

    2015-07-20

    A thermoelectric device that can generate electricity from waste heat can play an important role in a global energy solution. However, the strongly correlated thermoelectric properties have remained a major hurdle for the highly efficient conversion of thermoelectric energy. Herein, the electrical and thermal properties of Si and SiO2 nanowires with few-layer graphitic shells are demonstrated; these structures exhibit enhanced electrical properties but no increase in thermal conductivity. The main path of the phonons through the structures is the core nanowire, which has a large cross-sectional area relative to that of the graphitic shell layer. However, the electrical conductivities of the nanowires with shell structures are high because of the good electrical conductivity of the graphitic shell, despite its small cross-sectional area. PMID:25939904

  1. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and UHT-82). 54.25-20 Section 54.25... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  2. The influence of hydrogen charging on the glassy low temperature properties of a polycrystalline NbTi-alloy

    NASA Astrophysics Data System (ADS)

    Abens, S.; Gladun, A.; Jäckel, M.; Lipp, D.; Sahling, S.

    1999-03-01

    We measured the thermal conductivity, specific heat and heat release of polycrystalline Nb 37Ti 63 at low temperatures. Further we charged our samples with hydrogen and investigated the influence of different charging concentrations on these thermal properties. All physical features show low temperature behaviour similar to amorphous solids. The distribution parameter P¯ and the coupling constant γ, extracted from the experimental data, indicate two different tunneling systems in NbTi and hydrogen charged NbTi. In hydrogen charged NbTi the distribution parameter varies nearly proportional to the hydrogen concentration.

  3. The structure and magnetic properties of Sm-Fe-N powders prepared by ball milling at low temperature

    NASA Astrophysics Data System (ADS)

    Fang, Qiuli; An, Xiaoxin; Wang, Fang; Li, Ying; Du, Juan; Xia, Weixing; Yan, Aru; Liu, J. Ping; Zhang, Jian

    2016-07-01

    Sm-Fe-N powders have great potential to be used for preparing high-performance bonded permanent magnets because of their high anisotropy field and large saturation magnetization. In this work, we report the morphology, structure, oxygen content and magnetic properties of the Sm-Fe-N powders prepared by high energy ball milling at low temperature. Compared with the samples milled at room temperature, the Sm-Fe-N powders prepared at low temperature display more homogeneous morphology, less decomposition, lower oxygen content, and therefore enhanced magnetic performance. Our experimental results indicate that the low temperature milling will be a promising method for fabricating Sm-Fe-N bonded magnets with high-performance.

  4. Transport and thermoelectric properties of hot-pressed SnSe2

    NASA Astrophysics Data System (ADS)

    van Quang, Nguyen; Thi Minh Hai, Nguyen; Anh Tuan, Duong; van Thiet, Duong; Sunglae, Cho; Jae Yong, Song; Hyunmin, Park; Jae Yong Song Collaboration; Hyun-Min Park Collaboration

    Recently, SnSe has been reported as ultralow thermal conductivity material which make it become a very high thermoelectric fingure of merit ZT material, up to 2.6 at 923 K. But, it is hard to use SnSe for applications in high temperature range because SnSe decomposes at 700 K. Therefore, searching for crystalline materials with high ZT value at lower temperature is still an attracted field of research. SnSe2 is also 2D material which is expected to have low lattice thermal conductivity. However, less is known about thermoelectric property of SnSe2. Eutectic SnSe2-Bi2Se3 has been repoted as a promsising low-temperature thermoelectric material with ZT =0.56 at 593 K. Here, we prepared the polycrystalline SnSe2 using hot pressure method. At temperature range up to 573 K, it exhibited an anisotropic n-type charge carrier. Ultra low thermal conductivity is achieved along parallel direction, however, ZT value is still very low whose maximum was 0.045 at 573 K due to low electrical conductivity, and increased with temperature. Our work showed the possibility to enhance ZT of SnSe2 polycrystalline via n- and p-type doping experiments. Presenter.

  5. Electrical Transport of Topological Insulator-bismuth selenide and Thermoelectric Properties of Graphene

    NASA Astrophysics Data System (ADS)

    Wei, Peng

    2011-12-01

    This thesis summarizes our work in the past four years in the field of transport studies of the topological insulator materials and thermoelectric properties of graphene. The first half of the thesis is focused on the transport properties of topological insulator material-Bi2Se3. In our research, we systematically tune the position of the chemical potential in p-type Ca-doped Bi2Se3 thin devices first by eliminating excess holes with controlled post-fabrication electron beam irradiation that results in an insulating bulk state. In spite of the fact that the energetic electron beam creates defects to localize the bulk carriers and inevitably to cause additional scattering, we find a tenfold increase in carrier mobility associated with the extended states in the band gap. In addition, the resistance undergoes a fivefold increase and passes the maximum as the chemical potential is further tuned by electrostatic gating. A cusp-like low-field magnetoresistance feature also emerges which is indicative of strong spin-orbit interaction. The observed gate-tunable high-mobility is a signature of massless Dirac fermions in the band gap of Bi2Se3. The second half of this thesis is focused on graphene. Our work first reported the thermoelectric study of graphene and demonstrated the anomalous thermoelectric transport of massless Dirac fermions. As a direct consequence of the linear dispersion of massless particles, we find that the Seebeck coefficient Sxx diverges with 1/n2D , where n2D is the carrier density. We observe a very large Nernst signal Sxy (˜ 50 muV/K at 8 T) at the Dirac point, and an oscillatory dependence of both Sxx and Sxy on n 2D at low temperatures. Our results underscore the anomalous thermoelectric transport in graphene, which may be used as a highly sensitive probe for impurity bands near the Dirac point.

  6. Optical properties of single ZnTe nanowires grown at low temperature

    SciTech Connect

    Artioli, A.; Stepanov, P.; Den Hertog, M.; Bougerol, C.; Genuist, Y.; Donatini, F.; André, R.; Nogues, G.; Tatarenko, S.; Ferrand, D.; Cibert, J.; Inst NEEL, CNRS, F-38042 Grenoble ; Rueda-Fonseca, P.; Inst NEEL, CNRS, F-38042 Grenoble; INAC, CEA and Université de Grenoble, 17 rue des Martyrs, 38054 Grenoble ; Bellet-Amalric, E.; Kheng, K.

    2013-11-25

    Optically active gold-catalyzed ZnTe nanowires have been grown by molecular beam epitaxy, on a ZnTe(111) buffer layer, at low temperature (350 °C) under Te rich conditions, and at ultra-low density (from 1 to 5 nanowires per μm{sup 2}). The crystalline structure is zinc blende as identified by transmission electron microscopy. All nanowires are tapered and the majority of them are <111> oriented. Low temperature micro-photoluminescence and cathodoluminescence experiments have been performed on single nanowires. We observe a narrow emission line with a blue-shift of 2 or 3 meV with respect to the exciton energy in bulk ZnTe. This shift is attributed to the strain induced by a 5 nm-thick oxide layer covering the nanowires, and this assumption is supported by a quantitative estimation of the strain in the nanowires.

  7. Low-temperature sintering of silica-boric acid-doped willemite and microwave dielectric properties

    NASA Astrophysics Data System (ADS)

    Ando, Minato; Ohsato, Hitoshi; Igimi, Daisuke; Higashida, Yutaka; Kan, Akinori; Suzuki, Sadahiko; Yasufuku, Yoshitoyo; Kagomiya, Isao

    2015-10-01

    Millimeter-wave wireless communications in a high-level information society have been expanding in terms of high-density data transfer and radar for pre-crash safety systems. For these communications, millimeter-wave dielectrics have been expected for the development of substrates with high quality factor (Qf), low dielectric constant (ɛr), and near-zero temperature coefficient of resonance frequency (TCf). We have been studying several silicates such as forsterite, willemite, diopside, wollastonite, and cordierite/indialite glass ceramics. In this study, the synthesis of willemite and low-temperature-sintered willemite for low temperature co-fired ceramics (LTCC) is examined. The raw materials used for preparing slurries in doctor blade tape casting are also analyzed.

  8. Effective material properties of thermoelectric composites with elliptical fibers

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Ze

    2015-06-01

    In the present work, the effective material properties of thermoelectric composites with elliptical fibers are studied. Explicit solutions are derived by the conformal mapping function and Mori-Tanaka method. Numerical simulations are performed to present the behaviors of normalized effective material constants. From the results, it can be observed that both the effective electric and thermal conductivities can be reduced by increasing the filling ratio and a/ b. Such influences can also be found for the effective thermoelectric figure of merit. But they are different from those on the effective Seebeck and Peltier coefficients.

  9. Low-Temperature Magnetic and Thermal Properties of Some Low-Dimensional Compounds

    NASA Astrophysics Data System (ADS)

    Lukin, Jonathan Allen

    Heat capacity and A.C. susceptibility measurements of powdered alpha-rm MnC_2O_4cdot2H_2O have led to its description as a Heisenberg chain antiferromagnet with exchange J/k = -1.17(2) K. Anomalies in C_{p} signal the onset of long-range order at T_{N} = 2.4 K and an order-order transition at T_2 = 1.5 K. For T_2low-temperature C_{p}. From EPR spectra of doped alpha- rm ZnC_2O_4cdot2H_2O crystals, the properties of isolated Mn ^{2+}, Cu^{2+ }, and Co^{2+} ions in this lattice were deduced. The powder susceptibility and heat capacity of alpha- rm CoC_2O_4cdot2H_2O delineate a 2D Ising antiferromagnet with J/k = -30+/- 2 K, | J^'/J |~ 3times 10^{-3}, and an ordering temperature T_{N }=6.23(2) K. The measured susceptibility above 20 K of alpha-rm NiC _2O_4cdot2H_2O agrees with that of a spin-1 Heisenberg chain with J/k = -19.5+/- 1 K; a peak in C_{p } indicates magnetic ordering at T _{N} = 6.33(2) K. X-ray diffraction, heat capacity, and magnetic susceptibility measurements of rm ErBa_2Cu _3O_{x} with 6.12 <= x<=6.91 revealed several effects correlated with the oxygen concentration x. The fully -oxygenated orthorhombic material, with a superconducting transition temperature T_{c} = 92 K, exhibits a 2D Ising-like peak corresponding to magnetic ordering of the Er^{3+} moments at T_{m} = 0.604 K. Removal of oxygen reduces the lattice orthorhombicity and depresses both T_{c} and T_{m}, until in the 2 = 6.12, 6.23 tetragonal phases superconductivity and long-range magnetic order are quenched. These

  10. Thermoelectric transport properties of In2Se3 single crystal

    NASA Astrophysics Data System (ADS)

    Nguyen, Thi Huong; Duong, Van Thiet; Nguyen, Van Quang; Duong, Anh Tuan; Cho, Sunglae; Song, Jae Yong; Park, Hyun-Min

    In recent years the discovery and development of green energy source are one of the top concerns in science. The enormous efforts have been devoted to search for thermoelectric materials. Enhancement of thermoelectric figure of merit (ZT = (S2 σ / κ) T) is currently research goal of scientists. In2Se3 is one of semiconductors with layered structure, which is good for thermoelectric applications. In this study, we report on the transport and thermoelectric properties of In2Se3 single crystal. The layered crystal structure of In2Se3 was determined by XRD and FE-SEM measurements. Ellipsometry measurement illustrated the indirect band gap of In2Se3, about 1.61 eV. Transport properties have been studied in the temperature range from 20 to 400 K along axis which is parallel to the layers direction. Interestingly, Seebeck coefficient was n-type and increased with temperature and the electrical conductivity increased with temperature. Therefore, power factor increased up to 2.69 µWcm-1K-2at 400 K. In this talk, we will discuss more on transport properties.

  11. Thermoelectric properties and efficiency measurements under large temperature differences.

    PubMed

    Muto, A; Kraemer, D; Hao, Q; Ren, Z F; Chen, G

    2009-09-01

    The maximum efficiency of a thermoelectric generator is determined by the material's dimensionless figure of merit ZT. Real thermoelectric material properties are highly temperature dependent and are often measured individually using multiple measurement tools on different samples. As a result, reported ZT values have large uncertainties. In this work we present an experimental technique that eliminates some of these uncertainties. We measure the Seebeck coefficient, electrical conductivity, and thermal conductivity of a single element or leg, as well as the conversion efficiency, under a large temperature difference of 2-160 degrees C. The advantages of this technique include (1) the thermoelectric leg is mounted only once and all measurements are in the same direction and (2) the measured properties are corroborated by efficiency measurements. The directly measured power and efficiency are compared to the values calculated from the measured properties and agree within 0.4% and 2%, respectively. The realistic testing conditions of this technique make it ideal for material characterization prior to implementation in a real thermoelectric generator. PMID:19791947

  12. Thermoelectric Properties of Barium Plumbate Doped by Alkaline Earth Oxides

    NASA Astrophysics Data System (ADS)

    Eufrasio, Andreza; Bhatta, Rudra; Pegg, Ian; Dutta, Biprodas

    Ceramic oxides are now being considered as a new class of thermoelectric materials because of their high stability at elevated temperatures. Such materials are especially suitable for use as prospective thermoelectric power generators because high temperatures are encountered in such operations. The present investigation uses barium plumbate (BaPbO3) as the starting material, the thermoelectric properties of which have been altered by judicious cation substitutions. BaPbO3 is known to exhibit metallic properties which may turn semiconducting as a result of compositional changes without precipitating a separate phase and/or altering the basic perovskite crystal structure. Perovskite structures are noted for their large interstitial spaces which can accommodate a large variety of ``impurity'' ions. As BaPbO3 has high electrical conductivity, σ = 2.43x105Ω-1 m-1 at room temperature, its thermopower, S, is relatively low, 23 μV/K, as expected. With a thermal conductivity, k, of 4.83Wm-1K-1, the figure of merit (ZT =S2 σ Tk-1) of BaPbO3 is only 0.01 at T = 300K. The objective of this investigation is to study the variation of thermoelectric properties of BaPbO3 as Ba and Pb ions are systematically substituted by alkaline earth ions.

  13. Low Temperature Properties for Correlation Functions in Classical N-Vector Spin Models

    NASA Astrophysics Data System (ADS)

    Balaban, Tadeusz; O'Carroll, Michael

    We obtain convergent multi-scale expansions for the one-and two-point correlation functions of the low temperature lattice classical N- vector spin model in d>= 3 dimensions, N>= 2. The Gibbs factor is taken as where , , , are large and 0 < v<= 1. In the thermodynamic and limits, with h=e1, and Δ≡∂*∂, the expansion gives (spontaneous magnetization), , (Goldstone Bosons), , and , where , for some ρ > 0, and c0 is aprecisely determined constant.

  14. Low-temperature crystal structure, specific heat, and dielectric properties of lithium tetraborate Li2B4O7

    NASA Astrophysics Data System (ADS)

    Senyshyn, A.; Schwarz, B.; Lorenz, T.; Adamiv, V. T.; Burak, Ya. V.; Banys, J.; Grigalaitis, R.; Vasylechko, L.; Ehrenberg, H.; Fuess, H.

    2010-11-01

    Coherent neutron powder diffraction experiments were carried out together with specific heat, dilatometry, and dielectric spectroscopy studies on Li2B4O7 enriched with B11 isotope to 99.3% at low temperatures. Neither traces of phase transformations nor discontinuous changes in physical properties were observed. Negative thermal expansion, anomalous thermal behavior of selected interatomic distances/angles, isotropic displacement parameters on specific sites as well as dielectric constant were discussed in terms of dynamic lithium disorder.

  15. Low Temperature Properties and Quantum Criticality of CrAs1-x Px single crystal

    NASA Astrophysics Data System (ADS)

    Luo, Jianlin; Institute of Physics, Chinese Academy of Sciences Team

    We report a systematically study of resistivity and specific heat on phosphorus doped CrAs1-xPx single crystals with x =0 to 0.2. With the increasing of phosphorus doping concentration x, the magnetic and structural transition temperature TN is suppressed. Non-fermi liquid behavior and quantum criticality phenomenon are observed from low temperature resistivity around critical doping with xc ~0.05 where the long-range antiferromagnetic ordering is completely suppressed. The low temperature specific heat of CrAs1-xPx is contributed by the thermal excitation of phonons and electrons. The electronic specific heat coefficient γ, which reflects the effective mass of quasi-particles, shows maximum around xc ~0.05, also indicating the existence of quantum critical phenomenon around the critical doping. The value of Kadowaki-Woods ratio of CrAs1-xPx shows no significant different from that of CrAs. Work is done in collaboration with Fukun Lin, Wei Wu, Ping Zheng, Guozhi Fan, Jinguang Cheng.

  16. Thermoelectric properties of chalcopyrite type CuGaTe2 and chalcostibite CuSbS2

    NASA Astrophysics Data System (ADS)

    Kumar Gudelli, Vijay; Kanchana, V.; Vaitheeswaran, G.; Svane, A.; Christensen, N. E.

    2013-12-01

    Electronic and transport properties of CuGaTe2, a hole-doped ternary copper based chalcopyrite type semiconductor, are studied using calculations within the Density Functional Theory and solving the Boltzmann transport equation within the constant relaxation time approximation. The electronic band structures are calculated by means of the full-potential linear augmented plane wave method, using the Tran-Blaha modified Becke-Johnson potential. The calculated band gap of 1.23 eV is in agreement with the experimental value of 1.2 eV. The carrier concentration- and temperature dependent thermoelectric properties of CuGaTe2 are derived, and a figure of merit of zT = 1.69 is obtained at 950 K for a hole concentration of 3.7.1019 cm-3, in agreement with a recent experimental finding of zT = 1.4, confirming that CuGaTe2 is a promising material for high temperature thermoelectric applications. The good thermoelectric performance of p-type CuGaTe2 is associated with anisotropic transport from a combination of heavy and light bands. Also for CuSbS2 (chalcostibite), a better performance is obtained for p-type than for n-type doping. The variation of the thermopower as a function of temperature and concentration suggests that CuSbS2 will be a good thermoelectric material at low temperatures, similarly to the isostructural CuBiS2 compound.

  17. Optical properties of Sm-doped ceria nanostructured films grown by electrodeposition at low temperature

    NASA Astrophysics Data System (ADS)

    Ursaki, V. V.; Lair, V.; Żivković, L.; Cassir, M.; Ringuedé, A.; Lupan, O.

    2012-09-01

    Nanostructured undoped and samarium doped ceria thin nanocolumnar films are electrodeposited onto (FTO) glass substrates at low-temperature (30 °C) with a subsequent thermal annealing at 600 °C for 1 h. Films are obtained from mixed Sm3+/Ce3+ aqueous nitrate solutions, applying a -0.8 V/(SCE) potential for 1 h. Cubic fluorite type ceria nanostructured films of high crystal quality are synthesized as confirmed by X-ray diffraction and Raman spectroscopy. SEM analysis demonstrates that doping with Sm improves the quality of the film with respect to crack formation. The incorporation and activation of the Sm3+ ions in the ceria host as well as the Stark splitting of the manifolds responsible for emission in the red-orange spectral range are investigated by means of photoluminescence spectroscopy.

  18. Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

    SciTech Connect

    Demaurex, Bénédicte Bartlome, Richard; Seif, Johannes P.; Geissbühler, Jonas; Ballif, Christophe; De Wolf, Stefaan; Alexander, Duncan T. L.; Jeangros, Quentin

    2014-08-07

    Low-temperature (≤200 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-enhanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only from the growth conditions but also from unintentional contamination of the reactor. Based on our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.

  19. Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

    SciTech Connect

    Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; Geissbühler, Jonas; Alexander, Duncan T. L.; Jeangros, Quentin; Ballif, Christophe; De Wolf, Stefaan

    2014-08-05

    Low-temperature (≤ 180 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-ehanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only from the growth conditions but also from unintentional contamination of the reactor. As a result of our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.

  20. Tensile and impact properties of vanadium-base alloys irradiated at low temperatures in the ATR-A1 experiment

    SciTech Connect

    Tsai, H.; Nowicki, L.J.; Billone, M.C.; Chung, H.M.; Smith, D.L.

    1998-03-01

    Subsize tensile and Charpy specimens made from several V-(4-5)Cr-(4-5)Ti alloys were irradiated in the ATR-A1 experiment to study the effects of low-temperature irradiation on mechanical properties. These specimens were contained in lithium-bonded subcapsules and irradiated at temperatures between {approx}200 and 300 C. Peak neutron damage was {approx}4.7 dpa. Postirradiation testing of these specimens has begun. Preliminary results from a limited number of specimens indicate a significant loss of work-hardening capability and dynamic toughness due to the irradiation. These results are consistent with data from previous low-temperature neutron irradiation experiments on these alloys.

  1. A newly developed snow vehicle (SM100S) for Antarctica. Part 4: Low temperature properties of crawler belt

    NASA Astrophysics Data System (ADS)

    Maekawa, Etsuji; Terayama, Yoshihide

    1992-11-01

    In order to discover a high cold-resistance material for use in the crawler belt of snow vehicles, the physical properties at very low temperatures of a recently developed material, isoprene/butadiene (70/30) random copolymer filled with carbon black, was investigated in comparison with a blended rubber NR (Natural Rubber) / BR (Butadiene Rubber) (65/35) as well as a currently used NR. It has been found that this material can keep rubber elasticity even at low temperatures below - 70 C, though it is somewhat inferior to the other two materials as to strengths such as stress-at-break and tear; and hence, it is considered as quite worthy of a practical test for a snow vehicle in the Antarctic area.

  2. Thermoelectric properties of doped BaHfO3

    NASA Astrophysics Data System (ADS)

    Dixit, Chandra Kr.; Bhamu, K. C.; Sharma, Ramesh

    2016-05-01

    We have studied the structural stability, electronic structure, optical properties and thermoelectric properties of doped BaHfO3 by full potential linearized augmented plane wave (FP-LAPW) method. The electronic structure of BaHfO3 doped with Sr shows enhances the indirect band gaps of 3.53 eV, 3.58 eV. The charge density plots show strong ionic bonding in Ba-Hf, and ionic and covalent bonding between Hf and O. Calculations of the optical spectra, viz., the dielectric function, refractive index and extinction coefficient are performed for the energy range are calculated and analyzed. Thermoelectric properties of semi conducting are also reported first time. The doped BaHfO3 is approximately wide band gap semiconductor with the large p-type Seebeck coefficient. The power factor of BaHfO3 is increased with Sr doping, decreases because of low electrical resistivity and thermal conductivity.

  3. 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

    2016-06-01

    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.

  4. A study of thermoelectric properties of graphene materials

    NASA Astrophysics Data System (ADS)

    Twombly, Chris

    Graphene has very beneficial charge transport properties which make it an interesting potential thermoelectric material, but its thermoelectric efficiency is limited by large thermal conductivity. Nanostructuring graphene by incorporating periodic holes in the crystal structure produces graphene nanomesh with reduced thermal conductivity due to increased phonon scattering. The goal of this study was to investigate the thermoelectric properties of graphene nanomeshes and defected graphene using Density Functional Theory and semi-classical Boltzmann Transport Theory. We computed the Seebeck coefficient, electrical conductivity, and the electrical component of thermal conductivity from first principles. We first developed and verified the accuracy of our techniques using silicon. We then examined the properties of silicon nanowires in order to study systems with more complex geometry and to show that nanostructuring can improve thermoelectric properties. Our results agreed closely with previous experimental and theoretical studies of silicon systems. We then employed this suite of methods to study graphene, graphene nanomeshes, and periodically defected graphene. Our calculations for pristine graphene agreed closely with experimental measurements, proving that our methods work well with 2D systems. Our calculations suggest that there is up to a one order of magnitude increase in Seebeck coefficient for graphene nanomeshes compared to pristine graphene. This increase was found to be strongly dependent on a previously predicted geometrically based semimetal to semiconductor transition. We estimated a maximum ZT of 0.15-0.4 for graphene nanomeshes based on a simple scaling law for the thermal conductivity in these systems. The ZT value is strongly dependent on the purity and the quality of the graphene crystal lattice, which affects the relaxation time of charge carriers in these systems. We then studied defected graphene with partial hydrogen passivation and boron

  5. Thermoelectric and magnetic properties of Yb2MgSi2 prepared by spark plasma sintering method

    NASA Astrophysics Data System (ADS)

    Kubouchi, M.; Hayashi, K.; Miyazaki, Y.

    2016-08-01

    An intermediate-valence compound, Yb2MgSi2, has been prepared using a spark plasma sintering method. The magnetic susceptibility and thermoelectric properties of Yb2MgSi2 are measured in the temperature range from 5 to 300 K. From the magnetic susceptibility results, Yb valence of the Yb2MgSi2 is evaluated. As compared with YbAl3, which is one of the promising thermoelectric materials that can be used at low temperatures, Yb2MgSi2 exhibits a lower absolute value of Seebeck coefficient, higher electrical resistivity, and lower thermal conductivity over the measured temperature range. A maximum dimensionless figure of merit, ZT, of 0.0018 is achieved at around 200 K.

  6. Experimental Investigation on Mechanical Property of Metal Rubber Used in Lunar Rover at High or Low Temperature

    NASA Astrophysics Data System (ADS)

    Tao, J.; Deng, Z.; Gao, H.; Wang, S.; Hu, M.; Meng, X.

    Metal rubber is a kind of elastic damping material for aerospace environment It can keep its capacity even in some extreme environment such as high temperature high pressure high vacuum ultra-low temperature and violent vibration where traditional rubber can t deal with so it can be used in space craft as vibration reduction filter element and sealing element On the prototype of a lunar rover developed by Harbin Institute of Technology metal rubber is firstly used for the vibration dampers in the rover wheels In this paper the experimental investigation on rigidity and damping characteristic of metal rubber is carried out at high temperature and ultra-low temperature that corresponds to lunar environment The quasi-statics property of the samples made of metal rubber is tested at desired temperatures by the universal tensile testing machine model Y-71 The low temperatures down to -175° were realized by liquid nitrogen and the high temperatures up to 130° were realized by flexible electrical heater band Based on the method of least squares some curves to curve fit the experimental data on rigidity of the metal rubber samples at simulated temperatures to lunar environment were given The damping ratios of metal rubber at ordinary temperatures have been mentioned in some documents But there are hardly any reports about them at simulated temperatures to lunar environment Because it is difficult to know directly the exact damping mechanism of the metal rubber the free attenuation method is feasible to test its damping

  7. Biodiesel production by combined fatty acids separation and subsequently enzymatic esterification to improve the low temperature properties.

    PubMed

    Wang, Meng; Nie, Kaili; Cao, Hao; Deng, Li; Wang, Fang; Tan, Tianwei

    2014-12-01

    The poor low-temperature properties of biodiesel, which provokes easy crystallization at low temperature, can cause fuel line plugging and limits its blending amount with petro-diesel. This work aimed to study the production of biodiesel with a new process of improving the low temperature performance of biodiesel. Waste cooking oil was first hydrolyzed into fatty acids (FAs) by 60g immobilized lipase and 240g RO water in 15h. Then, urea complexation was used to divide the FAs into saturated and unsaturated components. The conditions for complexation were: FA-to-urea ratio 1:2 (w/w), methanol to FA ratio 5:1 (v/v), duration 2h. The saturated and unsaturated FAs were then converted to iso-propyl and methyl esters by lipase, respectively. Finally, the esters were mixed together. The CFPP of this mixture was decreased from 5°C to -3°C. Hydrolysis, urea complexation and enzymic catalyzed esterification processes are discussed in this paper. PMID:25441717

  8. Thermoelectric properties of MBE-grown HgCdTe-based superlattices from 100K to 300K

    NASA Astrophysics Data System (ADS)

    Zhang, Kejia; Yadav, Abhishek; Shao, Lei; Bommena, Ramana; Zhao, Jun; Velicu, Silviu; Pipe, Kevin P.

    2016-07-01

    We report on the thermoelectric properties of long-period HgCdTe superlattices (MCT SLs) from cryogenic temperature to room temperature. We find that the thermal conductivity is lower than the alloy value especially at low temperatures, the electrical conductivity is similar to that of alloy films, and the Seebeck coefficient is comparable to other SLs. Calculations based on Rytov's elastic model show that the phonon group velocity is reduced due to folding by more than a factor of two relative to its value in bulk CdTe or HgTe. Thermal conductivity is found to be relatively constant over a wide range of temperatures.

  9. Low-temperature plasma-deposited silicon epitaxial films: Growth and properties

    DOE PAGESBeta

    Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; Geissbühler, Jonas; Alexander, Duncan T. L.; Jeangros, Quentin; Ballif, Christophe; De Wolf, Stefaan

    2014-08-05

    Low-temperature (≤ 180 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-ehanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems notmore » only from the growth conditions but also from unintentional contamination of the reactor. As a result of our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.« less

  10. Structural, ferroelectric and piezoelectric properties of chemically processed, low temperature sintered piezoelectric BZT-BCT ceramics

    NASA Astrophysics Data System (ADS)

    Roy, Subir; Maharana, Rajalaxmi; Rangaswamy Reddy, S.; Singh, Sarabjit; Kumar, Pawan; Karthik, T.; Asthana, Saket; Bhanu Prasad, V. V.; Kamat, S. V.

    2016-03-01

    0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3TiO3) nanopowders were synthesized at very low temperature using a soft chemical approach. The synthesized powders and the consolidated disks were structurally characterized thoroughly by XRD, SEM, TEM and EPMA and also by ultraviolet and Raman spectroscopy. The 1350 °C sintered BZT-BCT disk displayed the highest density, underwent diffused phase transition centered at ˜100 °C and showed the highest dielectric constant (8917) and lowest dielectric loss (0.015). The sintered BZT-BCT sample with the highest density showed a maximum polarization (P max) of 13 μC cm-2 and remnant polarization of 6 μC cm-2. The same sample exhibited very high electrostrain of ˜0.12% under a relatively low electrical field of 3.5 kV mm-1.

  11. CaTiO3:Eu3+ red nanophosphor: low temperature synthesis and photoluminescence properties.

    PubMed

    Shivram, M; Prashantha, S C; Nagabhushana, H; Sharma, S C; Thyagarajan, K; Harikrishna, R; Nagabhushana, B M

    2014-01-01

    Nanoparticles of Eu3+ doped (1-9 mol%) CaTiO3 were prepared using low temperature (500°C) solution combustion technique using metal nitrates as precursors and urea as fuel. The powder X-ray diffraction patterns of the as-formed products show single orthorhombic phase. The crystallite size was estimated using Scherrer's method and found to be in the range 40-45 nm. The effect of Eu3+ ions on luminescence characteristics of CaTiO3 was studied and the results were discussed in detail. The phosphors exhibit bright red emission upon 398 nm excitation. The characteristic emission peaks recorded at ∼540, 593, 615, 653, 696 and 706 nm (5D0→7Fj=0,1,2,3,4,5) were attributed to Eu3+ ions. The electronic transition corresponding to 5D0→7F2 (615 nm) was stronger than the magnetic dipole transition 5D0→7F1 of Eu3+ ions (596 nm). The CIE chromaticity co-ordinates were calculated from emission spectra, the values (x,y) very close to NTSC standard value of red emission. Therefore, the present phosphors were highly useful for display applications. PMID:24211621

  12. Structural and magnetic properties of the low temperature phase MnBi with ball milling

    NASA Astrophysics Data System (ADS)

    Kavita, S.; Ramakrishna, V. V.; Srinivasan, A.; Gopalan, R.

    2016-05-01

    MnBi has been prepared by arc-melting method and subjected to low energy ball milling after homogenization heat treatment. X-ray diffraction data shows that the weight percentage of the low temperature MnBi (LTP MnBi) phase increases with milling. Microstructural and x-ray peak profile analysis show that milling leads to a reduction in average crystallite size and an increase in microstrain respectively. Magnetic hysteresis loops recorded for an applied field of ±20 kOe show that the alloy milled for 5 h exhibits a coercivity of 11.3 kOe. Although ball milling results in the growth of the LTP MnBi phase, the saturation magnetization (M s) decreases from 47 emu g‑1 (arc melted and homogenized) to 15 emu g‑1 upon milling for 5 h. It is also found that the Curie temperature (T c) of the system decreases with milling. The decrease in magnetization is discussed in terms of variation of Mn–Mn distance and the strain induced during milling. On the other hand, it has been found that the coercivity increases with temperature and reaches a value of 17.5 kOe at 500 K for the 5 h milled sample.

  13. Thermoelectric properties of non-stoichiometric lanthanum sulfides

    NASA Technical Reports Server (NTRS)

    Shapiro, E.; Danielson, L. R.

    1983-01-01

    The lanthanum sulfides are promising candidate materials for high-efficiency thermoelectric applications at temperatures up to 1300 C. The non-stoichiometric lanthanum sulfides (LaS(x), where x is in the range 1.33-1.50) appear to possess the most favorable thermoelectric properties. The Seebeck coefficient and resistivity vary significantly with composition, so that an optimum value of alpha sq/rho (where alpha is the Seebeck coefficient and rho is the resistivity) can be chosen. The thermal conductivity remains approximately constant with stoichiometry, so a material with an optimum value of alpha sq/rho should possess the optimum figure-of-merit. Data for the Seebeck coefficient and electrical resistivity of non-stoichiometric lanthanum sulfides will be pressed, together with structural properties of these materials.

  14. Bio-lubricants derived from waste cooking oil with improved oxidation stability and low-temperature properties.

    PubMed

    Li, Weimin; Wang, Xiaobo

    2015-01-01

    Waste cooking oil (WCO) was chemically modified via epoxidation using H2O2 followed by transesterification with methanol and branched alcohols (isooctanol, isotridecanol and isooctadecanol) to produce bio-lubricants with improved oxidative stability and low temperature properties. Physicochemical properties of synthesized bio-lubricants such as pour point (PP), cloud point (CP), viscosity, viscosity index (VI), oxidative stability, and corrosion resistant property were determined according to standard methods. The synthesized bio-lubricants showed improved low temperature flow performances compared with WCO, which can be attributing to the introduction of branched chains in their molecular structures. What's more, the oxidation stability of the WCO showed more than 10 folds improvement due to the elimination of -C=C-bonds in the WCO molecule. Tribological performances of these bio-lubricants were also investigated using four-ball friction and wear tester. Experimental results showed that derivatives of WCO exhibited favorable physicochemical properties and tribological performances which making them good candidates in formulating eco-friendly lubricants. PMID:25766933

  15. Holey topological thermoelectrics

    NASA Astrophysics Data System (ADS)

    Tretiakov, O. A.; Abanov, Ar.; Sinova, Jairo

    2011-09-01

    We study the thermoelectric properties of three-dimensional topological insulators with many holes (or pores) in the bulk. We show that at high density of these holes, the thermoelectric figure of merit, ZT, can be large due to the contribution of the conducting surfaces and the suppressed phonon thermal conductivity. The maximum efficiency can be tuned by an induced gap in the surface states dispersion through tunneling or external magnetic fields. The large values of ZT, much higher than unity for reasonable parameters, make this system a strong candidate for applications in heat management of nanodevices, especially at low temperatures.

  16. Thermoelectric properties of PEDOT nanowire/PEDOT hybrids

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Qiu, Jingjing; Wang, Shiren

    2016-04-01

    Freestanding poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires were synthesized by template-confined in situ polymerization, and then integrated into polystyrene sulfonate (PSS)-doped PEDOT and tosylate-doped PEDOT hosts, respectively. The hybrid morphologies were characterized by atomic force microscopy, indicating the homogeneous dispersion of PEDOT nanowires. The thermoelectric properties of the resultant hybrids were measured, and the power factor was found to be enhanced by 9-fold in comparison with PEDOT:PSS mixed with 5 vol% dimethyl sulfoxide while the low thermal conductivity was still maintained. Such a significant improvement could be attributed to the synergistic effects of interfacial energy filtering, component contributions, and changes of carrier concentrations in the host materials. Upon addition of 0.2 wt% PEDOT nanowires, the resultant composites demonstrated a power factor as high as 446.6 μW m-1 K-2 and the thermoelectric figure of merit could reach 0.44 at room temperature. The thermoelectric devices were investigated by using the PEDOT nanowire/PEDOT hybrid as a p-type leg and nitrogen-doped graphene as an n-type leg. The normalized power output was as high as ~0.5 mW m-2 for a temperature gradient of ΔT = 10.1 °C, indicating great potential for practical applications. These findings open up a new route towards high-performance organic thermoelectric materials and devices.Freestanding poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires were synthesized by template-confined in situ polymerization, and then integrated into polystyrene sulfonate (PSS)-doped PEDOT and tosylate-doped PEDOT hosts, respectively. The hybrid morphologies were characterized by atomic force microscopy, indicating the homogeneous dispersion of PEDOT nanowires. The thermoelectric properties of the resultant hybrids were measured, and the power factor was found to be enhanced by 9-fold in comparison with PEDOT:PSS mixed with 5 vol% dimethyl sulfoxide while the low

  17. Electronic band structure and low-temperature transport properties of the type-I clathrate Ba8Ni(x)Ge(46-x-y□y).

    PubMed

    Aydemir, U; Candolfi, C; Ormeci, A; Baitinger, M; Burkhardt, U; Oeschler, N; Steglich, F; Grin, Yu

    2015-04-28

    We present the evolution of the low-temperature thermodynamic, galvanomagnetic and thermoelectric properties of the type-I clathrate Ba8Ni(x)Ge(46-x-y□y) with the Ni concentration studied on polycrystalline samples with 0.0 ≤ x ≤ 6.0 by means of specific heat, Hall effect, electrical resistivity, thermopower and thermal conductivity measurements in the 2-350 K temperature range and supported by first-principles calculations. The experimental results evidence a 2a × 2a × 2a supercell described in the space group Ia3d for x ≤ 1.0 and a primitive unit cell a × a × a (space group Pm3n) above this Ni content. This concentration also marks the limit between a regime where both electrons and holes contribute to the electrical conduction (x ≤ 1.0) and a conventional, single-carrier regime (x > 1.0). This evolution is traced by the variations in the thermopower and Hall effect with x. In agreement with band structure calculations, increasing the Ni content drives the system from a nearly-compensated semimetallic state (x = 0.0) towards a narrow-band-gap semiconducting state (x = 4.0). A crossover from an n-type to a p-type conduction occurs when crossing the x = 4.0 concentration i.e. for x = 4.1. The solid solution Ba8Ni(x)Ge(46-x-y□y) therefore provides an excellent experimental platform to probe the evolution of the peculiar properties of the parent type-I clathrate Ba8Ge43□3 upon Ge/Ni substitution and filling up of the vacancies, which might be universal among the ternary systems at low substitution levels. PMID:25805335

  18. Magnetic and Thermoelectric Properties of Boron-Rich Solids

    NASA Astrophysics Data System (ADS)

    Mori, Takao

    Boron forms various compounds with metal atoms occupying voids in the boron framework. As a synthesis method it has been found that the addition of small amounts of third elements like carbon, nitrogen, and silicon can result in the formation of novel and varied rare earth boron cluster structures. A wide variation of 1D, 2D, and 3D magnetic behavior with unexpectedly strong magnetic interactions has been discovered in rare earth boron icosahedra compounds which are magnetically dilute, f-electron insulators. As an intriguing phenomenon, the B12 icosahedra cluster, which is a building block of the structure, has been indicated to function as a novel mediator of magnetic interaction. These phenomena are borides. Attractive high temperature thermoelectric properties are also emerging in borides. Attractive high temperature thermoelectric properties are also emerging in this group of compounds, which is striking due to the great potential of utilizing waste heat. Recent developments on the long awaited n-type counterpart to boron carbide, the homologous series of RE-B-C(N) compounds, REB17CN, REB22C2N, and REB28.5C4, will be presented together with those of p-type REB44Si2. General new ways to improve the thermoelectric properties are also discussed. For example, seeding with highly electrically conductive metallic borides like REB4 and REB6 is found to be a way to significantly increase the thermoelectric figure of merit. Electric resistivity significantly decreases while Seebeck coefficients and thermal conductivity are not sizably affected.

  19. Effect of low temperature baking on the RF properties of niobium superconducting cavities for particle accelerators

    SciTech Connect

    Gianluigi Ciovati

    2004-03-01

    Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some ''anomalous'' losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low temperature (100 C-150 C) ''in situ'' bake under ultra-high vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from ''anomalous'' losses (so-called ''Q-drop'') without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37 K-280 K and resonant frequency shift between 6 K-9.3 K provide information about the surface resistance, energy gap, penetration depth and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with Nuclear Reaction Analysis (NRA). The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models

  20. Oxide Thermoelectric Materials: A Structure-Property Relationship

    NASA Astrophysics Data System (ADS)

    Nag, Abanti; Shubha, V.

    2014-04-01

    Recent demand for thermoelectric materials for power harvesting from automobile and industrial waste heat requires oxide materials because of their potential advantages over intermetallic alloys in terms of chemical and thermal stability at high temperatures. Achievement of thermoelectric figure of merit equivalent to unity ( ZT ≈ 1) for transition-metal oxides necessitates a second look at the fundamental theory on the basis of the structure-property relationship giving rise to electron correlation accompanied by spin fluctuation. Promising transition-metal oxides based on wide-bandgap semiconductors, perovskite and layered oxides have been studied as potential candidate n- and p-type materials. This paper reviews the correlation between the crystal structure and thermoelectric properties of transition-metal oxides. The crystal-site-dependent electronic configuration and spin degeneracy to control the thermopower and electron-phonon interaction leading to polaron hopping to control electrical conductivity is discussed. Crystal structure tailoring leading to phonon scattering at interfaces and nanograin domains to achieve low thermal conductivity is also highlighted.

  1. Ester hydroxy derivatives of methyl oleate: tribological, oxidation and low temperature properties

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Five branched oleochemicals were prepared from commercially available methyl oleate and common organic acids and their lubricant properties were determined. These branched oleochemicals are characterized as alpha-hydroxy ester derivatives of methyl oleate. These derivatives show improved low tempe...

  2. Thermoelectric properties of Cr1-xMoxSi2

    NASA Astrophysics Data System (ADS)

    Ohishi, Yuji; Mohamad, Afiqa; Miyazaki, Yoshinobu; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke

    2015-12-01

    The thermoelectric properties of Mo-substituted CrSi2 were studied. Dense polycrystalline samples of Mo-substituted hexagonal C40 phase Cr1-xMoxSi2 (x=0-0.30) were fabricated by arc melting followed by spark plasma sintering. Mo substitution substantially increases the carrier concentration. The lattice thermal conductivity of CrSi2 at room temperature was reduced from 9.0 to 4.5 W m-1 K-1 by Mo substitution due to enhanced phonon-impurity scattering. The thermoelectric figure of merit, ZT, increases with increasing Mo content because of the reduced lattice thermal conductivity. The maximum ZT value obtained in the present study was 0.23 at 800 K, which was observed for the sample with x=0.30. This value is significantly greater than that of undoped CrSi2 (ZT=0.13).

  3. The effects of low-temperature plasma treatment on the capillary properties of inorganic fibers

    NASA Astrophysics Data System (ADS)

    Garifullin, A. R.; Abdullin, I. Sh; Skidchenko, E. A.; Krasina, I. V.; Shaekhov, M. F.

    2016-01-01

    Solving the problem of achieving high adhesion between the components in the polymeric composite material (PCM) based on carbon fibers (CF) and basalt fibers (BF) is proposed to use the radio-frequency (RF) plasma under lower pressure by virtue of efficiency, environmental friendliness and rationality of the method. The paper gives the results of studies of the properties of CF and BF after RF capacitive discharge plasma treatment. The plasma modification modes of carbon and basalt fiber were investigated. The efficiency of treatment tool in surface properties modification of carbon and basalt fibers was found, namely capillary properties of CF and BF were researched. The optimal treatment modes were selected. It was found that the method of plasma modification in the radio-frequency capacitive discharge under the lower pressure contributes enhancing the capillary properties of inorganic fibers, in particular carbon and basalt ones. It shows the tendency to increase of the adhesive properties in PCM, and, consequently, the increase of the physical and mechanical properties of the products.

  4. Structure and properties of nitrided surface layer produced on NiTi shape memory alloy by low temperature plasma nitriding

    NASA Astrophysics Data System (ADS)

    Czarnowska, Elżbieta; Borowski, Tomasz; Sowińska, Agnieszka; Lelątko, Józef; Oleksiak, Justyna; Kamiński, Janusz; Tarnowski, Michał; Wierzchoń, Tadeusz

    2015-04-01

    NiTi shape memory alloys are used for bone and cardiological implants. However, on account of the metallosis effect, i.e. the release of the alloy elements into surrounding tissues, they are subjected to various surface treatment processes in order to improve their corrosion resistance and biocompatibility without influencing the required shape memory properties. In this paper, the microstructure, topography and morphology of TiN surface layer on NiTi alloy, and corrosion resistance, both before and after nitriding in low-temperature plasma at 290 °C, are presented. Examinations with the use of the potentiodynamic and electrochemical impedance spectroscopy methods were carried out and show an increase of corrosion resistance in Ringer's solution after glow-discharge nitriding. This surface titanium nitride layer also improved the adhesion of platelets and the proliferation of osteoblasts, which was investigated in in vitro experiments with human cells. Experimental data revealed that nitriding NiTi shape memory alloy under low-temperature plasma improves its properties for bone implant applications.

  5. Structure and Thermoelectric Properties of Zinc Oxide Based Materials

    NASA Astrophysics Data System (ADS)

    Liang, Xin

    The present dissertation investigates the relationship between the structure and thermoelectric properties of ZnO based materials, with a focus on trivalent element doping on engineering the microstructure and altering the electrical and thermal transport properties. Within the solubility range, the addition of trivalent elements, such as In3+, Fe 3+ and Ga3+, is observed to increase the electrical conductivity of ZnO and decrease the thermal conductivity. As the solubility is exceeded, the consequent structure and thermoelectric properties varies with dopant species. The ZnO-In2O3 binary system, which we have chosen as one of the model systems, is of particular interests as it contains a variety of phase equilibria and microstructures. The In2O3(ZnO)k superlattice structures, which form as the indium solubility is reached, are observed to strongly scatter phonons while relatively permissive to electrons, resulting in a low thermal conductivity of about 2 W/mK and improved electrical conductivity. The thermal (Kapitza) resistance of In2O3(ZnO)k superlattice interfaces is found to be 5.0 +/- 0.6 x 10-10 m 2K/W by fitting the modified Klemens-Callaway's thermal conductivity model to the experimental data. Across the phase diagram, the materials behave as n-type free-electron semiconductors at high temperatures. An effective medium approximation model is for the first time successfully tested on the thermoelectrics of two-phase regions. Both Fe2O3-ZnO and Ga2O3-ZnO binary systems are also investigated. In the Fe doped ZnO system, a highly Fe concentrated ZnO solid solution phase as well as the significant grain refinement are observed after high temperature annealing. The Ga2O 3(ZnO)9 homologous superlattices in Ga2O 3-ZnO system is also found to strongly scatter phonons and induces a drastic reduction in thermal conductivity. Thermal conductivity, as one of the key factors in thermoelectrics, is highly sensitive to material defects. In this dissertation, I also

  6. Impact of fatty ester composition on low temperature properties of biodiesel-petroleum diesel blends

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Several biodiesel fuels along with neat fatty acid methyl esters (FAMEs) commonly encountered in biodiesel were blended with ultra-low sulfur diesel (ULSD) fuel at low blend levels permitted by ASTM D975 (B1-B5) and cold flow properties such as cloud point (CP), cold filter plugging point (CFPP), an...

  7. Mechanical properties of thin silicon films deposited at low temperatures by PECVD

    NASA Astrophysics Data System (ADS)

    Gaspar, J.; Paul, O.; Chu, V.; Conde, J. P.

    2010-03-01

    This paper presents elastic and fracture properties of hydrogenated amorphous and nanocrystalline silicon thin films and correlates them with optoelectronic and structural properties of the films. Properties are extracted from the load-deflection response of membranes and include the plane-strain modulus, residual stress and failure stress. Bilayer diaphragms made of hydrogenated amorphous and nanocrystalline silicon films obtained by plasma-enhanced chemical vapor deposition onto a reference silicon nitride layer are fabricated and characterized. A comprehensive study of the mechanical properties of these silicon thin films is presented as a function of the substrate temperature and hydrogen dilution used during deposition. The extracted plane-strain modulus, 118.5 ± 3.0 GPa, is insensitive to deposition conditions, in strong contrast to the residual stress, with values between -738 and 188 MPa. The tensile and compressive stress components in the silicon films, evaluated at membrane failure, increase from 0.11 to 0.96 GPa and from -3.40 to -2.25 GPa, respectively, with increasing residual stress.

  8. Thermoelectric properties of Bi-doped PbTe composites

    NASA Astrophysics Data System (ADS)

    Popescu, A.; Datta, A.; Nolas, G. S.; Woods, L. M.

    2011-05-01

    An experimental and theoretical study is presented for n-type Bi-doped PbTe composites with different grain sizes and doping levels. The bulk polycrystalline composites were prepared by spark plasma sintering of the nanocrystals synthesized via micro-emulsion and direct precipitation. This technique is particularly attractive due to its low cost, its reproducibility, and the control of the composition and nanocrystal size that it affords. The thermoelectric properties of the synthesized specimens were experimentally measured and theoretically modeled. Our calculations reveal that the inclusion of electron/grain and phonon/grain interface scattering is crucial for the correct description and interpretation of the measured properties.

  9. Low temperature synthesis, photoluminescence, magnetic properties of the transition metal doped wurtzite ZnS nanowires

    SciTech Connect

    Cao, Jian; Han, Donglai; Wang, Bingji; Fan, Lin; Fu, Hao; Wei, Maobin; Feng, Bo; Liu, Xiaoyan; Yang, Jinghai

    2013-04-15

    In this paper, we synthesized the transition metal ions (Mn, Cu, Fe) doped and co-doped ZnS nanowires (NWs) by a one-step hydrothermal method. The results showed that the solid solubility of the Fe{sup 2+} ions in the ZnS NWs was about two times larger than that of the Mn{sup 2+} or Cu{sup 2+} ions in the ZnS NWs. There was no phase transformation from hexagonal to cubic even in a large quantity transition metal ions introduced for all the samples. The Mn{sup 2+}/Cu{sup 2+}/Fe{sup 2+} related emission peaks can be observed in the Mn{sup 2+},Cu{sup 2+} and Fe{sup 2+} doped ZnS NWs. The ferromagnetic properties of the co-doped samples were investigated at room temperature. - graphical abstract: The stable wurtzite ZnS:TM{sup 2+} (TM=Mn, Cu, Fe) nanowires with room temperature ferromagnetism properties were obtained. The different elongation of unit cell caused by the different doped ions was observed. Highlights: ► The transition metal ions doped wurtzite ZnS nanowires were synthesized at 180 °C. ► There was no phase transformation from hexagonal to cubic even in a large quantity introduced for all the samples. ► The room temperature ferromagnetism properties of the co-doped nanowires were investigated.

  10. Characterization of low-temperature properties of plant-produced rap mixtures in the Northeast

    NASA Astrophysics Data System (ADS)

    Medeiros, Marcelo S., Junior

    The dissertation outlined herein results from a Federal Highway Administration sponsored project intended to investigate the impacts of high percentages of RAP material in the performance of pavements under cold climate conditions. It is comprised of two main sections that were incorporated into the body of this dissertation as Part I and Part II. In Part I a reduced testing framework for analysis of HMA mixes was proposed to replace the IDT creep compliance and strength testing by dynamic modulus and fatigue tests performed on an AMPT device. A continuum damage model that incorporates the nonlinear constitutive behavior of the HMA mixtures was also successfully implemented and validated. Mixtures with varying percentages of reclaimed material (RAP) ranging from 0 to 40% were used in this research effort in order to verify the applicability of the proposed methodology to RAP mixtures. Part II is concerned with evaluating the effects of various binder grades on the properties of plant-produced mixtures with various percentages of RAP. The effects of RAP on mechanical and rheological properties of mixtures and extracted binders were studied in order to identify some of the deficiencies in the current production methodologies. The results of this dissertation will help practitioners to identify optimal RAP usage from a material property perspective. It also establishes some guidelines and best practices for the use of higher RAP percentages in HMA.

  11. Mechanical property tests on structural materials for ITER magnet system at low temperatures in China

    NASA Astrophysics Data System (ADS)

    Huang, Chuanjun; Huang, Rongjin; Li, Laifeng

    2014-01-01

    High field superconducting magnets need strong non-superconducting components for structural reinforcement. For instance, the ITER magnet system (MS) consists of cable-in-conduit conductor, coil case, magnet support, and insulating materials. Investigation of mechanical properties at magnet operation temperature with specimens machined at the final manufacturing stages of the conductor jacket materials, magnet support material, and insulating materials, even the component of the full-size conductor jacket is necessary to establish sound databases for the products. In China, almost all mechanical property tests of structural materials for the ITER MS, including conductor jacket materials of TF coils, PF coils, CCs, case material of CCs, conductor jacket materials of Main Busbars (MB) and Corrector Busbars (CB), material of magnet supports, and insulating materials of CCs have been carried out at the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS). In this paper, the mechanical property test facilities are briefly demonstrated and the mechanical tests on the structural materials for the ITER MS, highlighting test rigs as well as test methods, are presented.

  12. DIELECTRIC PROPERTIES OF POLYVINYL ALCOHOL, POLY(METHYL METHACRYLATE), POLYVINYL BUTYRAL RESIN AND POLYIMIDE AT LOW TEMPERATURES

    SciTech Connect

    Tuncer, Enis; Sauers, Isidor; James, David Randy; Ellis, Alvin R

    2008-01-01

    Performance of materials and their compatibility determine the size of the electrical insulation in power equipment. For this reason dielectric properties of electrical insulation materials are needed for low temperature power applications. In this work we report the dielectric properties of four polymers: polyvinyl alcohol (PVA), poly(methyl methacrylate) (PMMA), polyvinyl butyral resin (PVB), and polyimide (PI--Kapton\\textregistered). The dielectric measurements are performed with an electrical impedance analyzer in the frequency domain. The impedances are recorded in a cryocooler in the temperature range from 45K to 350K. The dielectric breakdown characteristics of the polymers are measured in a liquid nitrogen bath at atmospheric pressure. It is observed that PI and \\pmma\\ dissolved in toluene have the lowest dielectric losses for temperatures lower than $100\\ \\kelvin$. \\Blx\\ and PI have the smallest spread in their breakdown strength data.

  13. Effect of Electropolishing and Low-Temperature Baking on the Superconducting Properties of Large-Grain Niobium

    SciTech Connect

    A. S. Dhavale, G. Ciovati, G. R. Myneni

    2011-03-01

    Measurements of superconducting properties such as bulk and surface critical fields and thermal conductivity have been carried out in the temperature range from 2 K to 8 K on large-grain samples of different purity and on a high-purity fine-grain sample, for comparison. The samples were treated by electropolishing and low temperature baking (120° C, 48 h). While the residual resistivity ratio changed by a factor of ~3 among the samples, no significant variation was found in their superconducting properties. The onset field for flux penetration at 2 K, Hffp, measured within a ~30 µm depth from the surface, was ~160 mT, close to the bulk value. The baking effect was mainly to increase the field range up to which a coherent superconducting phase persists on the surface, above the upper critical field.

  14. Dynamical thermoelectric properties of doped AA-stacked bilayer graphene

    NASA Astrophysics Data System (ADS)

    Rezania, Hamed; Yarmohammadi, Mohsen

    2016-01-01

    The frequency dependence of thermoelectric properties of doped biased bilayer graphene are investigated using the Green's function approach in the context of tight-binding model. We find that the thermoelectric figure of merit (ZT) can be remarkably enhanced by electronic chemical potential, temperature, bias voltage and frequency. The electronic contribution to thermal conductivity of doped materials is dominant and therefore we have considered this contribution. The improvement due to the combined increase in the Seebeck coefficient and the reduction in the thermal conductivity outweighing the decrease in the electrical conductance is studied. We have found a good ZT value for normal conditions in the lab, i.e, for room temperature (RT), high bias voltages and low frequencies. We have found the temperature dependence of ZT for different values of frequency, bias voltage and chemical potential. Also the dependence of ZT on the chemical potential and bias voltage has been investigated in details. The calculated ZT values qualify bilayer graphene as a very promising material for thermoelectric applications.

  15. Elastic Properties of Films of Water and Noble Gases Condensed at Low Temperatures

    NASA Technical Reports Server (NTRS)

    Pohl, Robert O.

    2003-01-01

    We have shown that there are extensive similarities between the quench-condensed noble gas films and those of amorphous water ice. In particular, both can be quite soft upon deposition and can stiffen considerably when annealed. Furthermore, this stiffening follows a logarithmic time dependence for all substances. The temperature dependence of these behaviors scales with the triple point. The results shown here show a strong thickness dependence, which has implications for any study of mechanical properties of films on substrates. The temperature dependence of the stiffening and the stiffening rate have now been characterized for the noble gases, and these observations provide a roadmap for new experiments on amorphous water ice.

  16. Microstructural and Mössbauer properties of low temperature synthesized Ni-Cd-Al ferrite nanoparticles

    PubMed Central

    2011-01-01

    We report the influence of Al3+ doping on the microstructural and Mössbauer properties of ferrite nanoparticles of basic composition Ni0.2Cd0.3Fe2.5 - xAlxO4 (0.0 ≤ x ≤ 0.5) prepared through simple sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray, transmission electron microscopy (TEM), Fourier transformation infrared (FTIR), and Mössbauer spectroscopy techniques were used to investigate the structural, chemical, and Mössbauer properties of the grown nanoparticles. XRD results confirm that all the samples are single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. SEM micrographs show the synthesized nanoparticles are agglomerated but spherical in shape. The average crystallite size of the grown nanoparticles was calculated through Scherrer formula and confirmed by TEM and was found between 2 and 8 nm (± 1). FTIR results show the presence of two vibrational bands corresponding to tetrahedral and octahedral sites. Mössbauer spectroscopy shows that all the samples exhibit superparamagnetism, and the quadrupole interaction increases with the substitution of Al3+ ions. PMID:21851597

  17. Molecular dynamics simulation of thermodynamic and transport properties of H-bonded low-temperature substances

    NASA Astrophysics Data System (ADS)

    Tychengulova, A.; Aldiyarov, A.; Drobyshev, A.

    2015-06-01

    The results of modeling of isotopic water mixture clusters in nitrogen and argon cryomatrices are presented. Earlier, our experimental studies of water mixture in cryomatrix have shown that changes in the concentration of analyte in matrix leads to a splitting of the absorption bands characteristic frequencies of the molecules in the IR spectrum. Moreover the multiplicity of characteristic absorption bands in the IR spectrum remained unchanged during heating of the samples from the condensation temperature to the sublimation temperature of the matrix element. In order to find out what structure of clusters is responsible for the immutability of the absorption bands in the vibrational spectrum during thermal cycling of the samples, computer research of water molecules enclosed in nitrogen and argon cryomatrices by the molecular dynamics simulation was conducted. For this purpose, theoretical studies were carried out using computer software packages, that implement used by us semi empirical and ab initio molecular dynamics methods. As a result of the research, the data must be obtained are of theoretical interest for summarizing the physical and chemical properties of systems, consisting of water molecules, and their combination with inert gases for studying the properties of molecular crystals composed of small molecules.

  18. Low temperature mechanical properties, fractographic and metallographic evaluation of several alloy steels

    NASA Technical Reports Server (NTRS)

    Montano, J. W.

    1973-01-01

    The mechanical properties are presented of alloy steels, 4130, 4140, 4340, 6150, and 8740. Test specimens were manufactured from approximately 1.00 inch (2.54 cm) diameter bar stock which had been heat treated to two different hardness levels. The following mechanical tests were performed at temperatures of 80 F (+26.7 C), 0 F (-17.8 C), -100 F (-73 C), and -200 F (-129 C): (1) tensile test (Ultimate, yield, modulus, elongation, and reduction of area), (2) notched tensile test, (3) charpy V-notched impact test (impact energy), and (4) double shear strength test (ultimate and yield). The test data indicate excellent tensile strength, notched/unnotched tensile ratios, ductility, impact, and shear properties at all test temperatures, except at -200 F (-129 C) where the impact strength of the higher strength group of alloy steels, 4130 (Rc-37) and 4140 (Rc-44) decreased to approximately 9 ft. lbs. (12 joules) and 6 ft. lbs. (8 joules), respectively. Chemical, metallographic, and fractographic analyses were also performed to evaluate microstructure, microhardness and the effect of decrease in temperature on the ductile to brittle failure transition.

  19. Electro-Mechanical Properties of Metal-Insulator-Metal Device Fabricated on Polymer Substrate Using Low-Temperature Process

    NASA Astrophysics Data System (ADS)

    Park, Sung Kyu; Han, Jeong In; Kim, Won Keun; Hong, Sung Jei; Kwak, Min Gi; Lee, Myung Jae; Chung, Kwan Soo

    2002-02-01

    High-performance metal-insulator-metal (MIM) devices on flexible polymer substrates were successfully fabricated without any defects such as cracks, delamination and blistering. This work examines the mechanical and electrical properties of MIM devices constructed using anodic Ta2O5 films. Using newly developed methods including stepped heating process and low-temperature post-annealing below 180°C, we obtained high-performances MIM devices on polymer substrates. Here, we propose the use of stacked bottom electrode and water barrier layer in order to enhance the ductility of the Ta electrode and to prevent blistering problems, respectively. Rutherford backscattering spectroscopy (RBS), auger electron spectroscopy (AES) and transmission electronic microscope (TEM) observations were performed for the structural investigation of the MIM devices on polymer substrates. Electrical measurements were also carried out for as-deposited and thermally treated MIM devices including Al/Ta/Ta2O5/Cr or Ti structures. They exhibit a low leakage current (below 10-7 A/cm2 at 2 MV) and reasonable breakdown voltage (5-7 MV/cm) with a uniformity of 92%. Finally, under low-temperature post-annealing conditions, The Current-Voltage (I-V) behaviors and conduction mechanisms of MIM devices on polymer substrates are discussed based on the results of electrical measurements, structural investigations and conduction band modeling.

  20. Effects of Low Temperature Anneal on the Interface Properties of Thermal Silicon Oxide for Silicon Surface Passivation.

    PubMed

    Balaji, Nagarajan; Park, Cheolmin; Chung, Sungyoun; Ju, Minkyu; Raja, Jayapal; Yi, Junsin

    2016-05-01

    High quality surface passivation has gained a significant importance in photovoltaic industry for reducing the surface recombination and hence fabricating low cost and high efficiency solar cells using thinner wafers. The formation of good-quality SiO2 films and SiO2/Si interfaces at low processing temperatures is a prerequisite for improving the conversion efficiency of industrial solar cells with better passivation. High-temperature annealing in inert ambient is promising to improve the SiO2/Si interface. However, annealing treatments could cause negative effects on SiO2/Si interfaces due to its chemical at high temperatures. Low temperature post oxidation annealing has been carried out to investigate the structural and interface properties of Si-SiO2 system. Quasi Steady State Photo Conductance measurements shows a promising effective carrier lifetime of 420 μs, surface recombination velocity of 22 cm/s and a low interface trap density (D(it)) of 4 x 10(11) states/cm2/eV after annealing. The fixed oxide charge density was reduced to 1 x 10(11)/cm2 due to the annealing at 500 degrees C. The FWHM and the Si-O peak wavenumber corresponding to the samples annealed at 500 degrees C reveals that the Si dangling bonds in the SiO2 films due to the oxygen defects was reduced by the low temperature post oxidation annealing. PMID:27483822

  1. The influence of low temperatures on dynamic mechanical properties of animal bone

    NASA Astrophysics Data System (ADS)

    Mardas, Marcin; Kubisz, Leszek; Mielcarek, Slawomir; Biskupski, Piotr

    2009-01-01

    Different preservation methods are currently used in bone banks, even though their effects on allograft quality are not fully understood. Freezing is one of the most popular methods of preservation in tissue banking. Yet, there is not a lot of data on dynamic mechanical properties of frozen bone. Material used in this study was femoral bones from adult bovine that were machine cut and frozen to the temperature 140°C. Both elastic modulus and loss modulus were measured at 1, 3, 5, 10, and 20 Hz in the temperature range of 30-200°C. Differences between frozen and control samples were observed. The frequency increase always led to the increase in elastic modulus values and decrease in loss modulus values. Freezing reduced the elastic modulus values of about 25% and the loss modulus values of about 45% when measured at 20°C.

  2. Low temperature electrical transport properties in p-SnSe single crystals

    NASA Astrophysics Data System (ADS)

    Sumesh, C. K.; Patel, M.; Patel, K. D.; Solanki, G. K.; Pathak, V. M.; Srivastav, R.

    2011-01-01

    The electronic transport properties of p-type tin selenide (SnSe) grown by direct vapor transport (DVT) technique were investigated via Hall effect in the temperature range 40 < T < 300 K. The temperature dependence of conductivity revealed the existence of impurity energy level in the band gap of the crystal. The temperature dependence of the carrier concentration was analyzed using the single-donor - single-acceptor model. The Hall mobility increases by decreasing temperature up to 120 K and then decreases along with temperature. The observed temperature dependant mobility in the temperature range 120 < T < 300 K and 40 < T < 120 K was found to be limited by homopolar and ionized impurity mode scatterings respectively.

  3. Low-Temperature Thermodynamic Properties of Superconducting Antiperovskite CdCNi_3

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, R.; Durajski, A. P.; Skoczylas, K. M.; Herok, Ł.

    2016-06-01

    We investigate the thermodynamic parameters of the superconducting antiperovskite CdCNi_3 using the Eliashberg approach which is an excellent tool to the exact characterization of the conventional superconductors. In particular, we reproduce the measured superconducting transition temperature (T_C=3.2 K) for a high value of the Coulomb pseudopotential (μ ^{star }C=0.22). Then we determine the energy gap, the thermodynamic critical field and the specific heat for the superconducting and normal state. On this basis, we show that the thermodynamic properties of CdCNi_3 differ slightly from the prediction of the Bardeen-Cooper-Schrieffer theory, which means that CdCNi_3 is a medium-coupling superconductor in contrast to related strong-coupling MgCNi_3.

  4. Measurement of low temperature thermal properties of microcalorimeters using Johnson noise thermometry

    NASA Astrophysics Data System (ADS)

    Bazzi, Khadije

    Lithium-ion batteries are the power source of choice for portable electronics, power tools and electric-based transportation. This outstanding commercial success has spawned great international interest in applying this technology to systems that demand higher power, such as the electric component of hybrid, extended range, and electric vehicles. This would require new electrode materials that are less expensive, more energetic, and more environmentally friendly than the present ones. Of particular interest is the olivine-structured LiFePO 4 cathode developed by Goodenough and co-workers, which offers several appealing features, such as a high, flat voltage profile and relatively high theoretical specific capacity (170 mAhg-1), combined with low cost and low toxicity. However, the intrinsically poor electronic and ionic conductivities of LiFePO4 limit the delivery of high specific capacity at high discharge rates. Several strategies have been devised to overcome the inherent limitations of LiFePO4. Carbon coating is one of the remedies to improve the performance of LiFePO 4. We studied the effect of carbon coating on the performance of LiFePO 4. First, we synthesized carbon-coated LiFePO4 samples with different amount of surfactant, lauric acid that acts as carbon source. We were able to show that an optimized amount of carbon results in greatly improved room-temperature electrochemical performance. On the other hand, because the electrochemical properties are strongly dependent on the quality of deposited carbon, we did also study the effect of carbon sources: lauric acid, myristic acid and oleic acid. We successfully showed that the proper carbon sources and carbon content played a key role on improving the initial charge-discharge capacity of the LiFePO4/C cathode. In addition, we did also shed the light of the positive impact of excess of Li on the electrochemical performance of C-LiFePO4. Knowing that Fe-site doping is considered to be an effective way to

  5. Shear/compressive properties of candidate ITER insulation systems at low temperatures

    NASA Astrophysics Data System (ADS)

    Fabian, P. E.; Reed, R. P.; Schutz, J. B.; Bauer-McDaniel, T. S.

    Shear/compression tests were performed at 76 and 4 K on candidate composite insulation systems for the International Thermonuclear Experimental Reactor (ITER) toroidal field coils. The insulation systems tested consisted of vacuum-pressure impregnated, pre-impregnated, and high-pressure laminate systems that included electrical barriers such as polyimide film or mica/glass. Sandwich-style specimens, in which the composite insulation is bonded to two AISI 316 stainless steel chips, were used. Two specimens were loaded at an angle, which resulted in combined shear and compressive stresses, and tested simultaneously. Various shear/compression ratios were achieved by using different test fixtures, each at a different angle (15 °, 45 °, 75 ° and 84 °) from the vertical direction. The shear strengths of specimens loaded at 15 ° to 75 ° increased with increasing compressive stress; these specimens experienced shear failures. For specimens loaded at 84 °, the compressive stress increased and the shear strength decreased; the failure modes of these specimens were more compressive than shear. The effects of electrical barriers on shear/compressive properties are also reported.

  6. Low Temperature Mechanical Properties of Cyanate Ester Insulation Systems After Irradiation

    NASA Astrophysics Data System (ADS)

    Fabian, P. E.; Munshi, N. A.; Feucht, S. W.; Bittner-Rohrhofer, K.; Humer, K.; Weber, H. W.

    2004-06-01

    Recent development of alternative resin chemistries has resulted in new, fiber-reinforced, insulation systems for use in superconducting and fusion magnet applications. When compared to traditional epoxy resins, these insulation systems, based on cyanate ester resin chemistry, offer increased radiation resistance and higher operating temperatures that are demanded by new fusion reactor designs, such as the Fusion Ignition Research Experiment (FIRE). The design parameters for FIRE Toroidal Field (TF) coils call for an insulation system capable of withstanding a combined gamma and neutron radiation dose greater than 108 Gy (1010 Rad) and operate at temperatures ranging from cryogenic (77 K) to elevated temperatures up to 373 K. Several of these newly developed composite insulation systems, suitable for the vacuum impregnation, pre-preg, and high-pressure laminate fabrication processes, were irradiated in the TRIGA reactor (Vienna) to varying levels of radiation to gauge their radiation resistance. The insulation materials' shear and compression properties measured at cryogenic temperatures before and after irradiation are presented.

  7. Surface and bulk electronic properties of low temperature synthesized InN microcrystals

    NASA Astrophysics Data System (ADS)

    Barick, B. K.; Dhar, S.

    2015-04-01

    Structural and electronic properties of InN microcrystals, which are synthesized by nitridation of LiInO2 with NaNH2 in a Teflon-lined autoclave at temperatures ranging between 170 and 240 °C, are studied as a function of the growth temperature using x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), photo-absorption, Raman spectroscopy and x-ray photo-emission spectroscopy (XPS) techniques. Our study shows the formation of wurtzite InN crystals with an average size of 100 nm even at 170 °C. The study, furthermore, suggests an enhancement of electron concentration and a reduction of electron mobility in the crystal as the synthesis temperature (TS) decreases. The density of certain defects lying very close to the band edge is also found to increase with the reduction of TS. These defects are expected to act as donors, which can explain the enhancement of carrier concentration as the growth temperature decreases.

  8. Scintillation properties of the silver doped lithium iodide single crystals at room and low temperature

    NASA Astrophysics Data System (ADS)

    Khan, Sajid; Kim, H. J.; Lee, M. H.

    2016-06-01

    This study presents luminescence and scintillation properties of Silver doped LiI crystals. Single crystals of LiI: x% Ag (x=0.02, 0.05, 0.1 and 0.5) were grown by using the Bridgman technique. X-ray induced luminescence spectra show emission bands spanning from 275 nm to 675 nm, dominated by Ag+ band having a peak at 300 nm. Under UV-luminescence, a similar emission band was observed with the peak excitation wavelength of 265 nm. Energy resolution, light yield and decay time profiles of the samples were measured under a 137Cs γ-ray irradiation. The LiI(0.1%Ag) showed the highest light yield and the best energy resolution among the samples. The light yield of LiI(0.1%Ag) is higher than commercially available LiI(Eu) crystal (15,000±1500 ph/MeV). The LiI(Ag) samples exhibit three exponential decay time components except the LiI(0.02%Ag), where the fitting found two decay time components. Temperature dependences of emission spectra, light yield and decay time were studied from 300 K to 10 K. The LiI(0.1%Ag) crystal showed an increase in the light yield and a shortening of decay time with a decrease in temperature..

  9. Low temperature dielectric properties of YMn0.95Ru0.05O3

    NASA Astrophysics Data System (ADS)

    Thakur, Rajesh K.; Thakur, Rasna; Okram, G. S.; Kaurav, N.; Gaur, N. K.

    2013-02-01

    The single phase hexagonal YMn0.95Ru0.05O3 compound has been synthesized via solid state reaction method at sintering temperature 1280°C with space group P63cm (25-1079). The detailed dielectric properties were evaluated over broad temperature and frequency ranges. An obvious dielectric relaxation was observed near the antiferromagnetic (AFM) transition temperature. The temperature dependence of the ac resistivity at low frequency infers the semiconducting behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the temperature scale T* ˜ 0.8 × 104 K and finally the density of state at Fermi level N(EF). The activation energy Ea ˜ 0.0314 eV is calculated from the plot, peak temperature of the loss tangent near the magnetic transition region versus frequency using Arrhenius law.

  10. Magnetic properties of low temperature phase MnBi of island structure

    NASA Astrophysics Data System (ADS)

    Suwa, Takahiro; Tanaka, Yoshitomo; Mankey, Gary; Schad, Rainer; Suzuki, Takao

    2016-05-01

    The magnetic and structural properties of island-structured LTP MnBi fabricated onto MgO single crystal substrates are discussed. The size and height of the "Volmer-Weber" type islands vary from place to place but are averagely a few microns and sub-microns, respectively. From the wetting angle (40 ˜ 60°) of those islands, the surface energy ΥMnBi of LTP MnBi is found to be 0.5˜0.8 J/m2. Those MnBi islands possesses the magnetic anisotropy constant Ku and saturation magnetization Ms close to those for bulk over a temperature range of 5 to 400 K. There seems to be a correlation between Ku and lattice constant c measured at 300K. The Ku is found to be inversely proportional to Ms5 over the temperature range from 5 K to 400 K, as compared to the Ms8 dependence for those fabricated onto fused silica glass substrates.

  11. Polycrystalline methane hydrate: Synthesis from superheated ice, and low-temperature mechanical properties

    USGS Publications Warehouse

    Stern, L.A.; Kirby, S.H.; Durham, W.B.

    1998-01-01

    We describe a new and efficient technique to grow aggregates of pure methane hydrate in quantities suitable for physical and material properties testing. Test specimens were grown under static conditions by combining cold, pressurized CH4 gas with granulated H2O ice, and then warming the reactants to promote the reaction CH4(g) + 6H2O(s???1) ??? CH4??6H2O (methane hydrate). Hydrate formation evidently occurs at the nascent ice/liquid water interface on ice grain surfaces, and complete reaction was achieved by warming the system above the ice melting point and up to 290 K, at 25-30 MPa, for approximately 8 h. The resulting material is pure, cohesive, polycrystalline methane hydrate with controlled grain size and random orientation. Synthesis conditions placed the H2O ice well above its melting temperature while reaction progressed, yet samples and run records showed no evidence for bulk melting of the unreacted portions of ice grains. Control experiments using Ne, a non-hydrate-forming gas, showed that under otherwise identical conditions, the pressure reduction and latent heat associated with ice melting are easily detectable in our fabrication apparatus. These results suggest that under hydrate-forming conditions, H2O ice can persist metastably to temperatures well above its ordinary melting point while reacting to form hydrate. Direct observations of the hydrate growth process in a small, high-pressure optical cell verified these conclusions and revealed additional details of the hydrate growth process. Methane hydrate samples were then tested in constant-strain-rate deformation experiments at T = 140-200 K, Pc = 50-100 MPa, and ?? = 10-4 10-6 s-1. Measurements in both the brittle and ductile fields showed that methane hydrate has measurably different strength than H2O ice, and work hardens to an unusually high degree compared to other ices as well as to most metals and ceramics at high homologous temperatures. This work hardening may be related to a changing

  12. Low-temperature specific heat and magnetic properties of the filled skutterudite ferromagnet NdRu4As12

    NASA Astrophysics Data System (ADS)

    Rudenko, A.; Henkie, Z.; Cichorek, T.

    2016-09-01

    We present the low-temperature specific heat and magnetic properties of the filled skutterudite compound NdRu4As12 that exhibits a ferromagnetic transition at TC ≃ 2.3 K . Magnetic entropy considerations point at a quartet ground state of the Nd3+ ions. Deep in the ferromagnetic state, the heat capacity shows a Schottky anomaly that we ascribe to the Zeeman splitting in the presence of a molecular field. Comparison of the specific heats of NdRu4As12 and its Os-based homologue near their Curie temperatures supports our earlier observation suggesting an unusual lowering of the Th cubic point symmetry in the latter filled skutterudite.

  13. Interpretation of thermoelectric properties of Cu substituted LaCoO{sub 3} ceramics

    SciTech Connect

    Choudhary, K. K.; Kaurav, N.; Sharma, U.; Ghosh, S. K.

    2014-04-24

    The thermoelectric properties of LaCo{sub 1−x}Cu{sub x}O{sub 3−δ} is theoretically analyzed, it is observed that thermoelectric figure of merit ZT (=S{sup 2}σT/κ) is maximized by Cu substitution in LaCoO{sub 3} Ceramics at x=0.15. The lattice thermal conductivity and thermoelectric power were estimated by the scattering of phonons with defects, grain boundaries, electrons and phonons to evaluate the thermoelectric properties. We found that Cu substitution increase the phonon scattering with grain boundaries and defects which significantly increase the thermoelectric power and decrease the thermal conductivity. The present numerical analysis will help in designing more efficient thermoelectric materials.

  14. [Study on the Properties of the Pc-Si Films Prepared by Magnetron Co-Sputtering at Low Temperature].

    PubMed

    Duan, Liang-fei; Yang, Wen; Zhang, Li-yuan; Li, Xue-ming; Chen, Xiao-bo; Yang, Pei-zhi

    2016-03-01

    The polycrystalline silicon thin films play an important role in the field of electronics. In the paper, α-SiAl composite membranes on glass substrates was prepared by magnetron co-sputtering. The contents of Al radicals encapsulated-in the α-Si film can be adjusted by changing the Al to Si sputtering power ratios. The as-prepared α-Si films were converted into polycrystalline films by using a rapid thermal annealing (RTP) at low temperature of 350 degrees C for 10 minutes in N2 atmosphere. An X-ray diffractometer, and Raman scattering and UV-Visible-NIR Spectrometers were used to characterize the properties of the Pc-Si films. The influences of Al content on the properties of the Pc-Si films were studied. The results showed that the polycrystalline silicon films were obtained from α-SiAl composite films which were prepared by magnetron co-sputtering at a low temperature following by a rapid thermal annealing. The grain size and the degree of crystallization of the Pc-Si films increased with the increase of Al content, while the optical band gap was reduced. The nc-Si films were prepared when the Al to Si sputtering power ratio was 0.1. And a higher Crystallization rate (≥ 85%) of polycrystalline silicon films were obtained when the ratio was 0.3. The band gaps of the polycrystalline silicon films can be controlled by changing the aluminum content in the films. PMID:27400496

  15. Computational modeling and analysis of thermoelectric properties of nanoporous silicon

    SciTech Connect

    Li, H.; Yu, Y.; Li, G.

    2014-03-28

    In this paper, thermoelectric properties of nanoporous silicon are modeled and studied by using a computational approach. The computational approach combines a quantum non-equilibrium Green's function (NEGF) coupled with the Poisson equation for electrical transport analysis, a phonon Boltzmann transport equation (BTE) for phonon thermal transport analysis and the Wiedemann-Franz law for calculating the electronic thermal conductivity. By solving the NEGF/Poisson equations self-consistently using a finite difference method, the electrical conductivity σ and Seebeck coefficient S of the material are numerically computed. The BTE is solved by using a finite volume method to obtain the phonon thermal conductivity k{sub p} and the Wiedemann-Franz law is used to obtain the electronic thermal conductivity k{sub e}. The figure of merit of nanoporous silicon is calculated by ZT=S{sup 2}σT/(k{sub p}+k{sub e}). The effects of doping density, porosity, temperature, and nanopore size on thermoelectric properties of nanoporous silicon are investigated. It is confirmed that nanoporous silicon has significantly higher thermoelectric energy conversion efficiency than its nonporous counterpart. Specifically, this study shows that, with a n-type doping density of 10{sup 20} cm{sup –3}, a porosity of 36% and nanopore size of 3 nm × 3 nm, the figure of merit ZT can reach 0.32 at 600 K. The results also show that the degradation of electrical conductivity of nanoporous Si due to the inclusion of nanopores is compensated by the large reduction in the phonon thermal conductivity and increase of absolute value of the Seebeck coefficient, resulting in a significantly improved ZT.

  16. Thermoelectric properties of p-type PbTe/Ag{sub 2}Te bulk composites by extrinsic phase mixing

    SciTech Connect

    Lee, Min Ho; Rhyee, Jong-Soo

    2015-12-15

    We investigated the thermoelectric properties of PbTe/Ag{sub 2}Te bulk composites, synthesized by hand milling, mixing, and hot press sintering. From x-ray diffraction and energy dispersive x-ray spectroscopy measurements, we observed Ag{sub 2}Te phase separation in the PbTe matrix without Ag atom diffusion. In comparison with previously reported pseudo-binary (PbTe){sub 1−x}(Ag{sub 2}Te){sub x} composites, synthesized by high temperature phase separation, the PbTe/Ag{sub 2}Te bulk composites fabricated with a low temperature phase mixing process give rise to p-type conduction of carriers with significantly decreased electrical conductivity. This indicates that Ag atom diffusion in the PbTe matrix changes the sign of the Seebeck coefficient to n-type and also increases the carrier concentration. Effective p-type doping with low temperature phase separation by mixing and hot press sintering can enhance the thermoelectric performance of PbTe/Ag{sub 2}Te bulk composites, which can be used as a p-type counterpart of n-type (PbTe){sub 1−x}(Ag{sub 2}Te){sub x} bulk composites.

  17. Low temperature thermoelastic properties of galena in a simple, self-consistent, two-term Debye model

    NASA Astrophysics Data System (ADS)

    Knight, Kevin S.

    2015-03-01

    The thermoelastic properties of the thermoelectric chalcogenide galena, lead sulfide (PbS), have been determined in the temperature interval 10-350 K from high resolution neutron powder diffraction data, and literature values of the isobaric heat capacity. Within this temperature range, galena can be described by a simple phenomenological model in which the cation and anion vibrate independently of one another in a Debye-like manner, with vibrational Debye temperatures of 120(1) K for the lead, and 324(2) K for the sulfur. Simultaneous fitting of the unit cell volume and the isochoric heat capacity to a two-term Debye internal energy function gives characteristic temperatures of 110(2), and 326(5) K in excellent agreement with the measured vibrational Debye temperatures derived from fitting the atomic displacement parameters. The thermodynamic Grüneisen constant derived from the isochoric heat capacity is found to monotonically increase with decreasing temperature, from 2.5 at 300 K, to 3.25 at 25 K, in agreement with the deductions of earlier work. The full phonon density of states calculated from the two-term Debye model shows fair agreement with that derived from density functional theory.

  18. 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.

  19. Thermoelectric properties of IV–VI-based heterostructures and superlattices

    SciTech Connect

    Borges, P.D.; Petersen, J.E.; Scolfaro, L.; Leite Alves, H.W.; Myers, T.H.

    2015-07-15

    Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature in the directions perpendicular to the doping planes, yet no improvement on the values of ZT is found when compared to bulk PbTe. For the PbTe/SnTe/PbTe heterostructures, the calculated S presents good agreement with recent experimental data, and an anisotropic behavior is observed for low carrier concentrations (n<10{sup 18} cm{sup −3}). A large value of ZT{sub ||} (parallel to the growth direction) of 3.0 is predicted for n=4.7×10{sup 18} cm{sup −3} and T=700 K, whereas ZT{sub p} (perpendicular to the growth direction) is found to peak at 1.5 for n=1.7×10{sup 17} cm{sup −3}. Both electrical conductivity enhancement and thermal conductivity reduction are analyzed. - Graphical abstract: Figure of merit for PbTe/SnTe/PbTe heterostructure along the [0 0 1] direction, P.D. Borges, J.E. Petersen, L. Scolfaro, H.W. Leite Alves, T.H. Myers, Improved thermoelectric properties of IV–VI-based heterostructures and superlattices. - Highlights: • Thermoelectric properties of IV

  20. The Study of the Thermoelectric Properties of Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Yin, Ming; Abdi, Mohammed; Noimande, Zibusisu; Mbamalu, Godwin; Alameeri, Dheyaa; Datta, Timir

    We study thermoelectric property that is electrical phenomena occurring in conjunction with the flow of heat of phase-change materials (PCM) in particular GeSbTe (GST225). From given sets of material parameters, COMSOL Multiphysics heat-transfer module is used to compute maps of temperature and voltage distribution in the PCM samples. These results are used to design an apparatus including the variable temperature sample holder set up. An Arbitrary/ Function generator and a circuit setup is also designed to control the alternation of heaters embedded on the sample holder in order to ensure sequential back and forward flow of heat current from both sides of the sample. Accurate values of potential differences and temperature distribution profiles are obtained in order to compute the Seebeck coefficient of the sample. The results of elemental analysis and imaging studies such as XRD, UV-VIS, EDEX and SEM of the sample are obtained. Factors affecting the thermoelectric properties of phase change memory are also discussed. NNSA/ DOD Consortium for Materials and Energy Studies.

  1. Improvement of thermoelectric properties of alkaline-earth hexaborides

    SciTech Connect

    Takeda, Masatoshi . E-mail: takeda@mech.nagaokaut.ac.jp; Terui, Manabu; Takahashi, Norihito; Ueda, Noriyoshi

    2006-09-15

    Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of the Seebeck coefficient decreased monotonically, while carrier mobility was almost unchanged. These results suggest that the electrical properties of the hexaboride depend largely on carrier concentration. Thermal conductivity of the hexaboride was higher than 10 W/m K even at 1073 K, which is relatively high among TE materials. Alloys of CaB{sub 6} and SrB{sub 6} were prepared in order to reduce lattice thermal conductivity. Whereas the Seebeck coefficient and electrical conductivity of the alloys were intermediate between those of CaB{sub 6} and SrB{sub 6} single phases, the thermal conductivities of the alloys were lower than those of both single phases. The highest TE performance was obtained in the vicinity of Ca{sub 0.5}Sr{sub 0.5}B{sub 6}, indicating that alloying is effective in improving the performance. - Graphical abstract: Thermoelectric figure-of-merit, ZT, for (Ca,Sr)B{sub 6} alloys. The highest ZT value of 0.35 at 1073 K was obtained due to effective reduction of thermal conductivity by alloying.

  2. Effect of Ag doping and annealing on thermoelectric properties of PbTe

    SciTech Connect

    Bala, Manju Tripathi, T. S.; Avasthi, D. K.; Asokan, K.; Gupta, Srashti

    2015-06-24

    The present study reveals that annealing Ag doped PbTe thin films enhance thermoelectric properties. Phase formation was identified by using X-ray diffraction measurement. Annealing increases the crystallinity of both undoped and Ag doped PbTe. Electrical resistivity and thermoelectric power measurements are done using four probe and bridge method respectively. The increase in thermoelectric power of Ag doped PbTe is 29 % in comparison to undoped PbTe and it further increases to 34 % after annealing at 250{sup o} C for 1 hour whereas thermoelectric power increases by 14 % on annealing undoped PbTe thin films at same temperature.

  3. New measuring techniques for the investigation of thermoelectric properties of nanowires

    NASA Astrophysics Data System (ADS)

    Schmitt, M. C.; Reith, H.; Huzel, D.; Völklein, F.

    2012-06-01

    The paper focuses on the determination of thermal and electrical transport properties of individual nanowires, preferably thermoelectric bismuth and bismuth compound nanowires, prepared by ion-track-technology. Also the thermoelectric parameters S, σ, λ, z (with S: Seebeck coefficient; σ: electrical conductivity; λ thermal conductivity; z: thermoelectric efficiency) of template-embedded nanowire arrays have been investigated. For measurements of S, σ, λ and z, specially designed microchips have been developed and employed. The microfabricated z-chip is designed and optimized to determine all thermoelectric parameters on one and the same individual nanowire.

  4. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2014-10-01 2014-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  5. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2011-10-01 2011-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  6. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2012-10-01 2012-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  7. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2013-10-01 2013-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  8. Thermoelectric properties of chalcopyrite type CuGaTe{sub 2} and chalcostibite CuSbS{sub 2}

    SciTech Connect

    Kumar Gudelli, Vijay; Kanchana, V.; Vaitheeswaran, G.; Svane, A.; Christensen, N. E.

    2013-12-14

    Electronic and transport properties of CuGaTe{sub 2}, a hole-doped ternary copper based chalcopyrite type semiconductor, are studied using calculations within the Density Functional Theory and solving the Boltzmann transport equation within the constant relaxation time approximation. The electronic band structures are calculated by means of the full-potential linear augmented plane wave method, using the Tran-Blaha modified Becke-Johnson potential. The calculated band gap of 1.23 eV is in agreement with the experimental value of 1.2 eV. The carrier concentration- and temperature dependent thermoelectric properties of CuGaTe{sub 2} are derived, and a figure of merit of zT = 1.69 is obtained at 950 K for a hole concentration of 3.7·10{sup 19} cm{sup −3}, in agreement with a recent experimental finding of zT = 1.4, confirming that CuGaTe{sub 2} is a promising material for high temperature thermoelectric applications. The good thermoelectric performance of p-type CuGaTe{sub 2} is associated with anisotropic transport from a combination of heavy and light bands. Also for CuSbS{sub 2} (chalcostibite), a better performance is obtained for p-type than for n-type doping. The variation of the thermopower as a function of temperature and concentration suggests that CuSbS{sub 2} will be a good thermoelectric material at low temperatures, similarly to the isostructural CuBiS{sub 2} compound.

  9. Theoretical and Experimental Investigation on the Low Temperature Properties of the NbCr{sub 2} Laves Phase

    SciTech Connect

    Thoma, D.J.; Chu, F.; Chen, K.C.; Kotula, P.G.; Mitchell, T.E.; Wills, J.M.; Ormeci, A.; Chen, S.P.; Albers, R.C.

    1999-06-03

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of the project was to develop methodologies in which to define and improve the properties of NbCr{sub 2} so that the high temperature structural applications of alloys based upon this would not be limited by the low-temperature brittle behavior of the intermetallic. We accomplished this task by (1) understanding the defect structure and deformation mechanisms in Laves phases, (2) electronic and geometric contributions to phase stability and alloying behavior, and (3) novel processing of dual phase (Laves/bcc) structures. As a result alloys with properties that in many cases surpass superalloys were developed. For example, we have tailored alloy design strategies and processing routes in a metal alloy to achieve ambient temperature ultimate strengths of 2.35 GPa as well as ultimate strengths of 1.5 GPa at 1000 C. This results i n one of the strongest metal alloys that currently exist, while still having deformability at room temperature.

  10. High-accuracy direct ZT and intrinsic properties measurement of thermoelectric couple devices.

    PubMed

    Kraemer, D; Chen, G

    2014-04-01

    Advances in thermoelectric materials in recent years have led to significant improvements in thermoelectric device performance and thus, give rise to many new potential applications. In order to optimize a thermoelectric device for specific applications and to accurately predict its performance ideally the material's figure of merit ZT as well as the individual intrinsic properties (Seebeck coefficient, electrical resistivity, and thermal conductivity) should be known with high accuracy. For that matter, we developed two experimental methods in which the first directly obtains the ZT and the second directly measures the individual intrinsic leg properties of the same p/n-type thermoelectric couple device. This has the advantage that all material properties are measured in the same sample direction after the thermoelectric legs have been mounted in the final device. Therefore, possible effects from crystal anisotropy and from the device fabrication process are accounted for. The Seebeck coefficients, electrical resistivities, and thermal conductivities are measured with differential methods to minimize measurement uncertainties to below 3%. The thermoelectric couple ZT is directly measured with a differential Harman method which is in excellent agreement with the calculated ZT from the individual leg properties. The errors in both the directly measured and calculated thermoelectric couple ZT are below 5% which is significantly lower than typical uncertainties using commercial methods. Thus, the developed technique is ideal for characterizing assembled couple devices and individual thermoelectric materials and enables accurate device optimization and performance predictions. We demonstrate the methods by measuring a p/n-type thermoelectric couple device assembled from commercial bulk thermoelectric Bi2Te3 elements in the temperature range of 30 °C-150 °C and discuss the performance of the couple thermoelectric generator in terms of its efficiency and materials

  11. First-principles study of thermoelectric properties of pyrite

    NASA Astrophysics Data System (ADS)

    Xia, Yi; Zhou, Fei; Ozolins, Vidvuds

    2014-03-01

    Due to its natural abundance, moderate band gap and good light absorption properties, pyrite (FeS2) is being considered for use in nanocrystalline solar cells. High-quality n-type samples show high electron mobility, but their adoption in solar cells is hampered by low open circuit voltages. Here, using density-functional theory (DFT), we study charge and thermal transport properties of FeS2. Using the Debye-Callaway model, we obtain lattice thermal conductivity in good agreement with experimental data, suggesting that significant reduction of lattice thermal conductivity would be needed for thermoelectric applications. In addition, we find that holes in p-type pyrite form localized small polaron states, which naturally explains low hole mobilities observed experimentally.

  12. Thermoelectric properties of iron-based superconductors and parent compounds

    NASA Astrophysics Data System (ADS)

    Pallecchi, Ilaria; Caglieris, Federico; Putti, Marina

    2016-07-01

    Herewith, we review the available experimental data of thermoelectric transport properties of iron-based superconductors and parent compounds. We discuss possible physical mechanisms into play in determining the Seebeck effect, from whence one can extract information about Fermi surface reconstruction and Lifshitz transitions, multiband character, coupling of charge carriers with spin excitations and its relevance in the unconventional superconducting pairing mechanism, nematicity, quantum critical fluctuations close to the optimal doping for superconductivity, correlation. Additional information is obtained from the analysis of the Nernst effect, whose enhancement in parent compounds must be related partially to multiband transport and low Fermi level, but mainly to the presence of Dirac cone bands at the Fermi level. In the superconducting compounds, large Nernst effect in the normal state is explained in terms of fluctuating precursors of the spin density wave state, while in the superconducting state it mirrors the usual vortex liquid dissipative regime. A comparison between the phenomenology of thermoelectric behavior of different families of iron-based superconductors and parent compounds allows to evidence the key differences and analogies, thus providing clues on the rich and complex physics of these fascinating unconventional superconductors.

  13. Tuning thermoelectric properties of graphene/boron nitride heterostructures

    NASA Astrophysics Data System (ADS)

    Algharagholy, Laith A.; Al-Galiby, Qusiy; Marhoon, Haider A.; Sadeghi, Hatef; Abduljalil, Hayder M.; Lambert, Colin J.

    2015-11-01

    Using density functional theory combined with a Green’s function scattering approach, we examine the thermoelectric properties of hetero-nanoribbons formed from alternating lengths of graphene and boron nitride. In such structures, the boron nitride acts as a tunnel barrier, which weakly couples states in the graphene, to form mini-bands. In un-doped nanoribbons, the mini bands are symmetrically positioned relative to the Fermi energy and do not enhance thermoelectric performance significantly. In contrast, when the ribbons are doped by electron donating or electron accepting adsorbates, the thermopower S and electronic figure of merit are enhanced and either positive or negative thermopowers can be obtained. In the most favourable case, doping with the electron donor tetrathiafulvalene increases the room-temperature thermopower to -284 μv K-1 and doping by the electron acceptor tetracyanoethylene increases S to 210 μv K-1. After including both electron and phonon contributions to the thermal conductance, figures of merit ZT up to of order 0.9 are obtained.

  14. Thermoelectric Properties of Carbon nanohybrids Incorporated Polymer Nanocomposites

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Wang, Shiren

    2015-03-01

    In this work, non-covalently functionalized graphene with fluorinated fullerene (F-C60) by π- π stacking was integrated into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). F-C60 as a p-type organic semiconductor with deep highest occupied molecular orbital (HOMO) level modulates the band structure of reduced graphene oxide (rGO). Altering HOMO levels of rGO has been achieved by changing the ratio between rGO and F-C60. Incorporating of rGO/F-C60 nanohybrids into highly conductivity metallic PEDOT:PSS formed Schottky barrier to selectively scatter low-energy carriers. Enhanced thermoelectric power factor of rGO/F-C60/PEDOT:PSS nanocomposites were observed with the optimized power factor of 83.2 μW/m.K2, which is 19 times of that of the highly conductive PEDOT:PSS. Additionally, the F-C60 nanoparticles on rGO surfaces hinder thermal transport by phonon scattering, resulting in the synergistic effect on enhancing thermoelectric properties. As a result, a figure of merit (ZT) of 0.10 was achieved. NSF

  15. Diameter Dependent Thermoelectric Properties of Individual SnTe Nanowires

    NASA Astrophysics Data System (ADS)

    Xu, E. Z.; Li, Z.; Martinez, J.; Sinitsyn, N.; Htoon, H.; Li, N.; Swartzentruber, B.; Hollingsworth, J.; Wang, J.; Zhang, S. X.

    2015-03-01

    Tin telluride (SnTe), a newly discovered topological crystalline insulator, has recently been suggested to be a promising thermoelectric material. In this work, we report on a systematic study of the thermoelectric properties of individual single-crystalline SnTe nanowires with different diameters. Measurements of thermopower, electrical conductivity and thermal conductivity were carried out on the same nanowires over a temperature range of 25 - 300 K. While the electrical conductivity does not show a strong diameter dependence, we found that the thermopower increases by a factor of two when the nanowire diameter is decreased from 913 nm to 218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may be attributed to the enhanced phonon - surface boundary scattering and phonon-defect scattering. We further calculated the temperature dependent figure of merit ZT for each individual nanowire. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-AC04-94AL85000). We acknowledge support by the Los Alamos LDRD program.

  16. Tuning the thermoelectric properties of metallo-porphyrins.

    PubMed

    Al-Galiby, Qusiy H; Sadeghi, Hatef; Algharagholy, Laith A; Grace, Iain; Lambert, Colin

    2016-01-28

    We investigated the thermoelectric properties of metalloporphyrins connected by thiol anchor groups to gold electrodes. By varying the transition metal-centre over the family Mn, Co, Ni, Cu, Fe, and Zn we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature thermopowers range from almost zero for Co and Cu centres, to +80 μV K(-1) and +230 μV K(-1) for Ni and Zn respectively. In contrast, the thermopowers with Mn(II) or Fe(II) metal centres are negative and lie in the range -280 to -260 μV K(-1). Complexing these with a counter anion to form Fe(III) and Mn(III) changes both the sign and magnitude of their thermopowers to +218 and +95 respectively. The room-temperature power factors of Mn(II), Mn(III), Fe(III), Zn and Fe(II) porphyrins are predicted to be 5.9 × 10(-5) W m(-1) K(-2), 5.4 × 10(-4) W m(-1) K(-2), 9.5 × 10(-4) W m(-1) K(-2), 1.6 × 10(-4) W m(-1) K(-2) and 2.3 × 10(-4) W m(-1) K(-2) respectively, which makes these attractive materials for molecular-scale thermoelectric devices. PMID:26754271

  17. Tuning thermoelectric properties of graphene/boron nitride heterostructures.

    PubMed

    Algharagholy, Laith A; Al-Galiby, Qusiy; Marhoon, Haider A; Sadeghi, Hatef; Abduljalil, Hayder M; Lambert, Colin J

    2015-11-27

    Using density functional theory combined with a Green's function scattering approach, we examine the thermoelectric properties of hetero-nanoribbons formed from alternating lengths of graphene and boron nitride. In such structures, the boron nitride acts as a tunnel barrier, which weakly couples states in the graphene, to form mini-bands. In un-doped nanoribbons, the mini bands are symmetrically positioned relative to the Fermi energy and do not enhance thermoelectric performance significantly. In contrast, when the ribbons are doped by electron donating or electron accepting adsorbates, the thermopower S and electronic figure of merit are enhanced and either positive or negative thermopowers can be obtained. In the most favourable case, doping with the electron donor tetrathiafulvalene increases the room-temperature thermopower to -284 μv K(-1) and doping by the electron acceptor tetracyanoethylene increases S to 210 μv K(-1). After including both electron and phonon contributions to the thermal conductance, figures of merit ZT up to of order 0.9 are obtained. PMID:26528629

  18. Microstructure and magnetic properties of low-temperature sintered CoTi-substituted barium ferrite for LTCC application

    NASA Astrophysics Data System (ADS)

    Chen, Daming; Liu, Yingli; Li, Yuanxun; Zhong, Wenguo; Zhang, Huaiwu

    2011-11-01

    In this article, the influences of the BaCu(B 2O 5) (BCB) additive on sintering behavior, structure and magnetic properties of iron deficient M-type barium ferrite Ba(CoTi) xFe 11.8-2 xO 19 (BaM) have been investigated. It is found that the maximum sintered densities of BaM change from 86% to 94% as the BCB content varies from 1 to 4 wt%. Single-phase BaM can be detected by the XRD analysis in the sample with 3 wt% BCB sintered at 900 °C, and the microstructure is hexagonal platelets with few intragranular pores. This is attributed to the formation of the BCB liquid phase. Meanwhile, the experimental results illuminate that the CoTi ions prefer to occupy the 4f2 and 2b sites and the magnetic properties depend on the amount of CoTi-substitution. In addition, the chemical compatibility between BaM and silver paste is also investigated; it can be seen that BaM is co-fired well with the silver paste and no other second phase is observed. Especially, the 3 wt% BCB-added Ba(CoTi) 0.9Fe 11O 19 sintered at 900 °C has good properties with the sintered density of 4.9 g/cm 3, saturation magnetization of 49.7 emu/g and coercivity of 656.6 Oe. These results indicate that it is cost effective in the production of Low Temperature Co-fired Ceramics (LTCC) multilayer devices.

  19. Nanostructured semiconductors for thermoelectric energy conversion: Synthesis and transport properties

    NASA Astrophysics Data System (ADS)

    Sahoo, Pranati

    Increasing energy demands and decreasing natural energy resources have sparked search for alternative clean and renewable energy sources. For instance, currently there is a tremendous interest in thermoelectric and photovoltaic solar energy production technologies. Half-Heusler (HH) alloys are among the most popular material systems presently under widespread investigations for high temperature thermoelectric energy conversion. Approaches to increase the thermoelectric figure of merit (ZT) of HH range from (1) chemical substitution of atoms with different masses within the same atomic position in the crystal structure to optimize carrier concentration and enhance phonon scattering via mass fluctuation and (2) embedding secondary phonon scattering centers in the matrix (nanostructuring) to further reduce thermal conductivity. This work focuses on three material systems. The first part describes the synthesis and properties (thermal conductivity, electrical conductivity, magnetic) of various oxide nanostructures (NiO, Co3O4) which were subsequently used as inclusion phases in a HH matrix to reduce the thermal conductivity. Detailed reviews of the past efforts along with the current effort to optimize synthetic routes are presented. The effects of the synthesis conditions on the thermoelectric properties of compacted pellets of NiO and Co3O4 are also discussed. The second part of the work discusses the development of synthetic strategies for the fabrication of p-type and n-type bulk nanostructured thermoelectric materials made of a half-Heusler matrix based on (Ti,Hf)CoSb, containing nanostructures with full-Heusler (FH) compositions and structures coherently embedded inside the half-Heusler matrix. The role of the nanostructures in the regulation of phonon and charge carrier transports within the half-heusler matrix is extensively discussed by combining transport data and electron microscopy images. It was found that the FH nanoinclusions form staggered

  20. Thermoelectric properties of cobalt antimonide>-based skutterudites

    NASA Astrophysics Data System (ADS)

    Yang, Jian

    Solid state cooling and power generation based on thermoelectric principles are regarded as one of the technologies with the potential of solving the current energy crisis. Thermoelectric devices could be widely used in waste heat recovery, small scale power generation and refrigeration. It has no moving parts and is environmental friendly. The limitation to its application is due to its low efficiency. Most of the current commercialized thermoelectric materials have figure of merit (ZT) around 1. To be comparable with kitchen refrigerator, ZT≃ 3 is required at room temperature. Skutterudites have emerged as member of the novel materials, which potentially have a higher ZT. In the dissertation, my investigation will be focused on the optimization of CoSb3-based skutterudites. Starting with Co and Sb elements, CoSb3 will form through a high energy ball mill. Unfortunately, even after 20 hours, only a small percentage of the powders have transformed in into CoSb3. Then the powders will be compacted into bulk samples by DC-controlled hot press. CoSb3 single phase will form after press. Characterization of the structure and thermoelectric properties will be presented with details. The effects of synthesis conditions on thermoelectric properties of skutterudites were studied and discussed. Several possible methods of improving the ZT of N type skutterudites were applied. The highest obtained ZT thus far is ˜1.2 from Yb doped CoSb3. For a group of samples with nominal composition YbxCo4Sb12, the increased Yb concentration in our samples not only enhanced the power factor due to electron doping effect but also decreased the thermal conductivity due to a stronger rattling effect. In addition, the increased grain boundary density per unit volume due to the small grains in our bulk skutterudite materials may have also helped to enhance the phonon scattering and thus to reduce the thermal conductivity. Single and double doping methods with different combinations were also

  1. Mechanical properties and XRD studies of silicon carbide inert matrix fuel fabricated by a low temperature polymer precursor route

    NASA Astrophysics Data System (ADS)

    Shih, Chunghao; Rohbeck, Nadia; Gopalakrishnan, Karthik; Tulenko, James S.; Baney, Ronald H.

    2013-01-01

    The mechanical properties of silicon carbide (SiC) inert matrix fuel (IMF) pellets fabricated by a low temperature (1050 °C) polymer precursor route were evaluated at room temperature. The Vickers hardness was mainly related to the chemical bonding strength between the amorphous SiC phase and the β-SiC particles. The biaxial fracture strength with pre-notch and fracture toughness were found to be mostly controlled by the pellet density. The maximum Vickers hardness, biaxial fracture strength with pre-notch and fracture toughness achieved were 5.6 GPa, 201 MPa and 2.9 MPa m1/2 respectively. These values appear to be superior to the reference MOX or UO2 fuels. Excellent thermal shock resistance for the fabricated SiC IMF was proven and the values were compared to conventional UO2 pellets. XRD studies showed that ceria (PuO2 surrogate) chemically reacted with the polymer precursor during sintering, forming cerium oxysilicate. Whether PuO2 will chemically react in a similar manner remains unclear.

  2. Dielectric Dispersion, Diffuse Phase Transition, and Electrical Properties of BCT-BZT Ceramics Sintered at a Low-Temperature

    NASA Astrophysics Data System (ADS)

    Tian, Yongshang; Gong, Yansheng; Meng, Dawei; Li, Yuanjian; Kuang, Boya

    2015-08-01

    Lead-free ceramics 0.50Ba0.9Ca0.1TiO3-0.50BaTi1- x Zr x O3 (BCT-BZT) were prepared via sintering BCT and BZT nanoparticles, which were synthesized using a modified Pechini polymeric precursor method, at a low temperature of 1260°C. The relative densities of the ceramics prepared with different zirconium contents ( x) were all above 95.3%, reaching a maximum of 97% when x = 0.08. X-ray diffraction results confirmed the onset of phase transformation from orthorhombic to rhombohedral symmetry with increasing zirconium contents, and the polymorphic phase transition was observed at x = 0.10. The dielectric dispersion, diffuse phase transition (DPT), and relaxor-like ferroelectric characteristics as a function of zirconium content were thoroughly studied. Optimum physical properties, remnant polarization ( P r) = 16.4 μC/cm2, piezoelectric constant ( d 33) = ~240 pC/N, and electromechanical coupling factor ( k p) = 0.22, were obtained at x = 0.10. The findings of the current DPT behavior study of BCT-BZT ceramics are believed to be insightful to the development of ferroelectric materials.

  3. Effect of Low Temperature and Calcium on Survival and Membrane Properties of Isolated Winter Wheat Cells 1

    PubMed Central

    Pomeroy, M. Keith; Andrews, Chris J.

    1985-01-01

    Isolated cells obtained by enzymic digestion of young primary leaves of cold-hardened, dark-grown Kharkov winter wheat (Triticum aestivum L.) were exposed to various low temperature stresses. The initial uptake of 86Rb was generally decreased by increasing concentrations of Ca2+, but after longer periods of incubation, the inhibiting effect of high Ca2+ levels diminished. Viability of isolated cells suspended in water declined rapidly when ice encased at −1°C, while in the presence of 10 millimolar Ca2+ viability declined only gradually over a 5-week period. Ice encasement markedly reduced 86Rb uptake prior to a significant decline in cell viability or increased ion efflux. Cell damage increased progressively when the icing temperature was reduced from −1 to −2 and −3°C, but the presence of Ca2+ in the suspending medium reduced injury. Cell viability and ion uptake were reduced to a greater extent following slow cooling than after rapid cooling to subfreezing temperatures ranging from −10 to −30°C. The results from this study support the view that an early change in cellular properties due to prolonged ice encasement at −1°C involves the ion transport system, whereas cooling to lower subfreezing temperatures for only a few hours results in more general membrane damage, including loss of semipermeability of the plasma membrane. PMID:16664270

  4. Electro-Optical Properties of Low-Temperature Growth Indium-tin-oxide Nanowires Using Polystyrene Spheres as Catalyst.

    PubMed

    Li, Qiang; Gong, Zhina; Li, Yufeng; Liu, Hao; Feng, Lungang; Liu, Shuo; Yun, Feng

    2016-12-01

    Polystyrene sphere was chosen as a catalyst to fabricate indium-tin-oxide (ITO) nanowires (NWs) with a low-temperature (280-300 °C) electron-beam deposition process, bearing high purity. The ITO NWs with diameter of 20-50 nm and length of ~2 um were obtained. X-ray diffraction and high-resolution transmission electron microscope show high crystal quality. The transmittance is above 90 % at a wavelength 400 nm or more, superior to the ITO bulk film. Owing to the unique morphology gradient of the ITO NWs, the effective refractive index of ITO NWs film is naturally graded from the bottom to the top. The ITO NWs have been used on LED devices (λ = 450 nm), which improved the light output power by 31 % at the current of 150 mA comparing to the one without NWs and did not deteriorate the electrical properties. Such ITO NWs open opportunity in LED devices to further improve light extraction efficiency. PMID:26956600

  5. Electro-Optical Properties of Low-Temperature Growth Indium-tin-oxide Nanowires Using Polystyrene Spheres as Catalyst

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Gong, Zhina; Li, Yufeng; Liu, Hao; Feng, Lungang; Liu, Shuo; Yun, Feng

    2016-03-01

    Polystyrene sphere was chosen as a catalyst to fabricate indium-tin-oxide (ITO) nanowires (NWs) with a low-temperature (280-300 °C) electron-beam deposition process, bearing high purity. The ITO NWs with diameter of 20-50 nm and length of ~2 um were obtained. X-ray diffraction and high-resolution transmission electron microscope show high crystal quality. The transmittance is above 90 % at a wavelength 400 nm or more, superior to the ITO bulk film. Owing to the unique morphology gradient of the ITO NWs, the effective refractive index of ITO NWs film is naturally graded from the bottom to the top. The ITO NWs have been used on LED devices ( λ = 450 nm), which improved the light output power by 31 % at the current of 150 mA comparing to the one without NWs and did not deteriorate the electrical properties. Such ITO NWs open opportunity in LED devices to further improve light extraction efficiency.

  6. Effect of defect saturation on terahertz emission and detection properties of low temperature GaAs photoconductive switches

    NASA Astrophysics Data System (ADS)

    Rihani, Samir; Faulks, Richard; Beere, Harvey; Page, Hideaki; Gregory, Ian; Evans, Michael; Ritchie, David A.; Pepper, Michael

    2009-08-01

    We present a study into the properties of terahertz (THz) emission and detection using low temperature grown GaAs photoconductive switches over a range of ex situ anneal temperatures. Our analysis focuses on the effect of defect saturation, which has been confirmed in many experiments. However its effect on the THz emission and detection has so far not been fully investigated. In this letter, we examine the dependence of the radiated THz pulse width (full width at half maximum) upon optical power, and show that the differences in the characteristics with annealing can be theoretically accounted for when defect saturation is taken into account. Defect saturation was found to substantially increase the trapping time of photoexcited electrons, which in turn can cause THz pulse broadening at high optical powers. This effect was found to increase with anneal temperature due to the decrease in defect density. The radiated peak THz amplitude from emitters increases monotonically with increasing optical power across the range of anneal temperatures investigated. In the detector configuration, however, the detected peak THz amplitude reaches a maximum before starting to decrease with increasing optical power. The latter trend was observed for devices annealed at temperatures higher than 300 °C and is attributed to the onset of defect saturation.

  7. Structural, electrical, and low-temperature dielectric properties of sol-gel derived SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Thomas, Reji; Dube, D. C.; Kamalasanan, M. N.; Chandra, Subhas; Bhalla, A. S.

    1997-11-01

    Strontium titanate sol was prepared using strontium ethyl haxanoate and titanium isopropoxide. The sol was then spin coated on fused silica, p-type single-crystal silicon wafers (100) and stainless-steel substrates and annealed to give polycrystalline, transparent, and crack-free films. The surface morphology and structural properties of the films were studied using scanning electron microscopy and x-ray diffraction, respectively, and differential thermal analysis was used to observe structural transition. The dielectric measurements were conducted on films with metal-insulator-metal and metal-insulator-semiconductor configurations. Capacitance-voltage (C-V) measurements were carried out and the effect of the annealing temperature was studied. The dielectric constant and loss tangent at 1 MHz at room temperature were found to be 105 and 0.02, respectively, for 1.1 μm thick films. These measurements were also carried out at low temperatures down to 20 K. There are indications for a phase transition from a cubic perovskite to tetragonal perovskite structure at about 100 K where the tan δ shows some fluctuation, a characteristic of such transitions. The absence of a peak in the dielectric constant and the absence of hysteresis below the transition temperature have been explained on the basis of the low value of the tetragonal distortion (c/a=1.003) reported on bulk material.

  8. Thermoelectric properties and nonstoichiometry of GaGeTe

    SciTech Connect

    Drasar, C.; Kucek, V.; Benes, L.; Lostak, P.; Vlcek, M.

    2012-09-15

    Polycrystalline samples of composition Ga{sub 1+x}Ge{sub 1-x}Te (x=-0.03 Division-Sign 0.07) and GaGeTe{sub 1-y} (y=-0.02 Division-Sign 0.02) were synthesized from elements of 5 N purity using a solid state reaction. The products of synthesis were identified by X-ray diffraction; phase purity and microstructure were examined by EDX/SEM. Samples for measurement of transport properties were prepared using hot-pressing. They were characterized by measurement of electrical conductivity, the Hall coefficient, and the Seebeck coefficient over a temperature range 80-480 K and of thermal conductivity over a temperature range 300-580 K. All samples show p-type conductivity. We discuss the influence of stoichiometry on the phase purity of the samples and on free carrier concentration. The investigation of thermoelectric properties shows that the power factor of these samples is low compared to state-of-the-art materials at room temperature but increases distinctly with temperature. - Graphical abstract: Structure and preparation of GaGeTe. Electrical conductivity {sigma}, the Hall coefficient R{sub H}, the Seebeck coefficient S and thermal conductivity {kappa} as a function of temperature for the Ga{sub 1.01}Ge{sub 0.99}Te{sub 0.99} sample. Highlights: Black-Right-Pointing-Pointer We explore thermoelectric and transport properties of Ga{sub 1+x}Ge{sub 1-x}Te and GaGeTe{sub 1-y}. Black-Right-Pointing-Pointer GaGeTe is p-type degenerate semiconductor; the hole concentration increase with x and y. Black-Right-Pointing-Pointer Maximum power factor {sigma}S{sup 2}=3.6 Multiplication-Sign 10{sup -4} Wm{sup -1} K{sup -2} at 475 K.

  9. Analytic Thermoelectric Couple Modeling: Variable Material Properties and Transient Operation

    NASA Technical Reports Server (NTRS)

    Mackey, Jonathan A.; Sehirlioglu, Alp; Dynys, Fred

    2015-01-01

    To gain a deeper understanding of the operation of a thermoelectric couple a set of analytic solutions have been derived for a variable material property couple and a transient couple. Using an analytic approach, as opposed to commonly used numerical techniques, results in a set of useful design guidelines. These guidelines can serve as useful starting conditions for further numerical studies, or can serve as design rules for lab built couples. The analytic modeling considers two cases and accounts for 1) material properties which vary with temperature and 2) transient operation of a couple. The variable material property case was handled by means of an asymptotic expansion, which allows for insight into the influence of temperature dependence on different material properties. The variable property work demonstrated the important fact that materials with identical average Figure of Merits can lead to different conversion efficiencies due to temperature dependence of the properties. The transient couple was investigated through a Greens function approach; several transient boundary conditions were investigated. The transient work introduces several new design considerations which are not captured by the classic steady state analysis. The work helps to assist in designing couples for optimal performance, and also helps assist in material selection.

  10. Physical Property Evaluation of ZnO Thin Film Fabricated by Low-Temperature Process for Flexible Transparent TFT.

    PubMed

    Khafe, Adie Bin Mohd; Watanabe, Hiraku; Yamauchi, Hiroshi; Kuniyoshi, Shigekazu; Iizuka, Masaaki; Sakai, Masatoshi; Kudo, Kazuhiro

    2016-04-01

    The usual silicon-based display back planes require fairly high process temperature and thus the development of a low temperature process is needed on flexible plastic substrates. A new type of flexible organic light emitting transistor (OLET) had been proposed and investigated in the previous work. By using ultraviolet/ozone (UV/O3) assisted thermal treatments on wet processed zinc oxide field effect transistor (ZnO-FET), through low-process temperature, ZnO-FETs were fabricated which succeeded to achieve target drain current value and mobility. In this study, physical property evaluation of ZnO was conducted in term of their crystallinity, the increase composition of ZnO formed inside the thin film and the decrease of the carbon impurities originated from aqueous solution of the ZnO itself. The X-ray diffraction (XRD) evaluation showed UV/03 assisted thermal treatment has no obvious effect towards crystallinity of ZnO in the range of low process temperature. Moreover, through X-ray photoelectron spectroscopy (XPS) evaluation and Fourier transform infrared (FT-IR) spectroscopy evaluation, more carbon impurities disappeared from the ZnO thin film and the increase of composition amount of ZnO, when the thin film was subjected to UV/O3 assisted thermal treatment. Therefore, UV/O3 assisted thermal treatment contributed in carbon impurities elimination and accelerate ZnO formation in ZnO thin film, which led to the improvement in the electrical property of ZnO-FET in the low-process temperature. PMID:27451599

  11. Low temperature thermoelastic and structural properties of LaGaO{sub 3} perovskite in the Pbnm phase

    SciTech Connect

    Knight, Kevin S.

    2012-10-15

    The thermoelastic and structural properties of LaGaO{sub 3} perovskite have been studied using high resolution neutron diffractometry at 158 temperatures between 11 K and 548 K. Data collected in 2 K intervals between 410 K and 430 K show no evidence for an intermediate phase between the low temperature phase in space group Pbnm and the high temperature phase in space group F3{sup Macron }2/n. From a simultaneous fit of the unit cell volume and the isochoric heat capacity, the phonon density of states in the Pbnm phase is shown to be approximated by a two-term Debye model, with characteristic temperatures 294(1) K and 831(1) K. Vibrational Debye temperatures, determined from fitting the temperature variation of the atomic displacement parameters, show the cations to be more associated with the lower characteristic temperature, whilst that for the anions, is closer to the higher characteristic temperature. Structural parameters are presented as the amplitudes of the seven symmetry-adapted basis-vectors of the aristotype phase, and a structural basis for the temperature-dependence of the bond lengths is outlined. The phase transition in both temperature and pressure arises when a non-bonded La-O distance approaches the La coordination sphere. - Graphical abstract: The weight fraction of the rhombohedral phase of LaGaO{sub 3} from the onset of the phase transition at 408 K to its completion at 430 K. Highlights: Black-Right-Pointing-Pointer Thermoelastic properties of LaGaO{sub 3} analyzed as a two-term Debye model. Black-Right-Pointing-Pointer Crystal structure and bonding analyzed in terms of symmetry-adapted basis-vectors. Black-Right-Pointing-Pointer Consistency between calorimetric and crystallographic measurements.

  12. Atomistic design of thermoelectric properties of silicon nanowires.

    PubMed

    Vo, Trinh T M; Williamson, Andrew J; Lordi, Vincenzo; Galli, Giulia

    2008-04-01

    We present predictions of the thermoelectric figure of merit ( ZT) of Si nanowires with diameter up to 3 nm, based upon the Boltzman transport equation and ab initio electronic structure calculations. We find that ZT depends significantly on the wire growth direction and surface reconstruction, and we discuss how these properties can be tuned to select silicon based nanostructures with combined n-type and p-type optimal ZT. Our calculations show that only by reducing the ionic thermal conductivity by about 2 or 3 orders of magnitudes with respect to bulk values, one may attain ZT larger than 1, for 1 or 3 nm wires, respectively. We also find that ZT of p-doped wires is considerably smaller than that of their n-doped counterparts with the same size and geometry. PMID:18302325

  13. 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

  14. 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

    2013-01-01

    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

  15. La 1-x Ca x MnO 3 semiconducting nanostructures: morphology and thermoelectric properties.

    PubMed

    Culebras, Mario; Torán, Raquel; Gómez, Clara M; Cantarero, Andrés

    2014-01-01

    Semiconducting metallic oxides, especially perosvkite materials, are great candidates for thermoelectric applications due to several advantages over traditionally metallic alloys such as low production costs and high chemical stability at high temperatures. Nanostructuration can be the key to develop highly efficient thermoelectric materials. In this work, La 1-x Ca x MnO 3 perosvkite nanostructures with Ca as a dopant have been synthesized by the hydrothermal method to be used in thermoelectric applications at room temperature. Several heat treatments have been made in all samples, leading to a change in their morphology and thermoelectric properties. The best thermoelectric efficiency has been obtained for a Ca content of x=0.5. The electrical conductivity and Seebeck coefficient are strongly related to the calcium content. PMID:25206315

  16. Low-Temperature Thermoelectric Properties of PtSb2- x Te x for Cryogenic Peltier Cooling Applications

    NASA Astrophysics Data System (ADS)

    Waldrop, Spencer; Morelli, Donald

    2015-06-01

    PtSb2 is a potential material for cryogenic Peltier cooling applications because of its semimetal character with a high Seebeck coefficient and low electrical resistivity. To investigate the effects of n-type doping we studied PtSb2- x Te x with x between 0 and 0.04. A clear doping effect was observed, and the power factor was maximized for samples with x = 0.005, 0.02, and 0.04. If thermal conductivity reduction techniques can be used, this material may be a promising candidate for cryogenic Peltier cooling applications.

  17. Mechanical properties and microstructure of 6061 aluminum alloy severely deformed by ARB process and subsequently aged at low temperatures

    NASA Astrophysics Data System (ADS)

    Terada, Daisuke; Kaneda, Yoma; Horita, Zenji; Matsuda, Kenji; Hirosawa, Shoichi; Tsuji, Nobuhiro

    2014-08-01

    In order to clarify the aging behavior in ultrafine grained (UFG) Al alloys, a commercial Al-Mg-Si alloy was severely deformed by accumulative roll-bonding (ARB) process and subsequently aged at 100°C or 170°C. The age-hardening behavior and microstructure change during aging were investigated. At 170 °C, age-hardening was observed in solution treated (ST) specimens, but solution-treated and ARB-processed specimens were not hardened by aging. On the other hand, the hardness of the both ST specimen and ARB-processed specimen increased by aging at 100°C. From TEM observation, it was found that the ARB- processed specimen had an ultrafine lamellar boundary structure and the structure was kept during aging at 170°C and 100°C. In the ST specimen aged at 170°C, fine precipitates were observed within coarse grains. In the specimen ARB-processed and subsequently aged at 170°C, coarser precipitates were observed within ultrafine grains and on grain boundaries. It was considered that the reason why the hardness of the specimens ARB-processed and subsequently aged did not increase was coarsening of precipitates. In the specimens aged at 100°C, obvious precipitates were not observed, but clusters Mg and Si seemed to form during the aging, leading to the increase in the hardness of the specimen. From the results, it was suggested that aging at low temperatures could improve mechanical properties of Al alloys through combining grain refinement and precipitation hardening.

  18. Bismuth telluride nanostructures: preparation, thermoelectric properties and topological insulating effect

    NASA Astrophysics Data System (ADS)

    Ashalley, Eric; Chen, Haiyuan; Tong, Xin; Li, Handong; Wang, Zhiming M.

    2015-05-01

    Bismuth telluride is known to wield unique properties for a wide range of device applications. However, as devices migrate to the nanometer scale, significant amount of studies are being conducted to keep up with the rapidly growing nanotechnological field. Bi2Te3 possesses distinctive properties at the nanometer level from its bulk material. Therefore, varying synthesis and characterization techniques are being employed for the realization of various Bi2Te3 nanostructures in the past years. A considerable number of these works have aimed at improving the thermoelectric (TE) figure-of-merit (ZT) of the Bi2Te3 nanostructures and drawing from their topological insulating properties. This paper reviews the various Bi2Te3 and Bi2Te3-based nanostructures realized via theoretical and experimental procedures. The study probes the preparation techniques, TE properties and the topological insulating effects of 0D, 1D, 2D and Bi2Te3 nanocomposites. With several applications as a topological insulator (TI), the topological insulating effect of the Bi2Te3 is reviewed in detail with the time reversal symmetry (TRS) and surface state spins which characterize TIs. Schematics and preparation methods for the various nanostructural dimensions are accordingly categorized.

  19. Tuning the thermoelectric properties of metallo-porphyrins

    NASA Astrophysics Data System (ADS)

    Al-Galiby, Qusiy H.; Sadeghi, Hatef; Algharagholy, Laith A.; Grace, Iain; Lambert, Colin

    2016-01-01

    We investigated the thermoelectric properties of metalloporphyrins connected by thiol anchor groups to gold electrodes. By varying the transition metal-centre over the family Mn, Co, Ni, Cu, Fe, and Zn we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature thermopowers range from almost zero for Co and Cu centres, to +80 μV K-1 and +230 μV K-1 for Ni and Zn respectively. In contrast, the thermopowers with Mn(ii) or Fe(ii) metal centres are negative and lie in the range -280 to -260 μV K-1. Complexing these with a counter anion to form Fe(iii) and Mn(iii) changes both the sign and magnitude of their thermopowers to +218 and +95 respectively. The room-temperature power factors of Mn(ii), Mn(iii), Fe(iii), Zn and Fe(ii) porphyrins are predicted to be 5.9 × 10-5 W m-1 K-2, 5.4 × 10-4 W m-1 K-2, 9.5 × 10-4 W m-1 K-2, 1.6 × 10-4 W m-1 K-2 and 2.3 × 10-4 W m-1 K-2 respectively, which makes these attractive materials for molecular-scale thermoelectric devices.We investigated the thermoelectric properties of metalloporphyrins connected by thiol anchor groups to gold electrodes. By varying the transition metal-centre over the family Mn, Co, Ni, Cu, Fe, and Zn we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature thermopowers range from almost zero for Co and Cu centres, to +80 μV K-1 and +230 μV K-1 for Ni and Zn respectively. In contrast, the thermopowers with Mn(ii) or Fe(ii) metal centres are negative and lie in the range -280 to -260 μV K-1. Complexing these with a counter anion to form Fe(iii) and Mn(iii) changes both the sign and magnitude of their thermopowers to +218 and +95 respectively. The room-temperature power factors of Mn(ii), Mn(iii), Fe(iii), Zn and Fe(ii) porphyrins are predicted to be 5.9 × 10-5 W m-1 K-2, 5.4 × 10-4 W m-1 K-2, 9.5 × 10-4 W m-1 K-2, 1.6 × 10-4 W m-1 K

  20. Thermoelectric properties of CuAlCh{sub 2} (Ch = S, Se and Te)

    SciTech Connect

    Gudelli, Vijay Kumar; Kanchana, V.; Vaitheeswaran, G.

    2015-06-24

    Electronic and thermoelectric properties of ternary chalcopyrite-type CuAlCh{sub 2} (S, Se and Te) were studied using the first principles density functional calculations implemented in the full potential linear augmented plane wave (FP-LAPW) method. The thermoelectric properties are calculated by solving the Boltzmann transport equation within the constant relaxation time approximation. The calculated band gap using the Tran-Blaha modified Becke-Johnson potential (TB-mBJ), of all the compounds are in good agreement with the available experiment and other theoretical reports. Thermoelectric properties like thermopower, electrical conductivity scaled by relaxation time are calculated as a function of carrier concentrations at different temperatures. The calculated thermoelectric properties are compared with the available experiment and other theoretical calculations of similar materials.

  1. Thermoelectric properties of binary LnN (Ln=La and Lu): First principles study

    SciTech Connect

    Sreeparvathy, P. C.; Gudelli, Vijay Kumar; Kanchana, V.; Vaitheeswaran, G.; Svane, A.; Christensen, N. E.

    2015-06-24

    First principles density functional calculations were carried out to study the electronic structure and thermoelectric properties of LnN (Ln = La and Lu) using the full potential linearized augmented plane wave (FP-LAPW) method. The thermoelectric properties were calculated by solving the Boltzmann transport equation within the constant relaxation time approximation. The obtained lattice parameters are in good agreement with the available experimental and other theoretical results. The calculated band gaps using the Tran-Blaha modified Becke-Johnson potential (TB-mBJ), of both compounds are in good agreement with the available experimental values. Thermoelectric properties like thermopower (S), electrical conductivity scaled by relaxation time (σ/τ) and power-factor (S{sup 2}σ/τ) are calculated as functions of the carrier concentration and temperature for both compounds. The calculated thermoelectric properties are compared with the available experimental results of the similar material ScN.

  2. Thermoelectric properties of CuAlCh2 (Ch = S, Se and Te)

    NASA Astrophysics Data System (ADS)

    Gudelli, Vijay Kumar; Vaitheeswaran, G.; Kanchana, V.

    2015-06-01

    Electronic and thermoelectric properties of ternary chalcopyrite-type CuAlCh2 (S, Se and Te) were studied using the first principles density functional calculations implemented in the full potential linear augmented plane wave (FP-LAPW) method. The thermoelectric properties are calculated by solving the Boltzmann transport equation within the constant relaxation time approximation. The calculated band gap using the Tran-Blaha modified Becke-Johnson potential (TB-mBJ), of all the compounds are in good agreement with the available experiment and other theoretical reports. Thermoelectric properties like thermopower, electrical conductivity scaled by relaxation time are calculated as a function of carrier concentrations at different temperatures. The calculated thermoelectric properties are compared with the available experiment and other theoretical calculations of similar materials.

  3. Thermoelectric properties of binary LnN (Ln=La and Lu): First principles study

    NASA Astrophysics Data System (ADS)

    Sreeparvathy P., C.; Gudelli, Vijay Kumar; Kanchana, V.; Vaitheeswaran, G.; Svane, A.; Christensen, N. E.

    2015-06-01

    First principles density functional calculations were carried out to study the electronic structure and thermoelectric properties of LnN (Ln = La and Lu) using the full potential linearized augmented plane wave (FP-LAPW) method. The thermoelectric properties were calculated by solving the Boltzmann transport equation within the constant relaxation time approximation. The obtained lattice parameters are in good agreement with the available experimental and other theoretical results. The calculated band gaps using the Tran-Blaha modified Becke-Johnson potential (TB-mBJ), of both compounds are in good agreement with the available experimental values. Thermoelectric properties like thermopower (S), electrical conductivity scaled by relaxation time (σ/τ) and power-factor (S2σ/τ) are calculated as functions of the carrier concentration and temperature for both compounds. The calculated thermoelectric properties are compared with the available experimental results of the similar material ScN.

  4. A Model for Predicting Thermoelectric Properties of Bi2Te3

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon; VonAllmen, Paul

    2009-01-01

    A parameterized orthogonal tight-binding mathematical model of the quantum electronic structure of the bismuth telluride molecule has been devised for use in conjunction with a semiclassical transport model in predicting the thermoelectric properties of doped bismuth telluride. This model is expected to be useful in designing and analyzing Bi2Te3 thermoelectric devices, including ones that contain such nano - structures as quantum wells and wires. In addition, the understanding gained in the use of this model can be expected to lead to the development of better models that could be useful for developing other thermoelectric materials and devices having enhanced thermoelectric properties. Bi2Te3 is one of the best bulk thermoelectric materials and is widely used in commercial thermoelectric devices. Most prior theoretical studies of the thermoelectric properties of Bi2Te3 have involved either continuum models or ab-initio models. Continuum models are computationally very efficient, but do not account for atomic-level effects. Ab-initio models are atomistic by definition, but do not scale well in that computation times increase excessively with increasing numbers of atoms. The present tight-binding model bridges the gap between the well-scalable but non-atomistic continuum models and the atomistic but poorly scalable ab-initio models: The present tight-binding model is atomistic, yet also computationally efficient because of the reduced (relative to an ab-initio model) number of basis orbitals and flexible parameterization of the Hamiltonian.

  5. Thermoelectric properties of bulk MoSi2 synthesized by solid state microwave heating

    NASA Astrophysics Data System (ADS)

    Lan, Yu; Xie, Mianyu; Ouyang, Ting; Yue, Song

    2016-07-01

    In this research, single phase α-MoSi2 was prepared by solid state hybrid microwave heating within 90 min at relatively low temperature 1273 K. Such precursor powders were then ball milled and sintered by microwave heating at different temperatures. The thermoelectric (TE) properties of MoSi2 bulks were investigated in the temperature range of 300-673 K. When the sintering temperature increases from 973 K to 1273 K, the electrical resistivity decreases significantly and the Seebeck coefficients increase obviously, leading to the maximum TE powder factor of 6.2 × 10‑6Wm‑1K‑2 at 673 K. These results demonstrate the feasibility of high efficient and economical synthesis of MoSi2 by microwave heating technique, with the final products having comparable TE performance in comparison to those from typical methods with long duration and energy-extensive consumption.

  6. Signature of the topological surface state in the thermoelectric properties of Bi2Te3

    NASA Astrophysics Data System (ADS)

    Rittweger, F.; Hinsche, N. F.; Zahn, P.; Mertig, I.

    2014-01-01

    We present ab initio electronic structure calculations based on density functional theory for the thermoelectric properties of Bi2Te3 films. Conductivity and thermopower are computed in the diffusive limit of transport based on the Boltzmann equation. Bulk and surface contributions to the transport coefficients are separated by a special projection technique. As a result we show clear signatures of the topological surface state in the thermoelectric properties.

  7. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    DOE PAGESBeta

    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.; et al

    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

  8. 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.

  9. Sterility, mechanical properties, and molecular stability of polylactide internal-fixation devices treated with low-temperature plasmas.

    PubMed

    Gogolewski, S; Mainil-Varlet, P; Dillon, J G

    1996-10-01

    The effect of low-temperature plasma on sterility, molecular, mechanical, and crystalline properties of poly (L-lactide), poly (L/D-lactide) and poly (L/DL-lactide) was investigated. Polymers were treated for 15 and 30 min at 100 W with nitrogen, argon, oxygen, and carbon dioxide plasma. All polymers treated with oxygen or carbon dioxide plasma were rendered sterile after 15 min of treatment. Only 70% of the samples treated under similar conditions with nitrogen or argon plasma were sterile. Extension of the exposure time to 30 min and increasing power to 200 W did not improve sterilization efficiency. Plasma sterilization, under the conditions used, caused no significant decrease or increase in overall molecular weight or polydispersity of the polylactides used. In most instances the effect of plasma sterilization was to slightly increase the overall molecular weight of the polymers studied. Treatment with argon plasma led to a more consistent increase in molecular weight than did treatment with nitrogen, oxygen, or carbon dioxide. Analysis of the surface (skin) of a poly(L-lactide) injection-molded rod following plasma sterilization indicated an increase in molecular weight as related to the interior (core) of the rod. Comparison of Mark-Houwink plots for the surface and interior of poly(L-lactide) injection-molded rods following plasma sterilization indicated an increase in chain branching for the surface relative to the interior of the rod. Generally the highly crystalline poly(L-lactide) was less susceptible to change upon plasma treatment than was the less crystalline poly(L/D-lactide) and poly(L/DL-lactide). The mechanical properties (shear strength, bending strength, and moduli) of the polylactides were not affected by plasma treatment. The overall melting temperature and the heat of melting of polylactides studied were not affected by plasma treatment. The melting temperature of the skin of the samples was about 1 degree C higher than the melting

  10. Photo-controllable thermoelectric properties with reversibility and photo-thermoelectric effects of tungsten trioxide accompanied by its photochromic phenomenon

    SciTech Connect

    Azuma, Chiori; Kawano, Takuto; Kakemoto, Hirofumi; Irie, Hiroshi

    2014-11-07

    The addition of photo-controllable properties to tungsten trioxide (WO{sub 3}) is of interest for developing practical applications of WO{sub 3} as well as for interpreting such phenomena from scientific viewpoints. Here, a sputtered crystalline WO{sub 3} thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W{sup 5+} ions. The thermoelectric properties (electrical conductivity (σ) and Seebeck coefficient (S)) and coloration of WO{sub 3} could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating the film with UV light, σ increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was detected. Notably, the opposite behavior was exhibited by WO{sub 3} after dark storage, and this reversible cycle could be repeated at least three times. Moreover, photo-thermoelectric effects (photo-conductive effect (photo-conductivity, σ{sub photo}) and photo-Seebeck effect (photo-Seebeck coefficient, S{sub photo})) were also detected in response to visible-light irradiation of the colored WO{sub 3} thin films. Under visible-light irradiation, σ{sub photo} and the absolute value of S{sub photo} increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W{sup 5+} state) to the conduction band of WO{sub 3}. Our findings demonstrate that the simultaneous, reversible switching of multiple properties of WO{sub 3} thin film is achieved by the application of an external stimulus and that this material exhibits photo-thermoelectric effects when irradiated with visible-light.

  11. Photo-controllable thermoelectric properties with reversibility and photo-thermoelectric effects of tungsten trioxide accompanied by its photochromic phenomenon

    NASA Astrophysics Data System (ADS)

    Azuma, Chiori; Kawano, Takuto; Kakemoto, Hirofumi; Irie, Hiroshi

    2014-11-01

    The addition of photo-controllable properties to tungsten trioxide (WO3) is of interest for developing practical applications of WO3 as well as for interpreting such phenomena from scientific viewpoints. Here, a sputtered crystalline WO3 thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W5+ ions. The thermoelectric properties (electrical conductivity (σ) and Seebeck coefficient (S)) and coloration of WO3 could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating the film with UV light, σ increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was detected. Notably, the opposite behavior was exhibited by WO3 after dark storage, and this reversible cycle could be repeated at least three times. Moreover, photo-thermoelectric effects (photo-conductive effect (photo-conductivity, σphoto) and photo-Seebeck effect (photo-Seebeck coefficient, Sphoto)) were also detected in response to visible-light irradiation of the colored WO3 thin films. Under visible-light irradiation, σphoto and the absolute value of Sphoto increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W5+ state) to the conduction band of WO3. Our findings demonstrate that the simultaneous, reversible switching of multiple properties of WO3 thin film is achieved by the application of an external stimulus and that this material exhibits photo-thermoelectric effects when irradiated with visible-light.

  12. Harvesting Nanocatalytic Heat Localized in Nanoalloy Catalyst as a Heat Source in a Nanocomposite Thin Film Thermoelectric Device.

    PubMed

    Zhao, Wei; Shan, Shiyao; Luo, Jin; Mott, Derrick M; Maenosono, Shinya; Zhong, Chuan-Jian

    2015-10-20

    This report describes findings of an investigation of harvesting nanocatalytic heat localized in a nanoalloy catalyst layer as a heat source in a nanocomposite thin film thermoelectric device for thermoelectric energy conversion. This device couples a heterostructured copper-zinc sulfide nanocomposite for thermoelectrics and low-temperature combustion of methanol fuels over a platinum-cobalt nanoalloy catalyst for producing heat localized in the nanocatalyst layer. The possibility of tuning nanocatalytic heat in the nanocatalyst and thin film thermoelectric properties by compositions points to a promising pathway in thermoelectric energy conversion. PMID:26444621

  13. Thermoelectric properties of two-dimensional topological insulators doped with nonmagnetic impurities

    SciTech Connect

    Li, L. L.; Xu, W.

    2014-07-07

    We present a theoretical study on the thermoelectric properties of two-dimensional topological insulators (2DTIs) doped with nonmagnetic impurities. We develop a tractable model to calculate the electronic band structure without additional input parameters and to evaluate the thermoelectric properties of 2DTIs based on CdTe/HgTe quantum wells. We find that with increasing the doping concentration of nonmagnetic impurity, the edge states dominate the thermoelectric transport and the bulk-state conduction is largely suppressed. For typical sample parameters, the thermoelectric figure of merit ZT (a quantity used to characterize the conversion efficiency of a thermoelectric device between the heat and electricity) can be much larger than 1, which is a great advance over conventional thermoelectric materials. Furthermore, we show that with decreasing the 2DTI ribbon width or the Hall-bar width, ZT can be considerably further improved. These results indicate that the CdTe/HgTe 2DTIs doped with nonmagnetic impurities can be potentially applied as high-efficiency thermoelectric materials and devices.

  14. Thermoelectric properties of two-dimensional topological insulators doped with nonmagnetic impurities

    NASA Astrophysics Data System (ADS)

    Li, L. L.; Xu, W.

    2014-07-01

    We present a theoretical study on the thermoelectric properties of two-dimensional topological insulators (2DTIs) doped with nonmagnetic impurities. We develop a tractable model to calculate the electronic band structure without additional input parameters and to evaluate the thermoelectric properties of 2DTIs based on CdTe/HgTe quantum wells. We find that with increasing the doping concentration of nonmagnetic impurity, the edge states dominate the thermoelectric transport and the bulk-state conduction is largely suppressed. For typical sample parameters, the thermoelectric figure of merit ZT (a quantity used to characterize the conversion efficiency of a thermoelectric device between the heat and electricity) can be much larger than 1, which is a great advance over conventional thermoelectric materials. Furthermore, we show that with decreasing the 2DTI ribbon width or the Hall-bar width, ZT can be considerably further improved. These results indicate that the CdTe/HgTe 2DTIs doped with nonmagnetic impurities can be potentially applied as high-efficiency thermoelectric materials and devices.

  15. Low-Temperature Aging of Delta-Ferrite in 316L SS Welds; Changes in Mechanical Properties and Etching Properties

    NASA Astrophysics Data System (ADS)

    Abe, Hiroshi; Shimizu, Keita; Watanabe, Yutaka

    Thermal aging embrittlement of LWR components made of stainless cast (e.g. CF-8 and CF-8M) is a potential degradation issue, and careful attention has been paid on it. Although welds of austenitic stainless steels (SSs) have γ-δ duplex microstructure, which is similar to that of the stainless cast, examination on thermal aging characteristics of the SS welds is very limited. In order to evaluate thermal aging behavior of weld metal of austenitic stainless steel, the 316L SS weld metal has been prepared and changes in mechanical properties and in etching properties at isothermal aging at 335°C have been investigated. The hardness of the ferrite phase has increased with aging, while the hardness of austenite phase has stayed same. It has been suggested that spinodal decomposition has occurred in δ-ferrite by the 335°C aging. The etching rates of δ-ferrite at immersion test in 5wt% hydrochloric acid solution have been also investigated using an AFM technique. The etching rate of ferrite phase has decreased consistently with the increase in hardness of ferrite phase. It has been thought that this characteristic is also caused by spinodal decomposition of ferrite into chromium-rich (α') and iron-rich (α).

  16. Improved thermoelectric properties in heavily doped FeGa3

    NASA Astrophysics Data System (ADS)

    Ponnambalam, V.; Morelli, Donald T.

    2015-12-01

    FeGa3, a hybridization gap semiconductor, has been substituted with an n-type dopant Ge to form a series of compositions FeGa3-xGex. Electrical and thermal transport properties of these compositions have been studied. Change in carrier density (n) is evident from the Hall measurements. The carrier density (n) can be as high as ˜1021 cm-3 in these compositions. In order to study the role of heavy doping on the thermoelectric properties of FeGa3, an alloy series Fe1-yCoyGa3-xGex has also been synthesized with higher concentrations of Ge (x = 0.1-0.35) and Co (y = 0.1-0.5). From resistivity and Seebeck coefficient measurements, it appears that heavy doping is accomplished by the simultaneous substitutions of Ge and Co. The systematic change in both resistivity (ρ) and Seebeck coefficient (α) is possibly due to change in the carrier density (n). The power factor (PF) α2/ρ improves steadily with increasing carrier density and the best PF ˜1.1 mW/m K2 is observed for the heavily doped compositions at 875 K. In the alloy series Fe1-yCoyGa3-xGex, thermal conductivity is also reduced substantially due to point defect scattering. Due to higher power factors, the figure of merit ZT improves to 0.25 at 875 K for the heavily doped compositions.

  17. Processing and nanostructure influences on mechanical properties of thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Schmidt, Robert David

    Thermoelectric (TE) materials are materials that can generate an electric current from a thermal gradient, with possible service in recovery of waste heat such as engine exhaust. Significant progress has been made in improving TE conversion efficiency, typically reported according to the figure of merit, ZT, with several recent papers publishing ZT values above 2. Furthermore, cost reductions may be made by the use of lower cost elements such as Mg, Si, Sn, Pb, Se and S in TE materials, while achieving ZT values between 1.3 and 1.8. To be used in a device, the thermoelectric material must be able to withstand the applied thermal and mechanical forces without failure. However, these materials are brittle, with low fracture toughness typically less than 1.5 MPa-m1/2, and often less than 0.5 MPa-m1/2. For comparison, window glass is approximately 0.75 MPa-m1/2. They have been optimized with nanoprecipitates, nanoparticles, doping, alterations in stoichiometry, powder processing and other techniques, all of which may alter the mechanical properties. In this study, the effect of SiC nanoparticle additions in Mg2Si, SnTe and Ag nanoparticle additions in the skutterudite Ba0.3Co 4Sb12 on the elastic moduli, hardness and fracture toughness are measured. Large changes (˜20%) in the elastic moduli in SnTe 1+x as a function of x at 0 and 0.016 are shown. The effect on mechanical properties of doping and precipitates of CdS or ZnS in a PbS or PbSe matrix have been reported. Changes in sintering behavior of the skutterudite with the Ag nanoparticle additions were explored. Possible liquid phase sintering, with associated benefits in lower processing temperature, faster densification and lower cost, has been shown. A technique has been proposed for determining additional liquid phase sintering aids in other TE materials. The effects of porosity, grain size, powder processing method, and sintering method were explored with YbAl3 and Ba0.3Co4Sb 12, with the porosity dependence of

  18. FAST TRACK COMMUNICATION: Thermoelectric properties of graphene nanoribbons, junctions and superlattices

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Jayasekera, T.; Calzolari, A.; Kim, K. W.; Buongiorno Nardelli, M.

    2010-09-01

    Using model interaction Hamiltonians for both electrons and phonons and Green's function formalism for ballistic transport, we have studied the thermal conductance and the thermoelectric properties of graphene nanoribbons (GNR), GNR junctions and periodic superlattices. Among our findings we have established the role that interfaces play in determining the thermoelectric response of GNR systems both across single junctions and in periodic superlattices. In general, increasing the number of interfaces in a single GNR system increases the peak ZT values that are thus maximized in a periodic superlattice. Moreover, we proved that the thermoelectric behavior is largely controlled by the width of the narrower component of the junction. Finally, we have demonstrated that chevron-type GNRs recently synthesized should display superior thermoelectric properties.

  19. Nonlinear thermoelectric response due to energy-dependent transport properties of a quantum dot

    NASA Astrophysics Data System (ADS)

    Svilans, Artis; Burke, Adam M.; Svensson, Sofia Fahlvik; Leijnse, Martin; Linke, Heiner

    2016-08-01

    Quantum dots are useful model systems for studying quantum thermoelectric behavior because of their highly energy-dependent electron transport properties, which are tunable by electrostatic gating. As a result of this strong energy dependence, the thermoelectric response of quantum dots is expected to be nonlinear with respect to an applied thermal bias. However, until now this effect has been challenging to observe because, first, it is experimentally difficult to apply a sufficiently large thermal bias at the nanoscale and, second, it is difficult to distinguish thermal bias effects from purely temperature-dependent effects due to overall heating of a device. Here we take advantage of a novel thermal biasing technique and demonstrate a nonlinear thermoelectric response in a quantum dot which is defined in a heterostructured semiconductor nanowire. We also show that a theoretical model based on the Master equations fully explains the observed nonlinear thermoelectric response given the energy-dependent transport properties of the quantum dot.

  20. Enhanced Thermoelectric Properties of Cu2ZnSnSe4 with Ga-doping

    DOE PAGESBeta

    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 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

  1. Anisotropic thermoelectric properties of layered compounds in SnX2 (X = S, Se): a promising thermoelectric material.

    PubMed

    Sun, Bao-Zhen; Ma, Zuju; He, Chao; Wu, Kechen

    2015-11-28

    Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 μW cm(-1) K(-2) along the a direction, while a relatively low value (11.72 μW cm(-1) K(-2)) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (κmin) along the a direction is estimated to be about 0.67 and 0.55 W m(-1) K(-1) for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m(-1) K(-1) at 300 K). The reasonable PF and κmin suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 10(19) (SnSe2) vs. 2.87 × 10(19) cm(-3) (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials. PMID:26486877

  2. Enhanced thermoelectric properties of Ga-doped In2O3 ceramics via synergistic band gap engineering and phonon suppression.

    PubMed

    Liu, Yong; Xu, Wei; Liu, Da-Bo; Yu, Meijuan; Lin, Yuan-Hua; Nan, Ce-Wen

    2015-05-01

    Ga doped In2O3-based thermoelectric materials were prepared by spark plasma sintering (SPS) using sintered powders in the low temperature solid phase. The solubility of Ga in In2O3 is about 10 at%, much larger than other elements such as Ge, Ce, etc. The larger solubility of Ga allows us to optimize the thermal and electrical transport properties of Ga doped In2O3 in a wider window. While tuning the concentration of dopants, the thermoelectric performance of Ga doped In2O3 was enhanced through a synergistic approach combining band-gap engineering and phonon suppression. The power factor increases from ∼0.5 × 10(-4) to ∼9.6 × 10(-4) W mK(-2) at 700 °C while thermal conductivity reduces from ∼4 to ∼2 W mK(-1) at 700 °C in In1.9Ga0.1O3. The maximum ZT of 0.37, increased by a factor of 4 from the pristine In2O3, is achieved in In1.9Ga0.1O3 at 700 °C. PMID:25829235

  3. Thermoelectric transport properties of pristine and Na-doped SnSe(1-x)Te(x) polycrystals.

    PubMed

    Wei, Tian-Ran; Wu, Chao-Feng; Zhang, Xiaozhi; Tan, Qing; Sun, Li; Pan, Yu; Li, Jing-Feng

    2015-11-28

    SnSe, a "simple" and "old" binary compound composed of earth-abundant elements, has been reported to exhibit a high thermoelectric performance in single crystals, which stimulated recent interest in its polycrystalline counterparts. This work investigated the electrical and thermal transport properties of pristine and Na-doped SnSe1-xTex polycrystals prepared by mechanical alloying and spark plasma sintering. It is revealed that SnSe1-xTex solid solutions are formed when x ranges from 0 to 0.2. An energy barrier scattering mechanism is suitable for understanding the electrical conducting behaviour observed in the present SnSe polycrystalline materials, which may be associated with abundant defects at grain boundaries. The thermal conductivity was greatly reduced upon Te substitution due to alloy scattering of phonons as well explained by the Debye model. Due to the increased carrier concentration by Na-doping, thermoelectric figure of merit (ZT) was enhanced in the whole temperature range with a maximum value of 0.72 obtained at a relatively low temperature (773 K) for Sn0.99Na0.01Se0.84Te0.16. PMID:26496971

  4. Investigation to the deep center related properties of low temperature grown InPBi with Hall and photoluminescence

    SciTech Connect

    Wang, Peng; Pan, Wenwu; Wu, Xiaoyan; Wang, Kai; Yue, Li; Gong, Qian; Wang, Shumin

    2015-12-15

    InP{sub 1-x}Bi{sub x} epilayers with bismuth (Bi) concentration x= 1.0% were grown on InP by gas source molecular beam epitaxy (GS-MBE) at low temperature (LT). Bi incorporation decreased the intrinsic free electron concentration of low temperature grown InP indicated by hall analysis. It is concluded that deep level center was introduced by Bi. Influence of Si doping on the InP{sub 1-x}Bi{sub x} films Photoluminescence (PL) was investigated. N-type doping in the InP{sub 1-x}Bi{sub x} epilayers was found to be effective at PL enhancement. Blue shift of InPBi PL emission wavelength was observed as the Si doping concentration increasing. Two independent peaks were fitted and their temperature dependence behavior was observed to be distinct obviously. Two individual radiative recombination processes were expected to be involved.

  5. Investigation to the deep center related properties of low temperature grown InPBi with Hall and photoluminescence

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Pan, Wenwu; Wang, Kai; Wu, Xiaoyan; Yue, Li; Gong, Qian; Wang, Shumin

    2015-12-01

    InP1-xBix epilayers with bismuth (Bi) concentration x= 1.0% were grown on InP by gas source molecular beam epitaxy (GS-MBE) at low temperature (LT). Bi incorporation decreased the intrinsic free electron concentration of low temperature grown InP indicated by hall analysis. It is concluded that deep level center was introduced by Bi. Influence of Si doping on the InP1-xBix films Photoluminescence (PL) was investigated. N-type doping in the InP1-xBix epilayers was found to be effective at PL enhancement. Blue shift of InPBi PL emission wavelength was observed as the Si doping concentration increasing. Two independent peaks were fitted and their temperature dependence behavior was observed to be distinct obviously. Two individual radiative recombination processes were expected to be involved.

  6. Atomistic calculation of the thermoelectric properties of Si nanowires

    NASA Astrophysics Data System (ADS)

    Bejenari, I.; Kratzer, P.

    2014-07-01

    The thermoelectric properties of 1.6-nm-thick Si square nanowires with [100] crystalline orientation are calculated over a wide temperature range from 0 K to 1000 K, taking into account atomistic electron-phonon interaction. In our model, the [010] and [001] facets are passivated by hydrogen and there are Si-Si dimers on the nanowire surface. The electronic structure was calculated by using the sp3 spin-orbit-coupled atomistic second-nearest-neighbor tight-binding model. The phonon dispersion was calculated from a valence force field model of the Brenner type. A scheme for calculating electron-phonon matrix elements from a second-nearest-neighbor tight-binding model is presented. Based on Fermi's golden rule, the electron-phonon transition rate was obtained by combining the electron and phonon eigenstates. Both elastic and inelastic scattering processes are taken into consideration. The temperature dependence of transport characteristics was calculated by using a solution of the linearized Boltzmann transport equation obtained by means of the iterative orthomin method. At room temperature, the electron mobility is 195 cm2 V-1 s-1 and increases with temperature, while a figure of merit ZT =0.38 is reached for n-type doping with a concentration of n =1019 cm-3.

  7. Zigzag nanoribbons of two-dimensional silicene-like crystals: magnetic, topological and thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Wierzbicki, Michał; Barnaś, Józef; Swirkowicz, Renata

    2015-12-01

    The effects of electron-electron and spin-orbit interactions on the ground-state magnetic configuration and on the corresponding thermoelectric and spin thermoelectric properties in zigzag nanoribbons of two-dimensional hexagonal crystals are analysed theoretically. The thermoelectric properties of quasi-stable magnetic states are also considered. Of particular interest is the influence of Coulomb and spin-orbit interactions on the topological edge states and on the transition between the topological insulator and conventional gap insulator states. It is shown that the interplay of both interactions also has a significant impact on the transport and thermoelectric characteristics of the nanoribbons. The spin-orbit interaction also determines the in-plane magnetic easy axis. The thermoelectric properties of nanoribbons with in-plane magnetic moments are compared to those of nanoribbons with edge magnetic moments oriented perpendicularly to their plane. Nanoribbons with ferromagnetic alignment of the edge moments are shown to reveal spin thermoelectricity in addition to the conventional one.

  8. Zigzag nanoribbons of two-dimensional silicene-like crystals: magnetic, topological and thermoelectric properties.

    PubMed

    Wierzbicki, Michał; Barnaś, Józef; Swirkowicz, Renata

    2015-12-01

    The effects of electron-electron and spin-orbit interactions on the ground-state magnetic configuration and on the corresponding thermoelectric and spin thermoelectric properties in zigzag nanoribbons of two-dimensional hexagonal crystals are analysed theoretically. The thermoelectric properties of quasi-stable magnetic states are also considered. Of particular interest is the influence of Coulomb and spin-orbit interactions on the topological edge states and on the transition between the topological insulator and conventional gap insulator states. It is shown that the interplay of both interactions also has a significant impact on the transport and thermoelectric characteristics of the nanoribbons. The spin-orbit interaction also determines the in-plane magnetic easy axis. The thermoelectric properties of nanoribbons with in-plane magnetic moments are compared to those of nanoribbons with edge magnetic moments oriented perpendicularly to their plane. Nanoribbons with ferromagnetic alignment of the edge moments are shown to reveal spin thermoelectricity in addition to the conventional one. PMID:26565114

  9. Electrical and thermoelectric properties of different compositions of Ge-Se-In thin films

    NASA Astrophysics Data System (ADS)

    Aly, K. A.; Dahshan, A.; Abbady, Gh.; Saddeek, Y.

    2016-09-01

    The effect of temperature in the range of 300-450 K and the indium content on the electrical and thermoelectric properties of Ge20Se80-xInx (0.0≤x≤24 at%) chalcogenide glassy thin films have been studied. From dc electrical and thermoelectric measurements, it was observed that the activation energies for electrical conductivity (ΔE) and for thermoelectric (ΔEs) decrease while the conductivity (σ) and Seebeck coefficient (S) increase upon introducing In into the Ge-Se glasses. In contrast to the behavior obtained with Bi or Pb doping, In incorporated in Ge-Se does not lead to a p-to n-type conduction inversion. The power factor (P) which is strongly depends on both of the Seebeck coefficient and the electrical conductivity. According to the obtained results, the Ge20Se80-xInx films can be considered potential candidates for incurring high action thermoelectric materials.

  10. Thermoelectric properties of Zintl compound Ca1-xNaxMg2Bi1.98

    NASA Astrophysics Data System (ADS)

    Shuai, Jing; Kim, Hee Seok; Liu, Zihang; He, Ran; Sui, Jiehe; Ren, Zhifeng

    2016-05-01

    Motivated by good thermoelectric performance of Bi-based Zintl compounds Ca1-xYbxMg2Biy, we further studied the thermoelectric properties of Zintl compound CaMg2Bi1.98 by doping Na into Ca as Ca1-xNaxMg2Bi1.98 via mechanical alloying and hot pressing. We found that the electrical conductivity, Seebeck coefficient, power factor, and carrier concentration can be effectively adjusted by tuning the Na concentration. Transport measurement and calculations revealed that an optimal doping of 0.5 at. % Na achieved better average ZT and efficiency. The enhancement in thermoelectric performance is attributed to the increased carrier concentration and power factor. The low cost and nontoxicity of Ca1-xNaxMg2Bi1.98 makes it a potentially promising thermoelectric material for power generation in the mid-temperature range.

  11. Joule heating and thermoelectric properties in short single-walled carbon nanotubes: Electron-phonon interaction effect

    NASA Astrophysics Data System (ADS)

    Jiang, Jin-Wu; Wang, Jian-Sheng

    2011-12-01

    The electron-phonon interaction (EPI) effect in single-walled carbon nanotube is investigated by the nonequilibrium Green's function approach within the Born approximation. Special attention is paid to the EPI induced Joule heating phenomenon and the thermoelectric properties in both metallic armchair (10, 10) tube and semiconductor zigzag (10, 0) tube. For Joule heat in the metallic (10, 10) tube, the theoretical results for the breakdown bias voltage is quite comparable with the experimental value. It is found that the Joule heat can be greatly enhanced by increasing the chemical potential, while the role of the temperature is not so important for Joule heat. In the zigzag (10, 0) tube, the Joule heat is smaller than the armchair tube, resulting from nonzero bandgap in the electron band structure. For the electronic conductance Ge and electron thermal conductance σel, the EPI has important effect at higher temperature or higher chemical potential. Compared with ballistic transport, there is an opposite tendency for Ge to decrease with increasing temperature after EPI is considered. This is due to the dominant effect of the electron phonon scattering mechanism in the electron transport in this situation. There is an interesting "electron-drag" phenomenon for the phonon thermal conductance in case of low temperature and high chemical potential, where phonons are dragged by electrons from low temperature region into high temperature region through EPI effect.

  12. Effect of Low Temperature Irradiation in ATR On The Mechanical Properties of Ternary V-Cr-Ti Alloys

    SciTech Connect

    Hamilton, Margaret L.; Toloczko, Mychailo B.; Oliver, Brian M.; Garner, Francis A.

    2000-09-01

    Tensile tests and shear punch teats were performed on a variety of vanadium alloys that were irradiated in the Advanced Test Reactor (ATR) at temperatures between 200 and 300 degrees C to doses between 3 and 5 dpa. Tests were performed at room temperature and the irradiation temperature. The results of both the tensile tests and the shear punch tests show that following low temperature irradiation, the yield strength increased by a factor of 3-4 while the ultimate strength increased by a factor of approximately 3.

  13. Novel Low Temperature Processing for Enhanced Properties of Ion Implanted Thin Films and Amorphous Mixed Oxide Thin Film Transistors

    NASA Astrophysics Data System (ADS)

    Vemuri, Rajitha

    This research emphasizes the use of low energy and low temperature post processing to improve the performance and lifetime of thin films and thin film transistors, by applying the fundamentals of interaction of materials with conductive heating and electromagnetic radiation. Single frequency microwave anneal is used to rapidly recrystallize the damage induced during ion implantation in Si substrates. Volumetric heating of the sample in the presence of the microwave field facilitates quick absorption of radiation to promote recrystallization at the amorphous-crystalline interface, apart from electrical activation of the dopants due to relocation to the substitutional sites. Structural and electrical characterization confirm recrystallization of heavily implanted Si within 40 seconds anneal time with minimum dopant diffusion compared to rapid thermal annealed samples. The use of microwave anneal to improve performance of multilayer thin film devices, e.g. thin film transistors (TFTs) requires extensive study of interaction of individual layers with electromagnetic radiation. This issue has been addressed by developing detail understanding of thin films and interfaces in TFTs by studying reliability and failure mechanisms upon extensive stress test. Electrical and ambient stresses such as illumination, thermal, and mechanical stresses are inflicted on the mixed oxide based thin film transistors, which are explored due to high mobilities of the mixed oxide (indium zinc oxide, indium gallium zinc oxide) channel layer material. Semiconductor parameter analyzer is employed to extract transfer characteristics, useful to derive mobility, subthreshold, and threshold voltage parameters of the transistors. Low temperature post processing anneals compatible with polymer substrates are performed in several ambients (oxygen, forming gas and vacuum) at 150 °C as a preliminary step. The analysis of the results pre and post low temperature anneals using device physics fundamentals

  14. Assessing the thermoelectric properties of single InSb nanowires: the role of thermal contact resistance

    NASA Astrophysics Data System (ADS)

    Yazji, S.; Swinkels, M. Y.; De Luca, M.; Hoffmann, E. A.; Ercolani, D.; Roddaro, S.; Abstreiter, G.; Sorba, L.; Bakkers, E. P. A. M.; Zardo, I.

    2016-06-01

    The peculiar shape and dimensions of nanowires (NWs) have opened the way to their exploitation in thermoelectric applications. In general, the parameters entering into the thermoelectric figure of merit are strongly interdependent, which makes it difficult to realize an optimal thermoelectric material. In NWs, instead, the power factor can be increased and the thermal conductivity reduced, thus boosting the thermoelectric efficiency compared to bulk materials. However, the assessment of all the thermoelectric properties of a NW is experimentally very challenging. Here, we focus on InSb NWs, which have proved to be promising thermoelectric materials. The figure of merit is accurately determined by using a novel method based on a combination of Raman spectroscopy and electrical measurements. Remarkably, this type of experiment provides a powerful approach allowing us to neglect the role played by thermal contact resistance. Furthermore, we compare the thermal conductivity determined by this novel method to the one determined on the same sample by the thermal bridge method. In this latter approach, the thermal contact resistance is a non-negligible parameter, especially in NWs with large diameters. We provide experimental evidence of the crucial role played by thermal contact resistance in the assessment of the thermal properties of nanostructures, using two different measurement methods of the thermal conductivity.

  15. Thermoelectric Properties of CuAgSe doped with Co, Cr

    NASA Astrophysics Data System (ADS)

    Czajka, Peter; Yao, Mengliang; Opeil, Cyril

    Thermoelectric materials represent one way that reliable cooling below the boiling point of nitrogen can be realized. Current materials do not exhibit sufficiently high efficiencies at cryogenic temperatures, but significant progress is being made. One material that has generated significant interest recently is CuAgSe. It has been demonstrated (Ishiwata et al., Nature Mater. 2013) that doping CuAgSe with 10% Ni at the Cu sites increases the material's thermoelectric figure of merit (ZT) at 100 K from 0.02 to 0.10. This is intriguing not just because of the dramatic effect that the Ni doping produces, but also because CuAgSe is a semimetal and semimetals are not usually able to exhibit the kind of asymmetric carrier activation necessary for strong thermoelectric performance. In order to further investigate the unusual nature of thermoelectricity in CuAgSe and its strong dependence on chemical composition, we have synthesized and measured the thermoelectric properties of a series of CuAgSe samples doped with Co and Cr. Temperature-dependent magnetic and thermoelectric transport properties of CuAgSe as a function of Co and Cr doping will be discussed. This work is supported by the Department of Defense, AFOSR, MURI Program Contract # FA9550-10-1-0533 and the Trustees of Boston College.

  16. Perspective: Web-based machine learning models for real-time screening of thermoelectric materials properties

    NASA Astrophysics Data System (ADS)

    Gaultois, Michael W.; Oliynyk, Anton O.; Mar, Arthur; Sparks, Taylor D.; Mulholland, Gregory J.; Meredig, Bryce

    2016-05-01

    The experimental search for new thermoelectric materials remains largely confined to a limited set of successful chemical and structural families, such as chalcogenides, skutterudites, and Zintl phases. In principle, computational tools such as density functional theory (DFT) offer the possibility of rationally guiding experimental synthesis efforts toward very different chemistries. However, in practice, predicting thermoelectric properties from first principles remains a challenging endeavor [J. Carrete et al., Phys. Rev. X 4, 011019 (2014)], and experimental researchers generally do not directly use computation to drive their own synthesis efforts. To bridge this practical gap between experimental needs and computational tools, we report an open machine learning-based recommendation engine (thermoelectrics.citrination.com">http://thermoelectrics.citrination.com) for materials researchers that suggests promising new thermoelectric compositions based on pre-screening about 25 000 known materials and also evaluates the feasibility of user-designed compounds. We show this engine can identify interesting chemistries very different from known thermoelectrics. Specifically, we describe the experimental characterization of one example set of compounds derived from our engine, RE12Co5Bi (RE = Gd, Er), which exhibits surprising thermoelectric performance given its unprecedentedly high loading with metallic d and f block elements and warrants further investigation as a new thermoelectric material platform. We show that our engine predicts this family of materials to have low thermal and high electrical conductivities, but modest Seebeck coefficient, all of which are confirmed experimentally. We note that the engine also predicts materials that may simultaneously optimize all three properties entering into zT; we selected RE12Co5Bi for this study due to its interesting chemical composition and known facile synthesis.

  17. Probing Electronic and Thermoelectric Properties of Single Molecule Junctions

    NASA Astrophysics Data System (ADS)

    Widawsky, Jonathan R.

    In an effort to further understand electronic and thermoelectric phenomenon at the nanometer scale, we have studied the transport properties of single molecule junctions. To carry out these transport measurements, we use the scanning tunneling microscope-break junction (STM-BJ) technique, which involves the repeated formation and breakage of a metal point contact in an environment of the target molecule. Using this technique, we are able to create gaps that can trap the molecules, allowing us to sequentially and reproducibly create a large number of junctions. By applying a small bias across the junction, we can measure its conductance and learn about the transport mechanisms at the nanoscale. The experimental work presented here directly probes the transmission properties of single molecules through the systematic measurement of junction conductance (at low and high bias) and thermopower. We present measurements on a variety of molecular families and study how conductance depends on the character of the linkage (metal-molecule bond) and the nature of the molecular backbone. We start by describing a novel way to construct single molecule junctions by covalently connecting the molecular backbone to the electrodes. This eliminates the use of linking substituents, and as a result, the junction conductance increases substantially. Then, we compare transport across silicon chains (silanes) and saturated carbon chains (alkanes) while keeping the linkers the same and find a stark difference in their electronic transport properties. We extend our studies of molecular junctions by looking at two additional aspects of quantum transport -- molecular thermopower and molecular current-voltage characteristics. Each of these additional parameters gives us further insight into transport properties at the nanoscale. Evaluating the junction thermopower allows us to determine the nature of charge carriers in the system and we demonstrate this by contrasting the measurement of amine

  18. Structural and optical properties of low temperature grown AlN films on sapphire using helicon sputtering system

    SciTech Connect

    Chen, Meei-Ru; Chen, Hou-Guang; Kao, Hui-Ling Wu, Ming-Guei; Tzou, An-Jye; Chen, Jyh Shin; Chou, Hsiung

    2015-05-15

    AlN thin films have been deposited directly on c-plane sapphire substrates at low temperatures by a helicon sputtering system. The structural quality of AlN epitaxial films was characterized by x-ray diffractometry and transmission electron microscopy. The films exhibit smooth surface with root-mean-square roughness as small as 0.7 nm evaluated by atomic force microscope. The optical transmittance spectra show a steep absorption edge at the wavelength of 200 nm and a high transmittance of over 80% in the visible range. The band-edge transition (6.30 eV) of AlN film was observed in the cathodoluminescence spectrum recorded at 11 K. The spectral response of metal–semiconductor–metal photodetectors constructed with AlN/sapphire reveals the peak responsivity at 200 nm and a UV/visible rejection ratio of about two orders of magnitude. The results of this low temperature deposition suggest the feasibility of the epitaxial growth of AlN on sapphire substrates and the incorporation of the AlN films in the surface acoustic wave devices and the optical devices at deep ultraviolet region.

  19. Thermoelectric and Lattice Dynamical Properties of Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Singh, David

    2015-03-01

    Ge2Sb2Te5 (GST) has been widely used as phase-change materials in optical data storage media and nonvolatile RAM devices. At elevated temperature, GST is known to undergo subsequent structural transitions from a non-conducting amorphous to (metastable) disordered cubic phase and then to a conducting hexagonal phase above 300°C. Given that hexagonal-GST has already been reported to have promising thermoelectric properties and transport properties critically depend on the bonding information, a direct correlation between its structural- and transport properties needs to be established. In this talk, we will present the evolution of thermoelectric and lattice dynamical properties of GST in different phases via first principles calculations based on density functional theory. A better understanding of the origin of low-thermal conductivity in hexagonal-GST may provide critical information for further improvement of its thermoelectric figure of merit (ZT).

  20. Influence of Mn on crystal structure and thermoelectric properties of GeTe compounds

    NASA Astrophysics Data System (ADS)

    Lee, J. K.; Oh, M. W.; Kim, B. S.; Min, B. K.; Lee, H. W.; Park, S. D.

    2014-07-01

    The thermoelectric properties of the Ge1- x Mn x Te compounds were investigated in the temperature range from 300 K to 773 K. The crystal structure of the compound was gradually changed with Mn, changing from a rhombohedral to a cubic-like cell. The Seebeck coefficient and the electrical resistivity were increased with Mn. From the Hall coefficient measurement, the reduction of the carrier concentration was confirmed and was responsible for the change of the electrical properties. The thermal conductivity was also reduced with Mn. The maximum dimensionless figure of merit, ZT, was obtained for x = 0.05 composition, where the value was ZT = 1.3 at 773 K. The evolution of the crystal structure with Mn attributed to the change of the thermoelectric properties. The Mn-doped compound which has a more cubic phase than a rhombohedral exhibited superior thermoelectric properties to the pure rhombohedral phase. [Figure not available: see fulltext.

  1. Thermoelectric properties of n-type PbSe revisited

    SciTech Connect

    Parker, David S; Singh, David J; Ren, Zhifeng; Zhang, Qinyong

    2012-01-01

    It was recently predicted \\cite{parker} and experimentally confirmed \\cite{sny_PbSe} that $p$-type PbSe would be a good thermoelectric material. Recent experimental work \\cite{pers2} now suggests that $n$-type PbSe can also be a good thermoelectric material. We now re-examine the thermoelectric performance of PbSe with a revised approximation which improves band gap accuracy. We now find that $n$-type PbSe {\\it can} be a high performance material, with thermopowers as high in magnitude as 250 $\\mu$V/K at 1000 K and 300 $\\mu$V/K at 800 K. Optimal 1000 K $n$-type doping ranges are between 2 $\\times 10^{19}$cm$^{-3}$ and 8 $\\times 10^{19}$cm$^{-3}$, while at 800 K the corresponding range is from 7 $\\times$10$^{18}$ to 4 $\\times $10$^{19}$ cm$^{-3}$.

  2. Microscopic theory of thermoelectric properties of silicon nanowires

    SciTech Connect

    Vo, T; Williamson, A; Lordi, V; Galli, G

    2007-06-14

    We present predictions of the thermoelectric figure of merit (ZT) of Si nanowires, as obtained using Boltzman transport equation and ab-initio electronic structure calculations. We find that ZT is strongly dependent on the nanowire growth direction and surface reconstruction and we discuss general rules to select silicon based nanostructures with combined n-type and p-type optimal ZT. In particular, our calculations indicate that 1 nm wires grown in the [001] and [011] directions can attain ZT values which are about twice as high as those of ordinary thermoelectric materials.

  3. Thermomechanical and thermoelectrical properties of vanadyl phosphate dihydrate

    SciTech Connect

    Zima, V.; Benes, L.; Malek, J.; Vlcek, M. . Joint Lab. of Solid State Chemistry Univ. of Pardubice )

    1994-06-01

    Thermoelectric power and XRD of layered VOPO[sub 4][center dot]2H[sub 2]O have been studied for dependence on temperature. The results of thermomechanical analysis (i.e. thermal changes of the thickness of the crystal across the layers) correspond to the changes of basal spacing during heating. The values of the dehydration temperatures have been determined. The conductivity caused by positive charge carriers is predominant in vanadyl phosphate hydrates, whereas conductivity in anhydrous VOPO[sub 4] is electronic, as it follows from the thermoelectric power measurements.

  4. Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

    NASA Astrophysics Data System (ADS)

    Yang, Q.; Tang, K.; Zuo, J.; Qian, Y.

    2004-12-01

    Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm.

  5. Low-temperature spray-pyrolysis of FeS2 films and their electrical and optical properties

    NASA Astrophysics Data System (ADS)

    Orletskii, I. G.; Mar'yanchuk, P. D.; Maistruk, E. V.; Solovan, M. N.; Brus, V. V.

    2016-01-01

    Iron disulfide (FeS2) films with a wide range of electrical resistivities 100 Ω cm ⩽ ρ ⩽ 800 kΩ cm, a high adhesion to the substrate, and a resistance to aggressive media have been prepared by the spray pyrolysis of aqueous solutions of the salts FeCl3 · 6H2O and (NH2)2CS at low temperatures in the range 250°C ⩽ T S ⩽ 400°C. It has been found that the FeS2 films have a high transmittance T ≈ 60-70% and are characterized by a sharp transmission edge. It has been shown that the optical band gap for direct ( E g op = 2.19-2.78 eV) and indirect ( E g 'op = 1.26-1.36 eV) optical transitions depends on the conditions of film preparation.

  6. INS, DFT and temperature dependent IR investigations of dynamical properties of low temperature phase of choline chloride

    NASA Astrophysics Data System (ADS)

    Pawlukojć, A.; Hetmańczyk, Ł.

    2014-12-01

    Within the framework of the research the inelastic neutron scattering and temperature dependent infra-red spectroscopy investigations of the low temperature phase of choline chloride were performed. The infra-red spectra in wavenumber region 4000-80 cm-1 and in a temperature range 9-300 K were collected. The density functional theory calculations with the periodic boundary conditions for determination and description of the normal modes in the vibration spectra of choline chloride were applied. Bands assigned to the CH3 torsional vibration were observed at 288 and 249 cm-1. From the analysis of the temperature dependence of the full-width-at-half-maximum the activation energy for CH3 group reorientation is found to be equal to 1.6 ± 0.2 kcal/mol.

  7. Optical and Magnetic Properties of ZnO Nanoparticles Doped with Co, Ni and Mn and Synthesized at Low Temperature.

    PubMed

    Hancock, Jared M; Rankin, William M; Hammad, Talaat M; Salem, Jamil S; Chesnel, Karine; Harrison, Roger G

    2015-05-01

    Zinc oxide nanomaterials were synthesized with small amounts of magnetic ions to create dilute magnetic semiconductors (DMS), by using a low temperature sol-gel method. Conditions were controlled such that a range of amounts of Co, Ni and Mn were incorporated. The incorporation could be tracked by color changes in the powders to blue for Co, green for Ni and yellow for Mn. XRD measurements showed the ZnO has the wurtzite structure with crystallites 8-12 nm in diameter. Nanoparticles were observed by SEM and TEM and TEM showed that the lattice fringes of different nanoparticles align. Nanoparticle alignment was disrupted when high concentrations of metal dopants were incorporated. Magnetic measurements showed a change in behavior from diamagnetic to paramagnetic with increasing concentration of metal dopants. PMID:26505009

  8. Long-term effect of silica fume on the principal properties of low-temperature-cured ceramics

    SciTech Connect

    Persson, B.

    1997-11-01

    This article outlines an experimental and numerical study of the long-term interaction between silica fume and Portland cement in low-temperature-cured ceramics such as concrete subjected to air, water and sealed curing. For this purpose about 2,000 kg of eight qualities of concrete were studied at 4 different ages, each over a period of 90 months. Half of the concretes contained 10% silica fume. Parallel studies of strength, heat of hydration, hydration and internal relative humidity were carried out. New and original results and analyses of the interaction between Portland cement and silica fume related to compressive strength, split tensile strength, hydration and internal relative humidity are presented. The project was carried out between 1989 and 1996.

  9. The Thermoelectric Properties of Rare Earths as Dopants in InGaAs Films

    NASA Astrophysics Data System (ADS)

    Koltun, Rachel Ann

    Current energy technologies lose over half of the energy input to waste heat. Thermoelectric materials can recover some of this waste heat by converting it into electricity. Thermoelectric devices have no moving parts, so they are low noise and highly reliable, making them particularly suitable for extreme environments. A good thermoelectric has low thermal conductivity to maintain large temperature gradients and high electrical conductivity to effectively transport carriers across that temperature gradient. One of the major challenges in engineering such thermoelectrics is effectively decoupling these parameters. These relationships are quantified in the dimensionless thermoelectric figure of merit, ZT, where a ZT of 1 is considered commercially viable. Doping MBE grown InGaAs films with rare earths forms embedded nanoparticles that have been shown to improve thermoelectric efficiency of InGaAs. Rare earth doping effectively overcomes the problematic relationship between electrical and thermal conductivities. These embedded particles effectively decouple thermal and electrical properties by contributing carriers to increase electrical conductivity as well as forming scattering centers for mid to long wavelength phonons to decrease thermal conductivity. However, the mechanism for carrier generation from rare earths is poorly understood. Comparing different rare earths as dopants in InGaAs, we find a positive correlation with the electrical activation efficiency as the rare earth arsenide nanoparticles are more closely lattice matched to the host matrix. This is in contrast to traditional Si doped InGaAs, which is fully ionized at room temperature. The high doping efficiency of Si leads it to be as good or better of a dopant for thermoelectrics compared to the best rare earths studied. We observe that rare earth doped InGaAs has thermal activation of carriers at high temperature, giving it the potential to be a more efficient thermoelectric in this regime than

  10. Low-Temperature Supercapacitors

    NASA Technical Reports Server (NTRS)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.

    2008-01-01

    An effort to extend the low-temperature operational limit of supercapacitors is currently underway. At present, commercially available non-aqueous supercapacitors are rated for a minimum operating temperature of -40 C. A capability to operate at lower temperatures would be desirable for delivering power to systems that must operate in outer space or in the Polar Regions on Earth. Supercapacitors (also known as double-layer or electrochemical capacitors) offer a high power density (>1,000 W/kg) and moderate energy density (about 5 to 10 Wh/kg) technology for storing energy and delivering power. This combination of properties enables delivery of large currents for pulsed applications, or alternatively, smaller currents for low duty cycle applications. The mechanism of storage of electric charge in a supercapacitor -- at the electrical double-layer formed at a solid-electrode/liquid-electrolyte interface -- differs from that of a primary or secondary electrochemical cell (i.e., a battery) in such a manner as to impart a long cycle life (typically >10(exp 6) charge/discharge cycles).

  11. First principle investigation of the electronic and thermoelectric properties of Mg2C

    NASA Astrophysics Data System (ADS)

    Kulwinder, Kaur; Ranjan, Kumar

    2016-02-01

    In this paper, electronic and thermoelectric properties of Mg2C are investigated by using first principle pseudo potential method based on density functional theory and Boltzmann transport equations. We calculate the lattice parameters, bulk modulus, band gap and thermoelectric properties (Seebeck coefficient, electrical conductivity, and thermal conductivity) of this material at different temperatures and compare them with available experimental and other theoretical data. The calculations show that Mg2C is indirect band semiconductor with a band gap of 0.75 eV. The negative value of Seebeck coefficient shows that the conduction is due to electrons. The electrical conductivity decreases with temperature and Power factor (PF) increases with temperature. The thermoelectric properties of Mg2C have been calculated in a temperature range of 100 K-1200 K. Kulwinder Kaur thanks Council of Scientific & Industrial Research (CSIR), India for providing fellowship.

  12. Thermoelectric properties of Nb3SbxTe7-x compounds

    NASA Technical Reports Server (NTRS)

    Snyder, J.; Wang, S.; Caillat, T.

    2002-01-01

    Niobium antimony telluride, Nb3Sbx,Te7-x, was synthesized and tested for thermoelectric properties in the Thermoelectrics group at the Jet Propulsion Laboratory. The forty atoms per unit cell of Nb3Sb2Te5 and its varied mixture of atoms yield acomplicated structure, suggesting that Nb3Sb2Te5 and related compounds may exhibit low thermal conductivity and hence a higher ZT value. Nb3SbxTe7-x, compounds were synthesized and subsequently analyzed for their Seebeck voltage, heat conduction, and electrical resistivity. Results indicate that Nb3Sb2Te5 is a heavily doped semiconductor whose thermoelectric properties are compromised by compensating n-type and p-type carriers. Attempts to dope in favor of either carrier by varying the Sb:Te ratio yielded samples containing secondary metallic phases that dominated the transport properties of the resulting compounds.

  13. 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.

  14. Thermoelectric effects in a rectangular Aharonov-Bohm geometry

    NASA Astrophysics Data System (ADS)

    Pye, A. J.; Faux, D. A.; Kearney, M. J.

    2016-04-01

    The thermoelectric transport properties of a rectangular Aharonov-Bohm ring at low temperature are investigated using a theoretical approach based on Green's functions. The oscillations in the transmission coefficient as the field is varied can be used to tune the thermoelectric response of the ring. Large magnitude thermopowers are obtainable which, in conjunction with low conductance, can result in a high thermoelectric figure of merit. The effects of single site impurities and more general Anderson disorder are considered explicitly in the context of evaluating their effect on the Fano-type resonances in the transmission coefficient. Importantly, it is shown that even for moderate levels of disorder, the thermoelectric figure of merit can remain significant, increasing the appeal of such structures from the perspective of specialist thermoelectric applications.

  15. First-Principles Study of Electronic Structure and Thermoelectric Properties of Ge-Doped Tin Clathrates

    NASA Astrophysics Data System (ADS)

    Akai, K.; Kishimoto, K.; Koyanagi, T.; Kono, Y.; Yamamoto, S.

    2014-06-01

    We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.

  16. Thermoelectric efficiency of holey topological insulators

    NASA Astrophysics Data System (ADS)

    Abanov, Artem; Tretiakov, Oleg; Sinova, Jairo

    2012-02-01

    We study the thermoelectric properties of three-dimensional topological insulators with many holes (or pores) in the bulk. We show that at high density of these holes the thermoelectric figure of merit, ZT, can be large due to the contribution of the conducting surfaces and the suppressed phonon thermal conductivity. The maximum efficiency can be tuned by an induced gap in the surface states dispersion through tunneling or external magnetic fields. The large values of ZT, much higher than unity for reasonable parameters, make this system a strong candidate for applications in heat management of nanodevices, especially at low temperatures.

  17. La3+ Alters the Response Properties of Neurons in the Mouse Primary Somatosensory Cortex to Low-Temperature Noxious Stimulation of the Dental Pulp

    PubMed Central

    Jin, Yanjiao

    2015-01-01

    Although dental pain is a serious health issue with high incidence among the human population, its cellular and molecular mechanisms are still unclear. Transient receptor potential (TRP) channels are assumed to be involved in the generation of dental pain. However, most of the studies were conducted with molecular biological or histological methods. In vivo functional studies on the role of TRP channels in the mechanisms of dental pain are lacking. This study uses in vivo cellular electrophysiological and neuropharmacological method to directly disclose the effect of LaCl3, a broad spectrum TRP channel blocker, on the response properties of neurons in the mouse primary somatosensory cortex to low-temperature noxious stimulation of the dental pulp. It was found that LaCl3 suppresses the high-firing-rate responses of all nociceptive neurons to noxious low-temperature stimulation and also inhibits the spontaneous activities in some nonnociceptive neurons. The effect of LaCl3 is reversible. Furthermore, this effect is persistent and stable unless LaCl3 is washed out. Washout of LaCl3 quickly revitalized the responsiveness of neurons to low-temperature noxious stimulation. This study adds direct evidence for the hypothesis that TRP channels are involved in the generation of dental pain and sensation. Blockade of TRP channels may provide a novel therapeutic treatment for dental pain. PMID:26604777

  18. 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

  19. Improved Superconducting properties in the Mg11B2 low activation superconductor prepared by low-temperature sintering

    NASA Astrophysics Data System (ADS)

    Cheng, Fang; Liu, Yongchang; Ma, Zongqing; Shahriar Al Hossain, M.; Somer, M.

    2016-05-01

    Mg11B2 has a great application prospect in the superconducting coils for fusion reactor as the “low activation superconductors”. The un-doped Mg11B2 and Cu-doped Mg11B2 bulks using 11B as a boron precursor were fabricated by low-temperature sintering in present work. It was found that the prepared Mg11B2 low activation superconductors exhibit better Jc performance than all of other Mg11B2 samples reported in previous studies. As for Cu doped Mg11B2, minor Cu addition can obviously improve the Mg11B2 grain crystallization and reduce the amount of MgO impurity. Hence, improved grain connectivity and higher Jc at low fields is obtained in Cu doped Mg11B2 samples. For un-doped samples, refined grains and more MgO impurity with proper size brought about more flux pinning centers, resulting in better Jc performance at high fields.

  20. Improved Superconducting properties in the Mg(11)B2 low activation superconductor prepared by low-temperature sintering.

    PubMed

    Cheng, Fang; Liu, Yongchang; Ma, Zongqing; Shahriar Al Hossain, M; Somer, M

    2016-01-01

    Mg(11)B2 has a great application prospect in the superconducting coils for fusion reactor as the "low activation superconductors". The un-doped Mg(11)B2 and Cu-doped Mg(11)B2 bulks using (11)B as a boron precursor were fabricated by low-temperature sintering in present work. It was found that the prepared Mg(11)B2 low activation superconductors exhibit better Jc performance than all of other Mg(11)B2 samples reported in previous studies. As for Cu doped Mg(11)B2, minor Cu addition can obviously improve the Mg(11)B2 grain crystallization and reduce the amount of MgO impurity. Hence, improved grain connectivity and higher Jc at low fields is obtained in Cu doped Mg(11)B2 samples. For un-doped samples, refined grains and more MgO impurity with proper size brought about more flux pinning centers, resulting in better Jc performance at high fields. PMID:27149682

  1. Improved Superconducting properties in the Mg11B2 low activation superconductor prepared by low-temperature sintering

    PubMed Central

    Cheng, Fang; Liu, Yongchang; Ma, Zongqing; Shahriar Al Hossain, M.; Somer, M.

    2016-01-01

    Mg11B2 has a great application prospect in the superconducting coils for fusion reactor as the “low activation superconductors”. The un-doped Mg11B2 and Cu-doped Mg11B2 bulks using 11B as a boron precursor were fabricated by low-temperature sintering in present work. It was found that the prepared Mg11B2 low activation superconductors exhibit better Jc performance than all of other Mg11B2 samples reported in previous studies. As for Cu doped Mg11B2, minor Cu addition can obviously improve the Mg11B2 grain crystallization and reduce the amount of MgO impurity. Hence, improved grain connectivity and higher Jc at low fields is obtained in Cu doped Mg11B2 samples. For un-doped samples, refined grains and more MgO impurity with proper size brought about more flux pinning centers, resulting in better Jc performance at high fields. PMID:27149682

  2. Electrical properties of solution-deposited ZnO thin-film transistors by low-temperature annealing.

    PubMed

    Lim, Chul; Oh, Ji Young; Koo, Jae Bon; Park, Chan Woo; Jung, Soon-Won; Na, Bock Soon; Chu, Hye Yong

    2014-11-01

    Flexible oxide thin-film transistors (Oxide-TFTs) have emerged as next generation transistors because of their applicability in electronic device. In particular, the major driving force behind solution-processed zinc oxide film research is its prospective use in printing for electronics. A low-temperature process to improve the performance of solution-processed n-channel ZnO thin-film transistors (TFTs) fabricated via spin-coating and inkjet-printing is introduced here. ZnO nanoparticles were synthesized using a facile sonochemical method that was slightly modified based on a previously reported method. The influence of the annealing atmosphere on both nanoparticle-based TFT devices fabricated via spin-coating and those created via inkjet printing was investigated. For the inkjet-printed TFTs, the characteristics were improved significantly at an annealing temperature of 150 degrees C. The field effect mobility, V(th), and the on/off current ratios were 3.03 cm2/Vs, -3.3 V, and 10(4), respectively. These results indicate that annealing at 150 degrees C 1 h is sufficient to obtain a mobility (μ(sat)) as high as 3.03 cm2/Vs. Also, the active layer of the solution-based ZnO nanoparticles allowed the production of high-performance TFTs for low-cost, large-area electronics and flexible devices. PMID:25958581

  3. Growth and surface properties of boehmite nanofibers and nanotubes at low temperatures using a hydrothermal synthesis route.

    PubMed

    Zhao, Yanyan; Frost, Ray L; Martens, Wayde N; Zhu, Huai Yong

    2007-09-11

    The growth of boehmite nanostructures at low temperature using a soft chemistry route with and without (PEO) surfactant is presented. Remarkably long boehmite 1D nanotubes/nanofibers were formed within a significantly short time by changing the reaction mechanism of aluminum hydroxide. By using the PEO surfactant as a templating agent, boehmite nanotubes up to 170 nm in length with internal and external diameters of 2-5 and 3-7 nm, respectively, were formed at 100 degrees C. A slightly higher temperature (120 degrees C) resulted in the formation of lath-like nanofibers with an average length of 250 nm. Using the cationic surfactant CTAB, nanotubes rather than nanofibers were formed at 120 degrees C. Without surfactant, nanotubes counted for around 20% of the entire sample. A regular interval supply of fresh boehmite precipitate resulted in a larger crystallite size distribution of nanotubes. The morphology of nanotubes was more uniform in samples without the regular addition of aluminum hydroxide. Moreover, for the same hydrothermal time, the final nanotubes for nanomaterials without a regular interval supply of fresh aluminum hydroxide precipitate were longer than those with a regular aluminum hydroxide precipitate supply, which is in contrast to previously published results. Higher Al/PEO concentrations resulted in the formation of shorter nanotubes. A detailed characterization and mechanism are presented. PMID:17705405

  4. Transmission line pulse properties for a bidirectional transient voltage suppression diode fabricated using low-temperature epitaxy

    NASA Astrophysics Data System (ADS)

    Bouangeune, Daoheung; Cho, Deok-Ho; Yun, Hyung-Joong; Shim, Kyu-Hwan; Choi, Chel-Jong

    2015-01-01

    Based on low temperature epitaxy technology, a bidirectional transient voltage suppression (TVS) diode with abrupt multi-junctions was developed. The bidirectional triggering voltage of ±16 V was controlled by the thickness and dopant concentration in the multi-junctions using a reduced-pressure chemical vapor deposition (RPCVD) process. The manufactured TVS diode showed a small leakage current density and dynamic resistance of less than 5.1 × 10-14 A/ µm2 and 1 O, respectively, which could be associated with the epitaxially grown abrupt multijunctions. The transmission line pulse (TLP) analysis results demonstrated that the bidirectional TVS diodes were capable of withstanding a peak pulse current of up to ±20 A or ±1.02 × 10-3 A/ µm2, which is equivalent to ±40 kV of the human body model (HBM) and ±12 kV of IEC61000-4-2 (IEC). Nevertheless, the electrostatic discharge (ESD) design window showed that bidirectional TVS diodes meet IEC level 4 standard ESD protection requirements (8 kV in contact discharge). In addition, because of the bidirectional structure, the TVS devices exhibited a small capacitance of 4.9 pF, which confirms that the TVS diode can be used for protecting high data rate communication lines (over 500 Mbps) from ESD shock.

  5. Electronic Properties of the Prussian Blue Analog Co3[Os(CN6)]2 at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Wellington, T.; Ford, A.; Teizer, W.; Hilfiger, M.; Avendano, C.; Dunbar, K.

    2009-10-01

    The Prussian blue analog Co3[Os(CN6)]2 exhibits photoinduced changes of magnetic behavior as well as charge transfer induced spin transitions at low temperatures (5-10K). Magnetic measurements on the bulk material show an increased magnetic susceptibility after illumination with red light, as the analog exhibits an abrupt spin transition due to enhanced cooperativity. We are studying the electronic interactions between this Prussian blue analog and gold films of varying thickness at temperature 2K

  6. Impact of electron doping on thermoelectric properties in filled skutterudite IrSb3

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Kikkawa, A.; Tokura, Y.; Taguchi, Y.

    2016-04-01

    We investigated the variation in electronic, thermal, and thermoelectric properties of skutterudite IrSb3 upon filling the voids with alkaline (Na or K) or alkaline-earth atoms (Sr or Ba). Specific heat measurements revealed that the fillers donate electrons with high effective mass, which dominate the electric transport properties of the system. Vibrations associated with the filler additionally contribute to the specific heat, and also scatter phonons efficiently in conjunction with the static disorder, giving rise to the reduced thermal conductivity. The dimensionless thermoelectric figure of merit Z T increases with temperature and electron concentration, and reaches to 0.44 for Ba0.4Ir4Sb12 at 685 K. The observed features for the filled IrSb3 are similar to those of filled CoSb3, indicating that n -type filled skutterudite antimonides have a potential as good thermoelectric materials universally.

  7. Atomic-level cotrol of the thermoelectric properties in polytypoid nanowires

    SciTech Connect

    Andrews, Sean C.; Fardy, Melissa A.; Moore, Michael C.; Aloni, Shaoul; Zhang, Minjuan; Radmilovic, Velimir; Yang, Peidong

    2010-10-23

    Thermoelectric materials have generated interest as a means of increasing the efficiency of power generation through the scavenging of waste heat. Materials containing nanometer-sized structural and compositional features can exhibit enhanced thermoelectric performance due to the decoupling of certain electrical and thermal properties, but the extent to which these features can be controlled is often limited. Here we report a simple synthesis of M{sub 2}O{sub 3}(ZnO){sub n} (M = In, Ga, Fe) nanowires with controllable polytypoid structures, where the nanostructured features are tuned by adjusting the amount of metal precursor. After the introduction of nanometer-scale features (individual atomic layers and alloying), thermal and electrical measurements on single In{sub 2-x}Ga{sub x}O3(ZnO){sub n} nanowires reveal a simultaneous improvement in all contributing factors to the thermoelectric figure of merit, indicating successful modification of the nanowire transport properties.

  8. Optoelectronic Properties, Elastic Moduli and Thermoelectricity of SrAlGa: An Ab Initio Study

    NASA Astrophysics Data System (ADS)

    Roshan, Ali; Murtaza, G.; Takagiwa, Y.; Khenata, R.; Haleem, Uddin; Ullah, H.; A. Khan, S.

    2014-04-01

    Half-Heusler compounds are an impressive class of materials with a huge potential for different applications such as in future energy, especially in the fields of thermoelectrics and solar cells. We present ab initio total energy calculations within the modified Becke—Johnson generalized gradient approximation (mBJ-GGA) to obtain the physical properties of SrAlGa compounds. The structural, elastic, acoustic, electronic, chemical bonding, optical, and thermoelectric properties are calculated and compared with the available calculation data. The SrAlGa is found to be a small-band-gap (0.125-0.175 eV) material, suitable for thermoelectric applications with a relatively high Seebeck coefficient. Also, SrAlGa has the potential in the optoelectronic applications due to high optical conductivity and reflectivity in the infrared and visible region of electromagnetic spectra.

  9. Effects of Defects and Strain on Thermoelectric Properties of Single-walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Ohnishi, Masato; Shiga, Takuma; Shiomi, Junichiro

    Carbon nanotubes (CNTs) have attracted much attention as a thermoelectric material. Although CNTs have large lattice thermal conductivity, CNT-based composites are promising candidates for thermoelectric material because the phonon transport is suppressed by scattering at contacts between CNTs. Therefore, previous studies have mainly focused on thermoelectric properties at contacts between CNTs. However, understanding the effects of defects and strain on the thermoelectric properties of CNTs themselves are important because they exist inevitably in real systems. In this study, we study the effects of defects, vacancy and Stone-Wales defect, and uniaxial compressive strain on single-walled CNTs (SWNTs) employing nonequilibrium molecular dynamics simulation and Green's function method. We find that the defects and buckling deformation significantly decrease electron conductance, and the effect is much stronger than that on thermal conductivity and Seebeck coefficient, resulting in severe reduction of the figure of merit. In addition, the estimation of thermoelectric performance including a inter-SWNT contact indicates that the effect of defects and strain can deteriorate the figure of merit of the SWNT networks. This work is partially supported by Thermal Management Materials and Technology Research Association (TherMAT).

  10. Thermoelectric properties of Sr0.61Ba0.39Nb2O6-δ ceramics in different oxygen-reduction conditions

    NASA Astrophysics Data System (ADS)

    Li, Yi; Liu, Jian; Wang, Chun-Lei; Su, Wen-Bin; Zhu, Yuan-Hu; Li, Ji-Chao; Mei, Liang-Mo

    2015-04-01

    The thermoelectric properties of Sr0.61Ba0.39Nb2O6-δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ˜0.19 at 1073 K in the heaviest oxygen reduced sample. Project supported by the National Basic Research Program of China (Grant No. 2013CB632506) and the National Natural Science Foundation of China (Grant Nos. 51202132 and 51002087).

  11. Thermoelectric properties of a Mn substituted synthetic tetrahedrite.

    PubMed

    Chetty, Raju; D S, Prem Kumar; Rogl, Gerda; Rogl, Peter; Bauer, Ernst; Michor, Herwig; Suwas, Satyam; Puchegger, Stephan; Giester, Gerald; Mallik, Ramesh Chandra

    2015-01-21

    Tetrahedrite compounds Cu(12-x)Mn(x)Sb4S13 (0 ≤x≤ 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu10.6Mn1.4Sb4S13 was performed by single crystal X-ray diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I4[combining macron]3m) of a tetrahedrite. The large atomic displacement parameter of the Cu2 atoms was described by splitting the 12e site into a partially and randomly occupied 24g site (Cu22) in addition to the regular 12e site (Cu21), suggesting a mix of dynamic and static off-plane Cu2 atom disorder. Rietveld powder XRD pattern and electron probe microanalysis revealed that all the Mn substituted samples showed a single tetrahedrite phase. The electrical resistivity increased with increasing Mn due to substitution of Mn(2+) at the Cu(1+) site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. Even though the thermal conductivity decreased as a function of increasing Mn, the thermoelectric figure of merit ZT decreased, because the decrease of the power factor is stronger than the decrease of the thermal conductivity. The maximum ZT = 0.76 at 623 K is obtained for Cu12Sb4S13. The coefficient of thermal expansion 13.5 ± 0.1 × 10(-6) K(-1) is obtained in the temperature range from 460 K to 670 K for Cu10.2Mn1.8Sb4S13. The Debye temperature, Θ(D) = 244 K for Cu10.2Mn1.8Sb4S13, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 μB/f.u. for Cu10.2Mn1.8Sb4S13 is fairly consistent with a high spin 3d(5) ground state of Mn. PMID:25463306

  12. Low temperature magnetic properties and spin dynamics in single crystals of Cr{sub 8}Zn antiferromagnetic molecular rings

    SciTech Connect

    Adelnia, Fatemeh; Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano; Ghirri, Alberto; Candini, Andrea; Cervetti, Christian; Evangelisti, Marco; Affronte, Marco; Sheikin, Ilya; Winpenny, Richard; Timco, Grigore; Borsa, Ferdinando; and others

    2015-12-28

    A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr{sub 8}Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ{sub 0}H{sub c1} = 2.15 T is found to be an almost true LC while the second LC at μ{sub 0}H{sub c2} = 6.95 T has an anti-crossing gap of Δ{sub 12} = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ{sub 0}H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10{sup 10} rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.

  13. Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings

    NASA Astrophysics Data System (ADS)

    Adelnia, Fatemeh; Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano; Ghirri, Alberto; Candini, Andrea; Cervetti, Christian; Evangelisti, Marco; Affronte, Marco; Sheikin, Ilya; Winpenny, Richard; Timco, Grigore; Borsa, Ferdinando; Lascialfari, Alessandro

    2015-12-01

    A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ˜ 1010 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.

  14. Structural and Thermoelectric Properties of Tungsten Diselenide Crystals

    NASA Astrophysics Data System (ADS)

    Patel, K. K.; Patel, K. D.; Patel, Mayur; Patel, C. A.; Pathak, V. M.; Srivastava, R.

    2011-12-01

    Crystals of Tungsten diselenide (WSe2) have been grown by direct vapour transport (DVT) technique using micro processor controlled dual zone horizontal furnace. The chemical composition and structure of grown crystals were confirmed using energy dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD). In the present investigation thermoelectric power measurements (TEP) have been carried out on the grown crystals. Different electrical transport parameters of semiconductors have been determined and discussed in the paper.

  15. Tribological Properties of a Pennzane(Registered Trademark)-Based Liquid Lubricant (Disubstituted Alkylated Cyclopentane) for Low Temperature Space Applications

    NASA Technical Reports Server (NTRS)

    Venier, Clifford; Casserly, Edward W.; Jones, William R., Jr.; Marchetti, Mario; Jansen, Mark J.; Predmore, Roamer E.

    2002-01-01

    The tribological properties of a disubstituted alkylated cyclopentane, Pennzane (registered) Synthesized Hydrocarbon Fluid X-1000, are presented. This compound is a lower molecular weight version of the commonly used multiply alkylated cyclopentane, Pennzane X-2000, currently used in many space mechanisms. New, lower temperature applications will require liquid lubricants with lower viscosities and pour points and acceptable vapor pressures. Properties reported include: friction and wear studies and lubricated lifetime in vacuum; additionally, typical physical properties (i.e., viscosity-temperature, pour point, flash and fire point, specific gravity, refractive index, thermal properties, volatility and vapor pressure) are reported.

  16. Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties

    DOE PAGESBeta

    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,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

  17. 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.

  18. 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. PMID:24848359

  19. Optimization of the thermoelectric properties of FeNbSb-based half-Heusler materials

    NASA Astrophysics Data System (ADS)

    Li, Wenfeng; Yang, Gui; Zhang, Jianwei

    2016-05-01

    FeNbSb-based half-Heusler compounds have recently been reported as promising materials for good high-temperature thermoelectric materials with a ZT  >  1. Their electronic structure and thermoelectric properties are investigated based on a first-principles simulation and the semi-classical Boltzmann transport theory. The band structures show not only light and heavy bands but also high band degeneracy near the valence band maximum, which is beneficial for thermoelectric performance. The calculated Seebeck coefficients of p-type FeNbSb at high carrier concentrations exhibit the expected high values, which is consistent with experimental data. The evolution of the electrical conductivity and power factor with carrier concentration at different temperatures is investigated. Our results show that the thermoelectric performance of p-type FeNbSb can be improved by appropriate substitution; for example, by doping Hf on the Nb site, the maximum ZT of the p-type FeNb1‑x Hf x Sb can reach ~1.5 at 1200 K. This study can provide some theoretical guidance for experimental research to improve the thermoelectric performance of FeNbSb-based half-Heusler compounds.

  20. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds.

    PubMed

    Hong, A J; Li, L; He, R; Gong, J J; Yan, Z B; Wang, K F; Liu, J-M; Ren, Z F

    2016-01-01

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley's deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens' equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials. PMID:26947395

  1. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Hong, A. J.; Li, L.; He, R.; Gong, J. J.; Yan, Z. B.; Wang, K. F.; Liu, J.-M.; Ren, Z. F.

    2016-03-01

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.

  2. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds

    DOE PAGESBeta

    Hong, A. J.; Li, L.; He, R.; Gong, J. J.; Yan, Z. B.; Wang, K. F.; Liu, J. -M.; Ren, Z. F.

    2016-03-07

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half- Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k codemore » and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Tidoped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. Lastly, the present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.« less

  3. Full-scale computation for all the thermoelectric property parameters of half-Heusler compounds

    PubMed Central

    Hong, A. J.; Li, L.; He, R.; Gong, J. J.; Yan, Z. B.; Wang, K. F.; Liu, J. -M.; Ren, Z. F.

    2016-01-01

    The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials. PMID:26947395

  4. Thermoelectric Properties of Indium-Selenium Nanocomposites Prepared by Mechanical Alloying and Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Yim, Ju-Hyuk; Park, Hyung-Ho; Jang, Ho Won; Yoo, Myong-Jae; Paik, Dong-Su; Baek, SeungHyub; Kim, Jin-Sang

    2012-06-01

    Indium-selenium-based compounds have received much attention as thermoelectric materials since a high thermoelectric figure of merit of 1.48 at 705 K was observed in In4Se2.35. In this study, four different compositions of indium-selenium compounds, In2Se3, InSe, In4Se3, and In4Se2.35, were prepared by mechanical alloying followed by spark plasma sintering. Their thermoelectric properties such as electrical resistivity, Seebeck coefficient, and thermal conductivity were measured in the temperature range of 300 K to 673 K. All the In-Se compounds comprised nanoscaled structures and exhibited n-type conductivity with Seebeck coefficients ranging from -159 μV K-1 to -568 μV K-1 at room temperature.

  5. Transport properties of nanocomposite thermoelectric materials based on Si and Ge

    NASA Astrophysics Data System (ADS)

    Ovsyannikov, D. A.; Popov, M. Yu.; Buga, S. G.; Kirichenko, A. N.; Tarelkin, S. A.; Aksenenkov, V. V.; Tat'yanin, E. V.; Blank, V. D.

    2015-03-01

    The modification of transport properties (thermal conductivity, electrical conductivity, and See-beck coefficient) of nanostructured thermoelectrics based on Ge and Si-Ge with inclusions of the second phase has been investigated experimentally. In the Ge-C60 nanocomposite, modifying inclusions are the fullerene C60 located along the germanium grain boundaries and 1- to 5-nm SiC nanocrystals in the Si-Ge-SiC nanocomposite. In particular, the presence of these inclusions in the nanocomposite leads to an increase of the Seebeck coefficient in the temperature range above 600 K and, in general, to an increase in the thermoelectric figure of merit ZT by a factor of 1.5-2 as compared to the corresponding characteristics of nanostructured thermoelectrics based on Si-Ge without modifying inclusions of the second phase.

  6. Improvement of Bipolar Switching Properties of Gd:SiOx RRAM Devices on Indium Tin Oxide Electrode by Low-Temperature Supercritical CO2 Treatment

    NASA Astrophysics Data System (ADS)

    Chen, Kai-Huang; Chang, Kuan-Chang; Chang, Ting-Chang; Tsai, Tsung-Ming; Liang, Shu-Ping; Young, Tai-Fa; Syu, Yong-En; Sze, Simon M.

    2016-02-01

    Bipolar switching resistance behaviors of the Gd:SiO2 resistive random access memory (RRAM) devices on indium tin oxide electrode by the low-temperature supercritical CO2-treated technology were investigated. For physical and electrical measurement results obtained, the improvement on oxygen qualities, properties of indium tin oxide electrode, and operation current of the Gd:SiO2 RRAM devices were also observed. In addition, the initial metallic filament-forming model analyses and conduction transferred mechanism in switching resistance properties of the RRAM devices were verified and explained. Finally, the electrical reliability and retention properties of the Gd:SiO2 RRAM devices for low-resistance state (LRS)/high-resistance state (HRS) in different switching cycles were also measured for applications in nonvolatile random memory devices.

  7. Improvement of Bipolar Switching Properties of Gd:SiOx RRAM Devices on Indium Tin Oxide Electrode by Low-Temperature Supercritical CO2 Treatment.

    PubMed

    Chen, Kai-Huang; Chang, Kuan-Chang; Chang, Ting-Chang; Tsai, Tsung-Ming; Liang, Shu-Ping; Young, Tai-Fa; Syu, Yong-En; Sze, Simon M

    2016-12-01

    Bipolar switching resistance behaviors of the Gd:SiO2 resistive random access memory (RRAM) devices on indium tin oxide electrode by the low-temperature supercritical CO2-treated technology were investigated. For physical and electrical measurement results obtained, the improvement on oxygen qualities, properties of indium tin oxide electrode, and operation current of the Gd:SiO2 RRAM devices were also observed. In addition, the initial metallic filament-forming model analyses and conduction transferred mechanism in switching resistance properties of the RRAM devices were verified and explained. Finally, the electrical reliability and retention properties of the Gd:SiO2 RRAM devices for low-resistance state (LRS)/high-resistance state (HRS) in different switching cycles were also measured for applications in nonvolatile random memory devices. PMID:26831690

  8. Attaining Low Temperatures

    ERIC Educational Resources Information Center

    Wheatley, John D.; Van Till, Howard J.

    1970-01-01

    Discusses the definition of temperature and the concept of order in non-mathematical terms. Describes the cooling techniques necessary in low temperature physics research, including magnetic cooling, the use of the Pomeranchuk Effect, and dilution refrigeration. Outlines the types of phenomena observed in matter within various temperature ranges…

  9. Low temperature fluid blender

    NASA Technical Reports Server (NTRS)

    Repas, G. A.

    1971-01-01

    Blender supplies hydrogen at temperatures from 289 deg K to 367 deg K. Hydrogen temperature is controlled by using blender to combine flow from liquid hydrogen tank /276 deg K/ and gaseous hydrogen cylinder /550 deg K/. Blenders are applicable where flow of controlled low-temperature fluid is desired.

  10. Photo- and gas-tuned, reversible thermoelectric properties and anomalous photo-thermoelectric effects of platinum-loaded tungsten trioxide

    NASA Astrophysics Data System (ADS)

    Suzuki, Kenta; Watanabe, Takuya; Kakemoto, Hirofumi; Irie, Hiroshi

    2016-06-01

    We report the photo- and gas-controllable properties of platinum-loaded tungsten trioxide (Pt/WO3), which is of interest for developing practical applications of WO3 as well as for interpreting such phenomena from scientific viewpoints. Here, a Pt/WO3 thin film generated a thermoelectric power due to the ultraviolet-light-induced band-gap excitation (photochromic (PC) reaction) and/or dark storage in formic acid vapor (gaschromic (GC) reaction) in the absence of O2, resulting from the generation of W5+ ions. After such chromic reactions, the electrical conductivity (σ) is increased, whereas the absolute value of the Seebeck coefficient (S) is decreased. The changes in σ and S and their rate of change for consistency increased in the order of: during the PC reaction < during the GC reaction < during simultaneous PC and GC reactions. The opposite behaviors, a decrease in σ and an increase in S, were exhibited by Pt/WO3 in the presence of O2 after dark storage or visible-light irradiation. This reversible cycle could be repeated. Moreover, anomalous, nontrivial photo-thermoelectric effects (a photoconductive effect (photoconductivity, σphoto) and a photo-Seebeck effect (photo-Seebeck coefficient, Sphoto)) were also detected in response to the visible-light irradiation of Pt/WO3 in the absence of O2 after chromic reactions. Under visible-light irradiation, both σphoto and the absolute value of Sphoto are increased. After the irradiation, both values were decreased, that is, σ and the absolute value of S were smaller than σphoto and the absolute value of Sphoto, respectively. These effects are likely to be due to the photoinduced charge carriers and the accumulated electrons in Pt contributing to the increase in σphoto. In addition, electrons are extracted from the W5+ state, decreasing the number of W5+ in HxWO3 and thus contributing to the increase in Sphoto. After light irradiation, the accumulated electrons in Pt are returned to the energetically favorable W

  11. Structural and optical properties of Ag-doped copper oxide thin films on polyethylene napthalate substrate prepared by low temperature microwave annealing

    SciTech Connect

    Das, Sayantan; Alford, T. L.

    2013-06-28

    Silver doped cupric oxide thin films are prepared on polyethylene naphthalate (flexible polymer) substrates. Thin films Ag-doped CuO are deposited on the substrate by co-sputtering followed by microwave assisted oxidation of the metal films. The low temperature tolerance of the polymer substrates led to the search for innovative low temperature processing techniques. Cupric oxide is a p-type semiconductor with an indirect band gap and is used as selective absorption layer solar cells. X-ray diffraction identifies the CuO phases. Rutherford backscattering spectrometry measurements confirm the stoichiometry of each copper oxide formed. The surface morphology is determined by atomic force microscopy. The microstructural properties such as crystallite size and the microstrain for (-111) and (111) planes are calculated and discussed. Incorporation of Ag led to the lowering of band gap in CuO. Consequently, it is determined that Ag addition has a strong effect on the structural, morphological, surface, and optical properties of CuO grown on flexible substrates by microwave annealing. Tauc's plot is used to determine the optical band gap of CuO and Ag doped CuO films. The values of the indirect and direct band gap for CuO are found to be 2.02 eV and 3.19 eV, respectively.

  12. Annealing effects on the optical and morphological properties of ZnO nanorods on AZO substrate by using aqueous solution method at low temperature

    PubMed Central

    2014-01-01

    Vertically aligned ZnO nanorods (NRs) on aluminum-doped zinc oxide (AZO) substrates were fabricated by a single-step aqueous solution method at low temperature. In order to optimize optical quality, the effects of annealing on optical and structural properties were investigated by scanning electron microscopy, X-ray diffraction, photoluminescence (PL), and Raman spectroscopy. We found that the annealing temperature strongly affects both the near-band-edge (NBE) and visible (defect-related) emissions. The best characteristics have been obtained by employing annealing at 400°C in air for 2 h, bringing about a sharp and intense NBE emission. The defect-related recombinations were also suppressed effectively. However, the enhancement decreases with higher annealing temperature and prolonged annealing. PL study indicates that the NBE emission is dominated by radiative recombination associated with hydrogen donors. Thus, the enhancement of NBE is due to the activation of radiative recombinations associated with hydrogen donors. On the other hand, the reduction of visible emission is mainly attributed to the annihilation of OH groups. Our results provide insight to comprehend annealing effects and an effective way to improve optical properties of low-temperature-grown ZnO NRs for future facile device applications. PMID:25520589

  13. 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.

  14. Thermoelectric properties of silicene in the topological- and band-insulator states

    NASA Astrophysics Data System (ADS)

    Wierzbicki, Michał; Barnaś, Józef; Swirkowicz, Renata

    2015-04-01

    Thermoelectric effects in silicene nanoribbons are analyzed theoretically and numerically. The main focus is on the influence of topological edge states and transition between the topological-insulator and conventional gap-insulator states on the thermoelectric properties, and especially on the spin-related thermoelectric effects. The model includes a staggered exchange field and also an external electric field normal to the atomic plane. Both fields separately open a gap in the edge states and therefore lead to a nonzero thermopower in the vicinity of the gap edges. Interplay of both fields leads to a spin-dependent gap, and thus gives rise to a spin thermopower in addition to the conventional Seebeck effect. The role of the Coulomb interaction taken in the form of the Hubbard term in the mean-field approximation is also analyzed. This interaction leads to antiparallel configuration of the edge magnetic moments in the ground state. It is shown that the Coulomb interaction significantly modifies topological properties of the materials, and thus also their transport and thermoelectric properties.

  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. Thermoelectric properties of Mg2Si-based compounds synthesized partially using magnesium alloy

    NASA Astrophysics Data System (ADS)

    Itoh, Takashi; Hagio, Kento

    2012-06-01

    Mg2Si compounds are promising eco-friendly thermoelectric materials because both constituent elements of Mg and Si have no toxicity and exist richly in earth crust. We have a plan to use the compounds in the applications that convert waste heat in the temperature range (600-900 K) into electric power. However, the thermoelectric performance of the compounds has not yet reached to the practical use level. In addition, the compounds don't have durability in the thermoelectric performance under atmospheric circumstances in the temperature range of 750-900 K. These issues have to be solved for the practical use. In our previous work, we obtained knowledge that Al doping in Mg2Si lower the electrical resistivity and improved the thermoelectric performance. We newly attempted to use a magnesium alloy (AZ61) that includes the main three elements of aluminum (5.8-7.2 wt%), zinc (0.4-1.5 wt%) and manganese (0.15-0.35 wt%) in order to synthesize the Mg2Si-based compounds. The Mg2Si-based compound powders were synthesized from the mixture of silicon powder, AZ61 chips and Mg powder by the liquid-solid phase reaction method. The compound powders were sintered by the pulse discharge sintering method. The influence of mixing ratio of two metals of AZ61 and pure Mg on the thermoelectric properties was investigated. Addition of AZ61 greatly decreased the electrical resistivity as well as Al-doped Mg2Si and the thermoelectric performance had improved most in the 50wt%AZ61 sample.

  17. Low temperature benefits discussed.

    PubMed

    2016-03-01

    At a recent educational workshop event hosted by Advanced Sterilization Products, expert speakers including Authorising Engineers, and delegates, discussed some of their experiences of low temperature sterilisation of 'hi-tech' medical devices, and highlighted the benefits of a process which allows decontamination of instruments and, for example, parts of robotic surgery systems, that cannot be decontaminated using standard methods. Also examined,and reported on here in an article that first appeared in HEJ's sister publication, The Clinical Services Journal, were some of the disadvantages of low temperature sterilisation, the key considerations and options when choosing such a system, and a focus on how the technology's use had benefited a major London-based NHS Trust. PMID:27132304

  18. Diameter dependent thermoelectric properties of individual SnTe nanowires

    DOE PAGESBeta

    Xu, E. Z.; Li, Z.; Martinez, J. A.; Sinitsyn, N.; Htoon, H.; Li, Nan; Swartzentruber, B.; Hollingsworth, J. A.; Wang, Jian; Zhang, S. X.

    2015-01-15

    The lead-free compound tin telluride (SnTe) has recently been suggested to be a potentially promising thermoelectric material because of its similar electronic band structure as the well-known lead telluride. Here we report on the first thermoelectric study of individual single crystalline SnTe nanowires (NWs) with different diameters ranging from ~200 to ~1000 nm. Measurements of thermopower S, electrical conductivity σ, and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25 - 300 K. While σ does not show a strong diameter dependence, the thermopower increases by a factor of 2 when the nanowiremore » diameter is decreased from 1000 nm to 200 nm. The thermal conductivities of the measured NWs are only about half of that of the bulk SnTe, which may arise from the enhanced phonon-grain boundary and phonon-defect scatterings. Temperature dependent figure-of-merit ZT was determined and the maximum value at room temperature is ~3 times higher than what was obtained in bulk samples of comparable carrier density.« less

  19. Diameter dependent thermoelectric properties of individual SnTe nanowires

    SciTech Connect

    Xu, E. Z.; Li, Z.; Martinez, J. A.; Sinitsyn, N.; Htoon, H.; Li, Nan; Swartzentruber, B.; Hollingsworth, J. A.; Wang, Jian; Zhang, S. X.

    2015-01-15

    The lead-free compound tin telluride (SnTe) has recently been suggested to be a potentially promising thermoelectric material because of its similar electronic band structure as the well-known lead telluride. Here we report on the first thermoelectric study of individual single crystalline SnTe nanowires (NWs) with different diameters ranging from ~200 to ~1000 nm. Measurements of thermopower S, electrical conductivity σ, and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25 - 300 K. While σ does not show a strong diameter dependence, the thermopower increases by a factor of 2 when the nanowire diameter is decreased from 1000 nm to 200 nm. The thermal conductivities of the measured NWs are only about half of that of the bulk SnTe, which may arise from the enhanced phonon-grain boundary and phonon-defect scatterings. Temperature dependent figure-of-merit ZT was determined and the maximum value at room temperature is ~3 times higher than what was obtained in bulk samples of comparable carrier density.

  20. Diameter dependent thermoelectric properties of individual SnTe nanowires.

    PubMed

    Xu, E Z; Li, Z; Martinez, J A; Sinitsyn, N; Htoon, H; Li, Nan; Swartzentruber, B; Hollingsworth, J A; Wang, Jian; Zhang, S X

    2015-02-21

    The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ∼218 to ∼913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25-300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ∼913 nm to ∼218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density. PMID:25623253

  1. Low-temperature elastic properties of Sr3NbGa3Si2O14 single crystals

    NASA Astrophysics Data System (ADS)

    Sotnikov, A. V.; Smirnova, E. P.; Schmidt, H.; Weihnacht, M.

    2015-06-01

    The elastic properties of new piezoelectric Sr3NbGa3Si2O14 crystals of the langasite (lanthanum gallium silicate) family have been investigated. The temperature dependences of the elastic constants C 11, C 33, C 66, and C 44 have been measured in a wide temperature range from 300 to 4.2 K. The characteristic parameters of the crystal associated with the Einstein temperature and the Grüneisen parameter have been estimated at cryogenic temperatures. It has been shown that the piezoelectric activity of the crystal remains almost unchanged with a decrease in temperature from 300 to 4.2 K.

  2. Effects of low-temperature fusion neutron irradiation on critical properties of a monofilament niobium-tin superconductor

    SciTech Connect

    Guinan, M.W.; Van Konynenburg, R.A.; Mitchell, J.B.

    1984-03-22

    The objective of this work was to irradiate a Nb/sub 3/Sn superconductor with 14.8 MeV neutrons at 4 K and measure critical current in transverse fields of up to 12 T, irradiating up to a fluence sufficient to decrease the critical current to below its initial value. Critical temperatures were also to be measured. The samples were to be kept near 4 K between the irradiation and the measurement of critical properties. This work is directed toward establishing an engineering design fluence limit for Nb/sub 3/Sn when used in fusion reactor superconducting magnets.

  3. Thermoelectric Properties of n-type SnSe Single Crystal

    NASA Astrophysics Data System (ADS)

    Nguyen, Phuong; Duong, Anh Tuan; Rhim, S. H.; Nguyen, Van Quang; Duong, Van Thiet; Shin, Yooleemi; Cho, Sunglae; Kwon, Suyong; Song, Jae Yong; Park, Hyun Min

    Although thermoelectric materials are well known for their reliability and have been used for many years, even in the field of space engineering, their performance is quite small due to low energy conversion efficiency. Dimensionless figure of merit, ZT = S2. σ.T.κ-1 (where S, σ, T, κ are Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity, respectively) is conveniently used to evaluate the conversion efficiency of a thermoelectric materials. Recently, the highest value of ZT to date has been reported for single crystal SnSe, ZT = 2.6 along the b axis of unit cell at 923 K. This temperature is rather high and the range of temperature for high reported ZT is quite narrow. Here we report an attempt to modify the thermoelectric properties of SnSe by using group V and VII as n-type dopant. A negative value of Seebeck coefficient was observed and the power factor reached a peak of 10 μW.K-2.cm-1 at around 600 K. The maximum n-type ZT was 0.57 at 650 K. We will discuss on dopant dependent thermoelectric properties of n-type SnSe single crystals.

  4. Influence of Sedimentation of Atoms on Structural and Thermoelectric Properties of Bi-Sb Alloys

    NASA Astrophysics Data System (ADS)

    Januszko, Kamila; Stabrawa, Artur; Ogata, Yudai; Tokuda, Makoto; Khandaker, Jahirur Islam; Wojciechowski, Krzysztof; Mashimo, Tsutomu

    2016-03-01

    Functionally graded thermoelectric materials (FGTMs) have been prepared by sedimentation of atoms under a strong gravitational field. Starting samples of Bi x Sb1- x alloys with different composition x were synthesized by melting of metals and subsequent annealing of quenched samples. The thermoelectric properties (Seebeck coefficient, electrical conductivity) of the starting materials were characterized over the temperature range from 300 K to 525 K. Strong gravity experiments were performed in a unique ultracentrifuge apparatus under acceleration of over 0.5 × 106 G at temperatures of 538 K and 623 K. Changes of the microstructure and chemical composition were analyzed using scanning electron microscopy with energy-dispersive x-ray spectroscopy analysis. The distribution of the Seebeck coefficient of the Bi-Sb alloys was characterized by scanning thermoelectric microprobe. As a result of sedimentation, large changes in chemical composition ( x = 0.45 to 1) were obtained. It was found that the changes in chemical composition were correlated with alterations of the Seebeck coefficient. The obtained experimental data allowed the development of a semiempirical model for the selection of optimal processing parameters for preparation of Bi-Sb alloys with required thermoelectric properties.

  5. Thermoelectric Properties and Thermal Stability of BiCuSeO

    NASA Astrophysics Data System (ADS)

    Sato, Toshiharu; Kohri, Hitoshi; Yagasaki, Takayoshi

    2016-07-01

    Although BiCuSeO has become of interest as a high performance thermoelectric material, it has been reported to be unstable in air above 548 K. However, the details of the thermal degradation of BiCuSeO have not yet been determined. In this study, the time dependence of the thermoelectric properties of BiCuSeO at 550 K was assessed along with the accompanying thermal degradation behavior. Variations in ρ and α over time at 550 K were determined using the direct current four-terminal method and small temperature difference method, respectively. In addition, the crystalline phases of the specimen after thermoelectric measurements were identified by x-ray diffraction (XRD) analysis, and the surface chemical states were analyzed by x-ray photoelectron spectroscopy (XPS). The results of thermoelectric property measurements over time showed that ρ abruptly increased between 135 min and 182 min then decreased from 182 min to 210 min, while the value of α exhibited the opposite trend. XPS and XRD data suggested that BiCuSeO was pyrolyzed upon heating at 550 K for 6 h in air. In contrast, thermogravimetric analysis demonstrated that BiCuSeO was stable below 800 K under inert gas flow, thus the pyrolysis observed at 550 K was the result of reaction with atmospheric oxygen.

  6. Good Low-Temperature Properties of Nitrogen-Enriched Porous Carbon as Sulfur Hosts for High-Performance Li-S Batteries.

    PubMed

    Zhu, Shaoyin; Wang, Yanqing; Jiang, Jicheng; Yan, Xiao; Sun, Deye; Jin, Yongcheng; Nan, Cewen; Munakata, Hirokazu; Kanamura, Kiyoshi

    2016-07-13

    Despite the increased attention devoted to exploring cathode construction based on various nitrogen-enriched carbon scaffolds at room temperature, the low-temperature behaviors of Li-S cathodes have yet to be studied. Herein, we demonstrate the good low-temperature electrochemical performances of nitrogen-enriched carbon/sulfur composite cathodes. Electrochemical evaluation indicates that a reversible capacity of 368 mAh g(-1) (0.5 C) over 100 cycles is achieved at -20 °C. After returning to 25 °C, a capacity of 620 mAh g(-1) (0.5 C) is achieved over 350 cycles with a low-capacity attenuation rate (0.071% per cycle) and an initial capacity of 1151 mAh g(-1) (0.1C). This positive electrochemical property was speculated to result from the good surface chemistry of the various amine groups in the nitrogen-enriched carbon materials with enhanced polysulfide immobilization. PMID:27320408

  7. Impact of low temperature annealing on structural, optical, electrical and morphological properties of ZnO thin films grown by RF sputtering for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Purohit, Anuradha; Chander, S.; Sharma, Anshu; Nehra, S. P.; Dhaka, M. S.

    2015-11-01

    This paper presents effect of low temperature annealing on the physical properties of ZnO thin films for photovoltaic applications. The thin films of thickness 50 nm were grown on glass and indium tin oxide (ITO) coated glass substrates employing radio frequency magnetron sputtering technique followed by thermal annealing within low temperature range 150-450 °C. These as-grown and annealed films were subjected to the X-ray diffraction (XRD), UV-Vis spectrophotometer, source meter and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of the as-grown ZnO film was also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the films have wurtzite structure of hexagonal phase with preferred orientation (1 0 0) and polycrystalline in nature. The crystallographic and optical parameters are calculated and discussed in detail. The optical band gap was found in the range 3.30-3.52 eV and observed to decrease with annealing temperature except 150 °C. The current-voltage characteristics show that the films exhibit approximately ohmic behavior. The SEM studies show that the films are uniform, homogeneous and free from crystal defects and voids. The experimental results reveal that ZnO thin films may be used as alternative materials for eco-friendly buffer layer to the thin film solar cell applications.

  8. Thermoelectric and mechanical properties of multi-walled carbon nanotube doped Bi0.4Sb1.6Te3 thermoelectric material

    NASA Astrophysics Data System (ADS)

    Ren, Fei; Wang, Hsin; Menchhofer, Paul A.; Kiggans, James O.

    2013-11-01

    Since many thermoelectrics are brittle in nature with low mechanical strength, improving their mechanical properties is important to fabricate devices such as thermoelectric power generators and coolers. In this work, multiwalled carbon nanotubes (CNTs) were incorporated into polycrystalline Bi0.4Sb1.6Te3 through powder processing, which increased the flexural strength from 32 MPa to 90 MPa. Electrical and thermal conductivities were both reduced in the CNT containing materials, leading to unchanged figure of merit. Dynamic Young's and shear moduli of the composites were lower than the base material, while the Poisson's ratio was not affected by CNT doping.

  9. Thermoelectric and mechanical properties of multi-wall carbon nanotube doped Bi0.4Sb1.6Te3 thermoelectric material

    SciTech Connect

    Ren, Fei; Wang, Hsin; Menchhofer, Paul A; Kiggans, Jim

    2013-01-01

    Since many thermoelectrics are brittle in nature with low mechanical strength, improving their mechanical properties is important in fabrication of devices such as thermoelectric power generators and coolers. In this work, multiwall carbon nanotubes (CNTs) were incorporated into polycrystalline Bi0.4Sb1.6Te3 through powder processing, which increased the flexural strength from 32 MPa to 90 MPa. Electrical and thermal conductivities were both reduced in the CNT containing materials, leading to unchanged figure of merit. Dynamic Young s modulus and shear modulus of the composites were lower than the base material, which is likely related to the grain boundary scattering due to the CNTs.

  10. Low temperature synthesis of diamond-based nano-carbon composite materials with high electron field emission properties

    SciTech Connect

    Saravanan, A.; Huang, B. R.; Yeh, C. J.; Leou, K. C.; Lin, I. N.

    2015-06-08

    A diamond-based nano-carbon composite (d/NCC) material, which contains needle-like diamond grains encased with the nano-graphite layers, was synthesized at low substrate temperature via a bias enhanced growth process using CH{sub 4}/N{sub 2} plasma. Such a unique granular structure renders the d/NCC material very conductive (σ = 714.8 S/cm), along with superior electron field emission (EFE) properties (E{sub 0} = 4.06 V/μm and J{sub e} = 3.18 mA/cm{sup 2}) and long lifetime (τ = 842 min at 2.41 mA/cm{sup 2}). Moreover, the electrical conductivity and EFE behavior of d/NCC material can be tuned in a wide range that is especially useful for different kind of applications.

  11. Synthesis and properties of boron doped ZnO nanorods on silicon substrate by low-temperature hydrothermal reaction

    NASA Astrophysics Data System (ADS)

    Yu, Qi; Li, Liuan; Li, Hongdong; Gao, Shiyong; Sang, Dandan; Yuan, Jujun; Zhu, Pinwen

    2011-05-01

    Boron doped ZnO nanorods were fabricated by hydrothermal technique on silicon substrate covered with a ZnO seed layer. It is found that the concentration of boric acid in the reaction solution plays a key role in varying the morphology and properties of the products. The growth rate along the [0 0 0 1] orientation (average size in diameter) of the doped ZnO nanorods decreased (increased) with the increase of boric acid concentration. Based on the results of XRD, EDX and XPS, it is demonstrated that the boron dopants tend to occupy the octahedral interstice sites. The photoluminescence of the ZnO nanorods related to boron doping are investigated.

  12. Effect of Al3+ ion addition on the magnetic properties of cobalt ferrite at moderate and low temperatures

    NASA Astrophysics Data System (ADS)

    Zaki, H. M.; Al-Heniti, Saleh. H.; Hashhash, A.

    2016-03-01

    The magnetic properties of aluminum-substituted cobalt ferrite, with the chemical formula CoAlxFe2-xO4, were investigated and synthesized using co-precipitation method. A coherent correlation between the saturation magnetization and aluminum concentration was observed. An increase in aluminum content lead to a decrease of coercivity (HC) retentivity (MR) and saturation magnetization (MS). According to the growth in the sub spectral areas obtained by Mössbauer spectroscopy, it was estimated that the agreeable ferric ions belong essentially to the site B, where the Mössbauer portion of site A does not vary appreciably. The dependence of Mössbauer parameters on hyperfine magnetic field, isomer shift and quadruple splitting on aluminum ions content were discussed.

  13. Simultaneous control of thermoelectric properties in p- and n-type materials by electric double-layer gating: New design for thermoelectric device

    NASA Astrophysics Data System (ADS)

    Takayanagi, Ryohei; Fujii, Takenori; Asamitsu, Atsushi

    2015-05-01

    We report a novel design of a thermoelectric device that can control the thermoelectric properties of p- and n-type materials simultaneously by electric double-layer gating. Here, p-type Cu2O and n-type ZnO were used as the positive and negative electrodes of the electric double-layer capacitor structure. When a gate voltage was applied between the two electrodes, holes and electrons accumulated on the surfaces of Cu2O and ZnO, respectively. The thermopower was measured by applying a thermal gradient along the accumulated layer on the electrodes. We demonstrate here that the accumulated layers worked as a p-n pair of the thermoelectric device.

  14. La 1−x Ca x MnO3 semiconducting nanostructures: morphology and thermoelectric properties

    PubMed Central

    2014-01-01

    Semiconducting metallic oxides, especially perosvkite materials, are great candidates for thermoelectric applications due to several advantages over traditionally metallic alloys such as low production costs and high chemical stability at high temperatures. Nanostructuration can be the key to develop highly efficient thermoelectric materials. In this work, La 1−x Ca x MnO3 perosvkite nanostructures with Ca as a dopant have been synthesized by the hydrothermal method to be used in thermoelectric applications at room temperature. Several heat treatments have been made in all samples, leading to a change in their morphology and thermoelectric properties. The best thermoelectric efficiency has been obtained for a Ca content of x=0.5. The electrical conductivity and Seebeck coefficient are strongly related to the calcium content. PMID:25206315

  15. Low-temperature precipitation synthesis of flower-like ZnO with lignin amine and its optical properties

    PubMed Central

    2013-01-01

    A facile precipitation method has been developed to synthesize ZnO with [bis(2-aminoethyl)amino]methyl lignin (lignin amine) that is chemically modified from low-cost pulp industrial lignin. The obtained ZnO crystallites have been characterized to exhibit a hexagonal wurtzite structure, and their sizes have been determined at ca. 24 nm (mean value). These ZnO nanocrystallites are of high purity and well crystallized. Our present synthetic approach apparently exempts the commonly used calcining purification procedure. It is found that the morphology of ZnO and its specific surface area are capable of being tuned by varying the added lignin amine amount. Using the optimal 10 mL lignin amine, the synthesized ZnO exhibits flower-like morphology with proper specific surface area. Additionally, photoluminescence property of the obtainable ZnO displays two emissive bands at 383 nm (sharp) and in the range of 480 to 600 nm (broad) at room temperature. Their intensities were revealed to depend on the added lignin amine amount as well as on the molar ratio of Zn2+/OH-. The present investigation demonstrates that our method is simple, eco-friendly, and cost-effective for the synthesis of small-size ZnO materials. PMID:24134715

  16. Low-temperature precipitation synthesis of flower-like ZnO with lignin amine and its optical properties.

    PubMed

    Miao, Ting-Ting; Sun, Dong-Xiao; Guo, Yuan-Ru; Li, Chuan; Ma, Yan-Li; Fang, Gui-Zhen; Pan, Qing-Jiang

    2013-01-01

    A facile precipitation method has been developed to synthesize ZnO with [bis(2-aminoethyl)amino]methyl lignin (lignin amine) that is chemically modified from low-cost pulp industrial lignin. The obtained ZnO crystallites have been characterized to exhibit a hexagonal wurtzite structure, and their sizes have been determined at ca. 24 nm (mean value). These ZnO nanocrystallites are of high purity and well crystallized. Our present synthetic approach apparently exempts the commonly used calcining purification procedure. It is found that the morphology of ZnO and its specific surface area are capable of being tuned by varying the added lignin amine amount. Using the optimal 10 mL lignin amine, the synthesized ZnO exhibits flower-like morphology with proper specific surface area. Additionally, photoluminescence property of the obtainable ZnO displays two emissive bands at 383 nm (sharp) and in the range of 480 to 600 nm (broad) at room temperature. Their intensities were revealed to depend on the added lignin amine amount as well as on the molar ratio of Zn2+/OH-. The present investigation demonstrates that our method is simple, eco-friendly, and cost-effective for the synthesis of small-size ZnO materials. PMID:24134715

  17. Low-temperature precipitation synthesis of flower-like ZnO with lignin amine and its optical properties

    NASA Astrophysics Data System (ADS)

    Miao, Ting-Ting; Sun, Dong-Xiao; Guo, Yuan-Ru; Li, Chuan; Ma, Yan-Li; Fang, Gui-Zhen; Pan, Qing-Jiang

    2013-10-01

    A facile precipitation method has been developed to synthesize ZnO with [bis(2-aminoethyl)amino]methyl lignin (lignin amine) that is chemically modified from low-cost pulp industrial lignin. The obtained ZnO crystallites have been characterized to exhibit a hexagonal wurtzite structure, and their sizes have been determined at ca. 24 nm (mean value). These ZnO nanocrystallites are of high purity and well crystallized. Our present synthetic approach apparently exempts the commonly used calcining purification procedure. It is found that the morphology of ZnO and its specific surface area are capable of being tuned by varying the added lignin amine amount. Using the optimal 10 mL lignin amine, the synthesized ZnO exhibits flower-like morphology with proper specific surface area. Additionally, photoluminescence property of the obtainable ZnO displays two emissive bands at 383 nm (sharp) and in the range of 480 to 600 nm (broad) at room temperature. Their intensities were revealed to depend on the added lignin amine amount as well as on the molar ratio of Zn2+/OH-. The present investigation demonstrates that our method is simple, eco-friendly, and cost-effective for the synthesis of small-size ZnO materials.

  18. Electromagnetic properties of microwave sintered ferromagnetic-ferroelectric composites for application in low temperature co-fired ceramic devices

    SciTech Connect

    Yang Qinghui; Zhang Huaiwu; Wen Qiye; Liu Yingli

    2011-04-01

    In this paper, microwave sintering (MS) technology has been applied in the preparation of ferromagnetic-ferroelectric composites. Several kinds of (Ni{sub 0.3}Zn{sub 0.6}Cu{sub 0.1})Fe{sub 2}O{sub 4} (NiCuZn) ferrite with different contents of BaTiO{sub 3}(BT) have been fabricated by MS technology. We found that the sintering time and temperature were significantly reduced from 22 h and 1100 deg. C for the conventional sintering (CS) process to 2 h and 840 deg. C for MS process, respectively. Experiments show that MS treated NiCuZn-BT composites possess both excellent ferromagnetic and ferroelectric properties. For the composites of NiCuZn added with 15% BaTiO{sub 3}, the real part of permittivity is larger than 50 below 20 MHz and the real part of dielectric constant is larger than 18 below 1 GHz. Our results indicate that the microwave sintering method is a potential important technique in LTCC technology.

  19. Low Temperature Magnetic Properties of the Late Archean Boolgeeda Iron Formation (Hamersley Group, Western Australia): Environmental Implications

    NASA Astrophysics Data System (ADS)

    Carlut, Julie; Isambert, Aude; Bouquerel, Hélène; Pecoits, Ernesto; Philippot, Pascal; Vennin, Emmanuelle; Ader, Magali; Thomazo, Christophe; Buoncristiani, Jean-François; Baton, Franck; Muller, Elodie; Deldicque, Damien

    2015-05-01

    The origin of the iron oxides in Archean and Paleoproterozoic Banded Iron Formations is still a debated question. We report low and high temperature magnetic properties, susceptibility and saturation magnetization results joined with scanning microscope observations within a 35 meters section of the Late Archean Boolgeeda Iron Formation of the Hamersley Group, Western Australia. With the exception of two volcanoclastic intervals characterized by low susceptibility and magnetization, nearly pure magnetite is identified as the main magnetic carrier in all iron-rich layers including hematite-rich jasper beds. Two populations of magnetically distinct magnetites are reported from a 2 meter-thick interval within the section. Each population shows a specific Verwey transition temperature: one around 120-124 K and the other in the range of 105-110 K. This temperature difference is interpreted to reflect two distinct stoichiometry and likely two episodes of crystallization. The 120-124K transition is attributed to nearly pure stoichiometric magnetite, SEM and microprobe observations suggest that the lower temperature transition is related to chemically impure silician magnetite. Microbial-induced partial substitution of iron by silicon is suggested here. This is supported by an increase in Total Organic Carbon (TOC) in the same interval.

  20. Low-temperature anomalies in the magnetic and thermal properties of molecular cryocrystals doped with oxygen impurity

    NASA Astrophysics Data System (ADS)

    Freiman, Yu. A.; Tretyak, S. M.; JeŻowski, A.

    2000-09-01

    The magnetic properties of oxygen pair clusters are investigated theoretically for different cluster geometries which can be realized by doping molecular cryomatrices with oxygen. Anomalous temperature and pressure behavior of the magnetic susceptibility, heat capacity, and entropy is predicted. It is proposed to use these anomalies for studying the parameters characterizing the oxygen clusters and the parameters of the host matrix: the effective spin-figure interaction constant D for the molecule in the matrix, the exchange parameter J, and the number of pair clusters Np, which can deviate markedly from the purely random value Np=6Nc2 (N is Avogadro's number, and c is the molar concentration of the impurity). The data on the magnetic susceptibility may be used to analyze the character of the positional and orientational short-range order in the solid solution. The value of D contains information about the orientational order parameter; the distance and angular dependence of the exchange interaction parameter are still subject to discussion in the literature. The temperature dependence of Np contains information about diffusion and clusterization processes in the system.

  1. Thermoelectric and thermodynamic properties of half-Heulser alloy YPdSb from first principles calculations

    NASA Astrophysics Data System (ADS)

    Kong, Fanjie; Hu, Yanfei; Hou, Haijun; Liu, Yanhua; Wang, Baolin; Wang, Lili

    2012-12-01

    The structural, electronic, thermoelectric and thermodynamic properties of ternary half-Heusler compound YPdSb are investigated using the first principle calculations. It is found that YPdSb is an indirect semiconductor. The calculated band gap is 0.161 eV with spin-orbital coupling including and 0.235 eV without spin-orbital coupling including, respectively. The electronic transport properties are obtained via Boltzman transport theory. The predicted Seebeck coefficient is 240 μV/K and the thermoelectric performance can be optimized by n-type doping at room temperature. Moreover, the lattice dynamical results regarding the phonon dispersion curves, phonon density of states and thermodynamic properties are reported. Thermodynamics (heat capacity and Debye temperature) as well as mean phonon free path and the thermal conductivity in a temperature range of 0-300 K are determined.

  2. Low temperature phase properties of water confined in mesoporous silica MCM-41: Thermodynamic and neutron scattering study

    NASA Astrophysics Data System (ADS)

    Kittaka, Shigeharu; Takahara, Shuichi; Matsumoto, Hideyuki; Wada, Yasuki; Satoh, Taku J.; Yamaguchi, Toshio

    2013-05-01

    The phase properties of water confined in mesoporous silica MCM-41 were investigated over a temperature range of 100-298 K as a function of pore size by specific heat capacity and inelastic neutron scattering (INS) measurements. The water content of the samples was carefully controlled to ensure the capillary filled state and no overloading of water. The values of heat capacity of the pore water are higher than those of bulk ice and liquid water over the whole temperature range measured. The contribution of water in the inner part of pores (abbreviated as the internal water) was elucidated by using the heat capacity data of monolayer water measured. The entropy of the internal water was then estimated from integration of the heat capacity of the internal water. The entropy values of the internal water increase by confinement in the pores of MCM-41 in both liquid and frozen regions, indicating an increase in the deformation of the structure and/or a change in the dynamics in both regions. The INS spectra show the density of states for the librational motion of water frozen at 50 K, suggesting that the confined water is similar to amorphous ice rather than to crystalline ice. When the sample is warmed to melt, the band edge of the librational motion for water frozen in large pores (diameter of 3.6 nm) shifts to a lower energy side, indicating the weakening of intermolecular hydrogen bonds. For water in small pores (2.1 nm), on the contrary, the librational band shifts slightly to a higher energy side, suggesting the low density liquid to high density liquid transition (L-L transition) at 225-250 K. A plausible mechanism of the L-L transition of water in confinement is proposed in terms of incomplete growth of homogeneous nucleation of ice due to an interfacial free energy effect to inhibit crystallization of water confined in small pores.

  3. Low temperature phase properties of water confined in mesoporous silica MCM-41: thermodynamic and neutron scattering study.

    PubMed

    Kittaka, Shigeharu; Takahara, Shuichi; Matsumoto, Hideyuki; Wada, Yasuki; Satoh, Taku J; Yamaguchi, Toshio

    2013-05-28

    The phase properties of water confined in mesoporous silica MCM-41 were investigated over a temperature range of 100-298 K as a function of pore size by specific heat capacity and inelastic neutron scattering (INS) measurements. The water content of the samples was carefully controlled to ensure the capillary filled state and no overloading of water. The values of heat capacity of the pore water are higher than those of bulk ice and liquid water over the whole temperature range measured. The contribution of water in the inner part of pores (abbreviated as the internal water) was elucidated by using the heat capacity data of monolayer water measured. The entropy of the internal water was then estimated from integration of the heat capacity of the internal water. The entropy values of the internal water increase by confinement in the pores of MCM-41 in both liquid and frozen regions, indicating an increase in the deformation of the structure and∕or a change in the dynamics in both regions. The INS spectra show the density of states for the librational motion of water frozen at 50 K, suggesting that the confined water is similar to amorphous ice rather than to crystalline ice. When the sample is warmed to melt, the band edge of the librational motion for water frozen in large pores (diameter of 3.6 nm) shifts to a lower energy side, indicating the weakening of intermolecular hydrogen bonds. For water in small pores (2.1 nm), on the contrary, the librational band shifts slightly to a higher energy side, suggesting the low density liquid to high density liquid transition (L-L transition) at 225-250 K. A plausible mechanism of the L-L transition of water in confinement is proposed in terms of incomplete growth of homogeneous nucleation of ice due to an interfacial free energy effect to inhibit crystallization of water confined in small pores. PMID:23742507

  4. Thermoelectric properties of symmetric and asymmetric double quantum well structures

    SciTech Connect

    Sur, I. V.

    2009-05-15

    The electronic states and carrier transport in (100)PbTe/Pb {sub 1-x} Eu{sub x} Te double quantum wells are theoretically analyzed. The dependences of the mobility and Seebeck coefficient on the thickness of the internal barrier in symmetric and asymmetric structures are investigated. It was found that at great distance between the wells even small violation of the structure symmetry and essential reconstruction of electron wave functions results in suppression of intersubband scattering with carriers transfer between the wells and provides the correct limit to isolated quantum well in kinetic coefficients. Some possibilities of increasing the thermoelectric power factor are found, and a suitable set of structure parameters is calculated within the proposed model.

  5. Coagulation behavior and floc properties of compound bioflocculant-polyaluminum chloride dual-coagulants and polymeric aluminum in low temperature surface water treatment.

    PubMed

    Huang, Xin; Sun, Shenglei; Gao, Baoyu; Yue, Qinyan; Wang, Yan; Li, Qian

    2015-04-01

    This study was intended to compare coagulation behavior and floc properties of two dual-coagulants polyaluminum chloride-compound bioflocculant (PAC-CBF) (PAC dose first) and compound bioflocculant-polyaluminum chloride (CBF-PAC) (CBF dose first) with those of PAC alone in low temperature drinking water treatment. Results showed that dual-coagulants could improve DOC removal efficiency from 30% up to 34%. Moreover, CBF contributed to the increase of floc size and growth rate, especially those of PAC-CBF were almost twice bigger than those of PAC. However, dual-coagulants formed looser and weaker flocs with lower breakage factors in which fractal dimension of PAC-CBF flocs was low which indicates a looser floc structure. The floc recovery ability was in the following order: PAC-CBF>PAC alone>CBF-PAC. The flocculation mechanism of PAC was charge neutralization and enmeshment, meanwhile the negatively charged CBF added absorption and bridging effect. PMID:25872730

  6. Dielectric and piezoelectric properties of Bi2O3 added (Pb,Ca,Sr)(Ti,Mn,Sb)O3 ceramics sintered at low temperature

    NASA Astrophysics Data System (ADS)

    Kim, Dohyung; Yoo, Juhyun; Kim, Insung; Song, Jaesung

    2009-03-01

    In this study, in order to develop low temperature sintering ceramics for a thickness mode multilayer piezoelectric transformer, (Pb,Ca,Sr)(Ti,Mn,Sb)O3 ceramics were fabricated using Na2CO3, Li2CO3, MnO2, and Bi2O3 as sintering aids at 870, 900, and 930 °C. Their respective dielectric and piezoelectric properties were investigated according to the amount of Bi2O3 addition. At the sintering temperature of 900 °C, the optimum value was shown for the density of 6.94 g/cm3, thickness vibration mode electromechanical coupling factor (henceforth, kt) of 0.497, thickness vibration mode mechanical quality factor (henceforth, Qmt) of 3162, and dielectric constant (henceforth, ɛr) of 209 for thickness mode multilayer piezoelectric transformer application.

  7. Thermoelectric properties of Ba_yNi_xCo_4-xSb_12

    NASA Astrophysics Data System (ADS)

    Uher, C.; Chen, W.; Dyck, J. S.; Chen, L. D.; Kawahara, T.; Tang, X. F.; Goto, T.; Hirai, T.

    2001-03-01

    Recently, the Barium-filled skutterudites, Ba_yCo_4Sb_12, were identified as promising thermoelectric materials [1]. The maximum filling fraction of Ba in Co_4Sb_12 is higher than the one usually associated with either rare-earth atoms or Tl. The thermoelectric figure of merit, ZT, for Ba_0.3Co_4Sb_12 is about 1 at 850K which is the highest value reported so far for n-type thermoelectric material. A further step in the optimization of the thermoelectric performance of this material is to tune the electrical properties via doping. In this study, we present thermopower, thermal conductivity, electrical resistivity, Hall effect, and magnetoresistance results on a series of samples with composition Ba_yNi_xCo_4-xSb_12 for temperatures up to room temperature. The effects of the incorporation of Ni into the structure will be discussed. [1] L. D. Chen, T. Kawahara, X. F. Tang, T. Goto, T. Hirai, J. S. Dyck, W. Chen, and C. Uher, Proc. 19th ICT, Cardiff, UK, Aug. 2000, in press.

  8. The role of plasma chemistry on functional silicon nitride film properties deposited at low-temperature by mixing two frequency powers using PECVD.

    PubMed

    Sahu, B B; Yin, Y Y; Tsutsumi, T; Hori, M; Han, Jeon G

    2016-05-14

    Control of the plasma densities and energies of the principal plasma species is crucial to induce modification of the plasma reactivity, chemistry, and film properties. This work presents a systematic and integrated approach to the low-temperature deposition of hydrogenated amorphous silicon nitride films looking into optimization and control of the plasma processes. Radiofrequency (RF) and ultrahigh frequency (UHF) power are combined to enhance significantly the nitrogen plasma and atomic-radical density to enforce their effect on film properties. This study presents an extensive investigation of the influence of combining radiofrequency (RF) and ultrahigh frequency (UHF) power as a power ratio (PR = RF : UHF), ranging from 4 : 0 to 0 : 4, on the compositional, structural, and optical properties of the synthesized films. The data reveal that DF power with a characteristic bi-Maxwellian electron energy distribution function (EEDF) is effectively useful for enhancing the ionization and dissociation of neutrals, which in turn helps in enabling high rate deposition with better film properties than that of SF operations. Utilizing DF PECVD, a wide-bandgap of ∼3.5 eV with strong photoluminescence features can be achieved only by using a high-density plasma and high nitrogen atom density at room temperature. The present work also proposes the suitability of the DF PECVD approach for industrial applications. PMID:27109293

  9. Thermoelectric power quantum oscillations in the ferromagnet UGe2

    NASA Astrophysics Data System (ADS)

    Palacio Morales, A.; Pourret, A.; Knebel, G.; Bastien, G.; Taufour, V.; Aoki, D.; Yamagami, H.; Flouquet, J.

    2016-04-01

    We present thermoelectric power and resistivity measurements in the ferromagnet UGe2 as a function of temperature and magnetic field. At low temperature, huge quantum oscillations are observed in the thermoelectric power as a function of the magnetic field applied along the a axis. The frequencies of the extreme orbits are determined and an analysis of the cyclotron masses is performed following different theoretical approaches for quantum oscillations detected in the thermoelectric power. They are compared to those obtained by Shubnikov-de Haas experiments on the same crystal and previous de Haas-van Alphen experiments. The agreement of the different probes confirms thermoelectric power as an excellent probe to extract simultaneously both microscopic and macroscopic information on the Fermi surface properties. Band structure calculations of UGe2 in the ferromagnetic state are compared to the experiment.

  10. Ab-initio study of thermoelectric properties of Mg2Ge

    NASA Astrophysics Data System (ADS)

    Kaur, Kulwinder; Kumar, Ranjan

    2016-05-01

    In this paper we investigate the thermoelectric properties of Mg2Ge material using first principles pseudo potential method based on density functional theory and Boltzmann transport equations. The calculations show n-type conduction, indicating that the electrical conduction is due to electron. The electrical conductivity decrease with temperature; the negative value of Seebeck Coefficient also shows that the conduction is due to electron. In this paper we have calculated Seebeck coefficient, electrical conductivity and thermal conductivity. The thermoelectric properties of system have been calculated in this temperature range 100K-1200K. The value of Figure of Merit (ZT) of this material is also increasing with temperature and maximum value is 4.58×10-5.

  11. Defect induced structural and thermoelectric properties of Sb{sub 2}Te{sub 3} alloy

    SciTech Connect

    Das, Diptasikha; Malik, K.; Deb, A. K.; Dhara, Sandip; Bandyopadhyay, S.; Banerjee, Aritra

    2015-07-28

    Structural and thermoelectric properties of metallic and semiconducting Sb{sub 2}Te{sub 3} are reported. X-Ray diffraction and Raman spectroscopy studies reveal that semiconducting sample has higher defect density. Nature and origin of possible defects are highlighted. Semiconducting Sb{sub 2}Te{sub 3} hosts larger numbers of defects, which act as scattering center and give rise to the increased value of resistivity, thermopower, and power factor. Thermopower data indicate p-type nature of the synthesized samples. It is evidenced that the surface states are often mixed with the bulk state, giving rise to metallicity in Sb{sub 2}Te{sub 3}. Role of different scattering mechanism on the thermoelectric property of Sb{sub 2}Te{sub 3} is discussed.

  12. Tuning the Thermoelectric Properties of a Single-Molecule Junction by Mechanical Stretching

    NASA Astrophysics Data System (ADS)

    Pontes, Renato; Torres, Alberto; da Silva, Antonio J. R.; Fazzio, Adalberto

    2015-03-01

    We theoretically investigate, as a function of the stretching, the behaviour of the thermoelectric properties - Seebeck coefficient (S), the electronic heat conductance (κel) and the figure of merit (ZT) - of a molecule-based junction composed by benzene-1,4-dithiol molecule (BDT) coupled to Au(111) surfaces at room temperature. We show that the thermoelectric properties of a single molecule junction can be tuned by mechanic stretching. The Seebeck coefficient is positive, indicating that it is dominated by the HOMO. Furthermore, it increases as the HOMO level, which is associated to the sulphur atom, goes to energies close to the Fermi energy. By modelling the transmission coefficient of the system as a single lorentzian peak, we propose a scheme to obtain the maximum ZT of any molecular junction. The authors thank the Brazilian funding agencies CNPq, CAPES and FAPESP. We also thank CENAPAD-SP for the computational facilities.

  13. Thermoelectric Properties of Tl-Doped SnSe: A Hint of Phononic Structure

    NASA Astrophysics Data System (ADS)

    Kucek, V.; Plechacek, T.; Janicek, P.; Ruleova, P.; Benes, L.; Navratil, J.; Drasar, C.

    2016-06-01

    Polycrystalline samples with composition Sn1- x Tl x Se (for x = 0 to 0.04) have been synthesized from elements of 5 N purity at elevated temperatures. The phase purity of the products was verified by x-ray diffraction analysis. Samples for measurement of transport properties were prepared by hot pressing. The samples were then characterized by measurement of electrical conductivity, Hall coefficient, Seebeck coefficient, and thermal conductivity over the temperature range from 300 K to 725 K. All samples demonstrated p-type conductivity. Tl markedly enhanced the carrier concentration. We discuss the influence of Tl substitution on the free carrier concentration and thermoelectric performance. Investigation of the thermoelectric properties showed an order-of-magnitude improvement, with ZT reaching 0.6 at 725 K. We discuss the distinctive nature of the thermal conductivity of SnSe.

  14. High-temperature thermoelectric properties of Hg-doped CuInTe{sub 2}

    SciTech Connect

    Kucek, V. Drasar, C.; Kasparova, J.; Plechacek, T.; Benes, L.; Navratil, J.; Vlcek, M.

    2015-09-28

    Polycrystalline samples of composition CuIn{sub 1−x}Hg{sub x}Te{sub 2} (x = 0–0.21) were synthesized from elements of 5N purity using a solid state reaction. The phase purity of the products was verified by X-ray diffraction. Samples for transport property measurements were prepared using hot-pressing. The samples were characterized by measurement of the electrical conductivity, Hall coefficient, Seebeck coefficient, and thermal conductivity over a temperature range of 300–675 K. All samples show p-type conductivity. We discuss the influence of Hg substitution on the free carrier concentration and thermoelectric performance. The investigation of the thermoelectric properties shows up to a 40% improvement of ZT in the temperature range of 300–600 K.

  15. Transport Properties of Bulk Thermoelectrics An International Round-Robin Study, Part I: Seebeck Coefficient and Electrical Resistivity

    SciTech Connect

    Wang, Hsin; Porter, Wallace D; Bottner, Harold; Konig, Jan; Chen, Lidong; Bai, Shengqiang; Tritt, Terry M.; Mayolett, Alex; Senawiratne, Jayantha; Smith, Charlene; Harris, Fred; Gilbert, Partricia; Sharp, Jeff; Lo, Jason; Keinke, Holger; Kiss, Laszlo I.

    2013-01-01

    Recent research and development of high temperature thermoelectric materials has demonstrated great potential of converting automobile exhaust heat directly into electricity. Thermoelectrics based on classic bismuth telluride have also started to impact the automotive industry by enhancing air conditioning efficiency and integrated cabin climate control. In addition to engineering challenges of making reliable and efficient devices to withstand thermal and mechanical cycling, the remaining issues in thermoelectric power generation and refrigeration are mostly materials related. The figure-of-merit, ZT, still needs to improve from the current value of 1.0 - 1.5 to above 2 to be competitive to other alternative technologies. In the meantime, the thermoelectric community could greatly benefit from the development of international test standards, improved test methods and better characterization tools. Internationally, thermoelectrics have been recognized by many countries as an important area for improving energy efficiency. The International Energy Agency (IEA) group under the implementing agreement for Advanced Materials for Transportation (AMT) identified thermoelectric materials as an important area in 2009. This paper is Part I of the international round-robin testing of transport properties of bulk thermoelectrics. The main focuses in Part I are on two electronic transport properties: Seebeck coefficient and electrical resistivity.

  16. Effect of plastic deformation on the electrophysical properties and structure of YBa2Cu3O y ceramics subjected to low-temperature treatment

    NASA Astrophysics Data System (ADS)

    Bobylev, I. B.; Zyuzeva, N. A.; Degtyarev, M. V.; Pilyugin, V. P.

    2015-12-01

    The electrophysical properties and structure of HTSC YBa2Cu3O y compound (123) subjected to plastic deformation by shear under a pressure of 1.7 GPa have been studied. After deformation, the electrophysical properties of samples prepared using the traditional ceramic technology were found to deteriorate. Subsequent annealing at 930°C cannot restore the critical current density ( j c) in low magnetic fields to initial magnitudes; however, in magnetic fields of more than 0.1 T, the j c magnitude increases compared to that for the starting state. The deformation of 123 ceramics treated at 200°C in a humid atmosphere that has undergone phase transformation into the 124 tetragonal phase allows its structure and electrophysical properties to be restored. In this case, the reverse transformation of phase 124 into 123, which is accompanied by the recrystallization of the material, takes place. The combination of low-temperature treatment and high shearing deformation leads to the appearance of texture and an increase of j c, in particular in high magnetic fields.

  17. Structural, optical, and electrical properties of ZnO thin films deposited by sol-gel dip-coating process at low temperature

    NASA Astrophysics Data System (ADS)

    Kim, Soaram; Nam, Giwoong; Yoon, Hyunsik; Park, Hyunggil; Choi, Hyonkwang; Kim, Jong Su; Kim, Jin Soo; Kim, Do Yeob; Kim, Sung-O.; Leem, Jae-Young

    2014-07-01

    Sol-gel dip-coating was used to prepare ZnO thin films with relaxed residual stress by lowering the deposition temperature from room temperature (25°C) to -25°C. The effect of deposition temperature on the structural, optical, and electrical properties of the films was characterized using scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL), ultraviolet-visible (UV-Vis) spectroscopy and reflectance accessory, and the van der Pauw method. All the thin films were deposited successfully onto quartz substrates and exhibited fibrous root morphology. At low temperature, the deposition rate was higher than at room temperature (RT) because of enhanced viscosity of the films. Further, lowering the deposition temperature affected the structural, optical, and electrical properties of the ZnO thin films. The surface morphology, residual stress, PL properties, and optical transmittance and reflectance of the films were measured, and this information was used to determine the absorption coefficient, optical band gap, Urbach energy, refractive index, refractive index at infinite wavelength, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator wavelength, moments M -1 and M -3, dielectric constant, optical conductivity, and electrical resistivity of the ZnO thin films.

  18. Estimates of the thermal conductivity and the thermoelectric properties of PbTiO3 from first principles

    NASA Astrophysics Data System (ADS)

    Roy, Anindya

    2016-03-01

    The lattice thermal conductivity (κL) of PbTiO3 is estimated using a combination of ab initio calculations and the semiclassical Boltzmann transport equation. The computed κL is remarkably low, nearly comparable with the κL of good thermoelectric materials such as PbTe. In addition, a semiclassical analysis of the electronic transport quantities is presented, which suggests excellent thermoelectric properties, with a figure of merit z T well over 1 for a wide range of temperatures. For thermoelectric applications, the κL could be further reduced by utilizing different morphologies and compositions.

  19. Effect of strain on electronic and thermoelectric properties of few layers to bulk MoS₂.

    PubMed

    Bhattacharyya, Swastibrata; Pandey, Tribhuwan; Singh, Abhishek K

    2014-11-21

    The sensitive dependence of the electronic and thermoelectric properties of MoS₂ on applied strain opens up a variety of applications in the emerging area of straintronics. Using first-principles-based density functional theory calculations, we show that the band gap of a few layers of MoS₂ can be tuned by applying normal compressive (NC) strain, biaxial compressive (BC) strain, and biaxial tensile (BT) strain. A reversible semiconductor-to-metal transition (S-M transition) is observed under all three types of strain. In the case of NC strain, the threshold strain at which the S-M transition occurs increases when the number of layers increase and becomes maximum for the bulk. On the other hand, the threshold strain for the S-M transition in both BC and BT strains decreases when the number of layers increase. The difference in the mechanisms for the S-M transition is explained for different types of applied strain. Furthermore, the effect of both strain type and the number of layers on the transport properties are also studied using Botzmann transport theory. We optimize the transport properties as a function of the number of layers and the applied strain. 3L- and 2L-MoS₂ emerge as the most efficient thermoelectric materials under NC and BT strain, respectively. The calculated thermopower is large and comparable to some of the best thermoelectric materials. A comparison among the feasibility of these three types of strain is also discussed. PMID:25354843

  20. Thermoelectric properties of DC-sputtered filled skutterudite thin film

    SciTech Connect

    Fu, Gaosheng; Zuo, Lei; Chen, Jie; Lu, Ming; Yu, Liangyao

    2015-03-28

    The Yb filled CoSb{sub 3} skutterudite thermoelectric thin films were prepared by DC magnetron sputtering. The electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit ZT of the samples are characterized in a temperature range of 300 K to 700 K. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy are obtained to assess the phase composition and crystallinity of thin film samples at different heat treatment temperatures. Carrier concentrations and Hall mobilities are obtained from Hall Effect measurements, which provide further insight into the electrical conductivity and Seebeck coefficient mechanisms. The thermal conductivity of thin film filled skutterudite was found to be much less compared with bulk Yb filled CoSb{sub 3} skutterudite. In this work, the 1020 K heat treatment was adopted for thin film post process due to the high degree of crystallinity as well as avoiding reverse heating effect. Thin film samples of different thicknesses were prepared with the same sputtering deposition rate and maximum ZT of 0.48 was achieved at 700 K for the 130 nm thick sample. This value was between half and one third of the bulk figure of merit which was due to the lower Hall mobility.

  1. Structural disorder, magnetism, and electrical and thermoelectric properties of pyrochlore Nd2Ru2O7.

    PubMed

    Gaultois, Michael W; Barton, Phillip T; Birkel, Christina S; Misch, Lauren M; Rodriguez, Efrain E; Stucky, Galen D; Seshadri, Ram

    2013-05-01

    Polycrystalline Nd2Ru2O7 samples have been prepared and examined using a combination of structural, magnetic, and electrical and thermal transport studies. Analysis of synchrotron x-ray and neutron diffraction patterns suggests some site disorder on the A-site in the pyrochlore sublattice: Ru substitutes on the Nd-site up to 7.0(3)%, regardless of the different preparative conditions explored. Intrinsic magnetic and electrical transport properties have been measured. Ru 4d spins order antiferromagnetically at 143 K, as seen both in the susceptibility and in the specific heat, and there is a corresponding change in the electrical resistivity. The onset of a second antiferromagnetic ordering transition seen below 5 K is attributed to ordering of Nd 4f spins. Nd2Ru2O7 is an electrical insulator, and this behaviour is believed to be independent of the Ru-antisite disorder on the Nd-site. The electrical properties of Nd2Ru2O7 are presented in the light of data published on all A2Ru2O7 pyrochlores, and we emphasize the special structural role that Bi(3+) ions on the A-site play in driving metallic behaviour. High-temperature thermoelectric properties have also been measured. When considered in the context of known thermoelectric materials with useful figures-of-merit, it is clear that Nd2Ru2O7 has excessively high electrical resistivity which prevents it from being an effective thermoelectric. A method for screening candidate thermoelectrics is suggested. PMID:23587787

  2. Effect of bismuth telluride concentration on the thermoelectric properties of PEDOT:PSS-glycerol organic films

    NASA Astrophysics Data System (ADS)

    Rahman, Airul Azha Abd; Ali Umar, Akrajas; Othman, Mohamad Habrul Ulum

    2015-02-01

    In this work, the effect of bismuth-telluride concentration on the thermoelectric properties of PEDOT:PSS-Glycerol thin films is investigated. A thermoelectric device was fabricated by depositing the n-type and the p-type Bi2Te3 (BT) doped-PEDOT:PSS-Glycerol on a glass substrate via a spin coating method at 500 rpm. Room-temperature electrical properties characterization shows that the electrical conductivity of both type thin film increases with increasing of BT doping concentration and optimum at concentration of 0.8 wt% for both p-type and n-type thin films, i.e. 17.9 S/cm and 7.78 S/cm, respectively. However, the study of the temperature effect on the thin films electrical conductivity suggested that the thermoelectric properties of both types' samples improved with increasing of BT concentration and optimum at 0.8 and 0.6 wt% for p-type and n-type thin films, respectively. It then decreased if the BT concentration further increased. The Sebeeck coefficient for these samples is as high as -11.9 and -15.7 uV/K, which is equivalent to a power factors of 0.26 and 0.19 μS V2/ (m K2), respectively. A thermoelectric device resembling a thermocouple system that was fabricated using the optimum p-type and n-type thin films can generate a voltage as high as 1.1 V at a temperature difference as low as 55 K, which is equivalent to a maximum power of 6.026 μW at Vmax.power of 0.5489 V (for an estimated matched-load of 50 Ω). The present materials system is potential for powering low power consumption electronic devices.

  3. 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.

  4. Low-temperature growth of well-aligned ZnO nanorods/nanowires on flexible graphite sheet and their photoluminescence properties

    SciTech Connect

    Zhong, Guo; Kalam, Abul; Al-Shihri, Ayed Sad; Su, Qingmei; Li, Jie; Du, Gaohui

    2012-06-15

    Highlights: ► Well-aligned ZnO nanostructures were grown on flexible graphite sheets at 500–650 °C. ► ZnO nanostructures are formed via self-catalytic vapor–solid process assisted by immiscibility of ZnO with graphite. ► The ZnO nanostructures show intensive green emission. ► The photoluminescence property can be easily tuned by changing growth condition or annealing treatment. -- Abstract: We have grown large-scale well-aligned ZnO nanorods/nanowires on commercial flexible graphite sheet (FGS) at low temperature via chemical vapor deposition method. The products were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The effects of the growth temperature and oxygen flow rate on the morphology of ZnO nanostructures have been investigated. The growth mechanism of ZnO is found to be a self-catalytic vapor–solid process assisted by the immiscibility of ZnO with graphite. The as-grown ZnO/FGS products show strong green emission and their photoluminescence properties can be tuned by changing growth condition or annealing treatment.

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

    PubMed Central

    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. PMID:26728992

  6. 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.

  7. Thermoelectric properties of IV-VI-based heterostructures and superlattices

    NASA Astrophysics Data System (ADS)

    Borges, P. D.; Petersen, J. E.; Scolfaro, L.; Leite Alves, H. W.; Myers, T. H.

    2015-07-01

    Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature in the directions perpendicular to the doping planes, yet no improvement on the values of ZT is found when compared to bulk PbTe. For the PbTe/SnTe/PbTe heterostructures, the calculated S presents good agreement with recent experimental data, and an anisotropic behavior is observed for low carrier concentrations (n<1018 cm-3). A large value of ZT|| (parallel to the growth direction) of 3.0 is predicted for n=4.7×1018 cm-3 and T=700 K, whereas ZTp (perpendicular to the growth direction) is found to peak at 1.5 for n=1.7×1017 cm-3. Both electrical conductivity enhancement and thermal conductivity reduction are analyzed.

  8. Thermoelectric Transport Properties of Gold-Iron at Millikelvin Temperatures.

    NASA Astrophysics Data System (ADS)

    Chesire, Daniel Patrick

    Measurements of the electrical resistivity, and both static and isoelectric thermopower have been made on a fine Au wire containing 1 ppm Fe over a range of temperatures between 7 K and 24 mK. A shallow minimum at higher temperatures and unitary limit in the resistivity data characteristic of the Kondo effect were observed in the lower temperature ranges. The minimum coincides with that observed by other workers. Both the resistivity and the two thermopowers were measured with a Superconducting Quantum Interference Detector (SQUID) which has extremely high sensitivity and a very good signal-to-noise ratio. The static and isoelectric thermopowers were measured under two different boundary conditions. The static thermopower was measured by keeping the electric current through the sample equal to zero by using a compensating current source. The isoelectric thermopower was measured under the condition that the electric field across the sample was kept equal to zero by using a superconducting short. The static and isoelectric thermopowers both exhibited a broad minimum attributed to the interaction of a dilute concentration of Fe impurities with the Au conduction electrons. The data have been analyzed in terms of linear transport theory, using the Mueller-Hartmann expression for the Kondo contribution. Since the measurements were made at low temperatures, the diffusion and phonon drag thermopowers were small enough that the major contribution to the measured thermopower was from the Kondo effect. The theory was shown to fit the data well down to 0.2 K. Below this temperature, the theoretical expression for the thermopower did not agree well with the measurements in this work. The static thermopower, S, was found to be related to the isoelectric thermopower, (SIGMA)(,E=0), and the resistivity, (rho), by the simple relation S = (rho)(SIGMA)(,E=0). The isoelectric data was found to have a better signal-to-noise ratio than the static thermopower and a large enough signal at

  9. Effect of silicon and sodium on thermoelectric properties of thallium doped lead telluride based materials

    SciTech Connect

    Zhang, Qinyong; Wang, H; Zhang, Qian; Liu, W.; Yu, Bo; Wang, H; Wang, D.; Ni, G; Chen, Gang; Ren, Z. F.

    2012-01-01

    Thallium (Tl)-doped lead telluride (Tl0.02Pb0.98Te) thermoelectric materials fabricated by ball milling and hot pressing have decent thermoelectric properties but weak mechanical strength. Addition of silicon (Si) nanoparticles strengthened the mechanical property by reducing the grain size and defect density but resulted in low electrical conductivity that was not desired for any thermoelectric materials. Fortunately, doping of sodium (Na) into the Si added Tl0.02Pb0.98Te brings back the high electrical conductivity and yields higher figure-of-merit ZT values of ~1.7 at 770 K. The ZT improvement by Si addition and Na doping in Tl0.02Pb0.98Te sample is the direct result of concurrent electron and phonon engineering by improving the power factor and lowering the thermal conductivity, respectively.

  10. Influence of rare earth doping on thermoelectric properties of SrTiO{sub 3} ceramics

    SciTech Connect

    Liu, J. Wang, C. L.; Li, Y.; Su, W. B.; Zhu, Y. H.; Li, J. C.; Mei, L. M.

    2013-12-14

    Thermoelectric properties of SrTiO{sub 3} ceramics, doped with different rare earth elements, were investigated in this work. It's found that the ionic radius of doping elements plays an important role on thermoelectric properties: SrTiO{sub 3} ceramics doped with large rare earth ions (such as La, Nd, and Sm) exhibit large power factors, and those doped with small ions (such as Gd, Dy, Er, and Y) exhibit low thermal conductivities. Therefore, a simple approach for enhancing the thermoelectric performance of SrTiO{sub 3} ceramics is proposed: mainly doped with large ions to obtain a large power factor and, simultaneously, slightly co-doped with small ions to obtain a low thermal conductivity. Based on this rule, Sr{sub 0.8}La{sub 0.18}Yb{sub 0.02}TiO{sub 3} ceramics were prepared, whose ZT value at 1 023 K reaches 0.31, increasing by a factor of 19% compared with the single-doped counterpart Sr{sub 0.8}La{sub 0.2}TiO{sub 3} (ZT = 0.26)

  11. Importance of non-parabolic band effects in the thermoelectric properties of semiconductors

    PubMed Central

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

    2013-01-01

    We present an analysis of the thermoelectric properties of of n-type GeTe and SnTe in relation to the lead chalcogenides PbTe and PbSe. We find that the singly degenerate conduction bands of semiconducting GeTe and SnTe are highly non-ellipsoidal, even very close to the band edges. This leads to isoenergy surfaces with a strongly corrugated shape that is clearly evident at carrier concentrations well below 0.005 e per formula unit (7–9 × 1019 cm−3 depending on material). Analysis within Boltzmann theory suggests that this corrugation may be favorable for the thermoelectric transport. Our calculations also indicate that values of the power factor for these two materials may well exceed those of PbTe and PbSe. As a result these materials may exhibit n-type performance exceeding that of the lead chalcogenides. PMID:24196778

  12. YB48 the metal rich boundary of YB66; crystal growth and thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Hossain, M. Anwar; Tanaka, Isao; Tanaka, Takaho; Khan, A. Ullah; Mori, Takao

    2015-12-01

    It was discovered that the well-known higher boride YB66, one of the first reported phonon glass electron crystals (PGEC), could be obtained in a much more metal-rich composition than previously thought possible. Using the floating zone growth method, YB48 single crystals with YB66 crystal structure could be obtained, and their thermoelectric properties measured. This expansion of the homogeneity range of the well-known YB66 compound is surprising and a new Y atomic site was discovered. YB48 exhibits much higher power factors than YB66 which increase rapidly with increasing temperature. The obtained dimensionless figure of merit of this compound at 990 K is approximately 30 times higher than that of previously reported YB66 samples, and higher than any other pristine higher boride. This discovery reveals YB48 as a promising high temperature thermoelectric material.

  13. Calculated transport properties of CdO: thermal conductivity and thermoelectric power factor

    DOE PAGESBeta

    Lindsay, Lucas R.; Parker, David S.

    2015-10-01

    We present first principles calculations of the thermal and electronic transport properties of the oxide semiconductor CdO. In particular, we find from theory that the accepted thermal conductivity κ value of 0.7 Wm-1K-1 is approximately one order of magnitude too small; our calculations of κ of CdO are in good agreement with recent measurements. We also find that alloying of MgO with CdO is an effective means to reduce the lattice contribution to κ, despite MgO having a much larger thermal conductivity. We further consider the electronic structure of CdO in relation to thermoelectric performance, finding that large thermoelectric powermore » factors may occur if the material can be heavily doped p-type. This work develops insight into the nature of thermal and electronic transport in an important oxide semiconductor.« less

  14. Thermoelectric properties of CuS/Ag2S nanocomposites synthesed by modified polyol method

    NASA Astrophysics Data System (ADS)

    Tarachand, Sharma, Vikash; Ganesan, V.; Okram, Gunadhor S.

    2016-05-01

    This is the report on successful synthesis of Ag doped CuS nanostructures by modified polyol method. The resulting samples were characterized by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and dynamic light scattering (DLS). Particle size of pure CuS nanoparticles (NPs) was 17 nm, 38 nm and 97 nm as determined from Scherrer formula, AFM and DLS, respectively. Introduction of Ag led to formation of CuS/Ag2S composites. A transition at 55 K in thermopower is ascribed to structural transformation from hexagonal to orthorhombic structure. Further, their thermoelectric properties exhibit remarkable change owing to Ag doping in CuS nanostructures. The power factor improves with increasing Ag content. They reveal that CuS/Ag2S nanocomposites are some of the potential candidates for generation of thermoelectricity in future.

  15. Calculated transport properties of CdO: Thermal conductivity and thermoelectric power factor

    NASA Astrophysics Data System (ADS)

    Lindsay, L.; Parker, D. S.

    2015-10-01

    We present first-principles calculations of the thermal and electronic transport properties of the oxide semiconductor CdO. In particular, we find from theory that the accepted thermal conductivity κ value of 0.7 W m-1K-1 is approximately one order of magnitude too small; our calculations of κ of CdO are in good agreement with recent measurements. We also find that alloying of MgO with CdO is an effective means to reduce the lattice contribution to κ , despite MgO having a much larger thermal conductivity. We further consider the electronic structure of CdO in relation to thermoelectric performance, finding that large thermoelectric power factors may occur if the material can be heavily doped p type. This work develops insight into the nature of thermal and electronic transport in an important oxide semiconductor.

  16. Tuning of thermoelectric properties with changing Se content in Sb2Te3

    NASA Astrophysics Data System (ADS)

    Das, D.; Malik, K.; Deb, A. K.; Kulbachinskii, V. A.; Kytin, V. G.; Chatterjee, S.; Das, D.; Dhara, S.; Bandyopadhyay, S.; Banerjee, A.

    2016-02-01

    Polycrystalline Sb2Te3-x Se x (0.0≤ x≤1.0) samples were synthesized by the solid-state reaction method. The structural analysis showed that up to the maximal concentration of Se, the samples possess rhombohedral crystal symmetry (space group R\\bar{3}m ). The increase of Se content increases the resistivity of the samples. The variation of phonon frequencies, observed from the Raman spectroscopic study, depicts an anomalous behaviour around x=0.2 . The sample Sb2Te2.8Se0.2 also shows maximum Seebeck coefficient, carrier concentration and thermoelectric power factor. The nature of the scattering mechanism controlling the thermopower data has been explored. The thermoelectric properties of the synthesized materials have been analyzed theoretically in the frame of the Boltzmann equation approach.

  17. Thermoelectric properties of n-type Nb-doped Ag8SnSe6

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao; Zhang, Cheng-Long; Lin, Siqi; Lu, Hong; Pei, Yanzhong; Jia, Shuang

    2016-04-01

    Electrical and thermoelectric (TE) properties for n-type Ag8SnSe6 and ( Ag1- x Nb x ) 8 SnSe 6 are investigated. Ag8SnSe6 has the thermoelectric figure of merit (ZT) close to 1.1 at 803 K due to its intrinsic ultralow thermal conductivity ˜ 0.3 Wm - 1 K - 1 , relatively low resistivity ˜0.01 Ω cm, and high Seebeck coefficient ˜-200 μV/K. The ZT for pure Ag8SnSe6 drops to 0.02 at room temperature due to its large resistivity. Niobium doping increases the carrier concentration nearly 10 times and thus enhances its ZT to 0.11 at room temperature. Ag8SnSe6 is a promising n-type candidate of TE materials which needs further elaborations.

  18. Modeling the Thermoelectric Properties of Ti5O9 Magnéli Phase Ceramics

    NASA Astrophysics Data System (ADS)

    Pandey, Sudeep J.; Joshi, Giri; Wang, Shidong; Curtarolo, Stefano; Gaume, Romain M.

    2016-07-01

    Magnéli phase Ti5O9 ceramics with 200-nm grain-size were fabricated by hot-pressing nanopowders of titanium and anatase TiO2 at 1223 K. The thermoelectric properties of these ceramics were investigated from room temperature to 1076 K. We show that the experimental variation of the electrical conductivity with temperature follows a non-adiabatic small-polaron model with an activation energy of 64 meV. In this paper, we propose a modified Heikes-Chaikin-Beni model, based on a canonical ensemble of closely spaced titanium t 2g levels, to account for the temperature dependency of the Seebeck coefficient. Modeling of the thermal conductivity data reveals that the phonon contribution remains constant throughout the investigated temperature range. The thermoelectric figure-of-merit ZT of this nanoceramic material reaches 0.3 K at 1076 K.

  19. Calculated transport properties of CdO: thermal conductivity and thermoelectric power factor

    SciTech Connect

    Lindsay, Lucas R.; Parker, David S.

    2015-10-01

    We present first principles calculations of the thermal and electronic transport properties of the oxide semiconductor CdO. In particular, we find from theory that the accepted thermal conductivity κ value of 0.7 Wm-1K-1 is approximately one order of magnitude too small; our calculations of κ of CdO are in good agreement with recent measurements. We also find that alloying of MgO with CdO is an effective means to reduce the lattice contribution to κ, despite MgO having a much larger thermal conductivity. We further consider the electronic structure of CdO in relation to thermoelectric performance, finding that large thermoelectric power factors may occur if the material can be heavily doped p-type. This work develops insight into the nature of thermal and electronic transport in an important oxide semiconductor.

  20. Improvement of thermoelectric properties for half-Heusler TiNiSn by interstitial Ni defects

    SciTech Connect

    Hazama, Hirofumi; Matsubara, Masato; Asahi, Ryoji; Takeuchi, Tsunehiro

    2011-09-15

    We have synthesized off-stoichiometric Ti-Ni-Sn half-Heusler thermoelectrics in order to investigate the relation between randomly distributed defects and thermoelectric properties. A small change in the composition of Ti-Ni-Sn causes a remarkable change in the thermal conductivity. An excess content of Ni realizes a low thermal conductivity of 2.93 W/mK at room temperature while keeping a high power factor. The low thermal conductivity originates in the defects generated by an excess content of Ni. To investigate the detailed defect structure, we have performed first-principles calculations and compared with x ray photoemission spectroscopy measurement. Based on these analyses, we conclude that the excess Ni atoms randomly occupy the vacant sites in the half-Heusler structure, which play as phonon scattering centers, resulting in significant improvement of the figure of merit without any substitutions of expensive heavy elements, such as Zr and Hf.

  1. WSi2 in Si(1-x)Ge(x) Composites: Processing and Thermoelectric Properties

    NASA Technical Reports Server (NTRS)

    Mackey, Jonathan A.; Sehirlioglu, Alp; Dynys, Fred

    2015-01-01

    Traditional SiGe thermoelectrics have potential for enhanced figure of merit (ZT) via nano-structuring with a silicide phase, such as WSi2. A second phase of nano-sized silicides can theoretically reduce the lattice component of thermal conductivity without significantly reducing the electrical conductivity. However, experimentally achieving such improvements in line with the theory is complicated by factors such as control of silicide size during sintering, dopant segregation, matrix homogeneity, and sintering kinetics. Samples were prepared using powder metallurgy techniques; including mechano-chemical alloying, via ball milling, and spark plasma sintering for densification. Processing, micro-structural development, and thermoelectric properties will be discussed. Additionally, couple and device level characterization will be introduced.

  2. Design and optimization of compatible, segmented thermoelectric generators

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey

    2003-01-01

    The thermoelectric compatiblity factor is used to rationally select materials for a segmented thermoelectric generator. the thermoelectric potential is used for the exact analytic expressions for materials with temperature dependent thermoelectric properties.

  3. Low Temperature Plasma Medicine

    NASA Astrophysics Data System (ADS)

    Graves, David

    2013-10-01

    Ionized gas plasmas near room temperature are used in a remarkable number of technological applications mainly because they are extraordinarily efficient at exploiting electrical power for useful chemical and material transformations near room temperature. In this tutorial address, I will focus on the newest area of low temperature ionized gas plasmas (LTP), in this case operating under atmospheric pressure conditions, in which the temperature-sensitive material is living tissue. LTP research directed towards biomedical applications such as sterilization, surgery, wound healing and anti-cancer therapy has seen remarkable growth in the last 3-5 years, but the mechanisms responsible for the biomedical effects have remained mysterious. It is known that LTP readily create reactive oxygen species (ROS) and reactive nitrogen species (RNS). ROS and RNS (or RONS), in addition to a suite of other radical and non-radical reactive species, are essential actors in an important sub-field of aerobic biology termed ``redox'' (or oxidation-reduction) biology. I will review the evidence suggesting that RONS generated by plasmas are responsible for their observed therapeutic effects. Other possible bio-active mechanisms include electric fields, charges and photons. It is common in LTP applications that synergies between different mechanisms can play a role and I will review the evidence for synergies in plasma biomedicine. Finally, I will address the challenges and opportunities for plasma physicists to enter this novel, multidisciplinary field.

  4. Synthesis and characterization of Bi-Te-Se thermoelectric materials

    SciTech Connect

    Tripathi, S. K.; Kumari, Ankita; Ridhi, R.; Kaur, Jagdish

    2015-08-28

    Bismuth Telluride (Bi{sub 2}Te{sub 3}) and its related alloys act as a promising thermoelectric material and preferred over other thermoelectric materials due to their high stability and efficiency under ambient conditions. In the present work, we have reported economical, environment friendly and low-temperature aqueous chemical method for the synthesis of Bi-Se-Te alloy. The prepared samples are characterized by X-Ray Diffraction to investigate the structural properties and UV-Visible spectroscopy for the spectroscopic analysis. The absorption spectrum reveals the sensitivity in the ultraviolet as well as in visible region.

  5. Thermoelectric transport properties of nanostructured FeSb 2 and Ce-based heavy-fermions CeCu and CeAl 3

    NASA Astrophysics Data System (ADS)

    Pokharel, Mani R.

    the thermal conductivities of nanostructured FeSb2 samples 7. We find a notably large value for Kapitza length at low temperatures indicating the dominance of inter-grain thermal resistance over bulk thermal resistance in determining the thermal properties of FeSb 2. 1Huaizhou Zhao, Mani Pokharel, Gaohua Zhu, Shuo Chen, Kevin Lukas, Qing Jie,Cyril Opeil, Gang Chen, and Zhifeng Ren, Appl. Phys. Lett. 99, 163101 (2011). 2Mani Pokharel, Tulashi Dahal, Zhifeng Ren, and Cyril Opeil, Journal of Alloys and Compounds 609 (2014) 228-232. 3Mani Pokharel, Tulashi Dahal, Zhensong Ren, Peter Czajka, Stephen Wilson, Zhifeng Ren, and Cyril Opeil, Energy Conversion and Management, 87 (2014) 584-588. 4Mani Pokharel, Machhindra Koirala, Huaizhau Zhao, Zhifeng Ren, and Cyril Opeil, J. Low Temp. Phys., 176 (2014) 122-130. 5Mani Pokharel, Huaizhou Zhao, Shuo Chen, Kevin Lukas, Hui Wang, Cyril Opeil1, Gang Chen, and Zhifeng Ren, Nanotechnology 23 (2012) 505402. 6Mani Pokharel, Huaizhou Zhao, Kevin Lukas, Bogdan Mihaila, Zhifeng Ren, and Cyril Opeil, MRS Communications 3 (2013) 31-36. 7Mani Pokharel, Huaizhau Zhao, Zhifeng Ren, and Cyril Opeil, International Journal of Thermal Science, 71 (2013) 32-35.

  6. High temperature thermoelectric properties of rock-salt structure PbS

    DOE PAGESBeta

    Parker, David S.; Singh, David J.

    2013-12-18

    We present an analysis of the high temperature transport properties of rock-salt structure PbS, a sister compound to the better studied lead chalcogenides PbSe and PbTe. In this study, we find thermopower magnitudes exceeding 200 V/K in a wide doping range for temperatures of 800 K and above. Based on these calculations, and an analysis of recent experimental work we find that this material has a potential for high thermoelectric performance. Also, we find favorable mechanical properties, based on an analysis of published data.

  7. Thermoelectric Properties of the Quasi-Binary MnSi1.73-FeSi2 System

    NASA Astrophysics Data System (ADS)

    Sadia, Yatir; Madar, Naor; Kaler, Ilan; Gelbstein, Yaniv

    2015-06-01

    The higher manganese silicides (HMS) are regarded as very attractive p-type thermoelectric materials for direct conversion of heat to electricity. To compete with other thermodynamic engines (e.g. the Stirling and Rankine cycles), however, the thermoelectric figure of merit of such silicides must be improved. HMS follow a complicated solidification reaction on cooling from the melt, which leads to formation of undesired secondary phases. Furthermore, the electronic carrier concentration of HMS is much higher than the optimum for thermoelectric applications and should be compensated by introduction of doping agents. In this research, the electronic donor action associated with substitution of HMS by FeSi2 was investigated. The effects of excess Si on phase distribution and thermoelectric properties are also discussed in detail.

  8. Phase Transition and Microwave Dielectric Properties of Low-Temperature Sintered BiCu2VO6 Ceramic and its Chemical Compatibility with Silver

    NASA Astrophysics Data System (ADS)

    Li, Chunchun; Xiang, Huaicheng; Fang, Liang

    2016-01-01

    In this work, a low-firing microwave dielectric ceramic BiCu2VO6 with monoclinic structure was prepared through a solid state reaction method. Dense ceramic could be obtained when sintered at 740°C with a relative density about 96.7%. A diffusive phase transition was observed from the temperature dependence of the relative permittivity and loss tangent. The best sintered sample at 740°C exhibited the optimum microwave dielectric properties with a relative permittivity ~22.7, a quality factor ~11,960 GHz (at 11.0 GHz), and a temperature coefficient of resonant frequency of -17.2 ppm/°C. From the x-ray diffraction, backscattered electron imaging results of the cofired sample with 20 wt.% silver, the BiCu2VO6 ceramic was found not to react with Ag at 740°C. It might be promising for the low-temperature cofired ceramics and dielectric resonator applications.

  9. Low-Temperature Sintering and Microwave Dielectric Properties of Zn2SiO4 Ceramic Added with Crystalline Zinc Borate

    NASA Astrophysics Data System (ADS)

    Chaware, Varsha; Deshmukh, Ravindra; Sarode, Chetan; Gokhale, Suresh; Phatak, Girish

    2015-07-01

    The physical and dielectric properties of composites of known microwave materials, Zn2SiO4 and Zn3B2O6, prepared by solid-state reaction, were investigated with the purpose of developing a low-loss dielectric material for low-temperature co-fired ceramic applications. An off-stoichiometric phase of Zn2SiO4 with extra SiO2 was used to avoid the occurrence of unreacted ZnO. During sintering, zinc borate was found to partially react with residual SiO2 to form Zn2SiO4. The residual zinc borate was converted to a boron-rich glassy phase which helped to reduce the sintering temperature of the composite. Good relative sintering density (>90%) at temperatures below the melting temperature of zinc borate is indicative of a sintering mechanism of diffusion-based mass transfer. Composites containing 15 wt.% zinc borate, 2.5 wt.% lithium carbonate and 20 wt.% zinc borate in zinc silicate had dielectric constants of 6.8 and 6.1, quality factors (Q×f) of 48,800 and 94,300 GHz when sintered at 900°C and 950°C, respectively. These quality factor results are close to the best values reported for zinc silicate at these sintering temperatures.

  10. Effect of thermo-mechanical processing on the material properties at low temperature of a large size Al-Ni stabilized Nb-Ti/Cu superconducting cable

    NASA Astrophysics Data System (ADS)

    Langeslag, S. A. E.; Curé, B.; Sgobba, S.; Dudarev, A.; ten Kate, H. H. J.; Neuenschwander, J.; Jerjen, I.

    2014-01-01

    For future high-resolution particle experiments, a prototype for a 60 kA at 5 T, 4.2 K class conductor is realized by co-extrusion of a large, 40-strand Nb-Ti/Cu superconducting cable with a precipitation type Al-0.1wt.%Ni stabilizer. Microalloying with nickel contributes to the strength of the stabilizer, and avoids significant degradation in residual resistivity ratio, owing to its low solid solubility in aluminum. Sections of the conductor are work hardened to increase the mechanical properties of the as-extruded temper. Mechanical and resistivity characteristics are assessed as function of the amount of work hardening, at room temperature as well as at 4.2 K. Thermal treatments, like resin curing after coil winding, can cause partial annealing of the cold-worked material and reverse the strengthening effect. However, targeted thermal treatments, applied at relatively low temperature can result in precipitation hardening. The depletion of nickel in the aluminum-rich matrix around the precipitates results in an increased strength and a decreased effect of nickel on the thermal and electrical resistivity of the material. The present work aims at identifying an optimal work hardening sequence, and an optimal thermal treatment, possibly coinciding with a suitable coil resin curing cycle, for the Al-Ni stabilized superconductor.

  11. Effect of low-temperature high-pressure sintering on BiFeO3 density, electrical magnetic and structural properties

    NASA Astrophysics Data System (ADS)

    Ponzoni, Chiara; Cannio, Maria; Rosa, Roberto; Chudoba, Tadeusz; Pietrzykowka, Elżbieta; Buscaglia, Vincenzo; Finocchio, Elisabetta; Nanni, Paolo; Łojkowski, Witold; Leonelli, Cristina

    2013-11-01

    Single-phase multiferroic BiFeO3 (BFO) powders were prepared by hydrothermal microwave synthesis and dense BiFeO3 ceramics were fabricated for the first time by the low-temperature high-pressure (LTHP) sintering technique. Effect of sintering temperature ranging from 400 to 800 °C (3 min and 10 min) and pressure of 3-8 GPa on structural, microstructural, electric and magnetic properties were investigated through X-ray diffraction, scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), density and magnetic measurements. The results highlighted that LTHP sintering method, thanks to the high pressure involved, requires lower temperature and shorter time than other techniques, avoiding BiFeO3 phase degradation. SEM images show that for short experimental time (t = 3 min) the average grain size of the sintered samples was approximately the same size of raw powder. Extending the sintering time up to 10 min the grain growth phenomena occurred. Moreover the results indicate that the best obtained density value was around 98% of theoretical density. The dielectric behavior of BiFeO3 ceramics was not significantly influenced by the LTHP sintering conditions. Magnetic measurements showed that ceramic BiFeO3 is weakly ferromagnetic at room temperature.

  12. Low-temperature synthesis of nanocrystalline NiCuZn ferrite and the effect of Cr substitution on its electrical properties

    NASA Astrophysics Data System (ADS)

    Gabal, M. A.; Al Angari, Y. M.

    2010-10-01

    In this study, nano-sized ferrites of compositions (Ni 0.6Cu 0.20Zn 0.20Fe 2- xCr xO 4), where x=0-1.0, were synthesized through nitrate-citrate auto-combustion method at relatively low temperature. XRD revealed the formation of nano-sized ferrite particles with cubic spinel structure. An exception was obtained for samples with Cr content ≤0.2, where weak diffraction peaks attributed to the presence of CuO and Fe 2O 3 were appeared. The average crystallite sizes are much dependent on the chromium content and were found to decrease with its increase. The lattice parameter ( a) slightly decreases with Cr substitution, which can be explained on the basis of the relative ionic radii of Cr 3+ and Fe 3+ ions. X-ray density was found also to decrease slightly with increase in chromium content, which indicates lower densification by the addition of Cr. FT-IR measurements show the characteristic ferrite bands. The Mössbauer spectra varied from Zeeman sextets to a relaxed doublet by increase in Cr content, which indicates a decrease in the hyperfine field at the octahedral site. Electrical property measurements revealed that Cr 3+ ions do not participate in conduction process but limit the degree of Fe 3+-O 2--Fe 3+ conduction resulting in a decrease in the conductivity and increase in conduction activation energy.

  13. Enhanced Thermoelectric Properties of La-Doped ZrNiSn Half-Heusler Compound

    NASA Astrophysics Data System (ADS)

    Akram, Rizwan; Zhang, Qiang; Yang, Dongwang; Zheng, Yun; Yan, Yonggao; Su, Xianli; Tang, Xinfeng

    2015-10-01

    The effect of La doping on ZrNiSn half-Heusler (HH) compound has been studied to explore the composition variation and structural modifications for improvement of its thermoelectric performance. A series of La x Zr1- x NiSn ( x = 0, 0.005, 0.01, 0.015, 0.02, 0.03) alloys were prepared by induction melting combined with plasma-activated sintering. Structural analysis using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) confirmed the resulting material to be a composite of HH, NiZr, and La3Sn4-type phases. The volume fraction for the phases other than HH ranged from 1.5% to 25% with increasing La content, as estimated by Rietveld analysis. The solubility of La in ZrNiSn is estimated to be 1.5%. Point defects may play a significant role in carrier and phonon transport. Interestingly, the thermoelectric transport properties exhibited a considerable increase in electrical conductivity σ with La doping and a significant drop in thermal conductivity κ, leading to a thermoelectric figure of merit ( ZT) of 0.53 at 923 K, representing an improvement of about 37% compared with the undoped sample.

  14. Thermoelectric Transport Properties of Fe-Enriched ZnO with High-Temperature Nanostructure Refinement.

    PubMed

    Liang, Xin

    2015-04-22

    Thermoelectric properties of Fe-doped ZnO materials are investigated and correlated with the phase and microstructural evolution. Both a ZnO solid solution phase and a ZnFe2O4 spinel phase are observed. Analysis was made of temperature measurements of Seebeck coefficients as combined with the law of mixture to estimate the Fermi level in the constituent phases, which are further correlated with the Fe solute concentration in ZnO lattices and the overall electrical conductivity. In addition, the thermoelectric figure of merit is found to increase with the actual Fe content in ZnO lattices, due to the reduced thermal conductivity by point defect scattering of phonons and enhanced electrical transport via electron doping. The maximum achievable power factor of Fe-doped ZnO material is found to be similar to that of the ZnO-In2O3 system. Another important finding of the present work is the significant nanostructure refinement in 18 month old FeO1.5-doped ZnO after high-temperature thermal treatment, leading to further reduced thermal conductivity, which is beneficial and promising for high-temperature thermoelectric performance. PMID:25839985

  15. Galvanic synthesis of Cu2-XSe thin films and their photocatalytic and thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Ghosh, Amrita; Kulsi, Chiranjit; Banerjee, Dipali; Mondal, Anup

    2016-04-01

    Cu2-XSe thin film with cubic berzelianite phase was prepared by a simple, low-cost two electrode electrochemical technique and the photocatalytic and thermoelectric properties of the thin films were investigated. The results showed that Cu2-XSe crystallized in the cubic berzelianite phase and found to possess both direct and indirect band gaps of 2.9 and 1.05 eV respectively, covering almost the entire range of solar-spectrum. The photocatalytic discoloration of aqueous methylene blue (MB) and rose-bengal (RB) dyes over Cu2-XSe thin films were investigated under visible light irradiation. Cu2-XSe thin films showed higher catalytic activity for MB compared to RB in presence of H2O2. The photocatalytic discoloration followed first-order reaction kinetics. Complete removal of aqueous MB was realized after visible light irradiation for 150 min with Cu2-XSe thin film catalyst in presence of H2O2. Thermoelectric performances through power factor and figure of merit have been evaluated. Carrier concentration obtained from thermoelectric power was used to evaluate the mobility of carriers from electrical conductivity measurement.

  16. Ab initio study of thermoelectric properties of doped SnO2 superlattices

    NASA Astrophysics Data System (ADS)

    Borges, P. D.; Silva, D. E. S.; Castro, N. S.; Ferreira, C. R.; Pinto, F. G.; Tronto, J.; Scolfaro, L.

    2015-11-01

    Transparent conductive oxides, such as tin dioxide (SnO2), have recently shown to be promising materials for thermoelectric applications. In this work we studied the thermoelectric properties of Fe-, Sb- and Zn-uniformly doping and co-doping SnO2, as well as of Sb and Zn planar (or delta)-doped layers in SnO2 forming oxide superlattices (SLs). Based on the semiclassical Boltzmann transport equations (BTE) in conjunction with ab initio electronic structure calculations, the Seebeck coefficient (S) and figure of merit (ZT) are obtained for these systems, and are compared with available experimental data. The delta doping approach introduces a remarkable modification in the electronic structure of tin dioxide, when compared with the uniform doping, and colossal values for ZT are predicted for the delta-doped oxide SLs. This result is a consequence of the two-dimensional electronic confinement and the strong anisotropy introduced by the doped planes. In comparison with the uniformly doped systems, our predictions reveal a promising use of delta-doped SnO2 SLs for enhanced S and ZT, which emerge as potential candidates for thermoelectric applications.

  17. Orientation dependency of mechanical properties of 1950's vintage Type 304 stainless steel weldment components before and after low temperature neutron irradiation

    SciTech Connect

    Sindelar, R.L.; Caskey, G.R. Jr.

    1992-01-01

    Databases of mechanical properties for both the piping and reactor vessels at the Savannah River Site (SRS) were developed from weldment components (base, weld, and weld heat-affected-zone (HAZ)) of archival piping specimens in the unirradiated and irradiated conditions. Tensile, Charpy V-notch (CVN), and Compact Tension C(T) specimens were tested at 25 and 125C before and after irradiation at low temperatures (90 to 150C) to levels of 0.065 to 2.1 dpa. irradiation hardened the weldment components and reduced the absorbed energy and toughness properties from the unirradiated values. A marked difference in the Charpy V-notch absorbed energy and the elastic-plastic fracture toughness (J[sub IC]) was observed for both the base and HAZ components with the C-L orientation being lower in toughness than the L-C orientation in both the unirradiated and irradiated conditions. Fracture surface examination of the base and HAZ components of unirradiated C(T) specimens showed a channel'' morphology in the fracture surfaces of the C-L specimens, whereas equiaxed ductile rupture occurred in the L-C specimens. Chromium carbide precipitation in the HAZ component reduced the fracture toughness of the C-L and L-C specimens compared to the respective base component C-L and L-C specimens. Optical metallography of the piping materials showed stringers of second phase particles parallel to the rolling direction along with a banding or modulation in the microchemistry perpendicular to the pipe axis or rolling direction of the plate material.

  18. Orientation dependency of mechanical properties of 1950`s vintage Type 304 stainless steel weldment components before and after low temperature neutron irradiation

    SciTech Connect

    Sindelar, R.L.; Caskey, G.R. Jr.

    1992-12-31

    Databases of mechanical properties for both the piping and reactor vessels at the Savannah River Site (SRS) were developed from weldment components (base, weld, and weld heat-affected-zone (HAZ)) of archival piping specimens in the unirradiated and irradiated conditions. Tensile, Charpy V-notch (CVN), and Compact Tension C(T) specimens were tested at 25 and 125C before and after irradiation at low temperatures (90 to 150C) to levels of 0.065 to 2.1 dpa. irradiation hardened the weldment components and reduced the absorbed energy and toughness properties from the unirradiated values. A marked difference in the Charpy V-notch absorbed energy and the elastic-plastic fracture toughness (J{sub IC}) was observed for both the base and HAZ components with the C-L orientation being lower in toughness than the L-C orientation in both the unirradiated and irradiated conditions. Fracture surface examination of the base and HAZ components of unirradiated C(T) specimens showed a ``channel`` morphology in the fracture surfaces of the C-L specimens, whereas equiaxed ductile rupture occurred in the L-C specimens. Chromium carbide precipitation in the HAZ component reduced the fracture toughness of the C-L and L-C specimens compared to the respective base component C-L and L-C specimens. Optical metallography of the piping materials showed stringers of second phase particles parallel to the rolling direction along with a banding or modulation in the microchemistry perpendicular to the pipe axis or rolling direction of the plate material.

  19. Thermal Cycling Effects on the Thermoelectric Properties of n-Type In, Ce based Skutterudite Compounds

    SciTech Connect

    Biswas, Krishnendu; Subramanian, Mas A.; Good, Morris S.; Roberts, Kamandi C.; Hendricks, Terry J.

    2012-06-14

    N-type In-filled CoSb3 are known skutterudite compounds that have shown promising thermoelectric (TE) properties resulting in high dimensionless figure of merit values at elevated temperatures. Their use in various waste heat recovery applications will require that they survive and operate after exposure to harsh thermal cycling environments. This research focused on uncovering the thermal cycling effects on thermoelectric properties of n-type In0.2Co4Sb12 and In0.2Ce0.15Co4Sb12 skutterudite compositions as well as quantifying their temperature-dependent structural properties (elastic modulus, shear modulus, and Poisson's ratio). It was observed that the Seebeck coefficient and resistivity increased only slightly in the double-filled In,Ce skutterudite materials upon thermal cycling. In the In-filled skutterudites the Seebeck coefficient remained approximately the same on thermal cycling, while electrical resistivity increased significantly after thermal cycling. Results also show that thermal conductivity marginally decreases in the case of In-filled skutterudites, whereas the reduction is more pronounced in In, Ce-based skutterudite compounds. The possible reason for this kind of reduction can be attributed to grain pinning effects due to formation of nano inclusions. High temperature structural property measurements (i.e., Young's modulus and shear modulus) are also reported and the results show that these structural properties decrease slowly as temperature increases and the compounds are structurally stable after numerous thermal cycles.

  20. Synthesis, Structure, and Transport Properties of YbSb2Te4 and YbSb4Te7 for Thermoelectric Applications

    NASA Technical Reports Server (NTRS)

    Guloy, Amado S.

    2005-01-01

    Very little work has been done in the Yb-Sb-Te system of compounds. Exploratory synthesis of various compounds in the system has been performed in the search for new thermoelectric materials. The compounds in the system were examined due to the fact that the system is known to act as a concentrated Kondo system, a heavy fermion. Heavy fermions are known to possess high densities of state which are useful in thermoelectric applications. TWO compounds in the system, YbSb2Te4 and YbSb4Te7, have been successfully synthesized in bulk by two methods: low temperature mechanical alloying and high temperature direct synthesis. The Hall mobility, Seebeck coefficient, electrical resistivity, and thermal conductivity were measured on both the unannealed and annealed compounds up to 550 C to determine the dimensionless thermoelectric figure of merit, ZT. The results indicate that both compounds make promising candidates for use in thermoelectric devices.

  1. Proposal for a phase-coherent thermoelectric transistor

    SciTech Connect

    Giazotto, F.; Robinson, J. W. A.; Moodera, J. S.; Bergeret, F. S.

    2014-08-11

    Identifying materials and devices which offer efficient thermoelectric effects at low temperature is a major obstacle for the development of thermal management strategies for low-temperature electronic systems. Superconductors cannot offer a solution since their near perfect electron-hole symmetry leads to a negligible thermoelectric response; however, here we demonstrate theoretically a superconducting thermoelectric transistor which offers unparalleled figures of merit of up to ∼45 and Seebeck coefficients as large as a few mV/K at sub-Kelvin temperatures. The device is also phase-tunable meaning its thermoelectric response for power generation can be precisely controlled with a small magnetic field. Our concept is based on a superconductor-normal metal-superconductor interferometer in which the normal metal weak-link is tunnel coupled to a ferromagnetic insulator and a Zeeman split superconductor. Upon application of an external magnetic flux, the interferometer enables phase-coherent manipulation of thermoelectric properties whilst offering efficiencies which approach the Carnot limit.

  2. Thermoelectric properties of PbSe0.5Te0.5: x (PbI2) with endotaxial nanostructures: a promising n-type thermoelectric material

    NASA Astrophysics Data System (ADS)

    Rawat, P. K.; Paul, B.; Banerji, P.

    2013-05-01

    In the present investigation, we report on the thermoelectric properties of PbSe0.5Te0.5: x (PbI2) from room temperature to 625 K. High-resolution transmission electron micrographs of the samples reveal endotaxial nanostructures embedded in a PbSe0.5Te0.5 matrix. The combined effect of mass fluctuation and nanostructures reduces the thermal conductivity to a great extent compared to PbTe and PbSe, without affecting the carrier mobility. As a result, a thermoelectric figure of merit with a value of 1.5 is achieved at 625 K. This value is significantly higher than that of the available state-of-the-art n-type materials.

  3. Thermoelectric properties of PbSe₀.₅Te₀.₅: x (PbI₂) with endotaxial nanostructures: a promising n-type thermoelectric material.

    PubMed

    Rawat, P K; Paul, B; Banerji, P

    2013-05-31

    In the present investigation, we report on the thermoelectric properties of PbSe₀.₅Te₀.₅: x (PbI₂) from room temperature to 625 K. High-resolution transmission electron micrographs of the samples reveal endotaxial nanostructures embedded in a PbSe₀.₅Te₀.₅ matrix. The combined effect of mass fluctuation and nanostructures reduces the thermal conductivity to a great extent compared to PbTe and PbSe, without affecting the carrier mobility. As a result, a thermoelectric figure of merit with a value of 1.5 is achieved at 625 K. This value is significantly higher than that of the available state-of-the-art n-type materials. PMID:23619430

  4. Thermoelectric and thermodynamic properties of half-Heulser alloy YPdSb from first principles calculations

    SciTech Connect

    Kong, Fanjie; Hu, Yanfei; Hou, Haijun; Liu, Yanhua; Wang, Baolin; Wang, Lili

    2012-12-15

    The structural, electronic, thermoelectric and thermodynamic properties of ternary half-Heusler compound YPdSb are investigated using the first principle calculations. It is found that YPdSb is an indirect semiconductor. The calculated band gap is 0.161 eV with spin-orbital coupling including and 0.235 eV without spin-orbital coupling including, respectively. The electronic transport properties are obtained via Boltzman transport theory. The predicted Seebeck coefficient is 240 {mu}V/K and the thermoelectric performance can be optimized by n-type doping at room temperature. Moreover, the lattice dynamical results regarding the phonon dispersion curves, phonon density of states and thermodynamic properties are reported. Thermodynamics (heat capacity and Debye temperature) as well as mean phonon free path and the thermal conductivity in a temperature range of 0-300 K are determined. - Graphical Abstract: (a) The dependence of the Seebeck coefficient on chemical potential at 300 K. (b) The dependence of the thermopower factor on chemical potential at 300 K. Highlights: Black-Right-Pointing-Pointer The Seebeck coefficient and the thermopower factor are calculated. Black-Right-Pointing-Pointer The lattice dynamics and thermodynamic properties are obtained.

  5. Effect of sulfur doping on thermoelectric properties of tin selenide – A first principles study

    SciTech Connect

    Jayaraman, Aditya; Molli, Muralikrishna Kamisetti, Venkataramaniah

    2015-06-24

    In this work we present the thermoelectric properties of tin selenide (SnSe) and sulfur doped tin selenide(SnSe{sub (1-x)}S{sub x}, x= 0.125 and 0.25) obtained using first principles calculations. We investigated the electronic band structure using the FP-LAPW method within the sphere of the density functional theory. Thermoelectric properties were calculated using BOLTZTRAP code using the constant relaxation time approximation at three different temperatures 300, 600 and 800 K. Seebeck coefficient (S) was found to decrease with increasing temperature, electrical conductivity (σ/τ) was almost constant in the entire temperature range and thermal conductivity (κ/τ) increased with increasing temperature for all samples. Sulfur doped samples showed enhanced seebeck coefficient, decreased thermal conductivity and decreased electrical conductivity at all temperatures. At 300 K, S increased from 1500 µV/K(SnSe) to 1720μV/K(SnSe{sub 0.75}S{sub 0.25}), thermal conductivity decreased from 5 × 10{sup 15} W/mKs(SnSe) to 3 × 10{sup 15} W/mKs(SnSe{sub 0.75}S{sub 0.25}), electrical conductivity decreased from 7 × 10{sup 20}/Ωms(SnSe) to 5 × 10{sup 20} /Ωms(SnSe{sub 0.75}S{sub 0.25}). These calculations show that sulfur doped tin selenide exhibit better thermoelectric properties than undoped tin selenide.

  6. DFT and post-DFT studies of metallic MXY3-type compounds for low temperature TE applications

    NASA Astrophysics Data System (ADS)

    Bilal, M.; Saifullah; Ahmad, Iftikhar; Jalali-Asadabadi, S.; Ahmad, Rashid; Shafiq, M.

    2016-10-01

    In this paper, thermoelectric properties of carbon and nitrogen based twenty metallic antiperovskites MXY3 (M=Al, Ga, Ir, Mg, Pd, Pt, Rh; X=C, N; Y=Mn, Ni, Sc, Ti, Cr, Fe) using ab-initio density functional theory and post-DFT Boltzmann's techniques are investigated. The electronic properties of these compounds are also discussed. We find high values of Seebeck coefficient and small values of electronic thermal conductivity for AlCTi3, AlNSc3, AlCNi3, AlNTi3, GaCCr3 and MgCNi3 between -0.25 and 0.25 eV chemical potential. These results show high dimensionless figure of merit in metallic materials and therefore, we predict these materials can be potential candidates for low temperature thermoelectric applications.

  7. Effect of low-temperature degradation on the mechanical and microstructural properties of tooth-colored 3Y-TZP ceramics.

    PubMed

    Nakamura, K; Harada, A; Ono, M; Shibasaki, H; Kanno, T; Niwano, Y; Adolfsson, E; Milleding, P; Örtengren, U

    2016-01-01

    The aim of the present study was to evaluate the effects of low-temperature degradation (LTD) induced by autoclaving on the mechanical and microstructural properties of tooth-colored 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). In total, 162 disc-shaped 3Y-TZP specimens were prepared. Two-thirds of the specimens were shaded by either the infiltration or powder mixing methods while the remaining specimens were used without coloring. The specimens were autoclaved at 134 °C for 0, 10, and 100 h to induce LTD (n=18 for each group). Chemical compositions were analyzed with X-ray fluorescence spectroscopy. Biaxial flexural strength was measured using a piston-on-three-ball test. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy, respectively. The tooth-colored 3Y-TZP specimens contained Fe2O3 and Er2O3 (infiltration technique), and Fe2O3 (powder mixing method) at concentrations of<0.5 wt%. The tooth-colored 3Y-TZP had higher strength than the non-colored material after 100 h of autoclaving. In terms of surface fraction and penetration depth, the generation of monoclinic phase was significantly lower in the tooth-colored 3Y-TZP than in the non-colored material. The tooth-colored 3Y-TZP possessed equivalent biaxial flexural strength to that of the non-colored material and higher resistance to LTD regardless of the coloring technique (infiltration technique or powder mixing method) when the coloring pigments were contained at concentrations used in the present study. PMID:26382971

  8. Structure and magnetic properties of low-temperature phase Mn-Bi nanosheets with ultra-high coercivity and significant anisotropy

    SciTech Connect

    Liu, Rongming E-mail: shenbg@iphy.ac.cn; Zhang, Ming; Niu, E; Li, Zhubai; Zheng, Xinqi; Wu, Rongrong; Zuo, Wenliang; Shen, Baogen; Hu, Fengxia; Sun, Jirong

    2014-05-07

    The microstructure, crystal structure, and magnetic properties of low-temperature phase (LTP) Mn-Bi nanosheets, prepared by surfactant assistant high-energy ball milling (SA-HEBM) with oleylamine and oleic acid as the surfactant, were examined with scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the coercivity of LTP Mn-Bi nanosheets was systematically investigated. Results show that the high energy ball milling time from tens of minutes to several hours results in the coercivity increase of Mn-Bi powders and peak values of 14.3 kOe around 10 h. LTP Mn-Bi nanosheets are characterized by an average thickness of tens of nanometers, an average diameter of ∼1.5 μm, and possess a relatively large aspect ratio, an ultra-high room temperature coercivity of 22.3 kOe, a significant geometrical and magnetic anisotropy, and a strong (00l) crystal texture. Magnetization and demagnetization behaviors reveal that wall pinning is the dominant coercivity mechanism in these LTP Mn-Bi nanosheets. The ultrafine grain refinement introduced by the SA-HEBM process contribute to the ultra-high coercivity of LTP Mn-Bi nanosheets and a large number of defects put a powerful pinning effect on the magnetic domain movement, simultaneously. Further magnetic measurement at 437 K shows that a high coercivity of 17.8 kOe and a strong positive temperature coefficient of coercivity existed in the bonded permanent magnet made by LTP Mn-Bi nanosheets.

  9. Structure and magnetic properties of low-temperature phase Mn-Bi nanosheets with ultra-high coercivity and significant anisotropy

    NASA Astrophysics Data System (ADS)

    Liu, Rongming; Zhang, Ming; Niu, E.; Li, Zhubai; Zheng, Xinqi; Wu, Rongrong; Zuo, Wenliang; Shen, Baogen; Hu, Fengxia; Sun, Jirong

    2014-05-01

    The microstructure, crystal structure, and magnetic properties of low-temperature phase (LTP) Mn-Bi nanosheets, prepared by surfactant assistant high-energy ball milling (SA-HEBM) with oleylamine and oleic acid as the surfactant, were examined with scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the coercivity of LTP Mn-Bi nanosheets was systematically investigated. Results show that the high energy ball milling time from tens of minutes to several hours results in the coercivity increase of Mn-Bi powders and peak values of 14.3 kOe around 10 h. LTP Mn-Bi nanosheets are characterized by an average thickness of tens of nanometers, an average diameter of ˜1.5 μm, and possess a relatively large aspect ratio, an ultra-high room temperature coercivity of 22.3 kOe, a significant geometrical and magnetic anisotropy, and a strong (00l) crystal texture. Magnetization and demagnetization behaviors reveal that wall pinning is the dominant coercivity mechanism in these LTP Mn-Bi nanosheets. The ultrafine grain refinement introduced by the SA-HEBM process contribute to the ultra-high coercivity of LTP Mn-Bi nanosheets and a large number of defects put a powerful pinning effect on the magnetic domain movement, simultaneously. Further magnetic measurement at 437 K shows that a high coercivity of 17.8 kOe and a strong positive temperature coefficient of coercivity existed in the bonded permanent magnet made by LTP Mn-Bi nanosheets.

  10. Properties of p- and n-Type PbTe Microwires for Thermoelectric Devices

    NASA Astrophysics Data System (ADS)

    Bhatta, Rudra P.; Henderson, Mark; Eufrasio, Andreza; Pegg, Ian L.; Dutta, Biprodas

    2014-11-01

    In thermopower measurements, microwires fabricated from as-purchased bulk PbTe exhibits p-type behavior between room temperature and ˜600 K. At higher temperatures, it undergoes majority carrier inversion and exhibits n-type behavior. We report on the preparation and properties of potassium oxide and Zn-doped PbTe microwires, which exhibit stable p- and n-type behavior, respectively, between room temperature and 725 K. Thermoelectric figures of merit (ZT) are reported for device components prepared from bundles of such p- and n-type microwires in a glass matrix.

  11. Effect of silver addition on thermoelectric properties of half-doped rare-earth manganite

    NASA Astrophysics Data System (ADS)

    Khade, Poonam; Bagwaiya, Toshi; Bhattacharya, Shovit; Aswal, D. K.; Gupta, S. K.; Shelke, Vilas

    2016-05-01

    We have synthesized polycrystalline samples with nominal compositions La0.5Ca0.5MnO3-Agx (0 ≤ x ≤ 0.1) by solid state reaction method and studied thermoelectric properties within the temperature range of 300K to 800K. The electrical resistivity decreases with increasing temperature for all the samples. The Seebeck coefficient (S) increases gradually with temperature and negative sign of indicates n-type nature. The addition of silver causes a drastic reduction in electrical resistivity and significant enhancement in Seebeck coefficient.

  12. Rubbing effect on surface morphology and thermoelectric properties of TTF-TCNQ thin films

    NASA Astrophysics Data System (ADS)

    Tamayo, E.; Hayashi, K.; Shinano, T.; Miyazaki, Y.; Kajitani, T.

    2010-05-01

    Thin films of tetrathiofulvalene-tetracyanoquinodimethane (TTF-TCNQ), a typical organic material of charge transfer salts, were prepared on glass substrates by evaporation using TTF-TCNQ powder. The rubbing effect on the surface morphology and thermoelectric properties was studied. TTF-TCNQ films exhibited a bush-like disordered growth on the as-received glass substrate, whereas those on the rubbed glass substrate had extremely flat surfaces tiled with small rectangular TTF-TCNQ single crystals. Due to the ordered alignment of TTF-TCNQ tiles, improvement in the electrical conductivity and enhancement of the Seebeck coefficient were achieved.

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

    SciTech Connect

    Chang, Taehoo; Kim, Jeongmin; Song, Min-Jung; Lee, Wooyoung

    2015-05-15

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

  14. Thermoelectric properties of Al doped Mg{sub 2}Si material

    SciTech Connect

    Kaur, Kulwinder Kumar, Ranjan; Rani, Anita

    2015-08-28

    In the present paper we have calculated thermoelectric properties of Al doped Mg{sub 2}Si material (Mg{sub 2−x}Al{sub x}Si, x=0.06) using Pseudo potential plane wave method based on DFT and Semi classical Boltzmann theory. The calculations showed n-type conduction, indicating that the electrical conduction are due to electron. The electrical conductivity increasing with increasing temperature and the negative value of Seebeck Coefficient also show that the conduction is due to electron. The thermal conductivity was increased slightly by Al doping with increasing temperature due to the much larger contribution of lattice thermal conductivity over electronic thermal conductivity.

  15. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    SciTech Connect

    Shi, Guangsha; Kioupakis, Emmanouil

    2015-02-14

    We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV, while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10{sup 19}–10{sup 20 }cm{sup −3} range.

  16. Towards Improved Thermoelectric Generator Materials

    NASA Astrophysics Data System (ADS)

    Julian Goldsmid, H.

    2016-07-01

    Over recent years, new thermoelectric materials have been developed with values for the dimensionless figure of merit, zT, substantially greater than unity. This has opened up the possibility of many new applications, particularly those involving the utilisation of waste heat. However, further improvements are necessary if thermoelectric generation is to have a significant impact on the world's energy problems. It is well known that zT for a single energy band can be related to the Fermi energy and a parameter (μ/λ L) (m*/m)3/2, where μ is the carrier mobility, m*/m is the ratio of the carrier effective mass to the mass of a free electron and λ L is the lattice thermal conductivity. However, even when this parameter tends towards infinity, zT does not become much greater than 1 unless the Fermi level lies within the energy gap, far from the appropriate band edge. Thus, the magnitude of the energy gap is becoming of increasing importance. The two-fold requirements of a high value of (μ/λ L) (m*/m)3/2 and a sufficiently large energy gap are discussed. It is also shown that the likelihood of the required conditions being met at elevated temperatures can be predicted from low-temperature observations. It is, of course, much more difficult to make accurate determinations of the thermoelectric properties at higher temperatures.

  17. Thermoelectric properties of rocksalt ZnO from first-principles calculations

    SciTech Connect

    Alvarado, Andrew; Attapattu, Jeevake; Zhang, Yi; Chen, Changfeng

    2015-10-28

    Zinc oxide (ZnO) undergoes a pressure-induced structural transition from its normal ambient-pressure wurtzite (WZ) phase to a rocksalt (RS) phase around 10 GPa. A recent experiment shows that the high-pressure RS ZnO phase can be recovered and stabilized at ambient conditions, which raises exciting prospects of expanding the range of properties of ZnO. For a fundamental understanding of the RS ZnO phase, we have performed first-principles calculations to determine its electronic, phonon, and thermodynamic properties at high (20 GPa) and ambient (0 GPa) pressure. Furthermore, we have calculated its electrical and thermal transport properties, which allow an evaluation of its thermoelectric figure of merit ZT at different temperature and doping levels. Our calculations show that the ambient-pressure RS ZnO phase can reach ZT values of 0.25 to 0.3 under both n-type and p-type doping in a large temperature range of 400 K to 800 K, which is considerably lower than the temperature range of 1400 K to 1600 K where WZ ZnO reaches similar ZT values. These results establish RS ZnO as a promising material for thermoelectric devices designed to operate at temperatures desirable for many heat recovery applications.

  18. Enhancement of Thermoelectric Properties of Molybdenum Diselenide Through Combined Mg Intercalation and Nb Doping

    NASA Astrophysics Data System (ADS)

    Ruan, Limin; Zhao, Huaizhou; Li, Dandan; Jin, Shifeng; Li, Shanming; Gu, Lin; Liang, Jingkui

    2016-06-01

    Thermoelectric properties of MoSe2.1 were enhanced through a combination of Mg intercalation and Nb doping. Magnesium intercalation simultaneously enhances the Seebeck coefficient and electrical conductivity, owing to a favorable modification of band structure upon Mg intercalation. And Nb substitution on the Mo site increases carrier concentration by two orders of magnitude, in addition to reducing the thermal conductivity of the lattice. With systematic study of the anisotropic thermal and electrical transport properties, an optimized ZT of 0.2 was achieved at 888 K for a Nb0.03 Mo0.97Se2.1Mg0.2 sample along its out-of-plane direction, far exceeding the ˜0.01 value for intrinsic MoSe2.1. While 2 dimensional (2D) transitional-metal dichalcogenides with layered structure have been extensively studied for the fields of ion batteries, optical and electronic devices, and so on, enhancement of thermoelectric properties for these intrinsic semiconductors has rarely been investigated.

  19. Thermoelectric properties of rocksalt ZnO from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Alvarado, Andrew; Attapattu, Jeevake; Zhang, Yi; Chen, Changfeng

    2015-10-01

    Zinc oxide (ZnO) undergoes a pressure-induced structural transition from its normal ambient-pressure wurtzite (WZ) phase to a rocksalt (RS) phase around 10 GPa. A recent experiment shows that the high-pressure RS ZnO phase can be recovered and stabilized at ambient conditions, which raises exciting prospects of expanding the range of properties of ZnO. For a fundamental understanding of the RS ZnO phase, we have performed first-principles calculations to determine its electronic, phonon, and thermodynamic properties at high (20 GPa) and ambient (0 GPa) pressure. Furthermore, we have calculated its electrical and thermal transport properties, which allow an evaluation of its thermoelectric figure of merit ZT at different temperature and doping levels. Our calculations show that the ambient-pressure RS ZnO phase can reach ZT values of 0.25 to 0.3 under both n-type and p-type doping in a large temperature range of 400 K to 800 K, which is considerably lower than the temperature range of 1400 K to 1600 K where WZ ZnO reaches similar ZT values. These results establish RS ZnO as a promising material for thermoelectric devices designed to operate at temperatures desirable for many heat recovery applications.

  20. Dielectrophoretic investigation of Bi2Te3 nanowires—a microfabricated thermoelectric characterization platform for measuring the thermoelectric and structural properties of single nanowires

    NASA Astrophysics Data System (ADS)

    Wang, Zhi; Kojda, Danny; Peranio, Nicola; Kroener, Michael; Mitdank, Rüdiger; Toellner, William; Nielsch, Kornelius; Fischer, Saskia F.; Gutsch, Sebastian; Zacharias, Margit; Eibl, Oliver; Woias, Peter

    2015-03-01

    In this article a microfabricated thermoelectric nanowire characterization platform to investigate the thermoelectric and structural properties of single nanowires is presented. By means of dielectrophoresis (DEP), a method to manipulate and orient nanowires in a controlled way to assemble them onto our measurement platform is introduced. The thermoelectric platform fabricated with optimally designed DEP electrodes results in a yield of nanowire assembly of approximately 90% under an applied peak-to-peak ac signal Vpp = 10 V and frequency f = 20 MHz within a series of 200 experiments. Ohmic contacts between the aligned single nanowire and the electrodes on the platform are established by electron beam-induced deposition. The Seebeck coefficient and electrical conductivity of electrochemically synthesized Bi2Te3 nanowires are measured to be -51 μV K-1 and (943 ± 160)/(Ω-1 cm-1), respectively. Chemical composition and crystallographic structure are obtained using transmission electron microscopy. The selected nanowire is observed to be single crystalline over its entire length and no grain boundaries are detected. At the surface of the nanowire, 66.1 ± 1.1 at.% Te and 34.9 ± 1.1 at.% Bi are observed. In contrast, chemical composition of 64.2 at.% Te and 35.8 at.% Bi is detected in the thick center of the nanowire.

  1. Electronic and thermoelectric transport properties for a zigzag graphene-silicene-graphene heterojunction modulated by external field

    NASA Astrophysics Data System (ADS)

    Zhou, Benhu; Zhou, Benliang; Zeng, Yangsu; Zhou, Guanghui; Duan, Manyi

    2016-04-01

    we investigate the electronic and thermoelectric transport properties for a graphene-silicene-graphene (GSG) heterojunction with zigzag-edge nanoribbons under the modulation of the effective spin-orbit coupling (SOC) and potential energy. Using the nonequilibrium Green's function method, it is demonstrated that both the transmission coefficient T and the charge Seebeck coefficient SC display the oscillatory behavior and can be effectively modulated by effective SOC λSO and the potential energy V0. Furthermore, the even-odd difference in transport and thermoelectric properties disappears in the GSG heterojunction. Additionally, the dependence of the transmission coefficient and the charge Seebeck coefficient on Anderson disorder strength has been studied.

  2. First-principles study on doping and temperature dependence of thermoelectric property of Bi{sub 2}S{sub 3} thermoelectric material

    SciTech Connect

    Guo, Donglin; Hu, Chenguo; Zhang, Cuiling

    2013-05-15

    Graphical abstract: The direction-induced ZT is found. At ZZ direction and n = 1.47 × 10{sup 19} cm{sup −3}, the ZT can reach maximal value, 0.36, which is three times as much as maximal laboratorial value. This result matches well the analysis of electron effective mass. Highlights: ► Electrical transportations of Bi{sub 2}S{sub 3} depend on the concentration and temperature. ► The direction-induced ZT is found. ► At ZZ direction and n = 1.47 × 10{sup 19} cm{sup −3}, the ZT can reach maximal value, 0.36. ► The maximal ZT value is three times as much as maximal laboratorial value. ► By doping and temperature tuning, Bi{sub 2}S{sub 3} is a promising thermoelectric material. - Abstract: The electronic structure and thermoelectric property of Bi{sub 2}S{sub 3} are investigated. The electron and hole effective mass of Bi{sub 2}S{sub 3} is analyzed in detail, from which we find that the thermoelectric transportation varies in different directions in Bi{sub 2}S{sub 3} crystal. Along ac plane the higher figure of merit (ZT) could be achieved. For n-type doped Bi{sub 2}S{sub 3}, the optimal doping concentration is found in the range of (1.0–5.0) × 10{sup 19} cm{sup −3}, in which the maximal ZT reaches 0.21 at 900 K, but along ZZ direction, the maximal ZT reaches 0.36. These findings provide a new understanding of thermoelectricity-dependent structure factors and improving ZT ways. The donor concentration N increases as T increases at one bar of pressure under a suitable chemical potential μ, but above this chemical potential μ, the donor concentration N keeps a constant.

  3. Comments on the thermoelectric properties of pressure-sintered Si0.8Ge0.2 thermoelectric alloys

    NASA Astrophysics Data System (ADS)

    Rowe, D. M.; Fu, L. W.; Williams, S. G. K.

    1993-05-01

    The recent results of C. B. Vining, W. Laskow, J. O. Hanson, R. R. Van der Beck, and P. D. Gorsuch [J. Appl. Phys. 69, 4333 (1991)] regarding the effect of grain size on the thermoelectric figure of merit of heavily doped p-type silicon germanium alloys are compared to earlier results on similar materials. The data confirm that the room-temperature figure-of-merit is significantly increased in materials with a small grain size.

  4. Thermoelectric transport properties of molybdenum from abinitio simulations

    NASA Astrophysics Data System (ADS)

    French, Martin; Mattsson, Thomas R.

    2014-10-01

    We employ abinitio simulations based on density functional theory (DFT) to calculate the electronic transport coefficients (electrical conductivity, thermal conductivity, and thermopower) of molybdenum over a broad range of thermodynamic states. By comparing to available experimental data, we show that DFT is able to describe the desired transport properties of this refractory metal with high accuracy. Most noteworthy, both the positive sign and the quantitative values of the thermopower of solid molybdenum are reproduced very well. We calculate the electrical and thermal conductivity in the solid and the fluid phase between 1000 and 20 000 K and a wide span in density and develop empirical fit formulas for direct use in practical applications, such as magneto-hydrodynamics simulations. The influence of thermal expansion in conductivity measurements at constant pressure is also discussed in some detail.

  5. Revealing the optoelectronic and thermoelectric properties of the Zintl quaternary arsenides ACdGeAs{sub 2} (A = K, Rb)

    SciTech Connect

    Azam, Sikander; Khan, Saleem Ayaz; Goumri-Said, Souraya

    2015-10-15

    Highlights: • Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) are chalcopyrite and semiconductors. • Their direct band gap is suitable for PV, optolectronic and thermoelectric applications. • Combination of DFT and Boltzmann transport theory is employed. • The present arsenides are found to be covalent materials. - Abstract: Chalcopyrite semiconductors have attracted much attention due to their potential implications in photovoltaic and thermoelectric applications. First principle calculations were performed to investigate the electronic, optical and thermoelectric properties of the Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) using the full potential linear augmented plane wave method and the Engle–Vosko GGA (EV–GGA) approximation. The present compounds are found semiconductors with direct band gap and covalent bonding character. The optical transitions are investigated via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity and energy-loss spectrum. Combining results from DFT and Boltzmann transport theory, we reported the thermoelectric properties such as the Seebeck’s coefficient, electrical and thermal conductivity, figure of merit and power factor as function of temperatures. The present chalcopyrite Zintl quaternary arsenides deserve to be explored for their potential applications as thermoelectric materials and for photovoltaic devices.

  6. Sb- and Bi-doped Mg2Si: location of the dopants, micro- and nanostructures, electronic structures and thermoelectric properties.

    PubMed

    Farahi, Nader; VanZant, Mathew; Zhao, Jianbao; Tse, John S; Prabhudev, Sagar; Botton, Gianluigi A; Salvador, James R; Borondics, Ferenc; Liu, Zhenxian; Kleinke, Holger

    2014-10-28

    Due to increasing global energy concerns, alternative sustainable methods to create energy such as thermoelectric energy conversion have become increasingly important. Originally, research into thermoelectric materials was focused on tellurides of bismuth and lead because of the exemplary thermoelectric properties of Bi2Te3 and PbTe. These materials, however, contain toxic lead and tellurium, which is also scarce and thus expensive. A viable alternative material may exist in Mg2Si, which needs to be doped and alloyed in order to achieve reasonable thermoelectric efficiency. Doping is a major problem, as p-type doping has thus far not produced competitive efficiencies, and n-type doping is problematic because of the low solubility of the typical dopants Sb and Bi. This investigation shows experimentally that these dopants can indeed replace Si in the crystal lattice, and excess Sb and Bi atoms are present in the grain boundaries in the form of Mg3Sb2 and Mg3Bi2. As a consequence, the carrier concentration is lower than the formal Sb/Bi concentration suggests, and the thermal conductivity is significantly reduced. DFT calculations are in good agreement with the experimental data, including the band gap and the Seebeck coefficient. Overall, this results in competitive efficiencies despite the low carrier concentration. While ball-milling was previously shown to enhance the solubility of the dopants and thus the carrier concentration, this did not lead to enhanced thermoelectric properties. PMID:25005794

  7. The time and temperature dependence of the thermoelectric properties of silicon-germanium alloy

    NASA Technical Reports Server (NTRS)

    Raag, V.

    1975-01-01

    Experimental data on the electrical resistivity and Seebeck coefficient of n-type and p-type silicon-germanium alloys are analyzed in terms of a solid-state dopant precipitation model proposed by Lifshitz and Slyozov (1961). Experimental findings on the time and temperature dependence of the thermal conductivity of these two types of alloy indicate that the thermal conductivity of silicon-germanium alloys changes with time, contrary to previous hypothesis. A preliminary model is presented which stipulates that the observed thermal conductivity decrease in silicon-germanium alloys is due partly to dopant precipitation underlying the electrical property changes and partly to enhanced alloying of the material. It is significant that all three properties asymptotically approach equilibrium values with time. Total characterization of these properties will enable the time change to be fully compensated in the design of a thermoelectric device employing silicon-germanium alloys.

  8. The structural properties of InGaN alloys and the interdependence on the thermoelectric behavior

    NASA Astrophysics Data System (ADS)

    Kucukgok, Bahadir; Wu, Xuewang; Wang, Xiaojia; Liu, Zhiqiang; Ferguson, Ian T.; Lu, Na

    2016-02-01

    The III-Nitrides are promising candidate for high efficiency thermoelectric (TE) materials and devices due to their unique features which includes high thermal stability. A systematic study of the room temperature TE properties of metalorganic chemical vapor deposition grown InxGa1-xN were investigated for x = 0.07 to 0.24. This paper investigated the role of indium composition on the TE properties of InGaN alloys in particular the structural properties for homogenous material that did not show significant phase separation. The highest Seebeck and power factor values of 507 μV K-1 and 21.84 × 10-4 Wm-1K-1 were observed, respectively for In0.07Ga0.93N at room temperature. The highest value of figure-of-merit (ZT) was calculated to be 0.072 for In0.20Ga0.80N alloy at room temperature.

  9. Improving thermoelectric properties of bulk Si by dispersing VSi2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Yusufu, Aikebaier; Kurosaki, Ken; Ohishi, Yuji; Muta, Hiroaki; Yamanaka, Shinsuke

    2016-06-01

    In order to enhance the thermoelectric properties of Si-based bulk materials, the lattice thermal conductivity (κlat) should be reduced with little degradation of the electrical properties. Our group had previously demonstrated that the phosphorus (P)-rich nanoscale precipitates formed naturally in heavily P-doped bulk Si scatter phonons more effectively than carriers, resulting in a high figure of merit (ZT) [A. Yusufu et al., Nanoscale 6, 13921 (2014)]. Here, we successfully prepared heavily P-doped bulk Si containing metallic VSi2 nanoparticles through the ball milling of Si, V, and P and subsequent spark plasma sintering. The VSi2 nanoparticles did not affect the electrical properties of Si significantly but greatly decreased the κlat, leading to a marked increase in ZT. The maximum ZT value, which was 0.4, was obtained at 1073 K, which is two times higher than that for Si.

  10. 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.

  11. Structural, electrical, and thermoelectric properties of bismuth telluride: Silicon/carbon nanocomposites thin films

    SciTech Connect

    Agarwal, Khushboo; Mehta, B. R.

    2014-08-28

    In this study, the effect of the presence of secondary phases on the structural, electrical, and thermoelectric properties of nanocomposite Bi{sub 2}Te{sub 3} films prepared by co-sputtering of silicon and carbon with Bi{sub 2}Te{sub 3} has been investigated. Growth temperature and the presence of Si and C phase are observed to have a strong effect on the topography and orientation of crystallites. X-ray diffraction study demonstrates that Bi{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3}:C samples have preferred (0 0 15) orientation in comparison to Bi{sub 2}Te{sub 3}:Si sample, which have randomly oriented crystallites. Atomic force, conducting atomic force, and scanning thermal microscopy analysis show significant differences in topographical, electrical, and thermal conductivity contrasts in Bi{sub 2}Te{sub 3}:Si and Bi{sub 2}Te{sub 3}:C samples. Due to the randomly oriented crystallites and the presence of Si along the crystallite boundaries, appreciable Seebeck coefficient, higher electrical conductivity, and lower thermal conductivity is achieved resulting in relatively higher value of power factor (3.71 mW K{sup −2} m{sup −1}) for Bi{sub 2}Te{sub 3}:Si sample. This study shows that by incorporating a secondary phase along crystallite boundaries, microstructural, electrical, and thermoelectric properties of the composite samples can be modified.

  12. Impact of parasitic thermal effects on thermoelectric property measurements by Harman method

    SciTech Connect

    Kwon, Beomjin Baek, Seung-Hyub; Keun Kim, Seong; Kim, Jin-Sang

    2014-04-15

    Harman method is a rapid and simple technique to measure thermoelectric properties. However, its validity has been often questioned due to the over-simplified assumptions that this method relies on. Here, we quantitatively investigate the influence of the previously ignored parasitic thermal effects on the Harman method and develop a method to determine an intrinsic ZT. We expand the original Harman relation with three extra terms: heat losses via both the lead wires and radiation, and Joule heating within the sample. Based on the expanded Harman relation, we use differential measurement of the sample geometry to measure the intrinsic ZT. To separately evaluate the parasitic terms, the measured ZTs with systematically varied sample geometries and the lead wire types are fitted to the expanded relation. A huge discrepancy (∼28%) of the measured ZTs depending on the measurement configuration is observed. We are able to separately evaluate those parasitic terms. This work will help to evaluate the intrinsic thermoelectric property with Harman method by eliminating ambiguities coming from extrinsic effects.

  13. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    SciTech Connect

    Wickramaratne, Darshana E-mail: rlake@ece.ucr.edu; Lake, Roger K. E-mail: rlake@ece.ucr.edu; Zahid, Ferdows

    2015-08-21

    The valence band of a variety of few-layer, two-dimensional materials consist of a ring of states in the Brillouin zone. The energy-momentum relation has the form of a “Mexican hat” or a Rashba dispersion. The two-dimensional density of states is singular at or near the band edge, and the band-edge density of modes turns on nearly abruptly as a step function. The large band-edge density of modes enhances the Seebeck coefficient, the power factor, and the thermoelectric figure of merit ZT. Electronic and thermoelectric properties are determined from ab initio calculations for few-layer III–VI materials GaS, GaSe, InS, InSe, for Bi{sub 2}Se{sub 3}, for monolayer Bi, and for bilayer graphene as a function of vertical field. The effect of interlayer coupling on these properties in few-layer III–VI materials and Bi{sub 2}Se{sub 3} is described. Analytical models provide insight into the layer dependent trends that are relatively consistent for all of these few-layer materials. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring these effects.

  14. Structural and Thermoelectric Properties of Polycrystalline p-Type Mg2- x Li x Si

    NASA Astrophysics Data System (ADS)

    Nieroda, P.; Kolezynski, A.; Oszajca, M.; Milczarek, J.; Wojciechowski, K. T.

    2016-07-01

    The aim of this study was to determine the location of Li atoms in Mg2Si structure, and verify the influence of Li dopant on the transport properties of obtained thermoelectric materials. The results of theoretical studies of the electronic band structure (full potential linearized augmented plane wave method) in Li-doped Mg2Si are presented. Theoretical calculations indicate that only in the case when Li is located in the Mg position, the samples will have p-type conduction. To confirm the theoretical predictions, a series of samples with nominal composition Mg2- x Li x Si ( x = 0-0.5) were prepared using the spark plasma sintering (SPS) method. Structural and phase composition analyses were carried out by x-ray and neutron powder diffraction, as well as scanning electron microscopy. Neutron diffraction studies confirmed that the lithium atoms substitute magnesium in the Mg2Si structure. The investigations of the influence of Li dopant on the transport properties, i.e. electrical conductivity, the Seebeck coefficient and the thermal conductivity, were carried out in a temperature range from 340 K to 720 K. Carrier concentration was measured with Hall method. The positive values of the Seebeck coefficient and Hall coefficient indicate that all examined samples show p-type conductivity. On the basis of the experimental data, the temperature dependencies of the thermoelectric figure of merit ZT were calculated.

  15. Top-down fabrication of silicon nanowire devices for thermoelectric applications: properties and perspectives

    NASA Astrophysics Data System (ADS)

    Pennelli, Giovanni

    2015-05-01

    In this paper, the most recent achievements in the field of device fabrication, based on nanostructured silicon, will be reviewed. Top-down techniques for silicon nanowire production based on lithography, oxidation and highly anisotropic etching (wet, plasma and metal assisted) will be discussed, illustrating both advantages and drawbacks. In particular, fabrication processes for a massive production of silicon nanowires, organized and interconnected in devices with macroscopic dimensions, will be shown and discussed. These macroscopic devices offer the possibility of exploiting the nanoscale thermoelectric properties of silicon in practical applications. In particular, the reduced thermal conductivity of silicon nanowires, with respect to bulk silicon, makes possible to obtain high efficiencies in the direct conversion of heat into electrical power, with intriguing applications in the field of green energy harvesting. The main experiments elucidating the electrical and thermal properties of silicon nanowire devices will be shown and discussed, and compared with the recent theoretical works developed on the subject. Contribution to the Topical Issue "Silicon and Silicon-related Materials for Thermoelectricity", edited by Dario Narducci.

  16. Effect of pressure on electronic and thermoelectric properties of magnesium silicide: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Kulwinder, Kaur; Ranjan, Kumar

    2016-05-01

    We study the effect of pressure on electronic and thermoelectric properties of Mg2Si using the density functional theory and Boltzmann transport equations. The variation of lattice constant, band gap, bulk modulus with pressure is also analyzed. Further, the thermoelectric properties (Seebeck coefficient, electrical conductivity, electronic thermal conductivity) have been studied as a function of temperature and pressure up to 1200 K. The results show that Mg2Si is an n-type semiconductor with a band gap of 0.21 eV. The negative value of the Seebeck coefficient at all pressures indicates that the conduction is due to electrons. With the increase in pressure, the Seebeck coefficient decreases and electrical conductivity increases. It is also seen that, there is practically no effect of pressure on the electronic contribution of thermal conductivity. The paper describes the calculation of the lattice thermal conductivity and figure of merit of Mg2Si at zero pressure. The maximum value of figure of merit is attained 1.83×10‑3 at 1000 K. The obtained results are in good agreement with the available experimental and theoretical results. Project supported by the Council of Scientific & Industrial Research (CSIR), India.

  17. Effect of Length and Contact Chemistry on the Electronic Structure and Thermoelectric Properties of Molecular Junctions

    SciTech Connect

    Tan, Aaron; Balachandran, Janakiraman; Sadat, Seid; Gavini, Vikram; Dunietz, Barry D.; Jang, Sung-Yeon; Reddy, Pramod

    2011-06-15

    We present a combined experimental and computational study that probes the thermoelectric and electrical transport properties of molecular junctions. Experiments were performed on junctions created by trapping aromatic molecules between gold electrodes. The end groups (-SH, -NC) of the aromatic molecules were systematically varied to study the effect of contact coupling strength and contact chemistry. When the coupling of the molecule with one of the electrodes was reduced by switching the terminal chemistry from -SH to -H, the electrical conductance of molecular junctions decreased by an order of magnitude, whereas the thermopower varied by only a few percent. This has been predicted computationally in the past and is experimentally demonstrated for the first time. Further, our experiments and computational modeling indicate the prospect of tuning thermoelectric properties at the molecular scale. In particular, the thiol-terminated aromatic molecular junctions revealed a positive thermopower that increased linearly with length. This positive thermopower is associated with charge transport primarily through the highest occupied molecular orbital, as shown by our computational results. In contrast, a negative thermopower was observed for a corresponding molecular junction terminated by an isocyanide group due to charge transport primarily through the lowest unoccupied molecular orbital.

  18. Effects of Cu5Zn3 addition on the thermoelectric properties of Zn4Sb3

    NASA Astrophysics Data System (ADS)

    Cui, J. L.; Fu, H.; Mao, L. D.; Chen, D. Y.; Liu, X. L.

    2009-07-01

    The structures and thermoelectric properties of mCu5Zn3ṡnZn4Sb3 with multiphase coexistence are reported. Rietveld analysis reveals that at least 92.3% wt % β-Zn4Sb3 phase can be obtained with only small quantities of ZnSb and Cu5Zn8 phases precipitated after proper Cu5Zn3 addition. Measurements indicate that although the β-Zn4Sb3 phase plays a determining role in controlling the transport properties involving the Seebeck coefficient, electrical conductivity, and thermal conductivity, the impurity phases Cu5Zn8 and ZnSb with a crooked riverlike and intertwined tree stump morphologies, respectively, are still of great significance to tune the thermoelectric performance. The highest ZT value of 0.84 can be obtained for the alloy mCu5Zn3ṡnZn4Sb3 (m /n=1/200) at 631 K, approximately 1.8 times that of undoped β-Zn4Sb3, proving that a good combination between the transports of carriers and phonons can be achieved if a proper dopant is introduced in the Zn4Sb3 matrix.

  19. CsBi4Te6: a new facile synthetic method and mid-temperature thermoelectric performance.

    PubMed

    Lin, Hua; Chen, Hong; Yu, Ju-Song; Zheng, Yu-Jun; Liu, Peng-Fei; Ali Khan, Muhammad; Wu, Li-Ming

    2016-07-26

    CsBi4Te6 is one of the best performing low-temperature thermoelectric (TE) materials. However, it has not received worldwide intensive investigation due to the limitation of synthetic methods. Here we report a new facile approach by not using the reactive Cs metal and the mid-temperature TE properties have been studied for the first time. PMID:27383416

  20. First-principles calculations of thermal, electrical, and thermoelectric transport properties of semiconductors

    NASA Astrophysics Data System (ADS)

    Zhou, Jiawei; Liao, Bolin; Chen, Gang

    2016-04-01

    The transport properties of semiconductors are key to the performance of many solid-state devices (transistors, data storage, thermoelectric cooling and power generation devices, etc). An understanding of the transport details can lead to material designs with better performances. In recent years simulation tools based on first-principles calculations have been greatly improved, being able to obtain the fundamental ground-state properties of materials (such as band structure and phonon dispersion) accurately. Accordingly, methods have been developed to calculate the transport properties based on an ab initio approach. In this review we focus on the thermal, electrical, and thermoelectric transport properties of semiconductors, which represent the basic transport characteristics of the two degrees of freedom in solids—electronic and lattice degrees of freedom. Starting from the coupled electron-phonon Boltzmann transport equations, we illustrate different scattering mechanisms that change the transport features and review the first-principles approaches that solve the transport equations. We then present the first-principles results on the thermal and electrical transport properties of semiconductors. The discussions are grouped based on different scattering mechanisms including phonon-phonon scattering, phonon scattering by equilibrium electrons, carrier scattering by equilibrium phonons, carrier scattering by polar optical phonons, scatterings due to impurities, alloying and doping, and the phonon drag effect. We show how the first-principles methods allow one to investigate transport properties with unprecedented detail and also offer new insights into the electron and phonon transport. The current status of the simulation is mentioned when appropriate and some of the future directions are also discussed.

  1. Thermoelectric Properties of In-Doped Cu2ZnGeSe4

    NASA Astrophysics Data System (ADS)

    Chetty, R.; Bali, A.; Femi, O. E.; Chattopadhyay, K.; Mallik, R. C.

    2016-03-01

    Recently, much research has been focused on finding new thermoelectric materials. Cu-based quaternary chalcogenides that belong to A2BCD4 (A = Cu; B = Zn, Cd; C = Sn, Ge; D = S, Se, Te) are wide band gap materials and one of the potential thermoelectric materials due to their complex crystal structures. In this study, In-doped quaternary compounds Cu2ZnGe1- x In x Se4 ( x = 0, 0.025, 0.05, 0.075, 0.1) were prepared by a solid state synthesis method. Powder x-ray diffraction patterns of all the samples showed a tetragonal crystal structure (space group I- 42m) of the main phase with a trace amount of impurity phases, which was further confirmed by Rietveld analysis. The elemental composition of all the samples showed a slight deviation from the nominal composition with the presence of secondary phases. All the transport properties were measured in the temperature range 373-673 K. The electrical resistivity of all the samples initially decreased up to ˜470 K and then increased with increase in temperature upto 673 K, indicating the transition from semiconducting to metallic behavior. Positive Seebeck coefficients for all the samples revealed that holes are the majority carriers in the entire temperature range. The substitution of In3+ on Ge4+ introduces holes and results in the decrease of resistivity as well as the Seebeck coefficient, thereby leading to the optimization of the power factor. The lattice thermal conductivity of all the samples decreased with increasing temperature, indicating the presence of phonon-phonon scattering. As a result, the thermoelectric figure of merit ( zT) of the doped sample showed an increase as compared to the undoped compound.

  2. Electronics Demonstrated for Low- Temperature Operation

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Hammond, Ahmad; Gerber, Scott S.

    2000-01-01

    The operation of electronic systems at cryogenic temperatures is anticipated for many NASA spacecraft, such as planetary explorers and deep space probes. For example, an unheated interplanetary probe launched to explore the rings of Saturn would experience an average temperature near Saturn of about 183 C. Electronics capable of low-temperature operation in the harsh deep space environment also would help improve circuit performance, increase system efficiency, and reduce payload development and launch costs. An ongoing research and development program on low-temperature electronics at the NASA Glenn Research Center at Lewis Field is focusing on the design of efficient power systems that can survive and exploit the advantages of low-temperature environments. The targeted systems, which are mission driven, include converters, inverters, controls, digital circuits, and special-purpose circuits. Initial development efforts successfully demonstrated the low-temperature operation and cold-restart of several direct-current/direct-current (dc/dc) converters based on different types of circuit design, some with superconducting inductors. The table lists some of these dc/dc converters with their properties, and the photograph shows a high-voltage, high-power dc/dc converter designed for an ion propulsion system for low-temperature operation. The development efforts of advanced electronic systems and the supporting technologies for low-temperature operation are being carried out in-house and through collaboration with other Government agencies, industry, and academia. The Low Temperature Electronics Program supports missions and development programs at NASA s Jet Propulsion Laboratory and Goddard Space Flight Center. The developed technologies will be transferred to commercial end users for applications such as satellite infrared sensors and medical diagnostic equipment.

  3. Thermoelectric efficiency of topological insulators in a magnetic field

    NASA Astrophysics Data System (ADS)

    Tretiakov, O. A.; Abanov, Ar.; Sinova, Jairo

    2012-04-01

    We study the thermoelectric properties of three-dimensional topological insulators in magnetic fields with many holes (or pores) in the bulk. We find that at a high density of these holes in the transport direction the thermoelectric figure of merit, ZT, can be large due to the contribution of the topologically protected conducting surfaces and the suppressed phonon thermal conductivity. By applying an external magnetic field, a subgap can be induced in the surface states' spectrum. We show that the thermoelectric efficiency can be controlled by this tunable subgap leading to values of ZT much greater than 1. Such high values of ZT for reasonable system parameters and its tunability by a magnetic field make this system a strong candidate for applications in the heat management of nanodevices, especially at low temperatures.

  4. A low temperature thermal conductivity database

    NASA Astrophysics Data System (ADS)

    Woodcraft, Adam L.; Gray, Adam

    2009-12-01

    Low temperature detectors necessarily require low temperature instruments. Constructing good low temperature instruments requires information on the properties of materials used in their construction, in particular the thermal conductivity. Unfortunately, this is poorly known for many materials. Collections of data in text books tend to be incomplete and in the worst cases are misleading. For most materials, what information is known is scattered through the literature. Searching out this data is time consuming, and in any case often results in conflicting information. We have started a programme to locate, consolidate and critically analyse thermal conductivity measurements from the literature, particularly for the challenging temperature range below 1 K. This has already produced useful results. We present some preliminary results here.

  5. Flux pinning properties in high magnetic field and low temperature of SmBa 2Cu 3O y thin films

    NASA Astrophysics Data System (ADS)

    Ichino, Y.; Yoshida, Y.; Miura, M.; Takai, Y.; Matsumoto, K.; Mukaida, M.; Ichinose, A.; Horii, S.; Awaji, S.; Watanabe, K.

    2007-10-01

    We have studied SmBa2Cu3Oy (Sm123) thin films fabricated by low temperature growth (LTG) technique. The critical current densities (Jcs) in magnetic fields at 77 K of the LTG-Sm123 film embedded nanosized low-Tc particles (NLP) were comparable to that of NbTi wire at 4.2 K. Furthermore, at low temperatures of 65 and 40 K, the Jc-B curves of the LTG-Sm123 film were superior to even that of Nb3Sn wire at 4.2 K and the anomalous peaks were observed on the Jc-B and Fp-B curves. Based on the scaling of the flux pinning force, we found that fluxes in the film would be pinned at grain boundary mainly and the anomalous peaks were caused by the NLP.

  6. Structural properties of relaxed thin film germanium layers grown by low temperature RF-PECVD epitaxy on Si and Ge (100) substrates

    SciTech Connect

    Cariou, R.; Ruggeri, R.; Tan, X.; Nassar, J.; Roca i Cabarrocas, P.; Mannino, Giovanni

    2014-07-15

    We report on unusual low temperature (175 °C) heteroepitaxial growth of germanium thin films using a standard radio-frequency plasma process. Spectroscopic ellipsometry and transmission electron microscopy (TEM) reveal a perfect crystalline quality of epitaxial germanium layers on (100) c-Ge wafers. In addition direct germanium crystal growth is achieved on (100) c-Si, despite 4.2% lattice mismatch. Defects rising from Ge/Si interface are mostly located within the first tens of nanometers, and threading dislocation density (TDD) values as low as 10{sup 6} cm{sup −2} are obtained. Misfit stress is released fast: residual strain of −0.4% is calculated from Moiré pattern analysis. Moreover we demonstrate a striking feature of low temperature plasma epitaxy, namely the fact that crystalline quality improves with thickness without epitaxy breakdown, as shown by TEM and depth profiling of surface TDD.

  7. Electronic and thermoelectric transport properties for an armchair graphene-silicene-graphene heterojunction modulated by external field

    NASA Astrophysics Data System (ADS)

    Zhou, Benhu; Zhou, Benliang; Zeng, Yangsu; Zhou, Guanghui; Duan, Manyi

    2016-08-01

    We analytically investigate effective spin-orbit coupling (SOC) and potential energy on electronic and thermoelectric transport properties for a graphene-silicene-graphene (GSG) heterojunction with armchair-edge nanoribbons using nonequilibrium Green's function method. The calculation shows that the transmission coefficient T and the charge Seebeck coefficient SC for armchair-edge GSG junctions display the oscillatory behavior and depend sensitively on both effective SOC λSO and the potential energy V0. Compared with zigzag-edge GSG heterojunctions, armchair-edge GSG heterojunctions are found to posses superior thermoelectric performance, their charge Seebeck coefficients can be improved by one order of magnitude.

  8. Thermoelectric properties of hot-pressed and PECS-sintered magnesium-doped copper aluminum oxide

    SciTech Connect

    Liu, Chang; Morelli, Donald T

    2011-02-03

    Copper aluminum oxide (CuAlO{sub 2}) is considered as a potential candidate for thermoelectric applications. Partially magnesium-doped CuAlO{sub 2} bulk pellets were fabricated using solid-state reactions, hot-pressing, and pulsed electric current sintering (PECS) techniques. X-ray diffraction and scanning electron microscopy were adopted for structural analysis. High-temperature transport property measurements were performed on hot-pressed samples. Electrical conductivity increased with Mg doping before secondary phases became significant, while the Seebeck coefficient displayed the opposite trend. Thermal conductivity was consistently reduced as the Mg concentration increased. Effects of Mg doping, preparation conditions, and future modification on this material’s properties are discussed.

  9. Effects of Lanthanum Substitution on Thermoelectric Properties of YbZn2Sb2

    NASA Astrophysics Data System (ADS)

    Zhang, Xiong; Peng, Kunling; Guo, Lijie; Yan, Yanchi; Zhan, Hen; Lu, Xu; Gu, Haoshuang; Zhou, Xiaoyuan

    2016-08-01

    La x Yb1-x Zn2Sb2 polycrystalline are prepared by solid-state reaction followed by spark plasma sintering. The effect of La substitution on the thermoelectric properties of La x Yb1-x Zn2Sb2 has been investigated. It is found that the substitution of La for Yb donates extra electrons to compensate for the vacancies and produces point defects to scatter phonons, leading to a significant reduction of the lattice thermal conductivity. As a result, a maximum ZT of 0.4 is obtained at x = 0.01, 18% enhancement in contrast to that of a pure sample as a result of the identical electrical properties and the largely reduced thermal conductivity.

  10. Synthesis, Structure, and Basic Magnetic and Thermoelectric Properties of the Light Lanthanide Aurobismuthides.

    PubMed

    Seibel, Elizabeth M; Xie, Weiwei; Gibson, Quinn D; Cava, Robert J

    2016-04-01

    We report the crystal structures and elementary properties of the new aurobismuthides La3Au3Bi4, Ce3Au3Bi4, Pr3Au3Bi4, Nd3Au3Bi4, Sm3Au3Bi4, and Gd3Au3Bi4. These ternary compounds are found only for the large lanthanides and crystallize in the cubic Y3Au3Sb4 structure type, which is a stuffed Th3P4-type derivative. The compounds are electron-precise, leading to semiconducting behavior, and display magnetic properties arising from localized lanthanide f states. Resistivity data, Seebeck coefficient measurements, and electronic structure calculations suggest that these phases are heavily doped, p-type semiconductors. Nd3Au3Bi4 and Sm3Au3Bi4 have Seebeck coefficients of 105 and 190 μV/K at 350 K, respectively, making them worthy of further thermoelectric studies. PMID:26974337

  11. Thermoelectric properties of InxGa1-xN alloys

    NASA Astrophysics Data System (ADS)

    Pantha, B. N.; Dahal, R.; Li, J.; Lin, J. Y.; Jiang, H. X.; Pomrenke, G.

    2008-01-01

    Thermoelectric (TE) properties of InxGa1-xN alloys grown by metal organic chemical vapor deposition have been investigated. It was found that as indium concentration increases, the thermal conductivity decreases and power factor increases, which leads to an increase in the TE figure of merit (ZT). The value of ZT was found to be 0.08 at 300K and reached 0.23 at 450K for In0.36Ga0.64N alloy, which is comparable to those of SiGe based alloys. The results indicate that InGaN alloys could be potentially important TE materials for many applications, especially for prolonged TE device operation at high temperatures, such as for recovery of waste heat from automobile, aircrafts, and power plants due to their superior physical properties, including the ability of operating at high temperature/high power conditions, high mechanical strength and stability, and radiation hardness.

  12. Thermoelectric properties of (α-, δ-, ζ-) Ti-Ru-B approximants for the decagonal quasicrystal

    NASA Astrophysics Data System (ADS)

    Takagiwa, Y.; Miyazaki, Y.; Yoshida, T.; Yanagihara, D.; Ueda, S.; Kitahara, K.; Kimura, K.

    2015-09-01

    The electronic structure and the thermoelectric properties of (α-, δ-, ζ-) Ti-Ru-B approximants related to its decagonal quasicrystal phase were investigated. The band structure calculation reveals that they form pseudogaps in the electronic density of states across the Fermi level. The samples were synthesized by arc-melting, followed by spark plasma sintering. The electrical conductivity at 373 K varies from 1600 to 4200 Ω-1 cm-1 and their temperature coefficients are negative. All measured compounds show n-type properties, judging from the sign of the Seebeck coefficient; however, the magnitudes are rather low of less than 25 μV K-1. The phonon thermal conductivity at 373 K have a range 3-5 W m-1 K-1 resulting from complex crystal structures with large unit cell volumes. The maximum dimensionless figure-of-merit of 0.008 is evaluated at 773 K for δ-Ti-Ru-B.

  13. Effect of the microstructure on the thermoelectric properties of polycrystalline lanthanum chalcogenides

    NASA Technical Reports Server (NTRS)

    Lockwood, A.; Wood, C.; Vandersande, J.; Zoltan, A.; Parker, J.; Danielson, L.; Alexander, M.; Whittenberger, D.

    1987-01-01

    Small amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline gamma-La(3-x)X4 (X-S, Te; X in the range of 0 to 1/3). Microscopic examination by SEM of hot pressed La(3-x)Te4 samples has revealed from 1-5 vol. pct of La2O2Te, an amount which is not detected by X-ray powder diffraction measurements. This amount of La2O2Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10 to 75 percent below the electron concentration calculated for single phase La(3-x)Te4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons. These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.

  14. Research In Thermoelectric Materials

    NASA Technical Reports Server (NTRS)

    Wood, Charles

    1989-01-01

    Report reviews current research in thermoelectric materials with view towards development of materials of greater energy-conversion efficiency. Emphasis on effort to understand and manipulate microstructure to increase thermoelectric figure of merit, Z. Thermoelectric properties of three broad categories of materials discussed. First category includes alloys of group IV elements like silicon and germanium. Second category is rare-earth chalcogenides. Third category includes narrow-band semiconductors, especially boron carbides.

  15. Quick Fabrication and Thermoelectric Properties of Cu12Sb4S13 Tetrahedrite

    NASA Astrophysics Data System (ADS)

    Wang, Juyi; Gu, Ming; Bao, Yefeng; Li, Xiaoya; Chen, Lidong

    2016-04-01

    Tetrahedrites, comprised mainly of earth-abundant and environment-friendly elements, copper and sulfur, may pave the way to many new and low-cost thermoelectric energy generation opportunities. However, the preparation of tetrahedrites is time- and energy-consuming. In this paper, we study the melting process and the effect of the annealing time on the microstructure and thermoelectric properties of the Cu12Sb4S13 tetrahedrite, in an effort to shorten the synthesis (melting and annealing) time. Our results show that the Cu12Sb4S13 tetrahedrite phase forms in the melt during cooling. Shortening the melting time does not affect the formation of Cu12Sb4S13. The cooled ingot consists of the principal phase of Cu12Sb4S13 and two secondary phases, Cu3SbS4 and CuSbS2. It is found that prolonged annealing cannot eliminate the impurity phases in Cu12Sb4S13 tetrahedrite, has a small effect on the electrical resistivity, and a negligible effect on the Seebeck coefficient and the thermal conductivity of the tetrahedrite. All our samples have a ZT above 0.47 at 600 K and the maximum ZT obtained was 0.52 when the sample was annealed for 1 day. Based on our experimental results, the time for preparing the Cu12Sb4S13 tetrahedrite can be considerably shortened.

  16. Thermoelectric properties of conducting polymers. Technical report, September 1991-June 1994

    SciTech Connect

    Howell, B.

    1994-07-01

    Development of an inexpensive thermoelectric material which has a better cooling capacity than any currently available would have many practical advantages. On board ships or submarines it would allow a quiet, decentralized cooling architecture, it would reduce usage of chlorofluorocarbons, and would provide less expensive and lighter weight cooling systems. To this end a number of organic materials have been obtained and tested for thermoelectric properties. These include conductive vinyl elastomer, conductive nylon 12, and conductive polyphenylene sulfide, all of which are made conductive by addition of carbon. Polymers made conductive in this way do not have a high Seebeck coefficient. other polymers tested include polyaniline, a Schiff's base polymer (poly-N,N'(1,3-phenylenedimethylidyne)bis(3-ethynylaniline)), TTF-TCNQ (tetrathiafulvalinium tetracyanoquinodimethanide), D sub S(TCNQ)2 (1,2-bis(4-N-methylpyridylium-TCNQ)ethane), and polyoctylthiophene (POT) doped (separately) with 33% of the following substances: iodine, tetraethylamineammonium tetrafluoroborate, potassium persulfate, and ferric chloride. Ferric chloride doped POT was found to have a high Seebeck coefficient (1800 gV/deg C), but the conductivity (0.0074 S/cm) is not high enough to provide a good figure of merit.

  17. Influence of Grain Size on the Thermoelectric Properties of Polycrystalline Silicon Nanowires

    NASA Astrophysics Data System (ADS)

    Suriano, F.; Ferri, M.; Moscatelli, F.; Mancarella, F.; Belsito, L.; Solmi, S.; Roncaglia, A.; Frabboni, S.; Gazzadi, G. C.; Narducci, D.

    2015-01-01

    The thermoelectric properties of doped polycrystalline silicon nanowires have been investigated using doping techniques that impact grain growth in different ways during the doping process. In particular, As- and P-doped nanowires were fabricated using a process flow which enables the manufacturing of surface micromachined nanowires contacted by Al/Si pads in a four-terminal configuration for thermal conductivity measurement. Also, dedicated structures for the measurement of the Seebeck coefficient and electrical resistivity were prepared. In this way, the thermoelectric figure of merit of the nanowires could be evaluated. The As-doped nanowires were heavily doped by thermal doping from spin-on-dopant sources, whereas predeposition from POCl3 was utilized for the P-doped nanowires. The thermal conductivity measured on the nanowires appeared to depend on the doping type. The P-doped nanowires showed, for comparable cross-sections, higher thermal conductivity values than As-doped nanowires, most probably because of their finer grain texture, resulting from the inhibition effect that such doping elements have on grain growth during high-temperature annealing.

  18. Improved thermoelectric property of cation-substituted CaMnO3

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Kashyap Subhash, C.; Sharma Vijay, Kumar; Gupta, H. C.

    2015-09-01

    Single-phase pristine and cation-substituted calcium manganite (Ca1-xBixMn1-yVyO3-δ) polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The Ca1-xBixMn1-yVyO3-δ sample with x = y = 0.04 has shown a power factor (S2σ) of 176 μW/m/K2 at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample (2.1 μW/m/K2). The power factor of the substituted oxide remains almost temperature independent as the Seebeck coefficient increases monotonically with temperature, along with the simultaneous decrease in electrical resistivity which is attributed to enhanced electron density due to co-doping of bismuth and vanadium and grain boundary scattering. These cation-substituted calcium manganites can be used as a potential candidate for an n-type leg in a thermoelectric generator (module).

  19. Electronic and thermoelectric properties of few-layer transition metal dichalcogenides

    SciTech Connect

    Wickramaratne, Darshana; Lake, Roger K.; Zahid, Ferdows

    2014-03-28

    The electronic and thermoelectric properties of one to four monolayers of MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2} are calculated. For few layer thicknesses, the near degeneracies of the conduction band K and Σ valleys and the valence band Γ and K valleys enhance the n-type and p-type thermoelectric performance. The interlayer hybridization and energy level splitting determine how the number of modes within k{sub B}T of a valley minimum changes with layer thickness. In all cases, the maximum ZT coincides with the greatest near-degeneracy within k{sub B}T of the band edge that results in the sharpest turn-on of the density of modes. The thickness at which this maximum occurs is, in general, not a monolayer. The transition from few layers to bulk is discussed. Effective masses, energy gaps, power-factors, and ZT values are tabulated for all materials and layer thicknesses.

  20. Improvement in Thermoelectric Properties by Tailoring at In and Te Site in In2Te5

    NASA Astrophysics Data System (ADS)

    Sanchela, Anup V.; Thakur, Ajay D.; Tomy, C. V.

    2016-07-01

    We study the role of substitutions at In and Te site in the thermoelectric behavior of In2Te5. Single crystals with compositions In2(Te1-x Se x )5 (x = 0, 0.05, 0.10) and Fe0.05In1.95(Te0.90Se0.10)5 were prepared using a modified Bridgman-Stockbarger technique. Electrical and thermal transport properties of these single crystals were measured in the temperature range of 6 K to 395 K. A substantial decrease in the thermal conductivity was observed in Fe-substituted samples, attributed to enhanced phonon scattering at point defects. Marked enhancement in the Seebeck coefficient S along with concomitant suppression of the electrical resistivity ρ was observed in Se-substituted single crystals. An overall enhancement of the thermoelectric figure of merit (zT) by a factor of 310 was observed in single-crystal Fe0.05In1.95(Te0.90Se0.10)5 compared with single crystals of the parent material In2Te5.