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Sample records for low-temperature thermoelectric properties

  1. Thermoelectric properties of LaFeAsO1-y at low temperature

    NASA Astrophysics Data System (ADS)

    Kihou, K.; Lee, C. H.; Miyazawa, K.; Shirage, P. M.; Iyo, A.; Eisaki, H.

    2010-08-01

    We have studied the thermoelectric properties of LaFeAsO1-y in the temperature range 10-300 K. The resistivity decreases with carrier doping induced by oxygen deficiency up to y =0.16. On the other hand, the Seebeck coefficient shows a maximum absolute value at a finite doping level. The power factor (PF) and the dimensionless thermoelectric figure of merit (ZT) in y =0.16 are PF=4.1 mW m-1 K-2 at T =75 K and ZT =0.061 at T =125 K. The results indicate that iron pnictides have potential as a good low temperature thermoelectric material.

  2. 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

  3. Thermoelectric properties of Au-based metallic glass at low temperatures

    NASA Astrophysics Data System (ADS)

    Pryadun, V. V.; Louzguine-Luzgin, D. V.; Shvanskaya, L. V.; Vasiliev, A. N.

    2015-04-01

    The thermoelectric properties of Au49Cu26.9Ag5.5Pd2.3Si16.3 glassy alloy have been studied using electrical resistivity, thermal conductivity and Seebeck coefficient measurements over temperature range 2-390 K. At heating, resistivity ρ decreases in a power-law manner from residual value ρ0 ˜ 150 μΩ cm. The temperature coefficient of resistivity, α = ρ-1(∂ρ/∂ T), is rather small and varies non-monotonously. Thermal conductivity κ rises linearly at low temperatures; it exhibits a plateau-like feature and sharply increases at elevated temperatures. Seebeck coefficient S increases with temperature and exhibits a characteristic "knee" feature. At elevated temperatures, S increases linearly with temperature but with a different slope. It total, thermoelectric properties of Au-based glassy alloy demonstrate behavior of a highly disordered system in a most pronounced manner.

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

    DOE PAGES

    Sun, Jifeng; Mukhopadhyay, Saikat; Subedi, Alaska; ...

    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

  5. Thermoelectric properties of Al substituted misfit cobaltite Ca3(Co1- x Al x )4O9 at low temperature

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Chen, Hong-mei; Hu, Jin-lian; Tang, Xu-bing; Li, Hai-jin; Wang, Wei

    2014-07-01

    Thermoelectric properties of Al substituted compounds Ca3(Co1- x Al x )4O9 ( x = 0, 0.03, 0.05), prepared by a sol-gel process, have been investigated in the temperature range 305-20 K. The results indicate that after Al substitution for Co in Ca3(Co1- x Al x )4O9, the direct current electrical resistivity and thermopower increase due to the reduction of carrier concentration. Experiments show that Al substitution results in decreased lattice thermal conductivity. The figure of merit of temperature behavior suggests that Ca3(Co0.97Al0.03)4O9 would be a promising candidate thermoelectric material for high-temperature thermoelectric application.

  6. Thermoelectric Materials Development for Low Temperature Geothermal Power Generation

    SciTech Connect

    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.

  7. 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.

  8. 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.

  9. Electronic Structure of CsBi(4 )Te(6 ): A New Low Temperature Thermoelectric

    NASA Astrophysics Data System (ADS)

    Larson, P.; Mahanti, S. D.; Chung, D.-Y.; Kanatzidis, M. G.

    2001-03-01

    Recently, it has been found that CsBi(4 )Te( 6 ) is a narrow-gap semiconductor with a larger thermoelectric figure of merit (ZT ( ~ ) 0.8) than traditional Bi(_2-x )Sb(x )Te(3 ) alloys at low temperatures (T < 225 K).(D-Y Chung, T. Hogan, P. Brazis, M. Rocci-Lane, C. Kannewurf, M. Bastea, C. Uher, M.G. Kanatzidis, Science 287), 1024 (2000). This improvement has been seen in the hole-doped samples. Since thermoelectric properties depend sensitively on the electronic structure of these narrow gap semiconductors, we have carried out detailed electronic structure calculations of CsBi(4 )Te(6 ) using ab initio all-electron linearized-augmented planewave (LAPW) method within density functional theory (DFT). The crystal structure of CsBi(4 )Te( 6 ) contains Bi-Bi bonds, unique for chalcogenide systems, which we find to play an important role in its electronic structure and thermoelectric properties. The predicted hole transport in this system is highly anisotropic and counterintuitive. Implications of our electronic structure calculations on the thermoelectric properties will be discussed.

  10. Low-temperature properties of aviation fuels

    SciTech Connect

    Brunton, C.; Voisey, M.A.; Willcock, C.R.

    1983-01-01

    A review is presented of work on the low-temperature properties of aviation turbine fuels that has been carried out in recent years at Thornton Research Centre. Details of both simulated full-scale aircraft tank tests and laboratory evaluations are included. Zero holdup is considered as a low-temperature specification parameter and a novel method for measuring its value is described. Experimental results are presented which demonstrate that a change from a freezing point to a flow criterion could provide an increase in fuel availability without prejudicing flight safety.

  11. An additive approach to low temperature zero pressure sintering of bismuth antimony telluride thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Catlin, Glenn C.; Tripathi, Rajesh; Nunes, Geoffrey; Lynch, Philip B.; Jones, Howard D.; Schmitt, Devin C.

    2017-03-01

    This paper presents an additive-based approach to the formulation of thermoelectric materials suitable for screen printing. Such printing processes are a likely route to such thermoelectric applications as micro-generators for wireless sensor networks and medical devices, but require the development of materials that can be sintered at ambient pressure and low temperatures. Using a rapid screening process, we identify the eutectic combination of antimony and tellurium as an additive for bismuth-antimony-telluride that enables good thermoelectric performance without a high pressure step. An optimized composite of 15 weight percent Sb7.5Te92.5 in Bi0.5Sb1.5Te3 is scaled up and formulated into a screen-printable paste. Samples fabricated from this paste achieve a thermoelectric figure of merit (ZT) of 0.74 using a maximum processing temperature of 748 K and a total thermal processing budget of 12 K-hours.

  12. 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.

  13. 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.

  14. Thermoelectric Properties of Complex Oxide Heterostructures

    NASA Astrophysics Data System (ADS)

    Cain, Tyler Andrew

    Thermoelectrics are a promising energy conversion technology for power generation and cooling systems. The thermal and electrical properties of the materials at the heart of thermoelectric devices dictate conversion efficiency and technological viability. Studying the fundamental properties of potentially new thermoelectric materials is of great importance for improving device performance and understanding the electronic structure of materials systems. In this dissertation, investigations on the thermoelectric properties of a prototypical complex oxide, SrTiO3, are discussed. Hybrid molecular beam epitaxy (MBE) is used to synthesize La-doped SrTiO3 thin films, which exhibit high electron mobilities and large Seebeck coefficients resulting in large thermoelectric power factors at low temperatures. Large interfacial electron densities have been observed in SrTiO3/RTiO 3 (R=Gd,Sm) heterostructures. The thermoelectric properties of such heterostructures are investigated, including the use of a modulation doping approach to control interfacial electron densities. Low-temperature Seebeck coefficients of extreme electron-density SrTiO3 quantum wells are shown to provide insight into their electronic structure.

  15. Reduction of phonon mean free path: From low-temperature physics to room temperature applications in thermoelectricity

    NASA Astrophysics Data System (ADS)

    Bourgeois, Olivier; Tainoff, Dimitri; Tavakoli, Adib; Liu, Yanqing; Blanc, Christophe; Boukhari, Mustapha; Barski, André; Hadji, Emmanuel

    2016-12-01

    It has been proposed for a long time now that the reduction of the thermal conductivity by reducing the phonon mean free path is one of the best way to improve the current performance of thermoelectrics. By measuring the thermal conductance and thermal conductivity of nanowires and thin films, we show different ways of increasing the phonon scattering from low-temperature up to room-temperature experiments. It is shown that playing with the geometry (constriction, periodic structures, nano-inclusions), from the ballistic to the diffusive limit, the phonon thermal transport can be severely altered in single crystalline semiconducting structures; the phonon mean free path is in consequence reduced. The diverse implications on thermoelectric properties will be eventually discussed.

  16. Properties of ferrites at low temperatures (invited)

    SciTech Connect

    Dionne, G.F.

    1997-04-01

    At cryogenic temperatures magnetic properties of ferrites change significantly from their values at room temperature, which has been the main regime for most device applications. Recently, microwave ferrite devices with superconducting microstrip circuits have been demonstrated at a temperature of 77 K with virtually no electrical conduction losses. Conventional ferrimagnetic garnet and spinel compositions, however, are not generally optimized for low temperatures and may require chemical redesign if the full potential of these devices is to be realized. Saturation magnetizations increase according to the Brillouin{endash}Weiss function dependence that is characteristic of all ferromagnetic materials. Increased magnetocrystalline anisotropy and magnetostriction can have large effects on hysteresis loop squareness and coercive fields that are essential for stable phase shift and efficient switching. Rare-earth impurities and other ions with short spin-lattice relaxation times can cause increased microwave losses. In this article, the basic magnetochemistry pertaining to ferrites will be examined for adaptation of ferrite technology to cryogenic environments. {copyright} {ital 1997 American Institute of Physics.}

  17. 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.

  18. Low Temperature Thermoelectric Properties and Aging Phenomena of Nanostructured p-TYPE Bi2-XSbXTe3 (x = 1.46, 1.48, 1.52 and 1.55)

    NASA Astrophysics Data System (ADS)

    Hitchcock, Dale; Liu, Yen-Liang; Liu, Yufei; Tritt, Terry M.; He, Jian; Liu, Chia-Jyi

    2013-08-01

    Over the past decade the widely used p-type (Bi2-xSbx)Te3 bulk thermoelectric materials have been subject to various nanostructuring processes for higher thermoelectric performance. However, these nanostructuring processing were conducted on compositions optimized for bulk materials (x 1.52-1.55). This leads to the question of whether the optimal composition for bulk materials is the same for their nanoscale counterparts. In this work we hydrothermally grew Bi2-xSbxTe3 nanopowders (nominally, x = 1.46, 1.48, 1.52 and 1.55) and measured their thermoelectric properties on cold-pressed vacuum-sintered pellets (74-78% of the theoretical density) below 300 K. The measurements were conducted 18 months apart to probe the aging phenomena, with the samples stored in ambient conditions. We have found that (i) the peak of thermopower shifts to lower temperatures upon nanostructuring but it shifts back to higher temperatures upon aging; (ii) the electrical conductivity degrades by a factor of 1.5-2.3 upon aging while the temperature dependence is largely retained; and (iii) the ZT of freshly made samples is sensitive to the x value, a maximum ZT 1.25( 0.62) at 270 K ( 255 K) was attained in the freshly made sample x = 1.55(x = 1.46), respectively; while the ZT of aged samples is significantly lowered by a factor of 2-4 but lesser x-dependent. These observations have been discussed in the context of charge buildup and compensation at grain boundaries.

  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. Low temperature properties of the Kondo insulator FeSi

    NASA Astrophysics Data System (ADS)

    Figueira, M. S.; Franco, R.

    2007-07-01

    In this paper we study the low temperature (T) properties of the Kondo insulator FeSi within the X-boson approach. We show that the ground state of the FeSi is metallic and highly correlated with a large effective mass; the low temperature contributions to the specific heat and the resistivity are of the Fermi-liquid type. The low temperature properties are governed by a reentrant transition into a metallic state, that occurs when the chemical potential crosses the gap and enters the conduction band, generating a metallic ground state. The movement of the chemical potential is due to the strong correlations present in the system. We consider the low temperature regime of the Kondo insulator FeSi, where the hybridization gap is completely open. In this situation we identify the two characteristic temperatures: the coherence temperature T0 and the Kondo temperature TKL. In the range T < T0, we identify a regime characterized by the formation of coherent states and Fermi-liquid behavior of the low temperature properties; in the range TKL > T > T0, we identify a regime characterized by an activation energy. Within the X-boson approach we study those low temperature regimes although we do not try to adjust parameters to recover the experimental energy scales.

  2. Hydrogen-incorporation stabilization of metallic VO2(R) phase to room temperature, displaying promising low-temperature thermoelectric effect.

    PubMed

    Wu, Changzheng; Feng, Feng; Feng, Jun; Dai, Jun; Peng, Lele; Zhao, Jiyin; Yang, Jinlong; Si, Cheng; Wu, Ziyu; Xie, Yi

    2011-09-07

    Regulation of electron-electron correlation has been found to be a new effective way to selectively control carrier concentration, which is a crucial step toward improving thermoelectric properties. The pure electronic behavior successfully stabilized the nonambient metallic VO(2)(R) to room temperature, giving excellent thermoelectric performance among the simple oxides with wider working temperature ranges.

  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. Thermoelectric properties of correlated materials

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  5. Development of Thermoelectric Power Generation and Peltier Cooling Properties of Materials for Thermoelectric Cryocooling Devices

    DTIC Science & Technology

    2015-05-12

    nanofabrication to develop nanostructured thermoelectric (TE) materials for application in high-efficiency thermoelectric power generators and solid...Distribution Unlimited Final Report: Development of Thermoelectric Power Generation and Peltier Cooling Properties of Materials for Thermoelectric...Thermoelectric Power Generation and Peltier Cooling Properties of Materials for Thermoelectric Cryocooling Devices Report Title The research

  6. 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.

  7. A Novel n-Type Organosilane-Metal Ion Hybrid of Rhodamine B and Copper Cation for Low-Temperature Thermoelectric Materials.

    PubMed

    Bertram, John R; Penn, Aubrey; Nee, Matthew J; Rathnayake, Hemali

    2017-03-29

    An n-type organosilane-metal ion hybrid of Rhodamine B-silane and copper cation (Cu-RBS) was investigated as a low-temperature thermoelectric material. Computational analysis revealed the most likely localized binding site of Cu(2+) was to the Rhodamine B core and provided predictions of molecular orbitals and electrostatic potentials upon complexation. The concentration-dependent optical absorption and emission spectra confirmed the effective metal-ligand charge transfer from Cu(2+) to the xanthene core of RBS, indicating the potential for improved electrical properties for the complex relative to RBS. The electrical conductivity and Seebeck thermoelectric (TE) behavior were evaluated and compared with its precursor complex of Rhodamine B and copper cation. While a moderately high electrical conductivity of 4.38 S m(-1) was obtained for the Cu-RBS complex, the relatively low Seebeck coefficient of -26.2 μV/K resulted in a low TE power factor. However, compared to other organic doped materials, these results were promising toward developing n-type thermoelectric materials with no doping agents. Both phase segregation and thin film heterogeneity remain to be optimized; thus, the balance between Cu(2+) domains and RBS domain phases will likely yield higher Seebeck coefficients and improved power factors.

  8. 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.

  9. 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.

  10. 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

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

    PubMed

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

    2015-09-18

    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.

  12. Linking membrane physical properties and low temperature tolerance in arthropods.

    PubMed

    Waagner, Dorthe; Bouvrais, Hélène; Ipsen, John H; Holmstrup, Martin

    2013-12-01

    Maintenance of membrane fluidity is of crucial importance in ectotherms experiencing thermal changes. This maintenance has in ectotherms most often been indicated using indirect measures of biochemical changes of phospholipid membranes, which is then assumed to modulate the physico-chemical properties of the membrane. Here, we measure bending rigidity characterizing the membrane flexibility of re-constituted membrane vesicles to provide a more direct link between membrane physical characteristics and low temperature tolerance. Bending rigidity of lipid bilayers was measured in vitro using Giant Unilamellar Vesicles formed from phospholipid extracts of the springtail, Folsomia candida. The bending rigidity of these membranes decreased when exposed to 0.4 vol% ethanol (0.23 mM/L). Springtails exposed to ethanol for 24h significantly increased their cold shock tolerance. Thus, by chemically inducing decreased membrane rigidity, we have shown a direct link between the physico-chemical properties of the membranes and the capacity to tolerate low temperature in a chill-susceptible arthropod.

  13. 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.

  14. 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.

  15. 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

  16. Solvent-Based Synthesis of Nano-Bi0.85Sb0.15 for Low-Temperature Thermoelectric Applications

    NASA Astrophysics Data System (ADS)

    Kaspar, K.; Fritsch, K.; Habicht, K.; Willenberg, B.; Hillebrecht, H.

    2017-01-01

    In this study we show a preparation method for nanostructured Bi0.85Sb0.15 powders via a chemical reduction route in a polyol medium, yielding material with particle sizes of 20-150 nm in scalable amounts. The powders were consolidated by spark plasma sintering (SPS) in order to maintain the nanostructure. To investigate influence of the sinter process, the powders were characterized by x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), and scanning electron microscopy (SEM) measurements before and after SPS. Transport properties, Seebeck effect, and thermal conductivity were determined in the low temperature range below 300 K. The samples showed excellent thermal conductivity of 2.3-2.6 W/m × K at 300 K and Seebeck coefficients from -97 μV/K to -107 μV/K at 300 K with a maximum of -141 μV/K at 110 K, thus leading to ZT values of up to 0.31 at room temperature. The results show that Bi-Sb-alloys are promising materials for low-temperature applications. Our wet chemical approach gives access to scalable amounts of nano-material with increased homogeneity and good thermoelectric properties after SPS.

  17. Crystal symmetry breaking in few quintuple Bi2Te3 nanosheets: applications in nanometrology of topological insulators and low-temperature thermoelectrics.

    PubMed

    Srivastava, Punita; Kumar, Pushpendra; Singh, Kedar

    2014-08-01

    Bismuth telluride (Bi2Te3) and its associated compounds are the best bulk thermoelectric (TE) materials known in present day. In addition, stacked two-dimensional (2D) layers of Bi2Te3 have attracted brawny interest due to topologically protected surface state property. The authors herein report results of micro-Raman spectroscopy study of the "graphene-like" crystalline Bi2Te3 nanosheets with a thickness of a few atoms (few-quintuples) synthesized by convenient solvothermal route which is chiefly attractive from physics point of view. It is investigated that the optical phonon mode A1u, which is not-Raman active in bulk Bi2Te3 crystals, appears in atomically-thin nanosheets due to crystal-symmetry breaking in few quintuples layers (FQLs) and can be used in nanometrology of topological insulators (TIs). It is also suggested that sheets thinning to FQLs and tuning of Fermi level can help in achieving TI surface transport regime with enhance thermoelectric power. From seebeck measurements, Bi2Te3 sample exhibit p-type conduction having higher TE power at low temperature (40 K). Thus, Bi2Te3 nanosheets with strong spatial confinement of charge carriers are beneficial for TE devices. The developed technology for producing 2D layers of -Te(1)-Bi-Te(2)-Bi-Te(1)- creates an thrust for exploration of TIs and their possibility in practical applications.

  18. Low temperature carrier transport properties in isotopically controlled germanium

    SciTech Connect

    Itoh, Kohei

    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 75Ge and 70Ge 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 [74Ge]/[70Ge] 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. 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.

  20. Physical properties of dense, low-temperature plasmas

    NASA Astrophysics Data System (ADS)

    Redmer, Ronald

    1997-04-01

    Plasmas occur in a wide range of the density-temperature plane. The physical quantities can be expressed by Green's functions which are evaluated by means of standard quantum statistical methods. The influences of many-particle effects such as dynamic screening and self-energy, structure factor and local-field corrections, formation and decay of bound states, degeneracy and Pauli exclusion principle are studied. As a basic concept for partially ionized plasmas, a cluster decomposition is performed for the self-energy as well as for the polarization function. The general model of a partially ionized plasma interpolates between low-density, nonmetallic systems such as atomic vapors and high-density, conducting systems such as metals or fully ionized plasmas. The equations of state, including the location of the critical point and the shape of the coexistence curve, are determined for expanded alkali-atom and mercury fluids. The occurrence of a metal-nonmetal transition near the critical point of the liquid-vapor phase transition leads in these materials to characteristic deviations from the behavior of nonconducting fluids such as the inert gases. Therefore, a unified approach is needed to describe the drastic changes of the electronic properties as well as the variation of the physical properties with the density. Similar results are obtained for the hypothetical plasma phase transition in hydrogen plasma. The transport coefficients (electrical and thermal conductivity, thermopower) are studied within linear response theory given here in the formulation of Zubarev which is valid for arbitrary degeneracy and yields the transport coefficients for the limiting cases of nondegenerate, weakly coupled plasmas (Spitzer theory) as well as degenerate, strongly coupled plasmas (Ziman theory). This linear response method is applied to partially ionized systems such as dense, low-temperature plasmas. Here, the conductivity changes from nonmetallic values up to those typical for

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  2. THERMAL PROPERTIES OF DOUBLE-ALUMINIZED KAPTON AT LOW TEMPERATURES

    SciTech Connect

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

    2008-03-03

    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.

  3. 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.

  4. 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.

  5. Thermoelectric properties of WS2 nanotube networks

    NASA Astrophysics Data System (ADS)

    Kawai, Hideki; Sugahara, Mitsunari; Okada, Ryotaro; Maniwa, Yutaka; Yomogida, Yohei; Yanagi, Kazuhiro

    2017-01-01

    We report the thermoelectric properties of WS2 nanotube networks. By using electrolyte-gating techniques, we turned on a conducting channel in the macroscopic networks of WS2 nanotubes in both the hole and electron regions and evaluated the thermoelectric properties of the networks. We manipulated the P- and N-type Seebeck coefficients in the WS2 nanotube networks by changing the shifts in the gate voltage potentials. The power factor of the WS2 nanotube networks increased as the gate voltage shifted and exhibited a high thermoelectric performance approaching that of single-crystalline WS2 flakes.

  6. Thermoelectric properties of the Kondo insulator FeSb2

    NASA Astrophysics Data System (ADS)

    Figueira, M. S.; Silva-Valencia, J.; Franco, R.

    2012-06-01

    Recently it was shown [A. Bentien, S. Johnsen, G.K.H. Madsen, B.B. Iversen, F. Steglich, Europhys. Lett. 80, 17008 (2007)], that the strongly correlated Kondo insulator FeSb2 exhibits a colossal Seebeck coefficient; however, due to its large lattice thermal conductivity, the dimensionless thermoelectric figure of merit (zT) is only 0.005 at 12 K. This experimental result motivate us to perform a theoretical study of the thermoelectric properties of Kondo insulators, within the framework of the X-boson approach [R. Franco, M.S. Figueira, M.E. Foglio, Phys. Rev. B 66, 045112 (2002)] for the periodic Anderson model. We consider a set of parameters adequate for describing the compound FeSb2, and we calculate the resistivity, the thermoelectric power (Seebeck coefficient), the charge carrier thermal conductance, the thermoelectric factor power (zT), the Wiedemann-Franz law, the specific heat, and the Sommerfeld's γ coefficient. The result of the colossal maximum of the Seebeck coefficient, at low temperatures, has the same order of magnitude as the experimental result [A. Bentien, S. Johnsen, G.K.H. Madsen, B.B. Iversen, F. Steglich, Europhys. Lett. 80, 17008 (2007)]. We also show that those temperature region presents an intermediate valence behavior, characterized by a moderate increase of the Sommerfeld's γ coefficient.

  7. Tribological properties of ultra-high molecular weight polyethylene at ultra-low temperature

    NASA Astrophysics Data System (ADS)

    Liu, Hongtao; Ji, Hongmin; Wang, Xuemei

    2013-12-01

    The hardness, compression properties, creep resistance and tribological properties of ultra-high molecular weight polyethylene at ultra-low temperature were researched in this paper, and the feasibility of its use in low temperature components was explored. Studies had shown that the UHMWPE sample at ultra-low temperature had a brittle tendency, and its compression curve was similar to the brittle material, for which the brittle fracture occurred in the 20% compression. Besides, the creep resistance of the sample at low temperature got worse, and its hardness showed an increasing tendency. With the increased experimental load, the friction coefficient varied seriously, and during the same load, the friction coefficient at low temperature was higher than that at room temperature. According to the worn morphology, the sample at low temperature showed a typical feature of fatigue wear and abrasive wear, while at room temperature it mainly for abrasive wear.

  8. 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.

  9. 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.

  10. Tensile properties of Inconel 718 after low temperature neutron irradiation

    NASA Astrophysics Data System (ADS)

    Byun, T. S.; Farrell, K.

    2003-05-01

    Tensile properties of Inconel 718 (IN718) have been investigated after neutron irradiation to 0.0006-1.2 dpa at 60-100 °C in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The alloy was exposed in solution-annealed (SA) and precipitation-hardened (PH) conditions. Before irradiation, the yield strength of PH IN718 was about 1170 MPa, which was 3.7 times higher than that of SA IN718. In the SA condition, an almost threefold increase in yield strength was found at 1.2 dpa, but the alloy retained a positive strain-hardening capability and a uniform ductility of more than 20%. Comparisons showed that the strain-hardening behavior of the SA IN718 is similar to that of a SA 316LN austenitic stainless steel. In the PH condition, the IN718 displayed no radiation-induced hardening in yield strength and significant softening in ultimate tensile strength. The strain-hardening capability of the PH IN718 decreased with dose as the radiation-induced dissolution of precipitates occurred, which resulted in the onset of plastic instability at strains less than 1% after irradiation to 0.16 or 1.2 dpa. An analysis on plastic instability indicated that the loss of uniform ductility in PH IN718 was largely due to the reduction in strain-hardening rate, while in SA IN718 and SA 316LN stainless steel it resulted primarily from the increase of yield stress.

  11. Influence of Anaerobiosis and Low Temperature on Bacillus cereus Growth, Metabolism, and Membrane Properties

    PubMed Central

    Clavel, Thierry; Clerté, Caroline; Carlin, Frédéric; Giniès, Christian; Nguyen-The, Christophe

    2012-01-01

    The impact of simultaneous anaerobiosis and low temperature on growth parameters, metabolism, and membrane properties of Bacillus cereus ATCC 14579 was studied. No growth was observed under anaerobiosis at 12°C. In bioreactors, growth rates and biomass production were drastically reduced by simultaneous anaerobiosis and low temperature (15°C). The two conditions had a synergistic effect on biomass reduction. In anaerobic cultures, fermentative metabolism was modified by low temperature, with a marked reduction in ethanol production leading to a lower ability to produce NAD+. Anaerobiosis reduced unsaturated fatty acids at both low optimal temperatures. In addition, simultaneous anaerobiosis and low temperatures markedly reduced levels of branched-chain fatty acids compared to all other conditions (accounting for 33% of total fatty acids against more 71% for low-temperature aerobiosis, optimal-temperature aerobiosis, and optimal-temperature anaerobiosis). This corresponded to high-melting-temperature lipids and to low-fluidity membranes, as indicated by differential scanning calorimetry, 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence anisotropy, and infrared spectroscopy. This is in contrast to requirements for cold adaptation. A link between modification in the synthesis of metabolites of fermentative metabolism and the reduction of branched-chain fatty acids at low temperature under anaerobiosis, through a modification of the oxidizing capacity, is assumed. This link may partly explain the impact of low temperature and anaerobiosis on membrane properties and growth performance. PMID:22247126

  12. 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.

  13. Thermoelectric Properties of Graphene Ribbons

    NASA Astrophysics Data System (ADS)

    Munoz, Enrique

    2011-03-01

    Several theoretical and experimental studies have been recently concerned with electric and thermal transport in graphene layers and ribbons, where propagation of electrons and phonons seems to be dominated by a ballistic mechanism. Of particular interest in this context is the identification and characterization of thermoelectric effects, which represent a promising alternative for energy recovery in technological applications. In the present work, the effect of the electron- phonon interaction over a predominantly ballistic transport mechanism in graphene ribbons is studied in the context of thermoelectricity. Theoretical estimations of the thermopower S, and the corresponding figure of merit ZT, are presented for this system as a function of temperature. I acknowledge financial support from the grant Fondecyt de Iniciacion 11100064.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Electrical transport and thermoelectric properties of boron carbide nanowires.

    PubMed

    Kirihara, Kazuhiro; Mukaida, Masakazu; Shimizu, Yoshiki

    2017-04-07

    The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples. In a temperature range of 200-450 K, there is a crossover between electrical conduction by variable-range hopping and phonon-assisted hopping. The inhomogeneous carbon concentration and planar defects, such as twins and stacking faults, in the nanowires are thought to modify the bonding nature and electronic structure of the boron carbide crystal substantially, causing differences in the electrical conductivity and Seebeck coefficient. The effect of boundary scattering of phonon at nanostructured surface on the thermal conductivity reduction is discussed.

  19. Electrical transport and thermoelectric properties of boron carbide nanowires

    NASA Astrophysics Data System (ADS)

    Kirihara, Kazuhiro; Mukaida, Masakazu; Shimizu, Yoshiki

    2017-04-01

    The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples. In a temperature range of 200–450 K, there is a crossover between electrical conduction by variable-range hopping and phonon-assisted hopping. The inhomogeneous carbon concentration and planar defects, such as twins and stacking faults, in the nanowires are thought to modify the bonding nature and electronic structure of the boron carbide crystal substantially, causing differences in the electrical conductivity and Seebeck coefficient. The effect of boundary scattering of phonon at nanostructured surface on the thermal conductivity reduction is discussed.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. Quantum locality and equilibrium properties in low-temperature parahydrogen: a multiscale simulation study.

    PubMed

    Potestio, R; Delle Site, L

    2012-02-07

    Parahydrogen is the spin-zero singlet state of molecular hydrogen, which at low temperature (between 14 and 25 K) is in a fluid state. A classical treatment of the system leads to unphysical freezing, and the inclusion of quantum delocalization of the molecule is then required to obtain a realistic description of its equilibrium properties. In the present work, we employ the classical-quantum adaptive resolution method AdResS to investigate the spatial extension of quantum delocalization effects in the bulk fluid at low temperature. Specifically, we simulate a small, spherical region of the system in full quantum detail: this region is coupled to a bulk of coarse-grained particles with classical, quantum-derived effective interactions obtained from quantum simulations. The two regions are interfaced through open boundaries and in conditions of thermodynamic equilibrium. Structural properties of the fluid, namely, pair distribution functions, are measured for different sizes of the quantum region. The results of this work show that, for the thermodynamic conditions corresponding to the range of temperature between 14 and 25 K, the bead-based, quantum structural properties of low-temperature parahydrogen are deemed local and do not require the support of an explicit quantum bulk.

  6. 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.

  7. Low Temperature Synthesis of Rutile TiO2 Nanocrystals and Their Photovoltaic and Photocatalytic Properties.

    PubMed

    Roy, Subhasis; Han, Gill Sang; Shin, Hyunjung; Lee, Jin Wook; Mun, Jinsoo; Shin, Hyunho; Jung, Hyun Suk

    2015-06-01

    We report a novel method of synthesizing rutile TiO2 nanocrystals at low temperature (200 degrees C) via a butanol rinsing process followed by heat treatment in an O2 atmosphere. The rutile nanocrystals show uniform size distribution of approximately 20 nm and good crystallinity confirmed by X-ray diffraction and transmission electron microscopy. A mechanism for the low temperature synthesis of rutile nanocrystals is rationalized in terms of an explosive thermal decomposition reaction of butoxy groups on TiO2 powders with O2 gas. Characterizations of the photovoltaic and photocatalytic properties of rutile nanocrystals exhibited higher photoactivity than large-sized conventional rutile powder, which demonstrates that this novel synthesis technology could expand applications of rutile powders to various photoactive devices beyond solar cells and photocatalysts.

  8. Interface properties of thin oxide layers grown on strained SiGe layers at low temperatures

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, M.; Ray, S. K.; Ghosh, T. B.; Sreemany, M.; Maiti, C. K.

    1996-03-01

    The chemical state and the electrical properties of the interfaces of thin oxide films grown on strained 0268-1242/11/3/014/img8 layers using plasma and thermal oxidation have been studied in detail. X-ray photoelectron spectroscopy studies show no Ge pile-up at the oxide/substrate interface. In the case of plasma oxidation, Ge at the oxide surface is found to be in a fully oxidized state, while the formation of an intermediate oxidized state is observed in the case of low-temperature thermal oxidation. High-frequency (1 MHz) capacitance - voltage (C - V) and conductance - voltage (G - V) measurements have indicated the growth of good quality gate oxides. The fixed oxide charge and interface state densities are comparable to those of low-temperature-grown metal - oxide - semiconductor capacitors on Si with aluminium gates.

  9. Low-temperature irradiation effects on tensile and Charpy properties of low-activation ferritic steels

    NASA Astrophysics Data System (ADS)

    Shiba, Kiyoyuki; Hishinuma, Akimichi

    2000-12-01

    Tensile and Charpy properties of low-activation ferritic steel, F82H irradiated up to 0.8 dpa at low temperature below 300°C were investigated. The helium effect on these properties was also investigated using the boron isotope doping method. Neutron irradiation increased yield stress accompanied with ductility loss, and it also shifted the ductile-to-brittle transition temperature (DBTT) from -50°C to 0°C. Boron-doped F82H showed larger degradation in DBTT and ductility than boron-free F82H, while they had the same yield stress before and after irradiation.

  10. 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.

  11. Solid Solutions Formation: Improving the Thermoelectric Properties of Skutterudites

    NASA Technical Reports Server (NTRS)

    Borshchevsky, A.; Caillat, T.; Fleurial, J. P.

    1996-01-01

    Materials with skutterudite structure have been known for a long time. Some of them are semiconductors. A typical skutterudite is CoSb(sub 3) and its thermoelectric properties were partially studied in the 1960's. Recently, it has been discovered that many skutterudite compounds are thermoelectrics with promising future.

  12. 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.

  13. 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

  14. 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.

  15. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  16. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  17. 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

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  18. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  19. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  20. Mechanical and Electrical Properties of Low Temperature Phase MnBi

    SciTech Connect

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

    2016-01-21

    The low temperature phase (LTP) MnBi is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and its large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have started to consider MnBi magnet for motor applications. In addition to the magnetic properties, there are other physical properties that could significantly affect a motor design. Here, we report the results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their dependence on temperature. We found at room temperature the sintered MnBi magnet fractures when the compression stress exceeds 193 MPa; and its room temperature electric resistance is about 6.85 μΩ-m.

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

    DOE PAGES

    Claudio, Tania; Stein, Niklas; Peterman, Nils; ...

    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

  2. Thermoelectric property measurements with computer controlled systems

    NASA Technical Reports Server (NTRS)

    Chmielewski, A. B.; Wood, C.

    1984-01-01

    A joint JPL-NASA program to develop an automated system to measure the thermoelectric properties of newly developed materials is described. Consideration is given to the difficulties created by signal drift in measurements of Hall voltage and the Large Delta T Seebeck coefficient. The benefits of a computerized system were examined with respect to error reduction and time savings for human operators. It is shown that the time required to measure Hall voltage can be reduced by a factor of 10 when a computer is used to fit a curve to the ratio of the measured signal and its standard deviation. The accuracy of measurements of the Large Delta T Seebeck coefficient and thermal diffusivity was also enhanced by the use of computers.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Atomistic design of semiconductor nanostructures with optimal thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Galli, Giulia

    2008-03-01

    The search for novel materials with optimal thermoelectric properties (for either thermoelectric power generation or heat dissipation) is an active field of research. We present atomistic and ab-initio simulations of selected nanomaterials, aimed at predicting thermal conductivities and electronic transport properties, and ultimately at designing materials with optimal thermoelectric figure of merit. In particular we focus on carbon nanotubes [1], silicon wires [2] and nanoporous silicon [3] and we discuss both strategies and algorithms to optimize thermoelectric properties at the nanoscale. [1] D. Donadio and G.Galli, Phys. Rev. Lett. 2007 (in press). [2] T.Vo, A.Williamson, V.Lordi and G.Galli (submitted) and J.Reed, A.Williamson, E.Schwegler and G.Galli (submitted). [3] J.-H. Lee, J.C.Grossman, J.Reed and G.Galli, Appl. Phys. Lett. 2007 (in press).

  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. 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.

  12. 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.

  13. Growth and low-temperature photoluminescence properties of hybrid ZnO-SnO2 nanobelts

    NASA Astrophysics Data System (ADS)

    Sinha, S. K.; Rakshit, T.; Ray, S. K.; Bysakh, S.; Manna, I.

    2012-09-01

    Hybrid ZnO-SnO2 nanobelts were synthesized through a simple thermal evaporation technique without using any catalyst. Detailed microstructural investigation showed that the nanobelts possessed doped/alloyed wurtzite (ZnO) and rutile (SnO2) structures. The diameter and length of the nanobelts were in the ranges 100-200 and 20-40 µm, respectively. Low-temperature photoluminescence properties of the hybrid ZnO-SnO2 nanostructured aggregate revealed a red shift of near-band-edge emission peaks of ZnO with increasing temperature. The method of synthesis offers a convenient and effective technique of producing hybrid ZnO-SnO2 nanobelts for gas sensing in the large quantity.

  14. 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.

  15. High-T c superconductor/polymer composites. Modeling of abnormal electrical properties at low temperature

    NASA Astrophysics Data System (ADS)

    Benlhachemi, A.; Gavarri, J. R.; Musso, J.; Alfred-Duplan, C.; Marfaing, J.

    1994-09-01

    High- Tc 2223-bismuth superconducting pigments have been inserted in a matrix of Fe 3+-doped polyphenylene sulphide (PPS) to obtain new composites with variable properties. The fabrication and the characterization of the various components are briefly described. The electrical resistivity at a low temperature of the composites is reported. In the case of multiphase super-conducting pigments presenting various Tc's and semiconducting fabrication residues inserted in the polymeric matrix, the composites are characterized by abnormal resistivity evolutions between 20 K and 300 K. A new electrical model is proposed to interpret the behavior of such composites in the full 5 K to 300 K temperature range. Percolation features are taken into account through an empirical description of the electrical complex impedances. The computer calculations allow one to characterize fabrication residues and interfaces between insulating, conducting and superconducting areas in the composites.

  16. Beyond mean-field properties of binary dipolar Bose mixtures at low temperatures

    NASA Astrophysics Data System (ADS)

    Pastukhov, Volodymyr

    2017-02-01

    We rigorously analyze the low-temperature properties of homogeneous three-dimensional two-component Bose mixture with dipole-dipole interaction. For such a system the effective hydrodynamic action that governs the behavior of low-energy excitations is derived. The infrared structure of the exact single-particle Green's functions is obtained in terms of macroscopic parameters, namely the inverse compressibility and the superfluid density matrices. Within the one-loop approximation we calculate some of the most relevant observable quantities and give the beyond mean-field stability condition for the binary dipolar Bose gas in the dilute limit. A brief variational derivation of the coupled equations that describe macroscopic hydrodynamics of the system in the external nonuniform potential at zero temperature is presented.

  17. 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.

  18. 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.

  19. 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

  20. Bi nanobelts, nanocubes and their thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Wang, Wenzhong; Chen, Shuo; Huang, Jianyu; Ren, Zhifeng; Harris, T.; Chen, Gang; Dresselhaus, M.

    2006-03-01

    Highly crystallized Bi nanobelts and monodispersed nanocubes have been synthesized via a low-temperature organic solution approach, in which sodium bismuthate was reduced by ethylene glycol in the presence of poly(vinylpyrrolidone) (PVP). By changing some experimental conditions, Bi nanobelts and nanocubes have been prepared successfully. The as-prepared Bi nanobelts are single crystal with high crystallinity. The width of the nanobelts is in the range of 50-500 nanometers and the length is up to of several tens of micrometers. The as-synthesized Bi nanocubes are highly crystallized and monodispersed with edge length of 50-60 nm. The electrical, thermal, and Seebeck properties of the as-grown nanobelts were studied by a TEM-STM probe inside a high resolution TEM. The same studies were also carried out on bulk samples made by hot-press using the nanocubes.

  1. Determining factors of thermoelectric properties of semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Demchenko, Denis O.; Heinz, Peter D.; Lee, Byounghak

    2011-08-01

    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.

  2. Measurements of anisotropic thermoelectric properties in superlattices

    NASA Astrophysics Data System (ADS)

    Yang, B.; Liu, W. L.; Liu, J. L.; Wang, K. L.; Chen, G.

    2002-11-01

    Thermoelectric properties, i.e., thermal conductivity, electrical conductivity, and the Seebeck coefficient, have been measured in the directions parallel (in-plane) and perpendicular to the interface of an n-type Si(80 A)/Ge(20 A) superlattice. A two-wire 3omega method is employed to measure the in-plane and cross-plane thermal conductivities. The cross-plane Seebeck coefficient is deduced by using a differential measurement between the superlattice and reference samples and the cross-plane electrical conductivity is determined through a modified transmission-line method. The in-plane thermal conductivity of the Si/Ge superlattice is 5-6 times higher than the cross-plane one, and the electrical conductivity shows a similar anisotropy. The anisotropy of the Seebeck coefficients is smaller in comparison to electrical and thermal conductivities in the temperature range from 150 to 300 K. However, the cross-plane Seebeck coefficient rises faster with increasing temperature than that of the in-plane direction.

  3. Thermoelectric properties of semiconductor nanowire networks

    DOE PAGES

    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

  4. Thermoelectric properties of semiconductor nanowire networks

    SciTech Connect

    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 an 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.

  5. Low temperature properties of spin filter NbN/GdN/NbN Josephson junctions

    NASA Astrophysics Data System (ADS)

    Massarotti, D.; Caruso, R.; Pal, A.; Rotoli, G.; Longobardi, L.; Pepe, G. P.; Blamire, M. G.; Tafuri, F.

    2017-02-01

    A ferromagnetic Josephson junction (JJ) represents a special class of hybrid system where different ordered phases meet and generate novel physics. In this work we report on the transport measurements of underdamped ferromagnetic NbN/GdN/NbN JJs at low temperatures. In these junctions the ferromagnetic insulator gadolinium nitride barrier generates spin-filtering properties and a dominant second harmonic component in the current-phase relation. These features make spin filter junctions quite interesting also in terms of fundamental studies on phase dynamics and dissipation. We discuss the fingerprints of spin filter JJs, through complementary transport measurements, and their implications on the phase dynamics, through standard measurements of switching current distributions. NbN/GdN/NbN JJs, where spin filter properties can be controllably tuned along with the critical current density (Jc), turn to be a very relevant term of reference to understand phase dynamics and dissipation in an enlarged class of JJs, not necessarily falling in the standard tunnel limit characterized by low Jc values.

  6. 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.

  7. Thermoelectric Property Dependence and Geometry Optimization of Peltier Current Leads Using Highly Electrically Conductive Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Fujii, Tomohiro; Fukuda, Shinji; Emoto, Masahiko; Osada, Koudai; Kawahara, Toshio; Hamabe, Makoto; Watanabe, Hirofumi; Ivanov, Yury; Sun, Jian; Yamaguchi, Satarou

    2011-05-01

    Thermoelectric materials are promising candidates for use in energy-saving devices in many fields. They are also useful in superconducting applications such as those using Peltier current leads (PCLs) to reduce system heat loss. In the case of PCLs, consideration must be given to Joule heating. Furthermore, the performance of PCLs is intricately dependent on their thermoelectric properties. In addition to the figure of merit Z, consideration of the electrical conductivity is also important for the design of high-performance PCLs. In this paper, we discuss the resistivity dependence of the performance of PCLs using model parameters obtained from real devices.

  8. Thermoelectric properties of gated graphene ribbons in the ballistic regime

    NASA Astrophysics Data System (ADS)

    Kliros, G. S.; Divari, P. C.

    2012-08-01

    We investigate the thermoelectric properties of gated graphene ribbons in the ballistic transport limit using linear response theory and the Landauer formalism. The dependence of the electronic conductance, thermopower as well as electronic thermal conductance on both Fermi level and temperature are clarified and the validity of Wiedemann-Franz law is examined. The electronic part of thermoelectric figure of merit ZTel which gives an upper bound for the thermoelectric efficiency of the gated ribbons, is also calculated. It is shown that ZTel of wide and short gated ribbons is directly related to geometric aspect ratio of the graphene ribbon and for very short ribbons can exceed unity at room temperature. Our results could be useful in the design of efficient graphene-based thermoelectric devices.

  9. 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.

  10. Milling properties of low temperature sintered zirconia blocks for dental use.

    PubMed

    Lan, Ting-Hsun; Wang, Chau-Hsiang; Chen, Ker-Kong; Wang, Moo-Chin; Lee, Huey-Er

    2017-04-01

    To investigate the milling properties of different yttria-tetragonal zirconia polycrystalline (Y-TZP) block materials by applying a dental computer numerical control (CNC) milling center. Low temperature sintering zirconia block denoted by KMUZ (experimental) with two commercial zirconia blocks for T block made in Taiwan and a G block made in Germany were compared for the milling properties. Seventy-two specimens were milled using the same CNC milling center, and properties were evaluated by measuring the weight loss (g), milling time (s), margin integrity (%) and broken diameter (μm). The crystalline phases contents were identified by X-ray diffraction and the microstructures of the sintering specimens were observed by scanning electron microscopy and transmission electron microscopy. The mean milling time of G and KMUZ were significantly shorter than T (P<0.05). The KMUZ samples exhibited the least weight loss among the three kinds of blocks (P<0.05). The percentages of marginal integrity after milling were high in G and KMUZ but low in T (P<0.05). The mean broken diameters were from 90μm to 120μm. The phase transformation of t-ZrO2 (KMUZ: 7.4%, G: 5.9%, T: 3.2%) to m-ZrO2 when facing the milling pressure in ZrO2 blocks was observed by XRD. The result of TEM microstructure of KMUZ revealed that Y and Si were soluble in grain boundaries. The results show that the milling properties of KMUZ were better than one commercial T and near the G. The hindered grain growth, as a result of the Y(3+) content in the grain boundaries, also plays a role in promoting the abnormal grain growth of 3Y-TZP.

  11. 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.

  12. 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

  13. Processing, microstructure, and electric properties of buried resistors in low-temperature co-fired ceramics

    SciTech Connect

    Yang, Pin; Rodriguez, Mark A.; Kotula, Paul; Miera, Brandon K.; Dimos, Duane

    2001-04-01

    The electrical properties of ruthenium oxide based devitrifiable resistors embedded within low-temperature co-fired ceramics were investigated from -100{sup o}C to 100{sup o}C. Special attention was given to the processing conditions and their effects on resistance and temperature coefficient of resistance (TCR). Results indicate that within this temperature range the conductance for these buried resistors is limited by tunneling of charge carriers through the thin glass layer between ruthenium oxide particles. A modified version of the tunneling barrier model is proposed to account for the microstructure ripening observed during thermal processing. The model parameters determined from curve fitting show that charging energy (i.e., the energy required for a charge carrier to tunnel through the glass barrier) is strongly dependent on particle size and particle--particle separation between ruthenium oxide grains. Initial coarsening of ruthenium oxide grains was found to reduce the charging energy and lower the resistance. However, when extended ripening occurs, the increase in particle--particle separation increases the charging energy, reduces the tunneling probability and gives rise to a higher resistance. The tradeoff between these two effects results in an optimum microstructure with a minimum resistance and TCR. Furthermore, the TCR of these buried resistors has been shown to be governed by the magnitude of the charging energy. Model parameters determined by our analysis appear to provide quantitative physical interpretations to the microstructural changes in the resistor, which in turn, are controlled by the processing conditions.

  14. Processing, Microstructure and Electric Properties of Buried Resistors in Low Temperature Co-Fired Ceramics

    SciTech Connect

    Dimos, D.B.; Kotula, P.G.; Miera, B.K.; Rodriguez, M.A.; Yang, Pin

    1999-09-17

    The electrical properties were investigated for ruthenium oxide based devitrifiable resistors embedded within low temperature co-fired ceramics. Special attention was given to the processing conditions and their affects on resistance and temperature coefficient of resistance (TCR). Results indicate that the conductance for these buried resistors is limited by tunneling of charge carriers through the thin glass layer between ruthenium oxide particles. A modified version of the tunneling barrier model is proposed to more accurately account for the microstructure ripening observed during thermal processing. The model parameters determined from curve fitting show that charging energy (i.e., the energy required for a charge carrier to tunnel through the glass barrier) is strongly dependent on particle size and particle-particle separation between ruthenium oxide grains. Initial coarsening of ruthenium oxide grains was found to reduce the charging energy and lower the resistance. However, when extended ripening occurs, the increase in particle-particle separation increases the charging energy, reduces the tunneling probability and gives rise to a higher resistance. The trade-off between these two effects results an optimum microstructure with a minimum resistance and TCR. Furthermore, the TCR of these resistors has been shown to be governed by the magnitude of the charging energy. Model parameters determined by our analysis appear to provide quantitative physical interpretations to the microstructural change in the resistor, which in turn, are controlled by the processing conditions.

  15. 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.

  16. 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.

  17. 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).

  18. 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.

  19. Modified Spin Wave Analysis of Low Temperature Properties of the Spin-1/2 Frustrated Ferromagnetic Ladder

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo; Iino, Takashi

    2012-03-01

    Low temperature properties of the spin-1/2 frustrated ladder with ferromagnetic rungs and legs, and two different antiferromagnetic next nearest neighbor interactions are investigated using the modified spin wave approximation in the region with ferromagnetic ground states. The temperature dependence of the magnetic susceptibility and magnetic structure factors is calculated. The results are consistent with the numerical exact diagonalization results in the intermediate temperature range. Below this temperature range, the finite size effect is significant in the numerical diagonalization results, while the modified spin wave approximation gives more reliable results. The low temperature properties near the limit of the stability of the ferromagnetic ground state are also discussed.

  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.

  1. Impacts of doping on thermal and thermoelectric properties of nanomaterials.

    PubMed

    Zhang, Gang; Li, Baowen

    2010-07-01

    Thermal transport in nanoscale structures has attracted an increasing interest in the last two decades. On the one hand, the low dimensional nanostructured materials are platforms for testing novel phonon transport theories. On the other hand, nanomaterials are promising candidates for nanoscale on-chip coolers. This review is focused on the thermal conductance, thermoelectric property, and impacts of doping on these properties.

  2. 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.

  3. Structure-processing-property relationships and thermoelectricity in strongly correlated cerium-tri(palladium) and related compounds

    NASA Astrophysics Data System (ADS)

    Boona, Stephen Richard

    The discovery of high performance thermoelectric materials would enable the development of a wide range of new thermal and electrical energy management technologies, including the possibility of solid state cryogenic coolers. Such discoveries have been sharply inhibited to date, however, by the contraindicated nature of the material properties that comprise the thermoelectric figure of merit ZT. Enhancement of ZT generally requires overcoming significant materials science and engineering challenges that become even more restrictive at low temperatures. One possible approach for overcoming these challenges is to shift away from conventional semiconductors and toward strongly correlated electron materials, as these systems often display unusual combinations of electronic and thermal properties that may be exploited to achieve high ZT in the cryogenic temperature regime. This perspective has motivated the current work, in which the thermoelectric properties of strongly correlated CePd3 and related compounds are explored. This work presents a comprehensive and systematic study of the ways in which composition and processing modifications affect the electronic, thermal, magnetic, and structural properties of these materials. The insights gained from this study have led to the highest ZT value reported to date of all p-type bulk polycrystalline materials at low temperatures. A detailed review of these developments is provided along with a discussion of how they may be applied to achieve further enhancements in ZT.

  4. 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.

  5. Thermoelectric properties of pressure-sintered Si(0.8)Ge(0.2) thermoelectric alloys

    NASA Technical Reports Server (NTRS)

    Vining, Cronin B.; Laskow, William; Hanson, Jack O.; Van Der Beck, Roland R.; Gorsuch, Paul D.

    1991-01-01

    The thermoelectric properties of 28 sintered Si(0.8)Ge(0.2) alloys, heavily doped with either B or P and prepared from powders with median particle sizes ranging from about 1 to over 100 microns, have been determined from 300 to 1300 K. The thermal conductivity decreases with decreasing particle size; however, the figure of merit is not significantly increased due to a compensating reduction in the electrical conductivity. The thermoelectric figure of merit is in good agreement with results of Dismukes et al. (1964) on similarly doped alloys prepared by zone-leveling techniques. The electrical and thermal conductivity are found to be sensitive to preparation procedure while the Seebeck coefficient and figure of merit are much less sensitive. The high-temperature electrical properties are consistent with charge carrier scattering by acoustic or optical phonons.

  6. Improving Thermoelectric Properties of Nanowires Through Inhomogeneity

    NASA Astrophysics Data System (ADS)

    González, J. Eduardo; Sánchez, Vicenta; Wang, Chumin

    2016-10-01

    Inhomogeneity in nanowires can be present in the cross-section and/or by breaking the translational symmetry along the nanowire. In particular, the quasiperiodicity introduces an unusual class of electronic and phononic transport with a singular continuous eigenvalue spectrum and critically localized wave functions. In this work, the thermoelectricity in periodic and quasiperiodically segmented nanobelts and nanowires is addressed within the Boltzmann formalism by using a real-space renormalization plus convolution method developed for the Kubo-Greenwood formula, in which tight-binding and Born models are, respectively, used for the calculation of electric and lattice thermal conductivities. For periodic nanowires, we observe a maximum of the thermoelectric figure-of-merit (ZT) in the temperature space, as occurred in the carrier concentration space. This maximum ZT can be improved by introducing into nanowires periodically arranged segments and an inhomogeneous cross-section. Finally, the quasiperiodically segmented nanowires reveal an even larger ZT in comparison with the periodic ones.

  7. Thermoelectric Properties of Solution Synthesized Nanostructured Materials.

    PubMed

    Finefrock, Scott W; Yang, Haoran; Fang, Haiyu; Wu, Yue

    2015-01-01

    Thermoelectric nanocomposites made by solution synthesis and compression of nanostructured chalcogenides could potentially be low-cost, scalable alternatives to traditional solid-state synthesized materials. We review the progress in this field by comparing the power factor and/or the thermoelectric figure of merit, ZT, of four classes of materials: (Bi,Sb)2(Te,Se)3, PbTe, ternary and quaternary copper chalcogenides, and silver chalcogenides. We also discuss the thermal conductivity reduction associated with multiphased nanocomposites. The ZT of the best solution synthesized materials are, in several cases, shown to be equal to or greater than the corresponding bulk materials despite the generally reduced mobility associated with solution synthesized nanocomposites. For the solution synthesized materials with the highest performance, the synthesis and processing conditions are summarized to provide guidance for future work.

  8. Thermoelectric properties of rare earth chalcogenides

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Raag, V.; Wood, C.

    1985-01-01

    The rare earth chalcogenides are important thermoelectric materials due to their high melting points, self-doping capabilities, and low thermal conductivities. Lanthanum sulfides and lanthanum tellurides have been synthesized in quartz ampules, hot-pressed into samples, and measured. The n-type Seebeck coefficients, electrical resistivities, and power factors generally all increased as the temperature increased from 200 to 1000 C. The figure-of-merit for nonstoichiometric lanthanum telluride was 0.001/deg C at 1000 C, considerably higher than for silicon-germanium. Thermoelectric measurements were made for LaTe(2) and YbS(1.4), and p-type behavior was observed for these compounds from 300 to 1100 C.

  9. Low-temperature magnetic properties of monoclinic pyrrhotite with particular relevance to the Besnus transition

    NASA Astrophysics Data System (ADS)

    Volk, Michael W. R.; Gilder, Stuart A.; Feinberg, Joshua M.

    2016-12-01

    in pseudo-single-domain (PSD) pyrrhotite. As PSD monoclinic pyrrhotite carries the magnetic remanence in some meteorites, it is likely that low-temperature cycling in space then warming to ambient conditions at the Earth's surface will have only a minor influence on palaeointensity values derived from those meteorites.

  10. Thermoelectric properties of single-layered SnSe sheet

    NASA Astrophysics Data System (ADS)

    Wang, Fancy Qian; Zhang, Shunhong; Yu, Jiabing; Wang, Qian

    2015-09-01

    Motivated by the recent study of inspiring thermoelectric properties in bulk SnSe [Zhao et al., Nature, 2014, 508, 373] and the experimental synthesis of SnSe sheets [Chen et al., J. Am. Chem. Soc., 2013, 135, 1213], we have carried out systematic calculations for a single-layered SnSe sheet focusing on its stability, electronic structure and thermoelectric properties by using density functional theory combined with Boltzmann transport theory. We have found that the sheet is dynamically and thermally stable with a band gap of 1.28 eV, and the figure of merit (ZT) reaches 3.27 (2.76) along the armchair (zigzag) direction with optimal n-type carrier concentration, which is enhanced nearly 7 times compared to its bulk counterpart at 700 K due to quantum confinement effect. Furthermore, we designed four types of thermoelectric couples by assembling single-layered SnSe sheets with different transport directions and doping types, and found that their efficiencies are all above 13%, which are higher than those of thermoelectric couples made of commercial bulk Bi2Te3 (7%-8%), suggesting the great potential of single-layered SnSe sheets for heat-electricity conversion.Motivated by the recent study of inspiring thermoelectric properties in bulk SnSe [Zhao et al., Nature, 2014, 508, 373] and the experimental synthesis of SnSe sheets [Chen et al., J. Am. Chem. Soc., 2013, 135, 1213], we have carried out systematic calculations for a single-layered SnSe sheet focusing on its stability, electronic structure and thermoelectric properties by using density functional theory combined with Boltzmann transport theory. We have found that the sheet is dynamically and thermally stable with a band gap of 1.28 eV, and the figure of merit (ZT) reaches 3.27 (2.76) along the armchair (zigzag) direction with optimal n-type carrier concentration, which is enhanced nearly 7 times compared to its bulk counterpart at 700 K due to quantum confinement effect. Furthermore, we designed four types of

  11. Thermoelectric properties of T-shaped graphene nanodevice

    NASA Astrophysics Data System (ADS)

    Jafari, A.; Ghoranneviss, M.; Boochani, A.; Hantehzadeh, M. R.

    2015-07-01

    The thermoelectric properties of a T-shaped graphene nanodevice (TGN) are investigated by means of the Landauer approach using the π-electron tight-binding model. The dependence of thermopower on the temperature is studied and the results are qualitatively in agreement with many features recently observed in thermoelectric measurements on graphene nanodevice which suggests the existence of a minimum when the EF is several kBT away from the Dirac point. Thermoconductance κ is proportional to transmission coefficient and thermal current has a linear dependence on the temperature. Further, both the electrical and thermal current of electrons in TGN are calculated. The results could be useful in designing efficient graphene-based thermoelectric devices.

  12. Experiments on the thermoelectric properties of quantum dots

    NASA Astrophysics Data System (ADS)

    Svilans, Artis; Leijnse, Martin; Linke, Heiner

    2016-12-01

    Quantum dots (QDs) are good model systems for fundamental studies of mesoscopic transport phenomena using thermoelectric effects because of their small size, electrostatically tunable properties and thermoelectric response characteristics that are very sensitive to small thermal biases. Here we provide a review of experimental studies on thermoelectric properties of single QDs realized in two-dimensional electron gases, single-walled carbon nanotubes and semiconductor nanowires. A key requirement for such experiments is to have some methods for nanoscale thermal biasing at one's disposal. We briefly review the main techniques used in the field, namely, heating of the QD contacts, side heating and top heating, and touch upon their relative advantages. The thermoelectric response of a QD as a function of gate potential has a characteristic oscillatory behavior with the same period as is observed for conductance peaks. Much of the existing literature focuses on the agreement between experiments and theory, particularly for amplitude and line-shape of the thermovoltage Vth. A general observation is that the widely used single-electron tunneling approximation for QDs has limited success in reproducing measured Vth. Landauer-type calculations are often found to describe measurement results better, despite the large electron-electron interactions in QDs. More recently, nonlinear thermoelectric effects have moved into the focus of attention, and we offer a brief overview of the experiments done so far. We conclude by discussing open questions and avenues for future work, including the role of asymmetries in tunnel- and capacitive couplings in the thermoelectric behavior of QDs. xml:lang="fr"

  13. Phase transformation and thermoelectric properties of bismuth-telluride nanowires

    NASA Astrophysics Data System (ADS)

    Hsin, Cheng-Lun; Wingert, Matthew; Huang, Chun-Wei; Guo, Hua; Shih, Ten-Jen; Suh, Joonki; Wang, Kevin; Wu, Junqiao; Wu, Wen-Wei; Chen, Renkun

    2013-05-01

    Thermoelectric materials have attracted much attention due to the current interest in energy conversion and recent advancements in nano-engineering. A simple approach to synthesize BiTe and Bi2Te3 micro/nanowires was developed by combining solution chemistry reactions and catalyst-free vapor-solid growth. A pathway to transform the as-grown BiTe nanostructures into Bi2Te3 can be identified through the Bi-Te phase diagram. Structural characterization of these products was identified using standard microscopy practices. Meanwhile, thermoelectric properties of individual Bi-Te compound micro/nanowires were determined by the suspended microdevice technique. This approach provides an applicable route to synthesize advanced high performance thermoelectric materials in quantities and can be used for a wide range of low-dimensional structures.Thermoelectric materials have attracted much attention due to the current interest in energy conversion and recent advancements in nano-engineering. A simple approach to synthesize BiTe and Bi2Te3 micro/nanowires was developed by combining solution chemistry reactions and catalyst-free vapor-solid growth. A pathway to transform the as-grown BiTe nanostructures into Bi2Te3 can be identified through the Bi-Te phase diagram. Structural characterization of these products was identified using standard microscopy practices. Meanwhile, thermoelectric properties of individual Bi-Te compound micro/nanowires were determined by the suspended microdevice technique. This approach provides an applicable route to synthesize advanced high performance thermoelectric materials in quantities and can be used for a wide range of low-dimensional structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00876b

  14. Structure and magnetic properties of the MnBi low temperature phase

    NASA Astrophysics Data System (ADS)

    Yang, J. B.; Yelon, W. B.; James, W. J.; Cai, Q.; Roy, S.; Ali, N.

    2002-05-01

    High purity MnBi low temperature phase has been prepared and analyzed using magnetic measurements and neutron diffraction. The low-temperature phase of the MnBi alloy has a coercivity μ0iHc of 2.0 T at 400 K, and exhibits a positive temperature coefficient from 0 to at least 400 K. The neutron data refinement indicated that the Mn atom changes its spin direction from c axis above room temperature to nearly perpendicular to the c axis at 50 K. A canted magnetic structure has been observed below 200 K. The anisotropy field increases with increasing temperature which gives rise to a high coercivity at the higher temperatures. The anisotropic bonded magnets have maximum energy products (BH)max of 7.7 and 4.6 MGOe at room temperature and 400 K, respectively.

  15. 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.

  16. Low-temperature study of the magnetic properties of finite atomic chains

    NASA Astrophysics Data System (ADS)

    Kolesnikov, S. V.

    2016-05-01

    A simple method for the calculation of the spontaneous remagnetization time and magnetization curves of atomic finite-length ferromagnetic chains at a low temperature within the Heisenberg model has been proposed. The applicability limits of the method have been studied. It has been shown that the proposed method gives results being in good agreement with the kinetic Monte Carlo simulation results. Formulas obtained within our model can also be used to determine the lower bound for the Curie temperature.

  17. Enhancement of Thermoelectric Properties of Lead Selenide by Doping

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  18. 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.

  19. Structural homogeneity of nanocrystalline VT1-0 titanium. Low-temperature micromechanical properties

    NASA Astrophysics Data System (ADS)

    Rusakova, A. V.; Lubenets, S. V.; Fomenko, L. S.; Moskalenko, V. A.

    2012-10-01

    The microhardness of samples of VT1-0 titanium with grain sizes ranging from 35 nm to 10 μm is measured at temperatures of 77-300 K. Nanocrystalline samples produced by rolling at low temperatures are found to be quite homogeneous, and their structure is stable with respect to thermal and mechanical interactions. The interrelationship between microhardness and grain size is well described by the Hall-Petch relationship, the parameters of which depend on temperature. Data on the temperature dependence of the microhardness and the Hall-Petch coefficient indicate that the microplastic deformation is of a thermally activated, dislocation character, regardless of grain size.

  20. Low-temperature electrolytic coloration and spectral properties of sucrose crystals.

    PubMed

    Gu, Hongen; Tian, Pin; Guo, Meili; Li, Yutong; Hao, Xiaoqing

    2012-06-01

    Sucrose crystals are colored electrolytically at low temperatures and various voltages by using a pointed cathode and a flat anode. Caramels, carbonyl compounds, glycosylamines and free radicals are produced in colored sucrose crystals. No obvious characteristic absorption band in UV and visible wavelength regions is observed in absorption spectrum of uncolored sucrose crystal. Intense characteristic absorption bands of glycosylamines, carbonyl compounds and caramels are observed in absorption spectra of colored sucrose crystals. Production of caramels, carbonyl compounds, glycosylamines and free radicals are explained. Current-time curve for electrolytic coloration of sucrose crystal and its relationship with electrolytic coloration process are given.

  1. Low-temperature electrolytic coloration and spectral properties of sucrose crystals

    NASA Astrophysics Data System (ADS)

    Gu, Hongen; Tian, Pin; Guo, Meili; Li, Yutong; Hao, Xiaoqing

    2012-06-01

    Sucrose crystals are colored electrolytically at low temperatures and various voltages by using a pointed cathode and a flat anode. Caramels, carbonyl compounds, glycosylamines and free radicals are produced in colored sucrose crystals. No obvious characteristic absorption band in UV and visible wavelength regions is observed in absorption spectrum of uncolored sucrose crystal. Intense characteristic absorption bands of glycosylamines, carbonyl compounds and caramels are observed in absorption spectra of colored sucrose crystals. Production of caramels, carbonyl compounds, glycosylamines and free radicals are explained. Current-time curve for electrolytic coloration of sucrose crystal and its relationship with electrolytic coloration process are given.

  2. 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.

  3. 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.

  4. Boron nitride nanowalls: low-temperature plasma-enhanced chemical vapor deposition synthesis and optical properties.

    PubMed

    Merenkov, Ivan S; Kosinova, Marina L; Maximovskii, Eugene A

    2017-05-05

    Hexagonal boron nitride (h-BN) nanowalls (BNNWs) were synthesized by plasma-enhanced chemical vapor deposition (PECVD) from a borazine (B3N3H6) and ammonia (NH3) gas mixture at a low temperature range of 400 °C-600 °C on GaAs(100) substrates. The effect of the synthesis temperature on the structure and surface morphology of h-BN films was investigated. The length and thickness of the h-BN nanowalls were in the ranges of 50-200 nm and 15-30 nm, respectively. Transmission electron microscope images showed the obtained BNNWs were composed of layered non-equiaxed h-BN nanocrystallites 5-10 nm in size. The parallel-aligned h-BN layers as an interfacial layer were observed between the film and GaAs(100) substrate. BNNWs demonstrate strong blue light emission, high transparency (>90%) both in visible and infrared spectral regions and are promising for optical applications. The present results enable a convenient growth of BNNWs at low temperatures.

  5. A high-throughput thermoelectric power-factor screening tool for rapid construction of thermoelectric property diagrams

    NASA Astrophysics Data System (ADS)

    Otani, M.; Lowhorn, N. D.; Schenck, P. K.; Wong-Ng, W.; Green, M. L.; Itaka, K.; Koinuma, H.

    2007-09-01

    The authors have developed a high-throughput screening tool that maps out thermoelectric power factors of combinatorial composition-spread film libraries. The screening tool allows one to measure the electrical conductivity and Seebeck coefficient of over 1000 sample points within 6h. Seebeck coefficients of standard films measured with the screening tool are in good agreement with those measured by traditional thermoelectric measurement apparatus. The rapid construction of thermoelectric property diagrams is illustrated for two systems: (Zn, Al)-O binary composition-spread film on Al2O3 (0001) and (Ca,Sr,La)3Co4O9 ternary composition-spread film on Si (100).

  6. Enhanced Thermoelectric Properties of W- and Fe-Substituted MnSi γ

    NASA Astrophysics Data System (ADS)

    Ghodke, Swapnil; Hiroishi, Naoya; Yamamoto, Akio; Ikuta, Hiroshi; Matsunami, Masaharu; Takeuchi, Tsunehiro

    2016-10-01

    We have investigated the effect of heavy-element (W) substitution on the thermoelectric properties of higher manganese silicide (HMS). Samples were prepared by arc melting followed by liquid quenching, where the latter assisted in achieving higher solubility for tungsten. We observed that Mn34.6W1.8Si63.6 was a p-type material, whereas simultaneous substitution of 12 at.% Fe made the higher manganese silicide an n-type material. The optimal carrier concentration was obtained by simultaneous substitution of Fe and W for Mn atoms. Although the samples were metastable, we successfully obtained bulk samples by a low-temperature (970 K), high-pressure (>100 MPa), long-duration sintering process. The lattice thermal conductivity was effectively reduced by W substitution, and the ZT value was improved to above 0.5 for both n- and p-type samples.

  7. 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.

  8. 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.

  9. Electrical properties of bilayer graphene synthesized using surface wave microwave plasma techniques at low temperature

    NASA Astrophysics Data System (ADS)

    Yamada, Takatoshi; Kato, Hiromitsu; Okigawa, Yuki; Ishihara, Masatou; Hasegawa, Masataka

    2017-01-01

    Bilayer graphene was synthesized at low temperature using surface wave microwave plasma techniques where poly(methyl metacrylate) (PMMA) and methane (CH4) were used as carbon sources. Temperature-dependent Hall effect measurements were carried out in a helium atmosphere. Sheet resistance, sheet carrier density and mobility showed weak temperature dependence for graphene from PMMA, and the highest carrier mobility is 740 cm2 V-1 s-1. For graphene from CH4, tunneling of the domain boundary limited carrier transport. The difference in average domain size was determined by Raman signal maps. In addition, residuals of PMMA were detected on graphene from PMMA. The low sheet resistances of graphene synthesized at a temperature of 280 °C using plasma techniques were explained by the PMMA related residuals rather than the domain sizes.

  10. 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.

  11. 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.

  12. Process dependent thermoelectric properties of EDTA assisted bismuth telluride

    NASA Astrophysics Data System (ADS)

    Kulsi, Chiranjit; Kargupta, Kajari; Banerjee, Dipali

    2016-04-01

    Comparison between the structure and thermoelectric properties of EDTA (Ethylene-diamine-tetra-acetic acid) assisted bismuth telluride prepared by electrochemical deposition and hydrothermal route is reported in the present work. The prepared samples have been structurally characterized by high resolution X-ray diffraction spectra (HRXRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopic images (HRTEM). Crystallite size and strain have been determined from Williamson-Hall plot of XRD which is in conformity with TEM images. Measurement of transport properties show sample in the pellet form (S1) prepared via hydrothermal route has higher value of thermoelectric power (S) than the electrodeposited film (S2). But due to a substantial increase in the electrical conductivity (σ) of the film (S2) over the pellet (S1), the power factor and the figure of merit is higher for sample S2 than the sample S1 at room temperature.

  13. Preparation and thermoelectric properties of some phosphide skutterudite compounds

    NASA Astrophysics Data System (ADS)

    Watcharapasorn, A.; DeMattei, R. C.; Feigelson, R. S.; Caillat, T.; Borshchevsky, A.; Snyder, G. J.; Fleurial, J.-P.

    1999-12-01

    Thermoelectric properties of CoP3 and CeFe4P12 have been measured. These compounds were synthesized by a flux technique using Sn as the solvent. The samples were characterized by x-ray diffractometry and electron microprobe analyses. The Seebeck coefficient, the electrical resistivity, the Hall effect, and the thermal conductivity were measured over a wide range of temperatures. The results indicate that CoP3 and CeFe4P12 are semiconductors, in agreement with theoretical predictions. The thermal conductivity of CeFe4P12 is about 10 times larger than that for CeFe4Sb12 which is primarily due to both reduced motion of the Ce ions in smaller voids and lower hole-phonon scattering. The results are analyzed and discussed to provide guidelines for optimization of the thermoelectric properties of these materials.

  14. Thermoelectric properties of topological insulator BaSn2

    NASA Astrophysics Data System (ADS)

    Guo, San-Dong; Qiu, Liang

    2017-01-01

    Recently, \\text{BaS}{{\\text{n}}2} has been predicted to be a strong topological insulator by the first-principle calculations. It is well known that topological insulators have a close connection to thermoelectric materials, such as the \\text{B}{{\\text{i}}2}\\text{T}{{\\text{e}}3} family. In this work, we investigate thermoelectric properties of \\text{BaS}{{\\text{n}}2} by the first-principles calculations combined with the Boltzmann transport theory. The electronic part is carried out by a modified Becke and Johnson (mBJ) exchange potential, including spin-orbit coupling (SOC), while the phonon part is performed using a generalized gradient approximation (GGA). It was found that the electronic transport coefficients between the in-plane and cross-plane directions showed strong anisotropy, while lattice-lattice thermal conductivities demonstrated almost complete isotropy. Calculated results revealed a very low lattice thermal conductivity for \\text{BaS}{{\\text{n}}2} , and the corresponding average lattice thermal conductivity at room temperature is 1.69 \\text{W}~{{\\text{m}}-1}~{{\\text{K}}-1} , which is comparable or lower than those of lead chalcogenides and bismuth-tellurium systems as classic thermoelectric materials. Due to the complicated scattering mechanism, calculating the scattering time τ is challenging. By using an empirical τ ={{10}-14} s, the n-type figure of merit ZT is greater than 0.40 in wide temperature ranges. Experimentally, it is possible to attain better thermoelectric performance by strain or tuning size parameters. This work indicates that \\text{BaS}{{\\text{n}}2} may be a potential thermoelectric material, which can stimulate further theoretical and experimental work.

  15. 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.

  16. Change in the magnetic properties of nanoferrihydrite with an increase in the volume of nanoparticles during low-temperature annealing

    NASA Astrophysics Data System (ADS)

    Balaev, D. A.; Krasikov, A. A.; Stolyar, S. V.; Iskhakov, R. S.; Ladygina, V. P.; Yaroslavtsev, R. N.; Bayukov, O. A.; Vorotynov, A. M.; Volochaev, M. N.; Dubrovskiy, A. A.

    2016-09-01

    The results of the investigation into the effect of low-temperature annealing of a powder of nanoparticles of bacterial ferrihydrite on its magnetic properties have been presented. It has been found that an increase in the time (up to 240 h) and temperature (in the range from 150 to 200°C) of annealing leads to a monotonic increase in the superparamagnetic blocking temperature, the coercive force, and the threshold field of the opening of the magnetic hysteresis loop (at liquid-helium temperatures), as well as to an increase in the magnetic resonance line width at low temperatures and in the magnetic susceptibility at room temperature. At the same time, according to the results of the analysis of the Mössbauer spectra, the annealing of ferrihydrite does not lead to the formation of new iron oxide phases. Most of these features are well consistent with the fact that the low-temperature annealing of ferrihydrite causes an increase in the size of nanoparticles, which is confirmed by the results of transmission electron microscopy studies.

  17. 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

  18. The photosynthetic properties of rice leaves treated with low temperature and high irradiance.

    PubMed

    Hirotsu, Naoki; Makino, Amane; Yokota, Satoshi; Mae, Tadahiko

    2005-08-01

    Photosynthetic characteristics in rice (Oryza sativa L.) leaves were examined after treatment with low temperature (15 degrees C) and high irradiance (1,500 micromol quanta m(-2) s(-1)). Decreases in quantum efficiencies in PSII (PhiPSII) and PSI (PhiPSI) and in the rate of CO2 assimilation were observed with a decrease in the maximal quantum efficiency of PSII (F(v)/F(m)) by simultaneous measurements of Chl fluorescence, P700+ absorbance and gas exchange. The decreases in PhiPSII were most highly correlated with those in CO2 assimilation. Although the initial (the activity immediately measured upon extraction) and total (the activity following pre-incubation with CO2 and Mg2+) activities of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) decreased slightly, the maximal activity (the activity following treatment with SO4(2-)) of Rubisco remained almost constant. These results indicate that the decrease in CO2 assimilation rate with the decreasing F(v)/F(m) was not caused by a decrease in Rubisco activity but rather by a decrease in RuBP regeneration capacity which resulted from the decrease in the rate of the linear electron transport. On the other hand, the decrease in PhiPSI was very small and the ratio of PhiPSI to PhiPSII increased. The de-epoxidation state of xanthophyll cycle pigments also increased. Thus, the cyclic electron transport around PSI occurred in photoinhibited leaves.

  19. Low-temperature collapsing boron nitride nanospheres into nanoflakes and their photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Li, Jie; Luo, Han; Lin, Jing; Xue, Yanming; Liu, Zhenya; Jin, Peng; Xu, Xuewen; Huang, Yang; Liu, Dong; Zhang, Jun; Tang, Chengchun

    2014-09-01

    Flake-like boron nitride (BN) nanocrystals with a uniform diameter of ˜200 nm and thickness of ˜20 nm were fabricated by directly transforming from BN nanospheres with the assistance of NaCl salt at 1300 °C. The transformation from nanospheres to nano-pies and further to nanoflakes was achieved in a simple procedure of Na or Cl ions intercalation/deintercalation procedure at such low temperature. The morphologies of the spherical precursor and resulting nanoflakes were almost identical. X-ray powder diffractions revealed that the BN nanoflakes (BNfs) were well crystallized in the hexagonal structure via graphitizing index calculation. Elemental content analysis, FTIR spectra and TEM images were also used to characterize the products. Strong ultraviolet (UV) emissions were detected by photoluminescence (PL) spectroscopic analysis, in which the emission regions could be facilely tuned by controlling the reaction temperature. Detailed studies indicated that the collapsing temperature of unstable BN nanospheres into nanoflakes was strongly dependent on the introduction of NaCl molten salts or not. We believe the use of the NaCl molten salt medium may enhance the kinetics of the crystallization and also purification. The green fabrication characteristics, such as using NaCl salt as the additive, energy saving (300 °C lower than the commercial process), non-toxicity of byproduct and easy scale-up, make the present novel synthetic route likely to be of interest to commercial-scale production of BN nanoflakes.

  20. Low-temperature acoustic properties of nanostructured zirconium obtained by intensive plastic deformation

    NASA Astrophysics Data System (ADS)

    Vatazhuk, E. N.; Pal-Val, P. P.; Natsik, V. D.; Pal-Val, L. N.; Tikhonovsky, M. A.; Velikodny, A. N.; Khaimovich, P. A.

    2011-02-01

    The temperature dependences of the logarithmic decrement and dynamic Young's modulus of polycrystalline coarse-grained and nanostructured Zr are studied at temperatures of 2.5-340K. A nanostructured state of samples with grain sizes on the order of 100nm was produced by intensive plastic deformation (IPD). The measurements were made using a two-component vibrator technique at frequencies of 73-350kHz. A relaxation peak in the internal friction near 250K was discovered in the coarse-grained, annealed Zr which is retained after IPD, but its height increases by roughly a factor of 10 and the localization temperature shifts to lower values. In addition, after IPD a new internal friction peak shows up at moderately low temperatures near 80K. The activation parameters for the observed peaks are estimated and it is shown that they arise from different thermally activated dislocation processes: interactions of dislocations with impurities and kink pair formation in dislocations. It was found that IPD is accompanied by a significant (1-8%) reduction in the Young's modulus because of quasistatic and dynamic dislocation effects. A glass-like anomaly appears in the temperature dependence of the Young's modulus of nanostructured Zr at T <20K which may be determined by tunnelling and thermally activated relaxation of quasilocal excitations.

  1. 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.

  2. The spectral properties of DNA and RNA macromolecules at low temperatures: fundamental and applied aspects

    NASA Astrophysics Data System (ADS)

    Yashchuk, Valeriy M.; Kudrya, Vladislav Yu

    2017-03-01

    This paper summarizes the results of studies of the spectral properties—optical absorption, fluorescence and phosphorescence—of DNA and RNA macromolecules and synthetic poly-, oligo- and mono-nucleotides, which have been carried out in our laboratory. The system of first excited singlet and triplet energy levels for DNA and RNA is evaluated using low-temperature (4.2 K-77 K) luminescent measurements. The traps of the singlet and triplet electronic excitations in these compounds are identified. An important self-protection mechanism against photo-damage of DNA and RNA by UV photons or penetrative radiation based on the capture of triplet electronic-energy excitations by the most photostable centers—in DNA, the complex formed by neighboring adenosine (A) and thymidine (T) links; in RNA, the adenosine links—is described. It is confirmed that despite similarities in the chemical and partly energy structures DNA is more stable than RNA. The spectral manifestation of the telomeres (the important functional system) in DNA macromolecules is examined. The results obtained on telomere fragments provide the possibility of finding the configuration peculiarities of the triplet excitations traps in DNA macromolecules. The resulting spreading length of the migrating singlet (l s) and triplet (l t) excitations for DNA and RNA macromolecules are evaluated.

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

    DOE PAGES

    Demaurex, Bénédicte; Bartlome, Richard; Seif, Johannes P.; ...

    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

  4. Thermal Properties of Two Materials Commonly Used in Low Temperature Laboratories

    NASA Astrophysics Data System (ADS)

    Colin, Angel

    2013-02-01

    We carried out measurements of thermal conductance and thermal contact resistance of two materials commonly used in low temperature laboratories such as an Electro-Magnetic Interference (EMI) Filter and Stycast 2850 FT epoxy. Both samples were attached on a heat sink made of oxygen-free high thermal conductivity (OFHC) copper and characterized at temperatures between 0.3 K and 4.5 K, using a 3He refrigerator mounted on a pumped 4He cryostat. For the EMI filter we applied a varied input power from 0.25 up to 50 μW to the heater which is soldered to its central pin, whereas for a thin layer of Stycast sandwiched between a copper strap and the heat sink we applied an input power from 10 up to 810 μW. The temperature dependences obtained in each case were K=3 {\\cdot} 10^{-5}T^{2.3} [W/K], and RK=8.4 {\\cdot} 10^{-3}T^{1.7} [W/cm^{2 K}] respectively.

  5. New monoclinic phase at the composition Cu2SnSe3 and its thermoelectric properties.

    PubMed

    Fan, Jing; Carrillo-Cabrera, Wilder; Akselrud, Lev; Antonyshyn, Iryna; Chen, Lidong; Grin, Yuri

    2013-10-07

    A new monoclinic phase (m2) of ternary diamond-like compound Cu2SnSe3 was synthesized by reaction of the elements at 850 K. The crystal structure of m2-Cu2SnSe3 was determined through electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data (space group Cc, a = 6.9714(2) Å, b = 12.0787(5) Å, c = 13.3935(5) Å, β = 99.865(5)°, Z = 8). Thermal analysis and annealing experiments suggest that m2-Cu2SnSe3 is a low-temperature phase, while the high-temperature phase has a cubic crystal structure. According to quantum chemical calculations, m2-Cu2SnSe3 is a narrow-gap semiconductor. A study of the chemical bonding, applying the electron localizability approach, reveals covalent polar Cu-Se and Sn-Se interactions in the crystal structure. Thermoelectric properties were measured on a specimen consolidated using spark plasma sintering (SPS), confirming the semiconducting character. The thermoelectric figure of merit ZT reaches a maximum value of 0.33 at 650 K.

  6. 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.

  7. Sperry low-temperature geothermal conversion system. Volume 1: Organic-working-fluid properties

    NASA Astrophysics Data System (ADS)

    Carroll, C.; Hules, K. R.; Langley, R.; Toekes, B.; Wilson, D. P.

    1981-11-01

    Measurements of the physical properties of R-114 refrigerant in the compressed liquid and dense gas regions are reported. Included are: experimental studies of the thermodynamic properties of R-114, enthalpy measurement by throttling experiment, engineering model of the thermodynamic properties of R-114, feasibility study to dissociate R-114 with a four cycle gasoline engine, transport properties of R-114, analytical procedure to determine impurities in R-114, toxicological information on Freons, and a literature search of published properties of R-114, other refrigerants, and other potential working fluids.

  8. Enhancing thermoelectric properties of organic composites through hierarchical nanostructures

    PubMed Central

    Zhang, Kun; Zhang, Yue; Wang, Shiren

    2013-01-01

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

  9. Thermoelectric properties of SnSe2 monolayer

    NASA Astrophysics Data System (ADS)

    Li, Guanpeng; Ding, Guangqian; Gao, Guoying

    2017-01-01

    The 2H (MoS2-type) phase of 2D transition metal dichalcogenides (TMDCs) has been extensively studied and exhibits excellent electronic and optoelectronic properties, but the high phonon thermal conductivity is detrimental to the thermoelectric performances. Here, we use first-principles methods combined with Boltzmann transport theory to calculate the electronic and phononic transport properties of 1T (CdI2-type) SnSe2 monolayer, a recently realized 2D metal dichalcogenide semiconductor. The calculated band gap is 0.85 eV, which is a little larger than the bulk value. Lower phonon thermal conductivity and higher power factor are obtained in 1T-SnSe2 monolayer compared to 2H-TMDCs monolayers. The low phonon thermal conductivity (3.27 W mK-1 at room temperature) is mainly due to the low phonon frequency of acoustic modes and the coupling of acoustic modes with optical modes. We also find that the p-type has better thermoelectric performance than the n-type, and the figure of merit within p-type can reach 0.94 at 600 K for 1T-SnSe2 monolayer, which is higher than those of most 2H-TMDCs monolayers, making 1T-SnSe2 monolayer a promising candidate for thermoelectric applications.

  10. Structural and Thermoelectric Properties of Ternary Full-Heusler Alloys

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    The thermoelectric properties of ternary full-Heusler alloys, Co2 YZ, which are in a ferromagnetic state up to high temperature above 300 K, were measured and are discussed in terms of the crystal structure and electronic states. Among the full-Heusler alloys studied, the Co2MnSi sample exhibited the highest absolute value of Seebeck coefficient and also the highest electrical conductivity in the temperature range from 300 K to 1023 K. The highest power factor of 2.9 × 10-3 W/m-K2 was obtained for the Co2MnSi sample at 550 K, demonstrating the potential of half-metallic full-Heusler alloys as thermoelectric materials.

  11. Thermoelectric properties of titanium dioxide polymorphs from first principles

    NASA Astrophysics Data System (ADS)

    Bayerl, Dylan; Kioupakis, Emmanouil

    2014-03-01

    Titanium oxides are promising materials for high-temperature thermoelectrics because of their high Seebeck coefficients, thermal stability, and natural abundance. We use first-principles calculations to investigate the thermoelectric transport properties of several titanium dioxide polymorphs. Our methodology is based on density functional and many-body perturbation theory within the GW approximation. The maximally localized Wannier function method is employed to interpolate the GW bands in the Brillouin zone. We use the Boltzmann transport formalism within the constant relaxation time approximation to determine the temperature and carrier-density dependence of the Seebeck coefficient, electron mobility, and electron thermal conductivity from the calculated electronic band structures. We demonstrate agreement with experimentally measured transport parameters and enhanced power factor at high temperature in certain heavily doped phases. This research was supported as part of CSTEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Computational resources were provided by the DOE NERSC facility.

  12. Compositional effects on the low-temperature transport properties of non-stoichiometric Bi2Te x Se y -based crystals

    NASA Astrophysics Data System (ADS)

    Ramachandran, B.; Wu, K. K.; Kuo, Y. K.; Guo, L. S.; Wang, L. M.

    2017-01-01

    We grew a series of non-stoichiometric crystals of the ternary alloy Bi2Te x Se y via a direct solidification route. The temperature-dependent electrical and thermal transport properties, such as electrical resistivity (ρ), Seebeck coefficient (S), Hall coefficient (R H), and thermal conductivity (κ), of six selected crystals of Bi2Te x Se y with x  +  y ~ 3 were studied. We found that the physical properties of the Bi2Te x Se y -based crystals varied significantly with the Te/Se (x/y) content. This is essentially due to the modification of the electronic band structure of the crystals with the change in sample composition, which ultimately leads to the formation of a p-type material (Bi2Te2.10Se0.66) from an n-type Bi2Te1.89Se0.98. Most importantly, the feature associated with surface-state conduction at low temperatures was also observed in some of these crystals, including Bi2Te1.89Se0.98, Bi2Te2.16Se0.71, and Bi2Te2.10Se0.66. In particular, two highly resistive compounds, Bi2Te2.16Se0.71 and Bi2Te2.10Se0.66 with low carrier densities were identified as potential materials for topological applications. The observed complex transport behavior was realized in connection with the formation of impurity bands (multiband effects) in the Bi2Te x Se y -based systems. Analysis of the lattice thermal conductivity of the Bi2Te x Se y -based crystals indicates that the sample composition has a major effect on low-temperature heat conduction via phonon-boundary and phonon-point-defect scattering. Finally, the highest room temperature thermoelectric figure of merit, a ZT of about 0.46, was achieved for n-type Bi2Te1.63Se1.23.

  13. Laboratory Assessment of the Changes in Thermal Properties of Polar Diving Suit Material When Exposed to Oils at Low Temperatures

    DTIC Science & Technology

    1981-02-01

    tests was the development and construction of a mechanism which could automatically raise the suit- material sample out of, and reinsert it into, the...I Report No. c--D.-4-..82 LABORATORY ASSESSMENT OF T1E CHANGES IN - THERMAL PROPERTIES OF POLAR DIVING SUIT MATERIAL WHEN EXPOSED TO OILS AT LOW...POLAR DIVING SUIT , Performing Organiat.in Cede MATERIAL WHEN EXPOSED TO OILS AT LOW TEMPERATURES 1. Per,•oring Orgenization Report No. 7. Autor1 ’s

  14. 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

  15. 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

  16. High Energy Effects on Thermoelectric and Optical Properties of Si/Si+Sb Nanolayered Thin Films

    DTIC Science & Technology

    2013-04-01

    REPORT High Energy Effects on Thermoelectric and Optical Properties of Si/Si+Sb Nanolayered Thin Films 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: We...Energy Effects on Thermoelectric and Optical Properties of Si/Si+Sb Nanolayered Thin Films Report Title ABSTRACT We have prepared thermoelectric...the cross plane Seebeck coefficient and increase the cross plane electrical conductivity to increase the figure of merit. Some optical

  17. Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains

    NASA Astrophysics Data System (ADS)

    Chang, Liao; Winklhofer, Michael; Roberts, Andrew P.; Heslop, David; Florindo, Fabio; Dekkers, Mark J.; Krijgsman, Wout; Kodama, Kazuto; Yamamoto, Yuhji

    2013-12-01

    marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties, including reversible humped low-temperature cycling (LTC) curves. Different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of LTC curves. A dipole spring mechanism in magnetosome chains is introduced to explain reversible LTC curves. This dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite, similar to published results for uniaxial stable single domain (SD) particles. The dipole spring mechanism reversibly restores the remanence during warming in LTC measurements. This supports a previous idea that remanence of magnetosome chains is completely reversible during LTC experiments. We suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains, although the presence of isolated uniaxial stable SD particles and magnetically interacting particles can complicate this test. Magnetic measurements through the Eocene section of ODP Hole 738B reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic "hard" component. Co-occurrence of these two magnetic fingerprints during the late Eocene in the Southern Ocean indicates less oxic conditions, probably due to increased oceanic primary productivity and organic carbon burial.

  18. Synthesis & Properties of Nano-Composite Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Tritt, Terry

    2007-03-01

    PbTe nanocrystals have been grown in our labs by chemical vapor deposition. These materials grow in size selective regions exhibiting very high yield and have size distributions of around 100 nm to 1000 nm. These nano-materials are incorporated into a bulk matrix, making a composite material in hopes of achieving a higher thermoelectric performance due to the increased phonon scattering that the nano-materials are expected to exhibit, as well as potential for enhancement of their Seebeck coefficient. Some of the advantages as well as the challenges will be discussed. These nanocomposites give a new level of potential control as a tuning parameter with which to vary the materials' thermoelectric properties. In addition, Bi2Te3, another state of the art thermoelectric material and skutterudites (CoSb3) have been synthesized as nanomaterials using hydrothermal techniques. A brief discussion of the synthesis techniques, the characterization techniques and highlights of several systems of materials will be presented. In collaboration with Xiaohua Ji, Jian He, Bo Zhang, Nick Gothard, and Paola Alboni, Dept. of Physics, Clemson University.

  19. Thermoelectric properties of isoelectronically substituted bismuth compounds: a computational study

    NASA Astrophysics Data System (ADS)

    Liangruksa, Monrudee

    2017-03-01

    This work focuses on using isoelectronic substitution to modify electronic density of states (DOS) of bismuth (Bi) compounds for thermoelectric property modification. The calculations include first-principle density functional theory (DFT) and analytical calculations based on Mott formula. The thermoelectric materials selected in the present study are Bi compounds, i.e. Bi2Te3, Bi2Se3, Bi2Se2Te, Bi2Te2Se, Bi2O2Te, and Bi2O2Se. The results reveal that isoelectronic substitution of Se and Te atoms with O atoms (Bi2O2Te and Bi2O2Se) introduces changes in DOS around the valence band maximum and the conduction band minimum, exhibiting the figure of merit (ZT) approaching the values 0.004 and 0.03 at room temperature, for Bi2O2Se and Bi2O2Te, respectively. Though the ZT of these oxide compounds are inferior to conventional thermoelectric materials, it is known that they show better stability and less toxicity which could be the alternative materials.

  20. 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.

  1. [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.

  2. 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...

  3. Improved electrical properties of atomic layer deposited tin disulfide at low temperatures using ZrO2 layer

    NASA Astrophysics Data System (ADS)

    Lee, Juhyun; Lee, Jeongsu; Ham, Giyul; Shin, Seokyoon; Park, Joohyun; Choi, Hyeongsu; Lee, Seungjin; Kim, Juyoung; Sul, Onejae; Lee, Seungbeck; Jeon, Hyeongtag

    2017-02-01

    We report the effect of zirconium oxide (ZrO2) layers on the electrical characteristics of multilayered tin disulfide (SnS2) formed by atomic layer deposition (ALD) at low temperatures. SnS2 is a two-dimensional (2D) layered material which exhibits a promising electrical characteristics as a channel material for field-effect transistors (FETs) because of its high mobility, good on/off ratio and low temperature processability. In order to apply these 2D materials to large-scale and flexible electronics, it is essential to develop processes that are compatible with current electronic device manufacturing technology which should be conducted at low temperatures. Here, we deposited a crystalline SnS2 at 150 °C using ALD, and we then annealed at 300 °C. X-ray diffraction (XRD) and Raman spectroscopy measurements before and after the annealing showed that SnS2 had a hexagonal (001) peak at 14.9° and A1g mode at 313 cm-1. The annealed SnS2 exhibited clearly a layered structure confirmed by the high resolution transmission electron microscope (HRTEM) images. Back-gate FETs with SnS2 channel sandwiched by top and bottom ZrO2 on p++Si/SiO2 substrate were suggested to improve electrical characteristics. We used a bottom ZrO2 layer to increase adhesion between the channel and the substrate and a top ZrO2 layer to improve contact property, passivate surface, and protect from process-induced damages to the channel. ZTZ (ZrO2/SnS2/ZrO2) FETs showed improved electrical characteristics with an on/off ratio of from 0.39×103 to 6.39×103 and a mobility of from 0.0076 cm2/Vs to 0.06 cm2/Vs.

  4. Mechanical properties of cold-rolled AISI 304LN steel at low temperatures

    SciTech Connect

    Ilola, R.J.; Haenninen, H.E.; Heinaekari, M.J.

    1996-12-01

    Mechanical properties of 0--70% cold-rolled AISI 304LN steel (0, 16 wt.% N) were investigated by means of tensile and Charpy V-notch impact tests between room temperature and {minus}196 C. Fracture surfaces of the tested specimens were investigated using SEM (scanning electron microscope). Austenite stability against {alpha}{prime}-martensite formation during cooling and during deformation in cold-rolling and mechanical testing was determined using magnetic measurements.

  5. 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.

  6. Unique magnetic and thermoelectric properties of chemically functionalized narrow carbon polymers

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    We analyze magnetic, transport and thermoelectric properties of narrow carbon polymers, which are chemically functionalized with nitroxide groups. Numerical calculations of the electronic band structure and the corresponding transmission function are based on density functional theory. Transport and thermoelectric parameters are calculated in the linear response regime, with particular interest in charge and spin thermopowers (charge and spin Seebeck effects). Such nanoribbons are shown to have thermoelectric properties described by large thermoelectric efficiency, which makes these materials promising from the application point of view.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Microstructure and Properties of Cu Coating Fabricated onto Diamond-Cu Substrate by Low-Temperature HVOF Process

    NASA Astrophysics Data System (ADS)

    Liu, Min; Yang, Kun; Deng, Chun-ming; Deng, Chang-guang; Zhou, Ke-song

    2016-12-01

    Diamond-Cu composites have been considered to be the next generation of electronic packing materials. One of the key stumbles for such an application is the joining problem between diamond-Cu composites and other materials due to the poor wettability of the diamond particles in the composites. In order to overcome this hurdle, pure Cu powder was thermally sprayed onto diamond-Cu substrate by low-temperature high-velocity oxygen fuel spraying process. Microstructure and some fundamental properties of the coating obtained were systematically investigated, and morphologies of the single splat deposited on the diamond-Cu substrate were also observed. The splats obtained have good adhesion with the substrate as fine particles flattened sufficiently, while the coarse particles were significantly deformed. The coating was quite dense with porosity lower than 1%, oxygen content under 0.5% and thermal conductivity about 266 Wm-1 K-1 and still remained on the diamond-Cu substrate after 50 thermal shock cycles between 300 °C and water bath at room temperature. Meanwhile, the solderability of the coating was significantly improved. Therefore, Cu coating deposited on diamond-Cu substrate by low-temperature high-velocity oxygen fuel spraying process can be beneficial in electronic industry assisting with soldering and improved wettability for joining of other materials.

  16. Rare earth chalcogenide stoichiometry determination. [of thermoelectric properties

    NASA Technical Reports Server (NTRS)

    Lockwood, R. A.

    1983-01-01

    Rare earth chalcogenides, and particularly lanthanum sulfide, are currently explored as candidate materials for thermoelectric applications. Since the electrical properties of LaS(x) are largely determined by its stoichiometry, a simple and accurate method has been developed for determining the value of x. The procedure involves dissolving a weighted sample in acid and measuring the amount of hydrogen evolved by the lanthanum that is in excess of the 1.500 ratio of S/La. The analytical error in the determination of x in LaS(x) is about 0.001.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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 Fe2+ ions in the ZnS NWs was about two times larger than that of the Mn2+ or Cu2+ 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 Mn2+/Cu2+/Fe2+ related emission peaks can be observed in the Mn2+,Cu2+ and Fe2+ doped ZnS NWs. The ferromagnetic properties of the co-doped samples were investigated at room temperature.

  19. 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

  20. 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.

  1. Optical properties and electronic requirements for low-temperature operation of yellow semiconductor LEDs

    NASA Astrophysics Data System (ADS)

    Lee, Susanne M.; Mueller, Eduard K.; Van de Workeen, Brian C.; Mueller, Otward M.

    2001-05-01

    In such LED applications as lighting, it is desirable to have the highest light output for the lowest power consumption. This paper investigates the optical properties and electronic requirements of a commercially available yellow LED as a function of temperature from ambient to liquid nitrogen temperatures. It was found that the illuminance increased by almost an order of magnitude, producing much higher light output at the same diode current. However, the operating voltage increased, increasing the overall power consumption slightly. The efficiency (light-watt output to electrical watts consumed) of the LED, though, improved by a factor of more than three. This, combined with the enhanced light output, compensates for the small increase in power consumption and added cooling costs. These improvements further translate into a comparable increase in the lifetime of the LEDs. In general, each ten-degree reduction in temperature corresponds to a doubling of the lifetime of semiconductor devices. It was also found that the maximum operating current increased significantly at liquid nitrogen temperatures over that at ambient temperatures. Lastly, the emitted wavelength range shifted to shorter values in addition to the significant increase in brightness. Thus, a yellow- colored LED at room temperature gave off a much brighter yellow-green-white color at liquid nitrogen temperatures.

  2. Hydrothermal synthesis and NH3 gas sensing property of WO3 nanorods at low temperature

    NASA Astrophysics Data System (ADS)

    Dien Nguyen, Dac; Vuong Dang, Duc; Chien Nguyen, Duc

    2015-09-01

    One-dimensional self-assembled single-crystalline hexagonal tungsten trioxide (WO3) nanostructures were synthesized by wet chemical-assisted hydrothermal processing at 120 °C for 24 h using sodium tungstate and hydrochloric acid. Urchin-like hierarchical nanorods (petal size: ∼16 nm diameter and 110 nm length) were obtained. The samples were characterized by field emission scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy and x-ray diffraction. Sensors based on WO3 nanorods were fabricated by coating them on SiO2/Si substrate attached with Pt interdigitated electrodes. NH3 gas-sensing properties of WO3 nanorods were measured at different temperatures ranging from 50 °C to 350 °C and the response was evaluated as a function of ammonia gas concentration. The gas-sensing results reveal that WO3 nanorods sensor exhibits high sensitivity and selectivity to NH3 at low operating temperature (50 °C). The maximum response reached at 50 °C was 192 for 250 ppm NH3, with response and recovery times of 10 min and 2 min, respectively.

  3. Low Temperature Study of the Electrical Properties of Sb- SnO2 Nanofibers

    NASA Astrophysics Data System (ADS)

    Reyna, Maritza; Ramos, Idalia; Pinto, Nicholas

    2011-03-01

    Antimony-doped tin oxide (ATO) can be used for many applications including the development of gas sensors, energy storage devices, and transparent electrodes. ATO nanofibers with sizes from 200 - 600 nm and a bandgap of 4.4 e.V were produced using the electrospinning method. The precursor was composed of tin chloride solution mixed with cellulose acetate solution and antimonium chloride. The XRD spectra of the nanofibers showed the characteristic peaks of Sb: Sn O2 with rutile structure. The electrical properties of single ATO nanofibers were studied following a cycle of cooling from 295 - 15 K and then heating from 15 - 295 K. These measurements were done in cold finger (close cycle helium refrigerator) in a vacuum. The conductivity measured at room temperature was 4.3 S/cm and decreases monotonically from 295 to 15K. As the temperature increases an anomalous peak is observed in the range of 250 to 300 K. This anomaly has been attributed to the chemi-absorbed molecules on the surface of the fiber and could be reduced by improving the vacuum conditions. PREM (NSF-DMR-0934195) and APS (Minority Scholarship for Undergraduates).

  4. 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.

  5. 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

  6. Magnetic and magnetocaloric properties of polycrystalline La0.48Ca0.52MnO3 compound at low temperature: Influence of glassy magnetic state

    NASA Astrophysics Data System (ADS)

    Das, Kalipada; Das, I.

    2017-04-01

    We report the magnetic, magnetocaloric and electrical transport properties of polycrystalline bulk La0.48Ca0.52MnO3 compound. In addition to earlier reported properties viz. charge ordering and antiferromagnetic ordering, we address the presence of glassy magnetic phase at low temperature (T < 40 K) in this compound. Studies on magnetic and magnetocaloric properties reveal that, pronounced glassy behavior in this compound is due to presence of ferromagnetic clusters in the low-temperature region. In addition to that, analysis of low-temperature x-ray diffraction measurements indicate increasing crystallographic unit cell volume which is attributed to the enhancement of eg-electron bandwidth at low temperature.

  7. Computation of the properties of liquid neon, methane, and gas helium at low temperature by the Feynman-Hibbs approach.

    PubMed

    Tchouar, N; Ould-Kaddour, F; Levesque, D

    2004-10-15

    The properties of liquid methane, liquid neon, and gas helium are calculated at low temperatures over a large range of pressure from the classical molecular-dynamics simulations. The molecular interactions are represented by the Lennard-Jones pair potentials supplemented by quantum corrections following the Feynman-Hibbs approach. The equations of state, diffusion, and shear viscosity coefficients are determined for neon at 45 K, helium at 80 K, and methane at 110 K. A comparison is made with the existing experimental data and for thermodynamical quantities, with results computed from quantum numerical simulations when they are available. The theoretical variation of the viscosity coefficient with pressure is in good agreement with the experimental data when the quantum corrections are taken into account, thus reducing considerably the 60% discrepancy between the simulations and experiments in the absence of these corrections.

  8. 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.

  9. Low temperature and high pressure thermoelastic and crystallographic properties of SrZrO3 perovskite in the Pbnm phase

    NASA Astrophysics Data System (ADS)

    Knight, Kevin S.; Bull, Craig L.

    2016-12-01

    The thermoelastic and structural properties of SrZrO3 perovskite in the Pnma (Pbnm) phase have been studied using neutron powder diffraction at 82 temperatures between 11 K and 406 K at ambient pressure, and at sixteen pressures between 0.07 and 6.7 GPa at ambient temperature. The bulk modulus, derived by fitting the equation of state to a second order Birch-Murnaghan equation-of-state, 157(5) GPa, is in excellent agreement with that deduced in a recent resonant ultrasound investigation. Experimental axial compressional moduli are in agreement with those calculated from the elastic stiffness coefficients derived by ab-initio calculation, although the experimental bulk modulus is significantly softer than that calculated. Following low temperature saturation for temperatures less than 40 K, the unit cell monotonically increases with a predicted high temperature limit in the volume expansivity of ∼2.65 × 10-5 K-1. Axial linear thermal expansion coefficients are found to be in the order αb < αc < αa for all temperatures greater than 20 K with the b axis indicating a weak, low temperature negative expansion coefficient at low temperatures. The thermoelastic properties of SrZrO3 can be approximated by a two-term Debye model for the phonon density of states with Debye temperatures of 238(4) K and 713(6) K derived in a self-consistent manner by simultaneously fitting the isochoric heat capacity and the unit cell volume. Atomic displacement parameters have been fitted to a modified Debye model in which the zero-point term is an additional refinable variable and shows the cations and anions have well separated Debye temperatures, mirroring the need for two Debye-like distributions in the vibrational density of states. The temperature dependence of the crystal structure is presented in terms of the amplitudes of the seven symmetry-adapted basis vectors of the aristotype phase that are consistent with space group Pbnm, thus permitting a direct measure of the order

  10. The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

    PubMed Central

    Kim, Hyung-Tae; Yang, Jae-Ho; Lee, Jai-Bong; Kim, Sung-Hun

    2009-01-01

    STATEMENT OF PROBLEM Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported. PURPOSE The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM). MATERIAL AND METHODS Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05). RESULTS The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low

  11. 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.

  12. 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.

  13. 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.

  14. Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models

    NASA Astrophysics Data System (ADS)

    Armstrong, Hannah; Boese, Matthew; Carmichael, Cody; Dimich, Hannah; Seay, Dylan; Sheppard, Nathan; Beekman, Matt

    2017-01-01

    Maximum thermoelectric energy conversion efficiencies are calculated using the conventional "constant property" model and the recently proposed "cumulative/average property" model (Kim et al. in Proc Natl Acad Sci USA 112:8205, 2015) for 18 high-performance thermoelectric materials. We find that the constant property model generally predicts higher energy conversion efficiency for nearly all materials and temperature differences studied. Although significant deviations are observed in some cases, on average the constant property model predicts an efficiency that is a factor of 1.16 larger than that predicted by the average property model, with even lower deviations for temperature differences typical of energy harvesting applications. Based on our analysis, we conclude that the conventional dimensionless figure of merit ZT obtained from the constant property model, while not applicable for some materials with strongly temperature-dependent thermoelectric properties, remains a simple yet useful metric for initial evaluation and/or comparison of thermoelectric materials, provided the ZT at the average temperature of projected operation, not the peak ZT, is used.

  15. 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.

  16. Low-temperature growth of aligned ZnO nanorods: effect of annealing gases on the structural and optical properties.

    PubMed

    Umar, Ahmad; Hahn, Yoon-Bong; Al-Hajry, A; Abaker, M

    2014-06-01

    Aligned ZnO nanorods were grown on ZnO/Si substrate via simple aqueous solution process at low-temperature of - 65 degrees C by using zinc nitrate and hexamethylenetetramine (HMTA). The detailed morphological and structural properties measured by FESEM, XRD, EDS and TEM confirmed that the as-grown nanorods are vertically aligned, well-crystalline possessing wurtzite hexagonal phase and grown along the [0001] direction. The room-temperature photoluminescence spectrum of the grown nanorods exhibited a strong and broad green emission and small ultraviolet emission. The as-prepared ZnO nanorods were post-annealed in nitrogen (N2) and oxygen (O2) environments and further characterized in terms of their morphological, structural and optical properties. After annealing the nanorods exhibit well-crystallinity and wurtzite hexagonal phase. Moreover, by annealing the PL spectra show the enhancement in the UV emission and suppression in the green emission. The presented results demonstrate that simply by post-annealing process, the optical properties of ZnO nanostructures can be controlled.

  17. The low-temperature scintillation properties of bismuth germanate and its application to high-energy gamma radiation imaging devices.

    PubMed

    Piltingsrud, H V

    1979-12-01

    Bismuth germanate is a scintillation material with very high z, and high density (7.13 g/cm3). It is a rugged, nonhygroscopic, crystalline material with room-temperature scintillation properties described by previous investigators as having a light yield approximately 8% of that of NaI(Tl), emission peak at approximately 480 nm, decay constant of 0.3 microsec, and energy resolution congruent to 15% (FWHM) for Cs-137 gamma radiations. These properties make it an excellent candidate for applications involving the detection of high-energy gamma photons and positron annihilation radiation, particularly when good spatial resolution is desired. At room temperature, however, the application of this material is somewhat limited by low light output and poor energy resolution. This paper presents new data on the scintillation properties of bismuth germanate as a function of temperature from -- 196 degrees C to j0 degrees C. Low-temperature use of the material is shown to greatly improve its light yield and energy resolution. The implications of this work to the design of imaging devices for high-energy radiation in health physics and nuclear medicine are discussed.

  18. Structural and room temperature ferromagnetic properties of Ni doped ZnO nanoparticles via low-temperature hydrothermal method

    NASA Astrophysics Data System (ADS)

    Xu, Kun; Liu, Changzhen; Chen, Rui; Fang, Xiaoxiang; Wu, Xiuling; Liu, Jie

    2016-12-01

    A series of Zn1-xNixO (x=0, 1%, 3%, 5%) nanoparticles have been synthesized via a low-temperature hydrothermal method. Influence of Ni doping concentration on the structure, morphology, optical properties and magnetism of the samples was investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-vis spectrophotometer and vibrating sample magnetometer instruments. The results show that the undoped and doped ZnO nanoparticles are both hexagonal wurtzite structures. The surface analysis was performed using X-ray photoelectron spectroscopic studies. The images of SEM reveal that the structure of pure ZnO and Ni doped samples are nanoparticles which intended to form flakes with thickness of few nanometers, being overlain with each one to develop the network with some pores and voids. Based on the ultraviolet-visible (UV-vis) spectroscopy analysis, it indicates that the band gap energy decreases with the increasing concentration of Ni. Furthermore, The Ni doped ZnO samples didn't exhibit higher ultraviolet-light-driven photocatalytic activity compared to the undoped ZnO sample. Vibrating sample magnetometer was used for the magnetic property investigations, and the result indicates that room temperature ferromagnetism property of 3% Ni doped sample is attributed to oxygen vacancy and interaction between doped ions.

  19. Levers for Thermoelectric Properties in Titania-Based Ceramics

    NASA Astrophysics Data System (ADS)

    Backhaus-Ricoult, Monika; Rustad, James R.; Vargheese, Deenamma; Dutta, Indrajit; Work, Kim

    2012-06-01

    While the beneficial impact of nanostructural engineering on thermoelectric performance has been demonstrated for many semiconducting materials (SiGe, skutterudites, PbTe2, etc.), no significant advantages have been reported for oxide nanomaterials. In this study, titania is used as a model material to compare the impact of grain size, doping and substitution, second-phase nanodispersion, and crystallographic defects on the electronic and thermal properties. It is shown that the lattice thermal conductivity can be most efficiently reduced by high densities of crystallographic planar defects in the Magnéli phases, while modification of grain size or introduction of second phases on length scales of 20 nm to 100 nm introduces only minor improvement. For the electronic properties, donor dopants such as niobium provide improvement of the power factor, but are not able to compete with the enhanced carrier concentration that is reached through oxygen vacancy introduction.

  20. Thermoelectric properties of β-Indium sulfide with sulphur deficiencies

    NASA Astrophysics Data System (ADS)

    Chen, Yue Xing; Kitahara, Koichi; Takeuchi, Tsunehiro

    2015-12-01

    We prepared a bulk sample of β-In2S3, which was predicted to possess high thermoelectric performance by ab initio calculations, using pulsed current sintering technique and conventional solid reaction method. The composition of prepared sample was In2S2.94, and the deficient in sulfur led to n-type behaviors of thermoelectric properties. The absolute value of Seebeck coefficient was |S| = 220 μV/K at room temperature, and monotonically increased with temperature up to 600 K then moderately decreased. The thermal conductivity was relatively low (0.68 W m-1 K-1) at 700 K presumably due to the phonon scattering with anharmonic lattice vibrations. The dimensionless figure of merit ZT consequently reached 0.38 at 700 K. We also estimated the value of ZT as a function of carrier concentration, and found that p-type β-In2S3 has potential to possess a large value of ZT exceeding 1.4.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. Low temperature sensing properties of a nano hybrid material based on ZnO nanotetrapods and titanyl phthalocyanine.

    PubMed

    Coppedè, Nicola; Villani, Marco; Mosca, Roberto; Iannotta, Salvatore; Zappettini, Andrea; Calestani, Davide

    2013-03-13

    ZnO nanotetrapods have recently been exploited for the realization of high-sensitivity gas sensors, but they are affected by the typical drawbacks of metal-oxides, i.e., poor selectivity and a relatively high working temperature. On the other hand, it has been also demonstrated that the combined use of nanostructured metal oxides and organic molecules can improve the gas sensing performance sensitivity or selectivity, even at lower temperatures. A gas sensor device, based on films of interconnected ZnO nanotetrapods properly functionalized by titanyl phthalocyanine (TiOPc), has been realized in order to combine the high surface to volume ratio and structural stability of the crystalline ZnO nanostructures with the enhanced sensitivity of the semiconducting TiOPc molecule, especially at low temperature. The electronic properties of the resulting nanohybrid material are different from those of each single component. The response of the hybrid nanostructure towards different gases has been compared with that of ZnO nanotetrapod without functionalization in order to highlight the peculiar properties of the hybrid interaction(s). The dynamic response in time has been studied for different gases and temperatures; in particular, an increase in the response to NO2 has been observed, even at room temperature. The formation of localized p-n heterojunctions and the possibility of exchanging charge carriers at the hybrid interface is shown to be crucial for the sensing mechanism.

  6. Low Temperature Sensing Properties of a Nano Hybrid Material Based on ZnO Nanotetrapods and Titanyl Phthalocyanine

    PubMed Central

    Coppedè, Nicola; Villani, Marco; Mosca, Roberto; Iannotta, Salvatore; Zappettini, Andrea; Calestani, Davide

    2013-01-01

    ZnO nanotetrapods have recently been exploited for the realization of high-sensitivity gas sensors, but they are affected by the typical drawbacks of metal-oxides, i.e., poor selectivity and a relatively high working temperature. On the other hand, it has been also demonstrated that the combined use of nanostructured metal oxides and organic molecules can improve the gas sensing performance sensitivity or selectivity, even at lower temperatures. A gas sensor device, based on films of interconnected ZnO nanotetrapods properly functionalized by titanyl phthalocyanine (TiOPc), has been realized in order to combine the high surface to volume ratio and structural stability of the crystalline ZnO nanostructures with the enhanced sensitivity of the semiconducting TiOPc molecule, especially at low temperature. The electronic properties of the resulting nanohybrid material are different from those of each single component. The response of the hybrid nanostructure towards different gases has been compared with that of ZnO nanotetrapod without functionalization in order to highlight the peculiar properties of the hybrid interaction(s). The dynamic response in time has been studied for different gases and temperatures; in particular, an increase in the response to NO2 has been observed, even at room temperature. The formation of localized p-n heterojunctions and the possibility of exchanging charge carriers at the hybrid interface is shown to be crucial for the sensing mechanism. PMID:23486215

  7. 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.

  8. Unique optical properties of Eu(3+) doped l-histidine hydrochloride mono hydrate single crystals from low temperature growth technique.

    PubMed

    Ramachandra Rao, K; Rajyalakshmi, S; Kamal, Ch Satya; Brahmaji, B; Jasinski, Jacek B; Visweswara Rao, T K

    2017-04-05

    A low-temperature solution method was utilized to grow single crystals of Eu(3+)doped l-histidine hydrochloride monohydrate. The quality of the crystals was confirmed by high-resolution X-ray diffraction measurements with full width at half maximum (FWHM) of rocking curve at 8arc per sec. The incorporation of Eu(3+) ions into the lattice was confirmed by functional group analysis using Fourier Transform Infrared (FTIR) spectroscopy. The amount of Eu(3+) ions was found to be 0.08 weight (%) using energy dispersive X-ray analysis. The crystal's thermal and mechanical properties were tested as well. The unique spectral properties such as UV-Vis transmittance, nonlinear optical efficiency (NLO), photoluminescence (PL) and its lifetime were measured. The PL study revealed that the intensity of (5)D0→(7)F2 emission of Eu(3+) is stronger than that of (5)D0→(7)F1 emission and the decay measurement showed a life time of 7.2410μs. The photoluminescence results prove that l-histidine hydrochloride monohydrate is a new, highly efficient host material for europium ion red emissions.

  9. Unique optical properties of Eu3 + doped L-histidine hydrochloride mono hydrate single crystals from low temperature growth technique

    NASA Astrophysics Data System (ADS)

    Ramachandra Rao, K.; Rajyalakshmi, S.; Kamal, Ch. Satya; Brahmaji, B.; Jasinski, Jacek B.; Visweswara Rao, T. K.

    2017-04-01

    A low-temperature solution method was utilized to grow single crystals of Eu3 + doped L-histidine hydrochloride monohydrate. The quality of the crystals was confirmed by high-resolution X-ray diffraction measurements with full width at half maximum (FWHM) of rocking curve at 8 arc per sec. The incorporation of Eu3 + ions into the lattice was confirmed by functional group analysis using Fourier Transform Infrared (FTIR) spectroscopy. The amount of Eu3 + ions was found to be 0.08 weight (%) using energy dispersive X-ray analysis. The crystal's thermal and mechanical properties were tested as well. The unique spectral properties such as UV-Vis transmittance, nonlinear optical efficiency (NLO), photoluminescence (PL) and its lifetime were measured. The PL study revealed that the intensity of 5D0 → 7F2 emission of Eu3 + is stronger than that of 5D0 → 7F1 emission and the decay measurement showed a life time of 7.2410 μs. The photoluminescence results prove that L-histidine hydrochloride monohydrate is a new, highly efficient host material for europium ion red emissions.

  10. A review on the fabrication of polymer-based thermoelectric materials and fabrication methods.

    PubMed

    Kamarudin, Muhammad Akmal; Sahamir, Shahrir Razey; Datta, Robi Shankar; Long, Bui Duc; Mohd Sabri, Mohd Faizul; Mohd Said, Suhana

    2013-11-12

    Thermoelectricity, by converting heat energy directly into useable electricity, offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts. In recent years, most of the efforts have been done on improving the thermoelectric efficiency using different approaches, that is, nanostructuring, doping, molecular rattling, and nanocomposite formation. The applications of thermoelectric polymers at low temperatures, especially conducting polymers, have shown various advantages such as easy and low cost of fabrication, light weight, and flexibility. In this review, we will focus on exploring new types of polymers and the effects of different structures, concentrations, and molecular weight on thermoelectric properties. Various strategies to improve the performance of thermoelectric materials will be discussed. In addition, a discussion on the fabrication of thermoelectric devices, especially suited to polymers, will also be given. Finally, we provide the challenge and the future of thermoelectric polymers, especially thermoelectric hybrid model.

  11. 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

  12. Cryogenic Thermoelectric Properties of the Bismuth-Magnesium and Bismuth-Antimony-Magnesium Systems

    NASA Astrophysics Data System (ADS)

    Orovets, Christine; Jin, Hyungyu; Wiendlocha, Bartlomiej; Heremans, Joseph P.

    2012-02-01

    There is a need to increase the Figure of Merit of thermoelectric materials used in low temperature cooling applications. Band structure calculations show that substitutional magnesium in bismuth can form sharp density of states peaks, suggesting the presence of a resonant level. Single crystal samples of (Bi1-xSbx)1-yMgy (0 <= x <= 12% and 0 <= y <= 0.7% nominally) were synthesized in evacuated ampoules. The composition of each ingot was analyzed using x-ray diffraction, and transport properties were measured using a Thermal Transport Option (TTO) in a Physical Properties Measurement System (PPMS) from 300K to 2K. It is apparent that the addition of magnesium strongly influences thermopower; the data for Bi90Sb10Mg0.7 shows a second minimum in thermopower at 20K, in addition to the expected minimum at approximately 50-60K. This could be due to the resonant scattering at the cryogenic temperatures which arises from the excess density of states. The addition of magnesium also appears to decrease thermal conductivity below 30K. We present systematic experimental approaches and the results to elucidate the role of magnesium in bismuth and bismuth-antimony systems.

  13. Thermoelectric Properties of NaxCoO2 and Prospects for Other Oxide Thermoelectrics

    SciTech Connect

    Singh, David J; Kasinathan, Deepa

    2007-01-01

    We discuss the thermoelectric properties of Na{sub x}CoO{sub 2} using the electronic structure, as determined in first principles calculations, and Boltzmann kinetic transport theory. The Fermi energy lies near the top of a manifold of Co t 2{sub g} bands. These t 2{sub g} bands are separated by a large gap from the higher-lying e{sub g} states. Although the large crystal-field splitting implies substantial Co-O hybridization, the bands are narrow. Application of standard Boltzmann transport theory to such a narrow band structure yields high thermopowers in accord with experimental observations, even for high metallic carrier densities. The high thermopowers observed for Na{sub x}CoO{sub 2} can therefore be explained by standard band theory and do not rely on low dimensionality or correlation effects specific to Co. We also present results for the cubic spinel structure ZnRh{sub 2}O{sub 4}. Like Na{sub x}CoO{sub 2}, this compound has very narrow valence bands. We find that if it could be doped with mobile carriers, it would also have a high thermopower, comparable with that of Na{sub x}CoO{sub 2}.

  14. 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.

  15. Synthesis and Thermoelectric Properties of Bi2Se3 Nanostructures

    PubMed Central

    2011-01-01

    Bismuth selenide (Bi2Se3) nanostructures were synthesized via solvothermal method. The crystallinity of the as-synthesized sample has been analyzed by X-ray diffraction, which shows the formation of rhombohedral Bi2Se3. Electron microscopy examination indicates that the Bi2Se3 nanoparticles have hexagonal flake-like shape. The effect of the synthesis temperature on the morphology of the Bi2Se3 nanostructures has also been investigated. It is found that the particle size increases with the synthesis temperature. Thermoelectric properties of the Bi2Se3 nanostructures were also measured, and the maximum value of dimensionless figure of merit (ZT) of 0.096 was obtained at 523 K. PMID:27502679

  16. Thermoelectric properties of Fe and Al co-added Ge

    NASA Astrophysics Data System (ADS)

    Sasaki, Takayuki; Kurosaki, Ken; Yusufu, Aikebaier; Ohishi, Yuji; Muta, Hiroaki; Yamanaka, Shinsuke

    2017-04-01

    The polycrystalline bulk samples of Fe and Al co-added Ge were synthesized by melt-spinning followed by spark plasma sintering and the thermoelectric properties were examined. Here, Al acts as a p-type dopant, while Fe is expected to form FeGe2 as precipitates. Since the lattice mismatch between Ge and FeGe2 is small (<4%), they would coherently connect with each other, reducing the thermal conductivity without affecting the electrical transport. In this study, a reduction in thermal conductivity was achieved by dispersing the FeGe2 precipitates in the Al-doped Ge matrix, while they had little influences on both the carrier mobility and the Seebeck coefficient. As the results, the maximum ZT value of 0.13 was obtained at 773 K, which is three times higher than that of single-crystal Ge reported by the authors’ group [Y. Ohishi et al., Jpn. J. Appl. Phys. 55, 051301 (2016)].

  17. Novel Transition Metal Compounds with Promising Thermoelectric Properties

    NASA Technical Reports Server (NTRS)

    Caillat, T.; Borshchevsky, A.; Fleurial, J. -P.

    1993-01-01

    Progress in the search for new high temperature thermoelectric materials at the Jet Propulsion Laboratory is reviewed. Novel transition metal compounds were selected as potential new high performance thermoelectric materials and criteria of selection are presented and discussed. Samples of these new compounds were prepared at JPL by a variety of techniques. Encouraging experimental results obtained on several of these compounds are reported and show that they have the potential to be the next generation of thermoelectric materials.

  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. Thermoelectric properties and oxidation behaviour of Magnesium Silicide

    NASA Astrophysics Data System (ADS)

    Tani, J.; Takahashi, M.; Kido, H.

    2011-05-01

    We study the oxidation behaviour of Mg2Si and the thermoelectric properties of Mg2Si composites. Above 723 K, Mg2Si reacts with O2 in air to yield MgO and Si. Using the Johnson-Mehl-Avrami (JMA) equation, the Avrami exponent (n) is equal to ~0.5, and it depends on the reaction temperature and time; this indicates that the oxidation is controlled by the diffusion-controlled reaction. In order to improve the oxidation-resistance of Mg2Si, β-FeSi2 films were fabricated on sintered Mg2Si samples by RF magnetron-sputtering deposition at RT followed by post-annealing at 873 K in vacuum. The β-FeSi2 layer effectively prevented the diffusion of oxygen at 873 K and improved the oxidation resistance of Mg2Si. The thermoelectric properties of impurity-doped Mg2Si composites fabricated using the reduction method of metal oxide / carbonate / hydroxide additives (Al2O3, Sb2O3, Bi2O3, Li2CO3, CuO, Ag2O, In2O3, La(OH)3, Ga2O3, Na2CO3, and Y2O3) have been characterized. The maximum values of ZT for impurity-doped Mg2Si composites fabricated using the reduction method of Al2O3, Bi2O3, Sb2O3, and La(OH)3 additives show 0.58 at 862 K, 0.68 at 864 K, 0.63 at 863 K, and 0.06 at 865 K, respectively.

  20. Synthesis and Mechanical and Electrical Properties of Carbon Nanotubes Grown at Low Temperatures by Thermal Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Wang, Yunyu; Shi, Li; Yao, Zhen; Ho, Paul

    2006-03-01

    Carbon nanotubes (CNTs) have shown great potentials in versatile applications such as electron sources, heat interface materials and drug delivery vehicles due to their unique aspect ratio, thermal conductivity, and biocompatibility. CNTs have also attracted wide interests in applications for the next generation microelectronics, including interconnects, mainly due to its high current carrying capacity, i.e. >10^9 A/cm^2. However, CNTs have been commonly synthesized under high temperatures, e.g. > 1000 ^oC for laser ablation and arc discharge and 600-900 ^oC for chemical vapor deposition (CVD), which is not compatible with the < 450 ^oC requirement for microelectronic technology, and makes it difficult to integrate CNTs into integrated circuit chips. In this study, we present a controlled growth of CNTs at 450 ^oC using a simple thermal CVD method. It has been shown that a combination of catalyst choice and preheating precursors is critical for the formation of CNTs at low temperatures. As-grown CNTs have been characterized using scanning electron microscopy, where vertically aligned dense short nanotubes films with lengths of ˜ 400 nm have been observed. For applications in microelectronics, mechanical and electrical properties of short CNT films are tested and the results will be discussed. .

  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. 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.

  3. Electronic, optical, mechanical and thermoelectric properties of graphene

    NASA Astrophysics Data System (ADS)

    Muley, Sarang Vilas

    prompted the study of thermoelectric (TE) effects in graphene based systems. TE devices are finding applications in power generation and solid state refrigeration. This study involves analyzing the electronic, thermal and electrical transport properties of these systems. Electronic thermal conductivity, of graphene based systems (kappae), is found to be negligible as compared to its phonon-induced lattice thermal conduction (kappa p). Variations in kappap of graphene and GNRs are evaluated as a function of their width and length of their edges, chiralities, temperature, and number of layers. The interdependence of transport parameters, i.e., electrical conductivity (sigma), thermoelectric power (TEP) or Seebeck coefficient (S), and kappa of graphene are discussed. The thermoelectric performance of these materials is determined mainly by a parameter called Figure-of-Merit. Effective methods to optimize the value of Figure-of-Merit are explored. Reducing the thermal conductivity and increasing the power factor of these systems are found to improve the Figure-of-Merit significantly. This involves correlation of structure and transport properties. Effects of doping on sigma, kappa and Hall coefficient are discussed.

  4. Thermoelectric Materials for Low Temperature Cooling

    DTIC Science & Technology

    2009-10-02

    Grauer , Y. S. Hor and R. J. Cava, Mat. Res. Bull. 44 1926 (2009). 4. Accomplishments/New Findings: Bi-Sb The elements Bi and Sb form a...students Christopher Holmes-Parker, David Grauer and Clifford Engle summer research.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  6. 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.

  7. 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.

  8. 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.

  9. Thermoelectric plastics: from design to synthesis, processing and structure–property relationships

    PubMed Central

    Kroon, Renee; Mengistie, Desalegn Alemu; Kiefer, David; Hynynen, Jonna; Ryan, Jason D.; Yu, Liyang

    2016-01-01

    Thermoelectric plastics are a class of polymer-based materials that combine the ability to directly convert heat to electricity, and vice versa, with ease of processing. Potential applications include waste heat recovery, spot cooling and miniature power sources for autonomous electronics. Recent progress has led to surging interest in organic thermoelectrics. This tutorial review discusses the current trends in the field with regard to the four main building blocks of thermoelectric plastics: (1) organic semiconductors and in particular conjugated polymers, (2) dopants and counterions, (3) insulating polymers, and (4) conductive fillers. The design and synthesis of conjugated polymers that promise to show good thermoelectric properties are explored, followed by an overview of relevant structure–property relationships. Doping of conjugated polymers is discussed and its interplay with processing as well as structure formation is elucidated. The use of insulating polymers as binders or matrices is proposed, which permit the adjustment of the rheological and mechanical properties of a thermoelectric plastic. Then, nanocomposites of conductive fillers such as carbon nanotubes, graphene and inorganic nanowires in a polymer matrix are introduced. A case study examines poly(3,4-ethylenedioxythiophene) (PEDOT) based materials, which up to now have shown the most promising thermoelectric performance. Finally, a discussion of the advantages provided by bulk architectures e.g. for wearable applications highlights the unique advantages that thermoelectric plastics promise to offer. PMID:27385496

  10. Thermoelectric plastics: from design to synthesis, processing and structure-property relationships.

    PubMed

    Kroon, Renee; Mengistie, Desalegn Alemu; Kiefer, David; Hynynen, Jonna; Ryan, Jason D; Yu, Liyang; Müller, Christian

    2016-11-07

    Thermoelectric plastics are a class of polymer-based materials that combine the ability to directly convert heat to electricity, and vice versa, with ease of processing. Potential applications include waste heat recovery, spot cooling and miniature power sources for autonomous electronics. Recent progress has led to surging interest in organic thermoelectrics. This tutorial review discusses the current trends in the field with regard to the four main building blocks of thermoelectric plastics: (1) organic semiconductors and in particular conjugated polymers, (2) dopants and counterions, (3) insulating polymers, and (4) conductive fillers. The design and synthesis of conjugated polymers that promise to show good thermoelectric properties are explored, followed by an overview of relevant structure-property relationships. Doping of conjugated polymers is discussed and its interplay with processing as well as structure formation is elucidated. The use of insulating polymers as binders or matrices is proposed, which permit the adjustment of the rheological and mechanical properties of a thermoelectric plastic. Then, nanocomposites of conductive fillers such as carbon nanotubes, graphene and inorganic nanowires in a polymer matrix are introduced. A case study examines poly(3,4-ethylenedioxythiophene) (PEDOT) based materials, which up to now have shown the most promising thermoelectric performance. Finally, a discussion of the advantages provided by bulk architectures e.g. for wearable applications highlights the unique advantages that thermoelectric plastics promise to offer.

  11. 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.

  12. 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.

  13. The low temperature specific heat and electrical transport, magnetic properties of Pr0.65Ca0.35MnO3

    NASA Astrophysics Data System (ADS)

    Han, Zhiyong

    2017-02-01

    The magnetic properties, electrical transport properties, and low temperature specific heat of polycrystalline perovskite manganese oxide Pr0.65Ca0.35MnO3 have been investigated experimentally. It is found that there exists cluster glass state in the sample at low temperature besides the antiferromagnetic insulating state. With the increase of magnetic field, antiferromagnetic insulating state converts to ferromagnetic metal state and the Debye temperature decreases gradually. In addition, the low temperature electron specific heat in zero magnetic field is obviously larger than that of ordinary rare-earth manganites oxide and this phenomenon is related to the itinerant electrons in ferromagnetic cluster state and the disorder in Pr0.65Ca0.35MnO3.

  14. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    SciTech Connect

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

    2016-04-04

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

  15. Tailored semiconducting carbon nanotube networks with enhanced thermoelectric properties

    DOE PAGES

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

    2016-04-04

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

  16. 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.

  17. Thermal and Thermoelectric Properties of Nanostructured Materials and Interfaces

    NASA Astrophysics Data System (ADS)

    Liao, Hao-Hsiang

    Many modern technologies are enabled by the use of thin films and/or nanostructured composite materials. For example, many thermoelectric devices, solar cells, power electronics, thermal barrier coatings, and hard disk drives contain nanostructured materials where the thermal conductivity of the material is a critical parameter for the device performance. At the nanoscale, the mean free path and wavelength of heat carriers may become comparable to or smaller than the size of a nanostructured material and/or device. For nanostructured materials made from semiconductors and insulators, the additional phonon scattering mechanisms associated with the high density of interfaces and boundaries introduces additional resistances that can significantly change the thermal conductivity of the material as compared to a macroscale counterpart. Thus, better understanding and control of nanoscale heat conduction in solids is important scientifically and for the engineering applications mentioned above. In this dissertation, I discuss my work in two areas dealing with nanoscale thermal transport: (1) I describe my development and advancement of important thermal characterization tools for measurements of thermal and thermoelectric properties of a variety of materials from thin films to nanostructured bulk systems, and (2) I discuss my measurements on several materials systems done with these characterization tools. First, I describe the development, assembly, and modification of a time-domain thermoreflectance (TDTR) system that we use to measure the thermal conductivity and the interface thermal conductance of a variety of samples including nanocrystalline alloys of Ni-Fe and Co-P, bulk metallic glasses, and other thin films. Next, a unique thermoelectric measurement system was designed and assembled for measurements of electrical resistivity and thermopower of thermoelectric materials in the temperature range of 20 to 350 °C. Finally, a commercial Anter Flashline 3000 thermal

  18. 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.

  19. 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.

  20. Thermoelectric properties of SbNCa3 and BiNCa3 for thermoelectric devices and alternative energy applications

    NASA Astrophysics Data System (ADS)

    Bilal, M.; Khan, Banaras; Rahnamaye Aliabad, H. A.; Maqbool, M.; Jalai Asadabadi, S.; Ahmad, I.

    2014-05-01

    Thermoelectric properties of two antiperovskites SbNCa3 and BiNCa3 are calculated using first principles calculations. High values of Seebeck coefficients are observed for these materials. Electrical and thermal conductivities are also calculated. Increase in thermal conductivity and decrease in electrical conductivity are found with increasing temperature. The maximum values of thermal conductivity are 92×1014 W/m K s and 88×1014 W/m K s for SbNCa3 and BiNCa3 respectively at a temperature of 900 K. The peak values of 5×1020/Ω m s and 5.2×1020/Ω m s are achieved for n-type SbNCa3 and BiNCa3 respectively at a temperature of 300 K. Figure of merit is achieved for these materials at room temperature which shows that these materials can be useful for thermoelectric devices and alternative energy sources.

  1. Seebeck Enhancement Through Miniband Conduction in III-V Semiconductor Superlattices at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Bahk, Je-Hyeong; Sadeghian, Ramin Banan; Bian, Zhixi; Shakouri, Ali

    2012-06-01

    We present theoretically that the cross-plane Seebeck coefficient of InGaAs/InGaAlAs III-V semiconductor superlattices can be significantly enhanced through miniband transport at low temperatures. The miniband dispersion curves are calculated by self-consistently solving the Schrödinger equation with the periodic potential, and the Poisson equation taking into account the charge transfer between the two layers. Boltzmann transport in the relaxation-time approximation is used to calculate the thermoelectric transport properties in the cross-plane direction based on the modified density of states and group velocity. It is found that the cross-plane Seebeck coefficient can be enhanced more than 60% over the bulk values at an equivalent doping level at 80 K when the Fermi level is aligned at an edge of the minibands. Other thermoelectric transport properties are also calculated and discussed to further enhance the thermoelectric power factor.

  2. The effect of electron-phonon interaction on the thermoelectric properties of defect zigzag nanoribbons

    NASA Astrophysics Data System (ADS)

    Kolesnikov, D. V.; Lobanov, D. A.; Osipov, V. A.

    2016-12-01

    Thermoelectric properties of graphene nanoribbons with periodic edge vacancies and antidot lattice are investigated. The electron-phonon interaction is taken into account in the framework of the Hubbard-Holstein model with the use of the Lang-Firsov unitary transformation scheme. The electron transmission function, the thermopower and the thermoelectric figure of merit are calculated. We have found that the electron-phonon interaction causes a decrease in the peak values of the thermoelectric figure of merit and the shift of the peak positions closer to the center of the bandgap. The effects are more pronounced for the secondary peaks that appear in the structures with periodic antidot.

  3. Friction properties of PTFE, h-BN and Al-4%Cu alloy in a vacuum at super low temperature

    NASA Astrophysics Data System (ADS)

    Yokoi, Koichi; Okada, Katsuzo

    Friction with ploughing components at super low temperature ina vacuum was studied on the soft plates of PTFE, h-BN and Al-4%Cu alloy sliding with the hard pins of 18-8 stainless steel with a pin-on-plate friction tester. The chief finding was that the friction was affected by low temperature ; for all the same load, friction forces of both of PTFE and h-BN were 16K > 300K, that of Al-4%Cu alloy was 16K <300K.

  4. 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.

  5. 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.

  6. Enhanced Thermoelectric Properties of Cu2ZnSnSe4 with Ga-doping

    DOE PAGES

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

    2015-08-10

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

  7. 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.

  8. Study of the Spectral Properties of Nanocomposites with CdSe Quantum Dots in a Wide Range of Low Temperatures

    NASA Astrophysics Data System (ADS)

    Magaryan, K. A.; Eremchev, I. Y.; Karimullin, K. R.; Knyazev, M. V.; Mikhailov, M. A.; Vasilieva, I. A.; Klimusheva, G. V.

    2015-09-01

    Luminescence spectra of the colloidal solution of CdSe quantum dots (in toluene) were studied in a wide range of low temperatures. Samples were synthesized in the liquid crystal matrix of cadmium octanoate (CdC8). A comparative analysis of the obtained data with previous results was performed.

  9. Evaluation of Thermoelectric Properties of Bite Alloys for the Optimization of Gas-Cooled Peltier Current Lead

    NASA Astrophysics Data System (ADS)

    Fujii, T.; Fukuda, S.; Kawahara, T.; Emoto, M.; Sugino, M.; Sun, J.; Hamabe, M.; Watanabe, H.; Yamaguchi, S.

    2010-04-01

    A direct current superconducting power transmission (DC-SCPT) test facility with 20-meter power cable has been developed in Chubu University. Heat leakage through current leads dominates in case of short-distance DC-SCPT. To solve this problem, we have developed special Peltier current lead (PCL) with bismuth telluride (BiTe) alloy is used as a Peltier material, and have studied a gas-cooled PCL as a novel type current lead for higher reduction of the heat leakage. In order to achieve high efficiency, highest thermoelectric figure of merit material is important to be used especially at low temperature conditions. In our work we measured the thermoelectric properties of BiTe samples, and optimized geometry of PCL by the numerical calculations. It was fount that the heat leakages through PCL and gas-cooled PCL are reduced to 55% and to 36% of the conventional copper current lead (CCL) at the self-cooling condition, correspondingly. PCL can reduce the total electric power consumption of the whole system. We also discuss the heat exchange ratio for the gas-cooled PCL, and extend this approach for further reduction of the heat leakage.

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

    PubMed

    Wierzbicki, Michał; Barnaś, Józef; Swirkowicz, Renata

    2015-12-09

    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.

  11. 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.

  12. The Features of Microstructure and Mechanical Properties of Metastable Austenitic Steel Subjected to Low-Temperature and Subsequent Warm Deformation

    NASA Astrophysics Data System (ADS)

    Litovchenko, I. Yu.; Akkuzin, S. A.; Polekhina, N. A.; Tyumentsev, A. N.; Naiden, E. P.

    2016-10-01

    The features of microstructure and phase composition of metastable austenitic steel subjected to thermomechanical treatment, including low-temperature processing accompanied by warm rolling deformation, are investigated. Direct (γ → α΄) and reverse strain-induced martensitic transformations are shown to take place, followed by the formation of submicrocrystalline states and 3-4-fold increase in the yield point values. The mechanisms of formation of submicrocrystalline states and the reasons for increased strength are discussed.

  13. 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.

  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. The effect of Coulomb interactions on thermoelectric properties of quantum dots

    NASA Astrophysics Data System (ADS)

    Zimbovskaya, Natalya; Kuzmin, Valery

    2014-03-01

    Thermoelectric effects in a quantum dot coupled to the source and drain charge reservoirs are explored using a nonequilibrium Green's functions formalism beyond the Hartree-Fock approxomation. We concentrate on theoretical analysis of the influence of Coulomb interactions on thermopower and the figure of merit ZT . Obtained results show that Coulomb interactions between charge carriers on the dot significantly contribute to its thermoelectric properties. In the present work, we trace the transition from the Coulomb blockade regime to Kondo regime in the thermoelectric properties of the quantum dot which occurs when we gradually strengthen the coupling of the dot to the charge reservoirs. We show that within the Coulomb blockade regime (when the coupling of the dot to the leads is weak compared to the characteristic strength of the charge carriers interactions) thermoelectric characteristics of the dot display distinct features caused by Coulomb interactions. These features indicate possibilities of enhancement of thermoelectric efficiency of the considered systems. Within the Kondo regime, when the couplings of the dot to the leads became stronger, the influence of Coulomb interactions declines bringing a decrease in the the thermoelectric efficiency.

  17. 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.

  18. Experimental Platform for Studying Thermoelectric Properties in Vacuum Gaps and Molecular Junctions

    NASA Astrophysics Data System (ADS)

    Jeong, Wonho; Kim, Youngsang; Kim, Kyeongtae; Lee, Woochul; Reddy, Pramod

    2014-03-01

    Electromigrated break junction (EBJ) based molecular devices have enabled many research groups to study nanoscale charge transport. Although EBJ devices have been extensively used due to the advantages of a three terminal configuration in tuning the electronic structure, it has not been possible to use them to study thermoelectric properties. This is because creating temperature differentials across the nanogap of EBJs is technically challenging. In order to overcome this experimental limitation, we carefully designed and created a new experimental platform (EBJIH, EBJ with integrated heater) that enables us to study thermoelectric properties in vacuum gaps and molecular junctions. To prove that temperature differentials can be established in these three terminal devices, we performed nanometer resolution thermal imaging using scanning thermal microscopy under UHV conditions. The results clearly show that temperature differentials can indeed be established in the devices. Further, we have used these devices to study the thermoelectric properties of vacuum gaps between gold electrodes and found that the thermoelectric properties were very sensitive to gap dimensions. We are also currently adopting this platform to study thermoelectric properties in molecular junctions.

  19. Thermoelectric properties of n-type polycrystalline BixSb2-xTe3 alloys

    NASA Technical Reports Server (NTRS)

    Snyder, J.; Gerovac, N.; Caillat, T.

    2002-01-01

    (BixSbl-x)2Te3(.5 = x = .7) polycrystalline samples were synthesized using a combination of melting and powder metallurgy techniques. The samples were hot pressed in graphite dies and cut perpendicular and parallel to the pressing direction. Samples were examined by microprobe analysis to determine their atomic composition. The thermoelectric properties were measured at room temperature in both directions. These properties include Seebeck coefficient, thermal conductivity, electrical resistivity, and Hall effect. The thermoelectric figure-of-merit, ZT, was calculated fiom these properties.

  20. 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$^{-3}$.

  1. Resonance electromagnetoacoustic method of measuring viscoelastic properties of amorphous ferromagnetic ribbons subjected to low-temperature annealing

    NASA Astrophysics Data System (ADS)

    Len'kov, S. V.; Fedorova, N. V.

    2014-08-01

    Stationary and damped vibrations of the s 0 Lamb mode in a viscoelastic amorphous ferromagnetic ribbon excited upon the electromagnetoacoustic (EMA) transformation have been considered. A resonance method is suggested that employs double EMA transformation for measuring elasticity moduli E and internal friction in amorphous ferromagnetic ribbons. The effect of low-temperature isochronous annealing on the field dependences of Young's modulus and internal friction of the Fe80Si10B10 and Fe73.7Cu1.0Nb3.2Si12.7B9.4 alloys has been studied.

  2. 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

  3. Effect of Initial Bulk Material Composition on Thermoelectric Properties of Bi2Te3 Thin Films

    NASA Astrophysics Data System (ADS)

    Budnik, A. V.; Rogacheva, E. I.; Pinegin, V. I.; Sipatov, A. Yu.; Fedorov, A. G.

    2013-07-01

    V2VI3 compounds and solid solutions based on them are known to be the best low-temperature thermoelectric (TE) materials. The predicted possibility of enhancement of the TE figure of merit in two-dimensional (2D) structures has stimulated studies of the properties of these materials in the thin-film state. The goal of the present work is to study the dependences of the Seebeck coefficient S, electrical conductivity σ, Hall coefficient R H, charge carrier mobility μ H, and TE power factor P = S 2 σ of Bi2Te3 thin films on the composition of the initial bulk material used for preparing them. Thin films with thickness d = 200 nm to 250 nm were grown by thermal evaporation in vacuum of stoichiometric Bi2Te3 crystals (60.0 at.% Te) and of crystals with 62.8 at.% Te onto glass substrates at temperatures T S of 320 K to 500 K. It was established that the conductivity type of the initial material is reproduced in films fairly well. For both materials, an increase in T S leads to an increase in the thin-film structural perfection, better correspondence between the film composition and that of the initial material, and increase in S, R H, μ H, σ, and P. The room-temperature maximum values of P for the films grown from crystals with 60.0 at.% and 62.8 at.% Te are P = 7.5 × 10-4 W/K2 m and 35 × 10-4 W/K2 m, respectively. Thus, by using Bi2Te3 crystals with different stoichiometry as initial materials, one can control the conductivity type and TE parameters of the films, applying a simple and low-cost method of thermal evaporation from a single source.

  4. Thermoelectric and mechanical properties of gapless Zr2MnAl compound

    NASA Astrophysics Data System (ADS)

    Yousuf, Saleem; Gupta, Dinesh C.

    2017-01-01

    We present the study of elastic and magnetic properties of Zr2MnAl full-Heusler alloys within the first-principles density functional theory. The lattice constant, magnetic moment, bulk modulus and density of states are calculated using the full potential linearized augmented plane wave method in the generalized gradient approximation scheme. The thermoelectric properties are studied between the temperature range of 50-800 K. Seebeck coefficient (S) measurements indicate the material as n-type with large S value of -83.06 μV/K at 400 K. The material shows higher efficiency for thermoelectric use with figure of merit equal to 0.92 at 400 K relatively higher in comparison for the other full Heusler compounds in these temperature ranges. The behaviour of gapless character is mainly responsible for the anomalous transport properties of the material required for the thermoelectric applications.

  5. Thermoelectric Properties of Indium and Gallium Dually Doped ZnO Thin Films.

    PubMed

    Tran Nguyen, Nhat Hong; Nguyen, Truong Huu; Liu, Yi-Ren; Aminzare, Masoud; Pham, Anh Tuan Thanh; Cho, Sunglae; Wong, Deniz P; Chen, Kuei-Hsien; Seetawan, Tosawat; Pham, Ngoc Kim; Ta, Hanh Kieu Thi; Tran, Vinh Cao; Phan, Thang Bach

    2016-12-14

    We investigated the effect of single and multidopants on the thermoelectrical properties of host ZnO films. Incorporation of the single dopant Ga in the ZnO films improved the conductivity and mobility but lowered the Seebeck coefficient. Dual Ga- and In-doped ZnO thin films show slightly decreased electrical conductivity but improved Seebeck coefficient. The variation of thermoelectric properties is discussed in terms of film crystallinity, which is subject to the dopants' radius. Small amounts of In dopants with a large radius may introduce localized regions in the host film, affecting the thermoelectric properties. Consequently, a 1.5 times increase in power factor, three times reduction in thermal conductivity, and 5-fold enhancement in the figure of merit ZT have been achieved at 110 °C. The results also indicate that the balanced control of both electron and lattice thermal conductivities through dopant selection are necessary to attain low total thermal conductivity.

  6. 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.

  7. 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.

  8. Role of the spin magnitude of the magnetic ion in determining the frustration and low-temperature properties of kagome lattices.

    PubMed

    Pati, Swapan K; Rao, C N R

    2005-12-15

    In view of the variety of low-temperature magnetic properties reported recently for kagome lattices with transition-metal ions in different oxidation states, we have investigated the low-energy spectrum and low-temperature thermodynamic properties of antiferromagnetic kagome lattices with varying magnitudes of site spins, employing quantum many-body Heisenberg models. The ground state and the low-lying excitation spectrum are found to depend strongly on the nature of the spin magnitude of the magnetic ions. The system remains highly frustrated if spins are half-odd-integer in magnitude, while the frustration is very weak or almost absent for integer spins or mixed-spin systems. In fact, for a mixed-spin kagome system with a certain magnitude, the whole system behaves as a classical magnet with a ferrimagnetic ground state without any frustration. These theoretical findings are consistent with a few experimental observations recently reported in the literature and would be of value in designing new kagome systems with unusual and interesting low-temperature magnetic properties.

  9. Preparation and Thermoelectric Properties of Semiconcucting Zn(sub 4) Sb(sub 3)

    NASA Technical Reports Server (NTRS)

    Caillat, T.; Fleurial, J. P.; Barshchevsky, A.

    1996-01-01

    Hot-pressed samples fothe semiconducting compound Beta - Zn(sub 4) Sb(sub 3) were prepared and characterized by x-ray and microprobe analysis. Some physical properties of Beta - Zn(sub 4) Sb(sub 3) were determined and its thermoelectric properties measured between room temperature and 650K.

  10. Effect of interfacial properties on polymer-nanocrystal thermoelectric transport.

    PubMed

    Coates, Nelson E; Yee, Shannon K; McCulloch, Bryan; See, Kevin C; Majumdar, Arun; Segalman, Rachel A; Urban, Jeffrey J

    2013-03-20

    The electrical behavior of a conducting-polymer/inorganic-nanowire composite is explained with a model in which carrier transport occurs predominantly through a highly conductive volume of polymer that exists at the polymer-nanowire interface. This result highlights the importance of controlling nanoscale interfaces for thermoelectric materials, and provides a general route for improving carrier transport in organic/inorganic composites.

  11. Chemical Precipitation Synthesis and Thermoelectric Properties of Copper Sulfide

    NASA Astrophysics Data System (ADS)

    Wu, Sixin; Jiang, Jing; Liang, Yinglin; Yang, Ping; Niu, Yi; Chen, Yide; Xia, Junfeng; Wang, Chao

    2017-04-01

    Earth-abundant copper sulfide compounds have been intensively studied as potential thermoelectric materials due to their high dimensionless figure of merit ZT values. They have a unique phonon-liquid electron-crystal model that helps to achieve high thermoelectric performance. Many methods, such as melting and ball-milling, have been adopted to synthesize this copper sulfide compound, but they both use expensive starting materials with high purity. Here, we develop a simple chemical precipitation approach to synthesize copper sulfide materials through low-cost analytically pure compounds as the starting materials. A high ZT value of 0.93 at 800 K was obtained from the samples annealed at 1273 K. Its power factor is around 8.0 μW cm-1 K-2 that is comparable to the highest record reported by traditional methods. But, the synthesis here has been greatly simplified with reduced cost, which will be of great benefit to the potential mass production of thermoelectric devices. Furthermore, this method can be applied to the synthesis of other sulfur compound thermoelectric materials.

  12. Thermoelectric properties of orthorhombic group IV-VI monolayers from the first-principles calculations

    NASA Astrophysics Data System (ADS)

    Guo, San-Dong; Wang, Yue-Hua

    2017-01-01

    Two-dimensional (2D) materials may have potential applications in thermoelectric devices. In this work, the thermoelectric properties of orthorhombic group IV-VI monolayers AB (A = Ge and Sn; B = S and Se) are systematically investigated by the first-principles calculations and semiclassical Boltzmann transport theory. The spin-orbit coupling (SOC) is considered for their electron part, which produces observable effects on the power factor, especially for n-type doping. According to the calculated ZT, the four monolayers exhibit diverse anisotropic thermoelectric properties although they have a similar hinge-like crystal structure. The GeS along zigzag and armchair directions shows the strongest anisotropy, while SnS and SnSe show mostly isotropic efficiency of thermoelectric conversion. This can be explained by the strength of anisotropy of their respective power factor and electronic and lattice thermal conductivities. The calculated results show that the ZT between n- and p-type doping has little difference for GeS, SnS, and SnSe. It is found that GeSe, SnS, and SnSe show better thermoelectric performance compared to GeS in n-type doping and that SnS and SnSe exhibit higher efficiency of thermoelectric conversion in p-type doping. Compared to other many 2D materials, orthorhombic group IV-VI monolayers AB (A = Ge and Sn; B = S and Se) may possess better thermoelectric performance due to lower lattice thermal conductivities. Our work would be beneficial to stimulate further theoretical and experimental works.

  13. 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).

  14. 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.

  15. Nitrogen-doped tungsten oxide nanowires: low-temperature synthesis on Si, and electrical, optical, and field-emission properties.

    PubMed

    Chang, Mu-Tung; Chou, Li-Jen; Chueh, Yu-Lun; Lee, Yu-Chen; Hsieh, Chin-Hua; Chen, Chii-Dong; Lan, Yann-Wen; Chen, Lih-Juann

    2007-04-01

    Very dense and uniformly distributed nitrogen-doped tungsten oxide (WO(3)) nanowires were synthesized successfully on a 4-inch Si(100) wafer at low temperature. The nanowires were of lengths extending up to 5 mum and diameters ranging from 25 to 35 nm. The highest aspect ratio was estimated to be about 200. An emission peak at 470 nm was found by photoluminescence measurement at room temperature. The suggested growth mechanism of the nanowires is vapor-solid growth, in which gaseous ammonia plays a significant role to reduce the formation temperature. The approach has proved to be a reliable way to produce nitrogen-doped WO(3) nanowires on Si in large quantities. The direct fabrication of WO(3)-based nanodevices on Si has been demonstrated.

  16. 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

  17. Nanostructuring and thermoelectric properties of bulk skutterudite compound CoSb{sub 3}

    SciTech Connect

    Mi, J. L.; Zhu, T. J.; Zhao, X. B.; Ma, J.

    2007-03-01

    Thermoelectric properties of nanostructured skutterudite CoSb{sub 3} have been reported. Nanosized CoSb{sub 3} powders were synthesized through a solvothermal route. The bulk materials with average grain sizes of 250 and 150 nm were prepared by hot pressing and spark plasma sintering from the solvothermally synthesized CoSb{sub 3} powders. Both the samples show n-type conduction and the thermal conductivities are reduced compared with that of the sample prepared by the melt-annealing/hot pressing method. A thermoelectric figure of merit of 0.61 has been obtained for the unfilled CoSb{sub 3} skutterudite by spark plasma sintering, which indicates that nanostructuring is an effective way to improve the thermoelectric properties of skutterudite compounds.

  18. Four-probe measurements of the in-plane thermoelectric properties of nanofilms

    SciTech Connect

    Mavrokefalos, Anastassios; Pettes, Michael T.; Zhou Feng; Shi Li

    2007-03-15

    Measuring in-plane thermoelectric properties of submicron thin films has remained a challenging task. Here we report a method based on a suspended microdevice for four-probe measurements of the Seebeck coefficient, thermal conductivity, electrical conductivity, and thermoelectric figure of merit of patterned indium arsenide (InAs) nanofilms assembled on the microdevice. The contact thermal resistance and intrinsic thermal resistance of the 40 nm thick InAs nanofilm sample were measured by using the nanofilm itself as a differential thermocouple to determine the temperature drops at the contacts. The microdevice was also used to measure a 190 nm thick silicon dioxide (SiO{sub 2}) film and the results were compared with those reported in the literature. A through-substrate hole under the suspended microdevice allows for transmission electron microscopy characterization of the nanofilm sample assembled on the device. This capability enables one to correlate the measured thermoelectric properties with the crystal structures of the nanofilm.

  19. Four-probe measurements of the in-plane thermoelectric properties of nanofilms.

    PubMed

    Mavrokefalos, Anastassios; Pettes, Michael T; Zhou, Feng; Shi, Li

    2007-03-01

    Measuring in-plane thermoelectric properties of submicron thin films has remained a challenging task. Here we report a method based on a suspended microdevice for four-probe measurements of the Seebeck coefficient, thermal conductivity, electrical conductivity, and thermoelectric figure of merit of patterned indium arsenide (InAs) nanofilms assembled on the microdevice. The contact thermal resistance and intrinsic thermal resistance of the 40 nm thick InAs nanofilm sample were measured by using the nanofilm itself as a differential thermocouple to determine the temperature drops at the contacts. The microdevice was also used to measure a 190 nm thick silicon dioxide (SiO(2)) film and the results were compared with those reported in the literature. A through-substrate hole under the suspended microdevice allows for transmission electron microscopy characterization of the nanofilm sample assembled on the device. This capability enables one to correlate the measured thermoelectric properties with the crystal structures of the nanofilm.

  20. Four-probe measurements of the in-plane thermoelectric properties of nanofilms

    NASA Astrophysics Data System (ADS)

    Mavrokefalos, Anastassios; Pettes, Michael T.; Zhou, Feng; Shi, Li

    2007-03-01

    Measuring in-plane thermoelectric properties of submicron thin films has remained a challenging task. Here we report a method based on a suspended microdevice for four-probe measurements of the Seebeck coefficient, thermal conductivity, electrical conductivity, and thermoelectric figure of merit of patterned indium arsenide (InAs) nanofilms assembled on the microdevice. The contact thermal resistance and intrinsic thermal resistance of the 40nm thick InAs nanofilm sample were measured by using the nanofilm itself as a differential thermocouple to determine the temperature drops at the contacts. The microdevice was also used to measure a 190nm thick silicon dioxide (SiO2) film and the results were compared with those reported in the literature. A through-substrate hole under the suspended microdevice allows for transmission electron microscopy characterization of the nanofilm sample assembled on the device. This capability enables one to correlate the measured thermoelectric properties with the crystal structures of the nanofilm.

  1. 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).

  2. Thermoelectric transport properties through a T-shaped single quantum dot

    NASA Astrophysics Data System (ADS)

    Castellanos, R.; Franco, R.; Silva-Valencia, J.; Figueira, M. S.

    2010-12-01

    We study the thermopower, thermal conductance, electric conductance and the thermoelectric figure of merit for a gate-defined T-shaped single quantum dot (QD). The QD is solved in the limit of strong Coulombian repulsion U→∞, inside the dot, and the quantum wire is modeled on a tight-binding linear chain. We employ the X-boson approach for the Anderson impurity model to describe the localized level within the quantum dot. Our results are in qualitative agreement with recent experimental reports and other theoretical researches for the case of a quantum dot embedded into a conduction channel, employing analogies between the two systems. The results for the thermopower sign as a function of the gate voltage (associated with the quantum dot energy) are in agreement with a recent experimental result obtained for a suspended quantum dot. The thermoelectric figure of merit times temperature results indicates that, at low temperatures and in the crossover between the intermediate valence and Kondo regimes, the system might have practical applicability in the development of thermoelectric devices.

  3. Thermoelectric property enhancement by Cu nanoparticles in nanostructured FeSb2

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  4. Electronic, Vibrational and Thermoelectric Properties of Two-Dimensional Materials

    NASA Astrophysics Data System (ADS)

    Wickramaratne, Darshana

    The discovery of graphene's unique electronic and thermal properties has motivated the search for new two-dimensional materials. Examples of these materials include the layered two-dimensional transition metal dichalcogenides (TMDC) and metal mono-chalcogenides. The properties of the TMDCs (eg. MoS 2, WS2, TaS2, TaSe2) and the metal mono-chalcogenides (eg. GaSe, InSe, SnS) are diverse - ranging from semiconducting, semi-metallic and metallic. Many of these materials exhibit strongly correlated phenomena and exotic collective states such as exciton condensates, charge density waves, Lifshitz transitions and superconductivity. These properties change as the film thickness is reduced down to a few monolayers. We use first-principles simulations to discuss changes in the electronic and the vibrational properties of these materials as the film thickness evolves from a single atomic monolayer to the bulk limit. In the semiconducting TMDCs (MoS2, MoSe2, WS2 and WSe2) and monochalcogenides (GaS, GaSe, InS and InSe) we show confining these materials to their monolayer limit introduces large band degeneracies or non-parabolic features in the electronic structure. These changes in the electronic structure results in increases in the density of states and the number of conducting modes. Our first-principles simulations combined with a Landauer approach show these changes can lead to large enhancements up to an order of magnitude in the thermoelectric performance of these materials when compared to their bulk structure. Few monolayers of the TMDCs can be misoriented with respect to each other due to the weak van-der-Waals (vdW) force at the interface of two monolayers. Misorientation of the bilayer semiconducting TMDCs increases the interlayer van-der-Waals gap distance, reduces the interlayer coupling and leads to an increase in the magnitude of the indirect bandgap by up to 100 meV compared to the registered bilayer. In the semi-metallic and metallic TMDC compounds (TiSe2, Ta

  5. 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

  6. Ab initio study of thermoelectric properties of doped SnO{sub 2} superlattices

    SciTech Connect

    Borges, P.D.; Silva, D.E.S.; Castro, N.S.; Ferreira, C.R.; Pinto, F.G.; Tronto, J.; Scolfaro, L.

    2015-11-15

    Transparent conductive oxides, such as tin dioxide (SnO{sub 2}), 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 SnO{sub 2}, as well as of Sb and Zn planar (or delta)-doped layers in SnO{sub 2} 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 SnO{sub 2} SLs for enhanced S and ZT, which emerge as potential candidates for thermoelectric applications. - Graphical abstract: Band structure and Figure of merit for SnO2:Sb superlattice along Z direction, P. D. Borges, D. E. S. Silva, N. S. Castro, C. R. Ferreira, F. G. Pinto, J. Tronto and L. Scolfaro, Ab initio study of thermoelectric properties of doped SnO2 superlattices. - Highlights: • Thermoelectric properties of SnO{sub 2}-based alloys and superlattices. • High figure of merit is predicted for planar-doped SnO{sub 2} superlattices. • Nanotechnology has an important role for the development of thermoelectric devices.

  7. Low-temperature properties of Ce(Ru 1- xM x) 2Ge 2, M  Fe, Au

    NASA Astrophysics Data System (ADS)

    Fontes, M. B.; Elmassalami, M.; Aliaga-Guerra, D.; Giordanengo, B.; Bud'ko, S. L.; Guimaraes, A. P.; Gavilano, J. L.; Baggio-Saitovitch, E. M.

    1995-02-01

    We have performed measurements of electrical resistivity, AC susceptibility, magnetization, Mössbauer effect and NMR on the series of intermetallic compounds Ce(Ru 1- xM x) 2Ge 2, M  Fe, Au for 0 ⩽ x ⩽ 0.1. The parent compound CeRu 2Ge 2 orders ferromagnetically below 7.5 K, with f-electrons showing only a small mass-enhancement at low temperatures. However, its crystal structure and Fermi surface are closely related to the heavy-electron superconductor CeRu 2Si 2. Analysis of X-ray diffraction patterns confirmed the structure to be of thCr 2Si 2-type, with no foreign phases detected. The results of our Mössbauer studies indicate that Fe goes into the Ru sites with no magnetic moment. NMR signals were observed in the Fe-doped samples with quadrupolar interaction that can be related to 73Ge nucleus ( I = 9/2).

  8. 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

    2016-05-05

    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.

  9. 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

  10. 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.

  11. Thermoelectric transport properties of high mobility organic semiconductors

    NASA Astrophysics Data System (ADS)

    Venkateshvaran, Deepak; Broch, Katharina; Warwick, Chris N.; Sirringhaus, Henning

    2016-09-01

    Transport in organic semiconductors has traditionally been investigated using measurements of the temperature and gate voltage dependent mobility of charge carriers within the channel of organic field-effect transistors (OFETs). In such measurements, the behavior of charge carrier mobility with temperature and gate voltage, studied together with carrier activation energies, provide a metric to quantify the extent of disorder within these van der Waals bonded materials. In addition to the mobility and activation energy, another potent but often-overlooked transport coefficient useful in understanding disorder is the Seebeck coefficient (also known as thermoelectric power). Fundamentally, the Seebeck coefficient represents the entropy per charge carrier in the solid state, and thus proves powerful in distinguishing materials in which charge carriers move freely from those where a high degree of disorder causes the induced carriers to remain trapped. This paper briefly covers the recent highlights in the field of organic thermoelectrics, showing how significant strides have been made both from an applied standpoint as well as from a viewpoint of fundamental thermoelectric transport physics. It shall be illustrated how thermoelectric transport parameters in organic semiconductors can be tuned over a significant range, and how this tunability facilitates an enhanced performance for heat-to-electricity conversion as well as quantifies energetic disorder and the nature of the density of states (DOS). The work of the authors shall be spotlighted in this context, illustrating how Seebeck coefficient measurements in the polymer indacenodithiophene-co-benzothiadiazole (IDTBT) known for its ultra-low degree of torsion within the polymer backbone, has a trend consistent with low disorder. 1 Finally, using examples of the small molecules C8-BTBT and C10-DNTT, it shall be discussed how the Seebeck coefficient can aid the estimation of the density and distribution of trap states

  12. 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.

  13. Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties

    DOE PAGES

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

    2014-12-21

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

  14. 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.

  15. 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

    2016-03-07

    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 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.

  16. 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.

  17. 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.

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

    DOE PAGES

    Hong, A. J.; Li, L.; He, R.; ...

    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

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

    SciTech Connect

    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 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 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.

  20. 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

  1. Structural Characterization and Thermoelectric Properties of Hot-Pressed CoSi Nanocomposites

    NASA Astrophysics Data System (ADS)

    Ioannou, Maria; Symeou, Elli; Giapintzakis, John; Kyratsi, Theodora

    2014-10-01

    Fabrication of nanocomposites by introduction of SiO2 metal oxide nanoparticles into a cobalt silicide thermoelectric matrix is studied. The CoSi matrix material was prepared through solid-state synthesis, and the nano-SiO2 metal oxide was introduced by mechanical grinding. The mixed powders were hot pressed to fabricate nanocomposites. The structural and morphological modifications were studied by powder x-ray diffraction analysis and scanning electron microscopy. The thermoelectric properties of the materials were followed through the Hall effect, Seebeck coefficient, and electrical and thermal conductivities in the temperature range from 300 K to 1000 K.

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

    SciTech Connect

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

    2012-11-01

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

  3. High thermopower and potential thermoelectric properties of crystalline LiH and NaH

    NASA Astrophysics Data System (ADS)

    Zhao, Yinchang; Dai, Zhenhong; Zhang, Chao; Lian, Chao; Zeng, Shuming; Li, Geng; Meng, Sheng; Ni, Jun

    2017-01-01

    We use first-principles calculations combined with the Boltzmann transport equation and semiclassical analysis to investigate the thermal conductivity κ , electrical conductivity σ , and thermopower S of crystalline LiH and NaH. Remarkably, the calculated S is extraordinarily high while the lattice thermal conductivity κL is fairly low, which, as a result, leads to a much high thermoelectric power factor σ S2 and good thermoelectric properties, with the figure of merit z T even larger than 1.5 in the p -type doped NaH. Further analyses reveal that (i) the large band gap and the flat band around the Fermi level cause the high S and (ii) strong anharmonic phonon scatterings and relevant phonon group velocities result in the low κL in these light materials. Our results support that crystalline LiH and NaH may be potential materials for thermoelectric applications.

  4. Novel Routes to Tune Thermal Conductivities and Thermoelectric Properties of Materials

    DTIC Science & Technology

    2012-11-15

    Nishimura, and T. Mori, “Microstructure and thermoelectric properties of YB22C2N dense samples fabricated through spark plasma sintering ”, Journal of...T. Mori, O. Sologub, and B. Baufeld, SPS- Sintering of NaTaO3-Fe2O3 Composites, J. Austr. Cer. Soc. 47, 57-60 (2011). 6) Y. Michiue, T. Mori, A

  5. 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.

  6. Optical properties of Eu and Er doped LaAlO{sub 3} nanopowders prepared by low-temperature method

    SciTech Connect

    Maczka, Miroslaw; Bednarkiewicz, Artur; Mendoza-Mendoza, Esmeralda; Fuentes, Antonio F.; Kepinski, Leszek

    2012-10-15

    LaAlO{sub 3} nanoparticles doped with Eu{sup 3+} and Er{sup 3+} ions were synthesized at 500 Degree-Sign C in a two-step process by combining a mechanically induced metathesis reaction and molten salt synthesis. The obtained samples were characterized by XRD and TEM methods, which showed that the mean crystallite size is {approx}45 and {approx}57 nm, respectively. Furthermore, excitation and luminescence spectra as well as decay profiles were measured for the synthesized samples. These studies suggested that the Eu{sup 3+} ions are located at three different local sites without inversion symmetry. Our studies also showed up-conversion emission in the samples doped with Er{sup 3+} ions. The up-conversion mechanism has been discussed. - Graphical abstract: The example up-conversion spectra of 1% and 2% Er{sup 3+}-doped samples under 980 nm photoexcitation (a) and energy transfer scheme (b) in Er{sup 3+}-doped LaAlO{sub 3} nanopowders. Highlights: Black-Right-Pointing-Pointer Er and Eu doped LaAlO{sub 3} samples were synthesized at remarkably low temperatures. Black-Right-Pointing-Pointer The mean crystallite size of the obtained samples is 45-57 nm. Black-Right-Pointing-Pointer Luminescence and excitation spectra as well as decay profiles were measured. Black-Right-Pointing-Pointer Eu{sup 3+} ions are located at three different local sites without inversion symmetry. Black-Right-Pointing-Pointer We discuss mechanism of the up-conversion mechanism in Er{sup 3+} doped samples.

  7. 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.

  8. 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

  9. An Experimental Investigation towards Improvement of Thermoelectric Properties of Strontium Titanate Ceramics

    NASA Astrophysics Data System (ADS)

    Mehdizadeh Dehkordi, Arash

    The direct energy conversion between heat and electricity based on thermoelectric effects is a topic of long-standing interest in condensed matter materials science. Experimental and theoretical investigations in order to understand the mechanisms involved and to improve the materials properties and conversion efficiency have been ongoing for more than half a century. While significant achievements have been accomplished in improving the properties of conventional heavy element based materials (such as Bi2Te 3 and PbTe) as well as the discovery of new materials systems for the close-to-room temperature and intermediate temperatures, high-temperature applications of thermoelectrics is still limited to one materials system, namely SiGe. Recently, oxides have exhibited great potential to be investigated for high-temperature thermoelectric power generation. The objective of this dissertation is to synthesize and investigate both electronic and thermal transport in strontium titanate (SrTiO3) ceramics in order to experimentally realize its potential and to ultimately investigate the possibility of further improvement of the thermoelectric performance of this perovskite oxide for mid- to high temperature applications. Developing a synthesis strategy and tuning various synthesis parameters to benefit the thermoelectric transport form the foundation of this study. It is worth mentioning that the results of this study has been employed to prepare targets for pulsed-laser deposition (PLD) to study the thermoelectric properties of corresponding thin films and superlattice structures at Dr. Husam Alshareef's group at King Abdullah University of Science and Technology (KAUST), Saudi Arabia. Considering the broad range of functionality of SrTiO3, the findings of this work will surely benefit other fields of research and application of this functional oxide such as photoluminescence, ferroelectricity or mixed-ionic electronic conductivity. This dissertation will ultimately

  10. Low-temperature crystal structure, specific heat, and dielectric properties of lithium tetraborate Li{sub 2}B{sub 4}O{sub 7}

    SciTech Connect

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

    2010-11-15

    Coherent neutron powder diffraction experiments were carried out together with specific heat, dilatometry, and dielectric spectroscopy studies on Li{sub 2}B{sub 4}O{sub 7} enriched with {sup 11}B 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.

  11. 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.

  12. 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

  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. Influence of Strain on the Thermoelectric Properties of electron-doped SrTiO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Sarantopoulos, Alexandros; Ferreiro-Vila, Elias; Magen, Cesar; Aguirre, Myriam H.; Pardo, Victor; Rivadulla, Francisco

    2015-03-01

    The discovery of a two dimensional electron gas with high mobility at the interface between insulating LaAlO3 / SrTiO3 (LAO/STO) opened the possibility of fabricating functional devices based on this interfacial effect. Therefore, it is important to study the influence of the growth parameters on the properties of the constituent materials. Here, we demonstrate that the thermoelectric properties of epitaxial thin films of Nb:STO can be finely tuned by adjusting the growth conditions in a PLD system. By growing the sample on different substrates, we demonstrate that the amount of vacancies depends on the degree of epitaxial compressive stress. The vacancies produced lead to impurity scattering at low temperatures. We show that the magnetoresistance response, and non-linear behavior of the Hall effect, characteristic of LAO/STO interfaces, can be reproduced in thin films of Nb:STO with a controlled number of vacancies. Moreover, we show that the Seebeck coefficient is a valid tool to obtain information about the degeneracy of the electronic band structure. We acknowledge support from the ERC 2D Therms project.

  15. 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…

  16. 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.

  17. Dielectric Properties and Microstructures of Low-Temperature-Sintered BaTiO3-Based Ceramics with CuBi2O4 Sintering Aid

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tomoyuki; Otagiri, Tadashi

    2006-09-01

    The low-temperature sintering of BaTiO3 (BT) ceramics was investigated by conventional ceramics processing using a CuBi2O4 sintering aid, and the dielectric properties and microstructures of the ceramics were examined. BT powders without CuBi2O4 could not be fully densified at sintering temperatures lower than 1300 °C. However, the addition of CuBi2O4 markedly enhanced the sinterbility of BT powders, and the sintering temperature decreased from 1300 to 920 °C. This may be due to the promotion of liquid-phase sintering. 6.0 wt % CuBi2O4-added BT ceramics sintered at 920 °C exhibited a high density of 5.95 g/cm3. Moreover, to obtain dielectric ceramics with a stable temperature coefficient of capacitance, the effects of ZnO addition on the dielectric properties and microstructures of low-temperature-sintered BT ceramics with a CuBi2O4 sintering aid were also studied. It was found that the addition of ZnO was very effective for improving the temperature coefficient of capacitance and reducing the dielectric loss of the low-temperature-sintered specimens. This is attributable to the microstructural change involving the formation of a core-shell structure, as shown by transmission electron microscopy and X-ray energy-dispersive spectrometry (TEM-EDS). Therefore, a high dielectric constant of 1900, a low dielectric loss of 0.6% and a stable temperature coefficient of capacitance (X7R EIA standard of Δ C/C25 {\\degC}=± 15% in the temperature range from -55 to +125 °C) were obtained for 1.0 wt % ZnO-added BT ceramics with 6.0 wt % CuBi2O4 sintered at 930 °C for 2 h.

  18. 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.

  19. 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.

  20. Annealing effects on the optical and morphological properties of ZnO nanorods on AZO substrate by using aqueous solution method at low temperature.

    PubMed

    Hang, Da-Ren; Islam, Sk Emdadul; Sharma, Krishna Hari; Kuo, Shiao-Wei; Zhang, Cheng-Zu; Wang, Jun-Jie

    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.

  1. Effects of Sn Substitution on Thermoelectric Properties of Ge4SbTe5

    NASA Astrophysics Data System (ADS)

    Williams, Jared B.; Mather, Spencer; Morelli, Donald T.

    2016-02-01

    Phase-change materials are identified by their ability to rapidly alternate between amorphous and crystalline phases upon heating, exhibiting large contrast in the optical/electrical properties of the respective phases. Such materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase-change materials studied today can be found on the pseudobinary (GeTe)1- x (Sb2Te3) x tie-line. Ge4SbTe5, a single-phase compound just off of the (GeTe)1- x (Sb2Te3) x tie-line, forms in a metastable rocksalt crystal structure at room temperature. It has been found that stoichiometric and undoped Ge4SbTe5 exhibits thermal conductivity of ~1.2 W/m-K at high temperature and a dramatic decrease in electrical resistivity at 623 K due to a structural phase transition, which leads to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. Introducing point defects via isoelectronic substitutions can be an effective means of reducing thermal conductivity and enhancing thermoelectric performance. We present a study of the effects of Sn substitution for Ge on the electrical and thermal transport properties of Ge4SbTe5.

  2. Thermoelectric properties and microstructure of Cu-In-O thin films.

    PubMed

    Gregory, Otto J; Tougas, Ian M; Amani, Matin; Crisman, Everett E

    2013-11-11

    Combinatorial chemistry techniques were used to study the thermoelectric properties of sputtered thin films in the system copper oxide (CuO) and indium oxide (In2O3). Seven hundred seventy thin film thermocouples or combinatorial library elements were simultaneously deposited, each with a unique spatially dependent chemistry, based on the relative position of the thermocouples to each sputtering target. The resulting thermoelectric properties of each element were determined along with electrical resistivity as a function of composition. Energy dispersive spectroscopy was used to identify the composition of each thermo-element, and electron and X-ray diffraction were used to determine the degree of crystallinity and phases present. Transmission electron microscopy was used to characterize the microstructure of selected thermo-elements. A change in sign of the thermoelectric voltage was observed in the thermo-element containing 40.0 atomic percent indium, which suggests a change in the dominant carrier type occurred, from p-type to n-type. Based on this finding, the fabrication of thermoelectric p-n junctions using the same base Cu-In-O semiconductor appears feasible.

  3. Thermoelectric properties of Bi2Sr2Co2Oy thin films and single crystals

    NASA Astrophysics Data System (ADS)

    Diao, Zhenyu; Lee, H. N.; Chisholm, M. F.; Jin, R.

    2017-04-01

    Bi2Sr2Co2O9 exhibits a misfit-layered structure with good thermoelectric properties. We have investigated the thermoelectric properties of Bi2Sr2Co2Oy in both thin-film and single-crystal forms. Among thin films grown at different temperatures, we find that both the in-plane thermoelectric power (Sab) and electrical resistivity (ρab) vary in an opposite trend, i.e., Sab is high when ρab is small. This results in large power factor (Sab2/ρab 5.5 μW/K2 cm for the film grown at 700 °C), comparable to that for whiskers. For single crystals, the electrical resistivity shows metallic behavior in a large temperature range, but has higher magnitude than that of films grown at 675 °C and 700 °C. The annealing of single crystals under Ar atmosphere leads to even higher resistivity while Sab is improved. We discuss the thermoelectric performance of this material considering both oxygen concentration and phase purity.

  4. Thermoelectric properties of the Ca(5)Al(2-x)In(x)Sb(6) solid solution.

    PubMed

    Zevalkink, Alex; Swallow, Jessica; Ohno, Saneyuki; Aydemir, Umut; Bux, Sabah; Snyder, G Jeffrey

    2014-11-14

    Zintl phases are attractive for thermoelectric applications due to their complex structures and bonding environments. The Zintl compounds Ca(5)Al(2)In(x)Sb(6)and Ca(5)Al(2)In(x)Sb(6) have both been shown to have promising thermoelectric properties, with zT values of 0.6 and 0.7, respectively, when doped to control the carrier concentration. Alloying can often be used to further improve thermoelectric materials in cases when the decrease in lattice thermal conductivity outweighs reductions to the electronic mobility. Here we present the high temperature thermoelectric properties of the Ca(5)Al(2-x)In(x)Sb(6)solid solution. Undoped and optimally Zn-doped samples were investigated. X-ray diffraction confirms that a full solid solution exists between the Al and In end-members. We find that the Al : In ratio does not greatly influence the carrier concentration or Seebeck effect. The primary effect of alloying is thus increased scattering of both charge carriers and phonons, leading to significantly reduced electronic mobility and lattice thermal conductivity at room temperature. Ultimately, the figure of merit is unaffected by alloying in this system, due to the competing effects of reduced mobility and lattice thermal conductivity.

  5. Thermoelectric Properties and Thermal Stability of BiCuSeO

    NASA Astrophysics Data System (ADS)

    Sato, Toshiharu; Kohri, Hitoshi; Yagasaki, Takayoshi

    2016-11-01

    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. Diameter dependent thermoelectric properties of individual SnTe nanowires

    DOE PAGES

    Xu, E. Z.; Li, Z.; Martinez, J. A.; ...

    2015-01-15

    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 ~more » 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. Lastly, 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.« less

  7. 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 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. Lastly, 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.

  8. Diameter dependent thermoelectric properties of individual SnTe nanowires

    DOE PAGES

    Xu, E. Z.; Li, Z.; Martinez, J. A.; ...

    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

  9. Thermoelectric properties of a plasma at megabar pressures

    NASA Astrophysics Data System (ADS)

    Starostin, A. N.; Gryaznov, V. K.; Filippov, A. V.

    2016-11-01

    A nonideal hydrogen plasma is theoretically studied for the first time as the working medium of a thermoelectric generator. A method is proposed for the calculation of the electrical conductivity, Seebeck coefficient, and thermal conductivity of the nonideal plasma in a wide range of densities and temperatures, including the region of strong degeneracy of electrons, which is achieved in experiments on the quasi-isentropic compression of deuterium and where a "plasma phase transition" (transition with a sharp change in the component composition) is possibly implemented. In this method, the kinetic coefficients are calculated together with the equation of states of the nonideal plasma. It is shown for the first time that the Seebeck coefficient in such a medium reaches 5500 μV/(K cm), which is an order of magnitude larger than that in currently available semiconductor materials used in thermoelectric generators. It is found that the figure of merit in hydrogen, which has a high thermal conductivity, at megabar pressures reaches 0.4, which is only slightly below that in currently available semiconductor materials.

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

    PubMed

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

    2011-10-12

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

  11. 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.

  12. Bismuth doped Mg2Si with improved homogeneity: Synthesis, characterization and optimization of thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Nieroda, P.; Leszczynski, J.; Kolezynski, A.

    2017-04-01

    Recent investigations on Bi doped Mg2Si have shown huge differences of the optimum doping level with respect to maximization of thermoelectric performance. A possible discrepancy among the published results can have origin in different homogeneity of the samples examined in different studies, but it is impossible to judge because of lack of the microstructural studies. Therefore, the aim of the study was to develop a method for obtaining a homogeneous Mg2Si doped with Bi samples and determine the influence of dopant on their thermoelectric properties as well as the solubility limit. The results of theoretical studies of the electronic structure employing FP-LAPW (Full Potential Linearized Augmented Plane Wave) method calculations within density functional theory DFT using the WIEN2k package in Bi-doped Mg2Si are presented. A series of samples with nominal composition Mg2Si1-xBix (x=0-0.06) were prepared using the spark plasma sintering (SPS) method and subsequent annealing. Structural, phase and chemical composition analyses were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning thermoelectric microprobe (STM). The solubility limit was found to be higher than in the previous reports. Carrier concentration was measured using the Hall method. The investigations of the influence of Bi dopant on the transport properties i.e.: electrical conductivity, the Seebeck coefficient and the thermal conductivity were carried out in the temperature range from 300 to 720 K. On the basis of the experimental data, the temperature dependencies of the thermoelectric figure of merit ZT were calculated. Detailed analysis of all obtained results was carried out providing additional insight into the role of the homogeneity of studied materials on their thermoelectric properties.

  13. Synthesis of Nanocrystalline CaWO4 as Low-Temperature Co-fired Ceramic Material: Processing, Structural and Physical Properties

    NASA Astrophysics Data System (ADS)

    Vidya, S.; Solomon, Sam; Thomas, J. K.

    2013-01-01

    Nanocrystalline scheelite CaWO4, a promising material for low-temperature co-fired ceramic (LTCC) applications, has been successfully synthesized through a single-step autoignition combustion route. Structural analysis of the sample was performed by powder x-ray diffraction (XRD), Fourier-transform infrared spectroscopy, and Raman spectroscopy. The XRD analysis revealed that the as-prepared sample was single phase with scheelite tetragonal structure. The basic optical properties and optical constants of the CaWO4 nanopowder were studied using ultraviolet (UV)-visible absorption spectroscopy, which showed that the material was a wide-bandgap semiconductor with bandgap of 4.7 eV at room temperature. The sample showed poor transmittance in the ultraviolet region but maximum transmission in the visible/near-infrared regions. The photoluminescence spectra recorded at different temperatures showed intense emission in the green region. The particle size estimated from transmission electron microscopy was 23 nm. The feasibility of CaWO4 for LTCC applications was studied from its sintering behavior. The sample was sintered at a relatively low temperature of 810°C to high density, without using any sintering aid. The surface morphology of the sintered sample was analyzed by scanning electron microscopy. The dielectric constant and loss factor of the sample measured at 5 MHz were found to be 10.50 and 1.56 × 10-3 at room temperature. The temperature coefficient of the dielectric constant was -88.71 ppm/°C. The experimental results obtained in this work demonstrate the potential of nano-CaWO4 as a low-temperature co-fired ceramic as well as an excellent luminescent material.

  14. Low-temperature CVD synthesis of patterned core-shell VO2@ZnO nanotetrapods and enhanced temperature-dependent field-emission properties.

    PubMed

    Yin, Haihong; Yu, Ke; Song, Changqing; Wang, Zhiliang; Zhu, Ziqiang

    2014-10-21

    VO2 nanostructures are attractive materials because of their reversible metal-insulator transition (MIT) and wide applications in devices. When they are used as field emitters, a new type of temperature-controlled field emission device can be fabricated. Vapor transport methods used to synthesize traditional VO2 nanostructures are energy-intensive, low yield, and produce simple morphology (quasi-1D) that exhibits substrate clamping; thus they are not suitable for field emission applications. To overcome these limitations, ZnO nanotetrapods were used as templates, and patterned core-shell VO2@ZnO nanotetrapods were successfully grown on an ITO/glass substrate via a low-temperature CVD synthesis. SEM, TEM, EDX, XPS analyses and X-ray diffraction revealed that the cores and shells of these nanotetrapods were single crystal wurtzite-type ZnO and polycrystalline VO2, respectively. The VO2@ZnO nanotetrapods show strongly MIT-related FE properties, the emission current density at low temperature is significantly enhanced in comparison with pure VO2 nanostructures, and the emission current density increased by about 20 times as the ambient temperature increased from 25 to 105 °C at a fixed field of 5 V μm(-1). Although the VO2@ZnO nanotetrapods show a worse FE performance at low temperatures compared with pure ZnO nanotetrapods, the FE performance was substantially improved at high temperatures, which was attributed to the MIT-related band bending near the interface and the abrupt resistance change across the MIT.

  15. 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

  16. Thermoelectric Study of Copper Selenide

    NASA Astrophysics Data System (ADS)

    Yao, Mengliang; Liu, Weishu; Ren, Zhifeng; Opeil, Cyril

    2014-03-01

    Nanostructuring has been shown to be an effective approach in reducing lattice thermal conductivity and improving the figure of merit of thermoelectric materials. Copper selenide is a layered structure material, which has a low thermal conductivity and p-type Seebeck coefficient at low temperatures. We have evaluated several hot-pressed, nanostructured copper selenide samples with different dopants for their thermoelectric properties. The phenomenon of the charge-density wave observed in the nanocomposite, resistivity, Seebeck, thermal conductivity and carrier mobility will be discussed. Funding for this research was provided by the Solid State Solar - Thermal Energy Conversion Center (S3TEC), an Energy Frontier Research Center sponsored by the DOE, Office of Basic Energy Science, Award No. DE-SC0001299/ DE-FG02-09ER46577.

  17. Second order nonlinear optical properties of zinc oxide films deposited by low temperature dual ion beam sputtering

    SciTech Connect

    Larciprete, M.C.; Passeri, D.; Michelotti, F.; Paoloni, S.; Sibilia, C.; Bertolotti, M.; Belardini, A.; Sarto, F.; Somma, F.; Lo Mastro, S.

    2005-01-15

    We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at {lambda}=1064 nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples.

  18. Improving the dielectric and piezoelectric properties of screen-printed Low temperature PZT/polymer composite using cold isostatic pressing

    NASA Astrophysics Data System (ADS)

    Almusallam, A.; Yang, K.; Cao, Z.; Zhu, D.; Tudor, J.; Beeby, S. P.

    2014-11-01

    This paper reports an improvement in dielectric and piezoelectric properties of screen-printed PZT/polymer films for flexible electronics applications using Cold Isostatic Pressing (CIP). The investigation involved half and fully cured PZT/polymer composite pastes with weight ratio of 12:1 to investigate the effect of the CIP process on the piezoelectric and dielectric properties. It was observed that the highest dielectric and piezoelectric properties are achieved at pressures of 5 and 10 MPa for half and fully cured films respectively. The relative dielectric constants were 300 and 245 measured at 1 kHz for the half and fully cured samples. Using unoptimised poling conditions, the initial d33 values were 30 and 35 pC/N for the half and fully cured films, respectively. The fully cured sample was then poled using optimized conditions and demonstrated a d33 of approximately 44 pC/N which is an increase of 7% compared with non-CIP processed materials.

  19. High temperature thermoelectric properties of strontium titanate thin films with oxygen vacancy and niobium doping.

    PubMed

    Kumar, S R Sarath; Barasheed, Abeer Z; Alshareef, H N

    2013-08-14

    We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m(-1) K(-1), and the estimated figure of merit is 0.29 at 1000 K.

  20. Material and optical properties of low-temperature NH3-free PECVD SiN x layers for photonic applications

    NASA Astrophysics Data System (ADS)

    Domínguez Bucio, Thalía; Khokhar, Ali Z.; Lacava, Cosimo; Stankovic, Stevan; Mashanovich, Goran Z.; Petropoulos, Periklis; Gardes, Frederic Y.

    2017-01-01

    SiN x layers intended for photonic applications are typically fabricated using LPCVD and PECVD. These techniques rely on high-temperature processing (>400 °C) to obtain low propagation losses. An alternative version of PECVD SiN x layers deposited at temperatures below 400 °C with a recipe that does not use ammonia (NH3-free PECVD) was previously demonstrated to be a good option to fabricate strip waveguides with propagation losses   <3 dB cm-1. We have conducted a systematic investigation of the influence of the deposition parameters on the material and optical properties of NH3-free PECVD SiN x layers fabricated at 350 °C using a design of experiments methodology. In particular, this paper discusses the effect of the SiH4 flow, RF power, chamber pressure and substrate on the structure, uniformity, roughness, deposition rate, refractive index, chemical composition, bond structure and H content of NH3-free PECVD SiN x layers. The results show that the properties and the propagation losses of the studied SiN x layers depend entirely on their compositional N/Si ratio, which is in fact the only parameter that can be directly tuned using the deposition parameters along with the film uniformity and deposition rate. These observations provide the means to optimise the propagation losses of the layers for photonic applications through the deposition parameters. In fact, we have been able to fabricate SiN x waveguides with H content  <20%, good uniformity and propagation losses of 1.5 dB cm-1 at 1550 nm and   <1 dB cm-1 at 1310 nm. As a result, this study can potentially help optimise the properties of the studied SiN x layers for different applications.

  1. Grain size and chemical controls on the ductile properties of mostly frictional faults at low-temperature hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Sleep, Norman H.

    1994-03-01

    A conceptually simple process which establishes a steady grain size distribution is envisioned to control the ductile creep properties of fault zones that mainly slip by frictional processes. Fracture during earthquakes and aseismic frictional creep tend to reduce grain size. However, sufficiently small grains tend to dissolve so that larger grains grow at their expense, a process called Ostwald ripening. A dynamic stedy state is reached where grain size reduction by fracture is balanced by grain growth from Ostwald ripening. The ductile creep mechanism within fault zones in hard rock is probably pressure solution where the rate is limited by diffusion along load-bearing grain-grain contacts. The diffusion paths that limit Ostwald repening are to a considerable extent the same as those for pressure solution. Active Ostwald ripening thus implies conditions suitable for ductile creep. An analytic theory allows estimation of the steady-state mean grain size and the viscosity for creep implied by this dynamic steady state from material properties and from the width, shear traction, and long-term slip velocity of the fault zone. Numerical models were formulated to compute the steady state grain size distribution. The results indicate that ductile creep, as suggested in the companion paper, is a plausible mechanism for transiently increasing fluid pressure within mostly sealed fault zones so that frictional failure occurs at relatively low shear tractions, ˜10 MPa. The relevant material properties are too poorly known, however, for the steady state theory (or its extension to a fault that slips in infrequent large earthquakes) to have much predictive value without additional laboratory experiments and studies of exhumed faults.

  2. Thermoelectric properties of Mg2X (X = Si, Ge) based bulk and quantum well systems

    NASA Astrophysics Data System (ADS)

    Yelgel, Övgü Ceyda

    2017-01-01

    Mg2X (X = Si, Ge) compounds are promising thermoelectric materials for middle temperature applications due to good thermoelectric properties, nontoxicity, and abundantly available constituent elements. So far, these materials used in applications have all been in bulk form. Herein we report a full theory of thermoelectric transport properties of 3D bulk and 2D quantum well systems. The main aim of this present work is to show the effect of quantum confinement on the enhancement of the thermoelectric figure of merit theoretically. Results are given for n-type Mg2 Si0.5 Ge0.5 solid solutions and n-type Mg2Si/Mg2Ge/Mg2Si quantum well systems where the values of well widths are taken as 10 nm, 15 nm, and 20 nm, respectively. The n-type doping is made by using Sb- and La-elements as dopants. Experimental results for solid solutions are included to provide demonstration of proof of principle for the theoretical model applied for 3D bulk structures. The maximum thermoelectric figure of merits of Lax Mg2 -x Si0.49 Ge0.5 Sb0.01 solid solutions are obtained to be 0.64 and 0.56 at 800 K for x = 0 and x = 0.01 sample, respectively. While, at the same temperature, due to the relatively low phonon thermal conductivity the state-of-the-art ZT values of 2.41 and 2.26 have been attained in the Mg2Si/Mg2Ge/Mg2Si quantum well samples with 0.01 wt. % Sb-doped and 0.01 wt. % Sb- and 0.01 wt. % La-doped, respectively.

  3. Thermoelectric properties of epitaxial TbAs:InGaAs nanocomposites

    SciTech Connect

    Clinger, Laura E.; Zide, Joshua M. O.; Pernot, Gilles; Shakouri, Ali; Buehl, Trevor E.; Burke, Peter G.; Gossard, Arthur C.; Palmstroem, Christopher J.

    2012-05-01

    InGaAs lattice-matched to InP was grown by molecular beam epitaxy with randomly distributed TbAs nanoparticles for thermoelectric power generation applications. TbAs:InGaAs is expected to have a large thermoelectric figure of merit, ZT, particularly at high temperatures, owing to energy band alignment between the nanoparticles and their surrounding matrix. Here, the room temperature thermoelectric properties were measured as a function of TbAs concentration, revealing a maximum thermoelectric power factor of 2.38 W/mK{sup 2} and ZT of 0.19 with 0.2% TbAs. Trends in the thermoelectric properties closely resemble those found in comparable ErAs:InGaAs nanocomposite materials. However, nanoparticles were not observed by scanning transmission electron microscopy in the highest ZT TbAs:InGaAs sample, unlike the highest ZT ErAs:InGaAs sample (0.2% ErAs) and two higher concentration TbAs:InGaAs samples examined. Consistent with expectations concerning the positioning of the Fermi level in these materials, ZT was enhanced by TbAs incorporation largely due to a high Seebeck coefficient, whereas ErAs provided InGaAs with higher conductivity but a lower Seebeck coefficient than that of TbAs:InGaAs. Thermal conductivity was reduced significantly from that of intrinsic thin-film InGaAs only with TbAs concentrations greater than {approx}1.7%.

  4. 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.

  5. Heavy hole effect on the thermoelectric properties of highly doped p-type lead telluride

    NASA Astrophysics Data System (ADS)

    Babenko, N. I.; Dmitriev, A. V.

    2017-01-01

    We study theoretically the thermoelectric properties of heavily doped p-type PbTe in the temperature interval of 300 to 900 K. In our calculations, we use the three-band model of PbTe electron energy spectrum that takes into account the heavy-hole Σ-band. On the base of the Boltzmann kinetic equation, the full set of the relevant kinetic characteristics is calculated including the electrical and thermal conductivities, the Seebeck coefficient, and the thermoelectric figure-of-merit. The thermoelectric characteristics appear to be very sensitive to parameters of the heavy hole band. The best fit with experiment was obtained at mh h=5 m0 and Eg Σ=0.5 eV. All calculated thermoelectric quantities then agree very well with the available experimental data. In particular, we were able to reproduce the significant increase of the figure-of-merit up to Z T ≈1.2 that was experimentally observed recently in heavily p-doped PbTe. Our results show that ZT maximum corresponds to the temperature wherein the light hole and heavy hole band edges coincide so that a prominent density-of-states singularity is formed in the valence band.

  6. Low-Temperature Sintering and Electromagnetic Properties of NiCuZn/CaTiO3 Composites

    NASA Astrophysics Data System (ADS)

    Yang, Haibo; Yang, Yanyan; Lin, Ying; Zhu, Jianfeng; Wang, Fen

    2012-04-01

    Dense CaTiO3/Ni0.37Cu0.20Zn0.43Fe1.92O3.88 (CTO/NiCuZn) composites were prepared by the conventional solid-state reaction method and sintered at 950°C. The phase compositions and surface morphologies of the composites were investigated using x-ray diffraction and scanning electron microscopy, respectively. The dielectric and magnetic properties of the composites were also investigated. The results show that the CTO/NiCuZn composites possess high dielectric constants and permeabilities, which can be used in high-frequency communications for capacitor-inductor integrating devices such as electromagnetic interference filters and antennas. With increasing NiCuZn concentration, the permeabilities of the CTO/NiCuZn composites increase, while the dielectric constants and cutoff frequencies decrease.

  7. 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.

  8. A novel low-temperature preparation of Ni-Zn ferrite and the properties of the ultrafine particles formed

    NASA Astrophysics Data System (ADS)

    Chen, C. J.; Bridger, K.; Winzer, S. R.; PaiVerneker, V.

    1988-04-01

    Ultrafine particles of nickel-zinc ferrite have been formed from solutions of metal nitrates by coprecipitation with hydrazine, followed by aging at 90 °C. The crystallites either aggregate into much larger clusters or form single particles, depending upon the preparation conditions, and vary in size from 30 to ≊300 Å. Saturation magnetizations (Ms) of the ferrites varied from 40 to 65 emu/g and the coercivities from 1 to ≊100 Oe. Increasing hydrazine concentrations tended to produce particles with lower Ms. However, for hydrazine/metal ratios below unity, decreasing the hydrazine concentration dramatically lowered the Ms value. Particles formed without hydrazine (e.g., by aging hydroxides precipitated with potassium hydroxide) did not appear to be magnetic. Variations of the magnetic properties and lattice parameters as a function of preparation conditions will be discussed.

  9. Influence of cation and anion substitutions on the thermoelectric properties of pnictide skutterudite compounds

    NASA Astrophysics Data System (ADS)

    Watcharapasorn, Anucha

    A good thermoelectric material is characterized by a high thermoelectric figure of merit (ZT), which involves high Seebeck coefficient, low electrical resistivity and low thermal conductivity. In 1995, it was discovered by a research group at the Jet Propulsion Laboratory that a skutterudite compound, CeFe4Sb12, had a higher ZT than that of the currently used materials. This discovery was partly based on a suggestion of Dr. Glenn A. Slack that skutterudite compounds might possess good thermoelectric properties because of their ability to accept extra atoms into its open structure which can then rattle and scatter heat-carrying phonons, hence reducing the lattice thermal conductivity. Since then, a number of research studies were initiated to investigate the preparation and thermoelectric properties of the skutterudites and other related compounds. This study involved the synthesis and thermoelectric property measurements of a number of phosphide and arsenide skutterudite compounds. The goal was to investigate their transport properties and to make a comparison with their antimonide counterparts. It was found that while the binary phosphide CoP 3 had very low resistivity, it possessed low Seebeck coefficient and high thermal conductivity which resulted in low ZT values. Replacing Co with Ir to form IrP3 resulted in a larger Seebeck coefficient and lower thermal conductivity, but the electrical resistivity was too high to give a high efficiency. The study of lanthanum filled CoP3 and a CoP3-xAsx solid solution, however, showed an improvement in the thermoelectric figure of merit. This was mainly due to an enhancement in the Seebeck coefficient and lower thermal conductivity, while their electrical resistivities were not significantly affected by the cation or anion substitutions. The study of ternary compounds, RT4X12 (R = Ce and Pr, T = Fe and Ru, X = P and As), showed that cerium-phosphorus based compounds exhibited semiconducting properties while the others showed

  10. 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.

  11. Low-temperature-dependent property in an avalanche photodiode based on GaN/AlN periodically-stacked structure

    PubMed Central

    Zheng, Jiyuan; Wang, Lai; Yang, Di; Yu, Jiadong; Meng, Xiao; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yanjun; Wang, Jian; Li, Hongtao; Li, Mo; Li, Qian

    2016-01-01

    In ultra-high sensitive APDs, a vibrate of temperature might bring a fatal decline of the multiplication performance. Conventional method to realize a temperature-stable APD focuses on the optimization of device structure, which has limited effects. While in this paper, a solution by reducing the carrier scattering rate based on an GaN/AlN periodically-stacked structure (PSS) APD is brought out to improve temperature stability essentially. Transport property is systematically investigated. Compared with conventional GaN homojunction (HJ) APDs, electron suffers much less phonon scatterings before it achieves ionization threshold energy and more electrons occupy high energy states in PSS APD. The temperature dependence of ionization coefficient and energy distribution is greatly reduced. As a result, temperature stability on gain is significantly improved when the ionization happens with high efficiency. The change of gain for GaN (10 nm)/AlN (10 nm) PSS APD from 300 K to 310 K is about 20% lower than that for HJ APD. Additionally, thicker period length is found favorable to ionization coefficient ratio but a bit harmful to temperature stability, while increasing the proportion of AlN at each period in a specific range is found favorable to both ionization coefficient ratio and temperature stability. PMID:27775088

  12. Low-temperature-dependent property in an avalanche photodiode based on GaN/AlN periodically-stacked structure

    NASA Astrophysics Data System (ADS)

    Zheng, Jiyuan; Wang, Lai; Yang, Di; Yu, Jiadong; Meng, Xiao; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yanjun; Wang, Jian; Li, Hongtao; Li, Mo; Li, Qian

    2016-10-01

    In ultra-high sensitive APDs, a vibrate of temperature might bring a fatal decline of the multiplication performance. Conventional method to realize a temperature-stable APD focuses on the optimization of device structure, which has limited effects. While in this paper, a solution by reducing the carrier scattering rate based on an GaN/AlN periodically-stacked structure (PSS) APD is brought out to improve temperature stability essentially. Transport property is systematically investigated. Compared with conventional GaN homojunction (HJ) APDs, electron suffers much less phonon scatterings before it achieves ionization threshold energy and more electrons occupy high energy states in PSS APD. The temperature dependence of ionization coefficient and energy distribution is greatly reduced. As a result, temperature stability on gain is significantly improved when the ionization happens with high efficiency. The change of gain for GaN (10 nm)/AlN (10 nm) PSS APD from 300 K to 310 K is about 20% lower than that for HJ APD. Additionally, thicker period length is found favorable to ionization coefficient ratio but a bit harmful to temperature stability, while increasing the proportion of AlN at each period in a specific range is found favorable to both ionization coefficient ratio and temperature stability.

  13. 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.

  14. The mechanical, optical and thermoelectric properties of MCoF3 (M = K and Rb) compounds

    NASA Astrophysics Data System (ADS)

    Mubarak, A. A.

    2017-02-01

    This is an ab initio study instituted on the density functional theory (DFT) and the full-potential linearized augmented plane wave (FP-LAPW) calculations that are performed to analyze the mechanical, electronic, optical and thermoelectric properties of the cubic MCoF3 compound (M = K and Rb). The studied compounds are found thermodynamically and mechanically stable. Moreover, these compounds are found to be elastically anisotropic and ductile. KCoF3 and RbCoF3 are classified as half-metallic and anti-ferromagnetic compounds. The optical properties are investigated from the dielectric function for the different energy ranges. The thermoelectric properties such as transport properties are determined as a function of temperature using BoltzTrape code in the range of 20-800 K. The present compounds are found to have p-type character. Also, the majority charge carriers are found to be electrons rather than hole. Useful mechanical, spintronic, optical and thermoelectric applications are predicted based upon the calculations.

  15. Thermoelectric Properties of Fe1+y Te Prepared by a High Pressure Sintering Method

    NASA Astrophysics Data System (ADS)

    Di, Jiaxin; Li, Hong-Tao; Xu, Gui-Ying

    2016-11-01

    Enhancing thermoelectric properties by utilizing topological properties of topological insulators has attracted increasing attention. Here, powder metallurgy technology combined with high pressure sintering (HPS) was used to prepare Fe1+y Te (y = 0.1, 0.15, 0.1978, 0.22) alloys at 1173 K. The prepared products were identified by x-ray diffraction, and their microstructures were examined by field-emission scanning electron microscopy (FE-SEM). Electric conductivities (σ) and Seebeck coefficient (S) were measured in the temperature range of 303-623 K. The influence of variation in Fe content on thermoelectric properties was studied. The experimental results show that all HPS samples are nanometer composites consisting of Fe3Te2 and FeTe2. Fe1+y Te have electrical charges on the boundaries of topological insulators, which have the potential to be studied in the future. The Fe1+y Te with y = 0.1 shows the best thermoelectric properties at room temperature.

  16. 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.

  17. Low Temperature Powder Coating

    DTIC Science & Technology

    2011-02-09

    Patterson AFB, OH David Piatkowski, Chris Mahendra NAVAIR James Davila, Chris Geib SAIC Beavercreek, OH O G D E N A I R L O G I S T I C S C E N T...PUBLICATIONS Geib , C.W., Davila J.A., Patterson W., et al. “Low Temperature Cure Powder Coating, ESTCP Project WP-0614.” Joint Services Environmental...Management Conference, Columbus, Ohio. 21 – 24 May 2007. Geib , C.W., Davila J.A., Patterson W., et al. “Advances and Testing of Powder Coatings for Aerospace

  18. 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.

  19. 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.

  20. Thermoelectric properties of Ni-doped CuInTe2

    NASA Astrophysics Data System (ADS)

    Kucek, V.; Drasar, C.; Navratil, J.; Plechacek, T.; Benes, L.

    2015-08-01

    Polycrystalline samples of composition Cu1-xNixInTe2 (for x=0-0.05) were synthesized from elements of 5 N purity using a solid-state reaction. The phase purity of the products was verified by X-ray diffraction. Samples for measurement of the transport properties were prepared using hot-pressing. The samples were then characterized by the measurement of electrical conductivity, the Hall coefficient, the Seebeck coefficient, and the thermal conductivity over a temperature range of 300-675 K. All of the samples demonstrate p-type conductivity. We discuss the influence of Ni substitution on the free carrier concentration and the thermoelectric performance. The investigation of the thermoelectric properties shows an improvement up to 50% of ZT in the temperature range of 300-600 K.

  1. Thickness Effects for Thermoelectric Property of Antimony Telluride Nanoplatelets via Solvothermal Method.

    PubMed

    Yan, Xinxin; Zheng, Wenwen; Liu, Fengming; Yang, Shuhua; Wang, Ziyu

    2016-11-29

    Nanostructures have the potential to exhibit good thermoelectric properties by tuning and controlling their size and thickness, and the competing electrical and thermal properties can be decoupled by engineering the interface and grain boundary. In the present study, Sb2Te3 nanoplatelets with different sizes were fabricated using a practical solvothermal method. The thickness of the platelets were regulated between sizes of 10 nm and 100 nm, and the opposite edge length was varied between 1 and 10 μm by altering chemical conditions. Consequently, manipulating the grain size made it suitable to benefit the carrier transport and also block phonons for the thin platelets, resulting in a significant decrease in thermal conductivity and simultaneous increase in electrical conductivity. The results showed that the optimized figure of merit ZT, increased from 0.2 to 1.0 for thin samples, providing a comprehensive understanding of size-dependent thermoelectric performance.

  2. Thickness Effects for Thermoelectric Property of Antimony Telluride Nanoplatelets via Solvothermal Method

    NASA Astrophysics Data System (ADS)

    Yan, Xinxin; Zheng, Wenwen; Liu, Fengming; Yang, Shuhua; Wang, Ziyu

    2016-11-01

    Nanostructures have the potential to exhibit good thermoelectric properties by tuning and controlling their size and thickness, and the competing electrical and thermal properties can be decoupled by engineering the interface and grain boundary. In the present study, Sb2Te3 nanoplatelets with different sizes were fabricated using a practical solvothermal method. The thickness of the platelets were regulated between sizes of 10 nm and 100 nm, and the opposite edge length was varied between 1 and 10 μm by altering chemical conditions. Consequently, manipulating the grain size made it suitable to benefit the carrier transport and also block phonons for the thin platelets, resulting in a significant decrease in thermal conductivity and simultaneous increase in electrical conductivity. The results showed that the optimized figure of merit ZT, increased from 0.2 to 1.0 for thin samples, providing a comprehensive understanding of size-dependent thermoelectric performance.

  3. Thermoelectric properties of V2O5 thin films deposited by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Santos, R.; Loureiro, J.; Nogueira, A.; Elangovan, E.; Pinto, J. V.; Veiga, J. P.; Busani, T.; Fortunato, E.; Martins, R.; Ferreira, I.

    2013-10-01

    This work reports the structural, optical, electrical and thermoelectric properties of vanadium pentoxide (V2O5) thin films deposited at room temperature by thermal evaporation on Corning glass substrates. A post-deposition thermal treatment up to 973 K under atmospheric conditions induces the crystallization of the as-deposited amorphous films with an orthorhombic V2O5 phase with grain sizes around 26 nm. As the annealing temperature rises up to 773 K the electrical conductivity increases. The films exhibit thermoelectric properties with a maximum Seebeck coefficient of -218 μV/K and electrical conductivity of 5.5 (Ω m)-1. All the films show NIR-Vis optical transmittance above 60% and optical band gap of 2.8 eV.

  4. 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.

  5. Modeling the transport properties of epitaxially grown thermoelectric oxide thin films using spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Sarath Kumar, S. R.; Abutaha, Anas I.; Hedhili, M. N.; Alshareef, H. N.

    2012-01-01

    The influence of oxygen vacancies on the transport properties of epitaxial thermoelectric (Sr,La)TiO3 thin films is determined using electrical and spectroscopic ellipsometry (SE) measurements. Oxygen vacancy concentration was varied by ex-situ annealing in Ar and Ar/H2. All films exhibited degenerate semiconducting behavior, and electrical conductivity decreased (258-133 S cm-1) with increasing oxygen content. Similar decrease in the Seebeck coefficient is observed and attributed to a decrease in effective mass (7.8-3.2 me), as determined by SE. Excellent agreement between transport properties deduced from SE and direct electrical measurements suggests that SE is an effective tool for studying oxide thin film thermoelectrics.

  6. Thermoelectric Properties of Bi2Te3 Nanocrystals with Diverse Morphologies Obtained via Modified Hydrothermal Method

    NASA Astrophysics Data System (ADS)

    Dharmaiah, Peyala; Hong, Soon-Jik

    2016-11-01

    Single-phase Bi2Te3 nanostructures (spherical and flower-like) have been synthesized using a modified hydrothermal method at different reaction temperatures (70°C, 100°C, and 150°C) and subsequently consolidated by spark plasma sintering. Their crystal structure, morphology, and thermoelectric and mechanical properties were investigated. The results suggest that the reaction temperature had a significant effect on the morphology and thermoelectric properties. The presence of nanostructures in bulk samples led to a remarkable decrease in thermal conductivity with a lesser effect on electrical conductivity. As a result, the figure of merit (ZT) of the spark-plasma-sintered sample processed from spherical nanoparticles reached 0.54 at 400 K. The Vickers microhardness of the bulk sample processed from spherical nanoparticles was higher than the best results found in literature.

  7. Thickness Effects for Thermoelectric Property of Antimony Telluride Nanoplatelets via Solvothermal Method

    PubMed Central

    Yan, Xinxin; Zheng, Wenwen; Liu, Fengming; Yang, Shuhua; Wang, Ziyu

    2016-01-01

    Nanostructures have the potential to exhibit good thermoelectric properties by tuning and controlling their size and thickness, and the competing electrical and thermal properties can be decoupled by engineering the interface and grain boundary. In the present study, Sb2Te3 nanoplatelets with different sizes were fabricated using a practical solvothermal method. The thickness of the platelets were regulated between sizes of 10 nm and 100 nm, and the opposite edge length was varied between 1 and 10 μm by altering chemical conditions. Consequently, manipulating the grain size made it suitable to benefit the carrier transport and also block phonons for the thin platelets, resulting in a significant decrease in thermal conductivity and simultaneous increase in electrical conductivity. The results showed that the optimized figure of merit ZT, increased from 0.2 to 1.0 for thin samples, providing a comprehensive understanding of size-dependent thermoelectric performance. PMID:27898107

  8. Low temperature synthesis and enhanced electrical properties by substitution of Al3+ and Cr3+ in Co-Ni nanoferrites

    NASA Astrophysics Data System (ADS)

    Pervaiz, Erum; Gul, I. H.

    2013-10-01

    Aluminum and chromium substituted Co-Ni spinel nanoferrites were prepared by sol-gel auto combustion method. Structural parameters along with electrical and magnetic properties have been investigated in the present work. Crystallite sizes of nano ferrite estimated from the peak (311) lies in the range of 13-21 nm ±2 nm and compared with crystallite sizes calculated from Williamsons-Hall plots. DC electrical resistivity variations due to the concentration of aluminum and chromium in the host ferrite have been measured from 368 K to 573 K. Increase in the room temperature DC electrical resistivity was observed up to a concentration x=0.2 and then decreases for x >0.2. Dielectric parameters (real and imaginary part of complex permittivity, dielectric loss tangent) were studied as a function of frequency (20 Hz-5 MHz) and a decrease in the dielectric parameters was observed due to substitution of nickel, aluminum and chromium ions in cobalt nanoferrites. AC conductivity, complex impedance and complex electrical modulus were studied as a function of frequency for the conduction and relaxation mechanisms in the present ferrite system. Saturation magnetization, coercivity, canting angles and magneto crystalline anisotropy variations with composition were observed and presented for the present ferrites under an applied magnetic field of 10 kOe at room temperature. It was found that both magnetization and coercivity decreases with increase in the concentration of aluminum and chromium along with a decrease in the anisotropy parameters. High DC resistivity with low dielectric parameters of the present nanoferrites make them suitable for high frequency and electromagnetic wave absorbing devices. High purity mixed Co-Ni-Al-Cr nanoferrites have been prepared by sol-gel auto combustion method. DC electrical resistivity increases due to substitution of Al3+ and Cr3+. Complex permittivity decrease for Co-Ni-Al-Cr nanoferrites. Detailed AC response analysis has been presented for

  9. Influence of the composition on electrical properties of low-temperature ionic conductors in the Cu1 - x Ag x GeAsSe3 system

    NASA Astrophysics Data System (ADS)

    Kheifets, O. L.; Mel'nikova, N. V.; Filippov, A. L.; Shakirov, E. F.; Babushkin, A. N.; Nugaeva, L. L.

    2012-08-01

    The chalcogenides Cu1 - x Ag x GeAsSe3 ( x = 0.5, 0.8, 0.9) have been synthesized and their electrical properties have been studied at low temperatures. Compounds of this type are electron-ionic conductors with a mixed character of conduction. It has been shown that the substitution of copper atoms for a part of silver atoms in the AgGeAsSe3 compound leads to a decrease in the total conductivity, a decrease in the fraction of ionic component of the conductivity, a significant increase in the polarization times, an increase in the temperature of the onset of a noticeable contribution (as compared to the electron contribution) of the ionic transport, and a decrease in the activation energy of carriers.

  10. [The arsenate Na3Fe2(AsO4) 3: structural study at low temperature and simulation of conduction properties of alkaline cations].

    PubMed

    Ouerfelli, Najoua; Guesmi, Abderrahmen; Mazza, Daniele; Zid, Mohamed Faouzi; Driss, Ahmed

    2008-05-01

    The crystal structure of the low-temperature garnet-like form of trisodium diiron(III) triarsenate, Na(3)Fe(2)(AsO(4))(3), exhibits a three-dimensional framework with small tunnels running along the [111] direction, in which the Na(+) cations are located. This study demonstrates the structural origins of the different ionic conductivities of the low- and high-temperature forms. Sodium conduction properties are simulated by means of the bond-valence-sum (BVS) model; the correlations between the low- and high-temperature crystal structures are discussed. The As, Fe and Na atoms lie on special positions (Wyckoff symbols 24d, 16a and 24c, respectively).

  11. Effect of stress ratio on high-cycle fatigue properties of Ti-6Al-4V ELI alloy forging at low temperature

    NASA Astrophysics Data System (ADS)

    Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Matsuoka, Saburo; Sunakawa, Hideo

    2014-01-01

    The effect of the stress ratio R (the ratio of minimum stress to maximum stress) on the high-cycle fatigue properties of Ti-6Al-4V extra-low interstitial (ELI) alloy forging was investigated at 293 and 77 K. At 293 K, the fatigue strength at 107 cycles exhibited deviations below the modified Goodman line in the R=0.01 and 0.5 tests. Moreover, at 77 K, larger deviations of the fatigue strength at 107 cycles below the modified Goodman line were confirmed in the same stress ratio conditions. The high-cycle fatigue strength of the present alloy forging exhibit an anomalous mean stress dependency at both temperatures and this dependency becomes remarkable at low temperature.

  12. 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.

  13. Prediction of thermomagnetic and thermoelectric properties for novel materials and systems

    NASA Astrophysics Data System (ADS)

    Varlamov, A. A.; Kavokin, Alexey V.

    2013-08-01

    We express the link between conductivity and coefficients of Seebeck, Nernst-Ettingshausen, Peltier, and Thompson and Reghi-Leduc via the temperature derivative of the chemical potential of a system. These general expressions are applied to three-, two- and one-dimensional systems of charge carriers having a parabolic or Dirac spectrum. The method allows for predicting thermoelectric and thermomagnetic properties of novel materials and systems.

  14. Thermoelectric properties of spark-plasma sintered nanoparticular FeSb2 prepared via a solution chemistry approach.

    PubMed

    Kieslich, Gregor; Birkel, Christina S; Veremchuk, Igor; Grin, Yuri; Tremel, Wolfgang

    2014-01-14

    Nanoparticular FeSb2 was prepared in solution from cyclopentadienyl iron(ii) dicarbonyl dimer [Fe(Cp(CO)2)]2 and antimony nanoparticles. Spark plasma sintering was used as consolidation method to maintain the particle size. The thermoelectric performance of FeSb2 is limited by its high thermal conductivity. In this work, the thermal conductivity was suppressed by nearly 80% compared to the bulk value by introducing grain boundary scattering of phonons on the nanoscale. The thermoelectric properties of the consolidated FeSb2 emphasize the possibility of altering thermal transport of promising thermoelectric compounds by phonon scattering by engineering the interfaces at the nanoscale.

  15. Thermoelectric and Magnetic Properties of Pt-Substituted {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} Compounds

    NASA Astrophysics Data System (ADS)

    Sertkol, Murat; Ballıkaya, Sedat; Aydoğdu, Fatih; Güler, Adil; Özdemir, Mustafa; Öner, Yıldırhan

    2017-01-01

    {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} ( x = 0, 0.1, 0.2) compounds were prepared by melting and annealing, followed by a spark plasma sintering method. Low-temperature thermoelectric and magnetic properties were investigated based on Seebeck coefficient, electrical and thermal conductivity and magnetization measurements. The structural properties of {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} ( x = 0, 0.1, 0.2) compounds were ascertained by powder x-ray diffraction analysis, confirming that all samples have a main phase of a skutterudite structure with the space group Im{bar{3}}. The lattice parameters obtained, 9.202(5), 9.199(5) and 9.202(1) Å for x = 0, 0.1 and 0.2, respectively, were found consistent with literature. The Seebeck coefficient sign shows that holes are dominant carriers in all compounds. The local maximum Seebeck coefficient was observed around 50 K which may be a trace of paramagnon-drag effect of charge carriers. Thermal conductivity and electrical resistivity measurements were carried out between 4.2 and 300 K. Temperature dependence of electrical resistivity reflects that all samples show semi-metallic behavior in our temperature range of 4.2-300 K. Samples for x = 0.1 and x = 0.2 show Kondo-like behavior. In magnetization measurement, we observe that there are two successive magnetic transitions in Pt-substituted compounds; however, there is only one (transition from a paramagnetic state to long-range magnetic ordering) in Pt-free compounds. In Pt-substituted compounds, the first transition appears at T _{ c} = 48 K. In addition, the second transition is observed at T _{ irr} = 30 K where an intermediate state is observed before the magnetic ordering transforms to an irreversible ferromagnetic state. We concluded that Pt substitution on the Fe side effectual on the thermoelectric and magnetic properties of {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} ( x = 0, 0.1, 0.2) compounds.

  16. Preparation and Thermoelectric Properties of Pb1-x Fe x Te Alloys Doped with Iodine

    NASA Astrophysics Data System (ADS)

    Cao, X. L.; Cai, W.; Deng, H. D.; Gao, R. L.; Fu, C. L.; Pan, F. S.

    2016-09-01

    This is the first systematic report on the preparation and thermoelectric properties of n-type Pb1-x Fe x Te alloys. Iodine-doped n-type Pb0.85Fe0.15Te polycrystalline was prepared by melting and hot-pressing techniques. The morphology and phase structure of the prepared materials were analyzed by scanning electron microscopy and x-ray diffraction, which indicated that the samples possessed a rock-salt crystal structure and showed a biphase structure. The major phase was the polycrystalline PbTe compound and the second phase was the FeTe compound. The FeTe nano-/micro-precipitates were homogeneously distributed in the PbTe matrix, which is beneficial for the reduction of the lattice thermal conductivity. The effects of the iodine content on the thermoelectric properties of I-doped Pb0.85Fe0.15Te have been investigated. The measurement results of electrical resistivity, carrier concentration, Seebeck coefficient, and thermal conductivity in the temperature range of 300-850 K indicate that the thermoelectric transport properties of the obtained samples are sensitive to the iodine content. When the concentration of iodine is about 0.6 at.%, the maximum dimensionless figure-of-merit value of ˜0.65 at 800 K was obtained.

  17. Study on the thermoelectric properties of PVDF/MWCNT and PVDF/GNP composite foam

    NASA Astrophysics Data System (ADS)

    Sun, Yu-Chen; Terakita, Daryl; Tseng, Alex C.; Naguib, Hani E.

    2015-08-01

    Thermoelectric effect is defined as the revisable translation between thermal and electrical energy. In this paper, we investigate the properties of p-type poly(vinylidene fluoride) (PVDF) based polymer composite foams that can be used in next generation energy harvesting applications. The composites were created using the continuous melt blending method. Multi-walled carbon nanotubes (MWCNTs) and graphene nano-platelets (GNPs) were used as secondary phases to strengthen the electrical conductivity of the composites. Foam structures were later generated using the super-critical carbon dioxide saturation method. We study the material properties between solid and foam samples; the results indicate a dramatic increase in overall thermoelectric properties for GNP foamed samples. We also report at least an order decrease in thermal conductivity, which is in favor of the thermoelectric effect. An unexpected drop in electrical conductivity was observed after the foaming process and can be explained by the large volumetric expansion of the foam. Finally, we report the Seebeck coefficient for both types of composite foams: 11 μV/K for 5 wt% MWCNT/PVDF foam and 58 μV/K for 15 wt% GNP/PVDF foam.

  18. Thermoelectric properties of electrolessly etched silicon nanowire arrays

    NASA Astrophysics Data System (ADS)

    Sadhu, Jyothi; Tian, Hongxiang; Ma, Jun; Valavala, Krishna; Singh, Piyush; Sinha, Sanjiv

    2013-03-01

    Patterning silicon as nanowires with roughened sidewalls enhances the thermoelectric figure-of-merit ZT by order of magnitude compared to the bulk at 300 K. The enhancement is mainly achieved by the remarkable reduction in the thermal conductivity below 5 W/mK at 300 K with only a negligible effect on the power factor of these nanowires. While the focus remained on understanding the implications of surface disorder on the thermal conductivity, the phonon transport effects on the Seebeck coefficient of these wires remains largely unexplored. We developed an electroless etching technique to generate nanowire arrays (NWAs) with controlled surface roughness, morphology, porosity and doping. We conduct the simultaneous device-level measurements of the Seebeck coefficient and thermal conductivity of the NWAs using frequency domain techniques. We observe that nano-structuring quenches the phonon drag in NWAs thereby reducing the Seebeck coefficient by ~25% compared to the bulk at degenerate doping levels. Further, we observe that the sidewall roughness greater than 3 nm roughness height lowers the thermal conductivity 75% below the Casimir limit with 10% - 15% increase in Seebeck coefficient. The porous NWAs show thermal conductivity close to the amorphous limit of Si with enhancement in the Seebeck coefficient primarily due to the carrier depletion.

  19. 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.

  20. 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.

  1. Towards High-Throughput, Simultaneous Characterization of Thermal and Thermoelectric Properties

    NASA Astrophysics Data System (ADS)

    Miers, Collier Stephen

    The extension of thermoelectric generators to more general markets requires that the devices be affordable and practical (low $/Watt) to implement. A key challenge in this pursuit is the quick and accurate characterization of thermoelectric materials, which will allow researchers to tune and modify the material properties quickly. The goal of this thesis is to design and fabricate a high-throughput characterization system for the simultaneous characterization of thermal, electrical, and thermoelectric properties for device scale material samples. The measurement methodology presented in this thesis combines a custom designed measurement system created specifically for high-throughput testing with a novel device structure that permits simultaneous characterization of the material properties. The measurement system is based upon the 3o method for thermal conductivity measurements, with the addition of electrodes and voltage probes to measure the electrical conductivity and Seebeck coefficient. A device designed and optimized to permit the rapid characterization of thermoelectric materials is also presented. This structure is optimized to ensure 1D heat transfer within the sample, thus permitting rapid data analysis and fitting using a MATLAB script. Verification of the thermal portion of the system is presented using fused silica and sapphire materials for benchmarking. The fused silica samples yielded a thermal conductivity of 1.21 W/(m K), while a thermal conductivity of 31.2 W/(m K) was measured for the sapphire samples. The device and measurement system designed and developed in this thesis provide insight and serve as a foundation for the development of high throughput, simultaneous measurement platforms.

  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. Synthesis, Characterization, and Low Temperature Transport Properties of Eu11-xYbxCd6Sb12 Solid-Solution Zintl Phases.

    PubMed

    Kazem, Nasrin; Cooley, Joya; Burks, Edward C; Liu, Kai; Kauzlarich, Susan M

    2016-12-05

    Eu11-xYbxCd6Sb12 Zintl solid solutions have been prepared by tin flux reaction by employing the elements Eu/Yb/Cd/Sb/Sn in the ratio 11 - xp:xp:6:12:30, where xp is an integer less than 11 representing the preparative amount of Eu (11 - xp) and Yb (xp). Efforts to make the Yb compositions for x exceeding ∼3 resulted in structures other than the Sr11Cd6Sb12 structure type. The crystal structures and compositions were determined by single-crystal and powder X-ray diffraction and wavelength-dispersive X-ray analysis measurements. The title solid-solution Zintl compounds crystallize in the centrosymmetric monoclinic space group C2/m (no. 12, Z = 2) as the Sr11Cd6Sb12 structure type (Pearson symbol mC58), and the lattice parameters decrease with increasing ytterbium content. Single crystal X-ray diffraction shows that Yb atoms are not randomly distributed in the Eu sites but have a site preference which can be attributed to size effects. The influence of the rare earth (RE) metal sites on thermal and electronic properties of RE11Cd6Sb12 solid solutions has been studied by measuring their thermoelectric properties from 5 to 300 K after consolidation by either spark plasma sintering (SPS) or hot pressing (HP). Electron microprobe analysis reveals that some of the rare earth metal is lost during SPS; as a result pellets formed through SPS have lower electrical resistivity by an order of magnitude due to increased hole-charge carrier concentrations. While the carrier concentration increases, the mobility decreases due to deficiencies in Eu content. Refinement of powder X-ray diffraction shows that Eu loss is mainly from the Eu1 crystallographic site, which has a unique coordination suggesting that this site plays a key role in the transport properties of RE11Cd6Sb12.

  4. 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.

  5. Electronic properties of GeTe and Ag- or Sb-substituted GeTe studied by low-temperature Te125 NMR

    DOE PAGES

    Cui, J.; Levin, E. M.; Lee, Y.; ...

    2016-08-18

    We have carried out 125Te nuclear magnetic resonance (NMR) in a wide temperature range of 1.5–300 K to investigate the electronic properties of Ge50 Te50, Ag2 Ge48Te50 , and Sb2 Ge48 Te50 from a microscopic point of view. From the temperature dependence of the NMR shift (K) and nuclear spin lattice relaxation rate (1/T1), we found that two bands contribute to the physical properties of the materials. One band overlaps the Fermi level providing the metallic state where no strong electron correlations are revealed by Korringa analysis. The other band is separated from the Fermi level by an energy gapmore » of Eg/kB ~67 K, which gives rise to semiconductorlike properties. First-principles calculation reveals that the metallic band originates from the Ge vacancy while the semiconductorlike band is related to the fine structure of the density of states near the Fermi level. We find low-temperature Te125 NMR data for the materials studied here clearly show that Ag substitution increases hole concentration while Sb substitution decreases it.« less

  6. Electronic properties of GeTe and Ag- or Sb-substituted GeTe studied by low-temperature 125Te NMR

    NASA Astrophysics Data System (ADS)

    Cui, J.; Levin, E. M.; Lee, Y.; Furukawa, Y.

    2016-08-01

    We have carried out 125Te nuclear magnetic resonance (NMR) in a wide temperature range of 1.5-300 K to investigate the electronic properties of Ge50Te50 ,Ag2Ge48Te50 , and Sb2Ge48Te50 from a microscopic point of view. From the temperature dependence of the NMR shift (K ) and nuclear spin lattice relaxation rate (1 /T1 ), we found that two bands contribute to the physical properties of the materials. One band overlaps the Fermi level providing the metallic state where no strong electron correlations are revealed by Korringa analysis. The other band is separated from the Fermi level by an energy gap of Eg/kB˜67 K, which gives rise to semiconductorlike properties. First-principles calculation reveals that the metallic band originates from the Ge vacancy while the semiconductorlike band is related to the fine structure of the density of states near the Fermi level. Low-temperature 125Te NMR data for the materials studied here clearly show that Ag substitution increases hole concentration while Sb substitution decreases it.

  7. 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.

  8. 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.

  9. 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)

  10. The Effect of Te Substitution for Sb on Thermoelectric Properties of Tetrahedrite

    NASA Astrophysics Data System (ADS)

    Lu, Xu; Morelli, Donald

    2014-06-01

    We present the study of the effect of Te substitution on the thermoelectric properties for Sb in Cu12Sb4- x Te x S13 tetrahedrite compounds with x ranging from 0.2 to 1.5 in the temperature range of room temperature to 723 K. Powder x-ray diffraction and electron microscopy results indicate a successful homogenous substitution without the alteration of the crystal structure or the introduction of secondary phases. Thermoelectric property measurements show that the excess electrons from Te during the substitution fill the unoccupied levels near the top of the valence bands in pure Cu12Sb4S13 compound, moving the Fermi level closer to the top of the valence bands. This leads to an enhancement in thermopower but also to an increase in electrical resistivity. Overall, the reduction in total thermal conductivity gives rise to improved ZT values in all substituted samples. The highest ZT value obtained in this study is 0.92 at 723 K for x = 1, which is comparable to that of other p-type bulk thermoelectric materials.

  11. Thermoelectric properties of Yb14MnSb11 from first-principles

    NASA Astrophysics Data System (ADS)

    Song, J.-H.; Kim, M.; Freeman, A. J.

    2009-03-01

    The complex Zintl compound, Yb14MnSb11, has been recently given much attention as a high-performance thermoelectric due to its nearly twice the figure of metrit (zT) of p-type SiGe at high temperatures ( > 900K)ootnotetextS. R. Brown et al., Chem. Mater. 18, 1873 (2006). Its high zT can be attributed to low lattice thermal conductivity combined with a large Seebeck coefficient (S) and high electrical conductivity (σ) at high temperatures. To understand the thermoelectric properties of Yb14MnSb11 and to find possible improvements for thermoelectric performance, we have investigated its electronic structures and electrical transport properties (S,σ) using the highly precise FLAPW methodootnotetextWimmer, Krakauer, Weinert, Freeman, Phys. Rev. B 24, 864 (1981) with the local spin density approximation (LSDA) and LSDA+UootnotetextShick et al, Phys. Rev. B 60, 10763, (1999) methods. We have found significantly different spin moments of Mn between the LSDA and the LSDA+U methods. Also, we determined the anisotropy of the conductivity. The linear temperature behavior of the Seebeck coefficients will be discussed from and related to the electronic structures.

  12. The Effect of Microstructure on the Thermoelectric Properties of Polycrystalline Higher Manganese Silicides

    NASA Astrophysics Data System (ADS)

    An, Tae-Ho; Choi, Soon-Mok; Seo, Won-Seon; Park, Chan; Kim, Il-Ho; Kim, Sun-Uk

    2013-10-01

    In order to obtain single-phase higher manganese silicides (HMS) and investigate the effect of sintering conditions on the thermoelectric properties of a HMS system, HMS compounds were synthesized using a vacuum induction melting method and sintered using spark plasma sintering (SPS) and hot pressing methods. Single-phase HMS with a small amount of second phases was obtained in all of the HMS samples produced. Changes in the electrical conductivity and Seebeck coefficient of the HMS were observed when the sintering temperature was changed, which can be attributed to the presence of the second phases. Similar changes of thermoelectric properties were observed in both the SPS and hot-pressed samples. However, the electrical conductivity and Seebeck coefficient of HMS samples (SPS-HMS) were higher than those of the hot-pressed samples, which can be attributed to SPS's shorter holding time and its ability to control the diffusion rate. The SPS-HMS sample sintered at 1123 K (1123 K SPS-HMS) had a higher figure of merit than any other sample although the sample had a lower power factor. The high value of the figure of merit of the sample can be attributed to its low thermal conductivity. The highest figure of merit value of 0.41 was measured at 850 K in the 1123 K SPS-HMS, which is comparable to the results reported earlier. The results of the present study can be used to optimize the fabrication process of HMS thermoelectric materials.

  13. Theoretical investigation on thermoelectric properties of Cu-based chalcopyrite compounds

    NASA Astrophysics Data System (ADS)

    Wang, Biao; Xiang, Hongjun; Nakayama, Tsuneyoshi; Zhou, Jun; Li, Baowen

    2017-01-01

    Cu-based materials are potential candidates for commercial thermoelectric materials due to their abundance, nontoxicity, and high performance. We incorporate the multiband Boltzmann transport equations with first-principles calculations to theoretically investigate the thermoelectric properties of Cu-based chalcopyrite compounds. As a demonstration of our method, the thermoelectric properties of quaternary compounds Cu2ZnSnX4 (X = S, Se) and ternary compounds CuBTe2 (B = Ga, In) are studied. We systematically calculate the electrical conductivity, the Seebeck coefficient, and the power factor of the four materials above based on parameters obtained from first-principles calculations and using several other fitting parameters. For quaternary compounds, our results reveal that Cu2ZnSnSe4 is better than Cu2ZnSnS4 and its optimal hole concentration is around 5 ×1019cm-3 with the peak power factor 4.7 μ W/cm K 2 at 600 K. For ternary compounds, we find that their optimal hole concentrations are around 1 ×1020cm-3 with the peak power factors over 26 μ W/cm K 2 at 800 K.

  14. Ab Initio Calculations and Measurements of Thermoelectric Properties of V2O5 Films

    NASA Astrophysics Data System (ADS)

    Chumakov, Yu.; Xiong, S.-Y.; Santos, J. R.; Ferreira, I.; Termentzidis, K.; Pokropivny, A.; Cortona, P.; Volz, S.

    2013-07-01

    Density functional theory and the Boltzmann transport equation were used to calculate the thermoelectric transport coefficients for bulk V2O5 and MV2O5 (M = Cr, Ti, Na, Li). The structural relaxation for the given compounds based on the ABINIT code was observed. The temperature dependences of the Seebeck coefficients as well as electrical and thermal electrical conductivities of all relaxed structures displayed anisotropic behavior. Electrooptical measurements of thermoelectric properties were carried out on V2O5 thin films obtained by thermal evaporation with different post-annealing treatments. A Seebeck coefficient of -148 μV/K at T = 300 K was obtained in the in-plane direction for V2O5 thin films with thickness less than 100 nm.

  15. Calculated transport properties of CdO: thermal conductivity and thermoelectric power factor

    DOE PAGES

    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

  16. 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.

  17. Thermoelectric Properties of Half-Heusler Heterostructures from Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Fiedler, Gregor; Kratzer, Peter

    2016-03-01

    Semiconducting half-Heusler alloys have recently emerged as a class of thermoelectric materials with outstanding performance in the medium- to high-temperature range. Heterostructures promise a further reduction of thermal conductivity as a result of phonon scattering at interfaces. Here, both the electronic and phononic spectra of half-Heusler compounds based on Ti, Zr, and Hf are calculated using density functional theory. With this input, thermoelectric properties are obtained, and the thermal conductivity of a heterostructure superlattice is estimated by extending the diffuse mismatch model of interface conductance. We find that a high power factor σ S^2 can be retained in a short-period superlattice, while thermal conductivity is reduced compared to that in single-phase half-Heusler crystals.

  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.

    2016-11-01

    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. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. Thermoelectric properties of Al-doped ZnO: experiment and simulation

    NASA Astrophysics Data System (ADS)

    Jantrasee, S.; Moontragoon, P.; Pinitsoontorn, S.

    2016-09-01

    Advancement in doping other elements, such as Ce, Dy, Ni, Sb, In and Ga in ZnO[1], have stimulated great interest for high-temperature thermoelectric application. In this work, the effects of Al-doping in a ZnO system on the electronic structure and thermoelectric properties are presented, by experiment and calculation. Nanosized powders of Zn1-x Al x O (x = 0,0.01, 0.02, 0.03 and 0.06) were synthesized by hydrothermal method. From XRD results, all samples contain ZnO as the main phase and ZnAl2O4 (spinel phase) peaks were visible when Al additive concentrations were just 6 at%. The shape of the samples changed and the particle size decreased with increasing Al concentration. Seebeck coefficients, on the other hand, did not vary significantly. They were negative and the absolute values increased with temperature. However, the electrical resistivity decreased significantly for higher Al content. The electronic structure calculations were carried out using the open-source software package ABINIT[2], which is based on DFT. The energy band gap, density of states of Al-doped ZnO were investigated using PAW pseudopotential method within the LDA + U. The calculated density of states was then used in combination with the Boltzmann transport equation[3] to calculate the thermoelectric parameters of Al-doped ZnO. The electronic band structures showed that the position of the Fermi level of the doped sample was shifted upwards in comparison to the undoped one. After doping Al in ZnO, the energy band gap was decreased, Seebeck coefficient and electrical conductivity were increased. Finally, the calculated results were compared with the experimental results. The good agreement of thermoelectric properties between the calculation and the experimental results were obtained.

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

    SciTech Connect

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

    2016-01-07

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

  6. 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.

  7. Magnetic properties and microwave absorption in Ni-Zn and Mn-Zn ferrite nanoparticles synthesized by low-temperature solid-state reaction

    NASA Astrophysics Data System (ADS)

    Amiri, Gh. R.; Yousefi, M. H.; Abolhassani, M. R.; Manouchehri, S.; Keshavarz, M. H.; Fatahian, S.

    2011-03-01

    In this work, Mn0.7Zn0.3Fe2O4 and Ni0.7Zn0.3Fe2O4 nanoparticles with super-paramagnetic properties and size distribution from 10 to 52 nm were investigated. These particles were produced by a low-temperature solid-state reaction method without the ball-milling process. The size and morphology of the nanocrystallites were determined by X-ray diffraction, transmission electron microscopy and scanning tunneling microscopy methods. Magnetic measurements such as alternating gradient field magnetometers were used to justify the super-paramagnetic properties of these nanoparticles. Their microwave absorption in the range of 8-18 GHz was studied by a vector network analyzer. Responses of the device under tests were studied. Also, the percentage of the resin, the size and thickness of the mount were determined. The band width of 2.3 GHz was obtained with reflection-loss/written-loss of -16 dB around 10.4 GHz.

  8. 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.

  9. Mechanical properties and rapid low-temperature consolidation of nanocrystalline Cu-ZrO2 composites by pulsed current activated heating

    NASA Astrophysics Data System (ADS)

    Kang, Bo-Ram; Yoon, Jin-kook; Hong, Kyung-Tae; Shon, In-Jin

    2015-07-01

    Metal-ceramic compositr can be obtained with an optimum combination of low density, high oxidation resistance, and high hardness of the ceramic and toughness of the metal. Therefore, metal matrix composites are recognized as candidates for aerospace, automotive, biomaterials, and defense applications. Despite its many attractive properties, the low fracture toughness of ZrO2 limits its wide application. One of the most obvious tactics to improve the mechanical properties has been to fabricate a nanostructured material and composite material. Nano-powders of Cu and ZrO2 were synthesized from 2CuO and Zr powders by high-energy ball milling. Nanocrystalline 2Cu-ZrO2 composite was consolidated within 5 minutes from mechanically synthesized powders of ZrO2 and 2Cu at low temperature, by a pulsed current activated sintering method. The relative density of the composite was 98.5%. The fracture toughness of 2Cu-ZrO2 composite in this study is higher than that of monolithic ZrO2, without great decrease of hardness.

  10. 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.

  11. High temperature thermoelectric properties of rock-salt structure PbS

    DOE PAGES

    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.

  12. 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.

  13. Low Temperature Rosseland Opacities

    NASA Astrophysics Data System (ADS)

    Alexander, D. R.

    1994-05-01

    A new, comprehensive set of low temperature opacity data for atoms and molecules has been assembled. From this basic data set, Rosseland and Planck mean opacities have been computed for temperatures between 12,500 K and 700 K. In addition to the standard continuous absorbers, atomic line absorption (with more than 8 million lines), molecular line absorption (with nearly 60 million lines), and grain absorption and scattering (by silicates, iron, carbon, and SiC) have been included. The absorption due to lines is computed monochromatically and included in the mean with the Opacity Sampling technique. Grains are assumed to form in chemical equilibrium and to form into a continuous distribution of ellipsoids which are randomly oriented. Agreement of these opacities with other recent tabulations of opacities (including OP (M. J. Seaton 1994, MNRAS, 266, 805) and OPAL (F. J. Rogers & C. A. Iglesias 1992, ApJS, 79, 507)) for temperatures above 5,000 K is excellent. It is shown that opacities which neglect molecules become unreliable for temperatures below 5,000 K. Similarly, grains must be included in the computation for temperatures below 1,000 - 1,700 K, depending upon the density. Opacity tables can be prepared for a wide variety of chemical compositions, and will be provided upon request. This research is supported by NSF grant AST-9217946.

  14. Role of O and Se defects in the thermoelectric properties of bismuth oxide selenide

    NASA Astrophysics Data System (ADS)

    Van Quang, Tran; Kim, Miyoung

    2016-11-01

    Bismuth oxygen selenide, Bi2O2Se, is a promising thermoelectric material because of its reduced thermal conductivity. In this study, we perform the first-principles calculation and utilize the solution of Boltzmann transport equation in a constant relaxation-time approximation to compute the electronic and thermoelectric properties of Bi2O2Se with O and Se defects. Oxygen vacancies trap bands located inside the band gap of Bi2O2Se, and the compound becomes a conductor. These bands lead to drastic reduction in the Seebeck coefficient. When vacancies are filled by selenide atoms (selenide point defect), the materials return to be a semiconductor and the Seebeck coefficient increases. The increase of S is also found in the system with defects formed by the substitution of oxygen atoms into selenide sites (oxygen point defect) in the pristine compound. The power factor significantly increases during p-type doping compared with that during n-type doping for the selenide point defect. However, differences in the two doping cases are less distinguished for the oxygen point defect. Hence, the selenide point defect, Bi2O2-δSe1+δ with p-type doping, is an effective way to increase the power factor and eventually the thermoelectric efficiency of Bi2O2Se.

  15. Thermoelectric properties of large-scale Zn3P2 nanowire assemblies.

    PubMed

    Brockway, Lance; Vasiraju, Venkata; Asayesh-Ardakani, Hasti; Shahbazian-Yassar, Reza; Vaddiraju, Sreeram

    2014-04-11

    Gram quantities of both unfunctionalized and 1,4-benzenedithiol (BDT) functionalized zinc phosphide (Zn3P2) nanowire powders, synthesized using direct reaction of zinc and phosphorus, were hot-pressed into highly dense pellets (≥98% of the theoretical density) for the determination of their thermoelectric performance. It was deduced that mechanical flexibility of the nanowires is essential for consolidating them in randomly oriented fashion into dense pellets, without making any major changes to their morphologies. Electrical and thermal transport measurements indicated that the enhanced thermoelectric performance expected of individual Zn3P2 nanowires is still retained within large-scale nanowire assemblies. A maximum reduction of 28% in the thermal conductivity of Zn3P2 resulted from nanostructuring. Use of nanowire morphology also led to enhanced electrical conductivity in Zn3P2. Interface engineering of the nanowires in the pellets, accomplished by hot-pressing BDT functionalized nanowires, resulted in an increase on both the Seebeck coefficient and the electrical conductivity of the nanowire pellets. It is believed that filtering of low energy carriers resulting from the variation of the chemical compositions at the nanowire interfaces is responsible for this phenomenon. Overall, this study indicated that mechanical properties of the nanowires along with the chemical compositions of their surfaces play a hitherto unknown, but vital, role in realizing highly efficient bulk thermoelectric modules based on nanowires.

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

    PubMed

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

    2017-02-01

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

  17. Thermoelectric properties of large-scale Zn3 P2 nanowire assemblies

    NASA Astrophysics Data System (ADS)

    Brockway, Lance; Vasiraju, Venkata; Asayesh-Ardakani, Hasti; Shahbazian-Yassar, Reza; Vaddiraju, Sreeram

    2014-04-01

    Gram quantities of both unfunctionalized and 1,4-benzenedithiol (BDT) functionalized zinc phosphide (Zn3P2) nanowire powders, synthesized using direct reaction of zinc and phosphorus, were hot-pressed into highly dense pellets (≥98% of the theoretical density) for the determination of their thermoelectric performance. It was deduced that mechanical flexibility of the nanowires is essential for consolidating them in randomly oriented fashion into dense pellets, without making any major changes to their morphologies. Electrical and thermal transport measurements indicated that the enhanced thermoelectric performance expected of individual Zn3P2 nanowires is still retained within large-scale nanowire assemblies. A maximum reduction of 28% in the thermal conductivity of Zn3P2 resulted from nanostructuring. Use of nanowire morphology also led to enhanced electrical conductivity in Zn3P2. Interface engineering of the nanowires in the pellets, accomplished by hot-pressing BDT functionalized nanowires, resulted in an increase on both the Seebeck coefficient and the electrical conductivity of the nanowire pellets. It is believed that filtering of low energy carriers resulting from the variation of the chemical compositions at the nanowire interfaces is responsible for this phenomenon. Overall, this study indicated that mechanical properties of the nanowires along with the chemical compositions of their surfaces play a hitherto unknown, but vital, role in realizing highly efficient bulk thermoelectric modules based on nanowires.

  18. 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.

  19. 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.

  20. Structural and thermoelectric properties of SiGe/Al multilayer systems during metal induced crystallization

    NASA Astrophysics Data System (ADS)

    Lindorf, M.; Rohrmann, H.; Span, G.; Raoux, S.; Jordan-Sweet, J.; Albrecht, M.

    2016-11-01

    While the process of metal induced crystallization (MIC) is widely used in the fabrication of thin film electronic devices, its application to the field of thermoelectrics is fairly new. Especially, its implementation in the field of the classic thermoelectric material SiGe could lead to a low cost approach by combining the benefits of low thermal budget, self-doping, and thin film and sputter deposition compatibility. In this work, samples consisting of SiGe/Al multilayers deposited on aluminum oxide based substrates have been prepared. Special emphasis was put on the ratio of Al to SiGe and the resulting changes in transport properties during annealing. On one hand, a certain amount of Al is needed to ensure a complete MIC process for the SiGe, but on the other hand, an excess of Al results in a metallic system with low thermoelectric efficiency. In-situ characterization during annealing of the samples was carried out via x-ray diffraction, electrical resistivity, and Seebeck measurements.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  2. 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.

  3. 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.

  4. Impact of torrefaction and low-temperature carbonization on the properties of biomass wastes from Arundo donax L. and Phoenix canariensis.

    PubMed

    Correia, Ricardo; Gonçalves, Margarida; Nobre, Catarina; Mendes, Benilde

    2017-01-01

    The impact of torrefaction and low-temperature carbonization on the properties of biomass wastes from Arundo donax L. and Phoenix canariensis was studied. Thermal treatments were performed at temperatures from 200°C to 350°C during 15 to 90min and temperature was the parameter that more influenced mass and energy yields as well as biochar composition. Torrefaction reduced moisture, volatile matter, O/C and H/C ratios of the biomass, while increasing heating value, ash content and fixed carbon. For torrefaction at 250°C or higher temperatures grindability of the biochars was significantly improved. The low volatile matter contents and high ash contents of these biochars restricts their use as solid fuels but they can be valorized otherwise. Raw biomasses and the biochars torrefied at 200°C could remove methylene blue from an aqueous solution, in fast adsorption test with a contact time of only 3s, with efficiencies higher than 50%.

  5. 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.

  6. 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.

  7. Improving low-temperature performance of infrared thin-film interference filters utilizing the intrinsic properties of IV-VI narrow-gap semiconductors.

    PubMed

    Li, Bin; Zhang, S; Jiang, J; Fan, B; Zhang, F

    2004-02-09

    Pb(1) (-x)Ge(x)Te is a pseudobinary alloy of IV-VI narrow-gap semiconductor, of which maximum refractive index corresponds to the ferroelectric phase transition. Since the temperature coefficient of refractive index can be tunable from negative to positive by changing the Ge composition, it is possible to utilize the intrinsic property in the fabrication of infrared thin-film interference filters. In this letter, we report a narrow-bandpass filter, in which Pb(0.94)Ge(0.06)Te was substituted for PbTe. It found that the low-temperature stability of the filter is obviously improved: in the temperature range of 80-300K, the shift of center wavelength with temperature is reduced from 0.48nm.K(-1) to 0.23nm K(-1); furthermore, the peak transmittance of filter fabricated with Pb(0.94)Ge(0.06)Te is ~3% over that fabricated with PbTe.

  8. Effect of Ca-Al-Si-O common glass on dielectric properties of low-temperature co-fired ceramic materials with different fillers.

    PubMed

    Park, Zee-Hoon; Yeo, Dong-Hun; Shin, Hyo-Soon

    2014-11-14

    High-density integration in single component used for mobile communication is highly demanded with the miniaturization trend in multi-functional light-weighted mobile communication devices. Embedding passive components into multi-layered ceramic chips is also increasingly needed for high integrity. The need for high strength materials to be used in handheld devices has also increased. To this end, many attempts to join different low-temperature co-fired ceramics (LTCC) materials with different dielectric constants have been made, but failed with de-laminations or internal cracks mainly due to difference of thermal expansion coefficients. It is thought that this difference could be minimized with the use of common glass in different LTCC materials. In this study, several candidates of common glass were mixed with various fillers of LTCC to have various dielectric constants in the radio-frequency, and to minimize the mismatch in joining. Ca-Al-Si-O glass was mixed with 1.3MgO-TiO2, cordierite and CaTiO3. Mixtures were tape-cast and sintered to be compared with their micro-structures, dielectric properties and thermo-mechanical characteristics. When 1.3MgO-TiO2 with volumetric ratio of 30% was mixed with Ca-Al-Si-O glass, the measured dielectric constant was 7.9, the quality factor was 3708. With 45 volumetric percent of cordierite, the dielectric constant was 5 and the quality factor was 1052.

  9. Low Temperature Properties of Charge-Density Wave Compounds POTASSIUM(0.3)-MOLYBDENUM-OXIDE, Tantalum-Sulfide and (TANTALUM-SELENIDE)(2)IODINE.

    NASA Astrophysics Data System (ADS)

    Chen, Ting

    Electrical transport and dielectric properties above and below a threshold electric field in three quasi -one-dimensional inorganic charge-density wave compounds, K_{0.3}MoO_3 , TaS_3 and (TaSe _4)_2I, are studied in the liquid helium temperature range, where all three materials are good insulators with a typical zero-field resistivity exceeding 10^{11}Omegacm. Nonlinear dc current-voltage characteristics are measured at T = 4.2K along the chain direction in all three materials. A linear length dependence of the low-temperature threshold voltage V_sp{rm T} {*} is established, and the corresponding threshold field, E_sp{rm T} {*} = V_sp{ rm T}{*}/L, is found to have the same impurity dependence as that of the threshold field measured at T = 77K. Nonlinear conduction above the threshold field, in K_{0.3} MoO_3, is characterized by a large differential conductivity {rm djover dE} > 10Omega^{-1} cm^{-1}, and a conduction anisotropy kappa = sigma _parallel/sigma_| > 10 ^4. In K_{0.3}MoO _3, the low-frequency response at finite ac drive amplitudes below the threshold field is described by both linear and nonlinear complex dielectric constants, and the latter is characterized by the third harmonic generation. Also in K_{0.3}MoO _3, detailed time and field dependence of the dielectric polarization below E_sp {rm T}{*} is studied in the time range of 10^{-8} -10^3 sec. Both reversible and remnant polarizations are measured as the response to a step electric field drive on samples with different initial states. While the reversible polarization follows a linear field dependence, the remnant polarization leads to a field-dependent dielectric constant which diverges as E to E _sp{rm T}{*} . Furthermore, as E is increased from below to above E_sp{rm T}{* }, the transition from the insulating to the conducting state in response to a step electric field drive is proceeded by delayed-switching, and the delay-time tau_{rm D}(E)is found to divege sharply as E to E _sp{rm T}{*} from

  10. Thermoelectric properties of Bi2Te2.7Se0.3 nanocomposites embedded with MgO nanoparticles

    NASA Astrophysics Data System (ADS)

    Joo, Sung-Jae; Son, Ji-Hee; Min, Bok-Ki; Lee, Ji-Eun; Kim, Bong-Seo; Ryu, Byungki; Park, Su-Dong; Lee, Hee-Woong

    2016-10-01

    Bi2Te2.7Se0.3 bulk materials containing x vol% MgO nanoparticles (average particle size ≈ 100 nm, x = 0, 0.5, 1.0, 1.5) were synthesized by using high-energy ball milling and plasma- activated sintering (PAS) without any special process for nanoparticle dispersion. A microstructure investigation using a scanning electron microscope (SEM) confirmed that MgO nanoparticles were properly dispersed in the Bi2Te2.7Se0.3 matrix and that the grain size was smaller in MgO-containing samples due to suppressed grain growth. The resistivity and the maximum Seebeck coefficient of Bi2Te2.7Se0.3 increased with increasing MgO content whereas the thermal conductivity decreased in the measurement temperature range of 298 K - 573 K. As a result, the maximum dimensionless figure of merit, ZT max, increased about 8.5% in this study, from 0.806 for pristine Bi2Te2.7Se0.3 to 0.875 when x = 1.5. The ZT max was observed to shift to lower temperature, the electron concentration to decrease, and the electron mobility to increase with increasing x, which were explained using a hypothesis that the Te Bi antisite defect concentration decreased as the MgO content increased. In summary, the addition of MgO nanoparticles has been shown to be a simple and effective method to improve the low-temperature thermoelectric properties of n-type Bi2Te3 materials.

  11. Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants

    NASA Astrophysics Data System (ADS)

    Takagiwa, Yoshiki; Kimura, Kaoru

    2014-08-01

    In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra- and inter-icosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.

  12. Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants.

    PubMed

    Takagiwa, Yoshiki; Kimura, Kaoru

    2014-08-01

    In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra- and inter-icosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.

  13. Crystal growth and anisotropy of high temperature thermoelectric properties of yttrium borosilicide single crystals

    SciTech Connect

    Hossain, M. Anwar; Tanaka, Isao; Tanaka, Takaho; Khan, A. Ullah; Mori, Takao

    2016-01-15

    We studied thermoelectric properties of YB{sub 41}Si{sub 1.3} single crystals grown by the floating zone method. The composition of the grown crystal was confirmed by electron probe micro-analysis. We have determined the growth direction for the first time for these borosilicides, and discovered relatively large anisotropy in electrical properties. We measured the electrical resistivity and Seebeck coefficient along [510] (the growth direction) and [052] directions and we found that this crystal exhibits strong electrical anisotropy with a maximum of more than 8 times. An interesting layered structural feature is revealed along [510] with dense boron cluster layers and yttrium layers, with conductivity enhanced along this direction. We obtained 3.6 times higher power factor along [510] compared to that along [052]. Although the ZT of the present system is low, anisotropy in the thermoelectric properties of a boride was reported for the first time, and can be a clue in developing other boride systems also. - Graphical abstract: The growth direction ([510]) was determined for the first time in YB{sub 41}Si{sub 1.3} single crystals and revealed an interesting layered feature of boron clusters and metal atoms, along which the electrical conductivity and thermoelectric power factor was strongly enhanced. - Highlights: • We have grown YB{sub 41}Si{sub 1.3} single crystals by the floating zone method. • Growth direction of [510] determined for first time in REB{sub 41}Si{sub 1.2}. • Electrical resistivity was strongly anisotropic with possible enhancement along metal layers. • The obtained power factor along [510] is 3.6 times higher than that along [052].

  14. 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.

  15. 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.

  16. Thermoelectric properties of electrically stressed Sb/Bi-Sb-Te multilayered films

    SciTech Connect

    Liao, Chien-Neng; Chang, Chih-Yu; Chu, Hsu-Shen

    2010-03-15

    Electrically stressed Bi-Sb-Te thin films have demonstrated markedly enhanced Hall mobility and moderately reduced carrier concentration. To lower electrical resistivity further, a Sb-inserted Bi-Sb-Te multilayer structure was prepared through consecutively sputtering Bi-Sb-Te and Sb layers followed by electric current stressing. The electrically stressed Sb/Bi-Sb-Te film demonstrates high carrier concentration and enhanced Hall mobility. We propose that the additional Sb supply suppresses electromigration-induced Sb depletion in crystal lattices, thus maintains high carrier concentration of the Bi-Sb-Te film. The presented approach provides a simple means to optimize thermoelectric properties of Bi-Sb-Te films.

  17. Thermoelectric properties of n-type SrTiO3

    NASA Astrophysics Data System (ADS)

    Sun, Jifeng; Singh, David J.

    2016-10-01

    We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

  18. 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.

  19. Electronic structure and thermoelectric properties of Bi2(Te1-xSex)3 compound

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Lu, P. F.; Yu, Z. Y.; Gao, T.; Wu, C. J.; Ding, L.; Wang, S. M.

    2013-02-01

    A first-principles study has been performed to evaluate the electronic structure and thermoelectric properties of Bi2(Te1-xSex)3 compound. The transport coefficients are then calculated within the semiclassical Boltzmann theory, and further evaluated as a function of chemical potential assuming a constant relaxation time and an averaged thermal conductivity. Our theoretical calculations show that the ZT value is 1.43 for Bi2(Te1-xSex)3 system, and it agrees well with previous experimental data.

  20. 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.

  1. Structure and thermoelectric properties of spark plasma sintered ultrathin PbTe nanowires.

    PubMed

    Finefrock, Scott W; Zhang, Genqiang; Bahk, Je-Hyeong; Fang, Haiyu; Yang, Haoran; Shakouri, Ali; Wu, Yue

    2014-06-11

    Solution-synthesized thermoelectric nanostructured materials have the potential to have lower cost and higher performance than materials synthesized by solid-state methods. Herein we present the synthesis of ultrathin PbTe nanowires, which are compressed by spark plasma sintering at various temperatures in the range of 405-500 °C. The resulting discs possess grains with sizes of 5-30 μm as well as grains with sizes on the order of the original 12 nm diameter PbTe nanowires. This micro- and nanostructure leads to a significantly reduced thermal conductivity compared to bulk PbTe. Careful electron transport analysis shows suppressed electrical conductivity due to increased short-range and ionized defect scatterings, while the Seebeck coefficient remains comparable to the bulk value. The PbTe nanowire samples are found unintentionally p-type doped to hole concentrations of 2.16-2.59 × 10(18) cm(-3). The maximum figure of merit achieved in the unintentionally doped spark plasma sintered PbTe nanowires is 0.33 at 350 K, which is among the highest reported for unintentionally doped PbTe at low temperatures.

  2. 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.

  3. Dielectrophoretic investigation of Bi₂Te₃ nanowires-a microfabricated thermoelectric characterization platform for measuring the thermoelectric and structural properties of single nanowires.

    PubMed

    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

    2015-03-27

    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.

  4. Phase Formation and Thermoelectric Properties of Doped Higher Manganese Silicides (Mn15Si26)

    NASA Astrophysics Data System (ADS)

    Lee, Hwijong; Kim, Gwansik; Lee, Byunghun; Lee, Kyu Hyoung; Lee, Wooyoung

    2016-10-01

    We herein report substitutional doping effects on the electronic and thermal transport properties of higher manganese silicides (HMS) Mn15Si26. Polycrystalline bulks of Mn0.972A0.028Si1.80 and MnSi1.75B0.028 (A = V, Cr, Mo/B = Al, Ge) were fabricated by a solid-state reaction combined with the spark plasma sintering technique, and their thermoelectric properties were evaluated. We found that thermoelectric performance of Mn15Si26 was significantly enhanced due to the simultaneous improvement in electronic transport and phonon scattering via partial substitution of foreign atoms at Mn- and/or Si-sites. Through the small amount of Cr doping at the Mn-site and Al and Ge doping at the Si-site, the power factor was improved due to enhancement in density of the state's effective mass. Thermal transport properties could be also manipulated due to the point defect phonon scattering effect, and reduced lattice thermal conductivity was obtained with Ge-doped HMS. As a consequence, the maximum dimensionless figure of merit ZT of 0.64 at 773 K (increased 50% compared to undoped Mn15Si26) was obtained in Ge-doped Mn15Si26.

  5. Thermoelectric properties of rocksalt ZnO from first-principles calculations

    DOE PAGES

    Alvarado, Andrew; Attapattu, Jeevake; Zhang, Yi; ...

    2015-10-22

    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 itsmore » 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. Lastly, these results establish RS ZnO as a promising material for thermoelectric devices designed to operate at temperatures desirable for many heat recovery applications.« less

  6. 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.

  7. Thermoelectric properties of rocksalt ZnO from first-principles calculations

    SciTech Connect

    Alvarado, Andrew; Attapattu, Jeevake; Zhang, Yi; Chen, Changfeng

    2015-10-22

    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. Lastly, these results establish RS ZnO as a promising material for thermoelectric devices designed to operate at temperatures desirable for many heat recovery applications.

  8. Predicted Thermoelectric Properties of the Layered XBi4S7 (X = Mn, Fe) Based Materials: First Principles Calculations

    NASA Astrophysics Data System (ADS)

    Azam, Sikander; Khan, Saleem Ayaz; Goumri-Said, Souraya; Kanoun, Mohammed Benali

    2017-01-01

    We report a theoretical investigation of electronic structures, optical and thermoelectric properties of two ternary-layered chalcogenides, MnBi4S7 and FeBi4S7 , by combining the first principles density functional calculations and semi-local Boltzmann transport theory. The calculated electronic band structure have demonstrated that both compounds exhibit indirect band gaps. The optical transitions are explored via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity, and energy loss spectrum. These chalcogenides have exhibited interesting thermoelectric properties such as Seebeck's coefficient, electrical and thermal conductivity, and power factor as function of temperatures.

  9. Energy from low temperature differences

    NASA Astrophysics Data System (ADS)

    Parsons, B. K.

    1985-05-01

    A number of energy conservation and alternative energy approaches utilize a low temperature heat source. Applications in this category include: solar ponds, ocean thermal energy conversion (OTEC), low temperature solar thermal, geothermal, and waste heat recovery and bottoming cycles. Low temperature power extraction techniques are presented and the differences between closed and open Rankine power cycles are discussed. Specific applications and technical areas of current research in OTEC along with a breakdown of plant operating conditions and a rough cost estimate illustrate how the use of low temperature power conversion technology can be cost effective.

  10. 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.

  11. 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.

  12. A study of synthesis of NiCuZn-ferrite sintering in low temperature by metal nitrates and its electromagnetic property

    NASA Astrophysics Data System (ADS)

    Kim, Chul Won; Koh, Jae Gui

    2003-02-01

    The initial NiCuZn synthetic ferrite was synthesized by thermally decomposing the metal nitrates Fe(NO 3) 3·9H 2O, Zn(NO 3) 2·6H 2O, Ni(NO 3) 2·6H 2O, and Cu(NO 3) 2·3H 2O at 150°C for 24 h, and then we calcined the synthetic ferrite powder at 500°C, pulverized each of those for 3, 6, 9, 12, and 15 h in a steel ball mill, sintered each at 700-1000°C for 1 h, and thus studied their microstructures and electromagnetic properties. We could make the initial specimens chemically bonded in liquid at a low-temperature of 150°C, by using the low melting points less than 200°C of the metal nitrates instead of the mechanical ball-mill pulverization, then narrow a distance between the particles into a molecular one, and thus lower the reaction point of sintering by at least 200-300°C. Their initial permeability was 50-400 and their maximum magnetic induction density and coercive force, 2400 G and 0.3-0.5 Oe each, which was similar to those of NiCuZn ferrite synthesized in the conventional process. In the graph of initial permeability versus frequencies, a 180° rotation of the magnetic domain, which appears in a broad band of micro-wave before and after the resonance frequency, could be perceived.

  13. 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.

  14. The optical properties of CuA in bovine cytochrome c oxidase determined by low-temperature magnetic-circular-dichroism spectroscopy.

    PubMed

    Greenwood, C; Hill, B C; Barber, D; Eglinton, D G; Thomson, A J

    1983-11-01

    The visible-near-i.r.-region m.c.d. (magnetic-circular-dichroism) spectrum recorded at low temperature in the range 450-900 nm is reported for oxidized resting mammalian cytochrome c oxidase. M.c.d. magnetization curves determined at different wavelengths reveal the presence of two paramagnetic species. Curves at 576, 613 and 640 nm fit well to those expected for an x,y-polarized haem transition with g values of 3.03, 2.21 and 1.45, i.e. cytochrome a3+. The m.c.d. features at 515, 785 and 817 nm magnetize as a S = 1/2 paramagnet with average g values close to 2, and simulated m.c.d. magnetization curves obtained by using the observed g values of CuA2+, i.e. 2.18, 2.03 and 1.99, fit well to the experimental observations. The form of the m.c.d. magnetization curve at 466 nm is curious, but it can be explained if CuA2+ and cytochrome a3+ contribute with oppositely signed bands at this wavelength. By comparing the m.c.d. spectrum of the enzyme with that of extracted haem a-bisimidazole complex it has been possible to deconvolute the m.c.d. spectrum of CuA2+, which shows transitions throughout the spectral region from 450 to 950 nm. The m.c.d.-spectral properties of CuA2+ were compared with those of a well-defined type I blue copper centre in azurin isolated from Pseudomonas aeruginosa. The absolute intensities of the m.c.d. signals at equal fields and temperatures for CuA2+ are 10-20-fold greater than those for azurin. The optical spectrum of CuA2+ strongly suggests an assignment as a d9 ion rather than Cu(I) bound to a thiyl radical.

  15. Influence of different supports on the physicochemical properties and denitration performance of the supported Mn-based catalysts for NH3-SCR at low temperature

    NASA Astrophysics Data System (ADS)

    Yao, Xiaojiang; Kong, Tingting; Yu, Shuohan; Li, Lulu; Yang, Fumo; Dong, Lin

    2017-04-01

    The commonly used supports of SiO2, γ-Al2O3, TiO2, and CeO2 were synthesized, and used for preparing MnOx/SiO2, MnOx/γ-Al2O3, MnOx/TiO2, and MnOx/CeO2 catalysts with the purpose of investigating the influence of crystal structure and coordination status on the physicochemical properties and denitration performance of these supported Mn-based catalysts for low-temperature NH3-SCR. The obtained samples were characterized by XRD, Raman, BET, H2-TPR, NH3-TPD, in situ DRIFTS, NO + O2-TPD, XPS, and NH3-SCR model reaction. XRD results indicate that MnOx species can be highly dispersed on the surface of γ-Al2O3, TiO2, and CeO2, which is because that there are some octahedral and tetrahedral vacancy sites, octahedral vacancy site, and cubic vacancy site exist on the surface of defective spinel structure γ-Al2O3, anatase TiO2, and cubic fluorite-type structure CeO2, respectively. However, there is no any vacancy site on the surface of SiO2 due to its unique SiO4 tetrahedral structure, which results in the appearance of crystalline β-MnO2 on the surface of MnOx/SiO2 catalyst. Furthermore, H2-TPR results exhibit obvious different reduction behavior among these supported Mn-based catalysts, which is explained by the coordination status of Mn species. Finally, NH3-SCR model reaction results show that MnOx/γ-Al2O3 catalyst presents the best catalytic performance among these supported Mn-based catalysts due to its high dispersion, suitable reduction behavior, largest amount of acid sites, optimal NOx adsorption capacity, and abundant Mn4+ content.

  16. 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.

  17. 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.

  18. Structural, electrical, and thermoelectric properties of bismuth telluride: Silicon/carbon nanocomposites thin films

    NASA Astrophysics Data System (ADS)

    Agarwal, Khushboo; Mehta, B. R.

    2014-08-01

    In this study, the effect of the presence of secondary phases on the structural, electrical, and thermoelectric properties of nanocomposite Bi2Te3 films prepared by co-sputtering of silicon and carbon with Bi2Te3 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 Bi2Te3 and Bi2Te3:C samples have preferred (0 0 15) orientation in comparison to Bi2Te3: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 Bi2Te3:Si and Bi2Te3: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-2 m-1) for Bi2Te3: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.

  19. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    NASA Astrophysics Data System (ADS)

    Wickramaratne, Darshana; Zahid, Ferdows; Lake, Roger K.

    2015-08-01

    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 Bi2Se3, 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 Bi2Se3 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.

  20. Effects of doping on transport properties in Cu-Bi-Se-based thermoelectric materials.

    PubMed

    Hwang, Jae-Yeol; Mun, Hyeon A; Kim, Sang Il; Lee, Ki Moon; Kim, Jungeun; Lee, Kyu Hyoung; Kim, Sung Wng

    2014-12-15

    The thermoelectric properties of Zn-, In-, and I-doped Cu1.7Bi4.7Se8 pavonite homologues were investigated in the temperature range from 300 to 560 K. On the basis of the comprehensive structural analysis using Rietveld refinement of synchrotron radiation diffraction for Cu(x+y)Bi(5-y)Se8 compounds with the inherently disordered crystallographic sites, we demonstrate a doping strategy that provides a simultaneous control for enhanced electronic transport properties by the optimization of carrier concentration and exceptionally low lattice thermal conductivity by the formation of point defects. Substituted Zn or In ions on Cu site was found to be an effective phonon scattering center as well as an electron donor, while doping on Bi site showed a moderate effect for phonon scattering. In addition, we achieved largely enhanced power factor in small amount of In doping on Cu site by increased electrical conductivity and moderately decreased Seebeck coefficient. Coupled with a low lattice thermal conductivity originated from intensified point defect phonon scattering by substituted In ions with host Cu ions, a thermoelectric figure of merit ZT of 0.24 at 560 K for Cu1.6915In0.0085Bi4.7Se8 was achieved, yielding 30% enhancement compared with that of a pristine Cu1.7Bi4.7Se8 at the same temperature.

  1. Impact of parasitic thermal effects on thermoelectric property measurements by Harman method

    NASA Astrophysics Data System (ADS)

    Kwon, Beomjin; Baek, Seung-Hyub; Keun Kim, Seong; Kim, Jin-Sang

    2014-04-01

    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.

  2. Excellent Thermoelectric Properties in monolayer WSe2 Nanoribbons due to Ultralow Phonon Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Wang, Jue; Xie, Fang; Cao, Xuan-Hao; An, Si-Cong; Zhou, Wu-Xing; Tang, Li-Ming; Chen, Ke-Qiu

    2017-01-01

    By using first-principles calculations combined with the nonequilibrium Green’s function method and phonon Boltzmann transport equation, we systematically investigate the influence of chirality, temperature and size on the thermoelectric properties of monolayer WSe2 nanoribbons. The results show that the armchair WSe2 nanoribbons have much higher ZT values than zigzag WSe2 nanoribbons. The ZT values of armchair WSe2 nanoribbons can reach 1.4 at room temperature, which is about seven times greater than that of zigzag WSe2 nanoribbons. We also find that the ZT values of WSe2 nanoribbons increase first and then decrease with the increase of temperature, and reach a maximum value of 2.14 at temperature of 500 K. It is because the total thermal conductance reaches the minimum value at 500 K. Moreover, the impact of width on the thermoelectric properties in WSe2 nanoribbons is not obvious, the overall trend of ZT value decreases lightly with the increasing temperature. This trend of ZT value originates from the almost constant power factor and growing phonon thermal conductance.

  3. Synthesis and Optimization of Thermoelectric Properties of Zn(x)Sb3

    NASA Technical Reports Server (NTRS)

    Doan-Nguyen, Vicky V.

    2005-01-01

    High-performance thermoelectric materials are studied to investigate their abilities to optimize electrical and minimize thermal conductivities. A stoichiometric range of p-type zinc antimonide compounds was synthesized to analyze the trends in their thermoelectric properties. Zn(x)Sb3 (x=3.80, 3.85, 3.90, 3.95, 4.00, 4.05, 4.10) was reacted at 750 C and annealed at 300 C for 24 hours at each temperature. Electronic transport properties such as Seebeck and Hall Effect were measured to analyze possible trends in the set of compositions. SEM, EDS, and XRD were used to quantify both ingots and hot-pressed samples to confirm that they were single-phase and of the expected stoichiometries. Recent SEM data indicated that Zn(3.90)Sb3 and Zn(4.00)Sb3 samples were actually Zn3Sb2. In hopes of further improving the figure-of-merit (ZT) of the binary system, V, Cr, Mn, Fe, Co, In, and Sn were used to dope (Zn(0.95)M(0.05))(3.95)Sb3.

  4. 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.

  5. 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.

  6. Structure and thermoelectric properties of EuTi(O,N)3 ± δ

    NASA Astrophysics Data System (ADS)

    Sagarna, L.; Rushchanskii, K. Z.; Maegli, A.; Yoon, S.; Populoh, S.; Shkabko, A.; Pokrant, S.; Ležaić, M.; Waser, R.; Weidenkaff, A.

    2013-07-01

    After partial substitution of nitrogen for oxygen in EuTiO3, the crystal structure, thermoelectric properties, morphology, and electronic structure of the products were analyzed and compared with pristine EuTiO3. The space group of EuTi(O,N)3 ± δ was orthorhombic Pnma due to the tilt and rotation of the anion octahedra, compared to cubic Pm3¯m of EuTiO3 (at room temperature). The thermoelectric properties of oxynitride polycrystalline bodies sintered in three different ways were investigated in the temperature range of 300 K < T < 950 K. The Seebeck coefficients (S) of the oxynitrides were lower compared with the oxide, and the electrical resistivities (ρ) were increased about one order of magnitude. The activation energies (EA) indicated a larger band gap of EuTi(O,N)3 ± δ when compared to the pristine EuTiO3 (˜1.3 eV compared to 0.98 eV). A morphological characterization by transmission electron microscopy and scanning electron microscopy illustrated intrinsic nanopores within the individual particles and weak grain-interconnections indicating poor intergrain electron transport. Ab initio calculations of the electronic structures confirmed a larger band gap of the distorted crystal structure of the oxynitride and showed a decrease of the density of states at the Fermi level, explaining the reduction of the measured S.

  7. Excellent Thermoelectric Properties in monolayer WSe2 Nanoribbons due to Ultralow Phonon Thermal Conductivity

    PubMed Central

    Wang, Jue; Xie, Fang; Cao, Xuan-Hao; An, Si-Cong; Zhou, Wu-Xing; Tang, Li-Ming; Chen, Ke-Qiu

    2017-01-01

    By using first-principles calculations combined with the nonequilibrium Green’s function method and phonon Boltzmann transport equation, we systematically investigate the influence of chirality, temperature and size on the thermoelectric properties of monolayer WSe2 nanoribbons. The results show that the armchair WSe2 nanoribbons have much higher ZT values than zigzag WSe2 nanoribbons. The ZT values of armchair WSe2 nanoribbons can reach 1.4 at room temperature, which is about seven times greater than that of zigzag WSe2 nanoribbons. We also find that the ZT values of WSe2 nanoribbons increase first and then decrease with the increase of temperature, and reach a maximum value of 2.14 at temperature of 500 K. It is because the total thermal conductance reaches the minimum value at 500 K. Moreover, the impact of width on the thermoelectric properties in WSe2 nanoribbons is not obvious, the overall trend of ZT value decreases lightly with the increasing temperature. This trend of ZT value originates from the almost constant power factor and growing phonon thermal conductance. PMID:28120912

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. High performance thermoelectric materials and methods of preparation

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  13. Thermoelectric and electrical properties of micro-quantity Sn-doped amorphous indium-zinc oxide thin films

    NASA Astrophysics Data System (ADS)

    Byeon, Jayoung; Kim, Seohan; Lim, Jae-Hong; Song, Jae Yong; Park, Sun Hwa; Song, Pungkeun

    2017-01-01

    To realize high thermoelectric performance, it was tried to control both high electrical conductivity (σ) and low thermal conductivity (K) for the Sn-doped indium-zinc oxide films prepared by DC magnetron sputtering. The highest power factor was obtained post-annealed at 200 °C due to the highest σ. However, the highest figure of merit was obtained annealed at 500 °C. It could be attributed to both amorphous structure with low K by phonon and the highest Hall mobility. Thermoelectric and electrical properties of the film could be controlled by both heat treatment and Sn doping with high bond enthalpy.

  14. Optical and thermoelectric properties of Tl-filled CoSb3 skutterudites from first-principles

    NASA Astrophysics Data System (ADS)

    Gee Kim, In; Freeman, Arthur J.

    2006-03-01

    Filled skutterudite antimonides have attracted much interest as a new class of thermoelectric materials. We have determined the electronic structures, optical and thermoelectric propertes of Tl-filled skutterudite CoSb3 by using the highly precise full-potential linearized augmented plane wave (FLAPW) method within the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA) to density functional theory. In contrast to the small-gap semiconducting CoSb3, Tl-filled CoSb3 is calculated to be metallic with Tl-sp bands stongly hybridized with all the other elements over the entire energy region. The thermoelectric properties, e.g. the Seebeck coefficient, are evaluated and discussed in terms of the diagonal terms of the optical matrix elements. B.C. Sales, D. Mandrus, and R. K. Williams, Science 272, 1325 (1996). Wimmer, Weinert, Krakauer, Freeman, Phys. Rev. B 24, 864 (1981). Perdew, Burke, Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).

  15. Beneficial influence of Ru on the thermoelectric properties of Mo{sub 3}Sb{sub 7}

    SciTech Connect

    Candolfi, Christophe; Lenoir, Bertrand; Leszczynski, Juliusz; Dauscher, Anne; Guilmeau, Emmanuel

    2009-04-15

    Zintl phases have recently been identified as potential thermoelectric materials typified by the discovery of a high thermoelectric figure of merit in the Yb{sub 14}MnSb{sub 11} compound above 1000 K. We report on the synthesis and the thermoelectric properties measurements over a wide temperature range (300-1000 K) of other Zintl phases exhibiting a complex crystalline structure, namely, Mo{sub 3}Sb{sub 7} and its related compounds Mo{sub 3-x}Ru{sub x}Sb{sub 7}. While the binary compound displays low figure of merit values due to its metallic nature, we show that the partial substitution of Mo by Ru significantly improves its value to reach 0.45 at 1000 K in Mo{sub 2.2}Ru{sub 0.8}Sb{sub 7}.

  16. Water-Processable, Air-Stable Organic Nanoparticle-Carbon Nanotube Nanocomposites Exhibiting n-Type Thermoelectric Properties.

    PubMed

    Nonoguchi, Yoshiyuki; Tani, Atsushi; Ikeda, Tomohiro; Goto, Chigusa; Tanifuji, Naoki; Uda, Ryoko M; Kawai, Tsuyoshi

    2017-03-01

    Water-dispersed organic base nanoparticles are utilized for the highly stable n-type doping of single-walled carbon nanotubes in aqueous dispersion. Long-term stability is often a critical challenge in the application of n-type organic conductors. The present n-type organic materials exhibit almost no degradation in the thermoelectric properties over months, in air.

  17. Enhanced Thermoelectric Properties of In-Doped ZnSb Thin Film with Surface Nanocrystallization

    NASA Astrophysics Data System (ADS)

    Zheng, Zhuang-hao; Fan, Ping; Luo, Jing-ting; Liang, Guang-xing

    2017-02-01

    This work establishes the high-temperature properties of In-doped ZnSb thin films prepared by a multistep cosputtering method on flexible substrates. The microstructure and thermoelectric properties of the In-doped ZnSb thin films were investigated. X-Ray diffraction results indicated that the main peaks of the In-doped ZnSb thin films were related to ZnSb phase, with some nanocrystallization on the surface after In doping. All samples exhibited p-type conduction behavior, with increased Seebeck coefficient after In doping. The thermal conductivity decreased sharply for the In-doped samples with nanocrystallization, resulting in a ZT value almost six times higher than for undoped ZnSb thin film.

  18. 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.

  19. Crystallization and Transport Properties of Amorphous Cr-Si Thin Film Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Burkov, A. T.; Schumann, J.

    2014-06-01

    We studied the thermoelectric properties, crystallization, and stability of amorphous and nanocrystalline states in Cr-Si composite films. Amorphous films, prepared by magnetron sputtering, were transformed into the nanocrystalline state by annealing with in situ thermopower and electrical resistivity measurements. We have found that the amorphous state is stable in these film composites to about 550 K. Prior to crystallization, the amorphous films undergo a structural relaxation, detected by peculiarities in the temperature dependences of the transport properties, but not visible in x-ray or electron diffraction. The magnitude and temperature dependences of electrical conductivity and thermopower indicate that electron transport in the amorphous films is through extended states. The amorphous films are crystallized at annealing temperatures above 550 K into a nanocrystalline composite with an average grain size of 10-20 nm.

  20. Nanostructure, Excitations, and Thermoelectric Properties of Bi2Te3-Based Nanomaterials

    NASA Astrophysics Data System (ADS)

    Aabdin, Z.; Peranio, N.; Eibl, O.; Töllner, W.; Nielsch, K.; Bessas, D.; Hermann, R. P.; Winkler, M.; König, J.; Böttner, H.; Pacheco, V.; Schmidt, J.; Hashibon, A.; Elsässer, C.

    2012-06-01

    The effect of dimensionality and nanostructure on thermoelectric properties in Bi2Te3-based nanomaterials is summarized. Stoichiometric, single-crystalline Bi2Te3 nanowires were prepared by potential-pulsed electrochemical deposition in a nanostructured Al2O3 matrix, yielding transport in the basal plane. Polycrystalline, textured Sb2Te3 and Bi2Te3 thin films were grown at room temperature using molecular beam epitaxy and subsequently annealed at 250°C. Sb2Te3 films revealed low charge carrier density of 2.6 × 1019 cm-3, large thermopower of 130 μV K-1, and large charge carrier mobility of 402 cm2 V-1 s-1. Bi2(Te0.91Se0.09)3 and (Bi0.26Sb0.74)2Te3 nanostructured bulk samples were prepared from as-cast materials by ball milling and subsequent spark plasma sintering, yielding grain sizes of 50 nm and thermal diffusivities reduced by 60%. Structure, chemical composition, as well as electronic and phononic excitations were investigated by x-ray and electron diffraction, nuclear resonance scattering, and analytical energy-filtered transmission electron microscopy. Ab initio calculations yielded point defect energies, excitation spectra, and band structure. Mechanisms limiting the thermoelectric figure of merit ZT for Bi2Te3 nanomaterials are discussed.