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Sample records for seebeck effect

  1. Paramagnetic spin seebeck effect.

    PubMed

    Wu, Stephen M; Pearson, John E; Bhattacharya, Anand

    2015-05-01

    We report the observation of the longitudinal spin Seebeck effect in paramagnetic insulators. By using a microscale on-chip local heater, we generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. Using this technique at low temperatures (<20??K), we resolve the paramagnetic spin Seebeck effect in the insulating paramagnets Gd3Ga5O12 (gadolinium gallium garnet) and DyScO3 (DSO), using either W or Pt as the spin detector layer. By taking advantage of the strong magnetocrystalline anisotropy of DSO, we eliminate contributions from the Nernst effect in W or Pt, which produces a phenomenologically similar signal. PMID:26001014

  2. Antiferromagnetic Spin Seebeck Effect.

    PubMed

    Wu, Stephen M; Zhang, Wei; Kc, Amit; Borisov, Pavel; Pearson, John E; Jiang, J Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-01

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30  nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9  T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected. PMID:26991198

  3. Antiferromagnetic Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-01

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2 . A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30 nm )/Pt (4 nm) grown by molecular beam epitaxy on a MgF2 (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T ) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  4. Longitudinal Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Uchida, Ken-Ichi

    2013-03-01

    The spin Seebeck effect (SSE) refers to the generation of a spin voltage as a result of a temperature gradient in magnetic materials. Here, a spin voltage is a potential for electron spins to drive a nonequilibrium spin current; when a conductor is attached to a magnet with a finite spin voltage, it induces a spin injection into the conductor. The SSE is of crucial importance in spintronics and spin caloritronics, since it enables simple and versatile generation of a spin current from heat. The simplest and most straightforward setup of the SSE is the longitudinal configuration, in which a spin current flowing parallel to a temperature gradient is measured via the inverse spin Hall effect (ISHE). The longitudinal SSE device consists of a ferromagnetic or ferrimagnetic insulator (FI, e.g. YIG) covered with a paramagnetic metal (PM, e.g. Pt) film. When a temperature gradient is applied perpendicular to the FI/PM interface, an ISHE-induced voltage is generated in the PM layer. In this talk, we report the observation of the longitudinal SSE in various FI/PM systems and provide evidence that the longitudinal SSE is free from thermoelectric artefact, i.e., the anomalous Nernst effect caused by extrinsic magnetic proximity. Then, we discuss the longitudinal SSE from an application point of view. We thank E. Saitoh, S. Maekawa, G. E. W. Bauer, X.-F. Jin, H. Adachi, D. Hou, D. Tian, T. Kikkawa, A. Kirihara, and M. Ishida for their support and valuable discussions.

  5. Current heating induced spin Seebeck effect

    SciTech Connect

    Schreier, Michael Roschewsky, Niklas; Dobler, Erich; Meyer, Sibylle; Huebl, Hans; Goennenwein, Sebastian T. B.; Gross, Rudolf; Physik-Department, Technische Universitt Mnchen, Garching

    2013-12-09

    A measurement technique for the spin Seebeck effect is presented, wherein the normal metal layer used for its detection is exploited simultaneously as a resistive heater and thermometer. We show how the various contributions to the measured total signal can be disentangled, allowing to extract the voltage signal solely caused by the spin Seebeck effect. To this end, we performed measurements as a function of the external magnetic field strength and its orientation. We find that the effect scales linearly with the induced rise in temperature, as expected for the spin Seebeck effect.

  6. Theory of the spin Seebeck effect.

    PubMed

    Adachi, Hiroto; Uchida, Ken-ichi; Saitoh, Eiji; Maekawa, Sadamichi

    2013-03-01

    The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet, which enables the thermal injection of spin currents from the ferromagnet into an attached nonmagnetic metal over a macroscopic scale of several millimeters. The inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device. Recent theoretical and experimental efforts have shown that the magnon and phonon degrees of freedom play crucial roles in the spin Seebeck effect. In this paper, we present the theoretical basis for understanding the spin Seebeck effect and briefly discuss other thermal spin effects. PMID:23420561

  7. Length Scale of the Spin Seebeck Effect.

    PubMed

    Kehlberger, Andreas; Ritzmann, Ulrike; Hinzke, Denise; Guo, Er-Jia; Cramer, Joel; Jakob, Gerhard; Onbasli, Mehmet C; Kim, Dong Hun; Ross, Caroline A; Jungfleisch, Matthias B; Hillebrands, Burkard; Nowak, Ulrich; Klui, Mathias

    2015-08-28

    We investigate the origin of the spin Seebeck effect in yttrium iron garnet (YIG) samples for film thicknesses from 20 nm to 50???m at room temperature and 50 K. Our results reveal a characteristic increase of the longitudinal spin Seebeck effect amplitude with the thickness of the insulating ferrimagnetic YIG, which levels off at a critical thickness that increases with decreasing temperature. The observed behavior cannot be explained as an interface effect or by variations of the material parameters. Comparison to numerical simulations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite magnon propagation length. This allows us to trace the origin of the observed signals to genuine bulk magnonic spin currents due to the spin Seebeck effect ruling out an interface origin and allowing us to gauge the reach of thermally excited magnons in this system for different temperatures. At low temperature, even quantitative agreement with the simulations is found. PMID:26371671

  8. Length Scale of the Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Kehlberger, Andreas; Ritzmann, Ulrike; Hinzke, Denise; Guo, Er-Jia; Cramer, Joel; Jakob, Gerhard; Onbasli, Mehmet C.; Kim, Dong Hun; Ross, Caroline A.; Jungfleisch, Matthias B.; Hillebrands, Burkard; Nowak, Ulrich; Klui, Mathias

    2015-08-01

    We investigate the origin of the spin Seebeck effect in yttrium iron garnet (YIG) samples for film thicknesses from 20 nm to 50 ? m at room temperature and 50 K. Our results reveal a characteristic increase of the longitudinal spin Seebeck effect amplitude with the thickness of the insulating ferrimagnetic YIG, which levels off at a critical thickness that increases with decreasing temperature. The observed behavior cannot be explained as an interface effect or by variations of the material parameters. Comparison to numerical simulations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite magnon propagation length. This allows us to trace the origin of the observed signals to genuine bulk magnonic spin currents due to the spin Seebeck effect ruling out an interface origin and allowing us to gauge the reach of thermally excited magnons in this system for different temperatures. At low temperature, even quantitative agreement with the simulations is found.

  9. Exciton Seebeck effect in molecular systems

    SciTech Connect

    Yan, Yun-An; Cai, Shaohong

    2014-08-07

    We investigate the exciton dynamics under temperature difference with the hierarchical equations of motion. Through a nonperturbative simulation of the transient absorption of a heterogeneous trimer model, we show that the temperature difference causes exciton population redistribution and affects the exciton transfer time. It is found that one can reproduce not only the exciton population redistribution but also the change of the exciton transfer time induced by the temperature difference with a proper tuning of the site energies of the aggregate. In this sense, there exists a site energy shift equivalence for any temperature difference in a broad range. This phenomenon is similar to the Seebeck effect as well as spin Seebeck effect and can be named as exciton Seebeck effect.

  10. Exciton Seebeck effect in molecular systems.

    PubMed

    Yan, Yun-An; Cai, Shaohong

    2014-08-01

    We investigate the exciton dynamics under temperature difference with the hierarchical equations of motion. Through a nonperturbative simulation of the transient absorption of a heterogeneous trimer model, we show that the temperature difference causes exciton population redistribution and affects the exciton transfer time. It is found that one can reproduce not only the exciton population redistribution but also the change of the exciton transfer time induced by the temperature difference with a proper tuning of the site energies of the aggregate. In this sense, there exists a site energy shift equivalence for any temperature difference in a broad range. This phenomenon is similar to the Seebeck effect as well as spin Seebeck effect and can be named as exciton Seebeck effect. PMID:25106568

  11. Domain wall magneto-Seebeck effect

    NASA Astrophysics Data System (ADS)

    Krzysteczko, Patryk; Hu, Xiukun; Liebing, Niklas; Sievers, Sibylle; Schumacher, Hans W.

    2015-10-01

    The interplay between charge, spin, and heat currents in magnetic nanostructures subjected to a temperature gradient has led to a variety of novel effects and promising applications studied in the fast-growing field of spin caloritronics. Here, we explore the magnetothermoelectrical properties of an individual magnetic domain wall in a permalloy nanowire. In thermal gradients of the order of few K /μ m along the long wire axis, we find a clear magneto-Seebeck signature due to the presence of a single domain wall. The observed domain wall magneto-Seebeck effect can be explained by the magnetization-dependent Seebeck coefficient of permalloy in combination with the local spin configuration of the domain wall.

  12. Time resolved spin Seebeck effect experiments

    SciTech Connect

    Roschewsky, Niklas Schreier, Michael; Schade, Felix; Ganzhorn, Kathrin; Meyer, Sibylle; Geprgs, Stephan; Kamra, Akashdeep; Huebl, Hans; Goennenwein, Sebastian T. B.; Gross, Rudolf

    2014-05-19

    In this Letter, we present the results of transient thermopower experiments, performed at room temperature on yttrium iron garnet/platinum bilayers. Upon application of a time-varying thermal gradient, we observe a characteristic low-pass frequency response of the ensuing thermopower voltage with cutoff frequencies of up to 37 MHz. We interpret our results in terms of the spin Seebeck effect, and argue that small wavevector magnons are of minor importance for the spin Seebeck effect in our thin film hybrid structures.

  13. Simple Demonstration of the Seebeck Effect

    ERIC Educational Resources Information Center

    Molki, Arman

    2010-01-01

    In this article we propose a simple and low-cost experimental set-up through which science educators can demonstrate the Seebeck effect using a thermocouple and an instrumentation amplifier. The experiment can be set up and conducted during a 1-hour laboratory session. (Contains 3 tables and 3 figures.)

  14. Photo-Seebeck effect of conjugated polymers

    NASA Astrophysics Data System (ADS)

    Kim, B.; Lim, H.; Kim, E.

    2014-08-01

    Photo-Seebeck effect of conjugated polymers (CPs) from thiophenes and selenophenes were explored for a flexible energy conversion device. CP films were obtained by oxidative polymerizations, which grow conductive channels as polymerization proceeds. Through an optimized polymerization condition, highly conductive CP films were obtained with lower oxidation level. Taking advantage of their high electrical conductivity, the CP films were further explored as a transparent photo-thermo-electric film, because their absorption energy is easily controlled by the degree of oxidation or doping. Upon exposure to a near IR source, the CP films got heated, to result in temperature rise on a substrate. The generated heat was effectively converted into electricity to confirm a photo-Seebeck effect from the CP film under a light exposure. Efficient near-IR photothermal effect and heat to electric conversion have been realized in CP films that could benefit in exploiting multifunctional film displays, invisible NIR sensors, and hybrid energy harvesters.

  15. Spin Seebeck Effect in a Compensated Ferrimagnet

    NASA Astrophysics Data System (ADS)

    Goennenwein, Sebastian T. B.; Geprgs, S.; Kehlberger, A.; Schulz, T.; Mix, C.; Della Coletta, F.; Meyer, S.; Kamra, A.; Jakob, G.; Althammer, M.; Huebl, H.; Gross, R.; Klui, M.

    2015-03-01

    Thermal gradients allow for driving pure spin currents in electrically insulating magnetic materials. In magnetic insulator/normal metal heterostructures, such thermally driven spin currents can be electrically detected via the inverse spin Hall effect in the normal metal, in so-called spin Seebeck effect (SSE) experiments. We have fabricated Gadolinium Iron Garnet/Platinum (GdIG/Pt) thin film heterostructures, and measured the spin Seebeck effect in these samples as a function of temperature. We observe two sign changes as a function of T in the SSE signal. The first sign change occurs around the GdIG magnetic compensation temperature, and can be straightforwardly understood in terms of the reorientation of the iron sublattice magnetizations at this temperature. The second, more gradual SSE sign change takes place around the ordering temperature of the Gd magnetic sublattice, suggesting that the thermally driven spin current is mainly determined by the Gd sublattice at low T. Our results thus show that the SSE spin currents do not simply replicate the effective magnetization of the magnetic insulator, but rather reflect a complex interplay of magnetic sublattice properties.

  16. Surface sensitivity of the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Aqeel, A.; Vera-Marun, I. J.; van Wees, B. J.; Palstra, T. T. M.

    2014-10-01

    We have investigated the influence of the interface quality on the spin Seebeck effect (SSE) of the bilayer system yttrium iron garnet (YIG)-platinum (Pt). The magnitude and shape of the SSE is strongly influenced by mechanical treatment of the YIG single crystal surface. We observe that the saturation magnetic field ( H sat SSE) for the SSE signal increases from 55.3 mT to 72.8 mT with mechanical treatment. The change in the magnitude of H sat SSE can be attributed to the presence of a perpendicular magnetic anisotropy due to the treatment induced surface strain or shape anisotropy in the Pt/YIG system. Our results show that the SSE is a powerful tool to investigate magnetic anisotropy at the interface.

  17. Surface sensitivity of the spin Seebeck effect

    SciTech Connect

    Aqeel, A.; Vera-Marun, I. J.; Wees, B. J. van; Palstra, T. T. M.

    2014-10-21

    We have investigated the influence of the interface quality on the spin Seebeck effect (SSE) of the bilayer system yttrium iron garnet (YIG)–platinum (Pt). The magnitude and shape of the SSE is strongly influenced by mechanical treatment of the YIG single crystal surface. We observe that the saturation magnetic field (H{sub sat}{sup SSE}) for the SSE signal increases from 55.3 mT to 72.8 mT with mechanical treatment. The change in the magnitude of H{sub sat}{sup SSE} can be attributed to the presence of a perpendicular magnetic anisotropy due to the treatment induced surface strain or shape anisotropy in the Pt/YIG system. Our results show that the SSE is a powerful tool to investigate magnetic anisotropy at the interface.

  18. Large Seebeck effect by charge-mobility engineering

    PubMed Central

    Sun, Peijie; Wei, Beipei; Zhang, Jiahao; Tomczak, Jan M.; Strydom, A.M.; Søndergaard, M.; Iversen, Bo B.; Steglich, Frank

    2015-01-01

    The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials. PMID:26108283

  19. Large Seebeck effect by charge-mobility engineering.

    PubMed

    Sun, Peijie; Wei, Beipei; Zhang, Jiahao; Tomczak, Jan M; Strydom, A M; Sndergaard, M; Iversen, Bo B; Steglich, Frank

    2015-01-01

    The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials. PMID:26108283

  20. Large Seebeck effect by charge-mobility engineering

    NASA Astrophysics Data System (ADS)

    Sun, Peijie; Wei, Beipei; Zhang, Jiahao; Tomczak, Jan M.; Strydom, A. M.; Søndergaard, M.; Iversen, Bo B.; Steglich, Frank

    2015-06-01

    The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

  1. Nernst and Seebeck effects in a graphene nanoribbon

    NASA Astrophysics Data System (ADS)

    Xing, Yanxia; Sun, Qing-Feng; Wang, Jian

    2009-12-01

    The thermoelectric power, including the Nernst and Seebeck effects, in graphene nanoribbon is studied. By using the nonequilibrium Greens function combining with the tight-binding Hamiltonian, the Nernst and Seebeck coefficients are obtained. Due to the electron-hole symmetry, the Nernst coefficient is an even function of the Fermi energy while the Seebeck coefficient is an odd function regardless of the magnetic field. In the presence of a strong magnetic field, the Nernst and Seebeck coefficients are almost independent of the chirality and width of the nanoribbon, and they show peaks when the Fermi energy crosses the Landau levels. The height of nth (excluding n=0 ) peak is [ln2/|n|] for the Nernst effect and is [ln2/n] for the Seebeck effect. For the zeroth peak, it is abnormal with height [2ln2] for the Nernst effect and the peak disappears for the Seebeck effect. When the magnetic field is turned off, however, the Nernst effect is absent and only Seebeck effect exists. In this case, the Seebeck coefficient strongly depends on the chirality of the nanoribbon. The peaks are equidistant for the nanoribbons with zigzag edge but are irregularly distributed for the armchair edge. In particular, for the insulating armchair ribbon, the Seebeck coefficient can be very large near the Dirac point. When the magnetic field varies from zero to large values, the differences among the Seebeck coefficients for different chiral ribbons gradually vanish and the nonzero value of Nernst coefficient appears first near the Dirac point then gradually extends to the whole energy region.

  2. An analytical solution for quantum size effects on Seebeck coefficient

    NASA Astrophysics Data System (ADS)

    Karabetoglu, S.; Sisman, A.; Ozturk, Z. F.

    2016-03-01

    There are numerous experimental and numerical studies about quantum size effects on Seebeck coefficient. In contrast, in this study, we obtain analytical expressions for Seebeck coefficient under quantum size effects. Seebeck coefficient of a Fermi gas confined in a rectangular domain is considered. Analytical expressions, which represent the size dependency of Seebeck coefficient explicitly, are derived in terms of confinement parameters. A fundamental form of Seebeck coefficient based on infinite summations is used under relaxation time approximation. To obtain analytical results, summations are calculated using the first two terms of Poisson summation formula. It is shown that they are in good agreement with the exact results based on direct calculation of summations as long as confinement parameters are less than unity. The analytical results are also in good agreement with experimental and numerical ones in literature. Maximum relative errors of analytical expressions are less than 3% and 4% for 2D and 1D cases, respectively. Dimensional transitions of Seebeck coefficient are also examined. Furthermore, a detailed physical explanation for the oscillations in Seebeck coefficient is proposed by considering the relative standard deviation of total variance of particle number in Fermi shell.

  3. Giant Seebeck effect in pure fullerene thin films

    NASA Astrophysics Data System (ADS)

    Kojima, Hirotaka; Abe, Ryo; Ito, Mitsuhiro; Tomatsu, Yasuyuki; Fujiwara, Fumiya; Matsubara, Ryosuke; Yoshimoto, Noriyuki; Nakamura, Masakazu

    2015-12-01

    The small thermal conductivity of molecular solids is beneficial for their thermoelectric applications. If Seebeck coefficients were sufficiently large to compensate for the relatively small electrical conductivity, these materials would be promising candidates for thermoelectric devices. In this work, the thermoelectric properties of C60 were studied by in situ measurements under ultrahigh vacuum after the deposition of a pure C60 thin film. An exceptionally large Seebeck coefficient of more than 150 mV/K was observed as a steady-state thermoelectromotive force. Even considering several extreme but realistic conditions, conventional semiclassical thermoelectric theories cannot explain this giant Seebeck effect.

  4. Longitudinal spin Seebeck effect contribution in transverse spin Seebeck effect experiments in Pt/YIG and Pt/NFO.

    PubMed

    Meier, Daniel; Reinhardt, Daniel; van Straaten, Michael; Klewe, Christoph; Althammer, Matthias; Schreier, Michael; Goennenwein, Sebastian T B; Gupta, Arunava; Schmid, Maximilian; Back, Christian H; Schmalhorst, Jan-Michael; Kuschel, Timo; Reiss, Gnter

    2015-01-01

    The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. Here, we investigate the inverse spin Hall voltage of a 10?nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 and NiFe2O4 with a temperature gradient in the film plane. We show characteristics typical of the spin Seebeck effect, although we do not observe the most striking features of the transverse spin Seebeck effect. Instead, we attribute the observed voltages to the longitudinal spin Seebeck effect generated by a contact tip induced parasitic out-of-plane temperature gradient, which depends on material, diameter and temperature of the tip. PMID:26394541

  5. Longitudinal spin Seebeck effect contribution in transverse spin Seebeck effect experiments in Pt/YIG and Pt/NFO

    NASA Astrophysics Data System (ADS)

    Meier, Daniel; Reinhardt, Daniel; van Straaten, Michael; Klewe, Christoph; Althammer, Matthias; Schreier, Michael; Goennenwein, Sebastian T. B.; Gupta, Arunava; Schmid, Maximilian; Back, Christian H.; Schmalhorst, Jan-Michael; Kuschel, Timo; Reiss, Gnter

    2015-09-01

    The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. Here, we investigate the inverse spin Hall voltage of a 10 nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 and NiFe2O4 with a temperature gradient in the film plane. We show characteristics typical of the spin Seebeck effect, although we do not observe the most striking features of the transverse spin Seebeck effect. Instead, we attribute the observed voltages to the longitudinal spin Seebeck effect generated by a contact tip induced parasitic out-of-plane temperature gradient, which depends on material, diameter and temperature of the tip.

  6. Longitudinal spin Seebeck effect contribution in transverse spin Seebeck effect experiments in Pt/YIG and Pt/NFO

    PubMed Central

    Meier, Daniel; Reinhardt, Daniel; van Straaten, Michael; Klewe, Christoph; Althammer, Matthias; Schreier, Michael; Goennenwein, Sebastian T. B.; Gupta, Arunava; Schmid, Maximilian; Back, Christian H.; Schmalhorst, Jan-Michael; Kuschel, Timo; Reiss, Günter

    2015-01-01

    The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. Here, we investigate the inverse spin Hall voltage of a 10 nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 and NiFe2O4 with a temperature gradient in the film plane. We show characteristics typical of the spin Seebeck effect, although we do not observe the most striking features of the transverse spin Seebeck effect. Instead, we attribute the observed voltages to the longitudinal spin Seebeck effect generated by a contact tip induced parasitic out-of-plane temperature gradient, which depends on material, diameter and temperature of the tip. PMID:26394541

  7. Giant spin Seebeck effect in a non-magnetic material.

    PubMed

    Jaworski, C M; Myers, R C; Johnston-Halperin, E; Heremans, J P

    2012-07-12

    The spin Seebeck effect is observed when a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material, where it gets converted into a measurable voltage. It has been previously observed with a magnitude of microvolts per kelvin in magnetically ordered materials, ferromagnetic metals, semiconductors and insulators. Here we describe a signal in a non-magnetic semiconductor (InSb) that has the hallmarks of being produced by the spin Seebeck effect, but is three orders of magnitude larger (millivolts per kelvin). We refer to the phenomenon that produces it as the giant spin Seebeck effect. Quantizing magnetic fields spin-polarize conduction electrons in semiconductors by means of Zeeman splitting, which spin-orbit coupling amplifies by a factor of ?25 in InSb. We propose that the giant spin Seebeck effect is mediated by phonon-electron drag, which changes the electrons' momentum and directly modifies the spin-splitting energy through spin-orbit interactions. Owing to the simultaneously strong phonon-electron drag and spin-orbit coupling in InSb, the magnitude of the giant spin Seebeck voltage is comparable to the largest known classical thermopower values. PMID:22785317

  8. Longitudinal spin Seebeck effect: from fundamentals to applications

    NASA Astrophysics Data System (ADS)

    Uchida, K.; Ishida, M.; Kikkawa, T.; Kirihara, A.; Murakami, T.; Saitoh, E.

    2014-08-01

    The spin Seebeck effect refers to the generation of spin voltage as a result of a temperature gradient in ferromagnetic or ferrimagnetic materials. When a conductor is attached to a magnet under a temperature gradient, the thermally generated spin voltage in the magnet injects a spin current into the conductor, which in turn produces electric voltage owing to the spin-orbit interaction. The spin Seebeck effect is of increasing importance in spintronics, since it enables direct generation of a spin current from heat and appears in a variety of magnets ranging from metals and semiconductors to insulators. Recent studies on the spin Seebeck effect have been conducted mainly in paramagnetic metal/ferrimagnetic insulator junction systems in the longitudinal configuration in which a spin current flowing parallel to the temperature gradient is measured. This ‘longitudinal spin Seebeck effect’ (LSSE) has been observed in various sample systems and exclusively established by separating the spin-current contribution from extrinsic artefacts, such as conventional thermoelectric and magnetic proximity effects. The LSSE in insulators also provides a novel and versatile pathway to thermoelectric generation in combination of the inverse spin-Hall effects. In this paper, we review basic experiments on the LSSE and discuss its potential thermoelectric applications with several demonstrations.

  9. Longitudinal spin Seebeck effect free from the proximity Nernst effect.

    PubMed

    Kikkawa, T; Uchida, K; Shiomi, Y; Qiu, Z; Hou, D; Tian, D; Nakayama, H; Jin, X-F; Saitoh, E

    2013-02-01

    This Letter provides evidence for intrinsic longitudinal spin Seebeck effects (LSSEs) that are free from the anomalous Nernst effect (ANE) caused by an extrinsic proximity effect. We report the observation of LSSEs in Au/Y(3)Fe(5)O(12) (YIG) and Pt/Cu/YIG systems, showing that the LSSE appears even when the mechanism of the proximity ANE is clearly removed. In the conventional Pt/YIG structure, furthermore, we separate the LSSE from the ANE by comparing the voltages in different magnetization and temperature-gradient configurations; the ANE contamination was found to be negligibly small even in the Pt/YIG structure. PMID:23432302

  10. Evaluation of thermal gradients in longitudinal spin Seebeck effect measurements

    NASA Astrophysics Data System (ADS)

    Sola, A.; Kuepferling, M.; Basso, V.; Pasquale, M.; Kikkawa, T.; Uchida, K.; Saitoh, E.

    2015-05-01

    In the framework of the longitudinal spin Seebeck effect (LSSE), we developed an experimental setup for the characterization of LSSE devices. This class of device consists in a layered structure formed by a substrate, a ferrimagnetic insulator (YIG) where the spin current is thermally generated, and a paramagnetic metal (Pt) for the detection of the spin current via the inverse spin-Hall effect. In this kind of experiments, the evaluation of a thermal gradient through the thin YIG layer is a crucial point. In this work, we perform an indirect determination of the thermal gradient through the measurement of the heat flux. We developed an experimental setup using Peltier cells that allow us to measure the heat flux through a given sample. In order to test the technique, a standard LSSE device produced at Tohoku University was measured. We find a spin Seebeck SSSE coefficient of 2.8 10 - 7 V K-1.

  11. Influence of interface condition on spin-Seebeck effects

    NASA Astrophysics Data System (ADS)

    Qiu, Z.; Hou, D.; Uchida, K.; Saitoh, E.

    2015-04-01

    The longitudinal spin-Seebeck effect (LSSE) has been investigated for Pt/yttrium iron garnet (YIG) bilayer systems. The magnitude of the voltage induced by the LSSE is found to be sensitive to the Pt/YIG interface condition. We observed a large LSSE voltage in a Pt/YIG system with a better crystalline interface, while the voltage decays steeply when an amorphous layer is introduced at the interface artificially.

  12. Seebeck effect in a battery-type thermocell

    NASA Astrophysics Data System (ADS)

    Kobayashi, Wataru; Kinoshita, Akemi; Moritomo, Yutaka

    2015-08-01

    We demonstrated that battery-type thermocells, which consist of two paste-type electrodes with the same active material and electrolyte, show the Seebeck effect. The magnitudes of electrochemical Seebeck coefficient (S) of the thermocells with several layered oxides were evaluated: -12.7 ?V/K for Na0.99CoO2, -29.7 ?V/K for Na0.52MnO2, -22.4 ?V/K for Na0.51Mn0.5Fe0.5O2, and -6.8 ?V/K for LiCoO2. In the thermocell with Na0.99CoO2, time-dependence of the electromotive force (?V) at a constant temperature difference (?T) was well reproduced by a mean-field approach of the chemical potential ( ?)Na+ concentration (x) relationship, indicating that the Na+ intercalation/deintercalation plays an intrinsic role in the electrochemical Seebeck effect.

  13. Intrinsic spin Seebeck effect in Au/YIG.

    PubMed

    Qu, D; Huang, S Y; Hu, Jun; Wu, Ruqian; Chien, C L

    2013-02-01

    The acute magnetic proximity effects in Pt/YIG compromise the suitability of Pt as a spin current detector. We show that Au/YIG, with no anomalous Hall effect and a negligible magnetoresistance, allows the measurements of the intrinsic spin Seebeck effect with a magnitude much smaller than that in Pt/YIG. The experiment results are consistent with the spin polarized density functional calculations for Pt with a sizable and Au with a negligible magnetic moment near the interface with YIG. PMID:23432301

  14. Charging of heated colloidal particles using the electrolyte Seebeck effect.

    PubMed

    Majee, Arghya; Wrger, Alois

    2012-03-16

    We propose a novel actuation mechanism for colloids, which is based on the Seebeck effect of the electrolyte solution: Laser heating of a nonionic particle accumulates in its vicinity a net charge Q, which is proportional to the excess temperature at the particle surface. The corresponding long-range thermoelectric field E is proportional to 1/r(2) provides a tool for controlled interactions with nearby beads or with additional molecular solutes. An external field E(ext) drags the thermocharged particle at a velocity that depends on its size and absorption properties; the latter point could be particularly relevant for separating carbon nanotubes according to their electronic band structure. PMID:22540514

  15. Skyrmionic spin Seebeck effect via dissipative thermomagnonic torques

    NASA Astrophysics Data System (ADS)

    Kovalev, Alexey A.

    2014-06-01

    We derive thermomagnonic torque and its "?-type" dissipative correction from the stochastic Landau-Lifshitz-Gilbert equation. The ?-type dissipative correction describes viscous coupling between magnetic dynamics and magnonic current and it stems from spin mistracking of the magnetic order. We show that thermomagnonic torque is important for describing temperature gradient induced motion of skyrmions in helical magnets while dissipative correction plays an essential role in generating transverse Magnus force. We propose to detect such skyrmionic motion by employing the transverse spin Seebeck effect geometry.

  16. Spin Seebeck effect in YIG-based systems

    NASA Astrophysics Data System (ADS)

    Siegel, Gene; Prestgard, Megan; Teng, Shiang; Tiwari, Ashutosh

    2015-03-01

    Recently, the use of magnetic insulators (yttrium iron garnet, YIG) in conjunction with platinum has sparked interest in spintronics research. This is due to the existence of the spin Seebeck effect which could potentially be a source of pure spin current for spintronic devices. Furthermore, these coatings could potentially show the versatility of spintronics by acting as a spin-based thermoelectric generator, thereby providing a new method of transforming heat into power. However, there remain questions regarding the origins and legitimacy of the spin Seebeck effect. Moreover, recent publications claim that the observed effects are a manifestation of magnetic proximity effects in platinum and not a true SSE signal. Because of these concerns, we are providing supporting evidence that the voltages observed in the YIG/Pt films are truly SSE voltages. We are reaffirming claims that magnon transport theory provides an accurate basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed laser deposition, as these YIG films possess a large SSE voltage compared to those films grown using liquid phase deposition techniques.

  17. Transverse Spin Seebeck Effect on YIG/Pt

    NASA Astrophysics Data System (ADS)

    Prakash, Arati; Boona, Stephen; Jin, Hyungyu; Heremans, Joseph

    2015-03-01

    The existence of the longitudinal spin-Seebeck effect (LSSE) is well established and supported by theory. Much more controversial is the nature of the signals observed in the transverse spin-Seebeck (TSSE) geometry, where the heat current (x) is orthogonal to the direction of spin current propagation (y). TSSE has been described as simply non-local thermal spin-injection, but questions remain about the fact that the effect is observed at macroscopic length scales. To explore possible explanations for the observed TSSE signals, we report data from new TSSE measurements on the YIG/Pt system. The system studied has multiple Pt strips deposited in series upon bulk single crystals of YIG. We investigate the TSSE coefficient as a function of four variables: (1) sample temperature; (2) magnitude of the temperature gradient; (3) position of Pt strips along x; and (4) width of Pt strips along x. We consider nonlinear effects and the role of magnon density in the interpretation of our results. Work supported by the ARO- MURI Grant W911NF-14-1-0016 and NSF MRSEC program, Grant No. DMR 1420451.

  18. Evaluation of thermal gradients in longitudinal spin Seebeck effect measurements

    SciTech Connect

    Sola, A. Kuepferling, M.; Basso, V.; Pasquale, M.; Kikkawa, T.; Uchida, K.; Saitoh, E.

    2015-05-07

    In the framework of the longitudinal spin Seebeck effect (LSSE), we developed an experimental setup for the characterization of LSSE devices. This class of device consists in a layered structure formed by a substrate, a ferrimagnetic insulator (YIG) where the spin current is thermally generated, and a paramagnetic metal (Pt) for the detection of the spin current via the inverse spin-Hall effect. In this kind of experiments, the evaluation of a thermal gradient through the thin YIG layer is a crucial point. In this work, we perform an indirect determination of the thermal gradient through the measurement of the heat flux. We developed an experimental setup using Peltier cells that allow us to measure the heat flux through a given sample. In order to test the technique, a standard LSSE device produced at Tohoku University was measured. We find a spin Seebeck S{sub SSE} coefficient of 2.8×10{sup −7} V K{sup −1}.

  19. Thermal Conductance and Seebeck Effect in Mesoscopic Systems

    NASA Astrophysics Data System (ADS)

    Aly, Arafa H.; El-Gawaad, N. S. Abd

    2015-09-01

    In this work, thermoelectric transport through a saddle-point potential is discussed with an emphasis on the effects of the chemical potential and temperature. In particular, the thermal conductance and the Seebeck coefficient are calculated for two-dimensional systems of a constriction defined by a saddle-point potential. The solution as a function of temperature and chemical potential has been investigated. The Peltier coefficient and thermal transport in a quantum point contact (QPC), under the influence of external fields and different temperatures, are presented. Also, the oscillations of the Peltier coefficient in external fields are obtained. Numerical calculations of the Peltier coefficient are performed at different applied voltages, amplitudes, and temperatures. Moreover, a method is proposed for measuring the sub-band energies and spin-splitting energies in a bottle-neck of the constriction. For weak non-linearities, the charge and entropy currents across a QPC are expanded as a series in powers of the applied bias voltage and the temperature difference. Expansions of the Seebeck voltage in terms of the temperature difference and the Peltier heat in terms of the current are obtained.

  20. Thermal Conductance and Seebeck Effect in Mesoscopic Systems

    NASA Astrophysics Data System (ADS)

    Aly, Arafa H.; El-Gawaad, N. S. Abd

    2015-11-01

    In this work, thermoelectric transport through a saddle-point potential is discussed with an emphasis on the effects of the chemical potential and temperature. In particular, the thermal conductance and the Seebeck coefficient are calculated for two-dimensional systems of a constriction defined by a saddle-point potential. The solution as a function of temperature and chemical potential has been investigated. The Peltier coefficient and thermal transport in a quantum point contact (QPC), under the influence of external fields and different temperatures, are presented. Also, the oscillations of the Peltier coefficient in external fields are obtained. Numerical calculations of the Peltier coefficient are performed at different applied voltages, amplitudes, and temperatures. Moreover, a method is proposed for measuring the sub-band energies and spin-splitting energies in a bottle-neck of the constriction. For weak non-linearities, the charge and entropy currents across a QPC are expanded as a series in powers of the applied bias voltage and the temperature difference. Expansions of the Seebeck voltage in terms of the temperature difference and the Peltier heat in terms of the current are obtained.

  1. Designing a study of the Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Riley, Grant; Liu, Jason; Roberts, Gerri; Buchanan, Kristen

    2012-10-01

    The Spin Seebeck Effect (SSE) refers to the recently discovered generation of a spin voltage as a result of an applied temperature gradient. The SSE has been observed in ferromagnetic (FM) metals, semiconductors, and insulators. This area of research has attracted much interest because it may provide a means to make use of waste heat from electronic devices. While several theories have been presented, there are still open questions regarding the physical mechanism of this effect. Recent experimental evidence suggests that magnons and phonons play a role in thermal spin physics; however, the experiments done to date are performed primarily through detection of a voltage via the Inverse Spin Hall Effect that is due to the steady-state accumulation of a spin distribution across the FM material and consequently provide only indirect information on the magnons. Here we will discuss an experimental setup that we have designed to explore the role of magnons in the SSE using Brillouin light scattering.

  2. Origin of the spin Seebeck effect in compensated ferrimagnets

    PubMed Central

    Geprägs, Stephan; Kehlberger, Andreas; Coletta, Francesco Della; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E. W.; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T. B.; Kläui, Mathias

    2016-01-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE. PMID:26842873

  3. Origin of the spin Seebeck effect in compensated ferrimagnets.

    PubMed

    Geprgs, Stephan; Kehlberger, Andreas; Coletta, Francesco Della; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E W; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T B; Klui, Mathias

    2016-01-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE. PMID:26842873

  4. Critical suppression of spin Seebeck effect by magnetic fields

    NASA Astrophysics Data System (ADS)

    Kikkawa, Takashi; Uchida, Ken-ichi; Daimon, Shunsuke; Qiu, Zhiyong; Shiomi, Yuki; Saitoh, Eiji

    2015-08-01

    The longitudinal spin Seebeck effect (LSSE) in Pt /Y3Fe5O12(YIG ) junction systems has been investigated at various magnetic fields and temperatures. We found that the LSSE voltage in a Pt/YIG-slab system is suppressed by applying high magnetic fields and this suppression is critically enhanced at low temperatures. The field-induced suppression of the LSSE in the Pt/YIG-slab system is too large at around room temperature to be explained simply by considering the effect of the Zeeman gap in magnon excitation. This result requires us to introduce a magnon-frequency-dependent mechanism into the scenario of LSSE; low-frequency magnons dominantly contribute to the LSSE. The magnetic field dependence of the LSSE voltage was observed to change by changing the thickness of YIG, suggesting that the thermospin conversion by the low-frequency magnons is suppressed in thin YIG films due to the long characteristic lengths of such magnons.

  5. Spectral characteristics of time resolved magnonic spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Etesami, S. R.; Chotorlishvili, L.; Berakdar, J.

    2015-09-01

    Spin Seebeck effect (SSE) holds promise for new spintronic devices with low-energy consumption. The underlying physics, essential for a further progress, is yet to be fully clarified. This study of the time resolved longitudinal SSE in the magnetic insulator yttrium iron garnet concludes that a substantial contribution to the spin current stems from small wave-vector subthermal exchange magnons. Our finding is in line with the recent experiment by S. R. Boona and J. P. Heremans [Phys. Rev. B 90, 064421 (2014)]. Technically, the spin-current dynamics is treated based on the Landau-Lifshitz-Gilbert equation also including magnons back-action on thermal bath, while the formation of the time dependent thermal gradient is described self-consistently via the heat equation coupled to the magnetization dynamics.

  6. Thermoelectric Seebeck effect in oxide-based resistive switching memory

    PubMed Central

    Wang, Ming; Bi, Chong; Li, Ling; Long, Shibing; Liu, Qi; Lv, Hangbing; Lu, Nianduan; Sun, Pengxiao; Liu, Ming

    2014-01-01

    Reversible resistive switching induced by an electric field in oxide-based resistive switching memory shows a promising application in future information storage and processing. It is believed that there are some local conductive filaments formed and ruptured in the resistive switching process. However, as a fundamental question, how electron transports in the formed conductive filament is still under debate due to the difficulty to directly characterize its physical and electrical properties. Here we investigate the intrinsic electronic transport mechanism in such conductive filament by measuring thermoelectric Seebeck effects. We show that the small-polaron hopping model can well describe the electronic transport process for all resistance states, although the corresponding temperature-dependent resistance behaviours are contrary. Moreover, at low resistance states, we observe a clear semiconductor–metal transition around 150 K. These results provide insight in understanding resistive switching process and establish a basic framework for modelling resistive switching behaviour. PMID:25141267

  7. Ultrafast Opto-thermal measurements of spin-Seebeck effect

    NASA Astrophysics Data System (ADS)

    Giles, Brandon; Yang, Zihao; Kent, Thomas; Myers, Roberto

    2014-03-01

    The spin-Seebeck effect (SSE) remains one of the most intriguing and potentially useful spin-thermal phenomena of the last decade. In conjunction with the inverse-spin hall effect, the SSE results in the generation of an electric potential from a thermally-induced spin current. It has been reported in magnetic metals, semiconductors, and insulators and has been measured in a variety of different configurations, most recently in the opto-thermal setup reported by Weiller. In this method a laser pulse generates a temperature gradient that induces a spin current to flow from an insulating ferromagnet into a spin Hall metal, thereby inducing a transverse voltage. The underlying physics of the SSE remain somewhat elusive, although theoretical work explains that the SSE develops due to temperature gradients between the local magnon, phonon and electron populations within the magnetic material. We attempt to clarify the physics by presenting the first SSE induced transient electric current measurements from a custom built cryogenic opto-thermal setup. Single femtosecond laser pulses are used to generate transient thermal gradients allowing insight to the time-dependence of the SSE. Photo-carrier effects on SSE materials acquired by systematically tuning the wavelength of the femtosecond laser above the bandgap of the material will also be reported.

  8. Theory of the spin Seebeck effect in antiferromagnets

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Rodrguez-Surez, R. L.; Azevedo, A.

    2016-01-01

    The spin Seebeck effect (SSE) consists in the generation of a spin current by a temperature gradient applied in a magnetic film. The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film resulting from the conversion of the spin current into charge current by means of the inverse spin Hall effect. The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin-orbit coupling such as platinum. Recently the SSE has been observed in bilayers made of the antiferromagnet Mn F2 and Pt, revealing dependences of the SSE voltage on temperature and field very different from the ones observed in YIG/Pt. Here we present a theory for the SSE in structures with an antiferromagnetic insulator (AFI) in contact with a normal metal (NM) that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the AFI/NM bilayer. The theory explains quite well the measured dependences of the SSE voltage on the sample temperature and on the applied magnetic field in Mn F2/Pt .

  9. Magneto-Seebeck effect in spin-valve with in-plane thermal gradient

    SciTech Connect

    Jain, S. Bose, A. Palkar, V. R. Tulapurkar, A. A.; Lam, D. D. Suzuki, Y.; Sharma, H. Tomy, C. V.

    2014-12-15

    We present measurements of magneto-Seebeck effect on a spin valve with in-plane thermal gradient. We measured open circuit voltage and short circuit current by applying a temperature gradient across a spin valve stack, where one of the ferromagnetic layers is pinned. We found a clear hysteresis in these two quantities as a function of magnetic field. From these measurements, the magneto-Seebeck effect was found to be same as magneto-resistance effect.

  10. Large spin Seebeck effects in zigzag-edge silicene nanoribbons

    SciTech Connect

    Yang, Xi-Feng; Liu, Yu-Shen Feng, Jin-Fu; Wang, Xue-Feng

    2014-08-15

    Using the first-principles methods, we investigate the thermospin properties of a two-probe model based on zigzag-edge silicene nanoribbons (ZSiNRs). Compared with the odd-width ZSiNRs, the spin Seebeck coefficient of the even-width ZSiNRs is obviously enhanced at room temperature. This fact is attributed to a nearly perfect symmetry of the linear conductance gap with the different spin index with respect to the Fermi level induced by the different parity of the wave functions. More interestingly, the corresponding charge Seebeck coefficient is near zero. Therefore, when a thermal bias is presented in the even-width ZSiNRs, a nearly pure spin current is achieved. Meanwhile, the spin polarization of the current approaches infinite.

  11. Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads

    SciTech Connect

    Zhou, Benhu Zeng, Yangsu; Zhou, Benliang; Zhou, Guanghui; Ouyang, Tao

    2015-03-14

    We theoretically investigate spin-dependent Seebeck effects for a system consisting of a narrow graphene nanoribbon (GNR) contacted to square lattice ferromagnetic (FM) electrodes with noncollinear magnetic moments. Both zigzag-edge graphene nanoribbons (ZGNRs) and armchair-edge graphene nanoribbons (AGNRs) were considered. Compared with our previous work with two-dimensional honeycomb-lattice FM leads, a more realistic model of two-dimensional square-lattice FM electrodes is adopted here. Using the nonequilibrium Green's function method combining with the tight-binding Hamiltonian, it is demonstrated that both the charge Seebeck coefficient S{sub C} and the spin-dependent Seebeck coefficient S{sub S} strongly depend on the geometrical contact between the GNR and the leads. In our previous work, S{sub C} for a semiconducting 15-AGNR system near the Dirac point is two orders of magnitude larger than that of a metallic 17-AGNR system. However, S{sub C} is the same order of magnitude for both metallic 17-AGNR and semiconducting 15-AGNR systems in the present paper because of the lack of a transmission energy gap for the 15-AGNR system. Furthermore, the spin-dependent Seebeck coefficient S{sub S} for the systems with 20-ZGNR, 17-AGNR, and 15-AGNR is of the same order of magnitude and its maximum absolute value can reach 8??V/K. The spin-dependent Seebeck effects are not very pronounced because the transmission coefficient weakly depends on spin orientation. Moreover, the spin-dependent Seebeck coefficient is further suppressed with increasing angle between the relative alignments of magnetization directions of the two leads. Additionally, the spin-dependent Seebeck coefficient can be strongly suppressed for larger disorder strength. The results obtained here may provide valuable theoretical guidance in the experimental design of heat spintronic devices.

  12. Molecular Dependence of the Large Seebeck Effect in ?-Type Organic Conductors

    NASA Astrophysics Data System (ADS)

    Aizawa, Hirohito; Kuroki, Kazuhiko; Yoshino, Harukazu; Mousdis, George A.; Papavassiliou, George C.; Murata, Keizo

    2014-10-01

    We study the Seebeck effect in the ?-type organic conductors, ?-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y and ?-(P-S,S-DMEDT-TTF)2(AuBr2)1+y, where EDO-S,S-DMEDT-TTF and P-S,S-DMEDT-TTF are abbreviated as OOSS and NNSS, respectively, both experimentally and theoretically. Theoretically in particular, we perform first-principles band calculation for the two materials and construct a two-orbital model, on the basis of which we calculate the Seebeck coefficient. We show that the calculated temperature dependence of the Seebeck coefficient S is semi-quantitatively consistent with the experimental observation. In both materials, the absolute value of the Seebeck coefficient is maximum at a certain temperature, and this temperature is lower for NNSS than for OOSS. From a band structure viewpoint, we find that this can be traced back to the narrowness of the band gap between the upper and the lower pudding-mold type bands. On the other hand, the Seebeck coefficient of NNSS in the low temperature regime steeply increases with increasing temperature, which is due to the narrowness of the upper band. These differences in thermoelectric properties demonstrate the effectiveness of controlling the band structure through molecular modification.

  13. Enhancement of Seebeck Coefficient in Bi Nanowires by Electric Field Effect

    NASA Astrophysics Data System (ADS)

    Komine, Takashi; Aono, Tomosuke; Nabatame, Yuta; Murata, Masayuki; Hasegawa, Yasuhiro

    2016-03-01

    In this study, we investigated the electric field effect on the transport properties of a Bi nanowire. These effects were modeled by a surface potential. The electron states of Bi nanowires were numerically analyzed by effective mass equations at the T-point and L-point taking into account surface potential due to an external electric field. The Seebeck coefficients of Bi nanowires were calculated by using the Boltzmann equation with a constant relaxation time. It was found that the Seebeck coefficients increased when the sign of the surface potential parameter was negative. In particular, when the surface potential parameter was -1 eV and the skin depth was 10 nm in a 20-nm-diameter nanowire, the maximum absolute value of the Seebeck coefficient was larger than 1 mV/K, which was greatly improved compared to that without an external electric field.

  14. Nernst and Seebeck effects in HgTe/CdTe topological insulator

    NASA Astrophysics Data System (ADS)

    Zhang, Yuan; Song, Juntao; Li, Yu-Xian

    2015-03-01

    The Seebeck and Nernst effects in HgTe/CdTe quantum wells are studied using the tight-binding Hamiltonian and the nonequilibrium Green's function method. The Seebeck coefficient, Sc, and the Nernst coefficient, Nc, oscillate as a function of EF, where EF is the Fermi energy. The Seebeck coefficient shows peaks when the Fermi energy crosses the discrete transverse channels, and the height of the nth peak of the Sc is [ln2 /(1/2 +|n |)] for EF > 0. For the case EF < 0, the values of the peaks are negative, but the absolute values of the first five peaks are the same as those for EF > 0. The 6th peak of Sc reaches the value [ln2 /1.35 ] due to a higher density of states. When a magnetic field is applied, the Nernst coefficient appears. However, the values of the peaks for Nc are all positive. For a weak magnetic field, the temperature suppresses the oscillation of the Seebeck and Nernst coefficients but increases their magnitude. For a large magnetic field, because of the highly degenerate Landau levels, the peaks of the Seebeck coefficient at position EF=-12 , 10 , 28 meV , and Nernst coefficient at EF=-7 , 10 meV are robust against the temperature.

  15. Photo-Seebeck effect in tetragonal PbO single crystals

    SciTech Connect

    Mondal, P. S.; Okazaki, R.; Taniguchi, H.; Terasaki, I.

    2013-11-07

    We report the observation of photo-Seebeck effect in tetragonal PbO crystals. The photo-induced carriers contribute to the transport phenomena, and consequently the electrical conductivity increases and the Seebeck coefficient decreases with increasing photon flux density. A parallel-circuit model is used to evaluate the actual contributions of photo-excited carriers from the measured transport data. The photo-induced carrier concentration estimated from the Seebeck coefficient increases almost linearly with increasing photon flux density, indicating a successful photo-doping effect on the thermoelectric property. The mobility decreases by illumination but the reduction rate strongly depends on the illuminated photon energy. Possible mechanisms of such photon-energy-dependent mobility are discussed.

  16. Separation of spin Seebeck effect and anomalous Nernst effect in Co/Cu/YIG

    SciTech Connect

    Tian, Dai; Li, Yufan; Qu, D.; Chien, C. L.; Jin, Xiaofeng

    2015-05-25

    The spin Seebeck effect (SSE) and Anomalous Nernst effect (ANE) have been observed in Co/Cu/YIG (yttrium iron garnet) multi-layer structure, where the ferromagnetic insulator YIG acts as the pure spin injector and the ferromagnetic metal Co layer acts as the spin current detector. With the insertion of 5?nm Cu layer, the two ferromagnetic layers are decoupled, thus allowing unambiguous separation of the SSE and ANE contributions under the same experimental conditions in the same sample.

  17. Separation of spin Seebeck effect and anomalous Nernst effect in Co/Cu/YIG

    NASA Astrophysics Data System (ADS)

    Tian, Dai; Li, Yufan; Qu, D.; Jin, Xiaofeng; Chien, C. L.

    2015-05-01

    The spin Seebeck effect (SSE) and Anomalous Nernst effect (ANE) have been observed in Co/Cu/YIG (yttrium iron garnet) multi-layer structure, where the ferromagnetic insulator YIG acts as the pure spin injector and the ferromagnetic metal Co layer acts as the spin current detector. With the insertion of 5 nm Cu layer, the two ferromagnetic layers are decoupled, thus allowing unambiguous separation of the SSE and ANE contributions under the same experimental conditions in the same sample.

  18. Transverse spin Seebeck effect versus anomalous and planar Nernst effects in Permalloy thin films.

    PubMed

    Schmid, M; Srichandan, S; Meier, D; Kuschel, T; Schmalhorst, J-M; Vogel, M; Reiss, G; Strunk, C; Back, C H

    2013-11-01

    Transverse magnetothermoelectric effects are studied in Permalloy thin films grown on MgO and GaAs substrates and compared to those grown on suspended SiN(x) membranes. The transverse voltage along platinum strips patterned on top of the Permalloy films is measured versus the external magnetic field as a function of the angle and temperature gradients. After the identification of the contribution of the planar and anomalous Nernst effects, we find an upper limit for the transverse spin Seebeck effect, which is several orders of magnitude smaller than previously reported. PMID:24237554

  19. Nernst and Seebeck effects in HgTe/CdTe topological insulator

    SciTech Connect

    Zhang, Yuan; Song, Juntao; Li, Yu-Xian

    2015-03-28

    The Seebeck and Nernst effects in HgTe/CdTe quantum wells are studied using the tight-binding Hamiltonian and the nonequilibrium Green's function method. The Seebeck coefficient, S{sub c}, and the Nernst coefficient, N{sub c}, oscillate as a function of E{sub F}, where E{sub F} is the Fermi energy. The Seebeck coefficient shows peaks when the Fermi energy crosses the discrete transverse channels, and the height of the nth peak of the S{sub c} is [ln2/(1/2 +|n|)] for E{sub F} > 0. For the case E{sub F} < 0, the values of the peaks are negative, but the absolute values of the first five peaks are the same as those for E{sub F} > 0. The 6th peak of S{sub c} reaches the value [ln2/1.35] due to a higher density of states. When a magnetic field is applied, the Nernst coefficient appears. However, the values of the peaks for N{sub c} are all positive. For a weak magnetic field, the temperature suppresses the oscillation of the Seebeck and Nernst coefficients but increases their magnitude. For a large magnetic field, because of the highly degenerate Landau levels, the peaks of the Seebeck coefficient at position E{sub F}=−12, 10, 28meV, and Nernst coefficient at E{sub F}=−7, 10meV are robust against the temperature.

  20. Extracting the effective mass of electrons in transparent conductive oxide thin films using Seebeck coefficient

    SciTech Connect

    Wang, Yaqin; Zhu, Junhao; Tang, Wu

    2014-05-26

    A method is proposed that combines Seebeck coefficient and carrier concentration to determine the electron effective mass of transparent conductive oxide (TCO) thin films. Experiments were conducted to test the validity of this approach on the transparent conductive Ga-doped ZnO thin films deposited by magnetron sputtering. An evident agreement of the calculated electron effective mass of the films is observed between the proposed approach and the previous studies. Besides, the optical carrier concentration and mobility derived from the calculated electron effective mass and spectroscopic ellipsometry using a complex dielectric function are consistent with those from direct Hall-effect measurement. The agreements suggest that Seebeck coefficient can serve as an alternative tool for extracting the effective mass of electrons in TCO films.

  1. On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect

    PubMed Central

    Boehnke, Alexander; Milnikel, Marius; von der Ehe, Marvin; Franz, Christian; Zbarsky, Vladyslav; Czerner, Michael; Rott, Karsten; Thomas, Andy; Heiliger, Christian; Reiss, Günter; Münzenberg, Markus

    2015-01-01

    Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a ”green” information technology. However, up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect. Here, we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic “1” state and off to “0” by simply changing the magnetic state of the CoFeB electrodes. This new functionality is achieved by combining a thermal gradient and an electric field. Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence, the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and energy-dependent transmission of electrons in the junction, the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration. Moreover, our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage, which are predicted for specific Co-Fe compositions. PMID:25755010

  2. On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect.

    PubMed

    Boehnke, Alexander; Milnikel, Marius; von der Ehe, Marvin; Franz, Christian; Zbarsky, Vladyslav; Czerner, Michael; Rott, Karsten; Thomas, Andy; Heiliger, Christian; Reiss, Gnter; Mnzenberg, Markus

    2015-01-01

    Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a "green" information technology. However, up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect. Here, we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic "1" state and off to "0" by simply changing the magnetic state of the CoFeB electrodes. This new functionality is achieved by combining a thermal gradient and an electric field. Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence, the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and energy-dependent transmission of electrons in the junction, the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration. Moreover, our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage, which are predicted for specific Co-Fe compositions. PMID:25755010

  3. On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect

    NASA Astrophysics Data System (ADS)

    Boehnke, Alexander; Milnikel, Marius; von der Ehe, Marvin; Franz, Christian; Zbarsky, Vladyslav; Czerner, Michael; Rott, Karsten; Thomas, Andy; Heiliger, Christian; Reiss, Günter; Münzenberg, Markus

    2015-03-01

    Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a ''green'' information technology. However, up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect. Here, we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic ``1'' state and off to ``0'' by simply changing the magnetic state of the CoFeB electrodes. This new functionality is achieved by combining a thermal gradient and an electric field. Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence, the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and energy-dependent transmission of electrons in the junction, the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration. Moreover, our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage, which are predicted for specific Co-Fe compositions.

  4. Comparison of the magneto-Peltier and magneto-Seebeck effects in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Shan, J.; Dejene, F. K.; Leutenantsmeyer, J. C.; Flipse, J.; Mnzenberg, M.; van Wees, B. J.

    2015-07-01

    Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction varies as the magnetic configuration changes from a parallel (P) to an antiparallel (AP) configuration. Here we report a study on its reciprocal effect, the magneto-Peltier effect, where the heat flow carried by the tunneling electrons is altered by changing the magnetic configuration of the MTJ. The magneto-Peltier signal that reflects the change in the temperature difference across the junction between the P and AP configurations scales linearly with the applied current in the small bias but is greatly enhanced in the large-bias regime, due to higher-order Joule heating mechanisms. By carefully extracting the linear response which reflects the magneto-Peltier effect, and comparing it with the magneto-Seebeck measurements performed on the same device, we observe results consistent with Onsager reciprocity. We estimate a magneto-Peltier coefficient of 13.4 mV in the linear regime using a three-dimensional thermoelectric model. Our result opens up the possibility of programmable thermoelectric devices based on the Peltier effect in MTJs.

  5. Spin-resolved Fano resonances induced large spin Seebeck effects in graphene-carbon-chain junctions

    SciTech Connect

    Liu, Yu-Shen; Zhang, Xue; Feng, Jin-Fu; Wang, Xue-Feng

    2014-06-16

    We propose a high-efficiency thermospin device constructed by a carbon atomic chain sandwiched between two ferromagnetic (FM) zigzag graphene nanoribbon electrodes. In the low-temperature regime, the magnitude of the spin figure of merit is nearly equal to that of the corresponding charge figure of merit. This is attributed to the appearances of spin-resolved Fano resonances in the linear conductance spectrum resulting from the quantum interference effects between the localized states and the expanded states. The spin-dependent Seebeck effect is obviously enhanced near these Fano resonances with the same spin index; meanwhile, the Seebeck effect of the other spin component has a smaller value due to the smooth changing of the linear conductance with the spin index. Thus, a large spin Seebeck effect is achieved, and the magnitude of the spin figure of merit can reach 1.2 at T = 25 K. Our results indicate that the FM graphene-carbon-chain junctions can be used to design the high-efficiency thermospin devices.

  6. The Third Way of Thermal-Electric Conversion beyond Seebeck and Pyroelectric Effects

    SciTech Connect

    Ren, Jie

    2014-02-14

    Thermal-electric conversion is crucial for smart energy control and harvesting, such as thermal sensing and waste heat recovering. So far, people are aware of only two ways of direct thermal-electric conversion, Seebeck and pyroelectric effects, each with distinct working conditions and limitations. Here, we report the third way of thermal-electric conversion beyond Seebeck and pyroelectric effects. In contrast to Seebeck effect that requires spatial temperature difference, the-third-way converts the time-dependent ambient temperature fluctuation into electricity, similar to the behavior of pyroelectricity. However, the-third-way is also distinct from pyroelectric effect in the sense that it does not require polar materials but applies to general conducting systems. We demonstrate that the-third-way results from the temperature-fluctuation-induced dynamical charge redistribution. It is a consequence of the fundamental nonequilibrium thermodynamics and has a deep connection to the topological phase in quantum mechanics. Our findings expand our knowledge and provide new means of thermal-electric energy harvesting.

  7. Unconventional scaling and significant enhancement of the spin Seebeck effect in multilayers

    NASA Astrophysics Data System (ADS)

    Ramos, R.; Kikkawa, T.; Aguirre, M. H.; Lucas, I.; Anadn, A.; Oyake, T.; Uchida, K.; Adachi, H.; Shiomi, J.; Algarabel, P. A.; Morelln, L.; Maekawa, S.; Saitoh, E.; Ibarra, M. R.

    2015-12-01

    Spin Seebeck effects (SSEs) have been investigated in highly crystalline magnetic multilayer [Fe3O4/Pt] n films. Voltage as well as power generated by the SSE were found to be significantly enhanced with increasing the number of layers n . This voltage enhancement defies the simple understanding of the SSE and suggests that spin current flowing between the magnetic layers in the thickness direction plays an important role in multilayer SSE systems and the observed voltage enhancement.

  8. Magneto-Seebeck effect in R FeAsO (R =rare earth) compounds: Probing the magnon drag scenario

    NASA Astrophysics Data System (ADS)

    Caglieris, F.; Braggio, A.; Pallecchi, I.; Provino, A.; Pani, M.; Lamura, G.; Jost, A.; Zeitler, U.; Galleani D'Agliano, E.; Manfrinetti, P.; Putti, M.

    2014-10-01

    We investigate the Seebeck effect in R FeAsO (R =rare earth) compounds as a function of temperature and magnetic field up to 30 T. The Seebeck curves are characterized by a broad negative bump around 50 K, which is sample dependent and strongly enhanced by the application of a magnetic field. A model for the temperature and field dependence of the magnon drag contribution to the Seebeck effect by antiferromagnetic (AFM) spin fluctuation is developed. It accounts for the magnitude and scaling properties of such bump feature in our experimental data in LaFeAsO. This analysis accounts for the apparent inconsistency of literature Seebeck effect data on these compounds and has the potential to extract precious information on the coupling between electrons and AFM spin fluctuations in these parent compound systems, with implications on the pairing mechanism of the related superconducting compounds.

  9. Observation of inverse spin Hall effect in ferromagnetic FePt alloys using spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Seki, Takeshi; Uchida, Ken-ichi; Kikkawa, Takashi; Qiu, Zhiyong; Saitoh, Eiji; Takanashi, Koki

    2015-08-01

    We experimentally observed the inverse spin Hall effect (ISHE) of ferromagnetic FePt alloys. Spin Seebeck effect due to the temperature gradient generated the spin current (Js) in the FePt|Y3Fe5O12 (YIG) structure, and Js was injected from YIG to FePt and converted to the charge current through ISHE of FePt. The significant difference in magnetization switching fields for FePt and YIG led to the clear separation of the voltage of ISHE from that of anomalous Nernst effect in FePt. We also investigated the effect of ordering of FePt crystal structure on the magnitude of ISHE voltage in FePt.

  10. Seebeck coefficient of one electron

    SciTech Connect

    Durrani, Zahid A. K.

    2014-03-07

    The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ?T between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ?T are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ?T, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

  11. Effect of phonon transport on the Seebeck coefficient and thermal conductivity of silicon nanowire arrays

    NASA Astrophysics Data System (ADS)

    Sadhu, Jyothi Swaroop

    Thermoelectrics enable solid-state conversion of heat to electricity by the Seebeck effect, but must provide scalable and cost-effective technology for practical waste heat harvesting. This dissertation explores the thermoelectric properties of electrochemically etched silicon nanowires through experiments, complemented by charge and thermal transport theories. Electrolessly etched silicon nanowires show anomalously low thermal conductivity that has been attributed to the increased scattering of heat conducting phonons from the surface disorder introduced by etching. The reduction is below the incoherent limit for phonon scattering at the boundary, the so-called Casimir limit. A new model of partially coherent phonon transport shows that correlated multiple scattering of phonons off resonantly matched rough surfaces can indeed lead to thermal conductivity below the Casimir limit. Using design guidelines from the theory, silicon nanowires of controllable surface roughness are fabricated using metal-assisted chemical etching. Extensive characterization of the nanowire surfaces using transmission electron microscopy provides surface roughness parameters that are important in testing transport theories. The second part of the dissertation focuses on the implications of increased phonon scattering on the Seebeck coefficient, which is a cumulative effect of non-equilibrium amongst charge carriers and phonons. A novel frequency-domain technique enables simultaneous measurements of the Seebeck coefficient and the thermal conductivity of nanowire arrays. The frequency response measurements isolate the parasitic contributions thus improving upon existing techniques for cross-plane thermoelectric measurements. While the thermal conductivity of nanowires reduces significantly with increased roughness, there is also a significant reduction in the Seebeck coefficient over a wide range of doping. Theoretical fitting of the data reveals that such reduction results from the annihilation of phonon drag in nanowires due to phonon boundary scattering. By exploring the effect of surface roughness and employing lattice non-equilibrium theories, the measurements are able to distinguish between long wavelength phonons that contribute to phonon drag and shorter wavelengths that contribute to heat conduction near room temperature. Phonon drag quenching in nanostructures has implications beyond silicon and this thesis paves the way toward spectrally selective phonon scattering for improving nanoscale thermoelectrics.

  12. Spin-dependent Seebeck effect and spin caloritronics in magnetic graphene

    NASA Astrophysics Data System (ADS)

    Rameshti, Babak Zare; Moghaddam, Ali G.

    2015-04-01

    We investigate the spin-dependent thermoelectric effects in magnetic graphene in both diffusive and ballistic regimes. Employing the Boltzmann and Landauer formalisms we calculate the spin and charge Seebeck coefficients (thermopower) in magnetic graphene varying the spin splitting, temperature, and doping of the junction. It is found that while in normal graphene the temperature gradient drives a charge current, in the case of magnetic graphene a significant spin current is also established. In particular we show that in the undoped magnetic graphene in which different spin carriers belong to conduction and valence bands, a pure spin current is driven by the temperature gradient. In addition it is revealed that profound thermoelectric effects can be achieved at intermediate easily accessible temperatures when the thermal energy is comparable with Fermi energy kBT ?? . By further investigation of the spin-dependent Seebeck effect and a significantly large figure of merit for spin thermopower ZspT , we suggest magnetic graphene as a promising material for spin-caloritronics studies and applications.

  13. Enhanced spin Seebeck effect in a germanene p-n junction

    SciTech Connect

    Zheng, Jun; Chi, Feng; Guo, Yong

    2014-12-28

    Spin Seebeck effect in a germanene p-n junction is studied by using the nonequilibrium Green's function method combined with the tight-binding Hamiltonian. We find that the thermal bias ?T can generate spin thermopower when a local exchange field is applied on one edge of the germanene nano-ribbon. The magnitude of the spin thermopower can be modulated by the potential drop across the two terminals of the p-n junction. When the value of the potential drop is smaller than the spin-orbit interaction strength, the spin thermopower is enhanced by two orders of magnitude larger as compared to the case of zero p-n voltage. Optimal temperature corresponding to maximum spin thermopower is insensitive to the potential drop. In the p-n region, maximum spin thermopower can be obtained at relatively higher temperatures. When the value of the potential drop is larger than that of the spin-orbit interaction, however, the spin Seebeck effect decays rapidly with increasing potential drop or temperature. By optimizing the structure parameters, the magnitude of the spin thermopower can be remarkably enhanced due to the coexistence of the exchange field and the potential drop.

  14. Enhanced spin Seebeck effect in a germanene p-n junction

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Chi, Feng; Guo, Yong

    2014-12-01

    Spin Seebeck effect in a germanene p-n junction is studied by using the nonequilibrium Green's function method combined with the tight-binding Hamiltonian. We find that the thermal bias ?T can generate spin thermopower when a local exchange field is applied on one edge of the germanene nano-ribbon. The magnitude of the spin thermopower can be modulated by the potential drop across the two terminals of the p-n junction. When the value of the potential drop is smaller than the spin-orbit interaction strength, the spin thermopower is enhanced by two orders of magnitude larger as compared to the case of zero p-n voltage. Optimal temperature corresponding to maximum spin thermopower is insensitive to the potential drop. In the p-n region, maximum spin thermopower can be obtained at relatively higher temperatures. When the value of the potential drop is larger than that of the spin-orbit interaction, however, the spin Seebeck effect decays rapidly with increasing potential drop or temperature. By optimizing the structure parameters, the magnitude of the spin thermopower can be remarkably enhanced due to the coexistence of the exchange field and the potential drop.

  15. Spin Seebeck Effect vs. Anomalous Nernst Effect in Ta/CoFeB /Ta Structures

    NASA Astrophysics Data System (ADS)

    Yang, Bowen; Xu, Yadong; Schneider, Mike; Shi, Jing; Univ of California-Riverside Team; Everspin Technologies Inc. Team

    2014-03-01

    We have studied the spin Seebeck effect (SSE) and anomalous Nernst effect (ANE) in a vertical trilayer structure under a vertical temperature gradient. The structure consists of a 3nm CoFeB layer sandwiched by ?-phase tantalum (Ta) layers. The samples are deposited by magnetron sputtering. The existence of Ta ?-phase is verified by the resistivity and its negative temperature coefficient of resistance(TCR). Under a fixed vertical temperature gradient, the measured transverse thermoelectric voltage is linearly proportional to the total sample resistance when the Ta thickness exceeds 2 nm, which can be explained by a shunting resistor model. When the Ta thickness is below 2 nm, the voltage deviates from the linear resistance dependence and merges to the ANE voltage of the CoFeB single layer, due to a weakened inverse spin Hall effect (ISHE) in Ta thinner than the spin diffusion length. In the linear regime, the slope contains both a varying SSE and a fixed ANE responses, thus the SSE contribution could be quantitatively separated out from the ANE of CoFeB. Our results indicate a large SSE from the ?-phase Ta due to its large Spin Hall Angle. This work was supported by CNN/DMEA and DOE.

  16. Effect of the magnon dispersion on the longitudinal spin Seebeck effect in yttrium iron garnets

    NASA Astrophysics Data System (ADS)

    Jin, Hyungyu; Boona, Stephen R.; Yang, Zihao; Myers, Roberto C.; Heremans, Joseph P.

    2015-08-01

    We study the temperature dependence of the longitudinal spin Seebeck effect (LSSE) in an yttrium iron garnet Y3F e5O12 (YIG)/Pt system for samples of different thicknesses. In this system, the thermal spin torque is magnon driven. The LSSE signal peaks at a specific temperature that depends on the YIG sample thickness. We also observe freeze-out of the LSSE signal at high magnetic fields, which we attribute to the opening of an energy gap in the magnon dispersion. We observe partial freeze-out of the LSSE signal even at room temperature, where kBT is much larger than the gap. This suggests that a subset of the magnon population with an energy below kBTC (TC40 K ) contributes disproportionately to the LSSE; at temperatures above TC, we label these magnons subthermal magnons. The T dependence of the LSSE at temperatures below the maximum is interpreted in terms of an empirical model that ascribes most of the temperature dependence to that of the thermally driven magnon flux, which is related to the details of the magnon dispersion.

  17. Observation of longitudinal spin-Seebeck effect in cobalt-ferrite epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Niizeki, Tomohiko; Kikkawa, Takashi; Uchida, Ken-ichi; Oka, Mineto; Suzuki, Kazuya Z.; Yanagihara, Hideto; Kita, Eiji; Saitoh, Eiji

    2015-05-01

    The longitudinal spin-Seebeck effect (LSSE) has been investigated in cobalt ferrite (CFO), an exceptionally hard magnetic spinel ferrite. A bilayer of a polycrystalline Pt and an epitaxially-strained CFO(110) exhibiting an in-plane uniaxial anisotropy was prepared by reactive rf sputtering technique. Thermally generated spin voltage in the CFO layer was measured via the inverse spin-Hall effect in the Pt layer. External-magnetic-field (H) dependence of the LSSE voltage (VLSSE) in the Pt/CFO(110) sample with H ? [001] was found to exhibit a hysteresis loop with a high squareness ratio and high coercivity, while that with H ? [ 1 1 0 ] shows a nearly closed loop, reflecting the different anisotropies induced by the epitaxial strain. The magnitude of VLSSE has a linear relationship with the temperature difference (?T), giving the relatively large VLSSE /?T of about 3 ?V/K for CFO(110) which was kept even at zero external field.

  18. Investigation of the magnetic properties of insulating thin films using the longitudinal spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Kehlberger, A.; Jakob, G.; Onbasli, M. C.; Kim, D. H.; Ross, C. A.; Klui, M.

    2014-05-01

    The longitudinal spin Seebeck effect is used as a detector for the magnetic properties and switching characteristics of magnetic thin insulating films. We use a 300 nm and a 20 nm thick Yttrium Iron Garnet (YIG, Y3Fe5O12) film prepared by pulsed laser deposition and afterwards coated by platinum for the detection of the thermally excited magnons by the inverse spin Hall effect. The inverse spin Hall signals reveal a magnetic uniaxial anisotropy along the direction of the platinum stripe in the thicker film. For the thin film we find a more isotropic behavior, which is complementarily observed using the magnetoresistance occurring at the platinum/YIG interface. We explain our results on the basis of x-ray diffraction data, which reveal a miscut of the substrate and film surface and an expansion of the YIG lattice. Both findings favor a growth-induced magnetic anisotropy that we observe.

  19. Investigation of the magnetic properties of insulating thin films using the longitudinal spin Seebeck effect

    SciTech Connect

    Kehlberger, A. Jakob, G.; Klui, M.; Onbasli, M. C.; Kim, D. H.; Ross, C. A.

    2014-05-07

    The longitudinal spin Seebeck effect is used as a detector for the magnetic properties and switching characteristics of magnetic thin insulating films. We use a 300 nm and a 20?nm thick Yttrium Iron Garnet (YIG, Y{sub 3}Fe{sub 5}O{sub 12}) film prepared by pulsed laser deposition and afterwards coated by platinum for the detection of the thermally excited magnons by the inverse spin Hall effect. The inverse spin Hall signals reveal a magnetic uniaxial anisotropy along the direction of the platinum stripe in the thicker film. For the thin film we find a more isotropic behavior, which is complementarily observed using the magnetoresistance occurring at the platinum/YIG interface. We explain our results on the basis of x-ray diffraction data, which reveal a miscut of the substrate and film surface and an expansion of the YIG lattice. Both findings favor a growth-induced magnetic anisotropy that we observe.

  20. Bose-Einstein condensation of magnons pumped by the bulk spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Tserkovnyak, Yaroslav; Bender, Scott A.; Duine, Rembert A.; Flebus, Benedetta

    2016-03-01

    We propose inducing Bose-Einstein condensation of magnons in a magnetic insulator by a heat flow oriented toward its boundary. At a critical heat flux, the oversaturated thermal gas of magnons accumulated at the boundary precipitates the condensate, which then grows gradually as the thermal bias is dialed up further. The thermal magnons thus pumped by the magnonic bulk (spin) Seebeck effect must generally overcome both the local Gilbert damping associated with the coherent magnetic dynamics as well as the radiative spin-wave losses toward the magnetic bulk, in order to achieve the threshold of condensation. We quantitatively estimate the requisite bias in the case of the ferrimagnetic yttrium iron garnet, discuss different physical regimes of condensation, and contrast it with the competing (so-called Doppler-shift) bulk instability.

  1. Robust longitudinal spin-Seebeck effect in Bi-YIG thin films

    NASA Astrophysics Data System (ADS)

    Siegel, Gene; Prestgard, Megan Campbell; Teng, Shiang; Tiwari, Ashutosh

    2014-03-01

    In recent years, the coupling of magnetic insulators (bismuth-doped yttrium iron garnet, Bi-YIG) with platinum has garnered significant interest in spintronics research due to applicability as spin-current-driven thermoelectric coatings. These coatings bridge the gap between spintronics technologies and thermoelectric materials, providing a novel means of transforming waste heat into electricity. However, there remain questions regarding the origins of the spin-Seebeck effect (SSE) as well as claims that observed effects are a manifestation of magnetic proximity effects, which would induce magnetic behavior in platinum. Herewith we provide support that the voltages observed in the Bi-YIG/Pt films are purely SSE voltages. We reaffirm claims that magnon transport theory provides an ample basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed-laser deposition, as these Bi-YIG films possess large SSE voltages (even in absence of an external magnetic field), as much as twice those of films fabricated via solution-based methods.

  2. Robust longitudinal spin-Seebeck effect in Bi-YIG thin films

    PubMed Central

    Siegel, Gene; Prestgard, Megan Campbell; Teng, Shiang; Tiwari, Ashutosh

    2014-01-01

    In recent years, the coupling of magnetic insulators (bismuth-doped yttrium iron garnet, Bi-YIG) with platinum has garnered significant interest in spintronics research due to applicability as spin-current-driven thermoelectric coatings. These coatings bridge the gap between spintronics technologies and thermoelectric materials, providing a novel means of transforming waste heat into electricity. However, there remain questions regarding the origins of the spin-Seebeck effect (SSE) as well as claims that observed effects are a manifestation of magnetic proximity effects, which would induce magnetic behavior in platinum. Herewith we provide support that the voltages observed in the Bi-YIG/Pt films are purely SSE voltages. We reaffirm claims that magnon transport theory provides an ample basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed-laser deposition, as these Bi-YIG films possess large SSE voltages (even in absence of an external magnetic field), as much as twice those of films fabricated via solution-based methods. PMID:24651124

  3. Robust longitudinal spin-Seebeck effect in Bi-YIG thin films.

    PubMed

    Siegel, Gene; Prestgard, Megan Campbell; Teng, Shiang; Tiwari, Ashutosh

    2014-01-01

    In recent years, the coupling of magnetic insulators (bismuth-doped yttrium iron garnet, Bi-YIG) with platinum has garnered significant interest in spintronics research due to applicability as spin-current-driven thermoelectric coatings. These coatings bridge the gap between spintronics technologies and thermoelectric materials, providing a novel means of transforming waste heat into electricity. However, there remain questions regarding the origins of the spin-Seebeck effect (SSE) as well as claims that observed effects are a manifestation of magnetic proximity effects, which would induce magnetic behavior in platinum. Herewith we provide support that the voltages observed in the Bi-YIG/Pt films are purely SSE voltages. We reaffirm claims that magnon transport theory provides an ample basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed-laser deposition, as these Bi-YIG films possess large SSE voltages (even in absence of an external magnetic field), as much as twice those of films fabricated via solution-based methods. PMID:24651124

  4. Bulk magnon spin current theory for the longitudinal spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Rodríguez-Suárez, R. L.; Cunha, R. O.; López Ortiz, J. C.; Azevedo, A.

    2016-02-01

    The longitudinal spin Seebeck effect (LSSE) consists in the generation of a spin current parallel to a temperature gradient applied across the thickness of a bilayer made of a ferromagnetic insulator (FMI), such as yttrium iron garnet (YIG), and a metallic layer (ML) with strong spin orbit coupling, such as platinum. The LSSE is usually detected by a DC voltage generated along the ML due to the conversion of the spin current into a charge current perpendicular to the static magnetic field by means of the inverse spin Hall effect. Here we present a model for the LSSE that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the FMI. We show that the spin current pumped into the metallic layer by the magnon accumulation in the FMI provides continuity of the spin current at the FMI/ML interface and is essential for the existence of the LSSE. The results of the theory are in good agreement with experimental LSSE data in YIG/Pt bilayers on the variation of the DC voltage with the sample temperature, with the FMI layer thickness and with the intensity of high magnetic fields.

  5. Subthermal-magnon-driven longitudinal spin Seebeck effect in yttrium iron garnets (YIG)

    NASA Astrophysics Data System (ADS)

    Jin, Hyungyu; Boona, Stephen; Yang, Zihao; Myers, Roberto; Heremans, Joseph

    2015-03-01

    Since its discovery in 2008, the spin Seebeck effect (SSE) has intrigued many interesting research all around the world, which has led to the birth of a new field of research, called ``spin-caloritronics''. Of the two different experimental configurations used for detecting SSE, the longitudinal geometry (LSSE) seems to be generally accepted. The yttrium iron garnet (YIG) / Pt bilayer structure has been most commonly used for LSSE experiments because absence of electrons in YIG excludes contaminations from other thermomagnetic effects. The dependence of the LSSE on YIG film thickness and on temperature have been reported, but not yet both together. Here we present experimental data on the temperature dependence of LSSE in Pt/YIG below room temperature in systems in which the thickness of YIG varies. Detailed discussion is given on the experimental results, with emphasis on the role of subthermal-magnons in the temperature dependence of LSSE in the YIG/Pt system. Work supported by the AFOSR-MURI #FA9550-10-1-0533 and the ARO-MURI #W911NF-14-1-0016.

  6. Surface sensitivity of the spin Seebeck effect in the Pt/YIG system

    NASA Astrophysics Data System (ADS)

    Aqeel, Aisha; Vera-Marun, Ivan J.; van Wees, Bart J.; Palstra, Thomas T. M.

    2015-03-01

    It is well-known that the surface plays an important role in the spin Seebeck effect (SSE). However the effect of mechanical treatment on the SSE has not been systematically studied yet. Here, we have investigated the influence of the interface quality on the SSE in a bilayer system of platinum and yttrium iron garnet (Pt/YIG). The surfaces of the YIG crystals are modified by different types of mechanical polishing before Pt deposition for different samples. We observed that the magnitude and magnetic field dependence of the SSE is strongly influenced by mechanical treatment of the YIG surface. No definite relation has been found between the SSE response and the sample roughness. However, we observe a direct correlation between the saturation magnetic field (Hsat) of the SSE and the roughness of sample, as the former increases by moving from soft toward coarse particle polishing. The change in the magnitude of Hsat can be attributed to the presence of a perpendicular magnetic anisotropy due to the treatment induced surface strain or shape anisotropy in the Pt/YIG system.

  7. A novel strongly correlated electronic thin-film laser energy/power meter based on anisotropic Seebeck effect

    NASA Astrophysics Data System (ADS)

    Zhang, G.-Y.; Zhang, H.; Tan, S.-L.; Zhang, P.-X.; Tseng, T.-Y.; Habermeier, H.-U.; Lin, C.-T.; Singjai, P.

    2014-09-01

    Strongly correlated electronic (SCE) materials including high-temperature superconducting cuprate and colossal magnetoresistance manganite thin films demonstrate tremendous anisotropic Seebeck effect which makes them very promising for developing high-performance laser detectors. In this work, laser-induced thermoelectric voltage (LITV) signals with nanosecond response time have been measured in SCE La1- x Pb x MnO3 thin films based on anisotropic Seebeck effect at room temperature. The magnitude of the LITV signals increases linearly with laser energy/power density in a wide range of laser wavelengths from ultraviolet, visible to infrared based on which a novel SCE thin-film laser energy/power meter has been developed.

  8. Spin Seebeck effect and spin Hall magnetoresistance at high temperatures for a Pt/yttrium iron garnet hybrid structure

    NASA Astrophysics Data System (ADS)

    Wang, Shuanhu; Zou, Lvkuan; Zhang, Xu; Cai, Jianwang; Wang, Shufang; Shen, Baogen; Sun, Jirong

    2015-10-01

    Based on unique experimental setups, the temperature dependences of the longitudinal spin Seebeck effect (LSSE) and spin Hall magnetoresistance (SMR) of the Pt/yttrium iron garnet (Pt/YIG) hybrid structure are determined in a wide temperature range up to the Curie temperature of YIG. From a theoretical analysis of the experimental relationship between the SMR and temperature, the spin mixing conductance of the Pt/YIG interface is deduced as a function of temperature. Adopting the deduced spin mixing conductance, the temperature dependence of the LSSE is well reproduced based on the magnon spin current theory. Our research sheds new light on the controversy about the theoretical models for the LSSE.

  9. Spin-current Seebeck effect in an interacting quantum dot: Atomic approximation for the Anderson impurity model

    NASA Astrophysics Data System (ADS)

    Ramos, E.; Silva-Valencia, J.; Franco, R.; Siqueira, E. C.; Figueira, M. S.

    2015-11-01

    We study the spin-current Seebeck effect through an immersed gate defined quantum dot, employing the U-finite atomic method for the single impurity Anderson model. Our description qualitatively confirms some of the results obtained by an earlier Hartree-Fock work, but as our calculation includes the Kondo effect, some new features will appear in the spin-current Seebeck effect S, which as a function of the gate voltage present an oscillatory shape. At intermediate temperatures, our results show a three zero structure and at low temperatures, our results are governed by the emergence of the Kondo peak in the transmittance, which defines the behavior of the shape of the S coefficient as a function of the parameters of the model. The oscillatory behavior obtained by the Hartree-Fock approximation reproduces the shape obtained by us in a non-interacting system (U=0). The S sign is sensitive to different polarization of the quantum dot, and as a consequence the device could be employed to experimentally detect the polarization states of the system. Our results also confirm that the large increase of S upon increasing U, obtained by the mean field approximation, is correct only for low temperatures. We also discuss the role of the Kondo peak in defining the behavior of the spin thermopower at low temperatures.

  10. Effect of silicide/silicon hetero-junction structure on thermal conductivity and Seebeck coefficient.

    PubMed

    Choi, Wonchul; Park, Young-Sam; Hyun, Younghoon; Zyung, Taehyoung; Kim, Jaehyeon; Kim, Soojung; Jeon, Hyojin; Shin, Mincheol; Jang, Moongyu

    2013-12-01

    We fabricated a thermoelectric device with a silicide/silicon laminated hetero-structure by using RF sputtering and rapid thermal annealing. The device was observed to have Ohmic characteristics by I-V measurement. The temperature differences and Seebeck coefficients of the proposed silicide/silicon laminated and bulk structure were measured. The laminated thermoelectric device shows suppression of heat flow from the hot to cold side. This is supported by the theory that the atomic mass difference between silicide and silicon creates a scattering center for phonons. The major impact of our work is that phonon transmission is suppressed at the interface between silicide and silicon without degrading electrical conductivity. The estimated thermal conductivity of the 3-layer laminated device is 126.2 +/- 3.7 W/m. K. Thus, by using the 3-layer laminated structure, thermal conductivity is reduced by around 16% compared to bulk silicon. However, the Seebeck coefficient of the thermoelectric device is degraded compared to that of bulk silicon. It is understood that electrical conductivity is improved by using silicide as a scattering center. PMID:24266143

  11. Effect of Interstitial Mg in Mg2+ x Si on Electrical Conductivity and Seebeck Coefficient

    NASA Astrophysics Data System (ADS)

    Kubouchi, M.; Ogawa, Y.; Hayashi, K.; Takamatsu, T.; Miyazaki, Y.

    2016-03-01

    The crystal structure, thermoelectric properties, and microstructure of polycrystalline samples with nominal compositions Mg2+ x Si ( x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) have been investigated. It is revealed that the Mg2+ x Si samples were composites consisting of Mg2Si matrix with dispersed Mg metal. The Mg2Si crystals contained a small amount of Mg atoms at interstitial (1/2 1/2 1/2) site (Mgi). In addition, Mg metal was present at grain boundaries between Mg2Si crystal grains (MgGB). Regarding thermoelectric properties, the electrical conductivity and Seebeck coefficient of Mg2+ x Si were measured and their x dependences were discussed in terms of the amounts of Mgi and MgGB. The amount of MgGB and the electrical conductivity indicate quite similar x dependences.

  12. Generation of pure spin currents via spin Seebeck effect in self-biased hexagonal ferrite thin films

    SciTech Connect

    Li, Peng; Ellsworth, David; Chang, Houchen; Janantha, Praveen; Richardson, Daniel; Phillips, Preston; Vijayasarathy, Tarah; Wu, Mingzhong; Shah, Faisal

    2014-12-15

    Light-induced generation of pure spin currents in a Pt(2.5?nm)/BaFe{sub 12}O{sub 19}(1.2??m)/sapphire(0.5?mm) structure is reported. The BaFe{sub 12}O{sub 19} film had strong in-plane uniaxial anisotropy and was therefore self-biased. Upon exposure to light, a temperature difference (?T) was established across the BaFe{sub 12}O{sub 19} thickness that gave rise to a pure spin current in the Pt via the spin Seebeck effect. Via the inverse spin Hall effect, the spin current produced an electric voltage across one of the Pt lateral dimensions. The voltage varied with time in the same manner as ?T and flipped its sign when the magnetization in BaFe{sub 12}O{sub 19} was reversed.

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

    PubMed

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

    2015-01-01

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

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

    PubMed Central

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

    2015-01-01

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

  15. Half-metallic properties, single-spin negative differential resistance, and large single-spin Seebeck effects induced by chemical doping in zigzag-edged graphene nanoribbons

    SciTech Connect

    Yang, Xi-Feng; Zhou, Wen-Qian; Hong, Xue-Kun; Liu, Yu-Shen Feng, Jin-Fu; Wang, Xue-Feng

    2015-01-14

    Ab initio calculations combining density-functional theory and nonequilibrium Green’s function are performed to investigate the effects of either single B atom or single N atom dopant in zigzag-edged graphene nanoribbons (ZGNRs) with the ferromagnetic state on the spin-dependent transport properties and thermospin performances. A spin-up (spin-down) localized state near the Fermi level can be induced by these dopants, resulting in a half-metallic property with 100% negative (positive) spin polarization at the Fermi level due to the destructive quantum interference effects. In addition, the highly spin-polarized electric current in the low bias-voltage regime and single-spin negative differential resistance in the high bias-voltage regime are also observed in these doped ZGNRs. Moreover, the large spin-up (spin-down) Seebeck coefficient and the very weak spin-down (spin-up) Seebeck effect of the B(N)-doped ZGNRs near the Fermi level are simultaneously achieved, indicating that the spin Seebeck effect is comparable to the corresponding charge Seebeck effect.

  16. Spin Seebeck effect and spin Hall magnetoresistance at high temperatures for a Pt/yttrium iron garnet hybrid structure.

    PubMed

    Wang, Shuanhu; Zou, Lvkuan; Zhang, Xu; Cai, Jianwang; Wang, Shufang; Shen, Baogen; Sun, Jirong

    2015-11-14

    Based on unique experimental setups, the temperature dependences of the longitudinal spin Seebeck effect (LSSE) and spin Hall magnetoresistance (SMR) of the Pt/yttrium iron garnet (Pt/YIG) hybrid structure are determined in a wide temperature range up to the Curie temperature of YIG. From a theoretical analysis of the experimental relationship between the SMR and temperature, the spin mixing conductance of the Pt/YIG interface is deduced as a function of temperature. Adopting the deduced spin mixing conductance, the temperature dependence of the LSSE is well reproduced based on the magnon spin current theory. Our research sheds new light on the controversy about the theoretical models for the LSSE. PMID:26455519

  17. Thermal spin-transfer torque driven by the spin-dependent Seebeck effect in metallic spin-valves

    NASA Astrophysics Data System (ADS)

    Choi, Gyung-Min; Moon, Chul-Hyun; Min, Byoung-Chul; Lee, Kyung-Jin; Cahill, David G.

    2015-07-01

    The coupling of spin and heat gives rise to new physical phenomena in nanoscale spin devices. In particular, spin-transfer torque (STT) driven by thermal transport provides a new way to manipulate local magnetization. We quantify thermal STT in metallic spin-valve structures using an intense and ultrafast heat current created by picosecond pulses of laser light. Our result shows that thermal STT consists of demagnetization-driven and spin-dependent Seebeck effect (SDSE)-driven components; the SDSE-driven STT becomes dominant after 3 ps. The sign and magnitude of the SDSE-driven STT can be controlled by the composition of a ferromagnetic layer and the thickness of a heat sink layer.

  18. Measuring Seebeck Coefficient

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey (Inventor)

    2015-01-01

    A high temperature Seebeck coefficient measurement apparatus and method with various features to minimize typical sources of errors is described. Common sources of temperature and voltage measurement errors which may impact accurate measurement are identified and reduced. Applying the identified principles, a high temperature Seebeck measurement apparatus and method employing a uniaxial, four-point geometry is described to operate from room temperature up to 1300K. These techniques for non-destructive Seebeck coefficient measurements are simple to operate, and are suitable for bulk samples with a broad range of physical types and shapes.

  19. High temperature Seebeck coefficient metrology

    SciTech Connect

    Martin, J.; Tritt, T.; Uher, C.

    2010-12-15

    We present an overview of the challenges and practices of thermoelectric metrology on bulk materials at high temperature (300 to 1300 K). The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at high temperature. This has led to the implementation of nonideal practices that have further complicated the confirmation of reported high ZT materials. To ensure meaningful interlaboratory comparison of data, thermoelectric measurements must be reliable, accurate, and consistent. This article will summarize and compare the relevant measurement techniques and apparatus designs required to effectively manage uncertainty, while also providing a reference resource of previous advances in high temperature thermoelectric metrology.

  20. Enhancement of spin-Seebeck effect by inserting ultra-thin Fe{sub 70}Cu{sub 30} interlayer

    SciTech Connect

    Kikuchi, D.; Ishida, M.; Murakami, T.; Uchida, K.; Qiu, Z.; Saitoh, E.

    2015-02-23

    We report the longitudinal spin-Seebeck effects (LSSEs) for Pt/Fe{sub 70}Cu{sub 30}/BiY{sub 2}Fe{sub 5}O{sub 12} (BiYIG) and Pt/BiYIG devices. The LSSE voltage was found to be enhanced by inserting an ultra-thin Fe{sub 70}Cu{sub 30} interlayer. This enhancement decays sharply with increasing the Fe{sub 70}Cu{sub 30} thickness, suggesting that it is not due to bulk phenomena, such as a superposition of conventional thermoelectric effects, but due to interface effects related to the Fe{sub 70}Cu{sub 30} interlayer. Combined with control experiments using Pt/Fe{sub 70}Cu{sub 30} devices, we conclude that the enhancement of the LSSE voltage in the Pt/Fe{sub 70}Cu{sub 30}/BiYIG devices is attributed to the improvement of the spin-mixing conductance at the Pt/BiYIG interfaces.

  1. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton

    PubMed Central

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-01-01

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology. PMID:26000658

  2. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton.

    PubMed

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-01-01

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology. PMID:26000658

  3. Thermal artifact on the spin Seebeck effect in metallic thin films deposited on MgO substrates

    NASA Astrophysics Data System (ADS)

    Bosu, S.; Sakuraba, Y.; Uchida, K.; Saito, K.; Kobayashi, W.; Saitoh, E.; Takanashi, K.

    2012-04-01

    Spin Seebeck effect (SSE) was investigated in Heusler compound Co2MnSi (CMS) and ferromagnetic binary alloy Ni80Fe20 (Py) thin films deposited on MgO substrates at different ambient temperatures, T = 30 K to 295 K, by maintaining a finite temperature gradient along the film plane. Low temperature enhancement of voltage signal and a peak around T = 70 K were detected in a Pt wire placed on the higher temperature end of CMS (or Py) film. It has been found that the low temperature enhancement was dominated by a thermal artifact, which was generated by the anomalous Nernst effect with an additional perpendicular temperature gradient across the film plane. The remarkable mismatch between thermal conductivities of MgO and CMS (or Py) at low temperatures is considered to give rise to the perpendicular temperature gradient causing the thermal artifact. We showed that consideration of thermal conductivity matching between thin film and substrate is essential for performing experiments of SSE correctly; moreover, the observation of SSE could be realized only when minimization of the thermal artifact is possible.

  4. Effects of Ge replacement in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration modified by local electron imbalance

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Howard, A.; Straszheim, W. E.

    2015-03-01

    XRD, SEM, EDS, 125Te NMR, Seebeck coefficient, and electrical resistivity of AgxGe50-xTe50 and SbxGe50-xTe50 alloys have been studied. Replacement of Ge in GeTe by Sb significantly increases the Seebeck coefficient, while replacement by Ag decreases it. These effects can be attributed to a change in carrier concentration observed via 125Te NMR spin-lattice relaxation measurements and NMR signal position, which mostly depends on the Knight shift. Variation in carrier concentration in AgxGe50-xTe50 and SbxGe50-xTe50 can be attributed to different electron configurations of valence electrons of Ag (4d105s1) and Sb (5s25p3) compared to that of Ge (4s24p2) resulting in local electron imbalances and changing the concentration of charge carrier (holes) generated by Ge vacancies. In contrast, our 125Te NMR and Seebeck coefficient data for Ag2Sb2Ge46Te50 are similar to those observed for GeTe. This shows that effects from Ag and Sb compensate each other and indicates the existence of [Ag +Sb] pairs. The effects of Ge replacement in GeTe by Ag, Sb, or [Ag +Sb] on rhombohedral lattice distortion also have been analyzed. Interplay between the Seebeck coefficient and electrical resistivity in these alloys results in variation of power factor; the value of 45 mW/cm K2, the highest among known tellurides, was found for Sb2Ge48Te50.

  5. ac current generation in chiral magnetic insulators and Skyrmion motion induced by the spin Seebeck effect.

    PubMed

    Lin, Shi-Zeng; Batista, Cristian D; Reichhardt, Charles; Saxena, Avadh

    2014-05-01

    We show that a temperature gradient induces an ac electric current in multiferroic insulators when the sample is embedded in a circuit. We also show that a thermal gradient can be used to move magnetic Skyrmions in insulating chiral magnets: the induced magnon flow from the hot to the cold region drives the Skyrmions in the opposite direction via a magnonic spin transfer torque. Both results are combined to compute the effect of Skyrmion motion on the ac current generation and demonstrate that Skyrmions in insulators are a promising route for spin caloritronics applications. PMID:24856718

  6. Anomalous spin and charge Seebeck effect in a quantum well with spin orbit interaction

    NASA Astrophysics Data System (ADS)

    Marinescu, D. C.; Manolescu, Andrei; Capps, Jeremy

    2014-08-01

    We discuss the possible existence of an anomalously high low-temperature charge and spin thermopower in a two dimensional electron system with Rashba and Dresselhaus spin-orbit coupling in the special case when the two interactions have equal strengths. The fundamental premise of the theory is the establishment of an weak itinerant antiferromagnetic order in the ground state, a spin alignment favored in the minimum-energy many-body state when the Coulomb interaction is considered. The transport in this state is modeled by using the solutions of a Boltzmann equation obtained within the relaxation time approximation. We show that when scattering on magnetic impurities is introduced, the energy dependence of the relaxation time enhances the value of the thermoelectric coefficient for both charge and spin currents. An estimate of the effect is provided for the case of a standard InAs quantum well and its variation with the strength of the magnetic scattering is studied.

  7. Joule heating-induced coexisted spin Seebeck effect and spin Hall magnetoresistance in the platinum/Y{sub 3}Fe{sub 5}O{sub 12} structure

    SciTech Connect

    Wang, W. X.; Wang, S. H.; Zou, L. K.; Cai, J. W.; Sun, J. R. E-mail: sun-zg@whut.edu.cn; Sun, Z. G.

    2014-11-03

    Spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) are observed simultaneously in the Pt/Y{sub 3}Fe{sub 5}O{sub 12} hybrid structure when thermal gradient is produced by Joule heating. According to their dependences on applied current, these two effects can be separated. Their dependence on heating power and magnetic field is systematically studied. With the increase of heating power, the SSE enhances linearly, whereas the SMR decreases slowly. The origin of the spin currents is further analyzed. The heating power dependences of the spin currents associated with the SSE and the SMR are found to be different.

  8. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

    PubMed Central

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-01-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management. PMID:26975208

  9. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films.

    PubMed

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-Ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-01-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as "ferrite plating". The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management. PMID:26975208

  10. Nanoscale Spin Seebeck Rectifier: Controlling Thermal Spin Transport across Insulating Magnetic Junctions with Localized Spin

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Fransson, Jonas; Zhu, Jian-Xin

    2014-06-01

    The spin Seebeck effect is studied across a charge insulating magnetic junction, in which thermal-spin conjugate transport is assisted by the exchange interactions between the localized spin in the center and electrons in metallic leads. We show that, in contrast with bulk spin Seebeck effect, the figure of merit of such nanoscale thermal-spin conversion can be infinite, leading to the ideal Carnot efficiency in the linear response regime. We also find that in the nonlinear spin Seebeck transport regime the device possesses the asymmetric and negative differential spin Seebeck effects. In the last, the situations with leaking electron tunneling are also discussed. This nanoscale thermal spin rectifier, by tuning the junction parameters, can act as a spin Seebeck diode, spin Seebeck transistor, and spin Seebeck switch, which could have substantial implications for flexible thermal and information control in molecular spin caloritronics.

  11. Reply to ``Comment on `Observation of vortex-lattice melting in YBa2Cu3O7-? by Seebeck-effect measurements' ''

    NASA Astrophysics Data System (ADS)

    Ghamlouch, H.; Aubin, M.; Gagnon, R.; Taillefer, L.

    1999-01-01

    The rapid rise in the Seebeck effect that we observed in single crystals of YBCO in the mixed state was interpreted by us [H. Ghamlouch, M. Aubin, R. Gagnon, and L. Taillefer, Phys. Rev. B 54, 9070 (1996)] as a manifestation of vortex-lattice melting. We maintain this interpretation despite the skepticism of the Comment [M. Ausloos, H. Bougrine, M. Houssa, and M. Pekala, Phys. Rev. B, preceding paper] who suggest that percolation or even experimental artifacts may be responsible. We point out the studies on various types of YBCO single crystals studied by our technique which all yielded plausible results. Recalling the resistivity measurements of Fendrich et al. we argue that percolation, if relevant in our measurements would only exist over ~160 mK and would be hidden in the observed transition. We also present as yet unpublished Nernst effect results as suggested by Ausloos et al. which corroborate our earlier interpretation.

  12. Spin-Hall magnetoresistance and spin Seebeck effect in spin-spiral and paramagnetic phases of multiferroic CoCr2O4 films

    NASA Astrophysics Data System (ADS)

    Aqeel, A.; Vlietstra, N.; Heuver, J. A.; Bauer, G. E. W.; Noheda, B.; van Wees, B. J.; Palstra, T. T. M.

    2015-12-01

    We report on the spin-Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) in multiferroic CoCr2O4 (CCO) spinel thin films with Pt contacts. We observe a large enhancement of both signals below the spin-spiral (Ts=28 K ) and the spin lock-in (Tlock -in=14 K ) transitions. The SMR and SSE responses in the spin lock-in phase are one order of magnitude larger than those observed at the ferrimagnetic transition temperature (Tc=94 K ), which indicates that the interaction between spins at the Pt |CCO interface is more efficient in the noncollinear magnetic state. At T >Tc , magnetic-field-induced SMR and SSE signals are observed, which can be explained by a high interface susceptibility. Our results show that the spin transport at the Pt |CCO interface is sensitive to the magnetic phases but cannot be explained solely by the bulk magnetization.

  13. Intrinsic surface magnetic anisotropy in Y3Fe5O12 as the origin of low-magnetic-field behavior of the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Uchida, Ken-ichi; Ohe, Jun-ichiro; Kikkawa, Takashi; Daimon, Shunsuke; Hou, Dazhi; Qiu, Zhiyong; Saitoh, Eiji

    2015-07-01

    The magnetic-field dependence of the longitudinal spin Seebeck effect (LSSE) in a Pt /Y3Fe5O12 (YIG)-slab junction system was found to deviate from a bulk magnetization curve of the YIG slab in a low field range. In this paper, we show that the deviation originates from the difference between surface and bulk magnetization processes in the YIG slab and that it appears even when removing possible extrinsic magnetic anisotropy due to surface roughness and replacing the Pt layer with different materials. This result indicates that the anomalous field dependence of the LSSE is due to an intrinsic magnetic property of the YIG surface. Our numerical calculation based on the Landau-Lifshitz-Gilbert equation shows that the deviation between the LSSE and bulk magnetization curves is qualitatively explained by introducing easy-axis perpendicular magnetic anisotropy near the surface of YIG.

  14. Seebeck effects in n-type and p-type polymers driven simultaneously by surface polarization and entropy differences based on conductor/polymer/conductor thin-film devices.

    PubMed

    Hu, Dehua; Liu, Qing; Tisdale, Jeremy; Lei, Ting; Pei, Jian; Wang, Hsin; Urbas, Augustine; Hu, Bin

    2015-05-26

    This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using photoinduced intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, respectively, based on vertical conductor/polymer/conductor thin-film devices. We obtain large Seebeck coefficients of -898 ?V/K from n-type IIDT and 1300 ?V/K from p-type IIDDT when the charge-transfer states are generated by a white light illumination of 100 mW/cm(2), compared with the values of 380 and 470 ?V/K in dark condition, respectively. Simultaneously, the electrical conductivities are increased from almost insulating state in dark condition to conducting state under photoexcitation in both n-type IIDT and p-type IIDDT based devices. The large Seebeck effects can be attributed to the following two mechanisms. First, the intramolecular charge-transfer states exhibit strong electron-phonon coupling, which leads to a polarization difference between high and low temperature surfaces. This polarization difference essentially forms a temperature-dependent electric field, functioning as a new driving force additional to entropy difference, to drive the energetic carriers for the development of Seebeck effects under a temperature difference. Second, the intramolecular charge-transfer states generate negative or positive majority carriers (electrons or holes) in the n-type IIDT or p-type IIDDT, ready to be driven between high and low temperature surfaces for developing Seebeck effects. On the basis of coexisted polarization difference and entropy difference, the intramolecular charge-transfer states can largely enhance the Seebeck effects in both n-type IIDT and p-type IIDDT devices. Furthermore, we find that changing electrical conductivity can switch the Seebeck effects between polarization and entropy regimes when the charge-transfer states are generated upon applying photoexcitation. Therefore, using intramolecular charge-transfer states presents an approach to develop thermoelectric effects in organic materials-based vertical conductor/polymer/conductor thin-film devices. PMID:25877512

  15. Seebeck tuning in chalcogenide nanoplate assemblies by nanoscale heterostructuring.

    PubMed

    Mehta, Rutvik J; Karthik, Chinnathambi; Singh, Binay; Teki, Ranganath; Borca-Tasciuc, Theo; Ramanath, Ganpati

    2010-09-28

    Chalcogenide nanostructures offer promise for obtaining nanomaterials with high electrical conductivity, low thermal conductivity, and high Seebeck coefficient. Here, we demonstrate a new approach of tuning the Seebeck coefficient of nanoplate assemblies of single-crystal pnictogen chalcogenides by heterostructuring the nanoplates with tellurium nanocrystals. We synthesized bismuth telluride and antimony telluride nanoplates decorated with tellurium nanorods and nanofins using a rapid, scalable, microwave-stimulated organic surfactant-directed technique. Heterostructuring permits two- to three-fold factorial tuning of the Seebeck coefficient, and yields a 40% higher value than the highest reported for bulk antimony telluride. Microscopy and spectroscopy analyses of the nanostructures suggest that Seebeck tunability arises from carrier-energy filtration effects at the Te-chalcogenide heterointerfaces. Our approach of heterostructuring nanoscale building blocks is attractive for realizing high figure-of-merit thermoelectric nanomaterials. PMID:20812700

  16. Longitudinal spin Seebeck effect in Nd2BiFe5-xGaxO12 prepared on gadolinium gallium garnet (001) by metal organic decomposition method

    NASA Astrophysics Data System (ADS)

    Asada, H.; Kuwahara, A.; Sakata, N.; Ono, T.; Ishibashi, T.; Meguro, A.; Hashinaka, T.; Kishimoto, K.; Koyanagi, T.

    2015-05-01

    Nd2BiFe5-xGaxO12 thin films with the Ga composition x = 0, 0.5, and 1.0 are prepared on (001) oriented gadolinium gallium garnet substrates by a metal organic decomposition method. Only (001) peaks are observed in x-ray diffraction patterns for all the films, suggesting that the highly oriented Nd2BiFe5-xGaxO12 thin films were formed. Increasing Ga composition, the saturation magnetization decreases, and the perpendicular easy axis is enhanced due to the decrease of the shape anisotropy. Longitudinal spin Seebeck effects (LSSEs) in Nd2BiFe5-xGaxO12 thin films with a Pt layer of 10 nm in thickness were investigated. Magnetic field dependence of the thermoelectric voltage caused by the LSSE in Nd2BiFe5-xGaxO12 films indicates the hysteresis loop with the small coercivity reflecting the magnetization curve. The decrease of LSSE voltage in Nd2BiFe5-xGaxO12 is clearly observed with the decrease of Fe composition.

  17. Uncertainty analysis for common Seebeck and electrical resistivity measurement systems.

    PubMed

    Mackey, Jon; Dynys, Frederick; Sehirlioglu, Alp

    2014-08-01

    This work establishes the level of uncertainty for electrical measurements commonly made on thermoelectric samples. The analysis targets measurement systems based on the four probe method. Sources of uncertainty for both electrical resistivity and Seebeck coefficient were identified and evaluated. Included are reasonable estimates on the magnitude of each source, and cumulative propagation of error. Uncertainty for the Seebeck coefficient includes the cold-finger effect which has been quantified with thermal finite element analysis. The cold-finger effect, which is a result of parasitic heat transfer down the thermocouple probes, leads to an asymmetric over-estimation of the Seebeck coefficient. A silicon germanium thermoelectric sample has been characterized to provide an understanding of the total measurement uncertainty. The electrical resistivity was determined to contain uncertainty of 7.0% across any measurement temperature. The Seebeck coefficient of the system is +1.0%/-13.1% at high temperature and 1.0% near room temperature. The power factor has a combined uncertainty of +7.3%/-27.0% at high temperature and 7.5% near room temperature. These ranges are calculated to be typical values for a general four probe Seebeck and resistivity measurement configuration. PMID:25173324

  18. Spin Seebeck devices using local on-chip heating

    NASA Astrophysics Data System (ADS)

    Wu, Stephen M.; Fradin, Frank Y.; Hoffman, Jason; Hoffmann, Axel; Bhattacharya, Anand

    2015-05-01

    A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe3O4 (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. By using the spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.

  19. Spin Seebeck devices using local on-chip heating

    SciTech Connect

    Wu, Stephen M. Fradin, Frank Y.; Hoffman, Jason; Hoffmann, Axel; Bhattacharya, Anand

    2015-05-07

    A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe{sub 3}O{sub 4} (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. By using the spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.

  20. Effects of Ge substitution in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration derived from 125Te NMR

    NASA Astrophysics Data System (ADS)

    Levin, E. M.

    2016-01-01

    GeTe, a self-doping p -type semiconductor where the high free hole concentration is determined by Ge vacancies is a well-known base for high-efficiency A gxS bxG e50 -2 xT e50 (a tellurium-antimony-germanium-silver series) thermoelectric materials. Here it is shown that the replacement of Ge by Ag in GeTe (a A gxG e50 -xT e50 system) significantly decreases the Seebeck coefficient, whereas the replacement by Sb (S bxG e50 -xT e50 ) increases it. These effects can be attributed to a change in carrier concentration and consistent with 125Te NMR spin-lattice relaxation measurements and NMR signal position, which is mostly dependent on the Knight shift. Opposite changes in carrier concentration in A gxG e50 -xT e50 and S bxG e50 -xT e50 can be explained by different valence electron configurations of Ag and Sb compared to that of Ge, which results in a different local electron imbalance and/or in a change in Ge vacancy formation energy and affects the total carrier concentration. Comparison of our data for GeTe, A g2G e48T e50 , and S b2G e48T e50 with those for A g2S b2G e46T e50 shows that the effects from Ag and Sb compensate for each other and supports the formation of [Ag +Sb ] atomic pairs suggested earlier based on theoretical calculations.

  1. Large Seebeck effect in electron-doped FeAs2 driven by a quasi-one-dimensional pudding-mold-type band

    NASA Astrophysics Data System (ADS)

    Usui, Hidetomo; Suzuki, Katsuhiro; Kuroki, Kazuhiko; Nakano, Seiya; Kudo, Kazutaka; Nohara, Minoru

    2013-08-01

    We investigate the thermoelectric properties of the electron-doped FeAs2 both experimentally and theoretically. Electrons are doped by partially substituting Se for As, which leads to a metallic behavior in the resistivity. A Seebeck coefficient of about -200 ?V/K is reached at 300 K for 1% doping, and about -120 ?V/K even at 5% doping. The origin of this large Seebeck coefficient, despite the metallic conductivity, is analyzed from a band structure point of view. The first-principles band calculation reveals the presence of a pudding-mold-type band just above the band gap, somewhat similar to NaxCoO2, but with a quasi-one-dimensional nature. We calculate the Seebeck coefficient using a tight-binding model that correctly reproduces this band structure, and this gives results roughly in agreement with the experiments. Moreover, a consideration of electron correlations beyond the generalized gradient approximation by the fluctuation exchange method gives even better agreement. The origin of this peculiar band shape is also discussed. Combined with previous studies, we now have good thermoelectric materials with quasi-one-, two-, and three-dimensional band structures that have partially flat portions. The present study reinforces the general efficiency of this peculiar band shape in thermoelectric materials.

  2. The Seebeck coefficient of superionic conductors

    SciTech Connect

    Mahan, G. D.

    2015-01-28

    We present a theory of the anomalous Seebeck coefficient found in the superionic conductor Cu{sub 2}Se. It has a phase transition at T = 400 K where the cations disorder but the anions do not. This disorder gives a temperature-dependent width to the electronic states in the conduction band. This width provides the anomalous Seebeck contribution.

  3. The Seebeck Coefficient of Insulators: Electrochemical Potential

    NASA Astrophysics Data System (ADS)

    Mahan, G. D.

    2016-03-01

    We discuss the theory behind low-temperature measurement of the Seebeck coefficient in materials with few electrons, such as insulators and lightly doped semiconductors. The Seebeck coefficient is defined thermodynamically as being related to the electrochemical potential. However, the measurement is of the voltage for a material with no current, which is not the same as the gradient of the electrochemical potential.

  4. Spin-dependent Seebeck coefficients of Ni80Fe20 and Co in nanopillar spin valves

    NASA Astrophysics Data System (ADS)

    Dejene, F. K.; Flipse, J.; van Wees, B. J.

    2012-07-01

    We have experimentally determined the spin-dependent Seebeck coefficient of permalloy (Ni80Fe20) and cobalt (Co) using nanopillar spin valve devices, a stack of two ferromagnetic layers separated by a nonmagnetic layer. The devices were specifically designed to separate heat-related effects from charge-related effects. A heat current, with no accompanying charge current, through the nanopillar spin valve leads to a thermovoltage proportional to the spin-dependent Seebeck coefficient SS=S?-S? of the ferromagnet, where S? and S? are the Seebeck coefficient for spin-up and spin-down electrons. By using a three-dimensional finite-element model based on spin-dependent thermoelectric theory, whose input material parameters were measured in separate devices, we were able to accurately determine a spin-dependent Seebeck coefficient of -1.8 ?V K-1 and -4.5 ?V K-1 for cobalt and permalloy, respectively, corresponding to a Seebeck coefficient polarization PS=SS/SF of 0.08 and 0.25, where SF is the Seebeck coefficient of the ferromagnet. The results are in agreement with earlier theoretical work in Co/Cu multilayers and spin-dependent Seebeck and spin-dependent Peltier measurements in Ni80Fe20/Cu spin valve structures.

  5. Apparatus Measures Seebeck Coefficient And Resistivity

    NASA Technical Reports Server (NTRS)

    Zoltan, Leslie D.; Wood, Charles; Fleurial, Jean-Pierre; Liu, Yixin

    1993-01-01

    Electrical measurements made by four point probes, two of which double as temperature probes. Laboratory apparatus measures both Seebeck coefficients and electrical resistivities of candidate thermoelectric materials at temperatures from ambient to 1,300 K. Apparatus makes possible to take both measurements alternately and in rapid succession during same heating cycle, thereby reducing distortion.

  6. Longitudinal spin Seebeck effect in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} prepared on gadolinium gallium garnet (001) by metal organic decomposition method

    SciTech Connect

    Asada, H. Kuwahara, A.; Sakata, N.; Ono, T.; Kishimoto, K.; Koyanagi, T.; Ishibashi, T.; Meguro, A.; Hashinaka, T.

    2015-05-07

    Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} thin films with the Ga composition x = 0, 0.5, and 1.0 are prepared on (001) oriented gadolinium gallium garnet substrates by a metal organic decomposition method. Only (001) peaks are observed in x-ray diffraction patterns for all the films, suggesting that the highly oriented Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} thin films were formed. Increasing Ga composition, the saturation magnetization decreases, and the perpendicular easy axis is enhanced due to the decrease of the shape anisotropy. Longitudinal spin Seebeck effects (LSSEs) in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} thin films with a Pt layer of 10 nm in thickness were investigated. Magnetic field dependence of the thermoelectric voltage caused by the LSSE in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} films indicates the hysteresis loop with the small coercivity reflecting the magnetization curve. The decrease of LSSE voltage in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} is clearly observed with the decrease of Fe composition.

  7. Combination of PVA with Graphene to Improve the Seebeck Coefficient for Thermoelectric Generator Applications

    NASA Astrophysics Data System (ADS)

    Mahmoud, L.; Abdul Samad, Y.; Alhawari, M.; Mohammad, B.; Liao, K.; Ismail, M.

    2015-01-01

    Ultrasensitive thermoelectric (TE) materials are essential for the next generation of self-powered electronic devices. In this work, a graphene-based TE generator was fabricated. For 50 to 1000 graphene layers the average Seebeck coefficient was 90 ?V/K. We also report improvement of the Seebeck coefficient by use of a hybrid material containing 10% poly(vinyl alcohol) (PVA) and 90% graphene oxide prepared and tested under the same conditions. The results show that the Seebeck coefficient is improved by an average of 30% compared with graphene alone. Because the fabrication process is facile, scalable, and cost effective, it could also be applicable to other fields of science and engineering.

  8. Description of a Sensitive Seebeck Calorimeter Used for Cold Fusion Studies

    NASA Astrophysics Data System (ADS)

    Storms, Edmund

    A sensitive and stable Seebeck calorimeter is described and used to determine the heat of formation of PdD. This determination can be used to show that such calorimeters are sufficiently accurate to measure the LENR effect and give support to the claims.

  9. System to Measure Thermal Conductivity and Seebeck Coefficient for Thermoelectrics

    NASA Technical Reports Server (NTRS)

    Kim, Hyun-Jung; Skuza, Jonathan R.; Park, Yeonjoon; King, Glen C.; Choi, Sang H.; Nagavalli, Anita

    2012-01-01

    The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at elevated temperatures. This has led to the implementation of nonstandardized practices that have further complicated the confirmation of reported high ZT materials. The major objective of the procedure described is for the simultaneous measurement of the Seebeck coefficient and thermal diffusivity within a given temperature range. These thermoelectric measurements must be precise, accurate, and reproducible to ensure meaningful interlaboratory comparison of data. The custom-built thermal characterization system described in this NASA-TM is specifically designed to measure the inplane thermal diffusivity, and the Seebeck coefficient for materials in the ranging from 73 K through 373 K.

  10. Microchip for the Measurement of Seebeck Coefficients of Single Nanowires

    NASA Astrophysics Data System (ADS)

    Vlklein, F.; Schmitt, M.; Cornelius, T. W.; Picht, O.; Mller, S.; Neumann, R.

    2009-07-01

    Bismuth nanowires were electrochemically grown in ion track-etched polycarbonate membranes. Micromachining and microlithography were employed to realize a newly developed microchip for Seebeck coefficient measurements on individual nanowires. By anisotropic etching of a (100) Si wafer, an 800-nm-thick SiO2/Si3N4 membrane was prepared in the chip center. The low thermal conductivity of the membrane is crucial to obtain the required temperature difference ? T along the nanowire. The wire is electrically contacted to thin metal pads which are patterned by a new method of microscopic exposure of photoresist and a lift-off process. A ? T between the two pairs of contact pads, located on the membrane, is established by a thin-film heater. Applying the known Seebeck coefficient of a reference film, the temperature difference at this gap is determined. Using ? T and the measured Seebeck voltage U of the nanowire, its Seebeck coefficient can be calculated.

  11. Measurement of Seebeck coefficient using a light pulse

    NASA Technical Reports Server (NTRS)

    Wood, C.; Zoltan, D.; Stapfer, G.

    1985-01-01

    A high-temperature (1900 K) Seebeck coefficient apparatus is described in which small thermal gradients are generated in a sample by light pulses transmitted via light pipes. By employing an analog subtraction circuit, the Seebeck coefficient is displayed directly on an X-Y recorder. This technique presents a convenient, accurate, and rapid method for measuring the Seebeck coefficient in highly doped semiconductors as a function of temperature. The nature of the resulting display (X-Y recording) is a valuable tool in determining validity of the data. A straight line results (i.e., a minimum of hysteresis) only if all potential experimental errors are minimized. Under these conditions, the error of measurements of the Seebeck coefficient is estimated to be less than + or - 1 percent.

  12. Nanoscale Thermoelectrics: A Study of the Absolute Seebeck Coefficient of Thin Films

    NASA Astrophysics Data System (ADS)

    Mason, Sarah J.

    The worlds demand for energy is ever increasing. Likewise, the environmental impact of climate change due generating that energy through combustion of fossil fuels is increasingly alarming. Due to these factors new sources of renewable energies are constantly being sought out. Thermoelectric devices have the ability to generate clean, renewable, energy out of waste heat. However promising that is, their inefficiency severely inhibits applicability and practical use. The usefulness of a thermoelectric material increases with the dimensionless quantity, ZT, which depends on the Seebeck coefficient and electrical and thermal conductivity. These characteristic material parameters have interdependent energy transport contributions that classically prohibit the optimization of one with out the detriment of another. Encouraging advancements of ZT have occurred in the past ten years due to the decoupling of the thermal and electrical conductivity. Further advancements are necessary in order to produce applicable devices. One auspicious way of decoupling or tuning energy transport properties, is through size reduction to the nanoscale. However, with reduced dimensions come complications in measuring material properties. Measurements of properties such as the Seebeck coefficient, S, are primarily contingent upon the measurement apparatus. The Seebeck coefficient is defined as the amount of voltage generated by a thermal gradient. Measuring a thermally generated voltage by traditional methods gives, the voltage measured as a linear function of the Seebeck coefficient of the leads and of the material being tested divided by the applied thermal gradient. If accurate values of the Seebeck coefficients of the leads are available, simple subtraction provides the answer. This is rarely the case in nanoscale measurement devices with leads exclusively made from thin film materials that do not have well known bulk-like thermopower values. We have developed a technique to directly measure, S, as a function of temperature using a micro-machined thermal isolation platform consisting of a suspended, patterned SiN membrane. By measuring a series of thicknesses of metallic films up to the infinitely thin film limit, in which the electrical resistivity is no longer decreasing with increasing film thickness, but still not at bulk values, along with the effective electron mean free path, we are able to show the contribution of the leads needed to measure this property. Having a comprehensive understanding of the background contribution we are able to determine the absolute Seebeck coefficient of a wide variety of thin films. The nature of the design of the SiN membrane also allows the ability to accurately and directly measure thermal and electrical transport of the thin films yielding a comprehensive measurement of the three quantities that characterize a material's efficiency. This can serve to further the development of thermoelectric materials through precise measurements of the material properties that dictate efficiency.

  13. Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling

    NASA Astrophysics Data System (ADS)

    Le Breton, Jean-Christophe; Sharma, Sandeep; Saito, Hidekazu; Yuasa, Shinji; Jansen, Ron

    2011-07-01

    Heat generation by electric current, which is ubiquitous in electronic devices and circuits, raises energy consumption and will become increasingly problematic in future generations of high-density electronics. The control and re-use of heat are therefore important topics for existing and emerging technologies, including spintronics. Recently it was reported that heat flow within a ferromagnet can produce a flow of spin angular momentum--a spin current--and an associated voltage. This spin Seebeck effect has been observed in metallic, insulating and semiconductor ferromagnets with temperature gradients across them. Here we describe and report the demonstration of Seebeck spin tunnelling--a distinctly different thermal spin flow, of purely interfacial nature--generated in a tunnel contact between electrodes of different temperatures when at least one of the electrodes is a ferromagnet. The Seebeck spin current is governed by the energy derivative of the tunnel spin polarization. By exploiting this in ferromagnet-oxide-silicon tunnel junctions, we observe thermal transfer of spins from the ferromagnet to the silicon without a net tunnel charge current. The induced spin accumulation scales linearly with heating power and changes sign when the temperature differential is reversed. This thermal spin current can be used by itself, or in combination with electrical spin injection, to increase device efficiency. The results highlight the engineering of heat transport in spintronic devices and facilitate the functional use of heat.

  14. Seebeck Coefficient Metrology: Do Contemporary Protocols Measure Up?

    NASA Astrophysics Data System (ADS)

    Martin, Joshua; Wong-Ng, Winnie; Green, Martin L.

    2015-06-01

    Comparative measurements of the Seebeck coefficient are challenging due to the diversity of instrumentation and measurement protocols. With the implementation of standardized measurement protocols and the use of Standard Reference Materials (SRMs), for example, the recently certified National Institute of Standards and Technology (NIST) SRM 3451 ``Low Temperature Seebeck Coefficient Standard (10-390 K)'', researchers can reliably analyze and compare data, both intra- and inter-laboratory, thereby accelerating the development of more efficient thermoelectric materials and devices. We present a comparative overview of commonly adopted Seebeck coefficient measurement practices. First, we examine the influence of asynchronous temporal and spatial measurement of electric potential and temperature. Temporal asynchronicity introduces error in the absolute Seebeck coefficient of the order of ?10%, whereas spatial asynchronicity introduces error of the order of a few percent. Second, we examine the influence of poor thermal contact between the measurement probes and the sample. This is especially critical at high temperature, wherein the prevalent mode of measuring surface temperature is facilitated by pressure contact. Each topic will include the comparison of data measured using different measurement techniques and using different probe arrangements. We demonstrate that the probe arrangement is the primary limit to high accuracy, wherein the Seebeck coefficients measured by the 2-probe arrangement and those measured by the 4-probe arrangement diverge with the increase in temperature, approaching ?14% at 900 K. Using these analyses, we provide recommended measurement protocols to guide members of the thermoelectric materials community in performing more accurate measurements and in evaluating more comprehensive uncertainty limits.

  15. Seebeck coefficient measurements on Li, Sn, Ta, Mo, and W

    NASA Astrophysics Data System (ADS)

    Fiflis, P.; Kirsch, L.; Andruczyk, D.; Curreli, D.; Ruzic, D. N.

    2013-07-01

    The thermopower of W, Mo, Ta, Li and Sn has been measured relative to stainless steel, and the Seebeck coefficient of each of these materials has then been calculated. These are materials that are currently relevant to fusion research and form the backbone for different possible liquid limiter concepts including TEMHD concepts such as LiMIT. For molybdenum the Seebeck coefficient has a linear rise with temperature from SMo = 3.9 ?V K-1 at 30 C to 7.5 ?V K-1 at 275 C, while tungsten has a linear rise from SW = 1.0 ?V K-1 at 30 C to 6.4 ?V K-1 at 275 C, and tantalum has the lowest Seebeck coefficient of the solid metals studied with STa = -2.4 ?V K-1 at 30 C to -3.3 ?V K-1 at 275 C. The two liquid metals, Li and Sn have also been measured. The Seebeck coefficient for Li has been re-measured and agrees with past measurements. As seen with Li there are two distinct phases in Sn also corresponding to the solid and liquid phases of the metal. In its solid phase the SSn-solid = -1.5 ?V K-1 at 30 C and -2.5 ?V K-1 near the melting temperature of 231 C. There is a distinct increase in the Seebeck coefficient around the melting temperature as the Sn melts and stays relatively constant over the rest of the measured temperatures, SSn-melt = -1.4 ?V K-1 from 235 C to 275 C.

  16. Design of seebeck coefficient measurement probe for powder library.

    PubMed

    Fujimoto, Kenjiro; Taguchi, Toru; Yoshida, Shogo; Ito, Shigeru

    2014-02-10

    A thermoelectric evaluation system, attachable to our developed materials exploration system "M-ist Combi" based on the electrostatic spray deposition method, was designed and established for high-throughput to explore new candidate thermoelectric materials. The developed Seebeck coefficient measurement probe consists of two chromel-alumel thermocouples, and one of thermocouples is able to control its own temperature to ensure a temperature difference between thermocouples. The measurement time for each sample was about 5 s. This provides a stabilized time for the thermoelectric power for each sample. And, it was found that the Seebeck coefficient measurement probe could be used as a high-throughput screening tool for exploring candidate thermoelectric materials. PMID:24367887

  17. Cu-induced Seebeck peak in HMS/Si film

    NASA Astrophysics Data System (ADS)

    Hou, Q. R.; Gu, B. F.; Chen, Y. B.

    2014-08-01

    It is well known that aluminum (Al), boron (B) and copper (Cu) are acceptor impurities with shallow- and deep-energy levels in silicon (Si), respectively. Thus, Al and B impurities with shallow-energy levels in Si are essentially completely ionized at room temperature while Cu impurities with deep-energy levels in Si at higher temperature. In this paper, Al, B and Cu co-doped Si layer is used as a barrier layer while the higher manganese silicide layer (HMS) as a well layer. The Seebeck coefficient (S) of Al and Cu modulation doped film, HMS/Si:(Al + Cu), increases sharply above 583 K, reaches a peak value of 0.300 mV/K at 683 K, and then decreases with further increasing temperature. Concomitance with the great increase in Seebeck coefficient, however, the electrical resistivity (R) is still smaller than that of only Al modulation doped film, HMS/Si:Al. The Cu-induced Seebeck peak, Smax = 0.303 mV/K at 733 K, and reduction in electrical resistivity are also observed in (B + Al + Cu) modulation doped film, Si:(B + Al + Cu)/HMS/Si:(B + Al + Cu), where B is used to reduce the electrical resistivity further. As a result, the thermoelectric power factor (PF = S2/R) is greatly enhanced and can reach 3.140 10-3 W/m-K2 at 733 K, which is larger than that of HMS bulk material.

  18. Seebeck Coefficient of Lithium and Lithium-Tin Alloys

    NASA Astrophysics Data System (ADS)

    Kirsch, L.; Fiflis, P.; Andruczyk, D.; Curreli, D.; Ruzic, D. N.

    2012-10-01

    Experiments into the viability of lithium as a first wall material in a fusion device have shown that it offers great benefits in reducing recycling of hydrogenic species at the wall, increasing energy confinement times, and gettering impurities. However, concerns have been raised about its practicality in regions of high heat fluxes, and one of the greatest is whether or not a lithium divertor concept can function at high steady state temperatures without significant evaporation of the lithium. Lithium-tin alloys might offer a solution by suppressing evaporation, but their performance in a TEMHD driven device such as the LIMIT device under development at UIUC is directly dependent on their thermoelectric properties, namely their unknown Seebeck coefficient. In support of the use of lithium-tin alloys in such a device, experiments are performed to recover the Seebeck coefficient of several different compositions of lithium-tin alloys. Experiments previously performed at the University of Illinois of the Seebeck coefficient of lithium [1] were confirmed and expanded upon by this study. Values of ranging from 12 +/-1 uV/K at 82C to 28 +/-1 uV/K at 240C were obtained.[4pt] [1] V. Surla et al. Journal of Nuclear Materials 415 (2011) 18-22.

  19. Design for a spin-Seebeck diode based on two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Fu, Hua-Hua; Wu, Dan-Dan; Gu, Lei; Wu, Menghao; Wu, Ruqian

    2015-07-01

    Studies of the spin-Seebeck effect (SSE) are very important for the development of fundamental science and novel low-power-consumption technologies. The spin-Seebeck diode (SSD), in which the spin current can be driven by a forward temperature gradient but not by a reverse temperature gradient, is a key unit in spin caloritronic devices. Here, we propose a SSD design using two-dimensional (2D) materials such as silicene and phosphorene nanoribbons as the source and drain. Due to their unique band structures and magnetic states, thermally driven spin-up and spin-down currents flow in opposite directions. This mechanism is different from that of the previous one, which uses two permalloy circular disks [Phys. Rev. Lett. 112, 047203 (2014), 10.1103/PhysRevLett.112.047203], and the SSD in our design can be easily integrated with gate voltage control. Since the concept of this design is rather general and applicable to many 2D materials, it is promising for the realization and exploitation of SSDs in nanodevices.

  20. High Temperature Seebeck Coefficient and Electrical Resistivity of Ge2Sb2Te5 Thin Films

    NASA Astrophysics Data System (ADS)

    Adnane, Lhacene; Dirisaglik, Faruk; Akbulut, Mustafa; Zhu, Yu; Lam, Chung; Gokirmak, Ali; Silva, Helena

    2012-02-01

    Phase-change memory (PCM) is a promising memory technology in which a small volume of a chalcogenide material can be reversibly and rapidly switched between amorphous and crystalline phases by an electrical pulse that brings it above crystallization ( 150-200 C) or melting ( 700 C) temperature. The large temperature levels involved and small dimensions of PCM devices give rise to very large temperature gradients ( 10 K/nm and higher) which result in strong thermoelectric effects. High-temperature characterization of the temperature-dependent thermoelectric properties of these materials is therefore critical to understand for the operation of these devices but to date there is only limited experimental data available. We have performed simultaneous measurements of Seebeck coefficient and electrical resistance of thin films of GST with different thicknesses, deposited on silicon dioxide, from room temperature to 600 C, under small temperature gradients. Two-point current-voltage (I-V) measurements were performed using a semiconductor parameter analyzer. The resistance of the material and the Seebeck voltage (open-circuit voltage) are calculated from the slope and intercept of the I-V characteristics. The details of the measurements and S(T) and R(T) results for the GST thin film samples will be presented and discussed.

  1. Long-range pure magnon spin diffusion observed in a nonlocal spin-Seebeck geometry

    NASA Astrophysics Data System (ADS)

    Giles, Brandon L.; Yang, Zihao; Jamison, John S.; Myers, Roberto C.

    2015-12-01

    The spin diffusion length for thermally excited magnon spins is measured by utilizing a nonlocal spin-Seebeck effect measurement. In a bulk single crystal of yttrium iron garnet (YIG) a focused laser thermally excites magnon spins. The spins diffuse laterally and are sampled using a Pt inverse spin Hall effect detector. Thermal transport modeling and temperature dependent measurements demonstrate the absence of spurious temperature gradients beneath the Pt detector and confirm the nonlocal nature of the experimental geometry. Remarkably, we find that thermally excited magnon spins in YIG travel over 120 m at 23 K, indicating that they are robust against inelastic scattering. The spin diffusion length is found to be at least 47 m and as high as 73 m at 23 K in YIG, while at room temperature it drops to less than 10 m. Based on this long spin diffusion length, we envision the development of thermally powered spintronic devices based on electrically insulating, but spin conducting materials.

  2. Seebeck rectification enabled by intrinsic thermoelectrical coupling in magnetic tunneling junctions.

    PubMed

    Zhang, Z H; Gui, Y S; Fu, L; Fan, X L; Cao, J W; Xue, D S; Freitas, P P; Houssameddine, D; Hemour, S; Wu, K; Hu, C-M

    2012-07-20

    An intrinsic thermoelectric coupling effect in the linear response regime of magnetic tunneling junctions (MTJ) is reported. In the dc response, it leads to a nonlinear correction to Ohm's law. Dynamically, it enables a novel Seebeck rectification and second harmonic generation, which apply for a broad frequency range and can be magnetically controlled. A phenomenological model on the footing of the Onsager reciprocal relation and the principle of energy conservation explains very well the experimental results obtained from both dc and frequency-dependent transport measurements performed up to GHz frequencies. Our work refines previous understanding of magnetotransport and microwave rectification in MTJs. It forms a new foundation for utilizing spin caloritronics in high-frequency applications. PMID:22861893

  3. Seebeck coefficient of tellurite vanadate glasses containing molybdenum

    NASA Astrophysics Data System (ADS)

    Souri, Dariush

    2008-05-01

    The Seebeck coefficient, Q, of ternary 40TeO2-(60-x)V2O5-xMoO3 bulk glasses was measured in the temperature range 260-450 K. The thermoelectric power at 400 K was measured and was in the range from -677 to -501 V K-1 for TeO2-V2O5-MoO3 glasses. For the present glass systems, Heikes' formula was satisfied and a small polaron hopping conduction mechanism was confirmed, which was in agreement with the results of dc electrical conductivity measurement of these glasses. The 40TeO2-50V2O5-10MoO3 glass system had the highest power factor, Q2?, and probably the highest figure of merit among the others.

  4. Conductivities and Seebeck Coefficients of Boron Carbides: ''Softening-Bipolaron'' Hopping

    SciTech Connect

    ASELAGE,TERRENCE L.; EMIN,DAVID JACOB; MCCREADY,STEVEN S.

    2000-07-20

    The most conspicuous feature of boron carbides' electronic transport properties is their having both high carrier densities and large Seebeck coefficients. The magnitudes and temperature dependencies of the Seebeck coefficients are consistent with large contributions from softening bipolarons: singlet bipolarons whose stabilization is significantly affected by their softening of local vibrations. Boron carbides' high carrier densities, small activation energies for hopping ({approx} 0.16 eV), and anomalously large Seebeck coefficients combine with their low, glass-like thermal conductivities to make them unexpectedly efficient high-temperature thermoelectrics.

  5. Multifold Seebeck increase in RuO{sub 2} films by quantum-guided lanthanide dilute alloying

    SciTech Connect

    Music, Denis Basse, Felix H.-U.; Schneider, Jochen M.; Han, Liang; Borca-Tasciuc, Theo; Devender; Gengler, Jamie J.; Voevodin, Andrey A.; Ramanath, Ganpati

    2014-02-03

    Ab initio predictions indicating that alloying RuO{sub 2} with La, Eu, or Lu can increase the Seebeck coefficient α manifold due to quantum confinement effects are validated in sputter-deposited La-alloyed RuO{sub 2} films showing fourfold α increase. Combinatorial screening reveals that α enhancement correlates with La-induced lattice distortion, which also decreases the thermal conductivity twentyfold, conducive for high thermoelectric figures of merit. These insights should facilitate the rational design of high efficiency oxide-based thermoelectrics through quantum-guided alloying.

  6. Colossal Seebeck Coefficient of Hopping Electrons in (TMTSF) 2 PF6

    NASA Astrophysics Data System (ADS)

    Machida, Yo; Lin, Xiao; Kang, Woun; Izawa, Koichi; Behnia, Kamran

    2016-02-01

    We report on a study of the Seebeck coefficient and resistivity in the quasi-one-dimensional conductor (TMTSF) 2 PF6 extended deep into the spin-density-wave state. The metal-insulator transition at TSDW=12 K leads to a reduction in carrier concentration by 7 orders of magnitude. Below 1 K, charge transport displays the behavior known as variable range hopping. Until now, the Seebeck response of electrons in this regime has barely been explored and is even less understood. We find that, in this system, residual carriers, hopping from one trap to another, generate a Seebeck coefficient as large as 400 kB/e . The results provide the first solid evidence for a long-standing prediction according to which hopping electrons in the presence of the Coulomb interaction can generate a sizable Seebeck coefficient in the zero-temperature limit.

  7. Studies on Seebeck Coefficient of Individual Bismuth Telluride Nanotube

    NASA Astrophysics Data System (ADS)

    Kim, Duksoo; Du, Renzhong; Yin, Yuewei; Dong, Sining; Li, Xiaoguang; Li, Qi; Tadigadapa, Srinivas

    2013-03-01

    We have studied on Seebeck coefficient (S) of freestanding individual Bismuth Telluride nanotubes using micro-fabricated thermoelectric workbench at the temperatures from 300 K to 25 K. The thermoelectric workbench is composed of three main elements: heater, thermocouple, and platinum pad. A polysilicon-gold thermocouple accurately measures the temperature, arising from the heat generated at the tips of the test sites from the polysilicon heater located 2 μm apart from the thermocouple. Platinum pads placed on top of the heater and thermocouple structures and electrically isolated from these constitute S measurement circuit. IPA solution containing Bi2Te3 nanotubes was drop-cast on the workbench and the Ebeam Induced Deposition of platinum was used to improve the electrical and thermal contacts between nanotube and platinum pads. The inner and outer diameter of nanotube is 50 nm and 70 nm, respectively. The sign of obtained S was positive which is indicating the nanotube is p-type. And the magnitude was increased compared to the bulk and nanowire types. The measured S (364 μV/K) of nanotube at T = 300 K is 1.65 times larger than that (220 μV/K) of bulk and 1.4 times larger than the previously reported value (260 μV/K) of nanowire. This work is supported by NSF MRSEC (Grant No. DMR-0820404)

  8. Characterization of Lorenz number with Seebeck coefficient measurement

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Sik; Gibbs, Zachary M.; Tang, Yinglu; Wang, Heng; Snyder, G. Jeffrey

    2015-04-01

    In analyzing zT improvements due to lattice thermal conductivity (?L) reduction, electrical conductivity (?) and total thermal conductivity (?Total) are often used to estimate the electronic component of the thermal conductivity (?E) and in turn ?L from ?L = ?Total - L?T. The Wiedemann-Franz law, ?E = L?T, where L is Lorenz number, is widely used to estimate ?E from ? measurements. It is a common practice to treat L as a universal factor with 2.44 10-8 W?K-2 (degenerate limit). However, significant deviations from the degenerate limit (approximately 40% or more for Kane bands) are known to occur for non-degenerate semiconductors where L converges to 1.5 10-8 W?K-2 for acoustic phonon scattering. The decrease in L is correlated with an increase in thermopower (absolute value of Seebeck coefficient (S)). Thus, a first order correction to the degenerate limit of L can be based on the measured thermopower, |S|, independent of temperature or doping. We propose the equation: L = 1 . 5 + exp [" separators=" - /| S | 116 ] (where L is in 10-8 W?K-2 and S in ?V/K) as a satisfactory approximation for L. This equation is accurate within 5% for single parabolic band/acoustic phonon scattering assumption and within 20% for PbSe, PbS, PbTe, Si0.8Ge0.2 where more complexity is introduced, such as non-parabolic Kane bands, multiple bands, and/or alternate scattering mechanisms. The use of this equation for L rather than a constant value (when detailed band structure and scattering mechanism is not known) will significantly improve the estimation of lattice thermal conductivity.

  9. A Study of the Measurement of Seebeck Coefficient of SiGe

    NASA Technical Reports Server (NTRS)

    Heung, King Yi

    2005-01-01

    In 1821 German Physicist Thomas J. Seebeck discovered that heat could be converted into electricity when a temperature difference was applied across two points on a material. Theoretically, the generated voltage has a directly proportional relationship with the temperature difference. This relationship is the Seebeck coefficient that scientists always referred to when determining the efficiency of a thermoelectricity convention. In our experiments, however, hysteresis loops appeared when we plotted voltage against temperature difference, and the measured Seebeck appeared differently when the measurements were run under vacuum, air, and helium gas. Measurements were done by using a low-frequency AC measuring method. By simulating the experimental setup into a; thermal circuit, we found that the loop and inconsistency in measuring Seebeck coefficient could be explained by studying the behaviors of a RC circuit in a thermal sense. Under vacuum, the gap of the hysteresis loop can be largely eliminated if the time period of the temperature difference increased up to 4800s. The trend of the variations in measuring Seebeck coefficients in different environments can also be predicted by using different thermal circuit models.

  10. Characterization of Lorenz number with Seebeck coefficient measurement

    SciTech Connect

    Kim, Hyun-Sik; Gibbs, Zachary M.; Tang, Yinglu; Wang, Heng; Snyder, G. Jeffrey

    2015-04-01

    In analyzing zT improvements due to lattice thermal conductivity (κ{sub L}) reduction, electrical conductivity (σ) and total thermal conductivity (κ{sub Total}) are often used to estimate the electronic component of the thermal conductivity (κ{sub E}) and in turn κ{sub L} from κ{sub L} = ∼ κ{sub Total} − LσT. The Wiedemann-Franz law, κ{sub E} = LσT, where L is Lorenz number, is widely used to estimate κ{sub E} from σ measurements. It is a common practice to treat L as a universal factor with 2.44 × 10{sup −8} WΩK{sup −2} (degenerate limit). However, significant deviations from the degenerate limit (approximately 40% or more for Kane bands) are known to occur for non-degenerate semiconductors where L converges to 1.5 × 10{sup −8} WΩK{sup −2} for acoustic phonon scattering. The decrease in L is correlated with an increase in thermopower (absolute value of Seebeck coefficient (S)). Thus, a first order correction to the degenerate limit of L can be based on the measured thermopower, |S|, independent of temperature or doping. We propose the equation: L=1.5+exp[−(|S|)/(116) ] (where L is in 10{sup −8} WΩK{sup −2} and S in μV/K) as a satisfactory approximation for L. This equation is accurate within 5% for single parabolic band/acoustic phonon scattering assumption and within 20% for PbSe, PbS, PbTe, Si{sub 0.8}Ge{sub 0.2} where more complexity is introduced, such as non-parabolic Kane bands, multiple bands, and/or alternate scattering mechanisms. The use of this equation for L rather than a constant value (when detailed band structure and scattering mechanism is not known) will significantly improve the estimation of lattice thermal conductivity.

  11. Thermal Modeling and Analysis of a Sub-Compact Seebeck Furnace

    NASA Technical Reports Server (NTRS)

    Wang, Francis C.; Peters, Palmer; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    The Sub-Compact Seebeck Furnace (SCSF) is a third generation furnace designed as an experimental facility to study the phenomena of undercooling associated with directional solidification. It is intended to provide a double peak temperature profile along the axial direction with gradient zones at each end. By keeping the temperature in the central portion above the melting point of the sample, and cooling the ends of the furnace, a solid/liquid (S/L) interface can be maintained in each one of the gradient zones. A motorized motion control provides a motion to one-half of the furnace. The undercooling associated with the interface being directionally solidified can thus be studied. Modeling of the temperature profile is important to help assure that the furnace design provides the correct thermal characteristics. The furnace is designed with two halves that telescope. Results of thermal analysis based on an analytical solution using simple assumptions will be presented. The resulting temperature profile will show the salient features of the desired thermal profile and provide the general directions for thermal design. Experimental results will be used to compare with the analytical profile. Approach for numerical modeling to provide more detailed information such as two-dimensional effects will be discussed.

  12. Seebeck and thermal conductivity analysis in amorphous/crystalline {beta}-K{<_2}Bi{<_8}Se{<_13} nanocomposite materials.

    SciTech Connect

    Kyratsi, Th.; Hatzikraniotis, E.; Ioannou, M.; Chung, D. Y.; Tsiaoussis, I.

    2011-01-01

    In this work, ball milling is applied on {beta}-K{sub 2}Bi{sub 8}Se{sub 13} compounds in order to explore the potential of the process for the fabrication of nano-based material. Polycrystalline {beta}-K{sub 2}Bi{sub 8}Se{sub 13}, synthesized from melt, was ball milled under inert atmosphere. Powder x-ray diffraction showed a significantly increased disorder with ball milling time. TEM studies confirmed the presence of nanocrystalline material in an amorphous matrix, suggesting the development of crystalline/amorphous {beta}-K{sub 2}Bi{sub 8}Se{sub 13} nanocomposite material via ball milling process. Seebeck coefficient and thermal conductivity were analyzed based on the effective medium theory and show a significant contribution of a nanocrystalline phase.

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

    SciTech Connect

    Bahk, JH; Sadeghian, RB; Bian, ZX; Shakouri, A

    2012-02-08

    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 Schrodinger 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.

  14. Correlation of Seebeck coefficient and electric conductivity in polyaniline and polypyrrole

    SciTech Connect

    Mateeva, N.; Niculescu, H.; Schlenoff, J.; Testardi, L.R.

    1998-03-01

    We have measured the Seebeck coefficient and electric conductivity in the air-stable conducting polymers polyaniline and polypyrrole at different doping levels. We find, at 300 K, the general correlation that the logarithm of the electrical conductivity varies linearly with the Seebeck coefficient on doping, but with a proportionality substantially in excess of a prediction from simple theory for a single type of mobile carrier. The correlation is unexpected in its universality and unfavorable in its consequences for thermoelectric applications. A standard model suggests that conduction by carriers of both signs may occur in these doped polymers, which thus leads to reduced thermoelectric efficiency. We also show that polyacetylene (which is not air stable), does exhibit the correlation with the expected proportionality, and, thus, its properties could be more favorable for thermoelectricity. {copyright} {ital 1998 American Institute of Physics.}

  15. Instrument for stable high temperature Seebeck coefficient and resistivity measurements under controlled oxygen partial pressure

    DOE PAGESBeta

    Ihlefeld, Jon F.; Brown-Shaklee, Harlan James; Sharma, Peter Anand

    2015-04-28

    The transport properties of ceramic materials strongly depend on oxygen activity, which is tuned by changing the partial oxygen pressure (pO2) prior to and during measurement. Within, we describe an instrument for highly stable measurements of Seebeck coefficient and electrical resistivity at temperatures up to 1300 K with controlled oxygen partial pressure. An all platinum construction is used to avoid potential materials instabilities that can cause measurement drift. Two independent heaters are employed to establish a small temperature gradient for Seebeck measurements, while keeping the average temperature constant and avoiding errors associated with pO2-induced drifts in thermocouple readings. Oxygen equilibriummore » is monitored using both an O2 sensor and the transient behavior of the resistance as a proxy. A pO2 range of 10-25–100 atm can be established with appropriate gas mixtures. Seebeck measurements were calibrated against a high purity platinum wire, Pt/Pt–Rh thermocouple wire, and a Bi2Te3 Seebeck coefficient Standard Reference Material. To demonstrate the utility of this instrument for oxide materials we present measurements as a function of pO2 on a 1 % Nb-doped SrTiO3 single crystal, and show systematic changes in properties consistent with oxygen vacancy defect chemistry. Thus, an approximately 11% increase in power factor over a pO2 range of 10-19–10-8 atm at 973 K for the donor-doped single crystals is observed.« less

  16. Instrument for stable high temperature Seebeck coefficient and resistivity measurements under controlled oxygen partial pressure

    SciTech Connect

    Ihlefeld, Jon F.; Brown-Shaklee, Harlan James; Sharma, Peter Anand

    2015-04-28

    The transport properties of ceramic materials strongly depend on oxygen activity, which is tuned by changing the partial oxygen pressure (pO2) prior to and during measurement. Within, we describe an instrument for highly stable measurements of Seebeck coefficient and electrical resistivity at temperatures up to 1300 K with controlled oxygen partial pressure. An all platinum construction is used to avoid potential materials instabilities that can cause measurement drift. Two independent heaters are employed to establish a small temperature gradient for Seebeck measurements, while keeping the average temperature constant and avoiding errors associated with pO2-induced drifts in thermocouple readings. Oxygen equilibrium is monitored using both an O2 sensor and the transient behavior of the resistance as a proxy. A pO2 range of 10-25–100 atm can be established with appropriate gas mixtures. Seebeck measurements were calibrated against a high purity platinum wire, Pt/Pt–Rh thermocouple wire, and a Bi2Te3 Seebeck coefficient Standard Reference Material. To demonstrate the utility of this instrument for oxide materials we present measurements as a function of pO2 on a 1 % Nb-doped SrTiO3 single crystal, and show systematic changes in properties consistent with oxygen vacancy defect chemistry. Thus, an approximately 11% increase in power factor over a pO2 range of 10-19–10-8 atm at 973 K for the donor-doped single crystals is observed.

  17. Simultaneous increase in electrical conductivity and Seebeck coefficient in highly boron-doped nanocrystalline Si.

    PubMed

    Neophytou, Neophytos; Zianni, Xanthippi; Kosina, Hans; Frabboni, Stefano; Lorenzi, Bruno; Narducci, Dario

    2013-05-24

    A large thermoelectric power factor in heavily boron-doped p-type nanograined Si with grain sizes ?30nm and grain boundary regions of ?2nm is reported. The reported power factor is ?5 times higher than in bulk Si. It originates from the surprising observation that for a specific range of carrier concentrations, the electrical conductivity and Seebeck coefficient increase simultaneously. The two essential ingredients for this observation are nanocrystallinity and extremely high boron doping levels. This experimental finding is interpreted within a theoretical model that considers both electron and phonon transport within the semiclassical Boltzmann approach. It is shown that transport takes place through two phases so that high conductivity is achieved in the grains, and high Seebeck coefficient by the grain boundaries. This together with the drastic reduction in the thermal conductivity due to boundary scattering could lead to a significant increase of the figure of merit ZT. This is one of the rare observations of a simultaneous increase in the electrical conductivity and Seebeck coefficient, resulting in enhanced thermoelectric power factor. PMID:23598565

  18. Uncertainty Analysis of Seebeck Coefficient and Electrical Resistivity Characterization

    NASA Technical Reports Server (NTRS)

    Mackey, Jon; Sehirlioglu, Alp; Dynys, Fred

    2014-01-01

    In order to provide a complete description of a materials thermoelectric power factor, in addition to the measured nominal value, an uncertainty interval is required. The uncertainty may contain sources of measurement error including systematic bias error and precision error of a statistical nature. The work focuses specifically on the popular ZEM-3 (Ulvac Technologies) measurement system, but the methods apply to any measurement system. The analysis accounts for sources of systematic error including sample preparation tolerance, measurement probe placement, thermocouple cold-finger effect, and measurement parameters; in addition to including uncertainty of a statistical nature. Complete uncertainty analysis of a measurement system allows for more reliable comparison of measurement data between laboratories.

  19. Economical Route to Produce High Seebeck Coefficient Calcium Cobaltate for Bulk Thermoelectric Applications

    SciTech Connect

    Selig, Jiri; Lin, Sidney; Lin, Hua-Tay; Johnson, D Ray; Wang, Hsin

    2011-01-01

    Phase pure calcium cobaltate (Ca1.24Co1.62O3.86) was prepared by Self-propagating High-temperature Synthesis (SHS) followed by a short post heat treatment. Prepared powders were characterized by XRD for phase purity, and SEM for particle size and distribution. Temperature histories at the center and on the surface of reaction pellet during the SHS process were monitored and recorded. Particles size of synthesized powders was reduced using a planetary mill to increase its specific surface area. Electrical conductivity, thermal conductivity and Seebeck coefficient of the prepared power were measured and figure of merit was reported.

  20. Laser Synthesis of Nanometric Iron Oxide Films with High Seebeck Coefficient and High Thermoelectric Figure of Merit

    NASA Astrophysics Data System (ADS)

    Mulenko, S. A.; Gorbachuk, N. T.; Stefan, N.

    2014-12-01

    Radiation of a KrF-laser ( λ = 248 nm) was used for the synthesis by reactive pulsed laser deposition (RPLD) of nanometric iron oxide [Fe2O3-X (0≤×≤1)] films with variable thickness, stoichiometry and electrical properties. Film deposition was carried out on <100>Si at its temperature to have being increased from 293 to 800 K. XRD analysis showed that films deposited on Si substrate had polycrystalline structure. Films demonstrated semiconductor temperature trend with variable band gap Eg about 1.0 eV or less depending on oxygen pressure, the number of laser pulses and substrate temperature. Film thickness (13-60 nm) depended on oxygen pressure, substrate temperature and number of laser pulses. The higher substrate temperature, the more crystallinity of the deposited iron oxides' films was resulting in increasing of thermo electromotive force coefficient (Seebeck coefficient, S). It was found out the optimum oxygen pressure in the reactor, substrate temperature and film thickness when the S coefficient was high as 12-4 mV/K in the range 240-330 K. The thermoelectric figure of merit (ZT) was high as 1-6 in the range 280-330 K. This makes nanometric Fe2O3-X films, synthesized by UV photons using RPLD method, an exceptionally strong candidate for effective thermo sensors and thermo converters operating at moderate temperature.

  1. A computer-controlled apparatus for Seebeck inhomogeneity testing of sheathed thermocouples

    NASA Technical Reports Server (NTRS)

    Burkett, Cecil G., Jr.; Bauserman, Willard A., Jr.

    1993-01-01

    Mineral-insulated metal-sheathed (MIMS) thermocouple assemblies are used throughout industry and research facilities as a method of temperature measurement where requirements for either harsh environmental conditions exist, or where rigidity of the measurement probe is required. Seebeck inhomogeneity is the abnormal variation of the Seebeck coefficient from point to point in a material. It is not disclosed in conventional calibration. A standardized method of measuring thermoelectric inhomogeneity along the thermocouple probe length is not available. Therefore, calibration for sheathed probes normally does not include testing of probe inhomogeneity. The measurement accuracy would be severely impacted if significant inhomogeneity and a temperature gradient were present in the same region of the probe. A computer-controlled system for determining inhomogeneities was designed, fabricated, and tested. This system provides an accurate method for the identification of the location of inhomogeneity along the length of a sheathed thermocouple and for the quantification of the inhomogeneity. This paper will discuss the apparatus and procedure used to perform these tests and will present data showing tests performed on sheathed thermocouple probes.

  2. Apparatus for measuring Seebeck coefficient and electrical resistivity of small dimension samples using infrared microscope as temperature sensor

    NASA Astrophysics Data System (ADS)

    Jaafar, W. M. N. Wan; Snyder, J. E.; Min, Gao

    2013-05-01

    An apparatus for measuring the Seebeck coefficient (?) and electrical resistivity (?) was designed to operate under an infrared microscope. A unique feature of this apparatus is its capability of measuring ? and ? of small-dimension (sub-millimeter) samples without the need for microfabrication. An essential part of this apparatus is a four-probe assembly that has one heated probe, which combines the hot probe technique with the Van der Pauw method for "simultaneous" measurements of the Seebeck coefficient and electrical resistivity. The repeatability of the apparatus was investigated over a temperature range of 40 C-100 C using a nickel plate as a standard reference. The results show that the apparatus has an uncertainty of 4.9% for Seebeck coefficient and 5.0% for electrical resistivity. The standard deviation of the apparatus against a nickel reference sample is -2.43 ?VK-1 (-12.5%) for the Seebeck coefficient and -0.4 ?? cm (-4.6%) for the electrical resistivity, respectively.

  3. Determining a hopping polaron's bandwidth from its Seebeck coefficient: Measuring the disorder energy of a non-crystalline semiconductor

    NASA Astrophysics Data System (ADS)

    Emin, David

    2016-01-01

    Charge carriers that execute multi-phonon hopping generally interact strongly enough with phonons to form polarons. A polaron's sluggish motion is linked to slowly shifting atomic displacements that severely reduce the intrinsic width of its transport band. Here a means to estimate hopping polarons' bandwidths from Seebeck-coefficient measurements is described. The magnitudes of semiconductors' Seebeck coefficients are usually quite large (>k/|q| = 86 ?V/K) near room temperature. However, in accord with the third law of thermodynamics, Seebeck coefficients must vanish at absolute zero. Here, the transition of the Seebeck coefficient of hopping polarons to its low-temperature regime is investigated. The temperature and sharpness of this transition depend on the concentration of carriers and on the width of their transport band. This feature provides a means of estimating the width of a polaron's transport band. Since the intrinsic broadening of polaron bands is very small, less than the characteristic phonon energy, the net widths of polaron transport bands in disordered semiconductors approach the energetic disorder experienced by their hopping carriers, their disorder energy.

  4. Record Seebeck coefficient and extremely low thermal conductivity in nanostructured SnSe

    SciTech Connect

    Serrano-Sánchez, F.; Gharsallah, M.; Nemes, N. M.; Mompean, F. J.; Martínez, J. L.; Alonso, J. A.

    2015-02-23

    SnSe has been prepared by arc-melting, as mechanically robust pellets, consisting of highly oriented polycrystals. This material has been characterized by neutron powder diffraction (NPD), scanning electron microscopy, and transport measurements. A microscopic analysis from NPD data demonstrates a quite perfect stoichiometry SnSe{sub 0.98(2)} and a fair amount of anharmonicity of the chemical bonds. The Seebeck coefficient reaches a record maximum value of 668 μV K{sup −1} at 380 K; simultaneously, this highly oriented sample exhibits an extremely low thermal conductivity lower than 0.1 W m{sup −1} K{sup −1} around room temperature, which are two of the main ingredients of good thermoelectric materials. These excellent features exceed the reported values for this semiconducting compound in single crystalline form in the moderate-temperatures region and highlight its possibilities as a potential thermoelectric material.

  5. A sintered nanoparticle p-n junction observed by a Seebeck microscan

    NASA Astrophysics Data System (ADS)

    Becker, A.; Schierning, G.; Theissmann, R.; Meseth, M.; Benson, N.; Schmechel, R.; Schwesig, D.; Petermann, N.; Wiggers, H.; Ziolkowski, P.

    2012-03-01

    A nanoparticular p-n junction was realized by a field-assisted sintering process, using p-type and n-type doped silicon nanoparticles. A spatially resolved Seebeck microscan showed a broad transition from the positively doped to the negatively doped range. Overshoots on both sides are characteristic for the transition. Despite the tip size being much larger than the mean particle size, information about the dopant distribution between the particles is deduced from modeling the measured data under different assumptions, including the limited spatial resolution of the tip. The best match between measured and modeled data is achieved by the idea of doping compensation, due to the sintering process. Due to a short time at high temperature during the field-assisted sintering process, solid state diffusion is too slow to be solely responsible for the observed compensation of donors and acceptors over a wide range. Therefore, these measurements support a densification mechanism based on (partial) melting and recrystallization.

  6. Record Seebeck coefficient and extremely low thermal conductivity in nanostructured SnSe

    NASA Astrophysics Data System (ADS)

    Serrano-Sánchez, F.; Gharsallah, M.; Nemes, N. M.; Mompean, F. J.; Martínez, J. L.; Alonso, J. A.

    2015-02-01

    SnSe has been prepared by arc-melting, as mechanically robust pellets, consisting of highly oriented polycrystals. This material has been characterized by neutron powder diffraction (NPD), scanning electron microscopy, and transport measurements. A microscopic analysis from NPD data demonstrates a quite perfect stoichiometry SnSe0.98(2) and a fair amount of anharmonicity of the chemical bonds. The Seebeck coefficient reaches a record maximum value of 668 μV K-1 at 380 K; simultaneously, this highly oriented sample exhibits an extremely low thermal conductivity lower than 0.1 W m-1 K-1 around room temperature, which are two of the main ingredients of good thermoelectric materials. These excellent features exceed the reported values for this semiconducting compound in single crystalline form in the moderate-temperatures region and highlight its possibilities as a potential thermoelectric material.

  7. Scanning Seebeck Coefficient Measurement System for Homogeneity Characterization of Bulk and Thin-Film Thermoelectric Materials

    SciTech Connect

    Iwanaga, S; Snyder, GJ

    2012-04-03

    Larger-scale production of thermoelectric materials is necessary when mass-producing thermoelectric devices at industrial level. Certain fabrication techniques can create inhomogeneity in the material through composition and doping fluctuations throughout the sample, causing local variations in thermoelectric properties. Some variations are in the range of sub-millimeter scale or larger but may be difficult to detect by traditional materials characterization techniques such as x-ray diffraction or scanning electron microscopy when the chemical variation is small but the doping variation, which strongly affects thermoelectric performance, is large. In this paper, a scanning apparatus to directly detect local variations of Seebeck coefficient on both bulk and thin-film samples is used. Results have shown that this technique can be utilized for detection of defective regions, as well as phase separation in the 100-m range or larger.

  8. Seebeck Coefficient Measurements on Micron-Size Single-Crystal Zinc Germanium Nitride Rods

    NASA Astrophysics Data System (ADS)

    Dyck, J. S.; Colvin, J. R.; Quayle, P. C.; Peshek, T. J.; Kash, K.

    2016-01-01

    II-IV-nitride compounds are tetrahedrally bonded, heterovalent ternary semiconductors that have recently garnered attention for their potential technological applications. These materials are derived from the parent III-nitride compounds; ZnGeN2 is the II-IV-nitride analogue to the III-nitride GaN. Very little is known about the transport properties of ZnGeN2. In this work, we present Seebeck coefficient (S) data on 3-micron-diameter, 70-micron-long, single-crystal ZnGeN2 rods, employing a novel measurement approach. The measurements of S show that the majority free carriers are electrons, and imply that the carrier gas is degenerate. Within a single-band model for the conduction band, a carrier concentration of order 1019 cm-3 was estimated for a measured S = -90 ?V/K. Together with electrical transport measurements, a lower limit for the electron mobility is estimated to be 20 cm2/V-s. A discussion of this material as a thermoelectric is presented. The background level of free electrons in this unintentionally doped ZnGeN2 is very near the predicted optimum value for maximum thermoelectric performance.

  9. Thermal conductivity and Seebeck coefficients of icosahedral boron arsenide films on silicon carbide

    SciTech Connect

    Gong, Y.; Kuball, M.; Zhang, Y.; Dudley, M.; Zhang, Y.; Edgar, J. H.; Heard, P. J.

    2010-10-15

    The thermal conductivity of icosahedral boron arsenide (B{sub 12}As{sub 2}) films grown on (0001) 6H-SiC substrates by chemical vapor deposition was studied by the 3{omega} technique. The room temperature thermal conductivity decreased from 27.0 to 15.3 W/m K as the growth temperature was decreased from 1450 to 1275 deg. C. This is mainly attributed to the differences in the impurity concentration and microstructure, determined from secondary ion mass spectrometry and high resolution transmission electron microscopy, respectively. Callaway's theory was applied to calculate the temperature-dependent thermal conductivity, and the results are in good agreement with the experimental data. Seebeck coefficients were determined as 107 {mu}V/K and 136 {mu}V/K for samples grown at 1350 deg. C with AsH{sub 3}/B{sub 2}H{sub 6} flow ratio equals to 1:1 and 3:5, respectively.

  10. The Seebeck Coefficient in Oxygen Enriched La2NiO4

    NASA Astrophysics Data System (ADS)

    Bach, Paul; Leboran, Victor; Rivadulla, Francisco

    2013-03-01

    Oxide-based devices show promise for themoelectric applications due to their chemical stability and straightforward fabrication. The La2NiO4+? system has been predicted to show an increased thermopower coupled with an increased electrical conductivity around ? = 0 . 05 [Pardo et al. PRB 86, 165114 (2012)] that could lead to a large thermoelectric figure of merit (ZT). We investigate the suitability of lanthanum nickelate as a candidate material for high-ZT devices through a systematic study of oxygenated thin films grown by pulsed laser deposition. We report the electrical conductivity, Seebeck coefficient, and structural morphology of La2NiO4 grown in a range of oxidizing atmospheres and discuss their implications for controlled engineering of thermoelectric properties. We have explored the possibility of gate-tuning these systems in order to fabricate single-oxide based devices. This work was supported by the Ministerio de Ciencia e Innovacin (Spain), grant MAT2010-16157, and the European Research Council, grant ERC-2010-StG 259082 2D THERMS.

  11. Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes.

    PubMed

    Lee, See Kei; Buerkle, Marius; Yamada, Ryo; Asai, Yoshihiro; Tada, Hirokazu

    2015-12-28

    Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C(82), Gd@C(82), and Ce@C(82). We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C(82) and Ce@C(82) junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C(82) based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C(82) and Ce@C(82) is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom. PMID:26583505

  12. A Thermoelectric Investigation of Selected Lead Salts and the Spin-Seebeck Effect in Semiconductors

    NASA Astrophysics Data System (ADS)

    Jaworski, Christopher M.

    The dimensionless thermoelectric figure of merit, zT, is used to characterize the conversion efficiency of thermoelectric materials. In this dissertation, we include experimental results on new p-type semiconducting alloys based on lead telluride that have higher zT values than historical materials. Through alloying PbTe:Tl with sulfur, we demonstrate an increase in zT over the parent material PbTe:Tl. Next, we remove the toxic element T1 from the PbTe/PbS alloy and retain the high efficiency via doping heavy valence band in PbTe, a separate mechanism than the high-zT resonant level doping achieved by the impurity Tl. We present experimental evidence relevant to the valence band structure of PbTe alloys at elevated temperature and demonstrate that these alloys remain direct gap semiconductors at temperatures relevant to automotive thermoelectric waste heat recovery (<850K).

  13. Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes

    NASA Astrophysics Data System (ADS)

    Lee, See Kei; Buerkle, Marius; Yamada, Ryo; Asai, Yoshihiro; Tada, Hirokazu

    2015-12-01

    Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C82, Gd@C82, and Ce@C82. We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C82 and Ce@C82 junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C82 based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C82 and Ce@C82 is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom.Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C82, Gd@C82, and Ce@C82. We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C82 and Ce@C82 junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C82 based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C82 and Ce@C82 is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05394c

  14. Band gap estimation from temperature dependent Seebeck measurement—Deviations from the 2e|S|{sub max}T{sub max} relation

    SciTech Connect

    Gibbs, Zachary M.; Kim, Hyun-Sik; Wang, Heng; Snyder, G. Jeffrey

    2015-01-12

    In characterizing thermoelectric materials, electrical and thermal transport measurements are often used to estimate electronic band structure properties such as the effective mass and band gap. The Goldsmid-Sharp band gap, E{sub g} = 2e|S|{sub max}T{sub max}, is a tool widely employed to estimate the band gap from temperature dependent Seebeck coefficient measurements. However, significant deviations of more than a factor of two are now known to occur. We find that this is when either the majority-to-minority weighted mobility ratio (A) becomes very different from 1.0 or as the band gap (E{sub g}) becomes significantly smaller than 10 k{sub B}T. For narrow gaps (E{sub g} ≲ 6 k{sub B}T), the Maxwell-Boltzmann statistics applied by Goldsmid-Sharp break down and Fermi-Dirac statistics are required. We generate a chart that can be used to quickly estimate the expected correction to the Goldsmid-Sharp band gap depending on A and S{sub max}; however, additional errors can occur for S < 150 μV/K due to degenerate behavior.

  15. High temperature setup for measurements of Seebeck coefficient and electrical resistivity of thin films using inductive heating.

    PubMed

    Adnane, L; Williams, N; Silva, H; Gokirmak, A

    2015-10-01

    We have developed an automated setup for simultaneous measurement of Seebeck coefficient S(T) and electrical resistivity ρ(T) of thin film samples from room temperature to ∼650 °C. S and ρ are extracted from current-voltage (I-V) measurements obtained using a semiconductor parameter analyzer and temperature measurements obtained using commercial thermocouples. The slope and the x-axis intercept of the I-V characteristics represent the sample conductance G and the Seebeck voltage, respectively. The measured G(T) can be scaled to ρ(T) by the geometry factor obtained from the room temperature resistivity measurement of the film. The setup uses resistive or inductive heating to control the temperature and temperature gradient on the sample. Inductive heating is achieved with steel plates that surround the test area and a water cooled copper pipe coil underneath that generates an AC magnetic field. The measurements can be performed using resistive heating only or inductive heating only, or a combination of both depending on the desired heating ranges. Inductive heating provides a more uniform heating of the test area, does not require contacts to the sample holder, can be used up to the Curie temperature of the particular magnetic material, and the temperature gradients can be adjusted by the relative positions of the coil and sample. Example results obtained for low doped single-crystal silicon with inductive heating only and with resistive heating only are presented. PMID:26520996

  16. High temperature setup for measurements of Seebeck coefficient and electrical resistivity of thin films using inductive heating

    NASA Astrophysics Data System (ADS)

    Adnane, L.; Williams, N.; Silva, H.; Gokirmak, A.

    2015-10-01

    We have developed an automated setup for simultaneous measurement of Seebeck coefficient S(T) and electrical resistivity ρ(T) of thin film samples from room temperature to ˜650 °C. S and ρ are extracted from current-voltage (I-V) measurements obtained using a semiconductor parameter analyzer and temperature measurements obtained using commercial thermocouples. The slope and the x-axis intercept of the I-V characteristics represent the sample conductance G and the Seebeck voltage, respectively. The measured G(T) can be scaled to ρ(T) by the geometry factor obtained from the room temperature resistivity measurement of the film. The setup uses resistive or inductive heating to control the temperature and temperature gradient on the sample. Inductive heating is achieved with steel plates that surround the test area and a water cooled copper pipe coil underneath that generates an AC magnetic field. The measurements can be performed using resistive heating only or inductive heating only, or a combination of both depending on the desired heating ranges. Inductive heating provides a more uniform heating of the test area, does not require contacts to the sample holder, can be used up to the Curie temperature of the particular magnetic material, and the temperature gradients can be adjusted by the relative positions of the coil and sample. Example results obtained for low doped single-crystal silicon with inductive heating only and with resistive heating only are presented.

  17. Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2 determined by polarized x-ray spectroscopy and Seebeck measurements

    NASA Astrophysics Data System (ADS)

    Magnuson, Martin; Mattesini, Maurizio; Nong, Ngo Van; Eklund, Per; Hultman, Lars

    2012-05-01

    Nanolaminated materials exhibit characteristic magnetic, mechanical, and thermoelectric properties, with large contemporary scientific and technological interest. Here we report on the anisotropic Seebeck coefficient in nanolaminated Ti3SiC2 single-crystal thin films and trace the origin to anisotropies in element-specific electronic states. In bulk polycrystalline form, Ti3SiC2 has a virtually zero Seebeck coefficient over a wide temperature range. In contrast, we find that the in-plane (basal ab) Seebeck coefficient of Ti3SiC2, measured on single-crystal films, has a substantial and positive value of 4-6 ?V/K. Employing a combination of polarized angle-dependent x-ray spectroscopy and density functional theory we directly show electronic structure anisotropy in inherently nanolaminated Ti3SiC2 single-crystal thin films as a model system. The density of Ti 3d and C 2p states at the Fermi level in the basal ab plane is about 40% higher than along the c axis. The Seebeck coefficient is related to electron and hole-like bands close to the Fermi level, but in contrast to ground state density functional theory modeling, the electronic structure is also influenced by phonons that need to be taken into account. Positive contribution to the Seebeck coefficient of the element-specific electronic occupations in the basal plane is compensated by 73% enhanced Si 3d electronic states across the laminate plane that give rise to a negative Seebeck coefficient in that direction. Strong phonon vibration modes with three to four times higher frequency along the c axis than along the basal ab plane also influence the electronic population and the measured spectra by the asymmetric average displacements of the Si atoms. These results constitute experimental evidence explaining why the average Seebeck coefficient of Ti3SiC2 in polycrystals is negligible over a wide temperature range. This allows the origin of anisotropy in physical properties of nanolaminated materials to be traced to anisotropies in element-specific electronic states.

  18. Seebeck and figure of merit enhancement in nanostructured antimony telluride by antisite defect suppression through sulfur doping.

    PubMed

    Mehta, Rutvik J; Zhang, Yanliang; Zhu, Hong; Parker, David S; Belley, Matthew; Singh, David J; Ramprasad, Ramamurthy; Borca-Tasciuc, Theodorian; Ramanath, Ganpati

    2012-09-12

    Antimony telluride has a low thermoelectric figure of merit (ZT < ?0.3) because of a low Seebeck coefficient ? arising from high degenerate hole concentrations generated by antimony antisite defects. Here, we mitigate this key problem by suppressing antisite defect formation using subatomic percent sulfur doping. The resultant 10-25% higher ? in bulk nanocrystalline antimony telluride leads to ZT ? 0.95 at 423 K, which is superior to the best non-nanostructured antimony telluride alloys. Density functional theory calculations indicate that sulfur increases the antisite formation activation energy and presage further improvements leading to ZT ? 2 through optimized doping. Our findings are promising for designing novel thermoelectric materials for refrigeration, waste heat recovery, and solar thermal applications. PMID:22891784

  19. Thermoelectric properties of the unfilled skutterudite FeSb3 from first principles and Seebeck local probes

    NASA Astrophysics Data System (ADS)

    Lemal, Sbastien; Nguyen, Ngoc; de Boor, Johannes; Ghosez, Philippe; Varignon, Julien; Klobes, Benedikt; Hermann, Raphal P.; Verstraete, Matthieu J.

    2015-11-01

    Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange correlation. The ground state is determined to be antiferromagnetic with an atomic magnetic moment of 1.6 ?B/Fe . The Nel temperature TN is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33 meV , also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6 ? V K-1 , slightly lower than the theoretical result. The theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.

  20. Effets Seebeck et Nernst dans les cuprates: Etude de la reconstruction de la surface de Fermi sous champ magnetique intense

    NASA Astrophysics Data System (ADS)

    Laliberte, Francis

    2010-06-01

    Ce memoire presente des mesures de transport thermoelectrique, les effets Seebeck et Nernst, dans une serie d'echantillons de supraconducteurs a haute temperature critique. Des resultats obtenus recemment au Laboratoire National des Champs Magnetiques Intenses a Grenoble sur La1.7Eu0.2Sr0.1 CuO4, La1.675Eu0.2Sr0.125CuO 4, La1.64Eu0.2Sr0.16CuO4, La1.74Eu0.1Sr0.16CuO4 et La 1.4Nd0.4Sr0.2CuO4 sont analyses. Une attention particuliere est accordee aux equations de la theorie semi-classique du transport et leur validite est verifiee. La procedure experimentale et les materiaux utilises pour concevoir les montages de mesures sont expliques en detail. Enfin, un chapitre est dedie a l'explication et l'interpretation des resultats de transport thermoelectrique sur YBa2Cu3O6+delta publies au cours de l'hiver 2010 dans les revues Nature et Physical Review Letters. Les donnees d'effet Seebeck dans les echantillons de La 1.8-x,Eu0.2SrxCuO 4, ou un changement de signe est observe, permettent de conclure a la presence d'une poche d'electrons dans la surface de Fermi qui domine le transport a basse temperature dans la region sous-dopee du diagramme de phase. Cette conclusion est similaire a celle obtenue par des mesures d'effet Hall dans YBa 2Cu3O6+delta et elle cadre bien dans un scenario de reconstruction de la surface de Fermi. Les donnees d'effet Nernst recueillies indiquent que la contribution des fluctuations supraconductrices est limitee a un modeste intervalle de temperature au-dessus de la temperature critique.

  1. Observations of Co4+ in a Higher Spin State and the Increase in the Seebeck Coefficient of Thermoelectric Ca3Co4O9

    SciTech Connect

    Klie, Robert F; Qiao, Q.; Paulauskas, T.; Gulec, A.; Rebola, A.; Ogut, Serdar; Prange, Micah P; Idrobo Tapia, Juan C; Pantelides, Sokrates T.; Kolesnik, S.; Dabrowski, B.; Ozdemir, M.; Boyraz, C.; Mazumdar, Dipanjan; Gupta, Dr. Arunava

    2012-01-01

    Ca{sub 3}Co{sub 4}O{sub 9} has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca{sub 3}Co{sub 4}O{sub 9} thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co4+-ions in a higher spin state compared to that of bulk Ca{sub 3}Co{sub 4}O{sub 9}. The higher Seebeck coefficient makes the Ca{sub 3}Co{sub 4}O{sub 9} system suitable for many high temperature waste-heat-recovery applications.

  2. Hall and Seebeck measurements estimate the thickness of a (buried) carrier system: Identifying interface electrons in In-doped SnO2 films

    NASA Astrophysics Data System (ADS)

    Papadogianni, Alexandra; White, Mark E.; Speck, James S.; Galazka, Zbigniew; Bierwagen, Oliver

    2015-12-01

    We propose a simple method based on the combination of Hall and Seebeck measurements to estimate the thickness of a carrier system within a semiconductor film. As an example, this method can distinguish "bulk" carriers, with homogeneous depth distribution, from "sheet" carriers, that are accumulated within a thin layer. The thickness of the carrier system is calculated as the ratio of the integral sheet carrier concentration, extracted from Hall measurements, to the volume carrier concentration, derived from the measured Seebeck coefficient of the same sample. For rutile SnO2, the necessary relation of Seebeck coefficient to volume electron concentration in the range of 3 1017 to 3 1020 cm-3 has been experimentally obtained from a set of single crystalline thin films doped with varying Sb-doping concentrations and unintentionally doped bulk samples, and is given as a "calibration curve." Using this calibration curve, our method demonstrates the presence of interface electrons in homogeneously deep-acceptor (In) doped SnO2 films on sapphire substrates.

  3. Transport Properties of Bulk Thermoelectrics—An International Round-Robin Study, Part I: Seebeck Coefficient and Electrical Resistivity

    NASA Astrophysics Data System (ADS)

    Wang, Hsin; Porter, Wallace D.; Böttner, Harald; König, Jan; Chen, Lidong; Bai, Shengqiang; Tritt, Terry M.; Mayolet, Alex; Senawiratne, Jayantha; Smith, Charlene; Harris, Fred; Gilbert, Patricia; Sharp, Jeff W.; Lo, Jason; Kleinke, Holger; Kiss, Laszlo

    2013-04-01

    Recent research and development of high-temperature thermoelectric materials has demonstrated great potential for 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 dimensionless figure of merit, ZT, still needs to be improved from the current value of 1.0 to 1.5 to above 2.0 to be competitive with 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 a key component 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 foci in part I are the measurement of two electronic transport properties: Seebeck coefficient and electrical resistivity.

  4. 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.

  5. Size effects on thermoelectric behavior of ultrathin Na{sub x}CoO{sub 2} films

    SciTech Connect

    Brinks, Peter; Rijnders, Guus; Huijben, Mark

    2014-11-10

    Size effects in thermoelectric Na{sub x}CoO{sub 2} thin films are studied, focusing on the electrical resisitivity and Seebeck coefficient. For very thin films below 10?nm, we have observed an increase in resistivity, which is in agreement with theoretical models. In contrast to a predicted simultaneous suppression of the Seebeck coefficient for ultrathin films, we observe a constant Seebeck coefficient as a function of layer thickness due to changes in the structural properties as well as the presence of strong electron correlations. This preserved high Seebeck coefficient opens up new directions for Na{sub x}CoO{sub 2} ultrathin films as basic building blocks in thermoelectric superlattices with enhanced phonon scattering.

  6. Apparatus for the measurement of electrical resistivity, Seebeck coefficient, and thermal conductivity of thermoelectric materials between 300 K and 12 K.

    PubMed

    Martin, Joshua; Nolas, George S

    2016-01-01

    We have developed a custom apparatus for the consecutive measurement of the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of materials between 300 K and 12 K. These three transport properties provide for a basic understanding of the thermal and electrical properties of materials. They are of fundamental importance in identifying and optimizing new materials for thermoelectric applications. Thermoelectric applications include waste heat recovery for automobile engines and industrial power generators, solid-state refrigeration, and remote power generation for sensors and space probes. The electrical resistivity is measured using a four-probe bipolar technique, the Seebeck coefficient is measured using the quasi-steady-state condition of the differential method in a 2-probe arrangement, and the thermal conductivity is measured using a longitudinal, multiple gradient steady-state technique. We describe the instrumentation and the measurement uncertainty associated with each transport property, each of which is presented with representative measurement comparisons using round robin samples and/or certified reference materials. Transport properties data from this apparatus have supported the identification, development, and phenomenological understanding of novel thermoelectric materials. PMID:26827351

  7. Apparatus for the measurement of electrical resistivity, Seebeck coefficient, and thermal conductivity of thermoelectric materials between 300 K and 12 K

    NASA Astrophysics Data System (ADS)

    Martin, Joshua; Nolas, George S.

    2016-01-01

    We have developed a custom apparatus for the consecutive measurement of the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of materials between 300 K and 12 K. These three transport properties provide for a basic understanding of the thermal and electrical properties of materials. They are of fundamental importance in identifying and optimizing new materials for thermoelectric applications. Thermoelectric applications include waste heat recovery for automobile engines and industrial power generators, solid-state refrigeration, and remote power generation for sensors and space probes. The electrical resistivity is measured using a four-probe bipolar technique, the Seebeck coefficient is measured using the quasi-steady-state condition of the differential method in a 2-probe arrangement, and the thermal conductivity is measured using a longitudinal, multiple gradient steady-state technique. We describe the instrumentation and the measurement uncertainty associated with each transport property, each of which is presented with representative measurement comparisons using round robin samples and/or certified reference materials. Transport properties data from this apparatus have supported the identification, development, and phenomenological understanding of novel thermoelectric materials.

  8. Dependence of transverse magnetothermoelectric effects on inhomogeneous magnetic fields

    NASA Astrophysics Data System (ADS)

    Shestakov, A. S.; Schmid, M.; Meier, D.; Kuschel, T.; Back, C. H.

    2015-12-01

    Transverse magnetothermoelectric effects are studied in permalloy thin films grown on MgO substrates. We find that small parasitic magnetic fields below 1 Oe can produce artifacts of the order of 1 % of the amplitude of the anisotropic magnetothermopower which is also detected in the experiments. The measured artifacts reveal a new source of uncertainties for the detection of the transverse spin Seebeck effect in conductive ferromagnets. Taking these results into account we conclude that the contribution of the transverse spin Seebeck effect in our permalloy-Pt devices to the detected voltages is below the noise level of 20 nV.

  9. Control of thermal gradient using thermoelectric coolers for study of thermal effects

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Gifford, J. A.; Zhao, G. J.; Kim, D. R.; Snider, C. N.; Vargas, N.; Chen, T. Y.

    2015-05-01

    Thermoelectric coolers based on the Peltier effect have been utilized to control temperature gradient to study thermal effects in both bulk and thin film samples. The temperature gradient is controlled by two coolers and the polarity of the thermal gradient can be reversed by reversing an electric driven voltage. With appropriate controlled thermal gradient using this technique, the Nernst and the Seebeck effects can be measured in both bulk and thin film samples free of spurious contributions. In an arbitrary direction of thermal gradient, the Seebeck and the Nernst components can be decomposed from the measured signal based on the symmetry of the effects in a magnetic field.

  10. Multi-band analysis of temperature-dependent transport coefficients (conductivity, Hall, Seebeck, and Nernst) of Ni-doped CoSb3

    NASA Astrophysics Data System (ADS)

    Kajikawa, Y.

    2016-02-01

    The experimental data on the temperature dependence of the four transport coefficients, i.e., the electrical conductivity (σ), Hall coefficient (RH), Seebeck coefficient (S), and Nernst coefficient (Q), of n-type Co0.999Ni0.001Sb3 reported by Sun et al. [Nat. Commun. 6, 7475 (2015)] have been analyzed in a multi-band model, especially focusing on the low temperature data. The multi-band model includes not only the lowest valley of the conduction band at the Γ point but also satellite valleys at the second minima together with an impurity band. The lowest valley at the Γ point is assumed to split into the c1 band and the spin-orbit split-off (so) band. For the analysis, the general expression of the Nernst coefficient in the multi-band model is derived. At such low temperatures that the other bands than the c1 and the impurity band can be neglected, this expression is shown to be approximated as the sum of three terms: the intrinsic terms due to the Nernst coefficients in the two bands themselves and a cross term proportional to the difference of Seebeck coefficients between the two bands. As a result of the analysis, it is proved that the anomalous positive peak of S(T) observed around T = 20 K as well as the sharp rise of the Hall mobility observed from 15 K to 40 K are due to the transition from hopping conduction in the impurity band to conduction in the c1 band. On the other hand, the pronounced peak of Q(T) observed slightly below 40 K is proved to be due to the cross term between the impurity band and the c1 band. In addition, a shoulder of Q(T) appeared around T = 80 K lends clear evidence of the existence of the so band, while the increase in both of σ(T) and | S ( T ) | above 150 K suggests the existence of the satellite valleys.

  11. Thermoelastic-strain-induced thermoelectric effect in n-Ge

    NASA Astrophysics Data System (ADS)

    Musaev, A. M.

    2014-10-01

    A new physical mechanism responsible for the appearance of anomalous thermo-emf in n-Ge, the sign of which is opposite to that of the Seebeck thermo-emf, is considered. It is shown that the anomalous thermoelectric effect is related to the redistribution of charge carriers in the energy extrema of bands during thermoelastic deformation of the crystal.

  12. Anomalous Enhancement of Seebeck Coefficient in Pr-Based 1-2-20 System with Non-Kramers Doublet Ground States

    NASA Astrophysics Data System (ADS)

    Machida, Y.; Yoshida, T.; Ikeura, T.; Izawa, K.; Nakama, A.; Higashinaka, R.; Aoki, Y.; Sato, H.; Sakai, A.; Nakatsuji, S.; Nagasawa, N.; Matsumoto, K.; Onimaru, T.; Takabatake, T.

    2015-03-01

    Low-temperature Seebeck coefficient S/T measurements have been performed on Pr-based 1-2-20 system, PrTr2X20 (Tr = Ti, Ta, V, Ir, X = Al, Zn) with non-Kramers doublet ground states. For PrTr2X20 with X = Al, we find a large S/T, which amounts to those of heavy fermion metals. By contrast, S/T for PrIr2Zn20 is found to be considerably small as the same order of magnitude as those of ordinary metals, despite the commonly enhanced Sommerfeld coefficient ? throughout the system. A satisfactory of the quasi-universal relation between S/T and ? as well as the Kadowaki-Woods relation demonstrates that the mass enhancement is realized in PrTr2Al20 due to the hybridization between f-electrons and the conduction electrons. We also find that the small S/T of PrIr2Zn20 is enhanced at low temperatures under the fields on the verge of quadrupole ordered phase, and in the same regime, the electrical resistivity follows the quadratic temperature dependence with a steep slope as a characteristic of Fermi liquid. The results imply an emergence of a nontrivial coherent state with sizable mass enhancement associated with the quadrupole degree of freedom.

  13. Magnon-driven longitudinal spin Seebeck effect in F | N and N | F | N structures: Role of asymmetric in-plane magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Chotorlishvili, L.; Toklikishvili, Z.; Etesami, S. R.; Dugaev, V. K.; Barna?, J.; Berakdar, J.

    2015-12-01

    The influence of an asymmetric in-plane magnetic anisotropy Kx ?Ky on the thermally activated spin current is studied theoretically for two different systems: (i) the F | N system consisting of a ferromagnetic insulator (F) in a direct contact with a nonmagnetic metal (N) and (ii) the sandwich structure N | F | N consisting of a ferromagnetic insulating part sandwiched between two nonmagnetic metals. It is shown that when the difference between the temperatures of the two nonmagnetic metals in a N | F | N structure is not large, the spin pumping currents from the magnetic part to the nonmagnetic ones are equal in amplitude and have opposite directions, so only the spin torque current contributes to the total spin current. The spin current flows then from the nonmagnetic metal with the higher temperature to the nonmagnetic metal having a lower temperature. Its amplitude varies linearly with the difference in temperatures. In addition, we have found that if the magnetic anisotropy is in the layer plane, then the spin current increases with the magnon temperature, while in the case of an out-of-plane magnetic anisotropy the spin current decreases when the magnon temperature enhances. Enlarging the difference between the temperatures of the nonmagnetic metals, the linear response becomes important, as confirmed by analytical expressions inferred from the Fokker-Planck approach and by the results obtained upon a full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.

  14. Analysis of Residual Acceleration Effects on Transport and Segregation During Directional Solidification of Tin-Bismuth in the MEPHISTO Furnace Facility

    NASA Technical Reports Server (NTRS)

    Alexander J. Iwan D. (Principal Investigator)

    1996-01-01

    The objective of this work is to approach the problem of determining the transport conditions (and effects of residual acceleration) during the plane-front directional solidification of a tin-bismuth alloy under low gravity conditions. The work involves using a combination of 2- and 3-D numerical models, scaling analyses, ID models and the results of ground-based and low-gravity experiments. The latter are to be conducted during the MEPHISTO experiment scheduled for USMP-3 in early 1996. The models will be used to predict the response of the transport conditions and consequent solute segregation in directionally solidifying tin-bismuth melt. Real-time Seebeck voltage variations across a Sn-Bi melt during directional solidification in MEPHISTO on USMP-1 show a distinct variation which can be correlated with thruster firings. The Seebeck voltage measurement is related to the response of the instantaneous average melt composition at the melt-solid interface. This allows a direct comparison of numerical simulations with the Seebeck signals obtained on USMP-1. The effects of such accelerations on composition for a directionally solidifying Sn-Bi alloy have been simulated numerically. USMP-1 acceleration data was used to assist in our choice of acceleration magnitude and orientation. The results show good agreement with experimental observations. The USMP-3 experiments took place earlier this year (February 22 through March 6). There were several differences between the USMP-3 experiments as compared to USMP-1. Firstly a more concentrated alloy was solidified and, secondly, Primary Reaction Control System thruster burns were requested at particular times during four separate growth runs. This allowed us to monitor the response Seebeck response under well-characterized growth conditions. In addition, we carried out simulations during the experiment in order to interpret the Seebeck signal. Preliminary results are described here.

  15. Effect of aluminum on the thermoelectric properties of nanostructured PbTe.

    PubMed

    Zhang, Qinyong; Yang, Siqi; Zhang, Qian; Chen, Shuo; Liu, Weishu; Wang, Hui; Tian, Zhiting; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-08-30

    In the present work, the effect of aluminum (Al) on the thermoelectric properties of PbTe is studied. Aluminum doped PbTe samples, fabricated by a ball milling and hot pressing, have Seebeck coefficients between -100 and -200 ?V K-1 and electrical conductivities of (3.6-18) 104 S m-1 at room temperature, which means that Al is an effective donor in PbTe. The first principle calculations clearly show an increase of the density of states close to the Fermi level in the conduction band due to Al doping, which averages up the energy and effective mass of electrons, resulting in enhancement of the Seebeck coefficient. The maximum figure-of-merit ZT of 1.2 is reached at 770 K in the Al0.03PbTe sample. PMID:23912680

  16. Doping effects on thermoelectric properties of the off-stoichiometric Heusler compounds Fe{sub 2?x}V{sub 1+x}Al

    SciTech Connect

    Nishino, Y. Tamada, Y.

    2014-03-28

    The thermoelectric properties of Heusler-type Fe{sub 2?x}V{sub 1+x}Al{sub 1?y}Si{sub y} and Fe{sub 2?x}V{sub 1+x?y}Ti{sub y}Al alloys have been investigated to clarify which off-stoichiometric alloy, i.e., V-rich (x?>?0) or V-poor (x?effective in enhancing the Seebeck coefficient when doped by Si and Ti, while retaining a low electrical resistivity. Large Seebeck coefficients of ?182??V/K and 110??V/K at 300?K are obtained for n-type Fe{sub 1.95}V{sub 1.05}Al{sub 0.97}Si{sub 0.03} and p-type Fe{sub 2.04}V{sub 0.93}Ti{sub 0.03}Al, respectively. When the Seebeck coefficient is plotted as a function of valence electron concentration (VEC), the VEC dependence for the doped off-stoichiometric alloys falls on characteristic curves depending on the off-stoichiometric composition x. It is concluded that a larger Seebeck coefficient with a negative sign can be obtained for the V-rich alloys rather than the V-poor alloys, whilst good p-type materials are always derived from the V-poor alloys. Substantial enhancements in the Seebeck coefficient for the off-stoichiometric alloys could be achieved by a favorable modification in the electronic structure around the Fermi level through the antisite V or Fe defect formation.

  17. Thermoelectric effects in graphene nanostructures.

    PubMed

    Dollfus, Philippe; Hung Nguyen, Viet; Saint-Martin, Jrme

    2015-04-10

    The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very useful in elucidating some details of the electronic band structure of graphene that cannot be probed by conductance measurements alone, due in particular to the ambipolar nature of this gapless material. For applications in thermoelectric energy conversion, graphene has two major disadvantages. It is gapless, which leads to a small Seebeck coefficient due to the opposite contributions of electrons and holes, and it is an excellent thermal conductor. The thermoelectric figure of merit ZT of a two-dimensional (2D) graphene sheet is thus very limited. However, many works have demonstrated recently that appropriate nanostructuring and bandgap engineering of graphene can concomitantly strongly reduce the lattice thermal conductance and enhance the Seebeck coefficient without dramatically degrading the electronic conductance. Hence, in various graphene nanostructures, ZT has been predicted to be high enough to make them attractive for energy conversion. In this article, we review the main results obtained experimentally and theoretically on the thermoelectric properties of graphene and its nanostructures, emphasizing the physical effects that govern these properties. Beyond pure graphene structures, we discuss also the thermoelectric properties of some hybrid graphene structures, as graphane, layered carbon allotropes such as graphynes and graphdiynes, and graphene/hexagonal boron nitride heterostructures which offer new opportunities. Finally, we briefly review the recent activities on other atomically thin 2D semiconductors with finite bandgap, i.e. dichalcogenides and phosphorene, which have attracted great attention for various kinds of applications, including thermoelectrics. PMID:25779989

  18. Thermoelectric effects in graphene nanostructures

    NASA Astrophysics Data System (ADS)

    Dollfus, Philippe; Nguyen, Viet Hung; Saint-Martin, Jrme

    2015-04-01

    The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very useful in elucidating some details of the electronic band structure of graphene that cannot be probed by conductance measurements alone, due in particular to the ambipolar nature of this gapless material. For applications in thermoelectric energy conversion, graphene has two major disadvantages. It is gapless, which leads to a small Seebeck coefficient due to the opposite contributions of electrons and holes, and it is an excellent thermal conductor. The thermoelectric figure of merit ZT of a two-dimensional (2D) graphene sheet is thus very limited. However, many works have demonstrated recently that appropriate nanostructuring and bandgap engineering of graphene can concomitantly strongly reduce the lattice thermal conductance and enhance the Seebeck coefficient without dramatically degrading the electronic conductance. Hence, in various graphene nanostructures, ZT has been predicted to be high enough to make them attractive for energy conversion. In this article, we review the main results obtained experimentally and theoretically on the thermoelectric properties of graphene and its nanostructures, emphasizing the physical effects that govern these properties. Beyond pure graphene structures, we discuss also the thermoelectric properties of some hybrid graphene structures, as graphane, layered carbon allotropes such as graphynes and graphdiynes, and graphene/hexagonal boron nitride heterostructures which offer new opportunities. Finally, we briefly review the recent activities on other atomically thin 2D semiconductors with finite bandgap, i.e. dichalcogenides and phosphorene, which have attracted great attention for various kinds of applications, including thermoelectrics.

  19. On the Quantum Hall Effect in mono(bi)-layer graphene

    NASA Astrophysics Data System (ADS)

    Cheremisin, M. V.

    2014-11-01

    Based on a thermodynamic approach, we have calculated the specific resistivity of mono(bi)-layer graphene assumed dissipationless in quantizing magnetic field. The resistivity arises from combination of Peltier and Seebeck effects. The current I causes heating (cooling) at the first (second) sample contacts, due to the Peltier effect. The voltage measured across the sample is equal to the Seebeck thermoemf, and thus provides finite resistivity as I?0. The resistivity is a universal function of the magnetic field, e-h plasma density and temperature, expressed in fundamental units h/e2. At fixed magnetic field the magneto-transport problem is resolved in the vicinity of the Dirac point taking into account the splitting of zeroth Landau level. For mono(bi)- layer graphene the B-dependent splitting of zeroth Landau level is recovered from experimental data.

  20. 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 ( ? 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 110C; ? 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 23C agree with published values.

  1. Effects of Spark Plasma Sintering Temperature on Thermoelectric Properties of Higher Manganese Silicide

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    Higher manganese silicide (HMS) is a promising p-type thermoelectric material. HMS samples were synthesized by a vacuum induction melting process and sintered by spark plasma sintering (SPS) at various temperatures to obtain a single phase of HMS and investigate the effect of the SPS temperature on the thermoelectric properties. A single phase of HMS was obtained, and the appearance and the amount of Mn2O3 and MnSi as secondary phases could be controlled via the SPS temperature. The effects of the SPS temperature on the electrical conductivity and Seebeck coefficient of the HMS samples were investigated. The changes in the electrical conductivity and Seebeck coefficient were attributed to changes in the density and the amount of Mn2O3 secondary phase.

  2. The effect of elemental substitution on the electronic properties of Ru2Ge3

    NASA Astrophysics Data System (ADS)

    Hayward, M. A.; Cava, R. J.

    2002-07-01

    The effect of chemical substitution on the electrical resistivity and Seebeck coefficients of Ru2Ge3 is reported, with a particular emphasis on enhancing the properties relevant to thermoelectric behaviour. The properties of Ru2Ge3 itself are shown to be strongly dependent on quenching temperature. The effects of metal doping for Ru and metalloid substitution (Sn and Si) for Ge are reported. It is shown that doping of both ruthenium and germanium sites is required to reduce the high resistivity of Ru2Ge3(~ 280 m? cm at 300 K) to a value of 1.5 m? cm, for Ru1.85Mn0.15Ge2.4Sn0.6 while maintaining high Seebeck coefficients. This latter composition has the highest thermoelectric figure of merit observed in this system: ZT 300 K = 1 10-2. Unfortunately this value is too small to be competitive with existing materials.

  3. Effect of La-doping on AgSbTe2 thermoelectric compounds

    NASA Astrophysics Data System (ADS)

    Min, Bok-Ki; Kim, Bong-Seo; Oh, Min-Wook; Ryu, Byung-Ki; Lee, Ji-Eun; Joo, Sung-Jae; Park, Su-Dong; Lee, Hee-Woong; Lee, Ho-seong

    2016-01-01

    Ag(Sb1- x La x )Te2 compounds ( x = 0, 0.01, 0.02, 0.03, and 0.05) were fabricated to study the effect of La-doping on the thermoelectric properties by using a spark-plasma-sintering process. All specimens were nearly single-phase AgSbTe2 with a small amount of Ag2Te. The La doping in AgSbTe2 resulted in a reduction in the electrical and the thermal conductivity but increased the Seebeck coefficient. A small amount of La doping increased the Seebeck coefficient because of the electron filtering effect. The maximum figure of merit was 1.50 due to the enhanced power factor and extremely low thermal conductivity.

  4. Effective material properties of thermoelectric composites with elliptical fibers

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Ze

    2015-06-01

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

  5. Enhancement of thermospin effect in germanene based normal/ferromagnetic stub/normal junction

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Chi, Feng; Guo, Yong

    2015-11-01

    Spin thermoelectric effects in ferromagnetic (FM) germanene are theoretically investigated by using the nonequilibrium Green's function method. It is found that the spin Seebeck effect can be generated by temperature bias ? T when a FM germanene is considered in the central region. However, the obtained spin resolved Seebeck coefficients is quite low with maximum value of S ? ? 700 ? V / K . The spin Seebeck effect is shown to increase enormously in different energy states with the assistance of electric field or stub structure. By modulating the geometric parameters of stub, the spin thermopower Ss has distinct peak values in the bulk states. Moreover, varying the Fermi energy within the bulk gap by the gate, Ss can be significantly enhanced by increasing the strength of electric field. The spin thermopower obtained by each method is predicted to be 2500 ? V / K , which is more than 300% larger relative to the case without electric field or stub. In addition, the magnitude and sign of spin thermopower can be manipulated by adjusting the Fermi energy. The results show that such FM germanene stub device exhibits much better thermoelectric performance and may be used as a wide energy range tunable spin thermoelectric generator.

  6. Synthetic conditions and their doping effect on {Beta}-K{sub 2}Bi{sub 8}Se{sub 13}.

    SciTech Connect

    Kyratsi, Th.; Kika, I.; Hatzikraniotis, E.; Paraskevopoulos, K. M.; Chrissafis, K.; Kanatzidis, M. G.

    2009-04-01

    In this work the synthetic conditions for K{sub 2}Bi{sub 8}Se{sub 13} and their effect on its thermoelectric properties were investigated. K{sub 2}Bi{sub 8}Se{sub 13} was prepared as a single phase using K{sub 2}Se and Bi{sub 2}Se{sub 3} as starting materials in a furnace or via a reaction using direct flame, followed by remelting or annealing. Seebeck coefficient measurements showed that the doping level in the material is sensitive to the synthetic conditions. Higher synthesis temperatures as well as the flame reaction technique followed by annealing gave more homogenous samples with higher Seebeck coefficient. IR optical spectroscopic measurements showed a wide range of doping level achieved among the different synthetic conditions. These findings suggest that synthetic conditions can act as a useful tool for the optimization of the thermoelectric properties of these materials.

  7. Colossal enhancement in thermoelectric effect in a laterally coupled double-quantum-dot chain by the Coulomb interactions

    NASA Astrophysics Data System (ADS)

    Xiong, Lun; Yi, Lin

    2014-04-01

    Thermoelectric effects, including Seebeck coefficient (S), thermal conductance (?), and figure of merit (ZT), in a laterally coupled double-quantum-dot (DQD) chain with two external nonmagnetic contacts are investigated theoretically by the nonequilibrium Green's function formalism. In this system, the DQD chain between two contacts forms a main channel for thermal electrons transporting, and each QD in the main chain couples laterally to a dangling one. The numerical calculations show that the Coulomb interactions not only lead to the splitting of the asymmetrical double-peak structure of the Seebeck coefficient, but also make the thermal spectrum show a strong violation of the Wiedemann-Franz law, leading to a colossal enhancement in ZT. These results indicate that the coupled DQD chain has potential applications in the thermoelectric devices with high thermal efficiency.

  8. Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion.

    PubMed

    Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S; Chen, Gang

    2015-12-01

    Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect-a coupling phenomenon between electrons and nonequilibrium phonons-in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ?0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons. PMID:26627231

  9. Anomalous effect of vanadium boride seeding on thermoelectric properties of YB{sub 22}C{sub 2}N

    SciTech Connect

    Prytuliak, A.; Maruyama, S.; Mori, T.

    2013-05-15

    Highlights: ► We doped YB{sub 22}C{sub 2}N; the long awaited n-type counterpart to p-type boron carbide. ► VB{sub 2} seeding of YB{sub 22}C{sub 2}N showed striking results. ► Thermal treatment effects led to VB{sub 2} being intrinsically doped. ► Large increase of both Seebeck coefficient and electrical conductivity was obtained. - Abstract: Vanadium boride seeded YB{sub 22}C{sub 2}N were synthesized and the thermoelectric properties investigated. YB{sub 22}C{sub 2}N is representative of the series of rare earth borocarbonitrides which is the potential long awaited n-type counterpart to p-type boron carbide. VB{sub 2} seeded samples of YB{sub 22}C{sub 2}N were prepared using VB{sub 2} directly as an initial additive and V{sub 2}O{sub 3} which also results in formation of vanadium diboride in the final product. The resistivity and Seebeck coefficient of samples were measured in the temperature range of 323 K to 1073 K. A dramatic effect of thermal treatment on the Seebeck coefficient of VB{sub 2} seeded samples was observed, and it is indicated that there is possible partial intrinsic doping of vanadium into YB{sub 22}C{sub 2}N. VB{sub 2} is revealed to be a promising additive to improve the thermoelectric properties of YB{sub 22}C{sub 2}N. An enhancement of more than 220% of the maximum absolute value of the Seebeck coefficient was obtained while the resistivity was also reduced considerably.

  10. Effect of Deposition Conditions on the Microstructure and the Thermoelectric Properties of Galvanostatically Electrodeposited Bi2Te3 Film

    NASA Astrophysics Data System (ADS)

    Rashid, Mohammad Mamunur; Chung, Gwiy-Sang

    2013-10-01

    Bismuth Telluride (Bi2Te3) films were deposited by a simple and cost-effective galvanostatic electrodeposition process from a solution containing bismuth tri-nitrate penta-hydrate and tellurium dioxide of different concentration ratios in 1 M nitric acid onto gold sputtered silicon substrate at various current densities. The effect of distinct current densities, electrolyte concentrations and electrodes distances on the microstructure and the thermoelectric properties of Bi2Te3 films were investigated. X-Ray diffraction (XRD) and field emission scanning electron microscope (FESEM) analysis ensured a high density, homogenous and near stoichiometric film. The surface morphology, crystalline structure and grain size were correlated with the applied current density. A prominent orientation (110) was observed for all the films and the grain size was acquired from 21 to 45 nm. The Seebeck measurement affirmed n-type semiconductor behavior of the deposited films. Enhancement in carrier mobility without significant change of the carrier concentration and Seebeck coefficient was achieved by tuning the electrodes distance. The thermoelectric film has a maximum measured Seebeck coefficient of -61.215 ?V/K and a very high electrical conductivity of 2.13 103 ?-1 ? cmn-1. The maximum calculated power factor was 8.2 ?W?K-2 ? cm-1.

  11. Anomalous photovoltaic effect in La{0.8}Sr{0.2}MnO3 films grown on SrTiO3 (001) substrates by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhao, Kun; Lu, Hui-Bin; He, Meng; Huang, Yan-Hong; Jin, Kui-Juan; Chen, Zheng-Hao; Zhou, Yue-Liang; Yang, Guo-Zhen; Ma, Xiu-Liang

    2006-09-01

    Transient laser-induced anomalous photovoltaic effect has been studied in La{0.8}Sr{0.2}MnO{3} films grown on the SrTiO{3} (001) substrates by laser molecular beam epitaxy. It is demonstrated that the signal polarity is reversed when the films are irradiated through the substrate rather than at the air/film interface. The microstructures in these films are clarified in terms of the oriented microdomains with their (101) plane parallel to the substrate surface, suggesting off-diagonal Seebeck effect plays an important role for our observation. From the results, we obtain the anisotropy of the thermoelectric power ? S=Sab-Sc=0.3 ?V/K, where Sab and Sc are the ab-plane and c-axis Seebeck coefficients.

  12. Designing a Spin-Seebeck Diode

    NASA Astrophysics Data System (ADS)

    Borlenghi, Simone; Wang, Weiwei; Fangohr, Hans; Bergqvist, Lars; Delin, Anna

    2014-01-01

    Using micromagnetic simulations, we have investigated spin dynamics in a spin-valve bilayer in the presence of a thermal gradient. The direction and the intensity of the gradient allow us to excite the spin wave modes of each layer selectively. This permits us to synchronize the magnetization precession of the two layers and to rectify the flows of energy and magnetization through the system. Our study yields promising opportunities for applications in spin caloritronics and nanophononics devices.

  13. A systematic study on the effect of electron beam irradiation on structural, electrical, thermo-electric power and magnetic property of LaCoO3

    NASA Astrophysics Data System (ADS)

    Benedict, Christopher J.; Rao, Ashok; Sanjeev, Ganesh; Okram, G. S.; Babu, P. D.

    2016-01-01

    In this communication, the effect of electron beam irradiation on the structural, electrical, thermo-electric power and magnetic properties of LaCoO3 cobaltites have been investigated. Rietveld refinement of XRD data reveals that all samples are single phased with rhombohedral structure. Increase in electrical resistivity data is observed with increase in dosage of electron beam irradiation. Analysis of the measured electrical resistivity data indicates that the small polaron hopping model is operative in the high temperature regime for all samples. The Seebeck coefficient (S) of the pristine and the irradiated samples exhibits a crossover from positive to negative values, and a colossal value of Seebeck coefficient (32.65 mV/K) is obtained for pristine sample, however, the value of S decreases with increase in dosage of irradiation. The analysis of Seebeck coefficient data confirms that the small polaron hopping model is operative in the high temperature region. The magnetization results give clear evidence of increase in effective magnetic moment due to increase in dosage of electron beam irradiation.

  14. Effect of Sb deficiency on the thermoelectric properties of Zn4Sb3

    NASA Astrophysics Data System (ADS)

    Sanchela, Anup V.; Tomy, C. V.; Thakur, Ajay D.

    2015-09-01

    We have investigated the effect of Sb-deficiency on the thermoelectric figure of merit (zT) of Zn4Sb3 prepared by solid state reaction route. At high temperatures, the Seebeck coefficient (S) and electrical conductivity (?) increases with increase in Sb deficiency whereas the thermal conductivity (?) decreases giving rise to an increase in the overall zT value. The observations suggest that creation of vacancies could be an effective route in improving the thermoelectric properties of Zn4Sb3 system.

  15. Effect of crystal size distribution on thermoelectric performance for Lanthanum-doped strontium titanate bulk material

    NASA Astrophysics Data System (ADS)

    Zhang, Boyu; Wang, Jun; Yaer, Xinba; Huo, Zhenzhen; Wu, Yin; Li, Yan; Miao, Lei; Liu, Chengyan; Zou, Tao; Ma, Wen

    2015-07-01

    Effect of crystal size distribution on thermoelectric performance of Lanthanum-doped strontium titanate (La-SrTiO3) ceramics are investigated in this study. Thermoelectric performance measurement, coupled with microstructure studies, shows that the electrical conductivity strongly depends on the crystal size, potential barrier on the grain boundary and porosity. Meantime, because the average potential barriers height are increased along with the reduction of crystal size, the Seebeck coefficients are increased by energy filtering effect at the large number of grain boundaries. As a result, by controlling of crystal size distribution, ZT value of La-SrTiO3 is improved.

  16. Spin-dependent thermoelectric effects in graphene-based spin valves.

    PubMed

    Zeng, Minggang; Huang, Wen; Liang, Gengchiau

    2013-01-01

    Using first-principles calculations combined with non-equilibrium Green's function (NEGF), we investigate spin-dependent thermoelectric effects in a spin valve which consists of zigzag graphene nanoribbon (ZGNR) electrodes with different magnetic configurations. We find that electron transport properties in the ZGNR-based spin valve are strongly dependent on the magnetic configurations. As a result, with a temperature bias, thermally-induced currents can be controlled by switching the magnetic configurations, indicating a thermal magnetoresistance (MR) effect. Moreover, based on the linear response assumption, our study shows that the remarkably different Seebeck coefficients in the various magnetic configurations lead to a very large and controllable magneto Seebeck ratio. In addition, we evaluate thermoelectric properties, such as the power factor, electron thermal conductance and figure of merit (ZT), of the ZGNR-based spin valve. Our results indicate that the power factor and the electron thermal conductance are strongly related to the transmission gap and electron-hole symmetry of the transmission spectrum. Moreover, the value of ZT can reach 0.15 at room temperature without considering phonon scattering. In addition, we investigate the thermally-controlled magnetic distributions in the ZGNR-based spin valve and find that the magnetic distribution, especially the local magnetic moment around the Ni atom, is strongly related to the thermal bias. The very large, multi-valued and controllable thermal magnetoresistance and Seebeck effects indicate the strong potential of ZGNR-based spin valves for extremely low-power consuming spin caloritronics applications. The thermally-controlled magnetic moment in the ZGNR-based spin valve indicates its possible applications for information storage. PMID:23151965

  17. Effective Mass of Thermoelectric Materials with Non-Parabolic Kane Bands

    NASA Astrophysics Data System (ADS)

    Snyder, G. Jeffrey

    2015-03-01

    Effective mass is a concept commonly used to describe electronic transport in semiconductors using a classical analogy to the kinetic theory of gasses. We describe many important electronic transport parameters explicitly with an electronic band mass including: Density of states, charge carrier concentration, mobility, and in particular for thermoelectrics, the Seebeck coefficient. For systems with known electronic band structures these properties can be calculated leading to subtly different definitions of effective mass. In the free electron or parabolic band model the effective masses are the same and we use the term effective mass interchangably. However the differences between these defintions or uses of effective mass become apparent in non-parabolic band structures where it is desirable to describe the transport in terms of a effective mass that changes with energy (or Fermi Level). For example Kane bands, which become more linear and less parabolic at higher energy, have an increased density of states and therefore higher DOS effective mass than a parabolic band. While it is often assumed that also results in a higher thermopower (Seebeck coefficient), calculations of thermopower and Hall carrier concentration from the Kane model show the thermpower is actually reduced. Examples in thermoelectric materials will be discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  19. 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.

  20. Thermoelectric properties of single-wall carbon nanotube films: Effects of diameter and wet environment

    NASA Astrophysics Data System (ADS)

    Hayashi, Daisuke; Ueda, Tomohiro; Nakai, Yusuke; Kyakuno, Haruka; Miyata, Yasumitsu; Yamamoto, Takahiro; Saito, Takeshi; Hata, Kenji; Maniwa, Yutaka

    2016-02-01

    The Seebeck coefficient S and the electrical resistivity ρ of single-wall carbon nanotube (SWCNT) films were investigated as a function of the SWCNT diameter and carrier concentration. The S and ρ significantly changed in humid environments through p-type carrier doping. Experiments, combined with theoretical simulations based on the non-equilibrium Green’s function theory, indicated that the power factor P can be increased threefold by the enrichment of semiconducting SWCNTs, but the nanotube diameter has little effect. The improvement of the film resistivity strongly enhances the film thermoelectric performance, manifested as increasing the value of P above 1200 µW/(m·K2).

  1. Large extrinsic spin Hall effect in Au-Cu alloys by extensive atomic disorder scattering

    NASA Astrophysics Data System (ADS)

    Zou, L. K.; Wang, S. H.; Zhang, Y.; Sun, J. R.; Cai, J. W.; Kang, S. S.

    2016-01-01

    Spin Hall angle, which denotes the conversion efficiency between spin and charge current, is a key parameter in the pure spin current phenomenon. The search for materials with large spin Hall angle is indeed important for scientific interest and potential application in spintronics. Here the large enhanced spin Hall effect (SHE) of Au-Cu alloy is reported by investigating the spin Seebeck effect, spin Hall anomalous Hall effect, and spin Hall magnetoresistance of the Y3F e5O12 (YIG)/A uxC u1 -x hybrid structure over the full composition. At the near equiatomic Au-Cu composition with maximum atomic disorder scattering, the spin Hall angle of the Au-Cu alloy increases by two to three times together with a moderate spin diffusion length in comparison with Au. The longitudinal spin Seebeck voltage and the spin Hall magnetoresistance ratio also increase by two to three times. More importantly, no evidence of anomalous Hall effect is observed in all YIG/Au-Cu samples, in contrast to the cases of other giant SHE materials Pt(Pd), Ta, and W. This behavior makes Au-Cu free from any suspicion of the magnetic proximity effect involved in the hybrid structure, and thus the Au-Cu alloy can be an ideal material for pure spin current study.

  2. Nernst Effect in HTC cuprate from BDW

    NASA Astrophysics Data System (ADS)

    Liu, Chunxiao

    2015-03-01

    The pseudogap regime in low hole doped high Tc cuprate superconductors exhibits peculiar experimental signatures like the detection of enhanced negative signals for Hall, Seebeck and Nernst coefficients. It has been suggested that some of these phenomena can be understood in terms of a competition between a bond density wave order and superconductivity. In this work, we theoretically studied the Nernst effect using a mean-field quasiparticle model with Q1 = (0 , 2 ? / 3) and Q2 = (2 ? / 3 , 0) . By employing semi-classical Boltzmann dynamics, we have shown that the thermoelectric coefficient depends linearly on the absolute value of order parameter for small values of the induced gap and the contribution mainly comes from the small area of hot spot.

  3. Observation of the Spin Peltier Effect for Magnetic Insulators

    NASA Astrophysics Data System (ADS)

    Flipse, J.; Dejene, F. K.; Wagenaar, D.; Bauer, G. E. W.; Youssef, J. Ben; van Wees, B. J.

    2014-07-01

    We report the observation of the spin Peltier effect (SPE) in the ferrimagnetic insulator yttrium iron garnet (YIG), i.e., a heat current generated by a spin current flowing through a platinum (Pt)|YIG interface. The effect can be explained by the spin transfer torque that transforms the spin current in the Pt into a magnon current in the YIG. Via magnon-phonon interactions the magnetic fluctuations modulate the phonon temperature that is detected by a thermopile close to the interface. By finite-element modeling we verify the reciprocity between the spin Peltier and spin Seebeck effect. The observed strong coupling between thermal magnons and phonons in YIG is attractive for nanoscale cooling techniques.

  4. Observation of the spin Peltier effect for magnetic insulators.

    PubMed

    Flipse, J; Dejene, F K; Wagenaar, D; Bauer, G E W; Ben Youssef, J; van Wees, B J

    2014-07-11

    We report the observation of the spin Peltier effect (SPE) in the ferrimagnetic insulator yttrium iron garnet (YIG), i.e., a heat current generated by a spin current flowing through a platinum (Pt)|YIG interface. The effect can be explained by the spin transfer torque that transforms the spin current in the Pt into a magnon current in the YIG. Via magnon-phonon interactions the magnetic fluctuations modulate the phonon temperature that is detected by a thermopile close to the interface. By finite-element modeling we verify the reciprocity between the spin Peltier and spin Seebeck effect. The observed strong coupling between thermal magnons and phonons in YIG is attractive for nanoscale cooling techniques. PMID:25062233

  5. Thermal Cycling Effects on the Thermoelectric Properties of n-Type In, Ce based Skutterudite Compounds

    SciTech Connect

    Biswas, Krishnendu; Subramanian, Mas A.; Good, Morris S.; Roberts, Kamandi C.; Hendricks, Terry J.

    2012-06-14

    N-type In-filled CoSb3 are known skutterudite compounds that have shown promising thermoelectric (TE) properties resulting in high dimensionless figure of merit values at elevated temperatures. Their use in various waste heat recovery applications will require that they survive and operate after exposure to harsh thermal cycling environments. This research focused on uncovering the thermal cycling effects on thermoelectric properties of n-type In0.2Co4Sb12 and In0.2Ce0.15Co4Sb12 skutterudite compositions as well as quantifying their temperature-dependent structural properties (elastic modulus, shear modulus, and Poisson's ratio). It was observed that the Seebeck coefficient and resistivity increased only slightly in the double-filled In,Ce skutterudite materials upon thermal cycling. In the In-filled skutterudites the Seebeck coefficient remained approximately the same on thermal cycling, while electrical resistivity increased significantly after thermal cycling. Results also show that thermal conductivity marginally decreases in the case of In-filled skutterudites, whereas the reduction is more pronounced in In, Ce-based skutterudite compounds. The possible reason for this kind of reduction can be attributed to grain pinning effects due to formation of nano inclusions. High temperature structural property measurements (i.e., Young's modulus and shear modulus) are also reported and the results show that these structural properties decrease slowly as temperature increases and the compounds are structurally stable after numerous thermal cycles.

  6. A Quantitative Model for the Thermocouple Effect Using Statistical and Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Bramley, Paul; Clark, Stewart

    2003-09-01

    This paper employs statistical and quantum mechanics to develop a model for the mechanism underlying the Seebeck effect. The conventional view of the equilibrium criterion for valence electrons in a material is that the Fermi Energy should be constant throughout the system. However, this criterion is an approximation and it is shown to be inadequate for thermocouple systems. An improved equilibrium criterion is developed by applying statistical and quantum mechanics to determine the total flow of electrons across an arbitrary boundary within a system. Dynamic equilibrium is then considered to be the situation where the Fermi Energy either side of the boundary is such that the flow of electrons in each direction is the same. This equilibrium criterion is then applied to the conditions along the thermocouple wires and at the junctions in order to generate a model for the Seebeck effect. The equations involved for calculating the electronic structure of a material cannot be solved analytically, so a solution is achieved using numeric models employing CASTEP code running on a Sun Beowulf cluster and iterative algorithms written in the Excel VBA language on a PC. The model is used to calculate the EMF versus temperature function for the gold versus platinum thermocouple, which is then compared with established experimental data.

  7. Enhancement of the thermoelectric figure of merit in DNA-like systems induced by Fano and Dicke effects.

    PubMed

    Fu, Hua-Hua; Gu, Lei; Wu, Dan-Dan; Zhang, Zu-Quan

    2015-04-28

    We report a theoretical study highlighting the thermoelectric properties of biological and synthetic DNA molecules. Based on an effective tight-binding model of duplex DNA and by using the nonequilibrium Green's function technique, the thermal conductance, electrical conductance, Seebeck coefficient and thermoelectric figure of merit in the system are numerically calculated by varying the asymmetries of energies and electronic hoppings in the backbone sites to simulate the environmental complications and fluctuations. We find that due to the multiple transport paths in the DNA molecule, the Fano antiresonance occurs, and enhances the Seebeck coefficient and the figure of merit. When the energy difference is produced in every opposite backbone site, the Dicke effect appears. This effect gives rise to a semiconducting-metallic transition, and enhances the thermoelectric efficiency of the DNA molecule remarkably. Moreover, as the Fano antiresonance point is close to the Dicke resonance one, a giant enhancement in the thermoelectric figure of merit in the DNA molecule has been found. These results provide a scenario to obtain effective routes to enhance the thermoelectric efficiency in the DNA molecules, and suggest perspectives for future experiments intending to control the thermoelectric transport in DNA-like nanodevices. PMID:25826287

  8. 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.

  9. Effect of a transverse magnetic field on solidification structure in directionally solidified Sn-Pb hypoeutectic alloys

    NASA Astrophysics Data System (ADS)

    Du, Dafan; Lu, Zhenyuan; Gagnoud, Annie; Fautrelle, Yves; Ren, Zhongming; Lu, Xionggang; Moreau, Rene; Li, Xi

    2014-09-01

    Effect of a transverse magnetic field on the macrosegregation and the growth of the Sn dendrite in the directionally solidified Sn-Pb alloys was investigated experimentally. The results indicated that the magnetic field modified the shape of the liquid/solid interface and the dendrite morphology significantly. Indeed, the application of the magnetic field caused the formation of the sloping interface and the refinement of the dendrite. It is also found that the magnetic field decreased the mushy zone length. These effects were enhanced with the increase of the magnetic field intensity and the decrease of the growth speed. Further, the Seebeck thermoelectric force (ES) at the liquid/solid interface in the Sn-20 wt%Pb alloy was measured in-situ and the results indicated that the value of the Seebeck thermoelectric force was about 1 ?V. The modification of the solidification structure during directional solidification under the magnetic field may be attributed to the interdendritic thermoelectric magnetic convection (TEMC).

  10. Thermoelectric Effects in Simulations of Phase Change Memory Mushroom Cells

    NASA Astrophysics Data System (ADS)

    Faraclas, Azer; Bakan, Gokhan; Gokirmak, Ali; Silva, Helena

    2012-02-01

    Phase change memory is a potential candidate for the future of high-speed non-volatile memory, however significant improvements in cell design is crucial for its success in the mainstream market. Due to the asymmetric geometry of phase change mushroom cells and the high temperature gradients generated, thermoelectric effects play a key role in determining energy consumption, cell performance, and reliability. In this study, rotationally symmetric 2D finite element simulations using COMSOL Multiphysics are implemented for GeSbTe (GST). Temperature dependent material parameters (electrical conductivity, thermal conductivity, heat capacity, and Seebeck coefficient) are included in the model for accuracy. Switching the direction of current shows a large change in peak molten volume within the cell, as well as current and power consumption.

  11. Competing spin pumping effects in magnetic hybrid structures

    SciTech Connect

    Azevedo, A. Alves Santos, O.; Fonseca Guerra, G. A.; Cunha, R. O.; Rezende, S. M.; Rodrguez-Surez, R.

    2014-02-03

    Pure spin current can be detected by its conversion into charge current in nanometer thick nonmagnetic metal layer with large spin-orbit coupling by means of the inverse spin Hall effect (ISHE). Recently, it has been shown that the metallic ferromagnet Permalloy (Py) can also be used as spin current detector in experiments in which an ISHE voltage is created in a Py layer in contact with the insulating ferromagnet yttrium iron garnet (YIG) under a thermal gradient in the longitudinal spin Seebeck configuration. Here, we report experiments with microwave driven spin pumping in heterostructures made with single crystal YIG film and a nanometer thick Py or Pt layer that show that Py behaves differently than nonmagnetic metals as a spin current detector. The results are attributed to the competition between the spin currents generated by the dynamics of the magnetizations in YIG and in Py, which are exchange coupled at the interface.

  12. The Effect of Adding Nano-Bi2Te3 on Properties of GeTe-Based Thermoelectric Material

    NASA Astrophysics Data System (ADS)

    Zhang, Lili; Wang, Wei; Ren, Baoguo; Guo, Jinjuan

    2013-07-01

    The efficient thermoelectric materials (GeTe)0.85- x (Mn0.6Sn0.4Te)0.15(Bi2Te3) x (0 ? x ? 0.05), in which Bi2Te3 is nanopowder, were prepared by hot pressing. The effect of adding neutral nano-Bi2Te3 content on the thermoelectric properties of germanium telluride was investigated. With increasing x, the thermal conductivity of the prepared samples decreased significantly and the Seebeck coefficient declined slightly, while there was no obvious change in electrical conductivity. In both electrical conductivity and Seebeck coefficient curves at different x values, there are inflection points around 600 K. The maximum dimensionless figure of merit ZT of the prepared materials is 1.54, attained in the temperature range from 700 K to 750 K for x = 0.03. The x-ray diffraction (XRD) pattern shows that Bi2Te3 has been alloyed into the GeTe-MnTe-SnTe alloy, which is consistent with the high-resolution scanning electron microscopy (HRSEM) images. Adding nano-Bi2Te3 to GeTe-based materials could also increase their performance stability at high temperature as a result of decreasing the phase-transition temperature T c.

  13. Performance Prediction of Commercial Thermoelectric Cooler Modules using the Effective Material Properties

    NASA Astrophysics Data System (ADS)

    Lee, HoSung; Attar, Alaa M.; Weera, Sean L.

    2015-06-01

    This work examines the validity of formulating the effective thermoelectric material properties as a way to predict thermoelectric module performance. The three maximum parameters (temperature difference, current, and cooling power) of a thermoelectric cooler were formulated on the basis of the hot junction temperature. Then, the effective material properties (Seebeck coefficient, electrical resistance, and thermal conductivity) were defined in terms of the three maximum parameters that were taken from either a commercial thermoelectric cooler module or the measurements. It is demonstrated that the simple standard equation with the effective material properties predicts well the performance curves of the four selected commercial products. Normalized parameters over the maximum parameters were also formulated to present the characteristics of the thermoelectric coolers along with the normalized charts. The normalized charts would be universal for a given thermoelectric material.

  14. Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review.

    PubMed

    Niimi, Yasuhiro; Otani, YoshiChika

    2015-12-01

    Spin Hall effect and its inverse provide essential means to convert charge to spin currents and vice versa, which serve as a primary function for spintronic phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck effect. These effects can oscillate magnetization or detect a thermally generated spin splitting in the chemical potential. Importantly this conversion process occurs via the spin-orbit interaction, and requires neither magnetic materials nor external magnetic fields. However, the spin Hall angle, i.e. the conversion yield between the charge and spin currents, depends severely on the experimental methods. Here we discuss the spin Hall angle and the spin diffusion length for a variety of materials including pure metals such as Pt and Ta, alloys and oxides determined by the spin absorption method in a lateral spin valve structure. PMID:26513299

  15. Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review

    NASA Astrophysics Data System (ADS)

    Niimi, Yasuhiro; Otani, YoshiChika

    2015-12-01

    Spin Hall effect and its inverse provide essential means to convert charge to spin currents and vice versa, which serve as a primary function for spintronic phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck effect. These effects can oscillate magnetization or detect a thermally generated spin splitting in the chemical potential. Importantly this conversion process occurs via the spin-orbit interaction, and requires neither magnetic materials nor external magnetic fields. However, the spin Hall angle, i.e. the conversion yield between the charge and spin currents, depends severely on the experimental methods. Here we discuss the spin Hall angle and the spin diffusion length for a variety of materials including pure metals such as Pt and Ta, alloys and oxides determined by the spin absorption method in a lateral spin valve structure.

  16. Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Shirataki, Ritsuko

    2014-09-01

    The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8Al x Si46-x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

  17. Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Shirataki, Ritsuko

    2015-06-01

    The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8Al x Si46- x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

  18. Observation of pure inverse spin Hall effect in ferromagnetic metals via ferromagnetic/antiferromagnetic exchange-bias structures

    NASA Astrophysics Data System (ADS)

    Wu, H.; Wan, C. H.; Yuan, Z. H.; Zhang, X.; Jiang, J.; Zhang, Q. T.; Wen, Z. C.; Han, X. F.

    2015-08-01

    We report that the spin current generated by the spin Seebeck effect (SSE) in yttrium iron garnet (YIG) can be detected by a ferromagnetic metal (NiFe). By using the ferromagnetic/antiferromagnetic (FM/AFM) exchange bias structure (NiFe/IrMn), the inverse spin Hall effect (ISHE) and planar Nernst effect (PNE) of NiFe can be unambiguously separated, allowing us to observe a pure ISHE signal. After eliminating the in-plane temperature gradient in NiFe, we can even observe a pure ISHE signal without PNE from NiFe itself. It is worth noting that a large spin Hall angle (0.098) of NiFe is obtained, which is comparable with Pt. This work provides a kind of FM/AFM exchange bias structure to detect the spin current by charge signals, and highlights that ISHE in ferromagnetic metals can be used in spintronic research and applications.

  19. Spin Hall magnetoresistance at Pt/CoFe2O4 interfaces and texture effects

    NASA Astrophysics Data System (ADS)

    Isasa, Miren; Bedoya-Pinto, Amilcar; Vlez, Sal; Golmar, Federico; Snchez, Florencio; Hueso, Luis E.; Fontcuberta, Josep; Casanova, Flix

    2014-10-01

    We report magnetoresistance measurements on thin Pt bars grown on epitaxial (001) and (111) CoFe2O4 (CFO) ferrimagnetic insulating films. The results can be described in terms of the recently discovered spin Hall magnetoresistance (SMR). The magnitude of the SMR depends on the interface preparation conditions, being optimal when the Pt/CFO samples are prepared in situ, in a single process. The spin-mixing interface conductance, the key parameter governing SMR and other relevant spin-dependent phenomena, such as spin pumping or spin Seebeck effect, is found to be different depending on the crystallographic orientation of CFO, highlighting the role of the composition and density of magnetic ions at the interface on spin mixing.

  20. Ultraviolet fast-response photoelectric effect in tilted orientation SrTiO{sub 3} single crystals

    SciTech Connect

    Zhao Kun; Jin Kuijuan; Huang Yanhong; Zhao Songqing; Lu Huibin; He Meng; Chen Zhenghao; Zhou Yueliang; Yang Guozhen

    2006-10-23

    Ultraviolet photoelectricity based on the vicinal cut as-supplied SrTiO{sub 3} single crystals has been experimentally studied in the absence of an applied bias at room temperature. An open-circuit photovoltage of 130 ps rise time and 230 ps full width at half maximum was observed under the irradiation of a 355 nm pulsed laser of 25 ps in duration. The dependence of the photoelectric effect on the tilting angles was studied, and the optimum angle is 20.9 deg. . Seebeck effect is proposed to elucidate the tilting angle dependence of laser-induced photovoltage. This work demonstrates the potential of SrTiO{sub 3} single crystals in ultraviolet detection.

  1. The effect of the precursor nanopowder size on the thermoelectric properties of nanostructured Bi-Sb-Te bulk materials

    NASA Astrophysics Data System (ADS)

    Ren, Weili; Cheng, Chunxia; Ren, Zhongming; Zhong, Yunbo

    2010-12-01

    This paper presents the effect of precursor powder size on the thermoelectric properties of sintered nanostructured bulk materials. The transport properties of the nanostructured bulk show a dramatic size effect. There are a lower thermal and electrical conductivity for the bulk with smaller nanopowders. The dimensionless figure-of merit values ( ZT) of almost all the samples are much lower than those of the list reported data in the paper because the decrease in the thermal conductivity is counteracted by the reduction in the electrical conductivity and the Seebeck coefficient. The combination route of hydro/solvothermal synthesis and spark-plasma-sintering method provide a well controlled way to significantly reduce the thermal conductivity.

  2. Annealing effects on the structural and electrical transport properties of n-type Bi 2Te 2.7Se 0.3 thin films deposited by flash evaporation

    NASA Astrophysics Data System (ADS)

    Duan, Xingkai; Jiang, Yuezhen

    2010-10-01

    N-type Bi 2Te 2.7Se 0.3 thermoelectric thin films with thickness 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. Annealing effects on the thermoelectric properties of Bi 2Te 2.7Se 0.3 thin films were examined in the temperature range 373-573 K. The structures, morphology and chemical composition of the thin films were characterized by X-ray diffraction, field emission scanning electron microscope and energy dispersive X-ray spectroscopy, respectively. Thermoelectric properties of the thin films have been evaluated by measurements of the electrical resistivity and Seebeck coefficient at 300 K. The Hall coefficients were measured at room temperature by the Van der Pauw method. The carrier concentration and mobility were calculated from the Hall coefficient. The films thickness of the annealed samples was measured by ellipsometer. When annealed at 473 K, the electrical resistivity and Seebeck coefficient are 2.7 m? cm and -180 ?V/K, respectively. The maximum of thermoelectric power factor is enhanced to 12 ?W/cm K 2.

  3. Inserting Tin or Antimony Atoms into Mg2Si: Effect on the Electronic and Thermoelectric Properties

    NASA Astrophysics Data System (ADS)

    Balout, H.; Boulet, P.; Record, M.-C.

    2015-11-01

    Density functional and Boltzmann transport theories have been used to investigate the effect of constraints generated by substituting tin for silicon atoms or by inserting antimony atoms into Mg2Si on the electronic and thermoelectric properties of this compound. The investigated hypothetical structures are Mg2Si1- x Sn x with x equal to 0.125, 0.25, 0.375, 0.625, 0.75, and 0.875, and Mg8Si4Sb, Mg8Si4Sb3, and Mg2SiSb. The transport properties are presented with respect to the energy at three predefined temperatures and with respect to temperature for low and high electron and hole dopings. The effects of Sn-for-Si substitution are very similar to those observed for Mg2Si subjected to uniaxial and biaxial tensile strains. Overall, the power factor decreases as the doping level or tensile strain increases. In contrast, the maximum of the power factor increases with temperature. Irrespective of the temperature and electron or hole doping levels, the electrical conductivity ? of the Sb-inserted Mg2Si structures is far higher than that of Mg2Si. In the Fermi level energy region, the Seebeck coefficient S of the Sb-inserted Mg2Si structures is lower than that of Mg2Si. For Mg8Si4Sb3 and Mg2SiSb, the opposite is observed in the region where the electron density is very small (about 2 eV below the Fermi level). As a consequence, the power factor follows the same trends as the Seebeck coefficient.

  4. Al insertion and additive effects on the thermoelectric properties of yttrium boride

    SciTech Connect

    Maruyama, Satofumi; Prytuliak, Anastasiia; Miyazaki, Yuzuru; Hayashi, Kei; Kajitani, Tsuyoshi; Mori, Takao

    2014-03-28

    The aluminoboride Y{sub x}Al{sub y}B{sub 14} (x ∼ 0.57, 0.41 ≤ y ≤ 0.63) has been found to show striking p-n control of the thermoelectric properties through variations of the y occupancy of the Al site. The effect of Al was investigated in further extremes. Polycrystalline samples of Al-free Y{sub x}B{sub 14}(x ∼ 0.55; “YB{sub 25}”) were successfully synthesized in sufficient amounts for bulk spark plasma sintering (SPS) samples and their thermoelectric properties were investigated. Y{sub 0.56}Al{sub 0.57}B{sub 14} was also prepared in comparison, and further Al was added to the samples through SPS treatment. We observed that Y{sub 0.55}B{sub 14} exhibits large positive Seebeck coefficients, ∼1000 μV K{sup −1}, around room temperature and the absolute value of the Seebeck coefficient largely decreases with increase of temperature while that of Y{sub 0.56}Al{sub 0.57}B{sub 14} is proportional to T{sup −1/2}, indicating a strong effect of Al on the electronic structure around the Fermi level. Y{sub 0.55}B{sub 14} was found to be strongly disordered with a relatively low thermal conductivity and short localization length of 0.65 Å which is close to that previously determined for the disordered and thermally glass-like compound YB{sub 66}. Occupancy of Al could not be increased further for the Al-rich sample, although Al was discovered to act as a sintering aid to enhance density and ZT could be significantly improved by 50%.

  5. Ion beam irradiation effect on thermoelectric properties of Bi2Te3 and Sb2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Fu, Gaosheng; Zuo, Lei; Lian, Jie; Wang, Yongqiang; Chen, Jie; Longtin, Jon; Xiao, Zhigang

    2015-09-01

    Thermoelectric energy harvesting is a very promising application in nuclear power plants for self-maintained wireless sensors. However, the effects of intensive radiation on the performance of thermoelectric materials under relevant reactor environments such as energetic neutrons are not fully understood. In this work, radiation effects of bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric thin film samples prepared by E-beam evaporation are investigated using Ne2+ ion irradiations at different fluences of 5 × 1014, 1015, 5 × 1015 and 1016 ions/cm2 with the focus on the transport and structural properties. Electrical conductivities, Seebeck coefficients and power factors are characterized as ion fluence changes. X-ray diffraction (XRD) and transmission electron microscopy (TEM) of the samples are obtained to assess how phase and microstructure influence the transport properties. Carrier concentration and Hall mobility are obtained from Hall effect measurements, which provide further insight into the electrical conductivity and Seebeck coefficient mechanisms. Positive effects of ion irradiations from Ne2+ on thermoelectric material property are observed to increase the power factor to 208% for Bi2Te3 and 337% for Sb2Te3 materials between fluence of 1 and 5 × 1015 cm2, due to the increasing of the electrical conductivity as a result of ionization radiation-enhanced crystallinity. However, under a higher fluence, 5 × 1015 cm2 in this case, the power factor starts to decrease accordingly, limiting the enhancements of thermoelectric materials properties under intensive radiation environment.

  6. Control of valley degeneracy in Mo S2 by layer thickness and electric field and its effect on thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Hong, Jisook; Lee, Changhoon; Park, Jin-Seong; Shim, Ji Hoon

    2016-01-01

    We have investigated the valley degeneracy of Mo S2 multilayers and its effect on thermoelectric power factors. By modulating the layer thickness and external electric field strength, the hole valleys in the highest energy valence band at Γ and K points and the electron valleys in the lowest energy conduction band at K and Σmin points are shifted differently. The hole valley degeneracy is observed in Mo S2 monolayer, while that of electron valley is in Mo S2 bilayer and monolayer under the external electric field. By tuning the valley degeneracy, the Seebeck coefficient and electrical conductivity can be separately controlled, and the maximum power factor can be obtained in n -type (p -type) Mo S2 monolayer with (without) the external electric field. We suggest that the transition metal dichalcogenides are good examples to investigate the role of valley degeneracy in the thermoelectric and optical properties with the control of interlayer interaction and external electric field strength.

  7. Nitrogen composition dependence of electron effective mass in GaAs1-xNx

    SciTech Connect

    Dannecker, T.; Jin, Y.; Cheng, H.; Gorman, C. F.; Buckeridge, J.; Uher, Ctirad; Fahy, S.; Kurdak, C.; Goldman, Rachel S.

    2010-09-03

    We have investigated the N composition, x , and temperature, T , dependence of the electron effective mass, m*, of GaAs1-x Nx films with sufficiently low carrier concentration that carriers are expected to be confined to near the bottom of the conduction-band edge (CBE). Using Seebeck and Hall measurements, in conjunction with assumptions of parabolic bands and Fermi-Dirac statistics, we find a nonmonotonic dependence of m* on x and an increasing T dependence of m* with x . These trends are not predicted by the two-state band anticrossing model but instead are consistent with the predictions of the linear combination of resonant nitrogen states model, which takes into account several N-related states and their interaction with the GaAs CBE.

  8. Spin Hall magnetoresistance at Pt/CoFe{sub 2}O{sub 4} interfaces and texture effects

    SciTech Connect

    Isasa, Miren; Bedoya-Pinto, Amilcar; Vlez, Sal; Golmar, Federico; Snchez, Florencio; Fontcuberta, Josep; Hueso, Luis E.; Casanova, Flix

    2014-10-06

    We report magnetoresistance measurements on thin Pt bars grown on epitaxial (001) and (111) CoFe{sub 2}O{sub 4} (CFO) ferrimagnetic insulating films. The results can be described in terms of the recently discovered spin Hall magnetoresistance (SMR). The magnitude of the SMR depends on the interface preparation conditions, being optimal when the Pt/CFO samples are prepared in situ, in a single process. The spin-mixing interface conductance, the key parameter governing SMR and other relevant spin-dependent phenomena, such as spin pumping or spin Seebeck effect, is found to be different depending on the crystallographic orientation of CFO, highlighting the role of the composition and density of magnetic ions at the interface on spin mixing.

  9. Phonon-Drag Effect of Ultra-Thin FeSi2 and MnSi1.7/FeSi2 Films

    NASA Astrophysics Data System (ADS)

    Hou, Q. R.; Gu, B. F.; Chen, Y. B.; He, Y. J.

    Phonon-drag effect usually occurs in single crystals at very low temperatures (10-200 K). Strong phonon-drag effect is observed in ultra-thin ?-FeSi2 films at around room temperature. The Seebeck coefficient of a 23 nm-thick ?-FeSi2 film can reach -1.375 mV/K at 343 K. However, the thermoelectric power factor of the film is still small, only 0.4210-3 W/m-K2, due to its large electrical resistivity. When a 27 nm-thick MnSi1.7 film with low electrical resistivity is grown on it, the thermoelectric power factor of the MnSi1.7 film can reach 1.510-3 W/m-K2 at around room temperature. This value is larger than that of bulk MnSi1.7 material in the same temperature range.

  10. Transverse thermoelectric effect in La{sub 0.67}Sr{sub 0.33}MnO{sub 3}|SrRuO{sub 3} superlattices

    SciTech Connect

    Shiomi, Y.; Handa, Y.; Kikkawa, T.; Saitoh, E.

    2015-06-08

    Transverse thermoelectric effects in response to an out-of-plane heat current have been studied in an external magnetic field for ferromagnetic superlattices consisting of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} and SrRuO{sub 3} layers. The superlattices were fabricated on SrTiO{sub 3} substrates by pulsed laser deposition. We found that the sign of the transverse thermoelectric voltage for the superlattices is opposite to that for La{sub 0.67}Sr{sub 0.33}MnO{sub 3} and SrRuO{sub 3} single layers at 200 K, implying an important role of spin Seebeck effects inside the superlattices. At 10 K, the magnetothermoelectric curves shift from the zero field due to an antiferromagnetic coupling between layers in the superlattices.

  11. Effects of Nano-?-Al2O3 Dispersion on the Thermoelectric and Mechanical Properties of CoSb3 Composites

    NASA Astrophysics Data System (ADS)

    Wen, Pengfei; Mei, Hong; Zhai, Pengcheng; Duan, Bo

    2013-11-01

    Nano-?-Al2O3/CoSb3 composites with different ?-Al2O3 contents were prepared by spark plasma sintering. The effects of ?-Al2O3 addition on the microstructure, the thermoelectric properties, and the mechanical properties were studied in this article. It is found that ?-Al2O3 nanoparticles locate mainly at grain boundaries of the matrix. The dispersed particles decrease both the electrical conductivity and the thermal conductivity, but make the Seebeck coefficient increase. The dimensionless figure of merit is nearly unchanged by the dispersion. However, the introduction of nano-?-Al2O3 is very effective in improving the mechanical performance of the composites. The compressive strength and flexural strength of the 1.0 wt.% nano-?-Al2O3 dispersed samples are improved by 42.7 and 52.0%, respectively, compared with the nondispersed samples.

  12. Terahertz ratchet effects in graphene with a lateral superlattice

    NASA Astrophysics Data System (ADS)

    Olbrich, P.; Kamann, J.; König, M.; Munzert, J.; Tutsch, L.; Eroms, J.; Weiss, D.; Liu, Ming-Hao; Golub, L. E.; Ivchenko, E. L.; Popov, V. V.; Fateev, D. V.; Mashinsky, K. V.; Fromm, F.; Seyller, Th.; Ganichev, S. D.

    2016-02-01

    Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A lateral superlattice deposited on top of monolayer graphene is formed either by periodically repeated metal stripes having different widths and spacings or by interdigitated comblike dual-grating-gate (DGG) structures. We show that the ratchet photocurrent excited by terahertz radiation and sensitive to the radiation polarization state can be efficiently controlled by the back gate driving the system through the Dirac point as well as by the lateral asymmetry varied by applying unequal voltages to the DGG subgratings. The ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of "linear" and "circular" ratchets, sensitive to the corresponding polarization of the driving electromagnetic force. The experimental data are analyzed for the electronic and plasmonic ratchets taking into account the calculated potential profile and the near field acting on carriers in graphene. We show that the photocurrent generation is based on a combined action of a spatially periodic in-plane potential and the spatially modulated light due to the near-field effects of the light diffraction.

  13. Transport Magnetic Proximity Effects in Platinum

    NASA Astrophysics Data System (ADS)

    Huang, Ssu-Yen

    2013-03-01

    Platinum (Pt) metal, being non-magnetic and having a strong spin-orbit coupling interaction, has been central in detecting pure spin current and establishing most of the recent spin-based phenomena. Thus, it is important to ascertain the transport and magnetic characteristics of thin Pt films in contact with a ferromagnet. In this work, we use both electric and thermal means to conclusively show the transport magnetic proximity effects (MPE) of thin Pt film in contact with ferromagnetic insulator YIG. At thicknesses comparable to, and less than, the spin diffusion length, the strong ferromagnetic characteristics in Pt films on YIG are indistinguishable from those of ferromagnetic permalloy on YIG. The MPE occurs at the interface and decreases exponentially away from the interface, concentrating in only a few monolayers. As a result, the pure spin current detected by a thin Pt is tainted with a spin polarized current. The pure spin current phenomena, such as the inverse spin Hall effect and the spin Seebeck effect, have been contaminated with the anomalous Hall effect and the anomalous Nernst effect respectively. These results raise serious questions about the suitability, and the validity, of using Pt in establishing pure spin current phenomena; on the other hand, a much stronger spin-based effect can be induced by the MPE at the interface. This research is in collaboration with X. Fin, Y. P. Chen, J. Wu, and J. Q. Xiao (University of Delaware), T. Y. Chen (Arizona State University) and D. Qu, W. G. Wang, and C. L. Chien (The Johns Hopkins University).

  14. Effects of Mn substitution on the thermoelectric properties of the electron-doped perovskite Sr1-xLaxTiO3

    NASA Astrophysics Data System (ADS)

    Okuda, T.; Hata, H.; Eto, T.; Nishina, K.; Kuwahara, H.; Nakamura, M.; Kajimoto, R.

    2014-12-01

    We have tried to improve the n-type thermoelectric properties of the electron- doped Perovskite Sr1-xLaxTiO3 by a Mn substitution. The 1 ~ 2 % Mn substitution enhances the Seebeck coefficient (S) and reduces the thermal conductivity (κ) by about 50 % at room temperature (RT) without largely increasing the resistivity for the 5 % electron-doped SrTiO3. Consequently, the power factor at RT keeps a large value comparable to that of Bi2Te3 and the dimensionless figure-of-merits at RT increases twofold by the slight Mn substitution. Such a large reduction of κ at RT is perhaps due to the effect of Jahn-Teller active Mn3+ ions, around which dynamical local lattice distortion may occur.

  15. Phonon and magnon heat transport and drag effects

    NASA Astrophysics Data System (ADS)

    Heremans, Joseph P.

    2014-03-01

    Thermoelectric generators and coolers constitute today's solid-state energy converters. The two goals in thermoelectrics research are to enhance the thermopower while simultaneously maintaining a high electrical conductivity of the same material, and to minimize its lattice thermal conductivity without affecting its electronic properties. Up to now the lattice thermal conductivity has been minimized by using alloy scattering and, more recently, nanostructuring. In the first part of the talk, a new approach to minimize the lattice thermal conductivity is described that affects phonon scattering much more than electron scattering. This can be done by selecting potential thermoelectric materials that have a very high anharmonicity, because this property governs phonon-phonon interaction probability. Several possible types of chemical bonds will be described that exhibit such high anharmonicity, and particular emphasis will be put on solids with highly-polarizable lone-pair electrons, such as the rock salt I-V-VI2 compounds (e.g. NaSbSe2). The second part of the talk will give an introduction to a completely new class of solid-state thermal energy converters based on spin transport. One configuration for such energy converters is based on the recently discovered spin-Seebeck effect (SSE). This quantity is expressed in the same units as the conventional thermopower, and we have recently shown that it can be of the same order of magnitude. The main advantage of SSE converters is that the problem of optimization is now distributed over two different materials, a ferromagnet in which a flux of magnetization is generated by a thermal gradient, and a normal metal where the flux of magnetization is converted into electrical power. The talk will focus on the basic physics behind the spin-Seebeck effect. Recent developments will then be described based on phonon-drag of spin polarized electrons. This mechanism has made it possible to reach magnitudes of SSE that are comparable to the highest values of classical thermopower measured in semiconductors. This work is supported as part of the Revolutionary Materials for Solid State Energy Conversion (RMSSEC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, by AFOSR MURI ``Cryogenic Peltier Cooling'' Contract #FA9550-10-1-0533and by NSF-CBET-1133589. Department of Mechanical and Aerospace Engineering; and Department of Physics.

  16. Giant Nernst effect in CeCoIn5.

    PubMed

    Bel, R; Behnia, K; Nakajima, Y; Izawa, K; Matsuda, Y; Shishido, H; Settai, R; Onuki, Y

    2004-05-28

    We present a study of Nernst and Seebeck coefficients of the heavy-fermion superconductor CeCoIn5. Below 18 K, concomitant with a field-dependent Seebeck coefficient, a large sublinear Nernst signal emerges with a magnitude drastically exceeding what is expected for a multiband Fermi-liquid metal. In the mixed state, in contrast with all other superconductors studied before, this signal overwhelms the one associated with the motion of superconducting vortices. The results point to a hitherto unknown source of transverse thermoelectricity in strongly interacting electrons. PMID:15245310

  17. MeV Si ion beam modification effects on the thermoelectric generator from Er 0.1Fe 1.9SbGe 0.4 thin film

    NASA Astrophysics Data System (ADS)

    Budak, S.; Guner, S.; Muntele, C.; Ila, D.

    2009-05-01

    Effective thermoelectric materials and devices have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT. The purpose of this study is to improve the figure of merit of the single layer of Er0.1Fe1.9SbGe0.4 thin film used as thermoelectric generators. We have deposited the monolayer of Er0.1Fe1.9SbGe0.4 thin film on silicon and silica substrates with thickness of 302 nm using ion beam assisted deposition (IBAD). Rutherford backscattering spectrometry (RBS) was used to determine the total film thickness and stoichiometry. The MeV Si ion bombardments were performed on single layer of Er0.1Fe1.9SbGe0.4 thin films at five different fluences between 5 1013-5 1015 ions/cm2.The defect and disorder in the lattice caused by ion beam modification and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of annihilation of the phonon. The increase of the electron density of states in the miniband of the quantum dot structure formed by bombardment also increases the Seebeck coefficient and the electrical conductivity. We measured the thermoelectric efficiency of the fabricated device by measuring the cross plane thermal conductivity by the 3rd harmonic (3?) method, the cross plane Seebeck coefficient, and the electrical conductivity using the Van Der Pauw method before and after the MeV ion bombardments.

  18. Possible undercompensation effect in the Kondo insulator (Yb,Tm)B12

    NASA Astrophysics Data System (ADS)

    Alekseev, P. A.; Nemkovski, K. S.; Mignot, J.-M.; Clementyev, E. S.; Ivanov, A. S.; Rols, S.; Bewley, R. I.; Filipov, V. B.; Shitsevalova, N. Yu.

    2014-03-01

    The effects of Tm substitution on the dynamical magnetic response of Yb1-xTmxB12 (x=0, 0.08, 0.15, and 0.75) and Lu0.92Tm0.08B12 compounds have been studied using time-of-flight inelastic neutron scattering. Major changes were observed in the spectral structure and temperature evolution of the Yb contribution to the inelastic response for a rather low content of magnetic Tm ions. A sizable influence of the RB12 host (YbB12, as compared to LuB12 or pure TmB12) on the crystal-field splitting of the Tm3+ ion is also reported. The results point to a specific effect of impurities carrying a magnetic moment (Tm, as compared to Lu or Zr) in a Kondo insulator, which is thought to reflect the "undercompensation" of Yb magnetic moments, originally Kondo screened in pure YbB12. A parallel is made with the strong effect of Tm substitution on the temperature dependence of the Seebeck coefficient in Yb1-xTmxB12, which was reported previously.

  19. Spin transport and spin-caloric effects in (Cr,Zn)Te half-metallic nanostructures: Effect of spin disorder at elevated temperatures from first principles

    NASA Astrophysics Data System (ADS)

    Kov?ik, Roman; Mavropoulos, Phivos; Blgel, Stefan

    2015-01-01

    An important contribution to the thermoelectric and spin-caloric transport properties in magnetic materials at elevated temperatures is the formation of a spin-disordered state due to local moment fluctuations. This effect has not been largely investigated so far. We focus on various magnetic nanostructures of CrTe in the form of thin layers or nanowires embedded in ZnTe matrix, motivated by the miniaturization of spintronics devices and by recent suggestions that magnetic nanostructures can lead to extraordinary thermoelectric effects due to quantum confinement. The electronic structure of the studied systems is calculated within the multiple scattering screened Korringa-Kohn-Rostoker Green function (KKR-GF) framework. The Monte Carlo method is used to simulate the magnetization in the temperature induced spin disorder. The transport properties are evaluated from the transmission probability obtained using the Baranger-Stone approach within the KKR-GF framework. We find qualitative and quantitative changes in the thermoelectric and spin-caloric coefficients when spin disorder is included in the calculation. Furthermore, we show that substitutional impurities in CrTe nanowires could considerably enhance the Seebeck coefficient and the thermoelectric figure of merit.

  20. Effect of Doping on Thermoelectric Properties of Delafossite-Type Oxide CuCrO2

    NASA Astrophysics Data System (ADS)

    Hayashi, Kei; Sato, Ken-ichi; Nozaki, Tomohiro; Kajitani, Tsuyoshi

    2008-01-01

    We have studied the effects of doping on the high-temperature thermoelectric properties of the delafossite-type oxide CuCrO2. The single or double doping of divalent cations for Cr3+ ions was carried out to introduce hole carriers. For the first step, we measured the electrical conductivity ? and Seebeck coefficient S of single-doped samples, and calculated the power factor P=?S2. Mg-, Zn-, Ca-, Ni-, and Co-doped samples showed a higher power factor than CuCrO2, while the Fe-, V-, and Mn-doped samples exhibited a lower power factor. The maximum power factor P=2.3610-4 W/mK2 at 1100 K was obtained with the Mg-doped sample. The above tendencies of the power factor are well explained by the valence states and ionic radii of the dopants. For the next step, Mg and M (M = Zn, Ca, Ni, or Co) double-doped samples were prepared. Since there was no impurity phase in the Mg+Ni cases, we have elucidated the structure and high-temperature thermoelectric properties of CuCr0.97-xMg0.03NixO2 (0Seebeck coefficient of the double-doped samples was higher than that of the Mg-doped sample, in which the total number of hole carriers (i.e., the sum of the hole carriers in the Cu and Cr sites) is decreasing. The Seebeck coefficient of the double-doped samples was higher than 225 V/K from 300 to 1100 K. The thermal conductivity of the double-doped samples (?>6 W/mK) was higher than that of the Mg-doped sample. As a result, the maximum dimensionless figure of merit ZT=?S2T/?=0.10 was realized with the sample of x=0.04 at 1100 K, which was twice as high as that of the Mg-doped sample.

  1. 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. PMID:25402498

  2. Photothermoelectric and photovoltaic effects both present in MoS2

    NASA Astrophysics Data System (ADS)

    Zhang, Youwei; Li, Hui; Wang, Lu; Wang, Haomin; Xie, Xiaomin; Zhang, Shi-Li; Liu, Ran; Qiu, Zhi-Jun

    2015-01-01

    As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

  3. Photothermoelectric and photovoltaic effects both present in MoS2

    PubMed Central

    Zhang, Youwei; Li, Hui; Wang, Lu; Wang, Haomin; Xie, Xiaomin; Zhang, Shi-Li; Liu, Ran; Qiu, Zhi-Jun

    2015-01-01

    As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice. PMID:25605348

  4. Programming Current Reduction via Enhanced Asymmetry-Induced Thermoelectric Effects in Vertical Nanopillar Phase-Change Memory Cells

    NASA Astrophysics Data System (ADS)

    Bahl, Jyotsna; Rajendran, Bipin; Muralidharan, Bhaskaran

    2015-12-01

    Thermoelectric effects are envisioned to reduce programming currents in nanopillar phase change memory cells. However, due to the inherent symmetry in such a structure, the contribution due to thermoelectric effects on programming currents is minimal. In this work, we propose a hybrid phase change memory structure which incorporates a two-fold asymmetry specifically aimed to favorably enhance thermoelectric effects. The first asymmetry is introduced via an interface layer of low thermal conductivity and high negative Seebeck coefficient, such as, polycrystalline SiGe, between the bottom electrode contact and the active region comprising the phase change material. This results in an enhanced Peltier heating of the active material. The second one is introduced structurally via a taper that results in an angle dependent Thomson heating within the active region. Various device geometries are analyzed using 2D-axis-symmetric simulations to predict the effect on programming currents as well as for different thicknesses of the interface layer. A programming current reduction of up to $60\\%$ is predicted for specific cell geometries. Remarkably, we find that due to an interplay of Thomson cooling in the electrode and the asymmetric heating profile inside the active region, the predicted programming current reduction is resilient to fabrication variability.

  5. Thermoelectric effect of silicon films prepared by aluminum-induced crystallization

    NASA Astrophysics Data System (ADS)

    Hou, Qing-run; Gu, Bing-fu; Chen, Yi-bao; He, Yuan-jin

    2012-10-01

    Aluminum-induced crystallized silicon films were prepared on glass substrates by magnetron sputtering. Aluminum was added in the silicon films intermittently by the regular pulse sputtering of an aluminum target. The amount of aluminum in the silicon films can be controlled by regulating the aluminum sputtering power and the sputtering time of the undoped silicon layer; thus, the Seebeck coefficient and electrical resistivity of the polycrystalline silicon films can be adjusted. It is found that, when the sputtering power ratio of aluminum to silicon is 16%, both the Seebeck coefficient and the electrical resistivity decrease with the increasing amount of aluminum as expected; the Seebeck coefficient and the electrical resistivity at room temperature are 0.185-0.285 mV/K and 0.30-2.4 ?cm, respectively. By reducing the sputtering power ratio to 7%, however, the Seebeck coefficient does not change much, though the electrical resistivity still decreases with the amount of aluminum increasing; the Seebeck coefficient and electrical resistivity at room temperature are 0.219-0.263 mV/K and 0.26-0.80 ?cm, respectively.

  6. Effect of Thermoelectric Modules' Topological Connection on Automotive Exhaust Heat Recovery System

    NASA Astrophysics Data System (ADS)

    Deng, Y. D.; Zheng, S. J.; Su, C. Q.; Yuan, X. H.; Yu, C. G.; Wang, Y. P.

    2016-03-01

    In automotive exhaust-based thermoelectric generators (AETEGs), a certain number of thermoelectric modules are connected in series and/or parallel to recover energy from exhaust gas, which provides a way to improve fuel efficiency of the vehicle. Because of the temperature distribution on the surfaces of heat exchanger, several types of modules are planned for use in an AETEG; however, property disparities among modules exist and wire resistance cannot be neglected in practical application, so experiments have been carried out to research effects of the two factors on the maximum output power of series and parallel connection. The performance of series and parallel connections have been characterized, and mathematic models have been built to analyze and predict the performance of each connection. Experiments and theoretical analysis reveal that parallel connection shows a better performance than series connection when large differences of Seebeck coefficient and resistivity exist. However, wire resistance will cause more significant power dissipation in parallel connection. The authors believe the research presented in this paper is the first to carry out an examination of the impact of module property disparity and wire resistance on the output power of an array of thermoelectric modules connected in series and parallel, which provides a reference for choosing module connection in AETEGs.

  7. Unravelling Doping Effects on PEDOT at the Molecular Level: From Geometry to Thermoelectric Transport Properties.

    PubMed

    Shi, Wen; Zhao, Tianqi; Xi, Jinyang; Wang, Dong; Shuai, Zhigang

    2015-10-14

    Tuning carrier concentration via chemical doping is the most successful strategy to optimize the thermoelectric figure of merit. Nevertheless, how the dopants affect charge transport is not completely understood. Here we unravel the doping effects by explicitly including the scattering of charge carriers with dopants on thermoelectric properties of poly(3,4-ethylenedioxythiophene), PEDOT, which is a p-type thermoelectric material with the highest figure of merit reported. We corroborate that the PEDOT exhibits a distinct transition from the aromatic to quinoid-like structure of backbone, and a semiconductor-to-metal transition with an increase in the level of doping. We identify a close-to-unity charge transfer from PEDOT to the dopant, and find that the ionized impurity scattering dominates over the acoustic phonon scattering in the doped PEDOT. By incorporating both scattering mechanisms, the doped PEDOT exhibits mobility, Seebeck coefficient and power factors in very good agreement with the experimental data, and the lightly doped PEDOT exhibits thermoelectric properties superior to the heavily doped one. We reveal that the thermoelectric transport is highly anisotropic in ordered crystals, and suggest to utilize large power factors in the direction of polymer backbone and low lattice thermal conductivity in the stacking and lamellar directions, which is viable in chain-oriented amorphous nanofibers. PMID:26406937

  8. Effect of local atomic and electronic structures on thermoelectric properties of chemically substituted CoSi

    NASA Astrophysics Data System (ADS)

    Hsu, C. C.; Pao, C. W.; Chen, J. L.; Chen, C. L.; Dong, C. L.; Liu, Y. S.; Lee, J. F.; Chan, T. S.; Chang, C. L.; Kuo, Y. K.; Lue, C. S.

    2014-05-01

    We report the effects of Ge partial substitution for Si on local atomic and electronic structures of thermoelectric materials in binary compound cobalt monosilicides (\\text{CoSi}_{1-x}\\text{Ge}_{x}\\text{:}\\ 0 \\le x \\le 0.15 ). Correlations between local atomic/electronic structure and thermoelectric properties are investigated by means of X-ray absorption spectroscopy. The spectroscopic results indicate that as Ge is partially substituted onto Si sites at x \\le 0.05 , Co in CoSi1-xGex gains a certain amount of charge in its 3d orbitals. Contrarily, upon further replacing Si with Ge at x \\ge 0.05 , the Co 3d orbitals start to lose some of their charge. Notably, thermopower is strongly correlated with charge redistribution in the Co 3d orbital, and the observed charge transfer between Ge and Co is responsible for the variation of Co 3d occupancy number. In addition to Seebeck coefficient, which can be modified by tailoring the Co 3d states, local lattice disorder may also be beneficial in enhancing the thermoelectric properties. Extended X-ray absorption fine structure spectrum results further demonstrate that the lattice phonons can be enhanced by Ge doping, which results in the formation of the disordered Co-Co pair. Improvements in the thermoelectric properties are interpreted based on the variation of local atomic and electronic structure induced by lattice distortion through chemical substitution.

  9. Effect of Thermoelectric Modules' Topological Connection on Automotive Exhaust Heat Recovery System

    NASA Astrophysics Data System (ADS)

    Deng, Y. D.; Zheng, S. J.; Su, C. Q.; Yuan, X. H.; Yu, C. G.; Wang, Y. P.

    2015-11-01

    In automotive exhaust-based thermoelectric generators (AETEGs), a certain number of thermoelectric modules are connected in series and/or parallel to recover energy from exhaust gas, which provides a way to improve fuel efficiency of the vehicle. Because of the temperature distribution on the surfaces of heat exchanger, several types of modules are planned for use in an AETEG; however, property disparities among modules exist and wire resistance cannot be neglected in practical application, so experiments have been carried out to research effects of the two factors on the maximum output power of series and parallel connection. The performance of series and parallel connections have been characterized, and mathematic models have been built to analyze and predict the performance of each connection. Experiments and theoretical analysis reveal that parallel connection shows a better performance than series connection when large differences of Seebeck coefficient and resistivity exist. However, wire resistance will cause more significant power dissipation in parallel connection. The authors believe the research presented in this paper is the first to carry out an examination of the impact of module property disparity and wire resistance on the output power of an array of thermoelectric modules connected in series and parallel, which provides a reference for choosing module connection in AETEGs.

  10. Thermopower and Nernst effect in the Dirac semimetal Cd3As2

    NASA Astrophysics Data System (ADS)

    Liang, Tian; Gibson, Quinn; Ali, Mazhar; Liu, Minhao; Cava, Robert; Ong, Nai Phuan

    2015-03-01

    Dirac semimetals and Weyl semimetals are 3D analogues of graphene in which crystalline symmetry protects the nodes against gap formation. Cd3As2 was predicted to be Dirac semimetal, and recently confirmed to be so by photoemission. Here we report an interesting property in Cd3As2 that was unpredicted, namely a remarkable protection mechanism that strongly suppresses backscattering in zero H. In single crystals, the protection results in ultrahigh mobility ~ 9 106 cm2 V-1 s-1 at 5 K. Suppression of backscattering results in a transport lifetime 104 times longer than the quantum lifetime. The lifting of this protection by H leads to a very large magnetoresistance. Quantum oscillations in resistivity, Seebeck and Nernst, show beating effect.We discuss how this may relate to changes to the Fermi surface induced by H. Supported by MURI Grant (ARO W911NF-12-1-0461), Army Research Office (ARO W911NF-11-1-0379) and NSF-MRSEC Grant DMR 0819860.

  11. Pyro-paraelectricity: a new effect in hetergeneous material architectures

    NASA Astrophysics Data System (ADS)

    Chin, Huai-An; Mao, Sheng; Visweswaran, Bhadrinarayana L.; Ohemeng, Kwaku K.; Wagner, Sigurd; Purohit, Prashant K.; McAlpine, Michael C.

    2015-03-01

    The electrical responses of materials and devices subjected to thermal inputs, such as the Seebeck effect and pyroelectricity, are of great interest in thermal-electric energy conversion applications. Of particular interest are phenomena which exploit heterogeneities in the mechanics of heterostructured materials for novel and unexplored mechanisms in thermal-electric conversion. Here we introduce a new and universal mechanism for converting thermal stimuli into electricity via structural heterogeneities, which we term "pyro-paraelectricity." Specifically, when a paraelectric material is grown on a substrate with a different lattice constant, the paraelectric layer experiences an inhomogeneous strain due to the lattice mismatch, establishing a strain gradient along the axis of the layer thickness. This induced strain gradient can be multiple orders of magnitude higher than strain gradients in bulk materials imparted by mechanical bending (0.1 m-1). Consequently, charge separation is induced in the paraelectric layer via flexoelectricity, leading to a polarization in proportion to the dielectric constant. The dielectric constant, and thus the polarization, changes with temperature. Therefore, when a strained metal-insulator-metal (MIM) heterostructure is subjected to a thermal input, changes in the permittivity generate an electrical response. We demonstrate this mechanism by employing a MIM heterostructure with a high permittivity sputtered barium strontium titanate (BST) film as the insulating layer in a platinum sandwich. The resulting strain gradient of more than 104 m-1, an enhancement of five orders of magnitude due to the structural heterogeneity, was verified by an X-ray diffraction scan. With an applied thermal input, the strained MIM heterostructure generated current which was highly correlated to the thermal input. A theoretical model was found to be consistent with the experimental data. These results demonstrate the existence of "pyro-paraelectricity," a flexoelectricity-mediated mechanism for thermal-electrical conversion.

  12. Static Magnetic Proximity Effect in Pt /NiFe2O4 and Pt /Fe Bilayers Investigated by X-Ray Resonant Magnetic Reflectivity

    NASA Astrophysics Data System (ADS)

    Kuschel, T.; Klewe, C.; Schmalhorst, J.-M.; Bertram, F.; Kuschel, O.; Schemme, T.; Wollschlger, J.; Francoual, S.; Strempfer, J.; Gupta, A.; Meinert, M.; Gtz, G.; Meier, D.; Reiss, G.

    2015-08-01

    The spin polarization of Pt in Pt /NiFe2O4 and Pt /Fe bilayers is studied by interface-sensitive x-ray resonant magnetic reflectivity to investigate static magnetic proximity effects. The asymmetry ratio of the reflectivity is measured at the Pt L3 absorption edge using circular polarized x-rays for opposite directions of the magnetization at room temperature. The results of the 2% asymmetry ratio for Pt /Fe bilayers are independent of the Pt thickness between 1.8 and 20 nm. By comparison with ab initio calculations, the maximum magnetic moment per spin polarized Pt atom at the interface is determined to be (0.6 0.1 ) ?B for Pt /Fe . For Pt /NiFe2O4 the asymmetry ratio drops below the sensitivity limit of 0.02 ?B per Pt atom. Therefore, we conclude, that the longitudinal spin Seebeck effect recently observed in Pt /NiFe2O4 is not influenced by a proximity induced anomalous Nernst effect.

  13. Static Magnetic Proximity Effect in Pt/NiFe2O4 and Pt/Fe Bilayers Investigated by X-Ray Resonant Magnetic Reflectivity.

    PubMed

    Kuschel, T; Klewe, C; Schmalhorst, J-M; Bertram, F; Kuschel, O; Schemme, T; Wollschlger, J; Francoual, S; Strempfer, J; Gupta, A; Meinert, M; Gtz, G; Meier, D; Reiss, G

    2015-08-28

    The spin polarization of Pt in Pt/NiFe2O4 and Pt/Fe bilayers is studied by interface-sensitive x-ray resonant magnetic reflectivity to investigate static magnetic proximity effects. The asymmetry ratio of the reflectivity is measured at the Pt L3 absorption edge using circular polarized x-rays for opposite directions of the magnetization at room temperature. The results of the 2% asymmetry ratio for Pt/Fe bilayers are independent of the Pt thickness between 1.8 and 20 nm. By comparison with ab initio calculations, the maximum magnetic moment per spin polarized Pt atom at the interface is determined to be (0.60.1)???B for Pt/Fe. For Pt/NiFe2O4 the asymmetry ratio drops below the sensitivity limit of 0.02???B per Pt atom. Therefore, we conclude, that the longitudinal spin Seebeck effect recently observed in Pt/NiFe2O4 is not influenced by a proximity induced anomalous Nernst effect. PMID:26371679

  14. Universal carrier thermoelectric-transport model based on percolation theory in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Lu, Nianduan; Li, Ling; Liu, Ming

    2015-05-01

    Recent measurements conducted over a large range of temperature and carrier density have found that the Seebeck coefficient exhibits an approaching disorder-free transport feature in high-mobility conjugated polymers [D. Venkateshvaran et al., Nature 515, 384 (2014), 10.1038/nature13854]. It is difficult for the current Seebeck coefficient model to interpret the feature of the charge transport approaching disorder-free transport. We present a general analytical model to describe the Seebeck effect for organic semiconductors based on the hopping transport and percolation theory. The proposed model can well explain the Seebeck feature of the polymers with approaching disorder-free transport, as well as that of the organic semiconductors with the general disorder. The simulated results imply that the Seebeck coefficient in the organic semiconductors would happen to transfer from temperature dependence to temperature independence with the decrease of the energetic disorder.

  15. Effect of Off-Stoichiometry on the Thermoelectric Properties of Heusler-Type Fe2VAl Sintered Alloys

    NASA Astrophysics Data System (ADS)

    Mikami, M.; Inukai, M.; Miyazaki, H.; Nishino, Y.

    2016-03-01

    Heusler-type Fe2V1- x Al1+ x sintered alloys with micrometer-sized grains were fabricated by the powder metallurgical process using mechanical alloying and pulse-current sintering. Both positive (˜90 μV/K) and negative (˜-140 μV/K) Seebeck coefficients were obtained for the composition ranges of x > 0 and x < 0, respectively, resulting from a Fermi level shift caused by the change in the valence electron concentration. The electrical resistivity was reduced by the carrier doping effect, especially at lower temperatures, resulting in an increased thermoelectric power factor of 2.8 mW/m-K2 for the p-type alloy with x = 0.06 and 5.0 mW/m-K2 for the n-type alloy with x = -0.06. In addition, the lattice thermal conductivity decreased with | x| because of phonon scattering at crystal lattice defects induced by the off-stoichiometry. Consequently, the thermoelectric figure of merit, ZT, was enhanced and reached 0.07 for p-type alloys with 0.06 < x < 0.15 and 0.18 for n-type alloys with -0.15 < x < -0.10 around 500 K. The ZT value was especially enhanced at higher temperatures by the off-stoichiometric composition control, which could extend the range of heat source temperatures for thermoelectric power generation applications using this alloy.

  16. Effect of heat treatment on the electrical and thermoelectric properties of Sb doped Bi2Se3

    NASA Astrophysics Data System (ADS)

    Ibrahim, E. M. M.; Abdel Hakeem, A. M.; Adam, A. M. M.; Shokr, E. Kh

    2015-04-01

    Polycrystalline samples of (Bi0.95Sb0.05)2Se3 were prepared using the conventional melting technique at 1273 K, followed by annealing at different temperatures (423, 473, 523 and 573 K) for different time intervals (4, 8, 12 and 16 h). The samples were crystallized in a single phase of Bi2Se3 and no other phases or impurities were observed. The electrical and thermoelectric properties were studied by measuring the electrical conductivity and Seebeck coefficient as functions of temperature in the range 100-400 K. The results exhibited a metal-n-type semiconductor transition for all samples. The power factor (Pf) was calculated to determine the effect of the annealing treatment on the performance of the prepared material as a thermoelectric power generator. The highest room temperature value of the Pf was 6.9 ?WK-2cm-1 and was recorded for the sample annealed at 573 K for 16 h. The results confirm the feasibility of using the annealing process to improve the performance of thermoelectric materials.

  17. Effect of Off-Stoichiometry on the Thermoelectric Properties of Heusler-Type Fe2VAl Sintered Alloys

    NASA Astrophysics Data System (ADS)

    Mikami, M.; Inukai, M.; Miyazaki, H.; Nishino, Y.

    2015-08-01

    Heusler-type Fe2V1-x Al1+x sintered alloys with micrometer-sized grains were fabricated by the powder metallurgical process using mechanical alloying and pulse-current sintering. Both positive (90 ?V/K) and negative (-140 ?V/K) Seebeck coefficients were obtained for the composition ranges of x > 0 and x < 0, respectively, resulting from a Fermi level shift caused by the change in the valence electron concentration. The electrical resistivity was reduced by the carrier doping effect, especially at lower temperatures, resulting in an increased thermoelectric power factor of 2.8 mW/m-K2 for the p-type alloy with x = 0.06 and 5.0 mW/m-K2 for the n-type alloy with x = -0.06. In addition, the lattice thermal conductivity decreased with |x| because of phonon scattering at crystal lattice defects induced by the off-stoichiometry. Consequently, the thermoelectric figure of merit, ZT, was enhanced and reached 0.07 for p-type alloys with 0.06 < x < 0.15 and 0.18 for n-type alloys with -0.15 < x < -0.10 around 500 K. The ZT value was especially enhanced at higher temperatures by the off-stoichiometric composition control, which could extend the range of heat source temperatures for thermoelectric power generation applications using this alloy.

  18. Exploring the doping effects of Ag in p-type PbSe compounds with enhanced thermoelectric performance

    NASA Astrophysics Data System (ADS)

    Wang, Shanyu; Zheng, Gang; Luo, Tingting; She, Xiaoyu; Li, Han; Tang, Xinfeng

    2011-11-01

    In this study, we prepared a series of Ag-doped PbSe bulk materials by a melting-quenching process combined with a subsequent spark plasma sintering process, and systematically investigated the doping effects of Ag on the thermoelectric properties. Ag substitution in the Pb site does not introduce resonant levels near the valence band edge or detectable change in the density of state in the vicinity of the Fermi level, but moves the Fermi level down and increases the carrier concentration to a maximum value of ~4.7 × 1019 cm-3 which is still insufficient for heavily doped PbSe compounds. Nonetheless, the non-monotonic variation in carrier concentration with increasing Ag content indicates that Ag doping reaches the solution limit at ~1.0% and the excessive Ag presumably acts as donors in the materials. Moreover, the large energy gap of the PbSe-based material wipes off significant 'roll-over' in the Seebeck coefficient at elevated temperatures which gives rise to high power factors, being comparable to p-type Te analogues. Consequently, the maximum ZT reaches ~1.0 for the 1.5% Ag-doped samples with optimized carrier density, which is ~70% improvement in comparison with an undoped sample and also superior to the commercialized p-type PbTe materials.

  19. Effect of Sn Doping on the Thermoelectric Properties of n-type Bi2(Te,Se)3 Alloys

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Uk; Lee, Deuk-Hee; Kwon, Beomjin; Hyun, Dow-Bin; Nahm, Sahn; Baek, Seung-Hyub; Kim, Jin-Sang

    2015-06-01

    In the present work, 0.01-0.05wt.% Sn-doped Bi2(Te0.9Se0.1)3 alloys were prepared by mechanical deformation followed by hot pressing, and their thermoelectric properties were studied. We observed that the Sn element is a very effective dopant as an acceptor to control the carrier concentration in the n-type Bi2(Te0.9Se0.1)3 alloys to optimize their thermoelectric property. The n-type carrier concentration can be controlled from 4.2 1019/cm3 to 2.4 1019/cm3 by 0.05wt.% Sn-doping. While the Seebeck coefficient and the electrical resistivity are both increased with doping, the power factor remains the same. Therefore, we found that the thermoelectric figure-of-merit becomes maximized at 0.75 when the thermal conductivity has a minimum value for the 0.03wt.% Sn-doped sample.

  20. Apparatus and method for measuring the Seebeck coefficient and resistivity of materials

    NASA Technical Reports Server (NTRS)

    Hadek, V. (Inventor)

    1973-01-01

    An apparatus for measuring the thermoelectric properties of materials under high pressure is described that includes a pair of force transmitting assemblies constructed of thermally and electrically conductive material positioned between the ram and anvil of a press. Each force transmitting assembly has a small diameter pressing portion for contacting a face of the sample so that the sample can be squeezed between them. Each assembly also includes a heat exchanger to maintain the sample face at a controlled temperature, and an electrical conductor to carry current generated by the sample. A sleeve of thermally and electrically insulative material closely surrounds the pressing portions of the two assemblies.

  1. Spin Hall effect and Landau spectrum of Dirac electrons in bismuth

    NASA Astrophysics Data System (ADS)

    Fuseya, Yuki

    2015-03-01

    Bismuth has played an important role in solid-state physics. Many key phenomena were first discovered in bismuth, such as diamagnetism, Seebeck, Nernst, Shubnikov-de Haas, and de Haas-van Alphen effects. These phenomena result from particular electronic states of bismuth. The strong spin-orbit interaction (~ 1.5eV) causes strong spin-dependent interband couplings resulting in an anomalous spin magnetic moment. We investigate the spin Hall effect and the angular dependent Landau spectrum of bismuth paying special attention to the effect of the anomalous spin magnetic moment. It is shown that the spin Hall insulator is possible and there is a fundamental relationship between the spin Hall conductivity and orbital diamagnetism in the insulating state of the Dirac electrons. Based on this theoretical finding, the magnitude of spin Hall conductivity is estimated for bismuth by that of orbital susceptibility. The magnitude of spin Hall conductivity turns out to be as large as 104?-1 cm-1, which is about 100 times larger than that of Pt. It is also shown that the ratio of the Zeeman splitting to the cyclotron energy, which reflects the effect of crystalline spin-orbit interaction, for holes at the T-point can be larger than 1.0 (the maximum of previous theories) and exhibit strong angular dependence, which gives a possible solution to the long-standing mystery of holes at the T-point. In collaboration with Masao Ogata, Hidetoshi Fukuyama, Zengwei Zhu, Benot Fauqu, Woun Kang, and Kamran Behnia. Supported by JSPS (KAKENHI 24244053, 25870231, and 13428660).

  2. The effect of structural vacancies on the thermoelectric properties of (Cu?Te){sub 1x}(Ga?Te?)x

    SciTech Connect

    Ye, Zuxin; Young Cho, Jung; Tessema, Misle M.; Salvador, James R.; Waldo, Richard A.; Wang, Hsin; Cai, Wei

    2013-05-01

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

  3. Effect of copper doping on kinetic phenomena in n-Bi{sub 2}Te{sub 2.85}Se{sub 0.15}

    SciTech Connect

    Zhitinskaya, M. K.; Nemov, S. A. Svechnikova, T. E.

    2007-10-15

    In single crystals of copper-doped and undoped Bi{sub 2}Te{sub 2.85}Se{sub 0.15} solid solutions with an electron concentration close to 1 x 10{sup 19} cm{sup -3}, the temperature dependences are investigated for the Hall (R{sub 123}, R{sub 321}) and Seebeck (S{sub 11}) kinetic coefficients, the electrical-conductivity ({sigma}{sub 11}), Nernst-Ettingshausen (Q{sub 123}), and thermal conductivity (k{sub 11}) coefficients in the temperature range of 77-400 K. The absence of noticeable anomalies in the temperature dependences of the kinetic coefficients makes it possible to use the one-band model when analyzing the experimental results. Within the framework of the one-band model, the effective mass of density of states (m{sub d} {approx} 0.8m{sub 0}), the energy gap ({epsilon}{sub g} {approx} 0.2 eV), and the effective scattering parameter (r{sub eff} {approx} 0.2) are estimated. The obtained value of the parameter r{sub eff} is indicative of the mixed electron-scattering mechanism with the dominant scattering by acoustic phonons. Data on the thermal conductivity and the lattice resistivity obtained by subtracting the electron contribution according to the Wiedemann-Franz law are presented.

  4. Effects of Pd substitution on the thermoelectric and electronic properties of delafossite Cu{sub 1−x}Pd{sub x}FeO{sub 2} (x=0.01, 0.03 and 0.05)

    SciTech Connect

    Ruttanapun, Chesta

    2014-07-01

    Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} (x=0.01, 0.03 and 005) delafossite was prepared by solid state reactions and was calcined/sintered at 1050 °C. The effect of Pd{sup 2+} substitution for the Cu{sup 1+} sites on the thermoelectric and electronic properties of Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} were investigated. The crystal structure, oxygen decomposition, thermoelectric and electronic properties were characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), Seebeck coefficient, electrical conductivity and thermal conductivity measurements. The characterization showed that Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} formed a hexagonal delafossite structure with R3−m symmetry. The existence of Pd{sup 2+}, Cu{sup 1+}, Cu{sup 2+}, Fe{sup 3+}, Fe{sup 4+} and O was revealed from the XPS results. Confirmation of Pd{sup 2+} substitution for the Cu{sup 1+} sites occurred by increasing the c-axis in the lattice parameter with a Pd content. The O content intercalated at the center of the triangular Cu acted as a support to produce Cu{sup 2+} ions and was reduced with an increasing Pd content. The mixed valencies of Cu{sup 1+}/Cu{sup 2+} and Cu{sup 1+}/Pd{sup 2+} in the Cu layer changed the electrical conductivity and the Fe{sup 3+}/Fe{sup 4+} mixed valencies in the FeO{sub 6} layer caused the Seebeck coefficient to increase. Both the electrical conductivity and Seebeck coefficient for Pd contents of x=0.01 and 0.03 were higher than that of non-doped CuFeO{sub 2}. The low thermal conductivity of Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} resulted from the substitution of Pd, which has a large atomic mass, into structure. The Jonker plot indicated that the electronic properties displayed a degenerate density of states and that Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} was a semiconductor. A high ZT value of 0.055 was obtained for a Pd content of 0.03 at 950 K. The Pd{sup 2+} substitution for the Cu{sup 1+} sites influenced the thermoelectric and electronic properties of the delafossite Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} samples. - Graphical abstract: Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} (x=0.01, 0.03 and 005) delafossite was prepared by solid state reactions. The characterization showed that Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} formed a hexagonal delafossite structure with R3−m symmetry. The existence of Pd{sup 2+}, Cu{sup 1+}, Cu{sup 2+}, Fe{sup 3+}, Fe{sup 4+} and O was revealed from the XPS results. The O content intercalated at the center of the triangular Cu acted as a support to produce Cu{sup 2+} ions and was reduced with an increasing Pd content. The mixed valencies of Cu{sup 1+}/Cu{sup 2+} and Cu{sup 1+}/Pd{sup 2+} in the Cu layer changed the electrical conductivity and the Fe{sup 3+}/Fe{sup 4+} mixed valencies in the FeO{sub 6} layer caused the Seebeck coefficient to increase. Both the electrical conductivity and Seebeck coefficient for Pd contents of x=0.01 and 0.03 were higher than that of non-doped CuFeO{sub 2}. The low thermal conductivity of Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} resulted from the substitution of Pd, which has a large atomic mass, into structure. A high ZT value of 0.055 was obtained for a Pd content of 0.03 at 950 K. The Pd{sup 2+} substitution for the Cu{sup 1+} sites influenced the thermoelectric and electronic properties of the delafossite Cu{sub (1−x)}Pd{sub (x)}FeO{sub 2} samples. - Highlights: • New compound of Cu{sub 1−x}Pd{sub x}FeO{sub 2} (x=0.01, 0.03 and 0.05) forms phase of delafossite. • The compound displays p-type thermoelectric materials. • The Pd-substituted for Cu{sup 1+} sites forms Pd{sup 2+}. • Mixed valencies of Cu{sup +}/Cu{sup 2+}, Cu{sup +}/Pd{sup 2+} and Fe{sup 3+}/Fe{sup 4+} appear in the compound. • Large atomic mass of Pd-substituted causes low thermal conductivity.

  5. Effects of spin entropy and lattice strain from mixed-trivalent Fe3+/Cr3+ on the electronic, thermoelectric and optical properties of delafossite CuFe1?x Cr x O2 (x??=??0.25, 0.5, 0.75)

    NASA Astrophysics Data System (ADS)

    Ruttanapun, Chesta; Maensiri, Santi

    2015-12-01

    Mixed-trivalent Fe3+/Cr3+ content CuFe1?x Cr x O2 (x??=??0.25, 0.5, and 0.75) compounds were synthesized to investigate the effects of spin entropy, and lattice strain on their electronic, thermoelectric and optical properties. The XPS results showed the existence of mixed Cu1+/Cu2+, Fe3+/Fe4+ and Cr2+/Cr3+ ion states in the structures. The mixed Fe3+/Cr3+ions caused a strong correlation to occur between the spin and the orbitals of the carriers in the octahedral layer of the sample, affecting the carrier degeneracy Seebeck coefficient behaviour, and the Cu2+ and Fe4+ ions caused an effect of enhancing the electric conductivity. These effects meant that CuFe0.75Cr0.25O2 had the highest electrical conductivity, an enhanced Seebeck coefficient compared to that of CuFeO2-based compounds, and the highest thermopower value. The lowest thermal conductivity was that of CuFe0.5Cr0.5O2, which was a result of the mismatched atomic radii of the mixed trivalent Fe3+(0.645 )/Cr3+(0.615 ), which caused the lattice strain to occur in the structure and thus affected the point defect scattering of the phonon thermal conductivity. The lowest total thermal conductivity was that of CuFe0.5Cr0.5O2, because it had the maximum lattice strain. Overall, the effect of the mixed trivalent elements caused CuFe0.75Cr0.25O2 to have the highest value of the dimensionless figure of merit ZT, with a value that was four times that of CuFeO2-based compounds and six times that of CuCrO2-based compounds. With regard to optical properties, the lattice strain causes the indirect optical gap to increase with increasing x content, but has no effect on the direct optical gap. These results verified that the mixed-trivalent Fe3+/Cr3+ content of CuFe1?x Cr x O2 (x??=??0.25, 0.5, and 0.75) affected the electronic, thermoelectric and optical properties of the structure by causing spin entropy and lattice strain to occur.

  6. Observation of the planar Nernst effect in Permalloy and Nickel Thin Films with In-plane Thermal Gradients

    NASA Astrophysics Data System (ADS)

    Zink, Barry

    2013-03-01

    The reliable generation of pure spin currents is an important ingredient in future spintronic circuits that may offer lower power consumption and greater processing capabilities than current technology. Over the past few years some groups have reported that such a spin current can be generated simply by applying a thermal gradient to a ferromagnetic material. This effect, called the spin Seebeck effect (SSE), has generated tremendous interest in the interaction of heat, charge and spin in ferromagnetic systems. In this talk we will present our own recent measurements of thermoelectric and thermomagnetic effects in thin film metallic ferromagnets. These are enabled by a micromachined thermal isolation platform that removes potentially confounding effects introduced in such measurements by the presence of a highly thermally conductive bulk substrate. One of the main results is the observation of a transverse thermopower, called the planar Nernst effect (PNE), that is caused by spin-dependent scattering. This PNE should therefore be present in any attempted measurement of the SSE in a metal system where spin-dependent scattering of electrons occurs. Furthermore our ``zero substrate'' experiment shows no signal with the expected symmetry of the SSE, suggesting that the presence of the substrate is required to cause such a signal. Further experiments are required to determine if a pure spin current is actually involved in the generation of the signal associated with the SSE in ferromagnetic metal films. This work was performed in collaboration with A. D. Avery, and M. R. Pufall. This work is supported by the NSF CAREER award (DMR-0847796)

  7. Effects of Sb Content (x) on (Bi(1-x)Sb(x))2Te3 Thermoelectric Thin Film Deposited by Effusion Cell Evaporator.

    PubMed

    Yong, Ho; Na, Sekwon; Gang, Jun-Gu; Jeon, Seong-Jae; Hyun, Seungmin; Lee, Hoo-Jeong

    2015-10-01

    This paper investigates the effects of the Sb content (x) on (Bi(1-x)Sb(x))2Te3 thermoelectric films with x changing widely from 0 (Sb2Te3) to 1 (Bi2Te3). First, the XRD analysis discloses that with the Sb content (x) increasing, the phase changed gradually from Bi2Te3 to Sb2Te3 as Sb atoms replaced substitutionally Bi atoms. Further microstructure analysis reveals that an extensive grain growth occurred during post-annealing for the samples with high Sb contents. According to the measurement of electrical and thermoelectric properties, the polarity of the charge carrier and Seebeck coefficient switched n-type to p-type in the range of x = 0.45~0.63. For the n-type samples, the power factor is highest when x = 0.18 around 46.01 ?W/K(2) whereas Sb2Te3, for the p-type samples, shows the highest value, 62.48 ?W/K(2)cm. PMID:26726497

  8. Effect of Oxygen Partial Pressure during Firing on Electrical Properties of Sintered Body Composed of Mn1.5CoNi0.5O4

    NASA Astrophysics Data System (ADS)

    Meguro, Takeshi; Abe, Yoshiaki; Yokoyama, Takashi; Murosawa, Syogo; Komeya, Katsutoshi; Tatami, Junichi

    2001-08-01

    The effect of PO2 during the oxidation of a sintered body with a molar ratio of Mn:Co:Ni=3:2:1 on conversion into a cubic spinel-type oxide was investigated. Moreover, the electrical properties of the sintered body with a monophase cubic spinel structure were evaluated in atmospheres with various PO2 values. A sintered body of monophase spinel-type oxide, Mn1.5CoNi0.5O4, was successfully obtained by heating a mixture of nitrates at 1400C in argon, followed by cooling to 1100C and holding at that temperature for over 168 h at PO2=0.40 atm, or for over 48 h in the PO2 range from 0.55 to 1.00 atm. The electrical conductivity, ?, of the specimens oxidized at PO2 of 0.40 to 1.00 atm increased exponentially with increasing temperature. In the region of 0.40?q PO2(atm)?q 0.85, ? increased with increasing PO2. All of the specimens oxidized at PO2 of 0.40 to 1.00 atm revealed p-type semiconductor properties, because the Seebeck coefficients were all positive. The PO2 dependence of ? was thought to be dependent on the existence ratio of Mn3+ to Mn4+ in octahedral sites. The conduction was considered to be controlled by a small polaron hopping mechanism.

  9. Effect of Bi Substitution on Microstructure and Thermoelectric Properties of Polycrystalline [Ca2CoO3] pCoO2

    NASA Astrophysics Data System (ADS)

    Mikami, Masashi; Ando, Naoko; Guilmeau, Emmanuel; Funahashi, Ryoji

    2006-05-01

    Partially Bi-substituted [Ca2CoO3] pCoO2 ceramics were synthesized using a hot-forging technique. Then, the effects of Bi-substitution on microstructure and thermoelectric properties were evaluated. The average grain size of the precursor powder prepared by a solid-state reaction increased concomitant with the increase in Bi content. Furthermore, the electrical resistivity (ρ) of the hot-forged sample was decreased accordingly. Seebeck coefficient (S) was increased slightly by Bi-substitution and was less affected by grain size. Therefore, power factor (\\mathit{PF}=S2/ρ) was improved. On the other hand, the ρ of the hot-forged sample was reduced using a large-grained precursor powder prepared by a solution growth method. Different from the case of the former samples made from as-sintered powder, the ρ of the sample made from large-grained powder was increased slightly with the increase in Bi content. These results indicate that the main advantage of Bi-substitution for the decrease in the ρ of the hot-forged sample is the enhanced grain growth during the heat treatment processes.

  10. Spray pyrolysis of tin selenide thin-film semiconductors: the effect of selenium concentration on the properties of the thin films

    NASA Astrophysics Data System (ADS)

    Fadavieslam, M. R.; Bagheri-Mohagheghi, M. M.

    2013-08-01

    Thin films of tin selenide (SnxSey) with an atomic ratio of , 1 and 1.5 were prepared on a glass substrate at T = 470C using a spray pyrolysis technique. The initial materials for the preparation of the thin films were an alcoholic solution consisting of tin chloride (SnCl4 5H2O) and selenide acide (H2SeO3). The prepared thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy, scanning tunneling microscopy, scanning helium ion microscopy, and UV-vis spectroscopy. The photoconductivity and thermoelectric effects of the SnxSey thin films were then studied. The SnxSey thin films had a polycrystalline structure with an almost uniform surface and cluster type growth. The increasing atomic ratio of r in the films, the optical gap, photosensitivity and Seebeck coefficient were changed from 1.6 to 1.37 eV, 0.01 to 0.31 and -26.2 to -42.7 mV/K (at T = 350 K), respectively. In addition, the XRD patterns indicated intensity peaks in r = 1 that corresponded to the increase in the SnSe and SnSe2 phases.

  11. Large transverse thermoelectric effects in single crystals of the quasi-one-dimensional metal Li0.9Mo6O17

    NASA Astrophysics Data System (ADS)

    Moshfeghyeganeh, Saeed; Cohn, Joshua; Dos Santos, Carlos A. M.; Neumeier, John J.

    2014-03-01

    We present measurements of transverse thermoelectric (TE) effects in the temperature range 300-500 K for single crystals of the quasi-one-dimensional (q1D) metal Li0.9Mo6O17 (lithium purple bronze). Prior work demonstrates a highly anisotropic Seebeck coefficient (S), with metallic n-type behavior along the q1D chains (crystallographic b axis), p-type semiconductor behavior in the perpendicular, inter-chain direction (c axis), and a difference ?S ~= 200 ? V/K near T = 450 K. Significant transverse TE voltages, induced by applied temperature differences, and Peltier cooling, induced by applied currents, in specimens with body axes misaligned with the b and c axes will be discussed. Work supported by the U.S. Department of Energy Office of Basic Energy Sciences (DE-FG02-12ER46888, Univ. Miami), the National Science Foundation (DMR-0907036, Mont. St. Univ.), and in Lorena by the CNPq (301334/2007-2) and FAPESP (2009/14524-6).

  12. Effects of (Al,Ge) double doping on the thermoelectric properties of higher manganese silicides

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Weathers, Annie; Salta, Daniel; Zhang, Libin; Zhou, Jianshi; Goodenough, John B.; Shi, Li

    2013-11-01

    Experiments and analysis have been carried out to investigate the effects of Al and (Al,Ge) doping on the microstructure and thermoelectric properties of polycrystalline higher manganese silicide (HMS) samples, which were prepared by solid-state reaction, ball milling, and followed by spark plasma sintering. It has been found that Al doping effectively increases the hole concentration, which leads to an increase in the electrical conductivity and power factor. By introducing the second dopant Ge into Al-doped HMS, the electrical conductivity is increased, and the Seebeck coefficient is decreased as a result of further increased hole concentration. The peak power factor is found to occur at a hole concentration between 1.8 1021 and 2.2 1021 cm-3 measured at room temperature. The (Al,Ge)-doped HMS samples show lower power factors owing to their higher hole concentrations. The mobility of Mn(Al0.0035GeySi0.9965-y)1.8 with y = 0.035 varies approximately as T-3/2 above 200 K, suggesting acoustic phonon scattering is the dominant scattering mechanism. The thermal conductivity of HMS does not change appreciably by Al or (Al,Ge) doping. The maximum ZT of (Al,Ge)-doped HMS is 0.57 at 823 K, which is similar to the highest value found in the Al-doped HMS samples. The ZT values were reduced in the Mn(Al0.0035GeySi0.9965-y)1.8 samples with high Ge concentration of y = 0.025 and 0.035, because of reduced power factor. In addition, a two-band model was employed to show that the hole contribution to the thermal conductivity dominates the bipolar and electron contributions for all samples from 300 to 823 K and accounts for about 12% of the total thermal conductivity at about 800 K.

  13. Nano-scale effects in bulk nanostructured thermoelectrics

    NASA Astrophysics Data System (ADS)

    Satyala, Nikhil

    The technique of energy harvesting via thermoelectric (TE) materials is one of the favorable directions towards manifesting sustainable energy resources. The ability of TE materials to directly convert heat energy to electricity facilitates the reduction in consumption of natural resources for power generation. The requirements of high electrical conductivity and Seebeck coefficient while maintaining a low thermal conductivity for attaining higher TE performance introduced newer material processing techniques. Several efficient techniques for nano-scale structural modifications such as alloying, point defects, nanostructuring etc. were implemented for improvement in the figure-of-merit. Quantum confinement techniques based on nanostructuring of compounds gained prominence due to the resulting reduction of the lattice thermal conductivity. In this dissertation, various aspects of theoretical and experimental techniques pertaining to the nano-scale effects in TE materials were investigated. As a first step, in order to better understand the advantages and disadvantages of nanostructuring, TE characteristics of silicide based materials such as Mg2Si and Si1-xGex were theoretically modeled. A comprehensive comparison of effects of nanostructuring in both the materials was deduced. The fact that nanostructuring may not always be beneficial was highlighted through estimation of phonon mean free path in nanostructured compounds. In the second phase of this dissertation, a novel technique through mixing of a conductive glass-frit for improving the mechanical stability of Mg2Si was successfully developed. The studies were followed up by investigations on the benefits of combinatorial effects of nano-inclusions, nanostructuring and long duration annealing based on Bi2Te 3. In the final phase of this dissertation work, the technique of rapid decrystallization of single crystal silicon by high energy microwaves was introduced and the beneficial effects of rapid decrystallization were experimentally deduced. It was shown that a significant reduction in room temperature thermal conductivity of single crystal silicon could be achieved by means of grain size reduction via microwave energy. The advantages of nanostructuring in thermoelectric materials combined with techniques such as nano-inclusions, long duration annealing and rapid decrystallization have been explored comprehensively in this dissertation work. Such combinatorial techniques could be beneficially used to further enhance the efficiencies of thermoelectric materials.

  14. Enhanced performance of dye-sensitized solar cell using Bi2Te3 nanotube/ZnO nanoparticle composite photoanode by the synergistic effect of photovoltaic and thermoelectric conversion

    NASA Astrophysics Data System (ADS)

    Dou, Yuanyao; Wu, Fang; Fang, Liang; Liu, Gaobin; Mao, Caiying; Wan, Kai; Zhou, Miao

    2016-03-01

    Ultralong and highly crystalline rhombohedral Bi2Te3 nanotubes were fabricated by a two-step solution phase reaction. A novel photoanode architecture has been fabricated by embedding 0-2.5 wt.% Bi2Te3 nanotubes into ZnO nanoparticles. The photocurrent density-voltage (J-V) characteristics reveal that the dye sensitized solar cells (DSSCs) with Bi2Te3/ZnO composite photoanode exhibit significantly enhanced photovoltaic performance. Notably, the DSSC incorporating 1.5 wt.% Bi2Te3 in the ZnO photoanode demonstrates an energy conversion efficiency (η) of 4.27%, which is 44.3% higher than that of the bare ZnO photoanode. The electrochemical impedance spectroscopy (EIS) analysis shows that the Bi2Te3 nanotubes can provide a direct pathway for electron transportation, prolong the lifetime of electrons, suppress the charge recombination and improve the electron collection efficiency. The thermoelectric effect analysis indicates that with the increase of irradiation time, Bi2Te3/ZnO composite photoanode could convert both heat and photon energies to electrical energy simultaneously and slow down the decline of η. The calculated electron density (ns) further proves that the increment of short-circuit current density (Jsc) is attributed to Seebeck effect in the composite photoanode. These results suggest that compositing 1D thermoelectric nano-materials in photoanode is a promising route to improve the performance of DSSCs.

  15. Are Effective Properties Effective?

    SciTech Connect

    Han, Ru; Ingber, Marc S.; Hsiao, S.-C.

    2008-02-15

    The effective moduli (effective Young's modulus, effective Poisson's ratio, effective shear modulus, and effective bulk modulus) of dispersed-phase-reinforced composite materials are determined at the mesoscopic level using three-dimensional parallel boundary element simulations. By comparing the mesoscopic BEM results and the macroscopic results based on effective properties, limitations in the effective property approach have been examined.

  16. Microwave-induced spin currents in ferromagnetic-insulator|normal-metal bilayer system

    SciTech Connect

    Agrawal, Milan; Serga, Alexander A.; Lauer, Viktor; Papaioannou, Evangelos Th.; Hillebrands, Burkard; Vasyuchka, Vitaliy I.

    2014-09-01

    A microwave technique is employed to simultaneously examine the spin pumping and the spin Seebeck effect processes in a YIG|Pt bilayer system. The experimental results show that for these two processes, the spin current flows in opposite directions. The temporal dynamics of the longitudinal spin Seebeck effect exhibits that the effect depends on the diffusion of bulk thermal-magnons in the thermal gradient in the ferromagnetic-insulator|normal-metal system.

  17. Field effect controlled ferromagnetism in transition metal doped ZnO

    NASA Astrophysics Data System (ADS)

    Bellingeri, E.; Pellegrino, L.; Biasotti, M.; Pallecchi, I.; Canu, G.; Gerbi, A.; Vignolo, M.; Siri, A. S.; Marr, D.; Rusponi, S.; Lehnert, A.; Nolting, F.

    2008-02-01

    The ability to externally control the properties of magnetic materials would be highly desirable both from fundamental and technological point of views. In this respect, dilute magnetic semiconductor (DMS), in which a fraction of atoms of the nonmagnetic semiconductor host is replaced by magnetic ions, have recently attracted broad interest for their potential application in spintronics. In this work, we focused on transition metal (TM) (Co, Mn and Cu) doped Zinc oxide (ZnO) because room temperature ferromagnetism was both theoretically predicted and experimentally observed. However, the origin of such ferromagnetism, in particular whether it is a signature of a true DMS behaviour (long range magnetic interaction between the doping ions) or it arises from the formation of secondary phases, segregation or clustering is still under debate. Measuring the dependence of the magnetic properties on the carrier concentration can clarify the underlying physics. The samples were characterized by resistivity, Hall effect, magnetoresistance, Seebeck effect, synchrotron X-ray adsorption spectra (XAS) and magnetic dichroism (XMD) while modulating the carrier density by electric field. The insulating-gate field-effect transistor structures are realized in ZnO/Strontium Titanate (SrTiO 3) heterostructures by pulsed laser deposition. These devices offers the capability to modulate the carrier density of a probe accessible (light, AFM tip, ...) channel, by more than 5 orders of magnitude (from ~10 15 to ~10 20 e -/cm 3, estimated by Hall effect measurements under FE). The Co and Mn films measured by DC SQUID magnetometer result ferromagnetic and anomalous Hall effect was observed at low temperature but nor ferromagnetic nor antiferromagnetic signal was detectable in the XMD spectra. Cu doped films are insulating and nonmagnetic. Photo Emission Electron Microscopy (x-PEEM) and magnetic force microscopy (MFM) showed that the sample are homogeneus and no clustering of TM were detected. A large effect of the magnetic ions, strongly dependent on the carrier concentration, was observed on the transport properties and this effect according can be explained by a giant s-d exchange leading to spin splitting of the s-type conduction band. Since the filling of such band can be modified by field effect a electric field control of the spin polarization can be achieved.

  18. Strategies for developing optimal thermoelectric metrology protocols

    NASA Astrophysics Data System (ADS)

    Martin, Joshua

    2012-02-01

    The Seebeck coefficient is an essential physical property routinely measured to evaluate the potential performance of new thermoelectric materials. These materials facilitate the inter-conversion of thermal and electrical energy and are useful in power generation or solid-state refrigeration applications. However, the diversity in Seebeck coefficient measurement techniques, conditions, and probe arrangements has resulted in conflicting materials data, further complicating the inter-laboratory confirmation of reported higher efficiency thermoelectric materials. In an effort to identify optimal thermoelectric measurement protocols, we have developed a complimentary strategy to both evaluate and compare these different probe arrangements and measurement methodologies: first, through the design of an innovative experimental apparatus, and second, through error modeling of Seebeck coefficient measurements using finite element analysis. This talk will include a discussion of key measurement challenges, example diagnostics, and recommended practices to effectively manage uncertainty in Seebeck coefficient measurements.

  19. Effects of surface band bending and scattering on thermoelectric transport in suspended bismuth telluride nanoplates.

    PubMed

    Pettes, Michael Thompson; Maassen, Jesse; Jo, Insun; Lundstrom, Mark S; Shi, Li

    2013-11-13

    A microdevice was used to measure the in-plane thermoelectric properties of suspended bismuth telluride nanoplates from 9 to 25 nm thick. The results reveal a suppressed Seebeck coefficient together with a general trend of decreasing electrical conductivity and thermal conductivity with decreasing thickness. While the electrical conductivity of the nanoplates is still within the range reported for bulk Bi2Te3, the total thermal conductivity for nanoplates less than 20 nm thick is well below the reported bulk range. These results are explained by the presence of surface band bending and diffuse surface scattering of electrons and phonons in the nanoplates, where pronounced n-type surface band bending can yield suppressed and even negative Seebeck coefficient in unintentionally p-type doped nanoplates. PMID:24164564

  20. Effect of rare earth substitution on the structural and electrical properties of Cu-Mg ferrite

    NASA Astrophysics Data System (ADS)

    Ateia, E.; Ahmed, M. A.; Ghouniem, R. M.

    2015-07-01

    The samples of Cu0.9Mg0.1RyFe2-yO4, where y = 0.01 and R = Sm, Dy, Ho and Hf, were prepared by standard ceramic method. All investigated samples were sintered at 1150C with a heating rate of 4C/min and sintering time of 8 h. X-ray diffraction study of the compositions revealed the formation of cubic spinel structure with the appearance of small peaks indicating the presence of secondary phases. Seebeck coefficient was obtained from thermo-electromotive force (emf) measurements. The alternation of the Seebeck coefficient sign between (+)ve and (-)ve means that the two conduction mechanisms take place simultaneously. The dielectric parameters such as dielectric constant, quality factor were determined as a function of temperature and at different frequencies. The decrease in Fe3+ ions on the octahedral site decreased the polarization of the system, through the dielectric transition point.

  1. Temperature Gradient Measurements by Using Thermoelectric Effect in CNTs-Silicone Adhesive Composite

    PubMed Central

    Chani, Muhammad Tariq Saeed; Karimov, Kh. S.; Asiri, Abdullah M.; Ahmed, Nisar; Bashir, Muhammad Mehran; Khan, Sher Bahadar; Rub, Malik Abdul; Azum, Naved

    2014-01-01

    This work presents the fabrication and investigation of thermoelectric cells based on composite of carbon nanotubes (CNT) and silicone adhesive. The composite contains CNT and silicon adhesive 1?1 by weight. The current-voltage characteristics and dependences of voltage, current and Seebeck coefficient on the temperature gradient of cell were studied. It was observed that with increase in temperature gradient the open circuit voltage, short circuit current and the Seebeck coefficient of the cells increase. Approximately 7 times increase in temperature gradient increases the open circuit voltage and short circuit current up to 40 and 5 times, respectively. The simulation of experimental results is also carried out; the simulated results are well matched with experimental results. PMID:24748375

  2. Effect of ruthenium substitution in layered sodium cobaltate Na{sub x}CoO{sub 2}: Synthesis, structural and physical properties

    SciTech Connect

    Strobel, Pierre; Muguerra, Herve; Hebert, Sylvie; Pachoud, Elise; Colin, Claire; Julien, Marc-Henri

    2009-07-15

    Solid-state synthesis of Na{sub 0.71}Co{sub 1-x}Ru{sub x}O{sub 2} compositions shows that ruthenium can be substituted for cobalt in the hexagonal Na{sub 0.71}CoO{sub 2} phase up to x=0.5. The cell expands continuously with increasing ruthenium content. All mixed Co-Ru phases show a Curie-Weiss behaviour with no evidence of magnetic ordering down to 2 K. Unlike the parent phase Na{sub 0.71}CoO{sub 2}, ruthenium-substituted phases are all semiconducting. They exhibit high thermoelectric power, with a maximum of 165 muV/K at 300 K for x=0.3. The Curie constant C and Seebeck coefficient S show a non-monotonic evolution as a function of ruthenium content, demonstrating a remarkable interplay between magnetic properties and thermoelectricity. The presence of ruthenium has a detrimental effect on water intercalation and superconductivity in this system. Applying to Ru-substituted phases the oxidative intercalation of water known to lead to superconductivity in the Na{sub x}CoO{sub 2} system yields a 2-water layer hydrate only for x=0.1, and this phase is not superconducting down to 2 K. - Graphical Abstract: Effect of ruthenium substitution on thermoelectric power in Na{sub 0.71}Co{sub 1-x}Ru{sub x}O{sub 2} (left) and on low-temperature ac susceptibility in hydrated derivative (right).

  3. Effects of Se substitution on the thermoelectric performance of n-type Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} skutterudites

    SciTech Connect

    Duan, Bo; Zhai, Pengcheng; Liu, Lisheng; Zhang, Qingjie

    2012-07-15

    Highlights: ? The simple solid state reaction technique was employed to prepare Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} skutterudites. ? The thermal conductivity decreases gradually with the increasing Se content. ? Doping with moderate Se is an effective way to enhance the thermoelectric performance of Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x}. ? The highest ZT of 1.11 at 800 K is obtained for the Co{sub 4}Sb{sub 11.3}Te{sub 0.58}Se{sub 0.12} sample. -- Abstract: A series of double-substituted Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} skutterudites have been fabricated by combining the solid state reaction and the spark plasma sintering method, and the effects of Se substitution on the thermoelectric properties are characterized by measurements of the electrical conductivity, the Seebeck coefficient and the thermal conductivity in the temperature range of 300800 K. Doping Se into the Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} matrix suppresses the carrier concentration, and the electrical conductivity actually decreases with the Se content. However, moderate Se doping is effective in enhancing the thermoelectric performance of the n-type Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x}, because of the resulted dramatically decreased thermal conductivity. Analyses indicate that the heightened point-defect scattering induced by Se doping together with the electronphonon scattering induced by Te doping is responsible for the reduction of lattice thermal conductivity of these compounds.

  4. Effects of (Al,Ge) double doping on the thermoelectric properties of higher manganese silicides

    SciTech Connect

    Chen, Xi; Salta, Daniel; Zhang, Libin; Weathers, Annie; Zhou, Jianshi; Goodenough, John B.; Shi, Li

    2013-11-07

    Experiments and analysis have been carried out to investigate the effects of Al and (Al,Ge) doping on the microstructure and thermoelectric properties of polycrystalline higher manganese silicide (HMS) samples, which were prepared by solid-state reaction, ball milling, and followed by spark plasma sintering. It has been found that Al doping effectively increases the hole concentration, which leads to an increase in the electrical conductivity and power factor. By introducing the second dopant Ge into Al-doped HMS, the electrical conductivity is increased, and the Seebeck coefficient is decreased as a result of further increased hole concentration. The peak power factor is found to occur at a hole concentration between 1.8??10{sup 21} and 2.2??10{sup 21}?cm{sup ?3} measured at room temperature. The (Al,Ge)-doped HMS samples show lower power factors owing to their higher hole concentrations. The mobility of Mn(Al{sub 0.0035}Ge{sub y}Si{sub 0.9965-y}){sub 1.8} with y?=?0.035 varies approximately as T{sup ?3/2} above 200?K, suggesting acoustic phonon scattering is the dominant scattering mechanism. The thermal conductivity of HMS does not change appreciably by Al or (Al,Ge) doping. The maximum ZT of (Al,Ge)-doped HMS is 0.57 at 823?K, which is similar to the highest value found in the Al-doped HMS samples. The ZT values were reduced in the Mn(Al{sub 0.0035}Ge{sub y}Si{sub 0.9965-y}){sub 1.8} samples with high Ge concentration of y?=?0.025 and 0.035, because of reduced power factor. In addition, a two-band model was employed to show that the hole contribution to the thermal conductivity dominates the bipolar and electron contributions for all samples from 300 to 823?K and accounts for about 12% of the total thermal conductivity at about 800?K.

  5. Effects of ppm-Level Imperfection on the Transport Properties of FeSb2 Single Crystals

    NASA Astrophysics Data System (ADS)

    Takahashi, Hidefumi; Yasui, Yukio; Terasaki, Ichiro; Sato, Masatoshi

    2011-05-01

    The magnetic susceptibilities, electrical resistivities, Hall coefficients, and Seebeck coefficients have been measured for single crystals of a narrow-gap semiconductor of FeSb2 prepared using Sb metals of different purities. Below 40 K, carriers supplied from impurities of the Sb metal used as the raw material determine the transport quantities, making them very sensitive even to a ppm-level impurity concentration. The Seebeck coefficients observed here is as large as {-1400} ?V/K at 20 K for crystals prepared using Sb of 99.9999% purity. We have not observed, however, the colossal value of {-45} mV/K reported by other group, even for the samples having almost equal impurity concentrations to those used in their work. Only the concentration dependence of S has been found to be similar to that of the previous data.

  6. Side Effects

    MedlinePLUS

    ... 2014 Select a Language: Fact Sheet 550 Side Effects WHAT ARE SIDE EFFECTS? WHO GETS SIDE EFFECTS? ... t assume that you will get every side effect that’s listed! Most people have few or only ...

  7. Effect of Heat Treatment on the Thermoelectric Properties of Bismuth-Antimony-Telluride Prepared by Mechanical Deformation and Mechanical Alloying

    NASA Astrophysics Data System (ADS)

    Lee, Deuk-Hee; Lee, Jae-Uk; Jung, Sung-Jin; Baek, Seung-Hyub; Kim, Ju-Heon; Kim, Dong-Ik; Hyun, Dow-Bin; Kim, Jin-Sang

    2014-06-01

    In this work, p-type 20%Bi2Te3-80%Sb2Te3 bulk thermoelectric (TE) materials were prepared by mechanical deformation (MD) of pre-melted ingot and by mechanical alloying (MA) of elemental Bi, Sb, and Te granules followed by cold-pressing. The dependence on annealing time of changes of microstructure and TE properties of the prepared samples, including Seebeck coefficient, electrical resistivity, thermal conductivity, and figure-of-merit, was investigated. For both samples, saturation of the Seebeck coefficient and electrical resistivity were observed after annealing for 1 h at 380C. It is suggested that energy stored in samples prepared by both MA and MD facilitated their recrystallization within short annealing times. The 20%Bi2Te3-80%Sb2Te3 sample prepared by MA followed by heat treatment had higher a Seebeck coefficient and electrical resistivity than specimens fabricated by MD. Maximum figures-of-merit of 3.00 10-3/K and 2.85 10-3/K were achieved for samples prepared by MA and MD, respectively.

  8. Model for Increasing the Power Obtained from a Thermoelectric Generator Module

    NASA Astrophysics Data System (ADS)

    Huang, Gia-Yeh; Hsu, Cheng-Ting; Yao, Da-Jeng

    2014-06-01

    We have developed a model for finding the most efficient way of increasing the power obtained from a thermoelectric generator (TEG) module with a variety of operating conditions and limitations. The model is based on both thermoelectric principles and thermal resistance circuits, because a TEG converts heat into electricity consistent with these two theories. It is essential to take into account thermal contact resistance when estimating power generation. Thermal contact resistance causes overestimation of the measured temperature difference between the hot and cold sides of a TEG in calculation of the theoretical power generated, i.e. the theoretical power is larger than the experimental power. The ratio of the experimental open-loop voltage to the measured temperature difference, the effective Seebeck coefficient, can be used to estimate the thermal contact resistance in the model. The ratio of the effective Seebeck coefficient to the theoretical Seebeck coefficient, the Seebeck coefficient ratio, represents the contact conditions. From this ratio, a relationship between performance and different variables can be developed. The measured power generated by a TEG module (TMH400302055; Wise Life Technology, Taiwan) is consistent with the result obtained by use of the model; the relative deviation is 10%. Use of this model to evaluate the most efficient means of increasing the generated power reveals that the TEG module generates 0.14 W when the temperature difference is 25°C and the Seebeck coefficient ratio is 0.4. Several methods can be used triple the amount of power generated. For example, increasing the temperature difference to 43°C generates 0.41 W power; improving the Seebeck coefficient ratio to 0.65 increases the power to 0.39 W; simultaneously increasing the temperature difference to 34°C and improving the Seebeck coefficient ratio to 0.5 increases the power to 0.41 W. Choice of the appropriate method depends on the limitations of system, the cost, and the environment.

  9. Detailed Uncertainty Analysis of the ZEM-3 Measurement System

    NASA Technical Reports Server (NTRS)

    Mackey, Jon; Sehirlioglu, Alp; Dynys, Fred

    2014-01-01

    The measurement of Seebeck coefficient and electrical resistivity are critical to the investigation of all thermoelectric systems. Therefore, it stands that the measurement uncertainty must be well understood to report ZT values which are accurate and trustworthy. A detailed uncertainty analysis of the ZEM-3 measurement system has been performed. The uncertainty analysis calculates error in the electrical resistivity measurement as a result of sample geometry tolerance, probe geometry tolerance, statistical error, and multi-meter uncertainty. The uncertainty on Seebeck coefficient includes probe wire correction factors, statistical error, multi-meter uncertainty, and most importantly the cold-finger effect. The cold-finger effect plagues all potentiometric (four-probe) Seebeck measurement systems, as heat parasitically transfers through thermocouple probes. The effect leads to an asymmetric over-estimation of the Seebeck coefficient. A thermal finite element analysis allows for quantification of the phenomenon, and provides an estimate on the uncertainty of the Seebeck coefficient. The thermoelectric power factor has been found to have an uncertainty of +9-14 at high temperature and 9 near room temperature.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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.

  11. Managerial Effectiveness.

    ERIC Educational Resources Information Center

    Reddin, William J.

    A conceptual framework (3-D theory of managerial effectiveness) which relates the effectiveness of managerial style to specific situations is provided in this book. The six parts of the book are as follows: 1. Key Concepts, 2. Situation, 3. Styles, 4. Flex, 5. Managerial Effectiveness, and 6. Organizational Effectiveness. The book contains many

  12. Ballistic thermoelectric transport in structured nanowires

    NASA Astrophysics Data System (ADS)

    Wang, Biao; Zhou, Jun; Yang, Ronggui; Li, Baowen

    2014-06-01

    Thermoelectric (TE) devices are solid-state energy converters that can be used for power generation through the Seebeck effect and TE cooling through the Peltier effect. Nanostructures give great opportunities to engineer TE energy conversion efficiency. In this work, we investigate TE transport properties in structured nanowires (NWs) in the ballistic transport regime, where the NWs are bent, kinked, stubbed and segmented like a superlattice nanowire using the Greens function method and the Landauer-Bttiker formula. A large Seebeck coefficient is found when the transmission gap appears due to the quantum interference effect of electrons. The sign of the Seebeck coefficient can be controlled by the geometries of these structured NWs. This finding is helpful for the design of nanoscale TE devices, such as thermocouple, with the same type of material doping rather than those comprised of n-type and p-type materials.

  13. Synthesis and thermoelectric properties of RuO{sub 2} nanorods

    SciTech Connect

    Music, Denis; Basse, Felix H.-U.; Schneider, Jochen M.; Hassdorf, Ralf

    2010-07-15

    We have explored the effect of the O/Ru ratio on the morphology and the Seebeck coefficient of RuO{sub 2} nanorods (space group P4{sub 2}/mnm) synthesized by reactive sputtering. At an O/Ru ratio of 1.69, a faceted surface is observed, while nanorod formation occurs at O/Ru ratios of 2.03 and 2.24. Using classical molecular dynamics with the potential parameters derived in this work, we show that volatile species enable nanorod formation. Based on ab initio calculations, two effects of the nanorod formation on the Seebeck coefficient are observed: (i) increase due to additional states in the vicinity of the Fermi level and (ii) decrease due to oxygen point defects (volatile species). These two competing effects give rise to a moderate increase in the Seebeck coefficient upon nanorod formation.

  14. Effect of Nickel Substitution on Defect Chemistry, Electrical Properties, and Dimensional Stability of Calcium-Doped Yttrium Chromite

    SciTech Connect

    Yoon, Kyung J.; Stevenson, Jeffry W.; Marina, Olga A.

    2011-06-30

    The effect of nickel substitution on defect chemistry, electrical properties, and dimensional stability of calcium-doped yttrium chromite was studied for use as an interconnect material in high temperature solid oxide fuel cells (SOFCs). The compositions of Y0.8Ca0.2Cr1-xNixO3? (x=0-0.15), prepared using the glycine nitrate process, showed single phase orthorhombic perovskite structures over a wide range of oxygen partial pressures (10^-17 atm ? pO2 ? 0.21 atm). X-ray diffraction (XRD) analysis indicated that most of the nickel ions replacing chromium ions are divalent and act as acceptor dopants, leading to a substantial increase in conductivity. In particular, the conductivity at 900 degree C in air increased from 10 S/cm to 34 S/cm with 15% nickel substitution, and an increase in charge carrier density was confirmed by Seebeck measurements. A point defect model was derived, and the relationship between electrical conductivity and oxygen partial pressure was successfully fitted into the proposed model. The defect modeling results indicated that nickel substitution improves the stability of calcium-doped yttrium chromite toward reduction and suppresses the oxygen vacancy formation, which results in significantly increased electrical conductivity in reducing environment. The electrical conductivity of Y0.8Ca0.2Cr0.85Ni0.15O3? at 900 degree C in reducing atmosphere (pO2=10^-17 atm) was 5.8 S/cm, which was more than an order of magnitude higher than that of Y0.8Ca0.2CrO3? (0.2 S/cm). Improved stability in reducing atmosphere was further confirmed by dilatometry measurements showing reduced isothermal "chemical" expansion, and the isothermal expansion in reducing atmosphere (pO2=10^-17 atm) at 900 degree C decreased from 0.07% for Y0.8Ca0.2CrO3? to 0.03% for Y0.8Ca0.2Cr0.85Ni0.15O3?. Based on these results, enhanced electrical performance and mechanical integrity is expected with nickel substitution on calcium-doped yttrium chromite in SOFC operating conditions.

  15. Chemotherapy Effects

    MedlinePLUS

    ... saved articles window. My Saved Articles » My ACS » Chemotherapy Side Effects Chemotherapy drugs are powerful medicines that can cause side ... on the side effects most commonly caused by chemotherapy, this is a good place to start. Managing ...

  16. Placebo Effect

    MedlinePLUS

    ... C. Spencer, MD Steven Karceski, MD The placebo effect Joseph H. Friedman, MD Richard Dubinsky, MD WHAT ... placebo: a “dummy” medication that should have no effect on the condition. Placebos are not only drugs. ...

  17. Silicide/Silicon Hetero-Junction Structure for Thermoelectric Applications.

    PubMed

    Jun, Dongsuk; Kim, Soojung; Choi, Wonchul; Kim, Junsoo; Zyung, Taehyoung; Jang, Moongyu

    2015-10-01

    We fabricated silicide/silicon hetero-junction structured thermoelectric device by CMOS process for the reduction of thermal conductivity with the scatterings of phonons at silicide/silicon interfaces. Electrical conductivities, Seebeck coefficients, power factors, and temperature differences are evaluated using the steady state analysis method. Platinum silicide/silicon multilayered structure showed an enhanced Seebeck coefficient and power factor characteristics, which was considered for p-leg element. Also, erbium silicide/silicon structure showed an enhanced Seebeck coefficient, which was considered for an n-leg element. Silicide/silicon multilayered structure is promising for thermoelectric applications by reducing thermal conductivity with an enhanced Seebeck coefficient. However, because of the high thermal conductivity of the silicon packing during thermal gradient is not a problem any temperature difference. Therefore, requires more testing and analysis in order to overcome this problem. Thermoelectric generators are devices that based on the Seebeck effect, convert temperature differences into electrical energy. Although thermoelectric phenomena have been used for heating and cooling applications quite extensively, it is only in recent years that interest has increased in energy generation. PMID:26726353

  18. Thermoelectric properties of Yb-filled CoSb3 skutterudites

    NASA Astrophysics Data System (ADS)

    Park, Kwan-Ho; Seo, Won-Seon; Shin, Dong-Kil; Kim, Il-Ho

    2014-08-01

    Yb-filled skutterudites Yb z Co4Sb12 (z = 0, 0.1, 0.2, 0.3, 0.4) were prepared by encapsulated melting and hot pressing. The filling effects of Yb on the transport and the thermoelectric properties of the skutterudites were examined. In the case of z ? 0.3, a secondary phase (YbSb2) was formed, indicating that the filling fraction limit of Yb was z = 0.2 - 0.3. The intrinsic CoSb3 had a high positive Seebeck coefficient, but Yb-filled CoSb3 exhibited a negative Seebeck coefficient. In the case of z ? 0.1, the maximum absolute value of the Seebeck coefficient was | -231| ?VK-1, and in the case of z ? 0.2, the absolute value of the Seebeck coefficient increased with increasing temperature. The electrical conductivity increased and the Seebeck coefficient decreased with increasing Yb filling content due to the increased carrier concentration. The thermal conductivity was reduced significantly by Yb filling, mainly due to a decrease in the lattice thermal conductivity. Also, the lattice thermal conductivity decreased with increasing Yb filling content, indicating that the phonon scattering was caused by the rattling of Yb fillers in the voids of the skutterudite structure. Yb0.2Co4Sb12 showed the highest figure of merit of 1.0 at 823 K.

  19. Thermoelectric properties of ZnSb films grown by MOCVD

    SciTech Connect

    Venkatasubramanian, R.; Watko, E.; Colpitts, T.

    1997-04-01

    The thermoelectric properties of metallorganic chemical vapor deposited (MOCVD) ZnSb films are reported. The growth conditions necessary to obtain stoichiometric ZnSb films and the effects of various growth parameters on the electrical conductivity and Seebeck coefficients of the films are described. The as-grown ZnSb films are p-type. It was observed that the growth of thicker ZnSb films lead to improved carrier mobilities and lower free-carrier concentrations. The Seebeck coefficient of ZnSb films was found to rise rapidly at approximately 160 to 170 C, with peak Seebeck coefficients as high as 470 {micro}V/K at 220 C. The various growth conditions, including the use of intentional dopants, to improve the Seebeck coefficients at room temperature and above, are discussed. A short annealing of the ZnSb films at temperatures of {approximately} 200 C resulted in reduced free-carrier levels and higher Seebeck coefficients at 300 K. Finally, ZT values based on preliminary thermal conductivity measurements using the 3-{omega} method are reported.

  20. Low effective mass and carrier concentration optimization for high performance p-type Mg2(1-x)Li2xSi0.3Sn0.7 solid solutions.

    PubMed

    Zhang, Qiang; Cheng, Long; Liu, Wei; Zheng, Yun; Su, Xianli; Chi, Hang; Liu, Huijun; Yan, Yonggao; Tang, Xinfeng; Uher, Ctirad

    2014-11-21

    Mg2Si1-xSnx solid solutions are promising thermoelectric materials for power generation applications in the 500-800 K range. Outstanding n-type forms of these solid solutions have been developed in the past few years with the thermoelectric figure of merit ZT as high as 1.4. Unfortunately, no comparable performance has been achieved so far with p-type forms of the structure. In this work, we use Li doping on Mg sites in an attempt to enhance and control the concentration of hole carriers. We show that Li as well as Ga is a far more effective p-type dopant in comparison to Na or K. With the increasing content of Li, the electrical conductivity rises rapidly on account of a significantly enhanced density of holes. While the Seebeck coefficient decreases concomitantly, the power factor retains robust values supported by a rather high mobility of holes. Theoretical calculations indicate that Mg2Si0.3Sn0.7 intrinsically possesses the almost convergent double valence band structure (the light and heavy band), and Li doping retains a low density of states (DOS) on the top of the valence band, contrary to the Ga doping at the sites of Si/Sn. Low temperature specific heat capacity studies attest to a low DOS effective mass in Li-doped samples and consequently their larger hole mobility. The overall effect is a large power factor of Li-doped solid solutions. Although the thermal conductivity increases as more Li is incorporated in the structure, the enhanced carrier density effectively shifts the onset of intrinsic excitations (bipolar effect) to higher temperatures, and the beneficial role of phonon Umklapp processes as the primary limiting factor to the lattice thermal conductivity is thus extended. The final outcome is the figure of merit ZT ? 0.5 at 750 K for x = 0.07. This represents a 30% improvement in the figure of merit of p-type Mg2Si1-xSnx solid solutions over the literature values. Hence, designing low DOS near Fermi level EF for given carrier pockets can serve as an effective approach to optimize the PF and thus ZT value. PMID:25178356

  1. Longitudinal and transverse thermoelectric transport in MnSi

    NASA Astrophysics Data System (ADS)

    Hirokane, Yuji; Tomioka, Yasuhide; Imai, Yoshinori; Maeda, Atsutaka; Onose, Yoshinori

    2016-01-01

    We have investigated the longitudinal and transverse thermoelectric phenomena (Seebeck and Nernst effects) in a single crystal of intermetallic compound MnSi. The Seebeck coefficient is largely decreased (?50 % ) by magnetic field around the helimagnetic transition temperature, which implies the large entropy release at the magnetic transition. We have discerned the anomalous and normal components of Nernst signal dependent on the magnetization and the magnetic field, respectively. For the anomalous Nernst effect, the intrinsic mechanism induced by the Berry phase of electrons seems dominant over the extrinsic mechanisms induced by scattering at least in the high temperature (T ?15 K) and resistive (? >4 ? ? cm ) region. The Nernst and Seebeck signals show little change in the course of the transition to skyrmion crystal.

  2. Anisotropic Effects on the Thermoelectric Properties of Highly Oriented Electrodeposited Bi2Te3 Films.

    PubMed

    Manzano, Cristina V; Abad, Begoña; Muñoz Rojo, Miguel; Koh, Yee Rui; Hodson, Stephen L; Lopez Martinez, Antonio M; Xu, Xianfan; Shakouri, Ali; Sands, Timothy D; Borca-Tasciuc, Theodorian; Martin-Gonzalez, Marisol

    2016-01-01

    Highly oriented [1 1 0] Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6 ± 1.2)·10(-2) and (10.4 ± 2.6)·10(-2), respectively. PMID:26776726

  3. Anisotropic Effects on the Thermoelectric Properties of Highly Oriented Electrodeposited Bi2Te3 Films

    PubMed Central

    Manzano, Cristina V.; Abad, Begoña; Muñoz Rojo, Miguel; Koh, Yee Rui; Hodson, Stephen L.; Lopez Martinez, Antonio M.; Xu, Xianfan; Shakouri, Ali; Sands, Timothy D.; Borca-Tasciuc, Theodorian; Martin-Gonzalez, Marisol

    2016-01-01

    Highly oriented [1 1 0] Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6 ± 1.2)·10−2 and (10.4 ± 2.6)·10−2, respectively. PMID:26776726

  4. Anisotropic Effects on the Thermoelectric Properties of Highly Oriented Electrodeposited Bi2Te3 Films

    NASA Astrophysics Data System (ADS)

    Manzano, Cristina V.; Abad, Begoa; Muoz Rojo, Miguel; Koh, Yee Rui; Hodson, Stephen L.; Lopez Martinez, Antonio M.; Xu, Xianfan; Shakouri, Ali; Sands, Timothy D.; Borca-Tasciuc, Theodorian; Martin-Gonzalez, Marisol

    2016-01-01

    Highly oriented [1 1 0] Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6??1.2)10?2 and (10.4??2.6)10?2, respectively.

  5. Infrared and thermoelectric power generation in thin atomic layer deposited Nb-doped TiO{sub 2} films

    SciTech Connect

    Mann, Harkirat S.; Lang, Brian N.; Schwab, Yosyp; Scarel, Giovanna; Niemelä, Janne-Petteri; Karppinen, Maarit

    2015-01-15

    Infrared radiation is used to radiatively transfer heat to a nanometric power generator (NPG) device with a thermoelectric Nb-doped TiO{sub 2} film deposited by atomic layer deposition (ALD) as the active element, onto a borosilicate glass substrate. The linear rise of the produced voltage with respect to the temperature difference between the “hot” and “cold” junctions, typical of the Seebeck effect, is missing. The discovery of the violation of the Seebeck effect in NPG devices combined with the ability of ALD to tune thermoelectric thin film properties could be exploited to increase the efficiency of these devices for energy harvesting purposes.

  6. Magnetization currents of fluctuating Cooper pairs

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    Recent experiments show that the Nernst-Ettingshausen effect is orders of magnitude stronger than the thermoelectric Seebeck effect in superconductors above the critical temperature. We explain different magnitudes of the two effects accounting for the magnetization current of virtual Cooper pairs. The method allows for detailed understanding of the surprising nonmonotonic dependence of the Nernst-Ettingshausen coefficient on the magnetic field.

  7. Tailoring thermopower of single-molecular junctions by temperature-induced surface reconstruction

    NASA Astrophysics Data System (ADS)

    Lin, Chiung-Yuan; Hsu, Bailey; Hsieh, Yau-Shian; Chen, Yu-Chang

    2014-03-01

    Recent experiments revealed that surface reconstruction occurs at around 300-400K in the interface of C60 adsorbed on Cu(111) substrate by scanning tunneling microscope techniques. To understand effects of such reconstruction on thermopower, we investigate the Seebeck coefficients of C60 single-molecular junctions without and with surface reconstruction as a function of temperature at different tip-to-molecule heights from first-principles. Our calculations show that surface reconstruction can enhance or suppress Seebeck coefficients according to junctions at different tip heights. We further observe that the Seebeck coefficient of the junction at d = 3.4 may change from p- to n-type under surface reconstruction. National Science Council (Taiwan), Grant NSC 100-2112-M-009-012-MY3.

  8. Photo-transport properties of Pb{sub 2}CrO{sub 5} single crystals

    SciTech Connect

    Mondal, P. S.; Okazaki, R. Taniguchi, H.; Terasaki, I.

    2014-11-21

    We report photo-thermoelectric transport phenomena in Pb{sub 2}CrO{sub 5} single crystals. Without illumination, this material exhibits an insulating behavior characterized by an activation-type temperature variation of the electrical conductivity. The Seebeck coefficient contrastingly shows a crossover from high-temperature insulating to low-temperature metallic behavior, which is attributed to degenerate carriers in a donor level. We have found that under illumination, both the conductivity and the Seebeck coefficient increase in magnitude with increasing photon flux density in the degenerate-conduction regime. This result is difficult to understand within a simple photo-doping effect, which usually leads to a decrease in the Seebeck coefficient under illumination. The observed phenomenon is discussed in terms of a two-carrier contribution to the transport properties.

  9. Thermal Effects.

    ERIC Educational Resources Information Center

    Talmage, Sylvia S.; Coutant, Charles C.

    1978-01-01

    Presents a literature review of the effect of temperature on the biosphere water, covering publications of 1976-77. This review includes the effects of temperature on growth, production, and embryonic and larval development. A list of 401 references is also presented. (HM)

  10. Gauging Effectiveness

    ERIC Educational Resources Information Center

    Foord, Kathleen A.; Haar, Jean M.

    2012-01-01

    Books by education experts and speakers at national professional conferences have inspired many school leaders to initiate professional learning communities (PLCs). Sustaining them effectively to raise student achievement is another matter. How can one know whether a PLC is moving toward a desired outcome? Measuring effectiveness requires an

  11. Thermal effects

    SciTech Connect

    Harrelson, M.E.; Talmadge, S.S.; Cravens, J.B.

    1984-06-01

    A literature review is presented of recent studies on the role of temperature effects and change in temperature caused by thermal power plants on aquatic life. Several of these studies involve the use of models that allow testing of hypotheses concerning the effects of temperature on fish and insects. 91 references.

  12. Thermal effects

    SciTech Connect

    Cravens, J.B.; Harrelson, M.E.; Talmage, S.S.

    1983-06-01

    A literature review of studies dealing with thermal effects on aquatic systems is presented. Site studies are discussed, along with biochemical reaction studies, the effects of temperature on the growth of organisms, and the interaction of temperature and other stresses. (JMT)

  13. 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.

  14. Thermoelectric conversion efficiency in IV-VI semiconductors with reduced thermal conductivity

    NASA Astrophysics Data System (ADS)

    Ishida, Akihiro; Thao, Hoang Thi Xuan; Yamamoto, Hidenari; Kinoshita, Yohei; Ishikiriyama, Mamoru

    2015-10-01

    Mid-temperature thermoelectric conversion efficiencies of the IV-VI materials were calculated under the Boltzmann transport theory of carriers, taking the Seebeck, Peltier, and Thomson effects into account. The conversion efficiency was discussed with respect to the lattice thermal conductivity, keeping other parameters such as Seebeck coefficient and electrical conductivity to the same values. If room temperature lattice thermal conductivity is decreased up to 0.5W/mK, the conversion efficiency of a PbS based material becomes as high as 15% with the temperature difference of 500K between 800K and 300K.

  15. Implications of nanostructuring on the thermoelectric properties in half-Heusler alloys

    NASA Astrophysics Data System (ADS)

    Bhardwaj, A.; Misra, D. K.; Pulikkotil, J. J.; Auluck, S.; Dhar, A.; Budhani, R. C.

    2012-09-01

    High energy ball milled Zr0.25Hf0.75NiSn alloys subjected to spark plasma sintering show an enhanced thermoelectric figure of merit in comparison with its normal bulk material synthesized by arc-melting process. The enhancement is due to increase in Seebeck coefficient with simultaneous decrease in thermal conductivity which follows due to increase in the cell volume. Theoretical calculations find that volume expansion facilitates band narrowing effects leading to high Seebeck coefficient and that decreasing orbital overlap which results in weak bonding leads to dampening the phonon propagation in addition to the interface scattering of phonons from phase boundaries.

  16. A study of transport properties in Cu and P doped ZnSb

    SciTech Connect

    Valset, K.; Song, X.; Finstad, T. G.

    2015-01-28

    ZnSb samples have been doped with copper and phosphorus and sintered at 798 K. Electronic transport properties are interpreted as being influenced by an impurity band close to the valence band. At low Cu dopant concentrations, this impurity band degrades the thermoelectric properties as the Seebeck coefficient and effective mass are reduced. At carrier concentrations above 1 × 10{sup 19 }cm{sup −3}, the Seebeck coefficient in Cu doped samples can be described by a single parabolic band.

  17. Psychopharmaceuticals: effects and side effects

    PubMed Central

    Kline, Nathan S.

    1959-01-01

    Drugs which affect psychological behaviour are being used in vast amounts nowadays, with, in all too many cases, but scant regard for their exact uses or possible side effects. This article contains a clinical classification of these drugs, followed by an account of their principal side effects and the means of obviating them. PMID:14409889

  18. Effective Schools Require Effective Principals

    ERIC Educational Resources Information Center

    LaPointe, Michelle; Davis, Stephen H.

    2006-01-01

    At long last, scholars and policy makers have come to realize what most school administrators have known for years--that effective schools require both outstanding teachers and strong leaders. Although there is considerable research about the characteristics of effective school leaders and the strategies principals can use to help manage…

  19. Modern Thermocouple Experiment.

    ERIC Educational Resources Information Center

    Chang, K. N.; And Others

    1978-01-01

    Describes a thermocouple circuit used to measure Joule heating as well as Peltier heating and cooling for a copper-Constantan metallic junction. Shows how the Seebeck effect from a thermocouple can monitor the temperature condition of a junction with regard to input power and Peltier effect. (Author/GA)

  20. Health Effects

    MedlinePLUS

    ... Search The CDC Cancel Submit Search The CDC Climate and Health Note: Javascript is disabled or is ... Guidance and Trainings Webinars Data and Tools Publications Climate Effects on Health Recommend on Facebook Tweet Share ...

  1. The Effect of Structural Vacancies on the Thermoelectric Properties of (Cu2Te)1-x(Ga2Te3)x

    SciTech Connect

    Ye, Zuxin; Cho, Jung Y; Tessema, Misle; Salvador, James R.; Waldo, Richard; Wang, Hsin; Cai, Wei

    2013-01-01

    We have studied the effects of structural vacancies on the thermoelectric properties of the ternary compounds (Cu2Te)1-x(Ga2Te3)x (x = 0.5, 0.55, 0.571, 0.6, 0.625, 0.667 and 0.75), which are solid solutions found in the pseudo-binary phase diagram for Cu2Te and Ga2Te3. This system possesses tunable structural vacancy concentrations. The x= 0.5 phase, CuGaTe2, is nominally devoid of structural vacancies, while the rest of the compounds contain varying amounts of these features, and the volume density of vacancies increases with Ga2Te3 content. The sample with x = 0.5, 0.55, 0.571, 0.6, 0.625 crystallize in the chalcopyrite structure while the x = 0.667 and 0.75 adopt the Ga2Te3 defect zinc blende structure. Strong scattering of heat carrying phonons by structural defects, leads to the reduction of thermal conductivity, which is beneficial to the thermoelectric performance of materials. On the other hand, these defects also scatter charge carriers and reduce the electrical conductivity. All the samples investigated are p-type semiconductors as inferred by the signs of their respective Hall (RH) and Seebeck (S) coefficients. The structural vacancies were found to scatter phonons strongly, while a combination of increased carrier concentration, and vacancies decreases the Hall mobility ( H), degrading the overall thermoelectric performance. The room temperature H drops from 90 cm2/V s for CuGaTe2 to 13 cm2/V s in Cu9Ga11Te21 and 4.6 cm2/V s in CuGa3Te5. The low temperature thermal conductivity decreases significantly with higher Ga2Te3 concentrations (higher vacancy concentration) due to increased point defect scattering which dominate thermal resistance terms. At high temperatures, the dependence of thermal conductivity on the Ga2Te3 content is less significant. The presence of strong Umklapp scattering leads to low thermal conductivity at high temperatures for all samples investigated. The highest ZT among the samples in this study was found for the defect-free CuGaTe2 with ZT ~ 1.0 at 840K.

  2. Measuring effectiveness.

    PubMed

    Stegenga, Jacob

    2015-12-01

    Measuring the effectiveness of medical interventions faces three epistemological challenges: the choice of good measuring instruments, the use of appropriate analytic measures, and the use of a reliable method of extrapolating measures from an experimental context to a more general context. In practice each of these challenges contributes to overestimating the effectiveness of medical interventions. These challenges suggest the need for corrective normative principles. The instruments employed in clinical research should measure patient-relevant and disease-specific parameters, and should not be sensitive to parameters that are only indirectly relevant. Effectiveness always should be measured and reported in absolute terms (using measures such as 'absolute risk reduction'), and only sometimes should effectiveness also be measured and reported in relative terms (using measures such as 'relative risk reduction')-employment of relative measures promotes an informal fallacy akin to the base-rate fallacy, which can be exploited to exaggerate claims of effectiveness. Finally, extrapolating from research settings to clinical settings should more rigorously take into account possible ways in which the intervention in question can fail to be effective in a target population. PMID:26199055

  3. Effect of Composition on Thermoelectric Properties of Polycrystalline CrSi2

    NASA Astrophysics Data System (ADS)

    Perumal, S.; Gorsse, S.; Ail, U.; Decourt, R.; Umarji, A. M.

    2013-06-01

    Ingots with compositions CrSi2- x (with 0 < x < 0.1) were synthesized by vacuum arc melting followed by uniaxial hot pressing for densification. This paper reports the temperature and composition dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity of CrSi2- x samples in the temperature range of 300 K to 800 K. The silicon-deficient samples exhibited substantial reductions in resistivity and Seebeck coefficient over the measured temperature range due to the formation of metallic secondary CrSi phase embedded in the CrSi2 matrix phase. The thermal conductivity was seen to exhibit a U-shaped curve with respect to x, exhibiting a minimum value at the composition of x = 0.04. However, the limit of the homogeneity range of CrSi2 suppresses any further decrease of the lattice thermal conductivity. As a consequence, the maximum figure of merit of ZT = 0.1 is obtained at 650 K for CrSi1.98.

  4. Effects and Effectiveness of Telemedicine

    PubMed Central

    Grigsby, Jim; Kaehny, Margaret M.; Sandberg, Elliot J.; Schlenker, Robert E.; Shaughnessy, Peter W.

    1995-01-01

    The use of telemedicine has recently undergone rapid growth and proliferation. Although the feasibility of many applications has been tested for nearly 30 years, data concerning the costs, effects, and effectiveness of telemedicine are limited. Consequently, the development of a strategy for coverage, payment, and utilization policy has been hindered. Telemedicine continues to expand, and pressure for policy development increases in the context of Federal budget cuts and major changes in health service financing. This article reviews the literature on the effects and medical effectiveness of telemedicine. It concludes with several recommendations for research, followed by a discussion of several specific questions, the answers to which might have a bearing on policy development. PMID:10153466

  5. Plasma Effects

    NASA Technical Reports Server (NTRS)

    Armstrong, J. W.

    1983-01-01

    Radio communication with space probes requires sending signals through the Earth's ionosphere and usually the solar wind. During planetary flybys, the signal may also pass through the ionosphere of another planet. These ionized media can perturb the radio signal in a variety of ways. Examples of these perturbations are variations in the electrical length between the spacecraft and the ground station, Faraday rotation of linearly polarized signals, amplitude and phase scintillations, and spectral and angular broadening. These plasma effects can have undesirable influences on telemetry performance and thus need to be understood from a communications engineering viewpoint. The plasma effects are, however, useful from a scientific viewpoint, since the effects on the communications link can often be inverted to estimate the physical conditions in the plasma.

  6. Physiological effects

    SciTech Connect

    Pearcy, R.W.; Bjoerkman, O.

    1983-01-01

    This chapter examines the effects of CO/sub 2/ on plants at the physiological level. The authors examine the potential effects of elevated CO/sub 2/ in concert with water, temperature, light, and salinity. They also examine plant allometric growth as it is affected by CO/sub 2/. The relationships between CO/sub 2/ uptake and temperature are examined in some detail. Stomatal function as it is now known is discussed, along with changes in water use efficiency correlated with increased levels of CO/sub 2/. Future research needs are identified. 71 references, 8 figures.

  7. Sleeper Effects

    ERIC Educational Resources Information Center

    Maurer, Daphne; Mondloch, Catherine J.; Lewis, Terri L.

    2007-01-01

    Early experience preserves and refines many capabilities that emerge prenatally. Here we describe another role that it plays--establishing the neural substrate for capabilities that emerge at a much later point in development. The evidence comes from sleeper effects: permanent deficits when early experience was absent in capabilities that normally

  8. Effective Evaluation

    ERIC Educational Resources Information Center

    Oliva, Michelle; Mathers, Carrie; Laine, Sabrina

    2009-01-01

    Principals know that effective teachers are the greatest school-based contributors to improved student outcomes. What is not always clear is how principals can help teachers adapt their instructional practices to the increasingly diverse learning styles they find in their classrooms. Teacher evaluation practices are typically not seen as a tool

  9. Effective Consumerism.

    ERIC Educational Resources Information Center

    Daugherty, Mabel

    This module, consisting of materials for use in conducting a consumer education mini-course, deals with effective consumerism. Covered in the individual lessons are the following topics: being prepared with information (sources of consumer information and subscription forms); evaluating warranties and service contracts; evaluating advertising and

  10. Communicating Effectively

    Cancer.gov

    The seventh module of the EPEC-O (Education in Palliative and End-of-Life Care for Oncology) Self-Study: Cultural Considerations When Caring for African Americans explores communication issues pertinent to African Americans with cancer and their health care providers, discusses strategies for culturally sensitive communication, and presents the SPIKES protocol, a practical framework for effective communication.

  11. Sleeper Effects

    ERIC Educational Resources Information Center

    Maurer, Daphne; Mondloch, Catherine J.; Lewis, Terri L.

    2007-01-01

    Early experience preserves and refines many capabilities that emerge prenatally. Here we describe another role that it plays--establishing the neural substrate for capabilities that emerge at a much later point in development. The evidence comes from sleeper effects: permanent deficits when early experience was absent in capabilities that normally…

  12. System Effectiveness

    SciTech Connect

    Powell, Danny H; Elwood Jr, Robert H

    2011-01-01

    An effective risk assessment system is needed to address the threat posed by an active or passive insider who, acting alone or in collusion, could attempt diversion or theft of nuclear material. It is critical that a nuclear facility conduct a thorough self-assessment of the material protection, control, and accountability (MPC&A) system to evaluate system effectiveness. Self-assessment involves vulnerability analysis and performance testing of the MPC&A system. The process should lead to confirmation that mitigating features of the system effectively minimize the threat, or it could lead to the conclusion that system improvements or upgrades are necessary to achieve acceptable protection against the threat. Analysis of the MPC&A system is necessary to understand the limits and vulnerabilities of the system to internal threats. Self-assessment helps the facility be prepared to respond to internal threats and reduce the risk of theft or diversion of nuclear material. MSET is a self-assessment or inspection tool utilizing probabilistic risk assessment (PRA) methodology to calculate the system effectiveness of a nuclear facility's MPC&A system. MSET analyzes the effectiveness of an MPC&A system based on defined performance metrics for MPC&A functions based on U.S. and international best practices and regulations. A facility's MC&A system can be evaluated at a point in time and reevaluated after upgrades are implemented or after other system changes occur. The total system or specific subareas within the system can be evaluated. Areas of potential performance improvement or system upgrade can be assessed to determine where the most beneficial and cost-effective improvements should be made. Analyses of risk importance factors show that sustainability is essential for optimal performance. The analyses reveal where performance degradation has the greatest detrimental impact on total system risk and where performance improvements have the greatest reduction in system risk. The risk importance factors show the amount of risk reduction achievable with potential upgrades and the amount of risk reduction actually achieved after upgrades are completed. Applying the risk assessment tool gives support to budget prioritization by showing where budget support levels must be sustained for MC&A functions most important to risk. Results of the risk assessment are also useful in supporting funding justifications for system improvements that significantly reduce system risk.

  13. Radiation effects

    SciTech Connect

    Holden, N.E.

    1985-01-01

    For the meeting of the Commission on Radiochemistry and Nuclear Techniques our chairman has submitted comments on potential problems that the Commission should consider in Lyon which had been posed by various members. In one of these comments, Prof. Roth has mentioned the problem of radiation effects in solids and in water and water solutions. The radiolysis of water has been of concern for a large number of years, but as Prof. Roth notes, the radiation effects on the first wall of fusion reactors is a problem that has arisen only in recent years and for which no critical data compilation is presently available. This paper has been prepared in response to Prof. Roth's comments and indicates a possible area, which the Commission might conceivably address at this meeting and/or in the near future. 7 refs.

  14. Blazhko Effect

    NASA Technical Reports Server (NTRS)

    Teays, Terry

    1996-01-01

    The cause of the Blazhko effect, the long-term modulation of the light and radial velocity curves of some RR Lyr stars, is still not understood. The observational characteristics of the Blazhko effect are discussed. Some preliminary results are presented from two recent campaigns to observe RR Lyr, using the International Ultraviolet Explorer along with ground-based spectroscopy and photometry, throughout a pulsation cycle, at a variety of Blazhko phases. A set of ultraviolet light curves have been generated from low dispersion IUE spectra. In addition, the (visual) light curves from IUE's Fine Error Sensor are analyzed using the Fourier decomposition technique. The values of the parameters Psi(sub 21) and R(sub 21) at different Blazhko phases of RR Lyr span the range of values found for non-Blazhko variables of similar period.

  15. Effective Presentations

    PubMed Central

    Spooner, H. James; Swanson, Richard W.

    1990-01-01

    Where the purpose of presentations is to inform, effective delivery is important to ensure that audiences receive the educational message. We offer six suggestions: introduce the topic in an interesting way; speak loudly enough; do not read; involve the audience actively; respect the attention span of the audience; and limit the amount of content. We conclude that the skills of live public presentation can be learned, but that the art of presentation is innate. Imagesp2063-ap2064-a PMID:21233951

  16. On the magnetotransport of 3D systems in quantizing magnetic field

    NASA Astrophysics Data System (ADS)

    Cheremisin, M. V.

    2014-12-01

    The resistivity components of 3D electron gas placed in quantizing magnetic field are calculated taking into account the correction caused by combined action of the Peltier and Seebeck thermoelectric effects. The longitudinal, transverse and the Hall magnetoresistivities exhibit familiar 1/B-period oscillations being universal functions of magnetic field and temperature.

  17. Thermoelectric metal comparator determines composition of alloys and metals

    NASA Technical Reports Server (NTRS)

    Stone, C. C.; Walker, D. E.

    1967-01-01

    Emf comparing device nondestructively inspects metals and alloys for conformance to a chemical specification. It uses the Seebeck effect to measure the difference in emf produced by the junction of a hot probe and the junction of a cold contact on the surface of an unknown metal.

  18. Thermally induced spin accumulation at Al/Co2TiSi and Al/Co2TiGe contacts

    NASA Astrophysics Data System (ADS)

    Popescu, Voicu; Geisler, Benjamin; Kratzer, Peter

    2014-03-01

    Spin injection from a ferromagnet in a semiconductor substrate can be accomplished either by applying an external voltage or a temperature gradient. In the latter case, one exploits the Seebeck effect, with the temperature gradient across the contact directly resulting in a difference in chemical potentials in the two spin channels due to the spin-dependence of the Seebeck coefficient. The magnetic Heusler alloys Co2TiSi or Co2TiGe exhibit half-metallic ferromagnetism in their ideal L21 crystal structure, with a potentially high degree of spin polarization of the injected current. As such, they recommend themselves for integrated spin injectors in combination with the closely lattice-matched Al contact layer. We investigate the possibility of employing Al/Co2TiX/Al (X=Si,Ge) trilayers as thermally driven spin injectors by means of first-principles calculations of the electronic structure and of the thermoelectric transport properties. Our results show that the spin-dependent Seebeck effect is sensitive to the atomic structure of the Heusler/Al interface. In particular, for a thin Co2TiSi or Co2TiGe layer terminated by a TiSi or TiGe atomic plane, the thermal spin accumulation is found to be of the same order of magnitude as the effective Seebeck coefficient. Funded by DFG, SPP 1538.

  19. Erosion Effects

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    The impact crater in this THEMIS image is a model illustration to the effects of erosion on Mars. The degraded crater rim and several landslides observed in crater walls is evidence to the mass wasting of materials. Layering in crater walls also suggests the presence of materials that erode at varying rates.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 31.6, Longitude 44.3 East (315.7 West). 19 meter/pixel resolution.

  20. High temperature experimental characterization of microscale thermoelectric effects

    NASA Astrophysics Data System (ADS)

    Favaloro, Tela

    Thermoelectric devices have been employed for many years as a reliable energy conversion technology for applications ranging from the cooling of sensors or charge coupled devices to the direct conversion of heat into electricity for remote power generation. However, its relatively low conversion efficiency has limited the implementation of thermoelectric materials for large scale cooling and waste heat recovery applications. Recent advances in semiconductor growth technology have enabled the precise and selective engineering of material properties to improve the thermoelectric figure of merit and thus the efficiency of thermoelectric devices. Accurate characterization at the intended operational temperature of novel thermoelectric materials is a crucial component of the optimization process in order to fundamentally understand material behavior and evaluate performance. The objective of this work is to provide the tools necessary to characterize high efficiency bulk and thin-film materials for thermoelectric energy conversion. The techniques developed here are not bound to specific material or devices, but can be generalized to any material system. Thermoreflectance imaging microscopy has proven to be invaluable for device thermometry owing to its high spatial and temporal resolutions. It has been utilized in this work to create two-dimensional temperature profiles of thermoelectric devices during operation used for performance analysis of novel materials, identification of defects, and visualization of high speed transients in a high-temperature imaging thermostat. We report the development of a high temperature imaging thermostat capable of high speed transient thermoelectric characterization. In addition, we present a noninvasive method for thermoreflectance coefficient calibration ideally suited for vacuum and thus high temperature employment. This is the first analysis of the thermoreflectance coefficient of commonly used metals at high-temperatures. High temperature vacuum thermostats are designed and fabricated with optical imaging capability and interchangeable measurement stages for various electrical and thermoelectric characterizations. We demonstrate the simultaneous measurement of in-plane electrical conductivity and Seebeck coefficient of thin-film or bulk thermoelectric materials. Furthermore, we utilize high-speed circuitry to implement the transient Harman technique and directly determine the cross-plane figure of merit of thin film thermoelectric materials at high temperatures. Transient measurements on thin film devices are subject to complications from the growth substrate, non-ideal contacts and other detrimental thermal and electrical effects. A strategy is presented for optimizing device geometry to mitigate the impact of these parasitics. This design enabled us to determine the cross-plane thermoelectric material properties in a single high temperature measurement of a 25mum InGaAs thin film with embedded ErAs (0.2%) nanoparticles using the bipolar transient Harman technique in conjunction with thermoreflectance thermal imaging. This approach eliminates discrepancies and potential device degradation from the multiple measurements necessary to obtain individual material parameters. Finite element method simulations are used to analyze non-uniform current and temperature distributions over the device area and determine the three dimensional current path for accurate extraction of material properties from the thermal images. Results match with independent measurements of thermoelectric material properties for the same material composition, validating this approach. We apply high magnification thermoreflectance imaging to create temperature maps of vanadium dioxide nanobeams and examine electro-thermal energy conversion along the nanobeam length. The metal to insulator transition of strongly correlated materials is subject to strong lattice coupling which brings about the unique one-dimensional alignment of metal-insulator domains along nanobeams. Many studies have investigated the effects of stress on the metal to insulator transition and hence the phase boundary, but few have directly examined the temperature profile across the metal-insulating interface. Here, thermoreflectance microscopy reveals the underlying behavior of single-crystalline VO2 nanobeams in the phase coexisting regime. We directly observe highly localized alternating Peltier heating and cooling as well as Joule heating concentrated at the domain interfaces, indicating the significance of the domain walls and band offsets. Moreover, we are able to elucidate strain accumulation along the nanobeam and distinguish between two insulating phases of VO 2 through detection of the opposite polarity of their respective thermoreflectance coefficients.

  1. Spin caloritronics of blue phosphorene nanoribbons.

    PubMed

    Liu, Y S; Zhang, X; Yang, X F; Hong, X K; Feng, J F; Si, M S; Wang, X F

    2015-04-28

    We report a first-principles study of the magnetic properties and spin caloritronics of zigzag-type blue phosphorene nanoribbons (zBPNRs). It is found that the bare zBPNR (0H-zBPNR) or monohydrogenated zBPNR (1H-zBPNR) exhibit spin-semiconducting properties arising from the edge electronic states. We further confirm that the py orbitals of the edge P atoms have the main contributions to these states. The spin-semiconducting property has a natural advantage for fabricating perfect thermospin devices with a stronger spin Seebeck effect than charge Seebeck effect at the Fermi level. When a temperature difference is applied, the electric current with the different spin index displays a bipolar behavior, and the spin-filtering efficiency can reach 1200%. By changing the widths of 0H-zBPNR and 1H-zBPNR, the ratio of the spin Seebeck coefficient to the charge Seebeck coefficient at the Fermi level is about 10 at room temperature. PMID:25801010

  2. Side Effects of Chemotherapy

    MedlinePLUS

    ... Men Living with Prostate Cancer Side Effects of Chemotherapy Side Effects Urinary Dysfunction Bowel Dysfunction Erectile Dysfunction ... Side Effects of Hormone Therapy Side Effects of Chemotherapy Side Effects: When to Seek Help PSA Rising ...

  3. Magnetic-Field Dependence of Thermoelectric Properties of Sintered Bi90Sb10 Alloy

    NASA Astrophysics Data System (ADS)

    Murata, Masayuki; Yamamoto, Atsushi; Hasegawa, Yasuhiro; Komine, Takashi

    2016-03-01

    The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit ( ZT) of a sintered Bi90Sb10 alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered Bi90Sb10 alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77-300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the Bi90Sb10 alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L- and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model.

  4. Development of Flexible Micro-Thermo-electrochemical Generators Based on Ionic Liquids

    NASA Astrophysics Data System (ADS)

    Uhl, Stefanie; Laux, Edith; Journot, Tony; Jeandupeux, Laure; Charmet, Jrme; Keppner, Herbert

    2014-10-01

    The unfavourable relationship between electrical and thermal conductivity limits the choice of solid-state materials for thermoelectric generators (TEG). Among ionic liquids (IOL), it appears that a large variety of thermoelectric (TE) materials with promising high Seebeck coefficients have potential for development. Furthermore, the novel solid-on-liquid deposition technology (SOLID) allows the encapsulation of liquid TE materials to create new, highly integrated TEG devices. Following this vision, this paper studies a large number of IOLs looking at TE-relevant parameters such as thermal and electrical conductivity, Seebeck coefficient and temperature-dependent viscosity. We show that positive and negative Seebeck coefficients can be obtained, depending on the molecular structure and the viscosity of the IOL. The properties of single-junction TEGs are presented in terms of I- V characteristics correlated with the IOL properties. We prove that the limiting effect of conversion efficiency is the current density that can be extracted from a device rather than the Seebeck coefficient.

  5. Magnetic-Field Dependence of Thermoelectric Properties of Sintered Bi90Sb10 Alloy

    NASA Astrophysics Data System (ADS)

    Murata, Masayuki; Yamamoto, Atsushi; Hasegawa, Yasuhiro; Komine, Takashi

    2015-12-01

    The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit (ZT) of a sintered Bi90Sb10 alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered Bi90Sb10 alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77-300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the Bi90Sb10 alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L- and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model.

  6. Convergence of valence bands for high thermoelectric performance for p-type InN

    NASA Astrophysics Data System (ADS)

    Li, Hai-Zhu; Li, Ruo-Ping; Liu, Jun-Hui; Huang, Ming-Ju

    2015-12-01

    Band engineering to converge the bands to achieve high valley degeneracy is one of effective approaches for designing ideal thermoelectric materials. Convergence of many valleys in the valence band may lead to a high Seebeck coefficient, and induce promising thermoelectric performance of p-type InN. In the current work, we have systematically investigated the electronic structure and thermoelectric performance of wurtzite InN by using the density functional theory combined with semiclassical Boltzmann transport theory. Form the results, it can be found that intrinsic InN has a large Seebeck coefficient (254 μV/K) and the largest value of ZeT is 0.77. The transport properties of p-type InN are better than that of n-type one at the optimum carrier concentration, which mainly due to the large Seebeck coefficient for p-type InN, although the electrical conductivity of n-type InN is larger than that of p-type one. We found that the larger Seebeck coefficient for p-type InN may originate from the large valley degeneracy in the valence band. Moreover, the low minimum lattice thermal conductivity for InN is one key factor to become a good thermoelectric material. Therefore, p-type InN could be a potential material for further applications in the thermoelectric area.

  7. Effective Teaching/Effective Urban Teaching

    ERIC Educational Resources Information Center

    Watson, Dyan; Charner-Laird, Megin; Kirkpatrick, Cheryl L.; Szczesiul, Stacy Agee; Gordon, Pamela J.

    2006-01-01

    This article considers the ways in which 17 novice teachers define and describe effective urban teaching and the stark contrasts that these teachers draw between effective urban teaching and effective teaching. The authors find that descriptions of students played a considerable role when participants made distinctions between effective teaching

  8. Pseudo-direct bandgap transitions in silicon nanocrystals: effects on optoelectronics and thermoelectrics.

    PubMed

    Singh, Vivek; Yu, Yixuan; Sun, Qi-C; Korgel, Brian; Nagpal, Prashant

    2014-12-21

    While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon. PMID:25367148

  9. Quenched phonon drag in silicon nanowires reveals significant effect in the bulk at room temperature.

    PubMed

    Sadhu, Jyothi; Tian, Hongxiang; Ma, Jun; Azeredo, Bruno; Kim, Junhwan; Balasundaram, Karthik; Zhang, Chen; Li, Xiuling; Ferreira, P M; Sinha, S

    2015-05-13

    Existing theory and data cannot quantify the contribution of phonon drag to the Seebeck coefficient (S) in semiconductors at room temperature. We show that this is possible through comparative measurements between nanowires and the bulk. Phonon boundary scattering completely quenches phonon drag in silicon nanowires enabling quantification of its contribution to S in bulk silicon in the range 25-500 K. The contribution is surprisingly large (?34%) at 300 K even at doping of ?3 10(19) cm(-3). Our results contradict the notion that phonon drag is negligible in degenerate semiconductors at temperatures relevant for thermoelectric energy conversion. A revised theory of electron-phonon momentum exchange that accounts for a phonon mean free path spectrum agrees well with the data. PMID:25831487

  10. Effect of Zn doping on improving crystal quality and thermoelectric properties of borosilicides.

    PubMed

    Mori, Takao; Berthebaud, David; Nishimura, Toshiyuki; Nomura, Akiko; Shishido, Toetsu; Nakajima, Kazuo

    2010-01-28

    Transition-metal (Mo, Mn, Fe, Rh, Ti, Cu, Zn) doping was carried out on the borosilicide compound REB(44)Si(2) (RE = rare earth). REB(44)Si(2) compounds exhibit Seebeck coefficients greater than 200 microV K(-1) at high temperatures and unlike most compounds, the figure of merit shows a steep increase at T > 1000 K making them promising high-temperature thermoelectric materials. Although zinc itself does not remain in the final product, zinc doping was found to improve the crystal quality, which has been a long-standing problem for the borosilicides. As a result, a significant increase of the thermoelectric power factor by more than 30% was achieved. PMID:20066187

  11. Effects of Mev Si Ions and Thermal Annealing on Thermoelectric and Optical Properties of SiO2/SiO2+Ge Multi-nanolayer thin Films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Alim, M. A.; Bhattacharjee, S.; Muntele, C.

    Thermoelectric generator devices have been prepared from 200 alternating layers of SiO2/SiO2+Ge superlattice films using DC/RF magnetron sputtering. The 5 MeV Si ionsbombardmenthasbeen performed using the AAMU Pelletron ion beam accelerator to formquantum dots and / or quantum clusters in the multi-layer superlattice thin films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient and increase the cross-plane electrical conductivity to increase the figure of merit, ZT. The fabricated devices have been annealed at the different temperatures to tailor the thermoelectric and optical properties of the superlattice thin film systems. While the temperature increased, the Seebeck coefficient continued to increase and reached the maximum value of -25 μV/K at the fluenceof 5x1013 ions/cm2. The decrease in resistivity has been seen between the fluence of 1x1013 ions/cm2 and 5x1013 ions/cm2. Transport properties like Hall coefficient, density and mobility did not change at all fluences. Impedance spectroscopy has been used to characterize the multi-junction thermoelectric devices. The loci obtained in the C*-plane for these data indicate non-Debye type relaxation displaying the presence of the depression parameter.

  12. Effects of Bi0.5Na0.5TiO3 Dopant on Microstructure and Thermoelectric Properties of Na(x)CoO2 Ceramics.

    PubMed

    Buntham, Suwapitcha; Jiansirisomboon, Sukanda; Watcharapasorn, Anucha

    2015-11-01

    Bi0.5Na0.5TiO3-doped Na(x)CoO2 ceramics with varied doping concentration of 0, 0.01, 0.03, 0.05 and 0.07 mol fraction were prepared by conventional solid state reaction method. The firing condition used was 950 degrees C for 8 h. X-ray diffraction pattern results showed that all produced ceramics were single phase with a hexagonal structure. Due to the substitution of BNT inside Na(x)CoO2 lattice, there was a slight shift of X-ray diffraction pattern to the left which indicated the lattice expansion. The scanning electron micrographs of ceramics indicated that small amount of BNT addition could eliminate pore and improved densification. A small amount of undissolved BNT was also present in Na(x)CoO2 matrix and dispersed at grain boundaries causing a decrease in grain size of the ceramic. The electrical conductivity and Seebeck coefficient of ceramics showed that all samples possessed metallic conduction behavior. However, BNT addition caused a reduction of electrical conductivity, Seebeck coefficient and power factor of Na(x)CoO2 ceramics. PMID:26726679

  13. Lunar Dust Biological Effects

    NASA Astrophysics Data System (ADS)

    Jones, L.; Jacques, S.; Rask, J. C.; Tranfield, E.; Taylor, L.; Kerschmann, R.; Loftus, D. J.

    2008-07-01

    We are investigating the biological effects of lunar dust collected during the Apollo missions to understand potential skin effects, inhalation toxicity, and ocular effects that may result from long duration human habitation of the Moon.

  14. Communicating Effectively PDF

    Cancer.gov

    Effective communication is essential for the delivery of quality cancer palliative care. And yet, healthcare providers often lack the skills to communicate effectively with their patients and families.

  15. Effects of Anesthesia

    MedlinePLUS

    ... Anesthesia Surgery Risks Anesthesia Awareness Obesity and Anesthesia Sleep Apnea and Anesthesia Smoking and Anesthesia Outpatient Surgery Effects of Anesthesia Side effects of anesthesia can occur ...

  16. On Effect Size

    ERIC Educational Resources Information Center

    Kelley, Ken; Preacher, Kristopher J.

    2012-01-01

    The call for researchers to report and interpret effect sizes and their corresponding confidence intervals has never been stronger. However, there is confusion in the literature on the definition of effect size, and consequently the term is used inconsistently. We propose a definition for effect size, discuss 3 facets of effect size (dimension,

  17. [Adverse effects of marijuana].

    PubMed

    Mallaret, Michel; Dal'Bo-Rohrer, Dominique; Demattis, Maurice

    2005-01-15

    When admitted in an emergency unit, young patients often present acute neurological effects of smoked marijuana. Other chronic adverse effects of marijuana are probably underestimated: postural syncope, arteritis, chronic bronchitis, amnesia. Marijuana may trigger a myocardial infarction and have a vasospastic effect. Marijuana has impairing effects on driving ability. Smoked marijuana is a potential respiratory tract carcinogen. PMID:15801396

  18. Improving School Effectiveness.

    ERIC Educational Resources Information Center

    MacBeath, John, Ed.; Mortimore, Peter, Ed.

    School effectiveness is an issue that has preoccupied researchers and policymakers for 3 decades. To study how ineffective schools become effective and what constitutes an effective school, the Improving School Effectiveness Project was carried out in Scotland from 1995 to 1997. This project forms the basis of discussion in this book, which has 11

  19. Gravitational Casimir Effect

    NASA Astrophysics Data System (ADS)

    Quach, James Q.

    2015-02-01

    We derive the gravitonic Casimir effect with nonidealized boundary conditions. This allows the quantification of the gravitonic contribution to the Casimir effect from real bodies. We quantify the meagerness of the gravitonic Casimir effect in ordinary matter. We also quantify the enhanced effect produced by the speculated Heisenberg-Couloumb (HC) effect in superconductors, thereby providing a test for the validity of the HC theory, and, consequently, the existence of gravitons.

  20. Gravitational Casimir effect.

    PubMed

    Quach, James Q

    2015-02-27

    We derive the gravitonic Casimir effect with nonidealized boundary conditions. This allows the quantification of the gravitonic contribution to the Casimir effect from real bodies. We quantify the meagerness of the gravitonic Casimir effect in ordinary matter. We also quantify the enhanced effect produced by the speculated Heisenberg-Couloumb (HC) effect in superconductors, thereby providing a test for the validity of the HC theory, and, consequently, the existence of gravitons. PMID:25768749

  1. Dimensional Analysis of Thermoelectric Modules Under Constant Heat Flux

    NASA Astrophysics Data System (ADS)

    Suzuki, Ryosuke O.; Fujisaka, Takeyuki; Ito, Keita O.; Meng, Xiangning; Sui, Hong-Tao

    2015-01-01

    Thermoelectric power generation is examined in the case of radiative heating. A constant heat flux is assumed in addition to consideration of the Seebeck effect, Peltier effect, and Joule heating with temperature-dependent material properties. Numerical evaluations are conducted using a combination of the finite-volume method and an original simultaneous solver for the heat transfer, thermoelectric, and electric transportation phenomena. Comparison with experimental results shows that the new solver could work well in the numerical calculations. The calculations predict that the Seebeck effect becomes larger for longer thermoelectric elements because of the larger temperature difference. The heat transfer to the cold surface is critical to determine the junction temperatures under a constant heat flux from the hot surface. The negative contribution from Peltier cooling and heating can be minimized when the current is smaller for longer elements. Therefore, a thicker TE module can generate more electric power even under a constant heat flux.

  2. On effect size.

    PubMed

    Kelley, Ken; Preacher, Kristopher J

    2012-06-01

    The call for researchers to report and interpret effect sizes and their corresponding confidence intervals has never been stronger. However, there is confusion in the literature on the definition of effect size, and consequently the term is used inconsistently. We propose a definition for effect size, discuss 3 facets of effect size (dimension, measure/index, and value), outline 10 corollaries that follow from our definition, and review ideal qualities of effect sizes. Our definition of effect size is general and subsumes many existing definitions of effect size. We define effect size as a quantitative reflection of the magnitude of some phenomenon that is used for the purpose of addressing a question of interest. Our definition of effect size is purposely more inclusive than the way many have defined and conceptualized effect size, and it is unique with regard to linking effect size to a question of interest. Additionally, we review some important developments in the effect size literature and discuss the importance of accompanying an effect size with an interval estimate that acknowledges the uncertainty with which the population value of the effect size has been estimated. We hope that this article will facilitate discussion and improve the practice of reporting and interpreting effect sizes. PMID:22545595

  3. Effects of Drug Abuse

    MedlinePLUS

    ... What To Say if You Were Once Addicted Drug Abuse Prevention Phone Numbers and Websites Search Share You are here Home » Effects of Drugs Effects of Drug Abuse Listen Drug abuse hurts the people who take ...

  4. Excited State Effective Masses

    SciTech Connect

    Lin, Huey-Wen; Cohen, Saul; Fleming, George

    2007-11-01

    The effective mass description of Euclidean time hadron correlation functions is extended to incorporate multiple excited states and multiple correlation functions. In general, the effective masses will be determined by finding the roots of some polynomial.

  5. Medications and Side Effects

    MedlinePLUS

    ... to fully work. You might feel some side effects of your medication before your feel the benefits – ... as sleepiness, anxiety or headache) is a side effect or a symptom of your illness. Many side ...

  6. Side Effects (Management)

    MedlinePLUS

    ... cancer care is relieving side effects, called symptom management, palliative care, or supportive care. It is important ... treat them. To learn about the symptoms and management of the long-term side effects of cancer ...

  7. The Hydrophobic Effect.

    ERIC Educational Resources Information Center

    Huque, Entazul M.

    1989-01-01

    Discusses the physical basis and current understanding of hydrophobic effects. The thermodynamic background of the effects, hydrophobic hydration, and hydrophobic interactions are described. Four existing controversies are outlined. (YP)

  8. Stormwater BMP Effectiveness Toolkit

    EPA Science Inventory

    US EPA has identified the effectiveness of Stormwater Best Management Practices (BMPs) as a priority research need. Effective protection of biotic integrity requires that processes maintaining the diversity of physical habitats be protected. Methods are needed to evaluate the e...

  9. Effective College Teaching.

    ERIC Educational Resources Information Center

    Caraway, James E.

    1978-01-01

    The author discusses other writings on effective college teaching and then presents his list of necessary characteristics for the effective teacher, stressing the interpersonal dimension of the teaching-learning situation. (MF)

  10. Memory effects in turbulence

    NASA Technical Reports Server (NTRS)

    Hinze, J. O.

    1979-01-01

    Experimental investigations of the wake flow of a hemisphere and cylinder show that such memory effects can be substantial and have a significant influence on momentum transport. Memory effects are described in terms of suitable memory functions.

  11. Effects of MeV Si ions bombardment on the thermoelectric generator from SiO 2/SiO 2 + Cu and SiO 2/SiO 2 + Au nanolayered multilayer films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Chacha, J.; Smith, C.; Pugh, M.; Colon, T.; Heidary, K.; Johnson, R. B.; Ila, D.

    2011-12-01

    The defects and disorder in the thin films caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We prepared the thermoelectric generator devices from 100 alternating layers of SiO 2/SiO 2 + Cu multi-nano layered superlattice films at the total thickness of 382 nm and 50 alternating layers of SiO 2/SiO 2 + Au multi-nano layered superlattice films at the total thickness of 147 nm using the physical vapor deposition (PVD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation have been used to determine the stoichiometry of the elements of SiO 2, Cu and Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardments have been performed using the AAMU-Center for Irradiation of Materials (CIM) Pelletron ion beam accelerator to make quantum (nano) dots and/or quantum (quantum) clusters in the multilayered superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured Seebeck coefficient, cross-plane electrical conductivity, and thermal conductivity in the cross-plane geometry for different fluences.

  12. Factors hampering program effectiveness.

    PubMed

    Phillips, J F; Zablan, Z C

    1976-01-01

    Findings of the University of the Philippines evaluation research of family planning programs in the Philippines identify 4 major problems which limit effectiveness: 1) acceptance is leveling off; 2) greater proportions of acceptors are choosing the less effective methods; 3) women who switch methods tend to choose a less effective method than the first used and 4) continuation rates for the effective methods are declining. The authors suggest causes and possible remedies for the problems. PMID:12307748

  13. Modeling thermoelectric transport in organic materials.

    PubMed

    Wang, Dong; Shi, Wen; Chen, Jianming; Xi, Jinyang; Shuai, Zhigang

    2012-12-28

    Thermoelectric energy converters can directly convert heat to electricity using semiconducting materials via the Seebeck effect and electricity to heat via the Peltier effect. Their efficiency depends on the dimensionless thermoelectric figure of merit of the material, which is defined as zT = S(2)?T/? with S, ?, ?, and T being the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature respectively. Organic materials for thermoelectric applications have attracted great attention. In this review, we present our recent progress made in developing theories and computational schemes to predict the thermoelectric figure of merit at the first-principles level. The methods have been applied to model thermoelectric transport in closely-packed molecular crystals and one-dimensional conducting polymer chains. The physical insight gained in these studies will help in the design of efficient organic thermoelectric materials. PMID:23086525

  14. Heat transport between antiferromagnetic insulators and normal metals

    NASA Astrophysics Data System (ADS)

    Brataas, Arne; Skarsvâg, Hans; Tveten, Erlend G.; Løhaugen Fjærbu, Eirik

    2015-11-01

    Antiferromagnetic insulators can become active spintronics components by controlling and detecting their dynamics via spin currents in adjacent metals. This cross talk occurs via spin transfer and spin pumping, phenomena that have been predicted to be as strong in antiferromagnets as in ferromagnets. Here, we demonstrate that a temperature gradient drives a significant heat flow from magnons in antiferromagnetic insulators to electrons in adjacent normal metals. The same coefficients as in the spin-transfer and spin-pumping processes also determine the thermal conductance. However, in contrast to ferromagnets, the heat is not transferred via a spin Seebeck effect which is absent in antiferromagnetic insulator-normal metal systems. Instead, the heat is proportional to a large staggered spin Seebeck effect.

  15. Effects of Nuclear Weapons.

    ERIC Educational Resources Information Center

    Sartori, Leo

    1983-01-01

    Fundamental principles governing nuclear explosions and their effects are discussed, including three components of a nuclear explosion (thermal radiation, shock wave, nuclear radiation). Describes how effects of these components depend on the weapon's yield, its height of burst, and distance of detonation point. Includes effects of three

  16. Special Effects Activity Guide.

    ERIC Educational Resources Information Center

    Boxer, Jennifer; Valenta, Carol

    This guide accompanies "Special Effects," a 40-minute IMAX film and "Special Effects II", a multimedia, interactive traveling exhibit designed by the California Museum of Science and Industry. The exhibit focuses on the underlying scientific and technical processes of special effects from the earliest motion picture to state-of-the-art digital

  17. Effects of Nuclear Weapons.

    ERIC Educational Resources Information Center

    Sartori, Leo

    1983-01-01

    Fundamental principles governing nuclear explosions and their effects are discussed, including three components of a nuclear explosion (thermal radiation, shock wave, nuclear radiation). Describes how effects of these components depend on the weapon's yield, its height of burst, and distance of detonation point. Includes effects of three…

  18. Nonlinear Talbot effect.

    PubMed

    Zhang, Yong; Wen, Jianming; Zhu, S N; Xiao, Min

    2010-05-01

    We propose and experimentally demonstrate the nonlinear Talbot effect from nonlinear photonic crystals. The nonlinear Talbot effect results from self-imaging of the generated periodic intensity pattern at the output surface of the crystal. To illustrate the effect, we experimentally observed second-harmonic Talbot self-imaging from 1D and 2D periodically poled LiTaO(3) crystals. Both integer and fractional nonlinear Talbot effects were investigated. The observation not only conceptually extends the conventional Talbot effect, but also opens the door for a variety of new applications in imaging technologies. PMID:20482176

  19. Enhancement of the thermoelectric figure of merit in n-type Cu0.008Bi2Te2.7Se0.3 by using Nb doping

    NASA Astrophysics Data System (ADS)

    Lee, Kyu Hyoung; Ryu, Byungki; Park, Hee Jung; Lee, Kimoon; Roh, Jong Wook; Kim, Sang Il; Hwang, Sungwoo; Choi, Soon-Mok; Kim, Jong-Young; Lee, Jeong Hoon; Lim, Jae-Hong; Kim, Sung Wng

    2016-01-01

    Doping with foreign atom has been shown to be an effective way to enhance the dimensionless figure of merit ZT of Bi2Te3-based thermoelectric raw materials. Herein, we report that doping with Nb is effective in enhancing the Seebeck coefficient of n-type Cu0.008Bi2Te2.7Se0.3 polycrystalline bulks. Considering compensation of the Seebeck coefficient due to decrease of the electrical conductivity in Nb-doped compositions, the absolute value of Seebeck coefficient rather increased benefiting from an enhancement of the density of states (DOS) effective mass m* from 1.09 m 0 (Cu0.008Bi2Te2.7Se0.3) to 1.21 m 0 - 1.27 m 0 (Cu0.008Bi2- x Nb x Te2.7Se0.3) due to a DOS engineering effect. The values of ZT were 0.84 at 300 K and 0.86 at 320 K for Cu0.008Bi1.99Nb0.01Te2.7Se0.3. This compositional tuning approach highlights the possibility of further enhancement of ZT for n-type Bi2Te3-based compounds by using a combination of nanostructuring technologies to reduce the thermal conductivity.

  20. Conduction mechanism in boron carbide

    NASA Technical Reports Server (NTRS)

    Wood, C.; Emin, D.

    1984-01-01

    Electrical conductivity, Seebeck-coefficient, and Hall-effect measurements have been made on single-phase boron carbides, B(1-x)C(x), in the compositional range from 0.1 to 0.2 X, and between room temperature and 1273 K. The results indicate that the predominant conduction mechanism is small-polaron hopping between carbon atoms at geometrically inequivalent sites.

  1. Running effective meetings, running effective groups.

    PubMed

    Ogborn, S E

    1994-12-01

    Meetings are effective if they meet the objectives of each person involved in the least amount of time possible. Different strategies are needed for different types of meetings. Different leadership styles are necessary depending on the members' personality preferences and the stages of the group's development. Good leaders know how to adapt to these preferences and stages. PMID:10139146

  2. Effective Internships for Effective New Administrators.

    ERIC Educational Resources Information Center

    Edmonson, Stacey

    One challenge faced by any educational leadership program is how to develop effective entry-level school administrators. Many administrative interns receive no real administrative practice at all through their internship, and yet upon completion of the internship, they are expected to be competent administrators. The internship at Sam Houston

  3. Enhanced magnetocaloric effect material

    DOEpatents

    Lewis, Laura J. H.

    2006-07-18

    A magnetocaloric effect heterostructure having a core layer of a magnetostructural material with a giant magnetocaloric effect having a magnetic transition temperature equal to or greater than 150 K, and a constricting material layer coated on at least one surface of the magnetocaloric material core layer. The constricting material layer may enhance the magnetocaloric effect by restriction of volume changes of the core layer during application of a magnetic field to the heterostructure. A magnetocaloric effect heterostructure powder comprising a plurality of core particles of a magnetostructural material with a giant magnetocaloric effect having a magnetic transition temperature equal to or greater than 150 K, wherein each of the core particles is encapsulated within a coating of a constricting material is also disclosed. A method for enhancing the magnetocaloric effect within a giant magnetocaloric material including the step of coating a surface of the magnetocaloric material with a constricting material is disclosed.

  4. Spincaloric properties of epitaxial Co2MnSi /MgO /Co2MnSi magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Geisler, Benjamin; Kratzer, Peter

    2015-10-01

    The electronic transport and spincaloric properties of epitaxial magnetic tunnel junctions with half-metallic Co2MnSi Heusler electrodes, MgO tunneling barriers, and different interface terminations are investigated by using first-principles calculations. An approach to spincaloric properties is presented that circumvents the linear response approximation inherent in the Seebeck coefficient and compared to the method of Sivan and Imry. This approach supports two different temperatures in the two electrodes and provides the exact current and/or voltage response of the system. Moreover, it accounts for temperature-dependent chemical potentials in the electrodes and finite-bias effects. We find that especially the former are important for obtaining qualitatively correct results, even if the variations of the chemical potentials are small. It is shown how the spincaloric properties can be tailored by the choice of the growth conditions. We find a large effective and spin-dependent Seebeck coefficient of -65 μ V /K at room temperature for the purely Co-terminated interface. We suggest to use such interfaces in thermally operated magnetoresistive random access memory modules, which exploit the magneto-Seebeck effect, to maximize the thermally induced readout voltage.

  5. Photon Thermal Hall Effect

    NASA Astrophysics Data System (ADS)

    Ben-Abdallah, P.

    2016-02-01

    A near-field thermal Hall effect (i.e., Righi-Leduc effect) in networks of magneto-optical particles placed in a constant magnetic field is predicted. This many-body effect is related to a symmetry breaking in the system induced by the magnetic field, which gives rise to preferential channels for the heat transport by near-field interaction thanks to the particle's anisotropy tuning.

  6. Atomic lighthouse effect

    NASA Astrophysics Data System (ADS)

    Mximo, C. E.; Kaiser, R.; Courteille, Ph. W.; Bachelard, R.

    2014-11-01

    We investigate the deflection of light by a cold atomic cloud when the light-matter interaction is locally tuned via the Zeeman effect using magnetic field gradients. This "lighthouse" effect is strongest in the single-scattering regime, where deviation of the incident field is largest. For optically dense samples, the deviation is reduced by collective effects, as the increase in linewidth leads to a decrease of the magnetic field efficiency.

  7. Dynamic ground effects

    NASA Technical Reports Server (NTRS)

    Paulson, John W., Jr.; Kemmerly, Guy T.; Gilbert, William P.

    1990-01-01

    A research program is underway at the NASA Langley Research Center to study the effect of rate of descent on ground effects. A series of powered models were tested in the Vortex Research Facility under conditions with rate of descent and in the 14 x 22 Foot Subsonic Tunnel under identical conditions but without rate of descent. These results indicate that the rate of descent can have a significant impact on ground effects particularly if vectored or reversed thrust is used.

  8. Atomic lighthouse effect.

    PubMed

    Mximo, C E; Kaiser, R; Courteille, Ph W; Bachelard, R

    2014-11-01

    We investigate the deflection of light by a cold atomic cloud when the light-matter interaction is locally tuned via the Zeeman effect using magnetic field gradients. This "lighthouse" effect is strongest in the single-scattering regime, where deviation of the incident field is largest. For optically dense samples, the deviation is reduced by collective effects, as the increase in linewidth leads to a decrease in magnetic field efficiency. PMID:25401364

  9. Magnetic Casimir effect

    SciTech Connect

    Metalidis, G.; Bruno, P.

    2002-12-01

    The Casimir effect results from alterations of the zero-point electromagnetic energy introduced by boundary conditions. For ferromagnetic layers separated by vacuum (or a dielectric), such boundary conditions are influenced by the magneto-optical Kerr effect. We will show that this gives rise to a long-range magnetic interaction and discuss the effect for two different configurations (magnetization parallel and perpendicular to the layers). Analytical expressions are derived for two models and compared to numerical calculations. Numerical calculations of the effect for Fe are also presented and the possibility of an experimental observation of the Casimir magnetic interaction is discussed.

  10. Rectenna related atmospheric effects

    NASA Technical Reports Server (NTRS)

    Lee, J.

    1980-01-01

    Possible meteorological effects arising from the existence and operations of a solar power satellite (SPS) system rectenna are examined. Analysis and model simulations in some chosen site situations and meteorological conditions indicate that the meteorological effects of the construction and operation of a rectenna are small, particularly outside the boundary of the structure. From weather and climate points of view, installation of an SPS rectenna seems likely to have effects comparable with those due to other nonindustrial land use changes covering the same area. The absorption and scattering of microwave radiation in the troposphere would have negligible atmospheric effects.

  11. Effective medication management.

    PubMed

    Howland, Robert H

    2012-03-01

    The effectiveness of a drug treatment is based on its efficacy, tolerability, safety, and acceptability. Effective medication management implies that the process of selecting and managing prescribed drugs results in an optimal patient outcome. Effectively prescribing medications includes gaining a mastery of drug knowledge, learning the nuts and bolts of treatment using medication, and appreciating the fundamental importance of psychotherapeutic and psychoeducational processes in medication management. Nurses have an essential role in providing effective medication management, given their direct level of patient contact and their collaborative relationship with physicians. PMID:22329622

  12. Thin-film growth of the quasi-one-dimensional metal Li0.9Mo6O17

    NASA Astrophysics Data System (ADS)

    Cote, Alexandra; Moshfeghyeganeh, Saeed; Cohn, Joshua L.; Neumeier, John J.

    2015-03-01

    Attempts to grow epitaxial thin films of Li0.9Mo6O17 by pulsed-laser deposition will be discussed. Single crystals of this quasi-one-dimensional (q1D) metal exhibit highly anisotropic Seebeck coefficients with ?S =Sc -Sb ~ 200 ? V/K near 450 K (the b axis corresponds to the most conducting, q1D chain direction). Suitably oriented thin films could enable possible applications in energy detection using the transverse Seebeck effect. X-ray diffraction results will be presented for films grown from a polycrystalline target on several substrates under a narrow range of temperature and pressure conditions. This material is based upon work supported by the U.S. Department of Energy Office of Basic Energy Sciences Grant DE-FG02-12ER46888 (Univ. Miami) and the National Science Foundation under Grant DMR-0907036 (Mont. St. Univ.)

  13. Structural and Thermoelectric Properties of Nanocrystalline Bismuth Telluride Thin Films Under Compressive and Tensile Strain

    NASA Astrophysics Data System (ADS)

    Kusagaya, K.; Hagino, H.; Tanaka, S.; Miyazaki, K.; Takashiri, M.

    2015-06-01

    To investigate the effect of strain on bismuth telluride films, we applied different compressive and tensile strains to thin films by changing the bending radius of a flexible substrate so the strain ranged from -0.3% (compressive) to +0.3% (tensile). The structural properties of the strained thin films, composed of nanosized grains, were analyzed by x-ray diffraction and scanning electron microscopy. For all samples the main peak was the (015) diffraction peak; crystal orientation along the (015) growth direction was slightly enhanced by application of compressive strain. The thermoelectric properties of strained bismuth telluride thin films were evaluated by measurement of electrical conductivity, Seebeck coefficient, and power factor. The magnitude and direction of the applied strain did not significantly affect the power factor, because when the strain changed from compressive to tensile the electrical conductivity increased and the absolute Seebeck coefficient decreased.

  14. Enhanced Thermoelectric Properties of Hole-Doped Lu1- x Pb x BaCo4O7 Ceramics

    NASA Astrophysics Data System (ADS)

    Chen, Y. B.; Cao, X. L.; Ma, R. X.; Gao, F.; Hu, X.; Song, H. Z.

    2015-10-01

    The effects of Pb doping on the thermoelectric properties of Lu1- x Pb x BaCo4O7 ( x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) ceramic samples prepared by the solid-state reaction method were investigated from 390 K to 973 K. The results show that Pb doping can reduce the electrical resistivity remarkably, increasing the Seebeck coefficient at lower temperatures and decreasing it at higher temperatures. As an overall result, Pb doping results in an enhancement of the power factor because the decrease in magnitude of the electrical resistivity is far greater than that of the Seebeck coefficient. The optimum Pb doping content is x = 0.08, reaching a power factor and ZT value of 85 ?W m-1 K-2 and 0.18, respectively, at 973 K.

  15. High temperature transport properties of thermoelectric CaMnO{sub 3−δ} — Indication of strongly interacting small polarons

    SciTech Connect

    Schrade, M. Finstad, T. G.; Kabir, R.; Li, S.; Norby, T.

    2014-03-14

    The conductivity and Seebeck coefficient of CaMnO{sub 3−δ} have been studied at temperatures up to 1000 °C and in atmospheres with controlled oxygen partial pressure. Both transport coefficients were varied in situ by the reversible formation of oxygen vacancies up to δ = 0.15. The charge carrier concentration was calculated using a defect chemical model. The Seebeck coefficient could be approximated by Heikes' formula, while the conductivity shows a maximum at a molar charge carrier concentration of 0.25. These results were interpreted as a signature of strong electronic correlation effects, and it was concluded that charge transport in CaMnO{sub 3−δ} occurs via strongly interacting small polarons. General prospects for strongly correlated materials as potential candidates for high temperature thermoelectric power generation were discussed.

  16. Magnetothermoelectric power in Co/Pt layered structures: Interface versus bulk contributions

    NASA Astrophysics Data System (ADS)

    Frauen, Axel; Kobs, Andr; Bhnert, Tim; Michel, Ann-Kathrin; Winkler, Gerrit; Nielsch, Kornelius; Oepen, Hans Peter

    2015-10-01

    The dependence of the longitudinal thermoelectric power on the orientation of magnetization in Pt/Co/Pt sandwiches is investigated. In the Co thickness range ?6 nm, where interface scattering is relevant, the thermoelectric power depends on the orientation of magnetization in the plane perpendicular to the temperature gradient. This behavior reveals the thermoelectric analog to the anisotropic interface magnetoresistance. It is shown that this interfacial magnetothermoelectric power fulfills Mott's formula, however, significant deviations from the bulk anisotropic magnetothermoelectric behavior are reported. The dependence of the Seebeck effect on magnetization orientation therefore provides experimental evidence of differences in the electronic states of the bulk and interface. We demonstrate that for the very same system the Seebeck coefficient does not show a one-to-one correspondence to the conductivity.

  17. Volcanic effects on climate

    NASA Technical Reports Server (NTRS)

    Robock, Alan

    1991-01-01

    Volcanic eruptions which inject large amounts of sulfur-rich gas into the stratosphere produce dust veils which last years and cool the earth's surface. At the same time, these dust veils absorb enough solar radiation to warm the stratosphere. Since these temperature changes at the earth's surface and in the stratosphere are both in the opposite direction of hypothesized effects from greenhouse gases, they act to delay and mask the detection of greenhouse effects on the climate system. Tantalizing recent research results have suggested regional effects of volcanic eruptions, including effects on El Nino/Southern Oscillation (ENSO). In addition, a large portion of the global climate change of the past 100 years may be due to the effects of volcanoes, but a definite answer is not yet clear. While effects of several years were demonstrated with both data studies and numerical models, long-term effects, while found in climate model calculations, await confirmation with more realistic models. Extremely large explosive prehistoric eruptions may have produced severe weather and climate effects, sometimes called a 'volcanic winter'. Complete understanding of the above effects of volcanoes is hampered by inadequacies of data sets on volcanic dust veils and on climate change. Space observations can play an increasingly important role in an observing program in the future. The effects of volcanoes are not adequately separated from ENSO events, and climate modeling of the effects of volcanoes is in its infancy. Specific suggestions are made for future work to improve the knowledge of this important component of the climate system.

  18. Institutional Effectiveness Report.

    ERIC Educational Resources Information Center

    College of the Canyons, Santa Clarita, CA.

    This is the first edition of the College of the Canyon's (California) Institutional Effectiveness Report, which is modeled after the statewide report prepared by the Chancellor's Office. The college is measuring 60 effectiveness indicators in four mission areas: student access, student success, staff composition, and fiscal condition. A brief

  19. Effects on Insects

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effects of controlled and modified atmospheres on insects is reviewed and summarized in this chapter. Traditionally, controlled and modified atmospheres are used to store and preserve fresh fruits and vegetables. The effects on insects and the potential of these treatments are secondary to the...

  20. The Pygmalion Effect Lives

    ERIC Educational Resources Information Center

    Rosenthal, Robert

    1973-01-01

    Briefly reviewing his own research, and that of critics of the Pygmalion Effect, the author proposes a four-factor "theory" of the influences that produce the effect: the relationship of teachers to special students differs in climate, input, feedback, and output. (JM)

  1. Presenting Food Science Effectively

    ERIC Educational Resources Information Center

    Winter, Carl K.

    2016-01-01

    While the need to present food science information effectively is viewed as a critical competency for food scientists by the Institute of Food Technologists, most food scientists may not receive adequate training in this area. Effective presentations combine both scientific content and delivery mechanisms that demonstrate presenter enthusiasm for…

  2. The Kaye Effect

    ERIC Educational Resources Information Center

    Binder, J. M.; Landig, A. J.

    2009-01-01

    The International Young Physicists' Tournament (IYPT) is a worldwide, annual competition for secondary school students. This is our solution to problem number 10, "The Kaye effect", as presented in the final round of the 21st IYPT in Trogir, Croatia. The Kaye effect occurs when a thin stream of shampoo or a different adequate non-Newtonian liquid…

  3. Effective Appraisal Systems.

    ERIC Educational Resources Information Center

    Winsor, Jerry L.

    An examination of the goals of an effective employee appraisal system of an effective employee evaluation procedure is the focus of this paper.The paper discusses the purposes of the appraisal system and its objectivity (or lack of it), the selection of items to be judged, the standards for judging the performance of an employee, and the person

  4. The Chelate Effect Redefined.

    ERIC Educational Resources Information Center

    da Silva, J. J. R. Frausto

    1983-01-01

    Discusses ambiguities of the accepted definition of the chelate effect, suggesting that it be defined in terms of experimental observation rather than mathematical abstraction. Indicates that the effect depends on free energy change in reaction, ligand basicity, pH of medium, type of chelates formed, and concentration of ligands in solution. (JN)

  5. Defining Effective Teaching

    ERIC Educational Resources Information Center

    Layne, L.

    2012-01-01

    The author looks at the meaning of specific terminology commonly used in student surveys: "effective teaching." The research seeks to determine if there is a difference in how "effective teaching" is defined by those taking student surveys and those interpreting the results. To investigate this difference, a sample group of professors and students

  6. Correlational effect size benchmarks.

    PubMed

    Bosco, Frank A; Aguinis, Herman; Singh, Kulraj; Field, James G; Pierce, Charles A

    2015-03-01

    Effect size information is essential for the scientific enterprise and plays an increasingly central role in the scientific process. We extracted 147,328 correlations and developed a hierarchical taxonomy of variables reported in Journal of Applied Psychology and Personnel Psychology from 1980 to 2010 to produce empirical effect size benchmarks at the omnibus level, for 20 common research domains, and for an even finer grained level of generality. Results indicate that the usual interpretation and classification of effect sizes as small, medium, and large bear almost no resemblance to findings in the field, because distributions of effect sizes exhibit tertile partitions at values approximately one-half to one-third those intuited by Cohen (1988). Our results offer information that can be used for research planning and design purposes, such as producing better informed non-nil hypotheses and estimating statistical power and planning sample size accordingly. We also offer information useful for understanding the relative importance of the effect sizes found in a particular study in relationship to others and which research domains have advanced more or less, given that larger effect sizes indicate a better understanding of a phenomenon. Also, our study offers information about research domains for which the investigation of moderating effects may be more fruitful and provide information that is likely to facilitate the implementation of Bayesian analysis. Finally, our study offers information that practitioners can use to evaluate the relative effectiveness of various types of interventions. PMID:25314367

  7. School Effectiveness and Leadership.

    ERIC Educational Resources Information Center

    Dow, I. I.; Oakley, W. F.

    1992-01-01

    Fiedler's contingency theory relates school effectiveness to a combination of principals' leadership style and situational favorability for the principal. Data from teacher questionnaires on school climate and effectiveness and measures of principal's leadership in 176 Canadian elementary schools did not support Fiedler's model. Contains 54

  8. JPL Radiation Effects Facilities

    NASA Technical Reports Server (NTRS)

    Thorbourn, Dennis

    2013-01-01

    Radiation Effects Group investigates the effects of space radiation on present and future microelectronic and optoelectronic technologies, evaluate the risk of using them in specific space missions, and recommend component and design techniques for JPL and NASA programs to reduce reliability risk from space radiation.

  9. Tomography with mirage effect

    NASA Astrophysics Data System (ADS)

    Jeanneau, P.; Bertrand, L.; Forget, B. C.; Fournier, D.

    1999-03-01

    We have designed an experimental set-up that allows us to obtain thermal images of small samples by associating the mirage effect with the tomographic techniques. Spectroscopic features, surface effects and thermal diffusivity changes have been used to illustrate the feasibility of the method.

  10. Radiation effects in space

    SciTech Connect

    Fry, R.J.M.

    1987-07-01

    As more people spend more time in space, and the return to the moon and exploratory missions are considered, the risks require continuing examination. The effects of microgravity and radiation are two potential risks in space. These risks increase with increasing mission duration. This document considers the risk of radiation effects in space workers and explorers. 17 refs., 1 fig., 4 tabs.

  11. The Kaye Effect

    ERIC Educational Resources Information Center

    Binder, J. M.; Landig, A. J.

    2009-01-01

    The International Young Physicists' Tournament (IYPT) is a worldwide, annual competition for secondary school students. This is our solution to problem number 10, "The Kaye effect", as presented in the final round of the 21st IYPT in Trogir, Croatia. The Kaye effect occurs when a thin stream of shampoo or a different adequate non-Newtonian liquid

  12. Presenting Food Science Effectively

    ERIC Educational Resources Information Center

    Winter, Carl K.

    2016-01-01

    While the need to present food science information effectively is viewed as a critical competency for food scientists by the Institute of Food Technologists, most food scientists may not receive adequate training in this area. Effective presentations combine both scientific content and delivery mechanisms that demonstrate presenter enthusiasm for

  13. Primacy Effects in Attributions.

    ERIC Educational Resources Information Center

    McAndrew, Francis T.

    Previous research has suggested the existence of a primacy effect in the attribution of ability. To test if the primacy effect occurs in situations where specific cues about the person and nature of the test materials are lacking or greatly reduced, college students corrected a multiple-choice test in which a phantom stimulus person correctly

  14. Parent Groups: How Effective?

    ERIC Educational Resources Information Center

    Veltkamp, Lane J.; Newman, Keith

    1976-01-01

    The educational approach in parent groups has not demonstrated itself effective, particularly in dysfunctional families. Parent groups, to be effective, must include, (a) an educational component, (b) a therapeutic component, and (c) an eclectic approach that gives parent specific management techniques but also focuses on the marital and family

  15. A ''Voice Inversion Effect?''

    ERIC Educational Resources Information Center

    Bedard, Catherine; Belin, Pascal

    2004-01-01

    Voice is the carrier of speech but is also an ''auditory face'' rich in information on the speaker's identity and affective state. Three experiments explored the possibility of a ''voice inversion effect,'' by analogy to the classical ''face inversion effect,'' which could support the hypothesis of a voice-specific module. Experiment 1 consisted

  16. The polarized EMC effect

    SciTech Connect

    W. Bentz; I. C. Cloet; A. W. Thomas

    2007-02-01

    We calculate both the spin independent and spin dependent nuclear structure functions in an effective quark theory. The nucleon is described as a composite quark-diquark state, and the nucleus is treated in the mean field approximation. We predict a sizable polarized EMC effect, which could be confirmed in future experiments.

  17. Bulk Topological Proximity Effect.

    PubMed

    Hsieh, Timothy H; Ishizuka, Hiroaki; Balents, Leon; Hughes, Taylor L

    2016-02-26

    Existing proximity effects stem from systems with a local order parameter, such as a local magnetic moment or a local superconducting pairing amplitude. Here, we demonstrate that despite lacking a local order parameter, topological phases also may give rise to a proximity effect of a distinctively inverted nature. We focus on a general construction in which a topological phase is extensively coupled to a second system, and we argue that, in many cases, the inverse topological order will be induced on the second system. To support our arguments, we rigorously establish this "bulk topological proximity effect" for all gapped free-fermion topological phases and representative integrable models of interacting topological phases. We present a terrace construction which illustrates the phenomenological consequences of this proximity effect. Finally, we discuss generalizations beyond our framework, including how intrinsic topological order may also exhibit this effect. PMID:26967436

  18. Bulk Topological Proximity Effect

    NASA Astrophysics Data System (ADS)

    Hsieh, Timothy H.; Ishizuka, Hiroaki; Balents, Leon; Hughes, Taylor L.

    2016-02-01

    Existing proximity effects stem from systems with a local order parameter, such as a local magnetic moment or a local superconducting pairing amplitude. Here, we demonstrate that despite lacking a local order parameter, topological phases also may give rise to a proximity effect of a distinctively inverted nature. We focus on a general construction in which a topological phase is extensively coupled to a second system, and we argue that, in many cases, the inverse topological order will be induced on the second system. To support our arguments, we rigorously establish this "bulk topological proximity effect" for all gapped free-fermion topological phases and representative integrable models of interacting topological phases. We present a terrace construction which illustrates the phenomenological consequences of this proximity effect. Finally, we discuss generalizations beyond our framework, including how intrinsic topological order may also exhibit this effect.

  19. Nocebo effect in Dermatology.

    PubMed

    Sonthalia, Sidharth; Sahaya, Kinshuk; Arora, Rahul; Singal, Archana; Srivastava, Ankur; Wadhawan, Ritu; Zartab, Hamed; Gupta, Kripa Shankar

    2015-01-01

    Nocebo effect, originally denoting the negative counterpart of the placebo phenomenon, is now better defined as the occurrence of adverse effects to a therapeutic intervention because the patient expects them to develop. More commonly encountered in patients with a past negative experience, this effect stems from highly active processes in the central nervous system, mediated by specific neurotransmitters and modulated by psychological mechanisms such as expectation and conditioning. The magnitude of nocebo effect in clinical medicine is being increasingly appreciated and its relevance encompasses clinical trials as well as clinical practice. Although there is hardly any reference to the term nocebo in dermatology articles, the phenomenon is encountered routinely by dermatologists. Dermatology patients are more susceptible to nocebo responses owing to the psychological concern from visibility of skin lesions and the chronicity, unpredictable course, lack of 'permanent cure' and frequent relapses of skin disorders. While finasteride remains the prototypical drug that displays a prominent nocebo effect in dermatologic therapeutics, other drugs such as isotretinoin are also likely inducers. This peculiar phenomenon has recently been appreciated in the modulation of itch perception and in controlled drug provocation tests in patients with a history of adverse drug reactions. Considering the conflict between patients' right to information about treatment related adverse effects and the likelihood of nocebo effect stemming from information disclosure, the prospect of ethically minimizing nocebo effect remains daunting. In this article, we review the concept of nocebo effect, its postulated mechanism, relevance in clinical dermatology and techniques to prevent it from becoming a barrier to effective patient management. PMID:25900939

  20. Preparation of Bi2Te3/Nano-SiC Composite Thermoelectric Films by Electrodeposition

    NASA Astrophysics Data System (ADS)

    Wang, Yilin; Zhang, Jingyi; Shen, Zhengwu; Yang, Mengqian; Liu, Xiaoqing; Wang, Wei

    2015-06-01

    Bi2Te3/nano-SiC composite thermoelectric films were prepared by electrodeposition in a nitric acid bath. The effects of SiC concentration and annealing treatment on the Seebeck coefficient and electrical resistivity of the films were investigated. The morphology, composition, and structure of the films were studied by scanning electron microscopy, x-ray fluorescence spectroscopy, and x-ray diffraction. The results showed that SiC nano-particles in electrodeposited Bi2Te3/nano-SiC composite films have readily apparent effects on the crystal orientation of the Bi2Te3 matrix and the morphology of the electrodeposited composite films. For nano-SiC particle concentrations <2 g/L the Seebeck coefficients of as-deposited films decrease with increasing nano-SiC particle concentration and decrease further after annealing treatment. Improvement in electrical conductivity compensated for the decrease in Seebeck coefficient and resulted in an enhanced power factor. Addition of nano-SiC particles to the composite films introduces more interfaces, which endows the composite films with lower electrical resistivity.

  1. Solid-Liquid Interface Characterization Hardware: Advanced Technology Development (ATD)

    NASA Technical Reports Server (NTRS)

    Peters, Palmer N.; Sisk, R. C.; Sen, S.; Kaukler, W. F.; Curreri, Peter A.; Wang, F. C.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    This ATD has the goal of enabling the integration of three separate measurement techniques to characterize the solid-liquid interface of directionally solidified materials in real-time. Arrays of film-based metal thermocouple elements are under development along with compact Seebeck furnaces suitable for interfacing with separately developed X-ray Transmission Microscopes. Results of applying film arrays to furnace profiling are shown, demonstrating their ability to identify a previously undetected hardware flaw in the development of a second-generation compact furnace. Results of real-time furnace profiling also confirmed that the compact furnace design effectively isolates the temperature profiles in two halves of the furnace, a necessary feature. This isolation had only been inferred previously from the characteristics of Seebeck data reported. Results from a 24-thermocouple array successfully monitoring heating and isothermal cooling of a tin sample are shown. The importance of non-intrusion by the arrays, as well as furnace design, on the profiling of temperature gradients is illustrated with example measurements. Further developments underway for effectively combining all three measurements are assessed in terms of improved x-ray transmission, increased magnification, integral arrays with minimum intrusion, integral scales for velocity measurements and other features being incorporated into the third generation Seebeck furnace under construction.

  2. Bustling argon: biological effect

    PubMed Central

    2013-01-01

    Argon is a noble gas in group 18 of the periodic table. Certificated to exist in air atmosphere merely one century ago, discovery of argon shows interesting stories of researching and exploring. It was assumed to have no chemical activity. However, argon indeed present its biological effect on mammals. Narcotic effect of argon in diving operation and neur-protective function of argon in cerebral injury demonstrate that argon has crucial effect and be concentrated on is necessary. Furthermore, consider to be harmless to human, argon clinical application in therapy would be another option. PMID:24088583

  3. Improving engineering effectiveness

    NASA Technical Reports Server (NTRS)

    Fiero, J. D.

    1985-01-01

    Methodologies to improve engineering productivity were investigated. The rocky road to improving engineering effectiveness is reviewed utilizing a specific semiconductor engineering organization as a case study. The organization had a performance problem regarding new product introductions. With the help of this consultant as a change agent the engineering team used a systems approach to through variables that were effecting their output significantly. Critical factors for improving this engineering organization's effectiveness and the roles/responsibilities of management, the individual engineers and the internal consultant are discussed.

  4. BSM Primary effects

    NASA Astrophysics Data System (ADS)

    Gupta, R.

    Using the predictive power of the effective field theory approach, we present a physical parametrization of the leading effects beyond the SM (BSM), that give us at present the best way to constrain heavy new-physics at low-energies. We show that other BSM effects are not independent from these ones, and we provide the explicit correlations. This information is useful to know where to primarily look for new physics in future experiments, and to know how this new physics is related to previous measurements, most importantly in electroweak-symmetry breaking processes or Higgs physics.

  5. Effects of New Technologies.

    ERIC Educational Resources Information Center

    Social and Labour Bulletin, 1980

    1980-01-01

    Transnational implications of technological change and innovation in telecommunications are discussed, including impact on jobs and industrial relations, computer security, access to information, and effects of technological innovation on international economic systems. (SK)

  6. Radiation effects in space

    SciTech Connect

    Fry, R.J.M.

    1986-01-01

    The paper discusses the radiation environment in space that astronauts are likely to be exposed to. Emphasis is on proton and HZE particle effects. Recommendations for radiation protection guidelines are presented. (ACR)

  7. Pulmonary effects of firefighting.

    PubMed

    Scannell, C H; Balmes, J R

    1995-01-01

    The authors examine the acute and chronic effects of exposure to smoke among firefighters and look at mortality studies for the risk of death due to nonmalignant respiratory disease and lung cancer. PMID:8903749

  8. [Aminoglycosides, their ototoxic effect].

    PubMed

    de la Rosa-Glvez, A; Juregui-Renaud, K; Hernndez-Goribar, M

    1998-01-01

    The aminoglycosides are broad-spectrum antibiotics especially effective against many strains of gramnegative bacteria. Since streptomycin was used for tuberculosis treatment, the toxic side effects of such antibiotics were identified. The kidney and the inner ear are affected. The nephrotoxicity is usually reversible, while the chronic ototoxicity is irreversible. Within the inner ear, it is the cochlear and vestibular sensory epithelium that is damaged. A toxic mechanism in which an interference with mitochondrial protein synthesis is central has been inferred. During the last fifty years, risk factors for aminoglycoside-induced-ototoxicity have been identified, including a genetically transmitted hypersensitivity to the ototoxic effect. Although several strategies to prevent the damage have been proposed, today it is not rare that patients suffer permanent loss of hearing and loss of balance due to aminoglycoside toxicity. This review gives a brief background of aminoglycoside ototoxicity, some strategies to prevent it, and the therapeutic use of the vestibulo-toxic effect. PMID:9927776

  9. Cytogenetic effects of cyclamates

    SciTech Connect

    Jemison, E.W.; Brown, K.; Rivers, B.; Knight, R.

    1984-01-01

    PHA-stimulated human peripheral lymphocytes were used as a model system for assessing the in vitro effects of calcium cyclamate. Techniques of autoradiography, cytological staining, cell counting, liquid scintillation and karyotyping were used to study the cytogenetic damage and biochemical effects of calcium cyclamate when assayed in 24 hour intervals for 96 hours. The cells were exposed to 10(-2) and 10(-3) molar concentrations of calcium cyclamate in TC 199 medium with fetal calf serum and antibiotics. It was noted that the addition of cyclamate increased mitotic rate of lymphocyte cells in cultures. It was determined that calcium cyclamate impaired the synthesis of deoxribonunucleic acid (as depicted by decreased incorporation of tritiated thymidine), reduced grain counts in autoradiographs and increased chromosome aberrations in cyclamate treated PHA stimulated peripheral blood lymphocytes in vitro. Morphological changes and growth rates showed significant effects. These studies indicate that calcium cyclamate has variable significant effects on leucocytes growth and chromosome morphology.

  10. Comparative effectiveness research.

    PubMed

    Hirsch, J A; Schaefer, P W; Romero, J M; Rabinov, J D; Sanelli, P C; Manchikanti, L

    2014-09-01

    The goal of comparative effectiveness research is to improve health care while dealing with the seemingly ever-rising cost. An understanding of comparative effectiveness research as a core topic is important for neuroradiologists. It can be used in a variety of ways. Its goal is to look at alternative methods of interacting with a clinical condition, ideally, while improving delivery of care. While the Patient-Centered Outcome Research initiative is the most mature US-based foray into comparative effectiveness research, it has been used more robustly in decision-making in other countries for quite some time. The National Institute for Health and Clinical Excellence of the United Kingdom is a noteworthy example of comparative effectiveness research in action. PMID:24874531

  11. [Genetic effects of radiation].

    PubMed

    Nakamura, Nori

    2012-03-01

    This paper is a short review of genetic effect of radiation. This includes methods and results of a large-scale genetic study on specific loci in mice and of various studies in the offspring of atomic-bomb survivors. As for the latter, there is no results obtained which suggest the effect of parental exposure to radiation. Further, in recent years, studies are conducted to the offspring born to parents who were survivors of childhood cancers. In several reports, the mean gonad dose is quite large whereas in most instances, the results do not indicate genetic effect following parental exposure to radiation. Possible reasons for the difficulties in detecting genetic effect of radiation are discussed. PMID:22514926

  12. Strategies for Effective Outsourcing.

    ERIC Educational Resources Information Center

    Moneta, Larry; Dillon, William L.

    2001-01-01

    Emphasizes strategies that can be employed for effective outsourcing in higher education settings. Several models of outsourcing are identified and described, and examples of institutions using each model are provided. (GCP)

  13. Cardiovascular Effects of Weightlessness

    NASA Technical Reports Server (NTRS)

    Short, K.

    1985-01-01

    Physiological changes resulting from long term weightlessness are reviewed and activities conducted to study cardiovascular deconditioning at NASA Ames are discussed. Emphasis is on using monkeys in chair rest, water immersion, and tilt table studies to simulate space environment effects.

  14. Coefficients of Effective Length.

    ERIC Educational Resources Information Center

    Edwards, Roger H.

    1981-01-01

    Under certain conditions, a validity Coefficient of Effective Length (CEL) can produce highly misleading results. A modified coefficent is suggested for use when empirical studies indicate that underlying assumptions have been violated. (Author/BW)

  15. Systems effectiveness evaluation program

    NASA Technical Reports Server (NTRS)

    Nicely, H. P., Jr.; Givens, W. D.

    1972-01-01

    Eight integrated computer programs provide needed capability to reduce man-hours needed to perform routine monitoring and assessment of effectiveness, reliability, and maintainability of large electronic equipment systems.

  16. Diuretic Effects of Cannabinoids

    PubMed Central

    Thakur, Ganesh A.; Bajaj, Shama; Nikas, Spyros P.; Vemuri, V. Kiran; Makriyannis, Alexandros; Bergman, Jack

    2013-01-01

    In vivo effects of cannabinoid (CB) agonists are often assessed using four well-established measures: locomotor activity, hypothermia, cataleptic-like effects, and analgesia. The present studies demonstrate that doses of CB agonists that produce these effects also reliably increase diuresis. Diuretic effects of several CB agonists were measured in female rats over 2 hours immediately after drug injection, and results were compared with hypothermic effects. Direct-acting CB1 agonists, including ?9-tetrahydrocannabinol, WIN 55,212 [R-(1)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate], AM2389 [9?-hydroxy-3-(1-hexyl-cyclobut-1-yl)-hexahydrocannabinol], and AM4054 [9?-(hydroxymethyl)-3-(1-adamantyl)-hexahydrocannabinol], produced dose-dependent increases in diuresis and decreases in colonic temperature, with slightly lower ED50 values for diuresis than for hypothermia. The highest doses of cannabinoid drugs yielded, on average, 2632 g/kg urine; comparable effects were obtained with 10 mg/kg furosemide and 3.0 mg/kg trans-(-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide (U50-488). Methanandamide (10.0 mg/kg) had lesser effect than other CB agonists, and the CB2 agonist AM1241 [1-(methylpiperidin-2-ylmethyl)-3-(2-iodo-5-nitrobenzoyl)indole], the anandamide transport inhibitor AM404, and the CB antagonist rimonabant did not have diuretic effects. In further studies, the diuretic effects of the CB1 agonist AM4054 were similar in male and female rats, displayed a relatively rapid onset to action, and were dose-dependently antagonized by 30 minutes pretreatment with rimonabant, but not by the vanilloid receptor type I antagonist capsazepine, nor were the effects of WIN 55,212 antagonized by the CB2 antagonist AM630 [(6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl](4-methoxyphenyl) methanone)]. These data indicate that cannabinoids have robust diuretic effects in rats that are mediated via CB1 receptor mechanisms. PMID:23019138

  17. The extraterrestrial Casimir Effect

    NASA Astrophysics Data System (ADS)

    Storti, Riccardo C.

    2011-09-01

    Application of the Electro-Gravi-Magnetic (EGM) Photon radiation method to the Casimir Effect (CE), suggests that the experimentally verified (terrestrially) neutrally charged Parallel-Plate configuration force, may differ within extraterrestrial gravitational environments from the gravitationally independent formulation by Casimir. Consequently, the derivation presented herein implies that a gravitationally dependent CE may become an important design factor in nanotechnology for extraterrestrial applications (ignoring finite conductivity + temperature effects and evading the requirement for Casimir Force corrections due to surface roughness).

  18. Centrifugal effects in Skyrmeons

    SciTech Connect

    Braaten, E.

    1984-01-01

    We give a qualitative discussion of centrifugal effects in the Skyrme model and methods for treating these effects. We show that there may be states in the spectrum which would not appear in a semiclassical expansion about the static soliton solution. We consider semiclassical expansions about static solutions and about uniformly-rotating solutions, and discuss the validity and limitations of both approaches. 11 references.

  19. Secondary pool boiling effects

    NASA Astrophysics Data System (ADS)

    Kruse, C.; Tsubaki, A.; Zuhlke, C.; Anderson, T.; Alexander, D.; Gogos, G.; Ndao, S.

    2016-02-01

    A pool boiling phenomenon referred to as secondary boiling effects is discussed. Based on the experimental trends, a mechanism is proposed that identifies the parameters that lead to this phenomenon. Secondary boiling effects refer to a distinct decrease in the wall superheat temperature near the critical heat flux due to a significant increase in the heat transfer coefficient. Recent pool boiling heat transfer experiments using femtosecond laser processed Inconel, stainless steel, and copper multiscale surfaces consistently displayed secondary boiling effects, which were found to be a result of both temperature drop along the microstructures and nucleation characteristic length scales. The temperature drop is a function of microstructure height and thermal conductivity. An increased microstructure height and a decreased thermal conductivity result in a significant temperature drop along the microstructures. This temperature drop becomes more pronounced at higher heat fluxes and along with the right nucleation characteristic length scales results in a change of the boiling dynamics. Nucleation spreads from the bottom of the microstructure valleys to the top of the microstructures, resulting in a decreased surface superheat with an increasing heat flux. This decrease in the wall superheat at higher heat fluxes is reflected by a "hook back" of the traditional boiling curve and is thus referred to as secondary boiling effects. In addition, a boiling hysteresis during increasing and decreasing heat flux develops due to the secondary boiling effects. This hysteresis further validates the existence of secondary boiling effects.

  20. The Fragility of Thermoelectric Power Factor in Cross-Plane Superlattices in the Presence of Nonidealities: A Quantum Transport Simulation Approach

    NASA Astrophysics Data System (ADS)

    Thesberg, M.; Pourfath, M.; Neophytou, N.; Kosina, H.

    2016-03-01

    Energy filtering has been put forth as a promising method for achieving large thermoelectric power factors in thermoelectric materials through Seebeck coefficient improvement. Materials with embedded potential barriers, such as cross-plane superlattices, provide energy filtering, in addition to low thermal conductivity, and could potentially achieve high figure of merit. Although there exist many theoretical works demonstrating Seebeck coefficient and power factor gains in idealized structures, experimental support has been scant. In most cases, the electrical conductivity is drastically reduced due to the presence of barriers. In this work, using quantum-mechanical simulations based on the nonequilibrium Green's function method, we show that, although power factor improvements can theoretically be observed in optimized superlattices (as pointed out in previous studies), different types of deviations from the ideal potential profiles of the barriers degrade the performance, some nonidealities being so significant as to negate all power factor gains. Specifically, the effect of tunneling due to thin barriers could be especially detrimental to the Seebeck coefficient and power factor. Our results could partially explain why significant power factor improvements in superlattices and other energy-filtering nanostructures mainly fail to be realized, despite theoretical predictions.

  1. Thermoelectric Properties of Double-Filled p-Type La1- z Yb z Fe4- x Co x Sb12 Skutterudites

    NASA Astrophysics Data System (ADS)

    Joo, Gyeong-Seok; Shin, Dong-Kil; Kim, Il-Ho

    2015-06-01

    La and Yb double-filled p-type skutterudites (La1- z Yb z Fe4- x Co x Sb12; 0.25 ? z ? 0.75 and 0.5 ? x ? 1) were synthesized by encapsulated melting and homogenized by use of heat treatment. It was apparent from the positive signs of the Seebeck coefficient and the Hall coefficient that all specimens had p-type characteristics. The carrier concentration decreased with charge compensation. The thermal conductivity and the electrical conductivity decreased and the Seebeck coefficient increased with increasing substitution of Co for Fe. However, the carrier concentration was increased by increasing the Yb filling ratio. Electrical conductivity increased and the Seebeck coefficient decreased with increasing Yb filling, because the electron valence of Yb2+ was lower than that of La3+. The thermal conductivity decreased with charge compensation, and the lattice thermal conductivity decreased with increasing Yb filling. Yb was more effective than La at reducing lattice thermal conductivity. The power factor ( PF) and dimensionless figure of merit ( ZT) increased with increasing temperature up to a specific temperature. The maximum PF = 2.81 mW/mK2 at 823 K was obtained for La0.75Yb0.25Fe3.5Co0.5Sb12 and the maximum ZT = 0.74 at 723 K was achieved for La0.5Yb0.5Fe3CoSb12.

  2. Preparation and thermoelectric properties of A8IIB16IIIB30IV clathrate compounds

    NASA Astrophysics Data System (ADS)

    Kuznetsov, V. L.; Kuznetsova, L. A.; Kaliazin, A. E.; Rowe, D. M.

    2000-06-01

    Polycrystalline samples of clathrate compounds Ba8Ga16Si30, Ba8Ga16Ge30, Ba8Ga16Sn30, and Sr8Ga16Ge30 were prepared by direct melting and characterized using X-ray powder diffraction and differential thermal analysis. The Ge- and Si-based clathrates melt congruently, whereas Ba8Ga16Sn30 melts incongruently. At room temperature the Ge- and Si-based clathrates possess a moderate negative Seebeck coefficient and a high electron concentration in the range of 71020-91020 cm-3 while Ba8Ga16Sn30 exhibits substantially lower electron concentration of 2.21019 cm-3. The Seebeck coefficient and electrical resistivity were measured over the range 100-870 K. The temperature dependence of transport properties of the clathrates is typical for heavily doped semiconductors. The transport properties were analyzed using a standard semiconductor transport model. There is a good agreement between the assumed model and experimental temperature dependence of the Seebeck coefficient in the extrinsic conductivity range for all studied clathrates apart from Ba8Ga16Ge30. The calculated effective masses of the clathrates range from 0.9 to 3 of the free electron mass. The estimated ZT values are 0.7 for Ba8Ga16Ge30 at 700 K and 0.87 for Ba8Ga16Si30 at 870 K. The potential for thermoelectric applications of these materials is assessed.

  3. The Fragility of Thermoelectric Power Factor in Cross-Plane Superlattices in the Presence of Nonidealities: A Quantum Transport Simulation Approach

    NASA Astrophysics Data System (ADS)

    Thesberg, M.; Pourfath, M.; Neophytou, N.; Kosina, H.

    2015-11-01

    Energy filtering has been put forth as a promising method for achieving large thermoelectric power factors in thermoelectric materials through Seebeck coefficient improvement. Materials with embedded potential barriers, such as cross-plane superlattices, provide energy filtering, in addition to low thermal conductivity, and could potentially achieve high figure of merit. Although there exist many theoretical works demonstrating Seebeck coefficient and power factor gains in idealized structures, experimental support has been scant. In most cases, the electrical conductivity is drastically reduced due to the presence of barriers. In this work, using quantum-mechanical simulations based on the nonequilibrium Green's function method, we show that, although power factor improvements can theoretically be observed in optimized superlattices (as pointed out in previous studies), different types of deviations from the ideal potential profiles of the barriers degrade the performance, some nonidealities being so significant as to negate all power factor gains. Specifically, the effect of tunneling due to thin barriers could be especially detrimental to the Seebeck coefficient and power factor. Our results could partially explain why significant power factor improvements in superlattices and other energy-filtering nanostructures mainly fail to be realized, despite theoretical predictions.

  4. Preparation and Characterization of P-Type and N-Type Doped Expanded Graphite Polymer Composites for Thermoelectric Applications.

    PubMed

    Javadi, Reza; Choi, Pyung Ho; Park, Hyoung Sun; Choi, Byoung Deog

    2015-11-01

    In this work, we demonstrate that expanded graphite can be sufficiently dispersed in polymer solution to form suspensions. Thin composite films were prepared by casting and drying the suspensions. The thermoelectric properties of expanded graphite (ExG)-polymer composites were easily modified by chemical doping. Electrically and thermally insulating polymers of PC, PS, and PMMA served as matrix materials. ExG composite films in PC, PMMA, and PS were prepared using thionyl chloride as the p-type dopant and PEI as the n-type dopant. By comparing the electrical conductivity and Seebeck coefficient values of the composite films, we observed that use of an electron acceptor material (thionyl chloride) in composites enhanced electrical conductivity and reduced the value of the positive Seebeck coefficient, which are p-type doping effects. In contrast, when the donor material PEI was used, there was an increase in electrical conductivity and changes in the value and sign of the Seebeck coefficient from positive to negative, confirming n-type doping. PMID:26726653

  5. Deposition and investigation of lanthanum-cerium hexaboride thin films

    SciTech Connect

    Kuzanyan, A.S. . E-mail: akuzan@ipr.sci.am; Harutyunyan, S.R.; Vardanyan, V.O.; Badalyan, G.R.; Petrosyan, V.A.; Kuzanyan, V.S.; Petrosyan, S.I.; Karapetyan, V.E.; Wood, K.S.; Wu, H.-D.

    2006-09-15

    Thin films of lanthanum-cerium hexaboride, the promising thermoelectric material for low-temperature applications, are deposited on various substrates by the electron-beam evaporation, pulsed laser deposition and magnetron sputtering. The influence of the deposition conditions on the films X-ray characteristics, composition, microstructure and physical properties, such as the resistivity and Seebeck coefficient, is studied. The preferred (100) orientation of all films is obtained from XRD traces. In the range of 780-800 deg. C deposition temperature the highest intensity of diffractions peaks and the highest degree of the preferred orientation are observed. The temperature dependence of the resistivity and the Seebeck coefficient of films are investigated in the temperature range of 4-300 K. The features appropriate to Kondo effect in the dependences {rho}(T) and S(T) are detected at temperatures below 20 K. Interplay between the value of the Seebeck coefficient, metallic parameters and Kondo scattering of investigated films is discussed. - Graphical abstract: Kondo scattering in (La,Ce)B{sub 6} films: temperature dependence of the resistivity of (La,Ce)B{sub 6} films on various substrates and the ceramics La{sub 0.99}Ce{sub 0.01}B{sub 6}.

  6. Spin Hall effects

    NASA Astrophysics Data System (ADS)

    Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

    2015-10-01

    Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical point of view, focusing on well-established and accepted physics. In such a young field, there remains much to be understood and explored, hence some of the future challenges and opportunities of this rapidly evolving area of spintronics are outlined.

  7. Barriers to effective teaching.

    PubMed

    DaRosa, Debra A; Skeff, Kelley; Friedland, Joan A; Coburn, Michael; Cox, Susan; Pollart, Susan; O'connell, Mark; Smith, Sandy

    2011-04-01

    Medical school faculty members are charged with the critical responsibility of preparing the future physician and medical scientist workforce. Recent reports suggest that medical school curricula have not kept pace with societal needs and that medical schools are graduating students who lack the knowledge and skills needed to practice effectively in the 21st century. The majority of faculty members want to be effective teachers and graduate well-prepared medical students, but multiple and complex factors-curricular, cultural, environmental, and financial-impede their efforts. Curricular impediments to effective teaching include unclear definitions of and disagreement on learning needs, misunderstood or unstated goals and objectives, and curriculum sequencing challenges. Student and faculty attitudes, too few faculty development opportunities, and the lack of an award system for teaching all are major culture-based barriers. Environmental barriers, such as time limitations, the setting, and the physical space in which medical education takes place, and financial barriers, such as limited education budgets, also pose serious challenges to even the most committed teachers. This article delineates the barriers to effective teaching as noted in the literature and recommends action items, some of which are incremental whereas others represent major change. Physicians-in-training, medical faculty, and society are depending on medical education leaders to address these barriers to effect the changes needed to enhance teaching and learning. PMID:21346500

  8. Temperature effects on electrophoresis.

    PubMed

    Rogacs, Anita; Santiago, Juan G

    2013-05-21

    We present a model capturing the important contributors to the effects of temperature on the observable electrophoretic mobilities of small ions, and on solution conductivity and pH. Our temperature model includes relations for temperature-dependent viscosity, ionic strength corrections, degree of ionization (pK), and ion solvation effects on mobility. We incorporate thermophysical data for water viscosity, temperature-dependence of the Onsager-Fuoss model for finite ionic strength effects on mobility, temperature-dependence of the extended Debye-Huckel theory for correction of ionic activity, the Clarke-Glew approach and tabulated thermodynamic quantities of ionization reaction for acid dissociation constants as a function of temperature, and species-specific, empirically evaluated correction terms for temperature-dependence of Stokes' radii. We incorporated our model into a MATLAB-based simulation tool we named Simulation of Temperature Effects on ElectroPhoresis (STEEP). We validated our model using conductivity and pH measurements across a temperature variation of 25-70 °C for a set of electrolytes routinely used in electrophoresis. The model accurately captures electrolyte solution pH and conductivity, including important effects not captured by simple Walden-type relations. PMID:23627294

  9. Pleiotropic effects of statins.

    PubMed

    Kavalipati, Narasaraju; Shah, Jay; Ramakrishan, Ananthraman; Vasnawala, Hardik

    2015-01-01

    Statins or 3-hydroxy-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors not only prevents the synthesis of cholesterol biosynthesis but also inhibits the synthesis of essential isoprenoid intermediates such as farnesyl pyrophosphate, geranylgeranyl pyrophosphate, isopentanyl adenosine, dolichols and polyisoprenoid side chains of ubiquinone, heme A, and nuclear lamins. These isoprenoid intermediates are required for activation of various intracellular/signaling proteins- small guanosine triphosphate bound protein Ras and Ras-like proteins like Rho, Rab, Rac, Ral, or Rap which plays an indispensible role in multiple cellular processes. Reduction of circulating isoprenoids intermediates as a result of HMG CoA reductase inhibition by statins prevents activation of these signalling proteins. Hence, the multiple effects of statins such as antiinflammatory effects, antioxidant effects, antiproliferative and immunomodulatory effects, plaque stability, normalization of sympathetic outflow, and prevention of platelet aggregation are due to reduction of circulating isoprenoids and hence inactivation of signalling proteins. These multiple lipid-independent effects of statins termed as statin pleiotropy would potentially open floodgates for research in multiple treatment domains catching attentions of researchers and clinician across the globe. PMID:26425463

  10. The real butterfly effect

    NASA Astrophysics Data System (ADS)

    Palmer, T. N.; Dring, A.; Seregin, G.

    2014-09-01

    Historical evidence is reviewed to show that what Ed Lorenz meant by the iconic phrase the butterfly effect is not at all captured by the notion of sensitive dependence on initial conditions in low-order chaos. Rather, as presented in his 1969 Tellus paper, Lorenz intended the phrase to describe the existence of an absolute finite-time predicability barrier in certain multi-scale fluid systems, implying a breakdown of continuous dependence on initial conditions for large enough forecast lead times. To distinguish from mere sensitive dependence, the effect discussed in Lorenz's Tellus paper is referred to as the real butterfly effect. Theoretical evidence for such a predictability barrier in a fluid described by the three-dimensional Navier-Stokes equations is discussed. Whilst it is still an open question whether the Navier-Stokes equation has this property, evidence from both idealized atmospheric simulators and analysis of operational weather forecasts suggests that the real butterfly effect exists in an asymptotic sense, i.e. for initial-time atmospheric perturbations that are small in scale and amplitude compared with (weather) scales of interest, but still large in scale and amplitude compared with variability in the viscous subrange. Despite this, the real butterfly effect is an intermittent phenomenon in the atmosphere, and its presence can be signalled a priori, and hence mitigated, by ensemble forecast methods.

  11. Attributing effects to interactions

    PubMed Central

    VanderWeele, Tyler J.; Tchetgen Tchetgen, Eric J.

    2014-01-01

    A framework is presented that allows an investigator to estimate the portion of the effect of one exposure that is attributable to an interaction with a second exposure. We show that when the two exposures are independent, the total effect of one exposure can be decomposed into a conditional effect of that exposure and a component due to interaction. The decomposition applies on difference or ratio scales. We discuss how the components can be estimated using standard regression models, and how these components can be used to evaluate the proportion of the total effect of the primary exposure attributable to the interaction with the second exposure. In the setting in which one of the exposures affects the other, so that the two are no longer independent, alternative decompositions are discussed. The various decompositions are illustrated with an example in genetic epidemiology. If it is not possible to intervene on the primary exposure of interest, the methods described in this paper can help investigators to identify other variables that, if intervened upon, would eliminate the largest proportion of the effect of the primary exposure. PMID:25051310

  12. Coulomb Interaction Effects In Semiconductor Heterostructures With Spin-Orbit Interaction

    NASA Astrophysics Data System (ADS)

    Capps, Jeremy Patrick

    In this thesis we analyze two different situations where the interplay between the spin-orbit coupling (SOI) of the Rashba and Dresselhaus type, linear in the electron momentum, and the Coulomb interaction generates a specific macroscopic phenomenology that can be experimentally observed. In the first problem, we investigate the Friedel oscillations that can be sustained in the presence of the Coulomb repulsion in a two-dimensional lateral superlattice with SOI and analyze the dependence on several system parameters. Then, we are concerned with the properties of a single quantum well in the special regime where the coupling strengths of the Rashba and Dresselhaus interactions are equal. Starting from general total-energy considerations, we demonstrate that the SU(2) spin-rotation symmetry and the resulting persistent helical state (PHS) predicted to occur are not in fact realized; the actual spin order being that of an itinerant antiferromagnet (IAF). We obtain numerical results that describe the temperature evolution of the order parameter in the IAF state and determine the critical temperature of the transition to the paramagnetic order. Transport in this state is modeled by using the solutions of a Boltzmann equation obtained within the relaxation time approximation. Numerical estimates performed for realistic GaAs and InAs samples indicate that at low temperatures, the amplitude of the spin-Seebeck coefficient can be increased by scattering on magnetic impurities.

  13. Giant thermoelectric effect in graphene-based topological insulators with heavy adatoms and nanopores.

    PubMed

    Chang, Po-Hao; Bahramy, Mohammad Saeed; Nagaosa, Naoto; Nikoli?, Branislav K

    2014-07-01

    Designing thermoelectric materials with high figure of merit ZT = S(2)GT/Ktot requires fulfilling three often irreconcilable conditions, that is, the high electrical conductance G, small thermal conductance Ktot, and high Seebeck coefficient S. Nanostructuring is one of the promising ways to achieve this goal as it can substantially suppress lattice contribution to Ktot. However, it may also unfavorably influence the electronic transport in an uncontrollable way. Here, we theoretically demonstrate that this issue can be ideally solved by fabricating graphene nanoribbons with heavy adatoms and nanopores. The adatoms locally enhance spin-orbit coupling in graphene thereby converting it into a two-dimensional topological insulator with a band gap in the bulk and robust helical edge states, which carry electrical current and generate a highly optimized power factor S(2)G per helical conducting channel due to narrow boxcar-function-shaped electronic transmission (surpassing even the Mahan-Sofo limit obtained for delta-function-shaped electronic transmission). Concurrently, the array of nanopores impedes the lattice thermal conduction through the bulk. Using quantum transport simulations coupled with first-principles electronic and phononic band structure calculations, the thermoelectric figure of merit is found to reach its maximum ZT ? 3 at low temperatures T ? 40 K. This paves a way to design high-ZT materials by exploiting the nontrivial topology of electronic states through nanostructuring. PMID:24932511

  14. Magnetothermoelectric effects in Fe1+dTe1-xSex

    NASA Astrophysics Data System (ADS)

    Matusiak, Marcin; Pomjakushina, Ekaterina; Conder, Kazimierz

    2012-12-01

    We report resistivity as well as the Hall, Seebeck and Nernst coefficients data for Fe1+dTe1-xSex single crystals with x = 0, 0.38, and 0.40. In the parent compound Fe1.04Te we observe at TN = 61 K a sudden change of all quantities studied, which can be described to the Fermi surface reconstruction due to onset of the antiferromagnetic order. Two very closely doped samples: Fe1.01Te0.62Se0.38 (Se38) and Fe1.01Te0.60Se0.40 (Se40) are superconductors with Tc = 13.4 K and 13.9 K, respectively. There are no evident magnetic transitions in either Se38 or Se40. Properties of these two single crystals are almost identical at high temperatures, but start to diverge below T ≈ 80 K. Perhaps we see the onset of scattering that might be a related to changes in short range magnetic correlations caused by selenium doping.

  15. Aviation noise effects

    NASA Astrophysics Data System (ADS)

    Newman, J. S.; Beattie, K. R.

    1985-03-01

    This report summarizes the effects of aviation noise in many areas, ranging from human annoyance to impact on real estate values. It also synthesizes the findings of literature on several topics. Included in the literature were many original studies carried out under FAA and other Federal funding over the past two decades. Efforts have been made to present the critical findings and conclusions of pertinent research, providing, when possible, a bottom line conclusion, criterion or perspective. Issues related to aviation noise are highlighted, and current policy is presented. Specific topic addressed include: annoyance; Hearing and hearing loss; noise metrics; human response to noise; speech interference; sleep interference; non-auditory health effects of noise; effects of noise on wild and domesticated animals; low frequency acoustical energy; impulsive noise; time of day weightings; noise contours; land use compatibility; and real estate values. This document is designed for a variety of users, from the individual completely unfamiliar with aviation noise to experts in the field.

  16. Effective Documentation Tools

    NASA Technical Reports Server (NTRS)

    Sleboda, Claire

    1997-01-01

    Quality assurance programs provide a very effective means to monitor and evaluate medical care. Quality assurance involves: (1) Identify a problem; (2) Determine the source and nature of the problem; (3) Develop policies and methods to effect improvement; (4) Implement those polices; (5) Monitor the methods applied; and (6) Evaluate their effectiveness. Because this definition of quality assurance so closely resembles the Nursing Process, the health unit staff was able to use their knowledge of the nursing process to develop many forms which improve the quality of patient care. These forms include the NASA DFRC Service Report, the occupational injury form (Incident Report), the patient survey (Pre-hospital Evaluation/Care Report), the Laboratory Log Sheet, the 911 Run Sheet, and the Patient Assessment Stamp. Examples and steps which are followed to generate these reports are described.

  17. The ``Cheerios effect''

    NASA Astrophysics Data System (ADS)

    Vella, Dominic; Mahadevan, L.

    2005-09-01

    Objects that float at the interface between a liquid and a gas interact because of interfacial deformation and the effect of gravity. We highlight the crucial role of buoyancy in this interaction, which, for small particles, prevails over the capillary suction that often is assumed to be the dominant effect. We emphasize this point using a simple classroom demonstration, and then derive the physical conditions leading to mutual attraction or repulsion. We also quantify the force of interaction in particular instances and present a simple dynamical model of this interaction. The results obtained from this model are validated by comparison to experimental results for the mutual attraction of two identical spherical particles. We consider some of the applications of the effect that can be found in nature and the laboratory.

  18. Security effectiveness review (SER)

    SciTech Connect

    Kouprianova, I.; Ek, D.; Showalter, R.; Bergman, M.

    1998-08-01

    As part of the on-going DOE/Russian MPC and A activities at the Institute of Physics and Power Engineering (IPPE) and in order to provide a basis for planning MPC and A enhancements, an expedient method to review the effectiveness of the MPC and A system has been adopted. These reviews involve the identification of appropriate and cost-effective enhancements of facilities at IPPE. This effort requires a process that is thorough but far less intensive than a traditional vulnerability assessment. The SER results in a quick assessment of current and needed enhancements. The process requires preparation and coordination between US and Russian analysts before, during, and after information gathering at the facilities in order that the analysis is accurate, effective, and mutually agreeable. The goal of this paper is to discuss the SER process, including the objectives, time scale, and lessons learned at IPPE.

  19. Disentangling the EMC effect

    NASA Astrophysics Data System (ADS)

    Piasetzky, E.; Hen, O.; Weinstein, L. B.

    2013-10-01

    The deep inelastic scattering cross section for scattering from bound nucleons differs from that of free nucleons. This phenomena, first discovered 30 years ago, is known as the EMC effect and is still not fully understood. Recent analysis of world data showed that the strength of the EMC effect is linearly correlated with the relative amount of Two-Nucleon Short Range Correlated pairs (2N-SRC) in nuclei. The latter are pairs of nucleons whose wave functions overlap, giving them large relative momentum and low center of mass momentum, where high and low is relative to the Fermi momentum of the nucleus. The observed correlation indicates that the EMC effect, like 2N-SRC pairs, is related to high momentum nucleons in the nucleus. This paper reviews previous studies of the EMC-SRC correlation and studies its robustness. It also presents a planned experiment aimed at studying the origin of this EMC-SRC correlation.

  20. Effective Nutritional Supplement Combinations

    NASA Astrophysics Data System (ADS)

    Cooke, Matt; Cribb, Paul J.

    Few supplement combinations that are marketed to athletes are supported by scientific evidence of their effectiveness. Quite often, under the rigor of scientific investigation, the patented combination fails to provide any greater benefit than a group given the active (generic) ingredient. The focus of this chapter is supplement combinations and dosing strategies that are effective at promoting an acute physiological response that may improve/enhance exercise performance or influence chronic adaptations desired from training. In recent years, there has been a particular focus on two nutritional ergogenic aidscreatine monohydrate and protein/amino acidsin combination with specific nutrients in an effort to augment or add to their already established independent ergogenic effects. These combinations and others are discussed in this chapter.

  1. Neuropsychological effects of marijuana

    PubMed Central

    Klonoff, Harry; Low, Morton; Marcus, Anthony

    1973-01-01

    This study assigned 81 non-nave subjects, divided into low- and high-dose groups, to four experimental conditions (marijuana/marijuana, marijuana/placebo, placebo/marijuana and placebo/placebo) for two sessions separated by about one week. The low dose was 4.8 mg. ?9-THC followed by 2.4 mg. one hour later. The high dose was 9.1 mg. followed by 4.5 mg. one hour later. A battery of neuropsychological tests was administered. The low dose produced generalized impairment of all mental processes (concept formation, memory, tactile form discrimination and motor function) and the effect was generalized to all modalities. The high dose resulted in more extensive impairment, again generalized. The drug effects noted were explained in terms of generalized impairment of central integrative processes. The effects of marijuana on learning as well as memory were explained in terms of impaired output (recall), but the impairment was transient. PMID:4405419

  2. Spin Hall Effect Transistor

    NASA Astrophysics Data System (ADS)

    Wunderlich, Jrg; Park, Byong-Guk; Irvine, Andrew C.; Zrbo, Liviu P.; Rozkotov, Eva; Nemec, Petr; Novk, Vt; Sinova, Jairo; Jungwirth, Toms

    2010-12-01

    The field of semiconductor spintronics explores spin-related quantum relativistic phenomena in solid-state systems. Spin transistors and spin Hall effects have been two separate leading directions of research in this field. We have combined the two directions by realizing an all-semiconductor spin Hall effect transistor. The device uses diffusive transport and operates without electrical current in the active part of the transistor. We demonstrate a spin AND logic function in a semiconductor channel with two gates. Our study shows the utility of the spin Hall effect in a microelectronic device geometry, realizes the spin transistor with electrical detection directly along the gated semiconductor channel, and provides an experimental tool for exploring spin Hall and spin precession phenomena in an electrically tunable semiconductor layer.

  3. Giving effective presentations.

    PubMed

    Englehart, Nadine

    2004-03-01

    Apprehension about oral communication, or public speaking is rated as the number one fear among most individuals. Developing skill in, and comfort with, public speaking is important whether we are presenting oral reports and proposals, responding to questions, or training co-workers. Effective speakers are able to communicate information in a way that stimulates interest, helps the audience to understand and remember, and influences attitudes and behaviours. Many of us think that effective speakers are born rather than made. In truth most successful speakers work hard and invest a great deal of time and effort in to improving their speaking capabilities. Effective public speaking is a learned skill and activity that requires lots of practice. Like other learned skills, having a strategy with clear action steps can help you achieve your goal. PMID:15116467

  4. Transgenerational genetic effects

    PubMed Central

    Nelson, Vicki R; Nadeau, Joseph H

    2012-01-01

    Since Mendel, studies of phenotypic variation and disease risk have emphasized associations between genotype and phenotype among affected individuals in families and populations. Although this paradigm has led to important insights into the molecular basis for many traits and diseases, most of the genetic variants that control the inheritance of these conditions continue to elude detection. Recent studies suggest an alternative mode of inheritance where genetic variants that are present in one generation affect phenotypes in subsequent generations, thereby decoupling the conventional relations between genotype and phenotype, and perhaps, contributing to missing heritability. Under some conditions, these transgenerational genetic effects can be as frequent and strong as conventional inheritance, and can persist for multiple generations. Growing evidence suggests that RNA mediates these heritable epigenetic changes. The primary challenge now is to identify the molecular basis for these effects, characterize mechanisms and determine whether transgenerational genetic effects occur in humans. PMID:22122083

  5. Relative age effect: implications for effective practice.

    PubMed

    Andronikos, Georgios; Elumaro, Adeboye Israel; Westbury, Tony; Martindale, Russell J J

    2016-06-01

    Physical and psychological differences related to birthdate amongst athletes of the same selection year have been characterised as the "relative age effects" (RAEs). RAEs have been identified in a variety of sports, both at youth and adult level, and are linked with dropout of athletes and a reduction of the talent pool. This study examined the existence, mechanisms and possible solutions to RAEs using qualitative methodology. Seven experts in the field of talent identification and development were interviewed. Inductive analysis of the data showed that, while there was mixed evidence for the existence of RAEs across sports, the eradication of RAEs was attributed to controllable features of the development environment. The factors reported included the structure of "categories" used to group athletes within the sport (e.g. age, weight, size, skills), recognition and prioritisation of long-term development over "short term win focus." Education of relevant parties (e.g. coaches, scouts, clubs) about RAEs and the nature of "talent" within a long-term context was suggested, along with careful consideration of the structure of the development environment (e.g. delayed selection, provision for late developers, focus on skills not results, use of challenge). Implications for research and practice are discussed. PMID:26417709

  6. Habituation of reinforcer effectiveness

    PubMed Central

    Lloyd, David R.; Medina, Douglas J.; Hawk, Larry W.; Fosco, Whitney D.; Richards, Jerry B.

    2014-01-01

    In this paper we propose an integrative model of habituation of reinforcer effectiveness (HRE) that links behavioral- and neural-based explanations of reinforcement. We argue that HRE is a fundamental property of reinforcing stimuli. Most reinforcement models implicitly suggest that the effectiveness of a reinforcer is stable across repeated presentations. In contrast, an HRE approach predicts decreased effectiveness due to repeated presentation. We argue that repeated presentation of reinforcing stimuli decreases their effectiveness and that these decreases are described by the behavioral characteristics of habituation (McSweeney and Murphy, 2009; Rankin etal., 2009). We describe a neural model that postulates a positive association between dopamine neurotransmission and HRE. We present evidence that stimulant drugs, which artificially increase dopamine neurotransmission, disrupt (slow) normally occurring HRE and also provide evidence that stimulant drugs have differential effects on operant responding maintained by reinforcers with rapid vs. slow HRE rates. We hypothesize that abnormal HRE due to genetic and/or environmental factors may underlie some behavioral disorders. For example, recent research indicates that slow-HRE is predictive of obesity. In contrast ADHD may reflect “accelerated-HRE.” Consideration of HRE is important for the development of effective reinforcement-based treatments. Finally, we point out that most of the reinforcing stimuli that regulate daily behavior are non-consumable environmental/social reinforcers which have rapid-HRE. The almost exclusive use of consumable reinforcers with slow-HRE in pre-clinical studies with animals may have caused the importance of HRE to be overlooked. Further study of reinforcing stimuli with rapid-HRE is needed in order to understand how habituation and reinforcement interact and regulate behavior. PMID:24409128

  7. Aharonov-Bohm effect revisited

    NASA Astrophysics Data System (ADS)

    Eskin, Gregory

    2015-04-01

    Aharonov-Bohm effect is a quantum mechanical phenomenon that attracted the attention of many physicists and mathematicians since the publication of the seminal paper of Aharonov and Bohm [1] in 1959. We consider different types of Aharonov-Bohm effects such as the magnetic AB effect, electric AB effect, combined electromagnetic AB effect, AB effect for the Schrdinger equations with Yang-Mills potentials, and the gravitational analog of AB effect. We shall describe different approaches to prove the AB effect based on the inverse scattering problems, the inverse boundary value problems in the presence of obstacles, spectral asymptotics, and the direct proofs of the AB effect.

  8. An acoustic Casimir effect

    NASA Astrophysics Data System (ADS)

    Larraza, Andrs; Denardo, Bruce

    1998-11-01

    Theoretical and experimental results are presented for the force law between two rigid, parallel plates due to the radiation pressure of band-limited acoustic noise. Excellent agreement is shown between theory and experiment. While these results constitute an acoustic analog for the Casimir effect, an important difference is that band-limited noise can cause the force to be attractive or repulsive as a function of the distance of separation of the plates. Applications of the acoustic Casimir effect to background noise transduction and non-resonant acoustic levitation are suggested.

  9. Nonequilibrium effects in Isoscaling

    SciTech Connect

    Dorso, C. O.; Lopez, J. A.

    2007-02-12

    In this work we study within a simple model different properties of the system that allow us to understand the properties of the isoscaling observable. We first show that isoscaling is a general property of fragmenting systems. We show this by using a simple generalized percolation model. We show that the usual isoscaling property can be obtained in the case of bond percolation in bichromatic lattices with any regular topology. In this case the probabilities of each color (isospin) are independent. We then explore the effect of introducing 'non-equilibrium' effects.

  10. Contamination effects study

    NASA Technical Reports Server (NTRS)

    1988-01-01

    The in-situ optical surface measurement system is a facility designed to study the deleterious effects of particulate materials on the surface reflectivities of optical materials in the vacuum ultraviolet (VUV). This arrangement is designed to simulate the on-orbit effects of contamination and degradation of optical surfaces. This simulation is accomplished through the use of non-coherent VUV sources illuminating optical surfaces located in a high vacuum chamber. Several sources of contamination are employed. The reflectivity is measured both at the specular reflection as well as at two scattered positions, forward and reverse. The system components are described and an operating procedure is given.

  11. Effective Temperature of Mutations

    NASA Astrophysics Data System (ADS)

    Dernyi, Imre; Szll?si, Gergely J.

    2015-02-01

    Biological macromolecules experience two seemingly very different types of noise acting on different time scales: (i) point mutations corresponding to changes in molecular sequence and (ii) thermal fluctuations. Examining the secondary structures of a large number of microRNA precursor sequences and model lattice proteins, we show that the effects of single point mutations are statistically indistinguishable from those of an increase in temperature by a few tens of kelvins. The existence of such an effective mutational temperature establishes a quantitative connection between robustness to genetic (mutational) and environmental (thermal) perturbations.

  12. Vascular effects of flavonoids.

    PubMed

    Almeida Rezende, Bruno; Pereira, Aline Carvalho; Cortes, Steyner F; Lemos, Virginia Soares

    2016-01-01

    Flavonoids are natural plant-derived polyphenolic compounds with various biological properties particularly in the cardiovascular system, including antiatherogenic, antioxidant, vasodilation, antihypertensive, and antiplatelet activities. These biological properties have been evaluated in several experimental and clinical studies. In addition, extensive reviews have discussed the antiatherogenic effect of these polyphenols. However, limited studies have investigated the potential therapeutic vascular effects of these compounds. This review brings together some recent studies, to establish the different signaling pathways involved in the molecular mechanisms that underlie the vasodilation induced by flavonoids. PMID:26555950

  13. Anticancer effects of fucoidan.

    PubMed

    Senthilkumar, Kalimuthu; Kim, Se-Kwon

    2014-01-01

    Recently, there has been an increased interest in the pharmacologically active natural compounds isolated and used for remedies of various kinds of diseases, including cancer. The great deal of interest has been developed to isolate bioactive compounds from marine resources because of their numerous health beneficial effects. Among marine resources, marine algae are valuable sources of structurally diverse bioactive compounds. Fucoidan is a sulfated polysaccharide derived from brown seaweeds and has been used as an ingredient in some dietary supplement products. Fucoidan has various biological activities including antibacterial, antioxidant, anti-inflammatory, anticoagulant, and antitumor activities. So this chapter deals with anticancer effects of fucoidan. PMID:25081084

  14. Creating an Effective Newsletter

    ERIC Educational Resources Information Center

    Shackelford, Ray; Griffis, Kurt

    2006-01-01

    Newsletters are an important resource or form of media. They offer a cost-effective way to keep people informed, as well as to promote events and programs. Production of a newsletter makes an excellent project, relevant to real-world communication, for technology students. This article presents an activity on how to create a short newsletter. The

  15. Cost effective technology

    NASA Astrophysics Data System (ADS)

    Miller, S. C.

    1989-09-01

    With relation to advanced technology for gas turbines, the overall process of product definition and development, concentrating particularly on the integration of activities between engineering design and manufacturing, is surveyed. The development of new philosophies in each of these spheres of activity is concluded to be cost effective technology and to make a highly significant contribution to the competitiveness and profitability of the industry.

  16. Effective Nonverbal Communication.

    ERIC Educational Resources Information Center

    Parratt, Smitty

    1995-01-01

    Discusses the importance of understanding nonverbal communication in enhancing the personal and work relationships of interpreters and increasing their effectiveness in meeting the needs of customers. Discusses the mystique of body language, cultural variation in the use of gestures, the stages of an encounter, interpreting gesture clusters, and…

  17. Assessing Library Effectiveness.

    ERIC Educational Resources Information Center

    Shaughnessy, Thomas W.

    1990-01-01

    Discusses the current emphasis on assessment of library effectiveness and describes several assessment techniques. It is argued that, by encouraging staff to develop an attitude of self-assessment based on their ability to add value to library services, the assessment phenomenon can be used to improve the overall quality of libraries. (11…

  18. Educator Effectiveness Administrative Manual

    ERIC Educational Resources Information Center

    Pennsylvania Department of Education, 2014

    2014-01-01

    The goal of this manual is to provide guidance in the evaluation of educators, highlight critical components of effectiveness training, and offer opportunities for professional growth. The term "educator" includes teachers, all professional and temporary professional employees, education specialists, and school administrators/principals.…

  19. Effective Team Participation.

    ERIC Educational Resources Information Center

    Male, Mary

    1991-01-01

    The Student Study Team (SST) is described as a California intervention model that encourages effective multidisciplinary team participation. The development, training, operation, and evaluation of such teams are discussed, and implementation recommendations are offered. The article includes a flow chart of the SST process, a meeting competency

  20. Biasing Effects of Experimenters.

    ERIC Educational Resources Information Center

    Rosenthal, Robert

    1977-01-01

    Explains the types of effects, usually unintentional, that psychologists can have upon the results of their research; describes the "Pygmalion Experiment," in which teachers' expectations for children's behavior proved to be self-fulfilling prophecies; and points to research needs in the area of interpersonal expectations. (GT)