bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modified Carbon Cryogel-Ammonia Borane Nanocomposites for Hydrogen Storage
Authors: Sepehri Saghar , Garcia Betzaida Batalla , Zhang Qifeng , Cao Guozhong 
Published: April 2011

AbstractThis paper reports the synthesis and characterization of coherent Boron/Nitrogen –doped –carbon cryogels- ammonia borane nanocomposites for hydrogen storage. Resorcinol formaldehyde derived doped carbon cryogels (CC) were obtained via chemical modification.CC- ammonia-borane nanocomposites were made by incorporation of ammonia borane (AB), in CCs. Nitrogen sorption analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy, are used to investigate the structure and morphology of the modified CCs. Differential scanning calorimetry is used to study the dehydrogenation of coherent doped-CC-AB nanocomposites. Modified CCs show higher mesoporosity, and more homogeneous porous structure compared to undoped CCs. Also, dehydrogenation kinetics of nanocomposites is enhanced as compared to neat AB. Possible nanoscale and catalytic effects of nanocomposites in improved dehydrogenation kinetics are discussed.
In situ high pressure XRD study on hydrogen uptake behavior of Pd-carbon systems
Authors: Bhat Vinay V , Gallego Nidia C , Contescu Cristian I , Payzant E Andrew , Rondinone Adam J , Tekinalp Halil , Edie Dan D 
Published: April 2011

AbstractEfficient storage of hydrogen for use in fuel cell-powered vehicles is a challenge that is being addressed in different ways, including adsorptive, compressive, and liquid storage approaches. In this paper we report on adsorptive storage in nanoporous carbon fibers in which palladium is incorporated prior to spinning and carbonization/activation of the fibers. Nanoparticles of Pd, when dispersed in activated carbon fibers (ACF), enhance the hydrogen storage capacity of ACF. The adsorption capacity of Pd-ACF increases with increasing temperature below 0.4 bar, and the trend reverses when the pressure increases. To understand the cause for such behavior, hydrogen uptake properties of Pd with different degrees of Pd-carbon contact (Pd deposited on carbon surface and Pd embedded in carbon matrix) are compared with Pd-sponge using in situ XRD under various hydrogen partial pressures (<10 bar).Rietveld refinement and profile analysis of diffraction patterns does not show any significant changes in carbon structure even under 10 bar H2. Pd forms β PdH0.67 under 10 bar H2, which transforms to α PdH0.02 as the hydrogen partial pressure is decreased. However, the equilibrium pressure of transition (corresponding to a 1:1 ratio of α and β phases) increases with increasing the extent of Pd-carbon contact. This pressure is higher for Pd embedded in carbon than for Pd deposited on carbon surface. Both these Pd-carbon materials have higher H2 desorption pressure than pure Pd, indicating that carbon “pumps out” hydrogen from PdHx and the pumping power depends on the extent of Pd-carbon contact. These results support the spillover mechanism (dissociative adsorption of H2 followed by surface diffusion of atomic H).
Microstuctural Characterization of the Radiation Effects in ZrC, a Potential Material for Next Generation Nuclear Plants
Authors: Baldinozzi Gianguido , Gosset Dominique , Simeone David , Dollé Mickael , Thomé Lionel , Surblé Suzy 
Published: April 2011

AbstractThe development of a new generation of nuclear reactors (Gen-IV), with improved thermodynamic yield and a reduction of waste production, makes necessary to consider materials able to withstand high operating temperatures. Transition metal carbides, like ZrC, are then under consideration. Despite their good thermal and neutron properties, they have unfortunately a brittle mechanical behaviour. This is the reason why it is important to investigate the properties of these systems with sub-micrometric grains and as a function of their composition. Therefore, samples having micrometric and nanometric grain sizes (and different oxygen content) were irradiated by low energy ions at room temperature to simulate their behaviour in a neutron flux. The irradiation effects in these materials were studied by grazing X-ray diffraction and transmission electron microscopy.
On Modeling the Evolution of Radiation Damage in Silicon Carbide
Authors: Weber William J , Gao Fei , Devanathan Ram , Zhang Yanwen , Jiang Weilin , Bae In-Tae 
Published: April 2011

AbstractExperimental charged-particle irradiations and multi-scale computer simulations have been used to investigate the primary damage state and evolution of damage in silicon carbide as functions of temperature and charged-particle mass and energy. Atomistic simulations of energetic C and Si collision cascades, similar to those created by reactor neutrons, indicate that single interstitials, vacancies, antisite defects, and small defect clusters are produced. The point defects are dominated by close Frenkel pairs, and atomistic simulations indicate that the activation energies for recombination of most close pairs range from 0.24 to 0.38 eV, which suggest significant reduction in defect survivability at room temperature. Atomistic simulations have also determined that the activation energies for long-range diffusion of C and Si interstitials are 0.7 and 1.5 eV, respectively. Using these activation energies and ab initio results as input parameters, a kinetic Monte Carlo (MC) simulation model has been developed to study isochronal annealing of defects in SiC between cascade events. The defects are produced by a 10 keV Si cascades in a molecular dynamics (MD) simulation cell, and these defects are then accurately transferred to defect lattice sites in the Monte Carlo model to investigate defect recovery. By transferring defects states back and forth between the MD and MC environments, damage accumulation can be investigated as a function of temperature. Charged particle irradiations are often used to simulate radiation damage from neutrons and radioactive decay; however, at extreme charged-particle fluxes used in irradiation studies to simulate radiation damage in nuclear materials, the ratio of ionization rate to displacement rate can have a significant impact on observed temperature-dependent processes, which can affect both interpretation and model development. At high charged-particle fluxes, the defect recovery rates in SiC increase nearly linearly with the ratio of ionization rate to displacement rate. A fundamental understanding of these ionization effects is needed if charged particle irradiation results are to be used to develop predictive models of damage evolution in nuclear materials, such as SiC, as functions of time, temperature and dose rates.
Characteristics of Radiation-induced Defects in Fluorite Structure Oxides Formed by Electron Irradiation
Authors: Yasuda Kazuhiro , Yasunaga Kazufumi , Matsumura Syo , Sonoda Takeshi 
Published: April 2011

AbstractOxide ceramics with fluorite structure attracts considerable attention as a host of inert matrix fuels and a transmutation target for minor actinides and long life fission products. We will report the characteristic features of defect clusters in oxide ceramics with fluorite structure, such as yttria stabilized zirconia (YSZ: 13 mol% Y2O3-ZrO2), ceria (CeO2), which were investigated in situ by transmission electron microscopy under electron irradiation. Results on calcium fluorite (CaF2) will be also shown for a comparison [1]. Electron irradiation with 100 to 1000 keV was found to induce large defect clusters in YSZ, which accompany strong black/black lobes contrast and multiply dislocation networks when they grow to a critical diameter of about 1.0 ìm. The defect clusters were considered to be charged oxygen platelets formed by the selective displacement damage of oxygen sublattice. A large difference in mass of constituent ions (O and Zr/Y ions) attributes the selective displacement damage under electron irradiation [2]. Similar defect clusters with strong diffraction contrast were formed in CaF2 under 200 keV electron irradiation, and they also multiplied dislocations at a critical diameter [1]. In the case of CeO2, a higher density of defect clusters was formed compared with YSZ and CaF2. Defect clusters formed under electron irradiation less than 1250 keV were found to be faulted-prismatic-interstitial loops lying on {111} planes with Burgers vector parallel to <111> directions [3], whereas electron irradiation with 1500, 2000 and 3000 keV induces perfect dislocation loops of 1/2<110>{110} in nature. Formation of radiation-induced defects is found to depend on electron energy for crystals with fluorite structure investigated in this study. Results will be discussed through selective displacement damage and charge accumulation. This work was financially supported by the Budget for Nuclear Research of MEXT, based on the screening and counseling by the Atomic Energy Commission, and by the Grant-in-Aid for Scientific Research (B) from JSPS. [1] M. Watanabe, T. Noma, K. Yasuda, K. Yasunaga, S. Matsumura and C. Kinoshita, Proc. of 16th Electron Mmicroscopy Congress, (2006) 1854. [2] K. Yasuda, C. Kinoshita, S. Matsumura, A.I. Ryazanov, J. Nucl. Mater., 319 (2003) 74. [3] K. Yasunaga, K. Yasuda, S. Matsumura and T. Sonoda, Nucl. Instr. and Meth. B, 250 (2006) 114.
Investigation of Thermoelectric Materials: Substitution effect of Bi on the Ag1-xPb18MTe20 (M = Sb, Bi) (x = 0, 0.14, 0.3)
Authors: Han Mi-kyung , Kong Huijun , Uher Ctirad , Kanatzidis Mercouri G 
Published: April 2011

AbstractWe performed comparative investigations of the Ag1-xPb18MTe20 (M = Bi, Sb) (x = 0, 0.14, 0.3) system to better understand the roles of Sb and Bi on the thermoelectric properties. In both systems, the electrical conductivity nearly keeps the same values, while the Seebeck coefficient decreases dramatically in going from Sb to Bi. Compared to the lattice thermal conductivity of PbTe, that of AgPb18BiTe20 is substantially reduced. The lattice thermal conductivity of the Bi analog, however, is higher than that of AgPb18SbTe20 and this is attributed largely to the decrease in the degree of mass fluctuation between the nanostructures and the matrix (for the Bi analog). As a result the dimensionless figure of merit ZT of Ag1-xPb18MTe20 (M = Bi) is found to be smaller than that of Ag1-xPb18MTe20 (M = Sb).
Variation in the Einstein Temperature of Guest Atoms in Ba-Ge-X type-III Clathrate Compounds
Authors: Tanaka Katsushi , Kim Jung-Hwan , Kishida Kyosuke , Inui Haruyuki 
Published: April 2011

AbstractEinstein temperatures of guest atoms in Ba-Ge-(Al, In) type-III clathrate compounds have been estimated from the temperature dependence of the atomic displacement parameters determined by synchrotron X-ray powder diffractions. The lowest temperature is obtained for the vibration of Ba(2) atoms along the x-direction, which corresponds to the “rattling motion” of the guest atoms in the compounds. The temperature estimated is significantly low of about 50 K, which agrees with the fact that the compounds have small lattice thermal conductivities of about 0.6 W/mK. Though the lattice thermal conductivity of Ba24Ge88Al12 is larger than that of Ba24Ge88In12, the Einstein temperature of Ba24Ge88Al12 is slightly smaller than that of Ba24Ge88In12. This discrepancy can be explained by the consideration of higher Debye temperature of Ba24Ge88Al12 than that of Ba24Ge88In12, that is, lattice thermal conductivity without “rattling motion” is larger for Ba24Ge88Al12 than that for Ba24Ge88In12.
Synthesis and Thermoelectric Properties of Y Doped SrTiO3by Modified Pechini's Method
Authors: Takenouchi Hirofumi , Imai Tomohiro , Mae Hideo , Fujimoto Masakatsu , Kineri Tohru , Iida Tsutomu , Hamada Noriaki , Watanabe Tsuneo , Nishio Keishi 
Published: April 2011

AbstractThermoelectric properties of Sr1-xYxTiO3(x = 0-0.08) were calculated using a virtual crystal method. Using a Pechini's method, Sr1-xYxTiO3(x = 0-0.06) precursor powder was prepared. Using this method, we prepared pure SrTiO3at a lower temperature than would be using the conventional solid-state reaction method. The precursor solution was heated at 823 K for 5 h after drying at 353 K for 8 h to produce the precursor powder. The powder was sintered using a hot pressing technique. The relative densities of ceramics were more than 98%. The Seebeck coefficient and electrical conductivity of the samples were measured using the standard four-probe method in a flowing He gas atmosphere in a temperature range of 323 to 923 K. The conductivities of SrTiO3, Sr0.97Y0.03TiO3, and Sr0.94Y0.06TiO3at room temperature were 6.61 × 102, 5.61 × 103, and 1.58 × 104S/m, respectively. The Seebeck coefficients of SrTiO3, Sr0.97Y0.03TiO3, and Sr0.94Y0.06TiO3at room temperature were -548, -264, and -196 μV/K, respectively.
Fabrication of Mg2Si from a Reused-silicon Source and its Thermoelectric Characteristics
Authors: Akasaka Masayasu , Iida Tsutomu , Mito Youhiko , Omori Takeru , Oguni Yohei , Yokoyama Shigeki , Nishio Keishi , Takanashi Yoshifumi 
Published: April 2011

AbstractPolycrystalline Mg2Si was fabricated from a reused-Silicon source, based on Si sludge, using Spark Plasma Sintering technique. The n-type and p-type dopants, bismuth (Bi) and silver (Ag), respectively, were incorporated into the Mg2Si. The thermoelectric properties were estimated from 300 to 873K. The power factors of undoped and Bi-doped samples from the reused-Si source were comparable to those from a solar grade Si source (99.99999%). The power factor was estimated to be 2.5 × 10-5 W/cmK2 for the Bi-doped sample from the reused-Si source. However, the power factor of the Ag-doped, p-type sample from the reused-Si source was lower than that from solar grade Si source. The dimensionless figures of merit of samples from the resused-Si source were slightly lower than those from a solar grade Si source. The dimensionless figure of merit was estimated to be 0.53 at 812 K for Bi-doped sample from the reused-Si source.
LSCO Ceramics as Possible Thermoelectric Material for Low Temperature Applications
Authors: Rodríguez Julio E. 
Published: April 2011

AbstractSeebeck coefficient S(T), thermal conductivity κ(T) and electrical resistivity ρ(T) measurements on polycrystalline La1.85Sr0.15CuO4-δ(LSCO) compounds grown by solid-state reaction method were carried out in the temperature range between 100 and 290K. The obtained samples were submitted to annealing processes of different duration in order to modify their oxygen stoichiometry. The Seebeck coefficient is positive over the measured temperature range and its magnitude increases with the annealing time up to reach values close to 150 µV/K. The electrical resistivity exhibits a metallic behavior, in all samples, ρ(T) takes values less than 1mΩ-cm. As the annealing time increases, the total thermal conductivity increases up to values close to 3 W/K-m. From S(T), κ(T) and ρ(T) data, the thermoelectric power factor (PF) and the dimensionless figure of merit (ZT) were determined. These parameters reach maximum values around 25 µW/K2-cm and 0.18, respectively. The observed behavior in the transport properties become these compounds potential thermoelectric materials, which could be used in low temperature thermoelectric applications.
Investigations of Bonding in Skutterudites by Electron Energy-Loss Spectroscopy
Authors: Prytz Oystein , Saterli Ragnhild , Holmestad Randi , Tafto Johan 
Published: April 2011

AbstractThe local electronic structure of phosphorus in the binary skutterudites CoP3 and NiP3, and in the filled skutterudite LaFe4P12 are studied using a combination of electron energy-loss spectroscopy and ab initio calculations. Relative to CoP3 we observe a filling of phosphorus s and d states in NiP3, while for LaFe4P12 increased EELS intensity indicates more empty s and d states close to the Fermi-level.
Preparation and Characterization of High Temperature Thermoelectrics Based on Metal/Oxide Nanocomposites
Authors: Gregory Otto J. , Chen Ximing , Fralick Gustave C. , Wrbanek John 
Published: April 2011

AbstractThermoelectric devices based on “n-type” oxide semiconductors and metal/oxide nanocomposites are being considered for high temperature thermocouples, heat flux sensors and energy harvesting devices. In terms of energy harvesting, preliminary 2D thermoelectric calculations indicated that enough electrical energy can be generated from the large thermal gradients that exist within a gas turbine engine to power active wireless devices. Several promising bi-ceramic junctions based on this concept were investigated in terms of their high temperature thermoelectric properties. The most promising bi-ceramic junction was based on indium tin oxide (ITO) and a NiCrCoAlY/alumina nanocomposite. The thermoelectric responses of these individual elements were evaluated relative to a platinum reference electrode. A maximum emf of 77 mV was achieved for a NiCrCoAlY/alumina nanocomposite/platinum thermocouple for an imposed temperature gradient of 1111 °C. The thermoelectric power for this couple was 78 μV/°C. When this NiCrCoAlY/alumina nanocomposite was combined with ITO to form a bi-ceramic junction, thermoelectric powers on the order of 700 μV/°C were obtained. A maximum electromotive force of 291mV was achieved for a hot junction temperature of 1100 °C. The thermoelectric response after repeated thermal cycling to 1200 °C was both repeatable and reproducible. The ITO was prepared in varying nitrogen, oxygen and argon partial pressures, which was used to control the charge carrier concentration, stability and thermoelectric response of the bi-ceramic junctions. The thermoelectric response decreased with increasing nitrogen partial pressure and increased with oxygen partial pressure in the plasma with the argon partial pressure constant. The relationship between the sputtering parameters and thermoelectric properties was investigated and the application of these bi-ceramic junctions as thermocouples and energy harvesting devices is discussed.
Thermoelectric Properties of Nearly Single-Phase Half-Heusler NbCoSn Alloys and Importance of Microstructures for Improving Performance
Authors: Kimura Yoshisato , Tamura Yukio , Kita Takuji 
Published: April 2011

AbstractIn order to evaluate the thermoelectric properties of n-type half-Heusler compound NbCoSn, single-phase NbCoSn alloy was prepared using directional solidification based on the phase diagram information of the Nb-Co-Sn ternary system which was investigated in this work. The isotherm at 1273 K and the reaction scheme together with the projection of liquidus surface were determined. Thermoelectric properties of NbCoSn based alloys were evaluated by Seebeck coefficient, electrical resistivity and power factor, which were measured in a temperature range from room temperature to 1073 K. NbCoSn has excellent values of Seebeck coefficient exceeding -250 μV/K at around 900 K and shows the metal-like temperature dependence of electrical resistivity.
Origin of Giant Seebeck Coefficient for High Density 2DEGs Confined in the SrTiO3/SrTi0.8Nb0.2O3 Superlattices
Authors: Mune Yoriko , Ohta Hiromichi , Mizoguchi Teruyasu , Ikuhara Yuichi , Koumoto Kunihito 
Published: April 2011

AbstractRecently, we have found that high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO3 exhibits extremely large Seebeck coefficient (|S|2D) [REF], approximately five times larger than |S|3D. Here we clarify the origin of giant |S|2D using [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]20 (x = 1∼60, y = 1∼20) superlattices. The |S|2D value increased proportionally to y{0.5, indicating that the density of states of the conduction band increases with decreasing y (quantum size effect). Superlattices of [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z (x = 0∼60, y = 1∼20, z = 20) were fabricated on the (001)-face of LaAlO3 substrate by PLD using RHEED to count the number of SrTiO3 or SrTi0.8Nb0.2O3 layers. HR-XRD and HAADF-STEM studies revealed that high-quality [(SrTiO3)17/(SrTi0.8Nb0.2O3)y]z superlattices were successfully fabricated. A dramatic increase of |S|2D is seen with decreasing y-value of the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices. The slope for the plots of log |S|2D - log y is -0.5, and reached 290 μVK−1 (y = 1), which is ∼5 times larger than that of the SrTi0.8Nb0.2O3 bulk (|S|3D = 61 μVK−1). Further, the |S|2D value monotonically increases with x-value and is saturated when x-value > 16 (6.25 nm). We clarified that the critical barrier thickness for electron tunneling in [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattice is 6.25 nm (16 unit cell layers of SrTiO3). The present results give very important information to utilize the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices for practical application.
New Approach for the Synthesis of IV-VI Thermoelectric Thin Film Materials and Devices on Si: (211) PbSnSeTe/ZnTe/Si Heterostructures
Authors: Taylor Patrick J. , Morgan Brian , Dhar Nibir K. , Chen Y. 
Published: April 2011

AbstractLow-dimensional thin-film thermoelectric materials including superlattices and quantum-dot heterostructures have shown significant potential for improving the thermoelectric properties. Highly structured thin film materials such as these would be useful for integrated microdevices such as power MEMS and thermally triggered MEMS actuators. For reasons including scalability and ease-of-integration, silicon is the choice material for the substrate, however there is a lattice and a thermal-expansion mismatch. In this work, a new approach for the synthesis of integrated PbSnSeTe based thermoelectric thin film materials on silicon is demonstrated by employing an epitaxial buffer layer of II-VI compound telluride materials (e.g., ZnTe, CdTe) to help bridge the lattice and thermal expansion mismatches with silicon. This multilayer can be used for subsequent growth of thick films having low-dimensionality structures. We report the initial results from studying the structural and thermoelectric properties of simple solid-solution alloy PbSnSeTe thin films on ZnTe/Si heterostructures. Data from transmission electron microscopy and in-situ electron diffraction will be presented that shows that despite the large lattice mismatch with silicon and the three different crystal structures, unusually high structural quality PbSnSeTe has been obtained by matching the (211) lattice symmetry and the lattice spacing along the [110] directions of the ZnTe and PbSnSeTe. The structural quality of the PbSnSeTe was studied by measuring the dislocation density through etch-pit counting and x-ray diffraction. Results presented will show that a dislocation density as low as 1.2 × 106/cm2can be achieved by strategic lattice-matching between the buffer and thermoelectric layers. Electrical resistivity, doping density, and Seebeck coefficient values for solid-solution alloys without low-dimensional structuring will be shown to approach those of high-performance bulk.
Enhanced Seebeck Coefficient of Amorphous Oxide Semiconductor Superlattices
Authors: Ohta Hiromichi , Huang Rong , Ikuhara Yuichi 
Published: April 2011

AbstractWe propose herein that amorphous oxide semiconductor (AOS) superlattices, which can be deposited on various substrate including glasses or plastics without any substrate heating, are appropriate for the realization of superlattice thermoelectric devices. As an example, thermoelectric properties of AOS superlattices composed of a-In-Zn-O (well) and a-In-Ga-Zn-O (barrier) layers, fabricated on SiO2 glass substrate by pulsed laser deposition at room temperature, were measured to clarify whether enhancement of Seebeck coefficient |S| occurs or not. The |S|2D value increases drastically with decreasing a-In-Zn-O thickness (dIZO) when the dIZO is < ∼5 nm, and reached 73 μV·K-1 (dIZO = 0.3 nm), which is ∼4 times larger than that of bulk |S|3D (19 μV·K-1), while it kept high electrical conductivity, clearly demonstrating that the quantum size effect can be utilized in AOS superlattices.