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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effect of intercalated hydrogen on the electron state of quasi-free graphene on a SiC substrate

To judge the role of intercalated hydrogen in the doping of quasi-free epitaxial graphene, two systems, specifically, (i) the graphene–NH-SiC{0001} and (ii) graphene–hydrogen single layer–NH-SiC{0001} structures (N = 4, 6) are considered. In case (i), the shift of the Dirac point of epitaxial graphene is induced by the electrostatic potential of spontaneous polarization of the substrate; in case (ii), the shift is due to the field of a double electrical layer formed because of the absorption of hydrogen atoms. It is shown that, in case (ii) compared to case (i), the concentration of holes in graphene is higher and the concentration of electrons is lower. This result is consistent with the currently available experimental data.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electronic and Magnetic Structure of Intercalated Graphene Films

Ab initio calculations of the electron spectrum of the graphene–cobalt–nickel system were performed in the slope of the spin density functional theory (SDFT). Dispersion curves E{sub σn}(k) are presented; they were used to determine partial and total densities of valence electron states, and also magnetic moments of all atoms in the supercell. Energy position of the “Dirac cone” defined by p{sub z} states in graphene is shown to depend only slightly on the number of Co layers intercalated into the gap between the cobalt and graphene layers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Electrical Properties of Intercalated Ag{sub x}MoSe{sub 2} Compounds in Constant and Alternating Fields

On intercalated Ag{sub x}MoSe{sub 2} samples, in addition to temperature measurements of the direct current electrical resistivity, measurements of the alternating current resistivity using the impedance spectroscopy technique are carried out in a wide frequency range and at different temperatures. The activation behavior of the d.c. conductivity, which increases with increasing silver content in the samples, is shown. The a.c. conductivity undergoes frequency dispersion, described by a “universal dynamic response” (UDR). It is shown that the relaxation processes during charge transfer in a variable field are accelerated with increasing silver content in the samples and with increasing temperature. The data obtained are analyzed using the models of the band and hopping conduction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Intercalation of Platinum into a Graphene Film Formed on Molybdenum Carbide Mo{sub 2}C

It has been shown that platinum atoms evaporation on graphene covering molybdenum carbide Mo{sub 2}C at T = 1000 K causes platinum intercalation into the graphene. In such a case, a continuous multilayer platinum film grows under the graphene, which makes it possible to distinguish graphene-related components in the complex Auger spectrum of carbon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Lithium Intercalation in Core-Shell Materials-Theoretical Analysis

Core-shell composite structures are potential candidates for Li-ion battery electrodes as they can take advantage of materials with higher energy density and materials with higher cyclability. This paper derives an analytical solution for isotropic 1-dimensional diffusion with galvanostatic boundary condition in composite slab, cylinder and sphere using separation of variables method. A general interfacial condition has been used to represent the dynamics at the interface of the composite material rendering the solution useful for wide variety of battery materials. Using the derived analytical solution for diffusion, intercalation induced stresses were estimated for spherical core-shell materials. (C) 2014 The Electrochemical Society. All rights reserved.

Suthar, B↗
DOE OSTI2017

Insights into the Li Intercalation and SEI Formation on LiSi Nanoclusters

We report a first-principles atomic level assessment of the lithiation and reactivity of pre-lithiated Si clusters. Density functional theory formation energy calculations reveal that the pre-lithiated Li 16 Si 16 cluster exposed to two different Li fluxes can store Li between the concentrations of Li 2.5 Si and Li 3.5 Si. This increase in storage capacity is attributed to the start of an amorphization process in the cluster, and more importantly these results show that the intercalation reaction can be controlled by the flux of the Li-ions. However, in a real battery, the lithiation of the anode occurs simultaneously to the electrode-electrolyte reactions. Here we simulate the solid-electrolyte interphase (SEI) formation and simultaneous lithiation of a Li 16 Si 16 cluster in contact with two different electrolyte solutions: one with pure ethylene carbonate (EC), and another with a 1 M solution of LiPF 6 in EC. Our ab initio molecular dynamics simulations show that the solvent and salt are decomposed leading to the initial stages of the SEI layer formation and large part of the added Li becomes part of the SEI. Interestingly, the pure EC solution results in lower storage capacity and higher reactivity, whereas the presence of the salt causes the opposite effect: higher lithiation and reduced reactivity.

25 ENERGY STORAGE↗
NASA NTRS1971

Electron microscopy and diffraction of layered, superconducting intercalation complexes.

Several layered, transition metal dichalcogenide intercalation complexes with unique superconducting properties have been examined by high-resolution electron microscopy and electron diffraction. Details of the crystalline lattice and of the lattice imperfections have been directly resolved. The results can be correlated with the available X-ray diffraction and chemical data, and they confirm and extend the postulated models.

Fernandez-Moran, H.↗
NASA NTRS1981

Effective masses, relaxation times, and carrier mobilities in some chloride intercalants of graphite

The effective masses, carrier scattering times and carrier mobilities have been measured in selected graphite intercalation compounds using the Shubnikov-de Haas effect at a series of temperatures between 4 and 50 K. Effective masses are less than or equal to 0.1 of the free-electron mass, scattering times are about 10 to the -13th/s and carrier mobilities are on the order of 10,000 sq cm/V s.

Woollam, J. A.↗
NASA NTRS1981

Moderate temperature Na cells. III - Electrochemical and structural studies of Cr0.5V0.5S2 and its Na intercalates

Experimental results are reported on the behavior of a rechargeable Na cell incorporating a Cr0.5V0.5S2 cathode. The cell operates at 130 C and uses as electrolyte a 1M solution of NaI in 1,2-bis(2-methoxy-ethoxy)ethane (triglyme). The mechanism of discharge of Cr0.5V0.5S2 involves Na intercalation. It is found that the maximum rechargeable capacity of the Cr0.5V0.5S2 cathode is 0.7 e(overbar)/mol. With an average cell voltage of 1.9 V, the theoretical specific energy of the cathode is 273 W-hr/kg.

Abraham, K. M.↗
NASA NTRS1985

Intercalated-Carbon Low-Resistivity Fibers

Experiments show feasiblity of making lightweight, electrically conductive fibers from graphite intercalation compounds. Fibers thermally stable in air up to 100 degrees C. These materials used as ingredients in composite enclosures for electronic equipment, especially where such equipment must be both light in weight and electrically conductive for electrostatic drainage or radio-frequency suppression.

Yavrouian, A. H.↗
NASA NTRS1985

The 13C nuclear magnetic resonance in graphite intercalation compounds

The (13)C NMR chemical shifts of graphite intercalation compounds were calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about -140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

Tsang, T.↗
NASA NTRS1984

Diamagnetism and charge transfer in graphite intercalation compounds

The magnetic susceptibilities at 300 K of the acceptor-type intercalation compounds of graphite with Br2 and ICl are calculated; the results are compared with published experimental measurements in graphs; and the charge-transfer parameter f is inferred using a rigid-band model (Loughin et al., 1978; Weinberger et al., 1978; Mattix et al., 1983). Assuming a screening length of 200 pm, the values determined are f = 0.3 for C(8N)Br2 and f = 0.09 for C(13N)ICl.

Tsang, T.↗
NASA NTRS1985

C-13 nuclear magnetic resonance in graphite intercalation compounds

The C-13 NMR chemical shifts of graphite intercalation compounds have been calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about - 140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal-conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

Tsang, T.↗
NASA NTRS1986

Simultaneous electrical resistivity and mass uptake measurements in bromine intercalated fibers

Changes in mass and electrical resistivity of several types of pitch-based and vapor-grown graphite fibers were monitored during reaction with bromine. The observed threshold pressure dependent reaction suggested that the fibers were intercalated. In the fully brominated compound, the mass was increased by 44 percent and the resistivity was improved by a factor of 17. In the residue compound, the mass was increased by 22 percent and the resistivity was improved by a factor of 5. Fibers possessing different degrees of graphitization had surprisingly similar changes in both mass and resistivity.

Jaworske, D. A.↗
NASA NTRS1988

Production and characterization of CdCl2 intercalated graphite fibers

Graphite fibers were intercalated using CdCl2 as a Cl source and Cl2 as carrier gas. Fibers were synthesized with a resistivity-density figure of merit comparable to that of copper. These fibers can withstand practical electrical current densities as high as 54,000 A/sq cm. Their thermal coefficient of resistivity is 0.0016 C, which is approximately 41 percent of those for copper and aluminum.

Gooden, Clarence E.↗
NASA NTRS1992

Kinetics of intercalation of lithium into NbSe3 and TiS2 cathodes

Titanium disulfide and niobium triselenide are two well-studied candidate materials for positive electrodes in rechargeable lithium cells. A comparative study of the kinetics of intercalation of lithium in both the cathodes is made here based on various electrochemical techniques, i.e., linear polarization, potentiodynamic polarization, and ac impedance under different experimental conditions such as prismatic or disk configuration of fresh, partially discharged, or cycled electrode. Further, the diffusion coefficients of lithium ions in these cathodes are estimated under these conditions using conventional techniques, i.e., ac impedance, chronocoulometry, chronoamperometry, and current pulse relaxation. Based on the values of the diffusion coefficients, the applicability of these methods for the determination of diffusion coefficients is discussed.

Ratnakumar, B. V.↗
NASA NTRS1993

Intercalated hybrid graphite fiber composite

The invention is directed to a highly conductive lightweight hybrid material and methods of producing the same. The hybrid composite is obtained by weaving strands of a high strength carbon or graphite fiber into a fabric-like structure, depositing a layer of carbon onto the structure, heat treating the structure to graphitize the carbon layer, and intercalating the graphitic carbon layer structure. A laminate composite material useful for protection against lightning strikes comprises at least one layer of the hybrid material over at least one layer of high strength carbon or graphite fibers. The composite material of the present invention is compatible with matrix compounds, has a coefficient of thermal expansion which is the same as underlying fiber layers, and is resistant to galvanic corrosion in addition to being highly conductive. These materials are useful in the aerospace industry, in particular as lightning strike protection for airplanes.

Gaier, James R.↗