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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO 4 [Accommodation of High Transformation Strain in Battery Electrodes via Formation of Nanoscale Intermediate Phases: Operando Structure Investigation of Olivine Sodium Iron Phosphate]

Virtually all intercalation compounds used as battery electrodes exhibit significant changes in unit cell volume during use. Na x FePO 4 (0 < x < 1, NFP) olivine, of interest as a cathode for sodium-ion batteries, is a model for topotactic, high strain systems as it exhibits one of the largest discontinuous volume changes (~17% by volume) during its first-order transition between two otherwise isostructural phases. Using synchrotron radiation powder X-ray diffraction (PXD) and pair distribution function (PDF) analysis, we discover a new strain-accommodation mechanism wherein a third, <10 nm scale nanocrystalline phase forms to buffer the large lattice mismatch between primary phases. The new phase has a and b lattice parameters matching one crystalline endmember phase and c lattice parameter matching the other, and is not detectable by powder diffraction alone. Finally, we suggest that this strain-accommodation mechanism may apply to systems with large transformation strains but in which true “amorphization” does not occur.

25 ENERGY STORAGE↗
DOE OSTI2017

Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν 3 / ν 4 CH stretch modes and CH 2 internal rotor dynamics of benzyl radical

Highly reactive benzyl radicals are generated by electron dissociative attachment to benzyl chloride doped into a neon–hydrogen–helium discharge and immediately cooled to T rot = 15 K in a high density, supersonic slit expansion environment. The sub-Doppler spectra are fit to an asymmetric-top rotational Hamiltonian, thereby yielding spectroscopic constants for the ground (v = 0) and first excited (v = 1, ν 3 , ν 4 ) vibrational levels of the ground electronic state. The rotational constants obtained for the ground state are in good agreement with previous laser induced fluorescence measurements (LIF), with vibrational band origins (ν 3 = 3073.2350 ± 0.0006 cm –1 , ν 4 = 3067.0576 ± 0.0006 cm –1 ) in agreement with anharmonically corrected density functional theory calculations. Furthermore, to assist in detection of benzyl radical in the interstellar medium, we have also significantly improved the precision of the ground state rotational constants through combined analysis of the ground state IR and LIF combination differences. Of dynamical interest, there is no evidence in the sub-Doppler spectra for tunneling splittings due to internal rotation of the CH 2 methylene subunit, which implies a significant rotational barrier consistent with partial double bond character in the CC bond. This is further confirmed with high level ab initio calculations at the CCSD(T)-f12b/ccpVdZ-f12 level, which predict a zero-point energy corrected barrier to internal rotation of ΔE tun ≈ 11.45 kcal mol –1 or 4005 cm –1 . In summary, the high-resolution infrared spectra are in excellent agreement with simple physical organic chemistry pictures of a strongly resonance-stabilized benzyl radical with a nearly rigid planar structure due to electron delocalization around the aromatic ring.

Kortyna, A.↗
DOE OSTI2018

Cobalt-substituted SrTi 0.3 Fe 0.7 O 3–δ : a stable high-performance oxygen electrode material for intermediate-temperature solid oxide electrochemical cells

A key need in the development of solid oxide cells (SOCs) is for electrodes that promote fast oxygen reduction and oxygen evolution reactions at reduced operating temperature (≤700 °C), with sufficient durability to allow operation over desired 40 000 h lifetimes. A wide range of electrode materials have been investigated, with some providing resistance low enough for cell operation below 700 °C, but it is generally found that the electrode performance degrades over time. Here we demonstrate an oxygen electrode material, Sr(Ti 0.3 Fe 0.7–x Co x )O 3–δ (STFC), that provides a unique combination of excellent oxygen electrode performance and long-term stability. The addition of a relatively small amount of Co to Sr(Ti 0.3 Fe 0.7 )O 3–δ , e.g., x = 0.07, reduces the electrode polarization resistance by >2 times. The STFC electrode yields stable performance in both fuel cell and electrolysis modes at 1 A cm –2 . The fundamental oxygen diffusion and surface exchange coefficients of STFC are determined, and shown to be substantially better than those of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3–δ , the most widely used SOC oxygen electrode material. Here, while other electrode materials have been shown to exhibit better oxygen transport coefficients than STFC, they do not match its stability.

25 ENERGY STORAGE↗
DOE OSTI2016

Planck intermediate results: XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes

The polarized thermal emission from diffuse Galactic dust is the main foreground present in measurements of the polarization of the cosmic microwave background (CMB) at frequencies above 100 GHz. In this study we exploit the uniqueness of the Planck HFI polarization data from 100 to 353 GHz to measure the polarized dust angular power spectra C ℓ EE and C ℓ BB over the multipole range 40 <ℓ< 600 well away from the Galactic plane. These measurements will bring new insights into interstellar dust physics and allow a precise determination of the level of contamination for CMB polarization experiments. Despite the non-Gaussian and anisotropic nature of Galactic dust, we show that general statistical properties of the emission can be characterized accurately over large fractions of the sky using angular power spectra. The polarization power spectra of the dust are well described by power laws in multipole, C ℓ ∝ ℓ α , with exponents α EE,BB = -2.42 ± 0.02. The amplitudes of the polarization power spectra vary with the average brightness in a way similar to the intensity power spectra. The frequency dependence of the dust polarization spectra is consistent with modified blackbody emission with β d = 1.59 and T d = 19.6 K down to the lowest Planck HFI frequencies. We find a systematic difference between the amplitudes of the Galactic B- and E-modes, C ℓ BB /C ℓ EE = 0.5. We verify that these general properties are preserved towards high Galactic latitudes with low dust column densities. We show that even in the faintest dust-emitting regions there are no “clean” windows in the sky where primordial CMB B-mode polarization measurements could be made without subtraction of foreground emission. Finally, we investigate the level of dust polarization in the specific field recently targeted by the BICEP2 experiment. Extrapolation of the Planck 353 GHz data to 150 GHz gives a dust power D ℓ BB ≡ ℓ(ℓ+1)C ℓ BB /(2π) of 1.32 × 10 -2 μK CMB 2 over the multipole range of the primordial recombination bump (40 <ℓ< 120); the statistical uncertainty is ± 0.29 × 10 -2 μK CMB 2 and there is an additional uncertainty (+0.28, -0.24) × 10 -2 μK CMB 2 from the extrapolation. Finally, this level is the same magnitude as reported by BICEP2 over this ℓ range, which highlights the need for assessment of the polarized dust signal even in the cleanest windows of the sky.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Reactive intermediates in {sup 4}He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

Singlet dihydroxycarbene (HOC{sup ¨}OH) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μ{sub a}, μ{sub b}) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HOC{sup ¨}OH torsional interconversion and tautomerization barriers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Reactive scattering calculations for {sup 87}Rb+{sup 87}RbHe→Rb{sub 2}({sup 3}Σ{sub u}{sup +},v)+He from ultralow to intermediate energies

We investigate atom-diatom reactive collisions, as a preliminary step, in order to assess the possibility of forming Rb{sub 2} molecules in their lowest triplet electronic state by cold collisions of rubidium atoms on the surface of helium nanodroplets. A simple model related to the well-known Rosen treatment of linear triatomic molecules [N. Rosen, J. Chem. Phys. 1, 319 (1933)] in relative coordinates is used, allowing to estimate reactive probabilities for different values of the total angular momentum. The best available full dimensional potential energy surface [Guillon et al., J. Chem. Phys. 136, 174307 (2012)] is employed through the calculations. Noticeable values of the probabilities in the ultracold regime, which numerically fulfill the Wigner threshold law, support the feasibility of the process. The rubidium dimer is mainly produced at high vibrational states, and the reactivity is more efficient for a bosonic helium partner than when the fermion species is considered.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Velocity map imaging of O-atom products from UV photodissociation of the CH{sub 2}OO Criegee intermediate

UV excitation of jet-cooled CH{sub 2}OO X{sup 1}A′ to the excited B{sup 1}A′ electronic states results in dissociation to two spin-allowed product channels: H{sub 2}CO X{sup 1}A{sub 1} + O {sup 1}D and H{sub 2}CO a{sup 3}A″ + O {sup 3}P. In this study, the higher energy H{sub 2}CO a{sup 3}A″ + O {sup 3}P channel is characterized by velocity map imaging and UV action spectroscopy, in both cases utilizing 2 + 1 resonance enhanced multiphoton ionization detection of O {sup 3}P products, which complements a prior experimental study on the lower energy H{sub 2}CO X{sup 1}A{sub 1} + O {sup 1}D channel [Lehman et al., J. Chem. Phys. 139, 141103 (2013)]. Anisotropic angular distributions indicative of rapid dissociation are obtained at 330 and 350 nm, along with broad and unstructured total kinetic energy distributions that provide insight into the internal excitation of the H{sub 2}CO a{sup 3}A″ co-fragment. A harmonic normal mode analysis points to significant vibrational excitation of the CH{sub 2} wag and C–O stretch modes of the H{sub 2}CO a{sup 3}A″ fragment upon dissociation. At each UV wavelength, the termination of the kinetic energy distribution reveals the energetic threshold for the H{sub 2}CO a{sup 3}A″ + O {sup 3}P product channel of ca. 76 kcal mol{sup −1} (378 nm) and also establishes the dissociation energy from CH{sub 2}OO X{sup 1}A′ to H{sub 2}CO X{sup 1}A{sub 1} + O{sup 1}D products of D{sub 0} ≤ 49.0 ± 0.3 kcal mol{sup −1}, which is in accord with prior theoretical studies. The threshold for the H{sub 2}CO a{sup 3}A″ + O {sup 3}P channel is also evident as a more rapid falloff on the long wavelength side of the O {sup 3}P action spectrum as compared to the previously reported UV absorption spectrum for jet-cooled CH{sub 2}OO [Beames et al., J. Am. Chem. Soc. 134, 20045 (2012)]. Modeling suggests that the O {sup 3}P yield increases uniformly from 378 to 300 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

A new direction for dark matter research: intermediate-mass compact halo objects

The failure to find evidence for elementary particles that could serve as the constituents of dark matter brings to mind suggestions that dark matter might consist of massive compact objects (MACHOs). In particular, it has recently been argued that MACHOs with masses > 15 M ⊙ may have been prolifically produced at the onset of the big bang. Although a variety of astrophysical signatures for primordial MACHOs with masses in this range have been discussed in the literature, we favor a strategy that uses the potential for magnification of stars outside our galaxy due to gravitational microlensing of these stars by MACHOs in the halo of our galaxy. In conclusion, we point out that the effect of the motion of the Earth on the shape of the micro-lensing brightening curves provides a promising approach to testing over the course of next several years the hypothesis that dark matter consists of massive compact objects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗