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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Effect of Composition and Local Environment on CO 2 Adsorption on Nickel and Magnesium Oxide Solid Solutions

CO 2 adsorption energies on the (100) surfaces of a nickel oxide doped with Mg, magnesium oxide doped with Ni, and their 50:50 solid solution were calculated using density functional theory. The composition and atomic arrangement of the adsorption site was varied to understand how the local environment affects CO 2 adsorption and the basicity of the surfaces at the atomic level. The dispersive and electronic contributions to the adsorption energies were quantified, and the results indicate that the variation of the adsorption energy with adsorption site configuration and metal composition is dominated by electronic interactions. Interestingly, for magnesium oxide doped with nickel, a single substitution can create stronger CO 2 binding sites, which implies stronger basic sites, even though nickel oxide is less basic than magnesium oxide. The effect of double substitution at the binding site can be reasonably approximated by summing the effects of single substitutions. Furthermore, this work provides guidance for the preparation of metal oxides with tailored Lewis basicity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Absence of Nanostructuring in NaPb m SbTe m+2 : Solid Solutions with High Thermoelectric Performance in the Intermediate Temperature Regime

Thermoelectric devices directly convert heat into electrical energy and are highly desired for emerging applications in waste heat recovery. Currently, PbTe based compounds are the leading thermoelectric materials in the intermediate temperature regime (~800 K); however, integration into commercial devices has been limited. This is largely because the performance of PbTe, which is maximized ~900 K, is too low over the temperatures of interest for most potential commercial applications (generally under 600 K). Improving the low temperature performance of PbTe based materials is therefore critical to achieve usage outside of existing niche applications. Here, we provide an in-depth study of the cubic NaPb m SbTe m+2 system of compounds (m = 1-20) and report that it is an excellent class of low- to medium-temperature thermoelectrics when m = 10-20. Here, we show that the as-cast polycrystalline ingots exhibit degenerate p-type conduction and high maximum ZTs of 1.2-1.4 at 650 K when m = 6-20. Because the ingots are found to be extremely brittle, we utilize spark plasma sintering (SPS) to prepare more mechanically robust samples, and surprisingly, find that SPS results in an undesired change in charge transport toward n-type behavior. We show this unanticipated transition from p-type behavior as ingots to n-type after SPS is due to dissolution of secondary phases that are present in the ingots into the primary matrix during the SPS process, resulting in a transformation from an inhomogeneous state to a solid solution without any observable evidence of nanoscale precipitation. This is in sharp contrast to the seemingly similar AgPb m SbTe m+2 (LAST) system, which is heavily nanostructured. The SPSed NaPb m SbTe m+2 is doped p-type by tuning the cation stoichiometry, i.e., Na 1+x Pb m-x Sb 1-y Te m+2 . The optimized compounds have very low lattice thermal conductivities of 1.1-0.55 W·m -1 ·K -1 over 300-650 K, which enhances the low intermediate temperature performance and gives rise to maximum ZT values up to 1.6 at 673 K as well as an excellent ZT avg of 1.1 over 323-673 K for m = 10, 20, making Na 1+x Pb m-x Sb 1-y Te m+2 among the highest performing PbTe-based thermoelectrics under 650 K.

Electrical conductivity↗
DOE OSTI2014

Sample-Averaged Biexciton Quantum Yield Measured by Solution-Phase Photon Correlation

The brightness of nanoscale optical materials such as semiconductor nanocrystals is currently limited in high excitation flux applications by inefficient multiexciton fluorescence. We have devised a solution-phase photon correlation measurement that can conveniently and reliably measure the average biexciton-to-exciton quantum yield ratio of an entire sample without user selection bias. This technique can be used to investigate the multiexciton recombination dynamics of a broad scope of synthetically underdeveloped materials, including those with low exciton quantum yields and poor fluorescence stability. Here in this study, we have applied this method to measure weak biexciton fluorescence in samples of visible-emitting InP/ZnS and InAs/ZnS core/shell nanocrystals, and to demonstrate that a rapid CdS shell growth procedure can markedly increase the biexciton fluorescence of CdSe nanocrystals.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Design principles for electronic charge transport in solution-processed vertically stacked 2D perovskite quantum wells

State-of-the-art quantum-well-based devices such as photovoltaics, photodetectors, and light-emission devices are enabled by understanding the nature and the exact mechanism of electronic charge transport. Ruddlesden–Popper phase halide perovskites are two-dimensional solution-processed quantum wells and have recently emerged as highly efficient semiconductors for solar cell approaching 14% in power conversion efficiency. However, further improvements will require an understanding of the charge transport mechanisms, which are currently unknown and further complicated by the presence of strongly bound excitons. Here, we unambiguously determine that dominant photocurrent collection is through electric field-assisted electron–hole pair separation and transport across the potential barriers. This is revealed by in-depth device characterization, coupled with comprehensive device modeling, which can self-consistently reproduce our experimental findings. These findings establish the fundamental guidelines for the molecular and device design for layered 2D perovskite-based photovoltaics and optoelectronic devices, and are relevant for other similar quantum-confined systems.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unique structural solution from a V H 3-30 antibody targeting the hemagglutinin stem of influenza A viruses

Broadly neutralizing antibodies (bnAbs) targeting conserved influenza A virus (IAV) hemagglutinin (HA) epitopes can provide valuable information for accelerating universal vaccine designs. Here, we report structural details for heterosubtypic recognition of HA from circulating and emerging IAVs by the human antibody 3I14. Somatic hypermutations play a critical role in shaping the HCDR3, which alone and uniquely among V H 3-30 derived antibodies, forms contacts with five sub-pockets within the HA-stem hydrophobic groove. 3I14 light-chain interactions are also key for binding HA and contribute a large buried surface area spanning two HA protomers. Comparison of 3I14 to bnAbs from several defined classes provide insights to the bias selection of V H 3-30 antibodies and reveals that 3I14 represents a novel structural solution within the V H 3-30 repertoire. The structures reported here improve our understanding of cross-group heterosubtypic binding activity, providing the basis for advancing immunogen designs aimed at eliciting a broadly protective response to IAV.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Early stage structural development of prototypical zeolitic imidazolate framework (ZIF) in solution

Given the wide-ranging potential applications of metal organic frameworks (MOFs), an emerging imperative is to understand their formation with atomic scale precision. This will aid in designing syntheses for next-generation MOFs with enhanced properties and functionalities. Major challenges are to characterize the early-stage seeds, and the pathways to framework growth, which require synthesis coupled with in situ structural characterization sensitive to nanoscale structures in solution. Here we report measurements of an in situ synthesis of a prototypical MOF, ZIF-8, utilizing synchrotron X-ray atomic pair distribution function (PDF) analysis optimized for sensitivity to dilute species, complemented by mass spectrometry, electron microscopy, and density functional theory calculations. We observe that despite rapid formation of the crystalline product, a high concentration of Zn(2-MeIm) 4 (2-MeIm=2-methylimidazolate) initially forms and persists as stable clusters over long times. A secondary, amorphous phase also pervades during the synthesis, which has a structural similarity to the final ZIF-8 and may act as an intermediate to the final product.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Monitoring solvent dynamics and ion associations in the formation of cubic octamer polyanion in tetramethylammonium silicate solutions

NMR methods were utilized to monitor the in situ structural and dynamic changes of various species in highly alkaline tetramethylammonium (TMA) silicate solutions. Quantitative 29Si NMR, 1H, 2H, and 17O relaxation NMR, and 1H and 29Si diffusion NMR of silicates, TMA, H2O and D2O demonstrate that the growth of the cubic octamer Q38 is accompanied by reduced water mobility and increasing TMA coordination number per Q38, which reaches an equilibrium value of 4.5 at 15 °C. Temperature-dependent measurements further reveal that the increased control over speciation by TMA at lower temperatures results from the more stable ion associations via slower solvent motions.

Chen, Ying↗
DOE OSTI2013

Ion-pairing in aqueous CaCl 2 and RbBr solutions. Simultaneous structural refinement of XAFS and XRD data

We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (X-ray Absorption/Diffraction Structural Refinement,XADSR), to study hydration and ion pair structure of CaCl 2 and RbBr salts in concentrated aqueous solutions. The XADSR analysis includes the XAFS spectra analysis of both the cation and anion as a probe of their short-range structure with an XRD spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0 m aqueous CaCl 2 reveals that there are an insignificant number of Ca 2+ -Cl- CIP’s, but there are approximately 3.4 SSIP’s separated by about 4.99 Å. In contrast XADSR analysis of aqueous RbBr yields about 0.7 pair CIP at a bond length 3.51 Å. The present work demonstrates a new approach for a direct co-refinement of XRD and XAFS spectra in a simple and reliable fashion, opening new opportunities for analysis in various disordered and crystalline systems. This work was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the U.S. Department of Energy by Battelle.

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

Numerical solution of the Sinanoǧlu equation using a multicentre radial-angular grid

The pair functions that minimize the correlation energy of second-order many-body perturbation (MP2) theory (the Hylleraas functional) are obtained as solutions to the corresponding Sinanoglu equation by expanding them on a six-dimensional, multicenter, radial-angular grid of two electrons. Cusps in the pair functions at the nuclei are described numerically accurately by the multicenter grid. A cusp in each singlet pair function at the coalescence of the two electrons is taken into account analytically by a correlation factor. With a grid of approximately 10,000 points per atom, the MP2 correlation energies for atoms and polyatomic molecules are obtained usually within 0.1 mE h of the complete-basis-set results. The correlation factor, auxiliary basis functions, and a judicious choice of integration algorithms are all necessary to stabilize the grid-based MP2 and underlying Hartree–Fock (HF) calculations. The auxiliary basis set, in particular, largely restores the Hermiticity and diagonal dominance of the Fock matrix as well as furnishes virtual orbitals used in a resolution-of-the-identity approximation to lower the dimension of some integrals. The results of the grid-based HF and MP2 calculations without a correlation factor are found to suffer from large, nonsystematic errors frequently.

Many-body perturbation theory↗