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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Simultaneous measurements of X-ray reflectivity and grazing incidence fluorescence at BL-16 beamline of Indus-2

A new multipurpose x-ray reflectometer station has been developed and augmented at the microfocus beamline (BL-16) of Indus-2 synchrotron radiation source to facilitate synchronous measurements of specular x-ray reflectivity and grazing incidence x-ray fluorescence emission from thin layered structures. The design and various salient features of the x-ray reflectometer are discussed. The performance of the reflectometer has been evaluated by analyzing several thin layered structures having different surface interface properties. The results reveal in-depth information for precise determination of surface and interface properties of thin layered materials demonstrating the immense potential of the combined measurements of x-ray reflectivity and grazing incidence fluorescence on a single reflectometer.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Characterizing mechanical and microstructural properties of novel montmorillonite-rich polyethylene composites

Montmorillonite (MMT) clays are important industrial materials used as catalysts, chemical sorbents and fillers in polymer–clay nanocomposites. The layered structure of these clays has motivated research into further applications of these low-cost materials, including use as ion exchange media and solid-state ionic conductors. In these applications, the mechanical properties of MMT are key when considering long-term, reliable performance. Previous studies have focused on the mechanical properties of nanocomposites with MMT as the minority component or pure MMT thin films. In this work, the microstructure and mechanical properties of pure MMT and majority MMT/polyethylene composites pressed into dense pellets are examined. Characterization methods such as X-ray diffraction, atomic force microscopy and scanning electron microscopy together with nanoindentation reveal important structure–property relationships in the clay-based materials. Here, utilizing these techniques, we have discovered that MMT processing impacts the layered microstructure, chemical stability and, critically, the elastic modulus and hardness of bulk MMT samples. Particularly, the density of the pellets and the ordering of the clay platelets within them strongly influence the elastic modulus and hardness of the pellets. By increasing pressing force or by incorporating secondary components, the density, and therefore mechanical properties, can be increased. If the layered structure of the clay is destroyed by exfoliation, the mechanical properties will be compromised. Understanding these relationships will help guide new studies to engineer mechanically stable MMT-based materials for industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Fluorescent solute-partitioning characterization of layered soft contact lenses

Partitioning of aqueous packaging, wetting, and care-solution agents into and out of soft contact lenses (SCLs) is important for improving wear comfort and also for characterizing lens physico-chemical properties. We illustrate both features of partitioning by application of fluorescent-solute partitioning into DAILIES TOTAL1® (delefilcon A) water-gradient SCLs, which exhibit a layered structure of a silicone-hydrogel (SiHy) core sandwiched between thin surface-gel layers. Two-photon fluorescence confocal laser-scanning microscopy and attenuated total-reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) characterize the lens and assess uptake profiles of six prototypical fluorescent solutes. Comparison of solute uptake in a SiHy-core prototype lens (i.e., O 2 OPTIX™) validates the core SiHy structure of DAILIESTOTAL1®. To establish surface-layer charge, partition coefficients and water contents are obtained for aqueous pH values of 4 and 7.4. Solute fluorescence-intensity profiles clearly confirm a layered structure for the DAILIES TOTAL1® lenses. In all cases, aqueous solute partition coefficients are greater in the surface layers than in the SiHy core, signifying higher water in the surface gels. ATR-FTIR confirms surface-layer mass water contents of 82 ± 3%. Water uptake and hydrophilic-solute uptake at pH 4 compared with that at pH 7.4 reveal that the surface-gel layers are anionic at physiologic pH 7.4, whereas both the SiHy core and O 2 OPTIX™ (lotrafilcon B) are nonionic. Here, we successfully confirm the layered structure of DAILIES TOTAL1®, consisting of an 80-μm-thick SiHy core surrounded by 10-μm-thick polyelectrolyte surface-gel layers of significantly greater water content and aqueous solute uptake compared with the core. Accordingly, fluorescent-solute partitioning in SCLs provides information on gel structure and composition, in addition to quantifying uptake and release amounts and rates.

Attenuated total-reflectance Fourier-transform inf↗
DOE OSTI2021

Iron(II) monosulfide (FeS) minerals reductively transform the insensitive munitions compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO)

As military applications of the insensitive munitions compounds (IMCs) 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO) increase, there is a growing need to understand their environmental fate and to develop remediation strategies to mitigate their impacts. Iron (II) monosulfide (FeS) minerals are abundant in freshwater and marine sediments, marshes, and hydrothermal environments. Here, this study shows that FeS solids can reduce DNAN and NTO to their corresponding amines under anoxic ambient conditions. The reactions between IMCs and the FeS minerals were surface-mediated since they did not occur when only dissolved Fe 2+ (aq) and S 2– (aq) were present. Mackinawite, a tetragonal FeS with a layered structure, reduced DNAN mainly to 2-methoxy-5-nitroaniline (MENA), which in turn was partially reduced to 2-4-diaminoanisole (DAAN). The layered structure of mackinawite provided intercalation sites likely responsible for partial adsorption of MENA and DAAN. Mackinawite entirely reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO). The reduction of IMCs showed concurrent oxidation of mackinawite to goethite and elemental sulfur. A commercial FeS product, composed mainly of pyrrhotite and troilite, reduced DNAN to DAAN and NTO to ATO. At pH 6.5, DNAN and NTO transformation rates were 667 and 912 μmol h –1 m –2 , respectively, on the mackinawite surface and 417 and 1344 μmol h –1 m –2 , respectively, on the commercial FeS surface. This is the first report of the reduction of a nitro-heterocyclic compound (NTO) by FeS minerals. The evidence indicates that DNAN and NTO can be rapidly transformed to their succeeding amines in anoxic subsurface environments and aquatic sediments rich in FeS minerals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Origin, nature, and the dynamic behavior of nanoscale vacancy clusters in Ni-rich layered oxide cathodes

Oxygen and transition metal (TM) vacancies in transition metal oxides (TMOs) play an important role in materials functionalities. For TMO cathodes of Li-ion batteries, vacancies can be introduced, either deliberately or inevitably, during materials synthesis or upon electrochemical cycling. Effects of vacancies on the electrochemical properties of cathodes critically depend on the dynamic characteristics of vacancies during the battery cycling. However, a fundamental understanding of such characteristics in the layer structured cathode remains elusive. Here, using scanning transmission electron microscopy (STEM), we reveal a cycling-induced aggregation behavior of oxygen and TM vacancies in a Ni-rich layer structured cathode of secondary particles. We discover that during the initial charging, vacancies aggregate to form visible vacancy-rich nanoregions (vacancy clusters) firstly at the outer layer of the secondary particle, and then the vacancy-cluster populated region extends to the inner part of particle upon fully charged. The spatial distinction of preferential nucleation of vacancy clusters at the outer layer indicates that the vacancy migration and clustering is associated with Li migration flux, which is larger at the outer layer, as all the Li from the inner part has to go through the outer layer. With extended cycling (> 50), these vacancy clusters become immobilized. We further reveal that the generation of these vacancy clusters is correlated to the material-synthesis conditions. Our findings solve a long-standing puzzle on the origin, nature, and behavior of the commonly visible vacancy clusters in the NMC cathode, providing insights on correlation between properties and dynamic behaviors of atomic-scale defects in layered oxide cathodes.

Li-ion batteries, layered oxide cathodes, NMC, cat↗
DOE OSTI2015

Effects of the slab thickness on the crystal and electronic structures of In{sub 2}O{sub 3}(ZnO){sub m} revealed by first-principles calculations

Many conflicting electron microscopy data for In{sub 2}O{sub 3}(ZnO){sub m} indicate that it may have the polymorphous and polytypoid structures. We investigate their stabilities based on four controversial models. The calculated results confirm that the models with the zigzag feature are more stable than the others and it is possible to form different zigzag configurations in the samples as observed in the experiments. The dynamic process of eliminating the dangling bonds and the requirements of maximizing the symmetry and the distances between the In atoms in the slabs can be regarded as the dominant rules to stabilize the system, but the statistical equilibrium processes have the chances to transform it from the ground state structures to the other model structures. The study of the electronic structures based on the plane and zigzag models reveals that their band gaps and effective masses increase monotonically with m. The predicted band gaps are consistent with the experimental results. The anisotropic feature of electron effective mass tensor exhibited in the plane model differs from that of the zigzag one, which is so notable that can be employed to determine which model is more close to the actual structure of a given sample. The calculated results confirm the possibilities of the separation of conduction electrons and defects and the existence of the natural optimized transport channels in the layered structures, which demonstrate its advantage over ZnO to transport electrons and benefit its applications in the optoelectronic devices. - Graphical abstract: The conduction electrons are mainly distributed around the boundaries of the plane or zigzag shape. The optimized transport channels can be formed around the boundaries. - Highlights: • The formation mechanisms for the polytypoid structure of In{sub 2}O{sub 3}(ZnO){sub m} are revealed. • The predicted band gaps are consistent with the experimental results. • The natural optimized transport channels in the layered structures are confirmed.

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

Liquid crystal mesophases beyond commensurate four-layer periodicity

For more than one decade, SMC* d4 , SmC* d3 , and SmC* A were the only three confirmed commensurate SmC* variant phases with periodicities less than or equal four layers. In 2006, employing ellipsometry and resonant X-ray diffraction (RXRD), our research team first discovered a new liquid crystal mesophase having a six-layer periodicity in one ternary mixture which includes one sulfur-containing compound. From our ellipsometric results, this phase showed antiferroelectric-like optical response. This novel discovery inspired renewed interest to search for liquid crystal mesophases with commensurate periodicities greater than four layers. Soon after, another mesophase having a six-layer structure and showing a ferrielectric-like dielectric response, instead, was uncovered by RXRD measurements on a different binary mixture which has one bromine-containing compound. Meanwhile mesophases having a 5-, 8-, 12- or 15-layer periodicity were reported. However, numerous questions remain to be addressed associated with these unusual reported phases. Theoretical models giving rise to mesophases with periodicities greater than four layers have been developed; but, to date, none of them have provided satisfactory explanations of all the physical phenomena related to the mesophases exhibiting a six-layer structure. Moreover, the question “what is the source of long-range interactions between liquid-like smectic layers, which are responsible for establishing mesophases with long periodicities and mean-field behavior of the smectic-A–smectic-C transition?” remains unanswered for more than three decades.

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

Influence of Zr{sup 4+} doping on structural and electrical properties of SrBi{sub 4}Ti{sub 4}O{sub 15} ceramic

This article reports a systematic study of doping effects on the structural and electrical properties of layer structured strontium bismuth titanate ceramic. In this study monophasic SrBi{sub 4}Ti{sub 4-x}Zr{sub x}O{sub 15} with x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25 ceramics were synthesized from the solid-state reaction route. X-ray diffraction analysis shows that the Zr-modified SBT ceramics have a pure four-layer Aurivillius phase structure. Dielectric properties revealed that the diffuseness of phase transition increases where as corresponding permittivity value decrease with increasing Zr content. Piezoelectric properties of SBTZ ceramics were improved by the modification of Zirconium ion. Moreover, the reason behind for improvement of piezoelectric properties of modified SBTZ ceramics was also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Electrochemical performances of co-substituted (La and Li) LiLa{sub x−y}Li{sub y}Ni{sub 1−x}O{sub 2} cathode materials for rechargeable lithium-ion batteries

Graphical abstract: - Highlights: • LiLa{sub x−y}Li{sub x}Ni{sub 1−x}O{sub 2} powders were prepared by a sol–gel method at 600 °C for 10 h. • LiLa{sub x−y}Li{sub x}Ni{sub 1−x}O{sub 2} powder materials had well defined layer structure, and no impurities. • LiLa{sub 0.10}Li{sub 0.10}Ni{sub 0.80}O{sub 2} crystallite size was reduced compared with those of LiNiO{sub 2}. • Li/LiPF{sub 6}/LiLa{sub x−y}Li{sub x}Ni{sub 1−x}O{sub 2} cells were of high charge/discharge capacity, with columbic efficiency at 25 °C and 45 °C. • LiLa{sub 0.10}Li{sub 0.10}Ni{sub 0.80}O{sub 2} good cyclic stability, rate capability and better 45 °C. - Abstract: Co-substituted LiLa{sub x−y}Li{sub y}Ni{sub 1−x}O{sub 2} cathode materials were synthesized by sol–gel method using aqueous solutions of metal nitrates and tartaric acid as chelating agent at 600 °C for 10 h. The structure and electrochemical properties of the synthesized materials were characterized by using XRD, SEM, EDAX, TEM, cyclic voltammetry, charge/discharge and electrochemical impedance spectroscopy. XRD studies revealed a well defined layer structure and a linear variation of lattice parameters with the addition of lanthanum and lithium confirmed phase pure compounds in a rhombohedral structure. TEM and SEM analysis shows that LiLa{sub 0.10}Li{sub 0.10}Ni{sub 0.80}O{sub 2} has smaller particle size and regular morphological structure with narrow size distribution than those of LiNiO{sub 2}. Variations of dual mixing and hexagonal ordering with the substituted elements have enhanced the charge/discharge capacities at both room (25 °C) and elevated temperatures (45 °C), respectively. LiLa{sub 0.10}Li{sub 0.10}Ni{sub 0.80}O{sub 2} had high charge/discharge capacity, low irreversible capacity and better elevated temperature performance.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Open‐Structured V 2 O 5 · n H 2 O Nanoflakes as Highly Reversible Cathode Material for Monovalent and Multivalent Intercalation Batteries

The high‐capacity cathode material V 2 O 5 · n H 2 O has attracted considerable attention for metal ion batteries due to the multielectron redox reaction during electrochemical processes. It has an expanded layer structure, which can host large ions or multivalent ions. However, structural instability and poor electronic and ionic conductivities greatly handicap its application. Here, in cell tests, self‐assembly V 2 O 5 · n H 2 O nanoflakes shows excellent electrochemical performance with either monovalent or multivalent cation intercalation. They are directly grown on a 3D conductive stainless steel mesh substrate via a simple and green hydrothermal method. Well‐layered nanoflakes are obtained after heat treatment at 300 °C (V 2 O 5 ·0.3H 2 O). Nanoflakes with ultrathin flower petals deliver a stable capacity of 250 mA h g −1 in a Li‐ion cell, 110 mA h g −1 in a Na‐ion cell, and 80 mA h g −1 in an Al‐ion cell in their respective potential ranges (2.0–4.0 V for Li and Na‐ion batteries and 0.1–2.5 V for Al‐ion battery) after 100 cycles.

Wang, Huali↗
DOE OSTI2015

Improve First-Cycle Efficiency and Rate Performance of Layered-Layered Li 1.2 Mn 0.6 Ni 0.2 O 2 Using Oxygen Stabilizing Dopant

The poor first-cycle Coulombic efficiency and rate performance of the Li-rich layered-layered oxides are associated with oxygen gas generation in the first activation charging and sluggish charge transportation along the layers. In this work, we report that barium doping improves the first-cycle efficiency of Li-rich layered-layered Li1.2Mn0.6Ni0.2O2 via suppression of the oxidation of O2– ions in the first charging. This effect can be attributed to the stabilizing effect of the barium cations on the oxygen radical intermediates generated during the oxidation of O2–. Meanwhile, because the stabilized oxygen radicals likely facilitate the charge transportation in the layered-layered structure, the barium-doped Li1.2Mn0.6Ni0.2O2 exhibits significant improvement in rate performance. Stabilizing the oxygen radicals could be a promising strategy to improve the electrochemical performance of Li-rich layered-layered oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Magnetic leverage effects in amorphous SmCo/CoAlZr heterostructures

Although magnetic heterostructures are the basis of many magnetic technologies, the mechanisms involved in magnetization reversals in such structures are not fully understood, especially in amorphous multilayers. Here, we report on the SmCo/CoAlZr system and exploit resonant magnetic x-ray scattering to probe the element specific magnetization reversals. When combined into a tri-layer structure, two different switching fields and reversal mechanisms are observed for the Sm and Co sub-lattices. We argue that the decoupling of the sub-lattices arises from the local distribution of atomic species within the amorphous matrix leading to a strong magnetic leverage effect and exchange pinning. The decoupling arises due to strong interactions between regions of high Co density which span the interface. The relatively sparse interactions between Sm and Co induce a localized pinning of the Co-rich areas, resulting in an exchange bias in minor loops and an enhanced coercivity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

A Monte Carlo study of reflection electron energy loss spectroscopy spectrum of a carbon contaminated surface

It has been experimentally found that the carbon surface contamination influences strongly the spectrum signals in reflection electron energy loss spectroscopy (REELS) especially at low primary electron energy. However, there is still little theoretical work dealing with the carbon contamination effect in REELS. Such a work is required to predict REELS spectrum for layered structural sample, providing an understanding of the experimental phenomena observed. In this study, we present a numerical calculation result on the spatially varying differential inelastic mean free path for a sample made of a carbon contamination layer of varied thickness on a SrTiO{sub 3} substrate. A Monte Carlo simulation model for electron interaction with a layered structural sample is built by combining this inelastic scattering cross-section with the Mott's cross-section for electron elastic scattering. The simulation results have clearly shown that the contribution of the electron energy loss from carbon surface contamination increases with decreasing primary energy due to increased individual scattering processes along trajectory parts carbon contamination layer. Comparison of the simulated spectra for different thicknesses of the carbon contamination layer and for different primary electron energies with experimental spectra clearly identifies that the carbon contamination in the measured sample was in the form of discontinuous islands other than the uniform film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film

In our recent work, record-high solar reflectance (exceeding 99%) has been demonstrated by placing a layer of highly scattering, semitransparent polytetrafluoroethylene (PTFE) sheet on top of a silver film. This can significantly improve the performance of daytime radiative cooling system. Although a PTFE slab of 10-mm thick acts as an excellent diffuse reflector, it is unclear how this dual-layer structure made of a thin PTFE on a mirror-like reflector will alter the bidirectional reflection. Here, we report measurements of the bidirectional reflectance distribution function (BRDF) of the dual-layer structure using a laser scatterometer at the wavelength of 635 nm. Measurements of the BRDF and the bidirectional transmittance distribution function (BTDF) of free-standing PTFE sheets are also performed. The measured BRDF for a PTFE sheet as thin as 236 μm on Ag is essentially diffuse except at large incidence angles. A Monte Carlo ray-tracing method incorporating both surface scattering and volumetric scattering is developed to theoretically model the BRDF in order to elucidate the underlying mechanisms. Finally, the numerical model captures the main features and can be used to study the bidirectional properties for PTFE sheets thinner than what is experimentally available.

42 ENGINEERING↗
DOE OSTI2014

High quantum efficiency and low dark count rate in multi-layer superconducting nanowire single-photon detectors

In this paper, we theoretically show that a multi-layer superconducting nanowire single-photon detector (SNSPD) is capable of approaching characteristics of an ideal SNSPD in terms of the quantum efficiency, dark count, and band-width. A multi-layer structure improves the performance in two ways. First, the potential barrier for thermally activated vortex crossing, which is the major source of dark counts and the reduction of the critical current in SNSPDs is elevated. In a multi-layer SNSPD, a vortex is made of 2D-pancake vortices that form a stack. It will be shown that the stack of pancake vortices effectively experiences a larger potential barrier compared to a vortex in a single-layer SNSPD. This leads to an increase in the experimental critical current as well as significant decrease in the dark count rate. In consequence, an increase in the quantum efficiency for photons of the same energy or an increase in the sensitivity to photons of lower energy is achieved. Second, a multi-layer structure improves the efficiency of single-photon absorption by increasing the effective optical thickness without compromising the single-photon sensitivity.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Structural Transformations in High-Capacity Li 2 Cu 0.5 Ni 0.5 O 2 Cathodes

Cathode materials that can cycle > 1 Li+ per transition metal are of substantial interest to increase the overall energy density of lithium-ion batteries. Li2Cu0.5Ni0.5O2 has a very high theoretical capacity of ~ 500 mAh/g assuming both Li+ are cycled reversibly. The Cu2+/3+ and Ni2+/3+/4+ redox couples are also at high voltage, which could further boost the energy density of this system. Despite such promise, Li2Cu0.5Ni0.5O2 undergoes irreversible phase changes during charge (delithiation) that result in large first-cycle irreversible loss and poor long-term cycling stability. Oxygen is evolved before the Cu2+/3+ or Ni3+/4+ transitions are accessed. In this contribution, XRD, TEM, and TXM-XANES are used to follow the chemical and structural changes that occur in Li2Cu0.5Ni0.5O2 during electrochemical cycling. Li2Cu0.5Ni0.5O2 is a solid solution of orthorhombic Li2CuO2 and Li2NiO2, but the structural changes more closely mimic the Li2NiO2 endmember. Li2Cu0.5Ni0.5O2 loses long-range order during charge, but TEM analysis provides clear evidence for particle exfoliation and the transformation from orthorhombic to a partially layered structure. Linear combination fitting and principal component analysis of TXM-XANES are used to map the different phases that emerge during cycling ex situ and in situ. Significant changes in the XANES at the Cu and Ni K-edges correlate with the onset of oxygen evolution.

Environmental Molecular Sciences Laboratory↗