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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Importance of Nucleation during Morphology Evolution of the Blade-Cast PffBT4T-2OD-Based Organic Solar Cells

Different temperatures, solvents, and additives are used as influencing parameters to drive molecular packing and phase separation for the development of the controlled evolution of nanostructures for organic solar cells (OSCs). The temperature-dependent aggregation (TDA) features of polymers are explored by investigating aggregation in solution and solid thin-film states using solution small-angle neutron scattering (SANS), soft/hard X-ray scattering, and transmission electron microscopy (TEM) characterizations. In situ grazing incidence wide angle X-ray scattering (GIWAXS) reveals that the nucleation process is highly significant and responsible for the ultimate film morphology. Processing conditions such as temperatures, solvents, and additives were used to influence the nucleation and evolution of film morphology. The nucleation process may improve the polymer packing and phase separation. It may also translate into optimized multilength scale domains and efficient charge percolation pathways, a strong implication to control the nucleation process for the efficient separation and transportation of charges in bulk heterojunction (BHJ) devices.

14 SOLAR ENERGY↗
DOE OSTI2024

Elucidate the Thermal Degradation Mechanism of Y6‐Based Organic Solar Cells by Establishing Structure‐Property Correlation

Abstract Organic solar cells (OSCs) achieved performance booming benefiting from the emerging of non‐fullerene acceptors, while inadequate device stability hampers their further application. At present, the prevalent belief attributes the inevitable thermal degradation of OSC device to morphological instability caused by excessive phase separation and crystallization in the active layer during device operation. However, it is inapplicable for state‐of‐art Y6‐based devices which strongly degrade before large‐scale morphology change. Herein, an alternative degradation mechanism is elucidated wherein molecular orientation change and demixing induced performance degradation in Y6‐based devices. Distinct from IT‐4F‐based counterpart, Y6‐based devices suffer severe thermal degradation dominated by open‐circuit voltage (V OC ) and fill factor (FF) losses. TheV OC loss is attributed to molecular orientation transition of polymer donors from edge‐on to face‐on, leading to a strong built‐in potential reduction and increase in non‐radiative loss due to energy level shifting. As forFFdecay, discontinuous acceptor phases result in electron mobility decrease by over orders of magnitude, originating from the increased molecular stacking and phase separation. This work reveals the thermal degradation mechanism for Y6‐based devices and correlates the photoelectric properties with morphology instability, which will offer guidance for improving the stability of high‐performance OSCs.

Chemistry↗
DOE OSTI2022

Analysis of Intermediates and Products from the Dehydrogenation of Mg(BH 4 ) 2

The thermodynamic properties of key compounds, Mg(B 3 H 8 ) 2 , MgB 2 H 6 , MgB 10 H 10 , Mg(B 11 H 14 ) 2 , Mg 3 (B 3 H 6 ) 2 , and MgB 12 H 12 , proposed to be formed in the release of hydrogen from magnesium borohydride Mg(BH 4 ) 2 and uptake of hydrogen by MgB 2 , have been investigated using solid–state density functional theory (DFT) calculations. Further, more accurate treatment of cell–size effects to the entropies were also investigated, in order to improve the accuracy of the thermodynamic properties of complex borohydrides. We find that the zero–point energy corrections can lower the electronic energies of reaction by 20–30 kJ/(mol H 2 ) for these intermediates, while adding the thermal and entropy contributions results in the total decrease up to ~50 kJ/(mol H 2 ). Although our treatment lowers the calculated formation energy of Mg(B 3 H 8 ) 2 , it is still too high to explain the experimental observation of B 3 H 8 – . We discuss possible reasons for this disparity and propose that the formation of B 3 H 8 – and H – in a disordered amorphous phase has a large energy difference compared to the phase–separated Mg(B 3 H 8 ) 2 and MgH 2 considered in calculations. Comparison of the experimental and NMR chemical shifts calculated within a DFT approach for known species Mg(BH 4 ) 2 , Mg(B 3 H 8 ) 2 , Mg(B 11 H 14 ) 2 , MgB 10 H 10 and MgB 12 H 12 provides validation for predicting the chemical shifts of the other compounds which are yet to be confirmed experimentally. These include MgB 2 H 6 and the proposed tri–anion species Mg 3 (B 3 H 6 ) 2 that both have favorable thermodynamics for reversible hydrogen storage in Mg(BH 4 ) 2 without the formation of MgH 2 as a co–product which could phase–separate and inhibit rehydrogenation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Sequence-dependent self-assembly of supramolecular nanofibers in periodic dynamic block copolymers

Block copolymers (BCPs) can spontaneously self-assemble into various nanostructured morphologies which enable their diverse applications in selective membranes, polymer electrolytes, and optoelectronics. To expand the range of nanostructures accessible to block copolymers, we designed dynamic block copolymers (DBCPs) that combine the phase separation of traditional block copolymers with the supramolecular self-assembly of periodic dynamic polymers. We demonstrate that DBCPs synthesized with a periodic block sequence self-assemble into high aspect ratio supramolecular nanofibers with well-ordered PEG and PDMS domains, in contrast to those synthesized with a random sequence which do not form nanofibers but have disordered morphologies. The periodicity of the block sequence ensures regular placement of dynamic bonds along the polymer chain, which enables stacking of the hydrogen bonding units into ordered 1D supramolecular nanofibers and delays the onset of terminal flow by up to 60 °C compared to the random block sequence. The hierarchically assembled supramolecular nanofibers display complex mechanical and thermal phase behavior arising from the interplay between phase separation of the dissimilar polymer backbones and supramolecular interactions between dynamic bonds. Despite identical bulk composition, the periodic DBCPs demonstrate ionic conductivity values over two orders of magnitude higher than their random counterparts due to the formation of well-ordered, interconnected, high aspect ratio ion-transporting PEG domains. In conclusion, these results highlight the potential for DBCPs as an emerging material platform to achieve advanced, self-assembled nanostructured morphologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Persistence of crystal orientations across sub-micron-scale "super-grains" in self-organized Cu-W nanocomposites

We use precession electron diffraction to investigate the crystallographic character of copper (Cu)-tungsten (W) nanocomposites fabricated via physical vapor co-deposition at 400 oC. We observe sub-micron-scale regions, where apparently disconnected Cu and W grains have near identical crystallographic orientations. This persistence of grain orientations suggests Cu and W grains within these regions are interconnected in 3-D when they first form and may be considered as intercalated, sub-micron-scale "super-grains". Indeed, atom probe tomography provides direct evidence of 3-D interconnectivity of W domains. Our findings shed light on the structure and self organization mechanisms of nanocomposites formed by spontaneous phase separation of co-deposited metals.

Yadav, Digvijay↗
DOE OSTI2015

Manipulating the ferromagnetism in narrow-bandwidth Pr{sub 1-x}Ca{sub x}MnO{sub 3} (0 ≤ x ≤ 0.6) by means of the Mn-Ru t{sub 2g} ferromagnetic super-exchanges

The concurrent ferromagnetic and metal-insulator transitions via the double-exchange route and electronic phase separation scenario represent the core ingredients of the physics of manganites. In this work, a Ca{sup 2+} and Ru{sup 4+} co-substitution of Pr{sup 3+} and Mn{sup 3+} in narrow-bandwidth and insulating PrMnO{sub 3}, namely, Pr{sub 1-x}Ca{sub x}Mn{sub 1-x}Ru{sub x}O{sub 3} (PCMRO, x ≤ 0.6), is carried out in order to investigate an alternative approach to effectively manipulate the ferromagnetism of PrMnO{sub 3}-based manganites. It is revealed that PCMRO over the whole substitution range is homogeneous solid solution with increased lattice distortion. The preference of Ru{sup 4+} valence state and the absence of Mn{sup 4+} valence state disable the Mn{sup 3+}-Mn{sup 4+} e{sub g}-orbital double-exchange, and the random occupation of Ru{sup 4+} in the lattice excludes the charge ordering and electronic phase separation. While all these consequences should favor antiferromagnetic insulating states, nevertheless, a high-temperature ferromagnetic transition is triggered by the co-substitution and the magnetization can reach up to ∼1.0 μ{sub B}/f.u. at x ∼ 0.2–0.3, much bigger than the moment (<0.1 μ{sub B}/f.u.) of Pr{sub 1−x}Ca{sub x}MnO{sub 3} in the weak ferromagnetic insulator state. It is suggested that this strong ferromagnetism is substantially ascribed to the Mn{sup 3+}-Ru{sup 4+} t{sub 2g}-orbital ferromagnetic super-exchange, and a simple geometric network illustration of the magnetism and electrical transport is presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Normal state above the upper critical field in Fe 1 + y Te 1 - x ( Se , S ) x

Here, we have investigated the magnetotransport above the upper critical field ( H c 2 ) in Fe 1.14 Te 0.7 Se 0.3 , Fe 1.02 Te 0.61 Se 0.39 , Fe 1.05 Te 0.89 Se 0.11 , and Fe 1.06 Te 0.86 S 0.14 . The μ SR measurements confirm electronic phase separation in Fe 1.06 Te 0.86 S 0.14 , similar to Fe 1 + y Te 1 - x Se x . We found that superconductivity is suppressed in high magnetic fields above 60 T, allowing us to gain insight into the normal-state properties below the zero-field superconducting transition temperature ( T c ). We also show that the resistivity of Fe 1.14 Te 0.7 Se 0.3 and Fe 1.02 Te 0.61 Se 0.39 above H c 2 is metallic as T → 0 , just like the normal-state resistivity above T c . On the other hand, the normal-state resistivity in Fe 1.05 Te 0.89 Se 0.11 and Fe 1.06 Te 0.86 S 0.14 is nonmetallic down to lowest temperatures, reflecting the superconductor-insulator transition due to electronic phase separation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2005

Development of a gravity-independent wastewater bioprocessor for advanced life support in space

Operation of aerobic biological reactors in space is controlled by a number of challenging constraints, mainly stemming from mass transfer limitations and phase separation. Immobilized-cell packed-bed bioreactors, specially designed to function in the absence of gravity, offer a viable solution for the treatment of gray water generated in space stations and spacecrafts. A novel gravity-independent wastewater biological processor, capable of carbon oxidation and nitrification of high-strength aqueous waste streams, is presented. The system, consisting of a fully saturated pressurized packed bed and a membrane oxygenation module attached to an external recirculation loop, operated continuously for over one year. The system attained high carbon oxidation efficiencies often exceeding 90% and ammonia oxidation reaching approximately 60%. The oxygen supply module relies on hydrophobic, nonporous, oxygen selective membranes, in a shell and tube configuration, for transferring oxygen to the packed bed, while keeping the gaseous and liquid phases separated. This reactor configuration and operating mode render the system gravity-independent and suitable for space applications.

NASA Discipline Life Support Systems↗
DOE OSTI2018

Upper limit for the effect of elastic bending stress on the saturation magnetization of L a 0.8 S r 0.2 Mn O 3

In this study, using polarized neutron reflectometry, we measured the influence of elastic bending stress on the magnetization depth profile of a La 0.8 Sr 0.2 MnO 3 (LSMO) epitaxial film grown on a SrTiO 3 substrate. The elastic bending strain of ±0.03% has no obvious effect on the magnetization depth profile at saturation. This result is in stark contrast to that of (La 1-x Pr x )1-yCayMnO 3 (LPCMO) films for which strain of ±0.01% produced dramatic changes in the magnetization profile and Curie temperature. We attribute the difference between the influence of strain on the saturation magnetization in LSMO (weak or none) and LPCMO (strong) to a difference in the ability of LSMO (weak or none) and LPCMO (strong) to phase separate. Our observation provides an upper limit of tuning LSMO saturation magnetization via elastic strain effect.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Viscosities and working region predictions for bismuth aluminoborosilicate glasses

Bismuth aluminoborosilicate glasses were prepared using a standard melt-quench technique, and the viscosity and thermal properties were measured and analyzed. Electron microprobe analysis was used to examine glass homogeneity. Fragility was calculated based on Mauro–Yue–Ellison–Gupta–Allan model fits to the viscosity curves. The system is characterized by an open structure with high fragility (44-59). Based on microanalysis and differential scanning calorimetry results, the addition of network intermediate Al2O3 appears to mitigate both phase separation and crystallization. From thermal property data, mixture models were created to predict the glass transition temperatures and softening temperatures as functions of composition. Based on K-fold validation findings, the first-order mixture model predictions of glass transition and softening appear to approximate actual values better than models with any additional second-order terms.

Gardner, Levi↗
DOE OSTI2022

Entrapped Molecule‐Like Europium‐Oxide Clusters in Zinc Oxide with Nearly Unaffected Host Structure

Abstract Nanocrystalline ZnO sponges doped with 5 mol% EuO 1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X‐ray diffraction, transmission electron microscopy, and extended X‐ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c ‐Eu 2 O 3 takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu‐doping and an average Eu 3+ ion coordination number of ≈5.2. Comparisons of 23 density functional theory‐generated structures having differently sized Eu‐oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu 3+ excitation, while c ‐Eu 2 O 3 phase separation results in loss of the characteristic Eu 3+ photoluminescence. The formation of molecule‐like Eu‐oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of thin films prepared by co-sputtering iron and titanium precursors and thermal oxidation under air atmosphere

Highlights: • Thin films of mixed iron and titanium oxide were prepared by Ti-Fe annealing. • Segregation and phase separation of iron and titanium oxides are observed. • Formation of iron rich (Fe{sub x}O) nanoparticles at the surface region is revealed. • Formation of thin films with high refractive index can be obtained. - Abstract: Nanocomposites of metal oxides are useful materials for operation in many energy conversion systems. In this study, such nanocomposites were prepared by oxidation of mixtures of iron and titanium precursor metallic thin films at 520 °C under air atmosphere. The metallic films with different iron percentages were obtained by radio frequency (RF) magnetron sputtering on glass and silicon substrates. The films were characterized by means of X-ray Diffraction (XRD), Raman spectroscopy, UV–Vis spectroscopy, High Resolution Scanning Transmission Electron Microscopy (HRSTEM), Ellipsometry and X-ray Photo-electron Spectroscopy (XPS). The results show that these films present mainly two nanometric phases, namely Fe{sub 2}O{sub 3} and TiO{sub 2}. A phase separation was observed; the film surface was found to be iron rich oxide or clusters of iron rich oxide (Fe{sub x}O{sub y}, x > y), whereas titanium accumulated deeply in the bulk, forming TiO{sub 2} far below the film surface. A red shift of optical absorption as well as a relatively stable high refractive index (varying between 3.1 and 3.5) over a broad band of optical frequencies was observed for the films containing higher iron initial concentrations.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Solvent-Free Melt-Processed Cathode Mitigates Li Anode Instability in Polymer-Based Solid-State Batteries

Solvent-free manufacturing of battery components is a promising alternative to traditional slurry processing for reducing the cost and environmental impact. In this work, we used twin-screw melt extrusion to fabricate a polymer-based high voltage composite cathode. The melt-processed cathode is dense (near zero porosity) and thick (65 μm) and has high active material loading (80 wt %). The active particles are distributed uniformly throughout the melt-processed cathode, unlike the traditional slurry-cast cathode, which exhibits inhomogeneous particle distribution. In the melt-processed cathode, polymer and carbon form separate phases, whereas in the slurry-cast cathode they blend into a single phase. Due to these structural differences, the melt-processed cathode shows smooth charge–discharge profiles, while the slurry-cast cathode shows noisy charging and soft-shorting behavior. In conclusion, this work highlights that twin-screw extrusion as a scalable, solvent-free manufacturing method is advantageous in producing uniform cathodes, which mitigates anode instability.

25 ENERGY STORAGE↗
DOE OSTI2017

Simultaneous Increase in Open-Circuit Voltage and Efficiency of Fullerene-Free Solar Cells through Chlorinated Thieno[3,4- b ]thiophene Polymer Donor

The chlorinated polymer, PBTCl, has been found to be an efficient donor in nonfullerene polymer solar cells (PSCs), which showed a blue-shifted absorbance compared to that of its fluorine analogue (PTB7-th) and resulted in more complementary light absorption with a nonfullerene acceptor, such as ITIC. Meanwhile, chlorine substitution lowered the HOMO level of PBTCl, which increased the open-circuit voltage of the corresponding polymer-based devices. The 2D GIWAXS analysis illustrated that the PBTCl/ITIC blend film exhibited a “face-on” orientation and scattering features of both PBTCl and ITIC, suggesting that the blend of PBTCl and ITIC was phase-separated and formed individual crystalline domains of the donor and acceptor, which promoted charge transfer in the bicontinuous film and eventually elevated the solar energy conversion efficiency. The PBTCl-based nonfullerene PSC exhibited a maximum PCE of 7.57% with a Voc of 0.91 V, which was an approximately 13% increasing in the PCE compared to that of the fluorine-analogue-based device.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Direct Exchange Mechanism for Interlayer Ions in Non-Swelling Clays

The mobility of radiocesium in the environment is largely mediated by cation exchange in micaceous clays, in particular Illite—a non-swelling clay mineral that naturally contains interlayer K + and has high affinity for Cs + . Although exchange of interlayer K + for Cs + is nearly thermodynamically nonselective, recent experiments show that direct, anhydrous Cs + -K + exchange is kinetically viable and leads to the formation of phase-separated interlayers through a mechanism that remains unclear. Here, using classical atomistic simulations and density functional theory calculations, we identify a molecular-scale positive feedback mechanism in which exchange of the larger Cs + for the smaller K + significantly lowers the migration barrier of neighboring K + , allowing exchange to propagate rapidly once initiated at the clay edge. Barrier lowering upon slight increase in layer spacing (~0.7 Å) during Cs + exchange is an example of “chemical-mechanical coupling” that likely explains the observed sharp exchange fronts leading to interstratification. Interestingly, we find that these features are thermodynamically favored even in the absence of a heterogeneous layer charge distribution.

Ruiz Pestana, Luis↗
DOE OSTI2015

Crystallization and preliminary crystallographic analysis of latent, active and recombinantly expressed aurone synthase, a polyphenol oxidase, from Coreopsis grandiflora

Latent and active aurone synthase purified from petals of C. grandiflora (cgAUS1) were crystallized. The crystal quality of recombinantly expressed latent cgAUS1 was significantly improved by co-crystallization with the polyoxotungstate Na{sub 6}[TeW{sub 6}O{sub 24}] within the liquid–liquid phase-separation zone. Aurone synthase (AUS), a member of a novel group of plant polyphenol oxidases (PPOs), catalyzes the oxidative conversion of chalcones to aurones. Two active cgAUS1 (41.6 kDa) forms that differed in the level of phosphorylation or sulfation as well as the latent precursor form (58.9 kDa) were purified from the petals of Coreopsis grandiflora. The differing active cgAUS1 forms and the latent cgAUS1 as well as recombinantly expressed latent cgAUS1 were crystallized, resulting in six different crystal forms. The active forms crystallized in space groups P2{sub 1}2{sub 1}2{sub 1} and P12{sub 1}1 and diffracted to ∼1.65 Å resolution. Co-crystallization of active cgAUS1 with 1,4-resorcinol led to crystals belonging to space group P3{sub 1}21. The crystals of latent cgAUS1 belonged to space group P12{sub 1}1 and diffracted to 2.50 Å resolution. Co-crystallization of recombinantly expressed pro-AUS with the hexatungstotellurate(VI) salt Na{sub 6}[TeW{sub 6}O{sub 24}] within the liquid–liquid phase separation zone significantly improved the quality of the crystals compared with crystals obtained without hexatungstotellurate(VI)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface

Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO 3 ) surfaces are detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H 2 O and CO 2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (for example, Sr La ') by the positively charged oxygen vacancies (V $••\atop{o}$) enriched at the surface. Here we show that reducing the surface V $••\atop{o}$ concentration improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O 2 molecules. We take La 0.8 Sr 0.2 CoO 3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while reducing the concentration of V $••\atop{o}$ and making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 °C achieved by Hf addition onto LSC. Finally, the results revealed a 'volcano' relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss.

36 MATERIALS SCIENCE↗