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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Dislocation cross-slip in precipitation hardened Mg–Nd alloys

An integrated experimental characterization and molecular dynamics (MD) simulation approach was used to explore the dislocation-precipitate interactions in a dilute Magnesium–Neodymium (Mg–Nd) precipitation hardened alloy. In situ indentation in a transmission electron microscope (TEM) and postmortem TEM characterization of deformed samples and MD simulations revealed that basal < a > type dislocations interacted differently with β 1 (Mg 3 Nd) and β"(Mg 3-7 Nd) precipitates. For β" precipitates, the basal dislocations directly shear the precipitates. For β 1 precipitates, such shearing becomes much more difficult because it requires the creation of antiphase boundaries in the ordered lattice of β 1 precipitates. Screw dislocations were observed to cross-slip from basal to the prismatic plane, which could be parallel to the broad facet of β 1 precipitates. It is postulated that double cross-slip (basal to prismatic to basal) via the Hirsch mechanism may enable screw dislocations to overcome the β 1 precipitates. MD simulations also revealed that an edge dislocation is unable to bypass the precipitate via the generation of screw dislocation segments plus the double cross-slip mechanism. The edge dislocation can bow around the precipitate, and the segment that adopts a screw character can cross-slip to the prismatic plane but with increasing applied stress, cross-slips back to the original basal plane to continue glide via precipitate shearing. Finally, the implication of glide dislocation - β 1 -precipitate interaction mechanisms on the strength and ductility of β 1 precipitate dominant microstructures is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

X-ray ptychographic tomography reveals buried 3D structural defects in metal halide perovskites

For the first of its kind, X-ray ptychographic imaging is utilized for probing metal halide perovskite crystals, revealing various 3D structural defects fully or partially buried underneath the perovskite surface. Here, this work demonstrates a powerful, non-intrusive 3D tomographic characterization method to illuminate the complete microstructure of perovskites for advanced energy applications.

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

Crosslinked Matrimid®-like polyimide membranes with unimodal network structure for enhanced stability and gas separation performance

Gas separation membranes have attracted academic and industrial attention, and crosslinking has been identified to be one of the most effective ways to enhance membrane stability. In this paper, a series of crosslinked Matrimid®-like films with unimodal network structures are prepared via thermally end-linking phenylethnyl-terminated BTDA-DAPI oligomers with well-controlled molecular weight (i.e., 3000–15,000 g/mol), wherein the crosslink density (the inter-crosslink chain length) of resulting unimodal networks is systematically varied by using oligomers with various molecular weight. Comprehensive characterizations of chemical structure, thermal properties, microstructures are performed. Pure-gas permeation measurements are performed focusing on H 2 /CH 4 and CO 2 /CH 4 separations as a function of crosslink density. In sharp contrast to the commonly observed permeability reduction in randomly crosslinked networks, all the crosslinked unimodal films, even when densely crosslinked, present markedly enhanced permeability and well-maintained ideal selectivity relative to the uncrosslinked linear counterpart, leading to almost horizontal movements towards upper bounds along with expectedly enhanced membrane stability. In conclusion, it is concluded that introducing bulky groups at the crosslink sites provide a practical means to counteract the densification effect induced by crosslinking and the construction of unimodal networks exemplifies a fundamentally new strategy to regulate the microstructure and property of crosslinked membranes for gas separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Green cubic GaInN/GaN light-emitting diode on microstructured silicon (100)

GaInN/GaN light-emitting diodes free of piezoelectric polarization were prepared on standard electronic-grade Si(100) substrates. Micro-stripes of GaN and GaInN/GaN quantum wells in the cubic crystal structure were grown on intersecting (111) planes of microscale V-grooved Si in metal-organic vapor phase epitaxy, covering over 50% of the wafer surface area. Crystal phases were identified in electron back-scattering diffraction. A cross-sectional analysis reveals a cubic structure virtually free of line defects. Electroluminescence over 20 to 100 μA is found fixed at 487 nm (peak), 516 nm (dominant). Such structures therefore should allow higher efficiency, wavelength-stable light emitters throughout the visible spectrum.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Influence of yttrium content on the location of rare earth ions in LYSO:Ce crystals

Single-crystal X-ray diffraction (SCD), X-ray fluorescence (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray excited luminescence (XEL) measurements were performed to investigate structure details and segregation coefficients of (Lu{sub 1−x}Y{sub x}){sub 2}SiO{sub 5}:Ce (x=0 at%, 8.7 at%, 25.7 at%, 44.7 at%, 65.7 at%, 87.9 at% and 100 at%). Y{sup 3+} cations were found to have a preferential occupation for RE1 site (7-oxygen-coordinated) over RE2 site (6-oxygen-coordinated), which results in a greater increase of cell parameter c than that of a with increase in Y content due to LYSO's microstructure characteristics. Results presented here revealed that the less the difference in electronegativity and effective ionic radius between the two ions, the easier substitution of one ion by the other, and hence the higher segregation coefficients. Besides, the contribution of luminescence of Ce1 and Ce2 in the whole XEL was evaluated, and the location of Ce{sup 3+} ion was discussed. - Graphical abstract: Segregation coefficients of (Lu{sub 1−x}Y{sub x}){sub 2}SiO{sub 5}:Cce:italic> at RT/ce:italic>. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Hierarchical hollow microsphere and flower-like indium oxide: Controllable synthesis and application as H{sub 2}S cataluminescence sensing materials

Graphical abstract: Hierarchical hollow microsphere and flower-like In{sub 2}O{sub 3} were controllable fabricated through a novel and simple hydrothermal process, and the former showed superior cataluminescence sensing performance to H{sub 2}S. Highlights: ► In{sub 2}O{sub 3} hierarchical hollow sphere were prepared via a hydrothermal route. ► The growth process of In{sub 2}O{sub 3} hierarchical hollow sphere has been investigated. ► The sensor based on prepared In{sub 2}O{sub 3} shows good sensing performance to H{sub 2}S. -- Abstract: In the present work, In{sub 2}O{sub 3} hierarchical hollow microsphere and flower-like microstructure were achieved controllably by a hydrothermal process in the sodium dodecyl sulfate (SDS)-N,N-dimethyl-formamide (DMF) system. XRD, SEM, HRTEM and N{sub 2} adsorption measurements were used to characterize the as-prepared indium oxide materials and the possible mechanism for the microstructures formation was briefly discussed. The cataluminescence gas sensor based on the as-prepared In{sub 2}O{sub 3} was utilized to detect H{sub 2}S concentrations in flowing air. Comparative gas sensing results revealed that the sensor based on hierarchical hollow microsphere exhibited much higher sensing sensitivity in detecting H{sub 2}S gas than the sensor based on flower-like microstructure. The present gas sensor had a fast response time of 5 s and a recovery time of less than 25 s, furthermore, the cataluminescence intensity vs. H{sub 2}S concentration was linear in range of 2–20 μg mL{sup −1} with a detection limit of 0.5 μg mL{sup −1}. The present highly sensitive, fast-responding, and low-cost In{sub 2}O{sub 3}-based gas sensor for H{sub 2}S would have many practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The Role of Local Inhomogeneities on Dendrite Growth in LLZO-Based Solid Electrolytes

The majority of the ceramic solid electrolytes (LLZO, LATP) demonstrate polycrystalline grain/grain-boundary (G/GB) microstructure. Higher lithium (Li) concentration and lower mechanical stiffness result in current focusing at the GBs. Growth of Li dendrites through local inhomogeneities and subsequent short circuit of the cell is a major concern. Recent studies have revealed that bulk Li metal is a viscoplastic material that has low (~0.3 MPa) and high (~1.0 MPa) yield strength during deformation at smaller and larger rates of strain, respectively. It has been argued that during deposition at smaller current densities, due to its lower yield strength, Li metal should demonstrate plastic flow against stiff ceramic electrolytes, and Li dendrites will be prevented from penetrating through solid electrolytes. In this manuscript, a multiscale modeling framework has been developed for predicting properties of GBs and the bulk of ceramic electrolytes using atomistic calculations for input to mesoscale models. Using the parameters obtained from the atomistic simulations, the mesoscale model reveals that, given enough time, even at low charge rates, lithium dendrites can grow through the GBs of LLZO. The present multiscale model results also provide information regarding the dendrite growth velocity through LLZO.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2018

Water-Rock Interactions in Outer Solar System Bodies: Evidence from the Coordinated Analysis of Interplanetary Dust

NASA has an ongoing program of collecting interplanetary dust particles (IDPs) in the stratosphere using high altitude research aircraft. The collected IDPs are derived from asteroids and comets and here we report studies of a subset of hydrated IDPs rich in carbonaceous matter that are proposed to have a cometary origin. Our studies are aimed at understanding the evolution of oxygen reservoirs in the Solar System and their interaction with cometary minerals and organic matter. The small size (<20 μm) and fragility of these IDPs present a number of analytical challenges. We have pioneered techniques for performing chemical, mineralogical, isotopic, and spectroscopic measurements on the same sample in a carefully coordinated sequence. Coordinated analyses of nanogram-size samples is made possible by several delicate sample preparation techniques. To avoid organic contamination, we embed IDPs in elemental sulfur and use ultramicrotomy to partly section the particles (the first few micrometers). Multiple thin sections (50-70 nm thick) are placed on different substrates depending on the analysis technique. We use a JEOL 2500SE scanning, transmission electron microscope (STEM) to determine the mineralogy, microstructure, and elemental compositions of constituent minerals in the thin sections through a combination of high resolution imaging, electron diffraction, quantitative energy-dispersive x-ray mapping, and electron energy-loss spectroscopy. Following the STEM analyses, we use a NanoSIMS 50L for high spatial resolution isotopic measurements of H, C, N, and O to search for presolar grains and to understand the origin of the indigenous organic matter. The isotopic analyses are performed on the same sections analyzed in the STEM in order to correlate isotopic properties with the elemental and mineralogical data. We reserve other thin sections for non-destructive analyses utilizing synchrotron-based techniques including Fourier-transform infrared (FTIR) micro-spectroscopy and X-ray absorption near-edge structure (XANES) analyses, especially for functional group analysis of organic matter in the particles. The remainder of the IDP is extracted from the sulfur bead that was used for microtomy and is pressed into Au foil for quantitative analysis (including light elements) using a JEOL 8530F field emission electron probe microanalyzer (EPMA). After the EPMA measurements, high precision oxygen isotopic analyses are obtained using Cameca IMS1270/1290 instruments at UCLA. The hydrated IDPs in this study are dominated by saponitic clays, with minor magnetite, carbonate and abundant organic matter. The remarkable oxygen isotopic compositions, high carbon contents, and the abundance of isotopically anomalous organic matter, together suggest that the high carbon, hydrated IDPs are derived from primitive sources not yet represented in meteorite collections such as outer main belt P- and D-type asteroids or comets.

Keller, Lindsay P.↗
DOE OSTI2015

Enhanced photocatalytic hydrogen evolution activity of CuInS{sub 2} loaded TiO{sub 2} under solar light irradiation

In this paper, p–n type CuInS{sub 2}/TiO{sub 2} particles were prepared in ethylenediamine by the solvothermal method. The microstructural properties of the synthesized p–n type catalysts were characterized by X-ray diffraction (XRD) in order to confirm the existence of crystalline CuInS{sub 2} on the surface of TiO{sub 2}, which was also confirmed by X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) images provided the detailed morphological properties about the CuInS{sub 2}/TiO{sub 2} heterostructure. UV–vis diffuse reflectance spectroscopy (UV–vis DRS) was used to investigate the optical properties of the CuInS{sub 2}/TiO{sub 2} particles. The DRS results indicated that both the p–n type structure and CuInS{sub 2} acting as a sensitizer can enhance significantly the absorption of UV and visible light. The photocatalytic activities of the CuInS{sub 2}/TiO{sub 2} particles were evaluated by hydrogen evolution reactions using Xe-lamp irradiation as a simulated solar light source. The greatly enhanced photocatalytic activity of hydrogen evolution under simulated solar light is about ~7 fold higher than that of pure commercial TiO{sub 2} (Degussa P25). - Graphical abstract: The heterojunction structure of CuInS{sub 2}/TiO{sub 2} promoted the efficiency of photoinduced charge carrier transfer and highly inherited the recombination of activated electrons and holes. - Highlight: • CuInS{sub 2}/TiO{sub 2} was prepared by a one-step solvothermal method. • 2.5% CuInS{sub 2}/TiO{sub 2} has the highest activity and keeps the activity stable. • Heterojunction structure of sample promoted the separation of electrons and holes.

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

Structural features of silver-doped phosphate glasses in zone of femtosecond laser-induced modification

Femtosecond (fs) laser writing of two-dimensional microstructures (waveguides) is demonstrated in bulk phosphate glasses doped with silver ions. Silver-content phosphate and silver-content niobium–phosphate glasses with high concentration of silver oxide 55 mol% were used as samples for fs laser writing. The chemical network structure of the synthesized samples is analyzed through Raman spectroscopy and was found to be strongly sensitive to Nb incorporation. It was found that the direct laser writing process enables not only reorganization of glass network, but also formation of color centers and silver nanoparticles that are revealed in appearance of luminescence signal and plasmon absorption. The process of NPs' formation is more efficient for Nb-phosphate glass, while color centers are preferably formed in phosphate glass. - Graphical abstract: Formation of silver NPs on the surface of 0.5Ag{sub 2}O–0.4P{sub 2}O{sub 5}–0,1Nb{sub 2}O{sub 5} glass induced by CW laser irradiation. - Highlights: • The structure of 0.5Ag{sub 2}O–0.1Nb{sub 2}O{sub 5}–0.4P{sub 2}O{sub 5} and 0.55Ag{sub 2}O–0.45P{sub 2}O{sub 5} glasses was investigated by Raman spectroscopy. • Fs laser writing induces formation of silver NPs in investigated glasses. • Surface plasmon resonance in the absorption spectra confirms the formation of NP. • The possibility of CW laser induced formation of silver NPs on the surface of sample with niobium is shown.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Preparation and characterization of one-dimensional GaN nanorods with Tb intermediate layer

Graphical abstract: Display Omitted Highlights: ► GaN nanorods have been prepared on Si substrates by magnetron sputtering. ► GaN nanorods are single crystal with hexagonal wurtzite structure. ► GaN nanorods are high-quality crystalline after ammoniating at 950 °C for 15 min. ► Ammoniating temperatures and times affect the growth of GaN nanorods significantly. -- Abstract: GaN nanorods have been successfully prepared on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga{sub 2}O{sub 3}/Tb thin films. X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), FT-IR spectrophotometer, scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), and photoluminescence (PL) spectroscopy were used to characterize the microstructures, morphologies compositions and optical properties of the GaN samples. The results demonstrate that the nanorods are single crystal GaN with hexagonal wurtzite structure and high-quality crystalline after ammoniating at 950 °C for 15 min, which have the size of 100–150 nm in diameter. Ammoniating temperatures and times affect the growth of GaN nanorods significantly. The growth procedure mainly follows the Tb catalyst-assisted VLS mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Adapting SAFT-γ perturbation theory to site-based molecular dynamics simulation. III. Molecules with partial charges at bulk phases, confined geometries and interfaces

In Paper I [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 139(23), 234104 (2013)], we showed that how a third-order Weeks–Chandler–Anderson (WCA) Thermodynamic Perturbation Theory and molecular simulation can be integrated to characterize the repulsive and dispersive contributions to the Helmholtz free energy for realistic molecular conformations. To this end, we focused on n-alkanes to develop a theory for fused and soft chains. In Paper II [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 141(2), 024708 (2014)], we adapted the classical Density Functional Theory and studied the microstructure of the realistic molecular fluids in confined geometries and vapor-liquid interfaces. We demonstrated that a detailed consistency between molecular simulation and theory can be achieved for both bulk and inhomogeneous phases. In this paper, we extend the methodology to molecules with partial charges such as carbon dioxide, water, 1-alkanols, nitriles, and ethers. We show that the electrostatic interactions can be captured via an effective association potential in the framework of Statistical Associating Fluid Theory (SAFT). Implementation of the resulting association contribution in assessing the properties of these molecules at confined geometries and interfaces presents satisfactory agreement with molecular simulation and experimental data. For example, the predicted surface tension deviates less than 4% comparing to full potential simulations. Also, the theory, referred to as SAFT-γ WCA, is able to reproduce the specific orientation of hydrophilic head and hydrophobic tail of 1-alkanols at the vapor-liquid interface of water.

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

Synthesis, structural and electrical properties of a new cobalt arsenate NaCo{sub 2}As{sub 3}O{sub 10}

The title compound sodium dicobalt triarsenate NaCo{sub 2}As{sub 3}O{sub 10} has been synthesized by solid state reaction. Crystal structure and electrical properties were studied by X-ray diffraction and complex impedance spectroscopy, respectively. The obtained structural model is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) validations tools. The structure (triclinic, P−1, a=6.800 (8) Å, b=7.816 (9) Å, c=8.718 (3) Å, α=108.03 (2)°, β=108.48 (3)°, γ=100.11 (2)°) can be described as a three-dimensional framework resulted from corner-connection between cobalt metallic chains running along [−110] and As{sub 3}O{sub 10} groups; the negative charge is balanced by Na{sup +} ions which house the two tunnels parallel to a and b axes. Ball milling was used as mechanical means to reduce the particles sizes of the synthesized powder. At the optimal sintering temperature of 650 °C, 85% of the relative density was obtained. The conductivity measurements show that NaCo{sub 2}As{sub 3}O{sub 10} is a cationic conductor with an activation energy of 0.48 eV and a conductivity of σ=1.2×10{sup −5} S cm{sup −1} at 310 °C. The BVS model is extended to simulate the ionic migration pathways of alkali cations in the anionic framework. - Graphical abstract: 1D pathways link Na atoms along the a-axis with bond valence mismatch |ΔV(Na)|=0.64 v.u. - Highlights: • A new single crystal NaCo{sub 2}As{sub 3}O{sub 10} was grown by solid state reaction and its structure determined by single-crystal X-ray diffraction. • The purity of the powder sample was verified by Rietveld refinement. • The CIS measurements were optimized and the obtained spectra were fitted by electrical equivalent circuits. • The conduction pathways for Na{sup +} cations are simulated by means of the bond valence sum model.

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

Examining the creep strengthening nanoprecipitation in novel highly reinforced heat resistant steels

Here we studied the creep strengthening nanoprecipitation in novel heat resistant steels strengthened by a high density of stable nanoprecipitates. The results show that the high number density of MX nanoprecipitates within the martensitic laths in these steels comes from the great amount of MX former elements present in their chemical compositions and the high dislocation density generated by the martensitic transformation that takes place during cooling after austenitization. These dislocations act as nucleation sites for these nanoprecipitates during the tempering applied after the austenitization and quenching. Atom probe tomography measurements show that these nanoprecipitates are rich in Nb, V, Cr and N for the HDSN1 and HDSN2 steels and V, Cr and N for the HDSN3 steel. The distribution of the nanoprecipitates within the martensitic laths suggests that the creep strengthening produced by the Nb, V, Cr and N nanoprecipitates in the HDSN1 and HDSN2 steels is more effective at pinning dislocations at high temperature than that obtained in the HDSN3 steel by the V, Cr and N nanoprecipitates. However, the high amount of W in the HDSN3 steel enhances the solid solution strengthening at high temperatures, resulting in a similar high temperature strength for all HDSN steels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis and thermoelectric/electrical characterization of electrodeposited Sb{sub x}Te{sub y} thin films

Sb{sub x}Te{sub y} films were potentiostatically electrodeposited from acidic nitric baths at room temperature by controlling the applied potential. Near-stoichiometric Sb{sub 2}Te{sub 3} thin films were obtained at applied potentials between −0.15 and −0.30 V vs. saturated calomel electrode (SCE). Post-annealing in a reducing environment resulted in an improvement in the crystal structure without the evaporation of the Te element. This result was indicated by a significant reduction in the electrical resistance and decrease in the FWHM of the main diffraction peaks. The power factor (σS{sup 2}) increased from 44.2 to 372.1 μW/m K{sup 2} after annealing at 473 K.

36 MATERIALS SCIENCE↗
DOE OSTI2012

La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowders prepared by the hydrothermal method

Graphical abstract: LRTEM image of the single-phase La{sub 0.5}Sr{sub 0.5}TiO{sub 3} particles. It is seen from the figure that the product has a plate-like morphology with average particles sizes in the range of 100–300 nm. In addition, the SAED data taken from an individual particle (lower inset) shows the presence of sharp diffraction rings, which are indicative of polycrystalline La{sub 0.5}Sr{sub 0.5}TiO{sub 3} formation. The high-resolution TEM image (upper inset) shows for further confirmation of a crystalline structure of La{sub 0.5}Sr{sub 0.5}TiO{sub 3} powder. This image shows a clearly resolved crystalline domain with uniform interplanar spacing of 0.276 nm. Highlights: ► La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowder is prepared in 2 M KOH solution by hydrothermal method. ► The solution is heat treated at 220 °C for 24 h in air. ► LRTEM reveals a plate-like morphology of particle with average size of 100–300 nm. ► HRTEM image shows a crystalline domain with interplanar spacing of 0.276 nm. -- Abstract: La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowders were prepared by the hydrothermal method. The influence of processing parameters, including KOH concentration, reaction temperature and reaction time on the obtained products were studied. The structure and morphology of the obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that pure phase La{sub 0.5}Sr{sub 0.5}TiO{sub 3} nanopowders can be successfully synthesized with 2 M KOH concentration at a low temperature of 220 °C for 24 h. In addition, the product has a plate-like shape with particle sizes in the range of 25–100 nm as estimated by TEM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗