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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Measuring the Burgers vector of dislocations with dark-field X-ray microscopy

The subsurface dynamics of dislocations are essential to many properties of bulk crystalline materials. However, it is challenging to characterize a bulk crystal by conventional transmission electron microscopy (TEM) due to the limited penetration depth of electrons. A novel X-ray imaging technique – dark-field X-ray microscopy (DFXM) – was developed to image hierarchical dislocation structures in bulk crystals. While today's DFXM can effectively map the line structures of dislocations, it is still challenging to quantify the Burgers vectors, the key characterization governing the dislocation behaviors. Here, we extend the 'invisibility criterion' formalism from the TEM theory to the geometrical-optics model of DFXM and demonstrate the consistency between DFXM and dark-field TEM using multi-diffraction-peak imaging for a single edge dislocation. Due to the practical difficulty of multi-peak DFXM experiments, we further study how the Burgers vector effect is encoded for a single-peak DFXM experiment. Using the geometrical-optics DFXM simulation, we explore the asymmetry of rocking tilt scans at different rolling tilts and develop a new method to characterize the Burgers vector. The conclusions of this study advance our understanding of the use of DFXM in characterizing individual dislocations, enabling the connection from bulk DFXM imaging to dislocation mechanics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Upscaling of asymmetric hollow fiber‐supported thin film membranes for oxygen separation from air: Proof of concept

Abstract Hollow fiber membranes demonstrate various advantages for high performance oxygen separation. However, the small diameters of hollow fibers and the brittleness of ceramics limit their mechanical strength, imposing great difficulties on stack and module development. Gas‐tight sealing is another challenge for upscaling of hollow fiber membrane technology. Low temperature sealant materials of epoxy resin or silicon are typically used for hollow fiber stacks, requiring that the sealing portions be located out of hot zone. Consequently, only partial length of hollow fibers participates in oxygen permeation. In this study, upscaling of our recently developed asymmetric hollow fiber‐supported thin film membranes is conducted, where individual hollow fibers are assembled in parallel to form a stack. A reliable gas‐tight sealing is obtained by combining ceramic paste with conductive adhesive ink cohesively. Comprehensive oxygen permeation test is conducted with the sealing portions being in hot zone and compared with a single hollow fiber membrane. Fundamental mechanism is discussed to understand the performances and their differences. An accelerated long‐term test (∼320 h, 16 thermal cycles) demonstrates excellent stability and robustness of the stack and sealing. The characterization of post‐test samples further confirms excellent stability and robustness of the phases and microstructures of the stack.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural, vibrational, thermal, and magnetic properties of mullite-type NdMnTiO 5 ceramic

Mullite-type $R$Mn 2 O 5 ($R$ = Y, rare-earth element) ceramics are of ongoing research attention because of their interesting crystal-chemical and magnetic properties. We report nuclear and magnetic structures of NdMnTiO 5 together with its spectroscopic, thermogravimetric, and magnetic properties. The polycrystalline sample is prepared by solid-state synthesis and characterized from neutron and X-ray powder diffraction data Rietveld refinements. NdMnTiO 5 crystallizes in the orthorhombic space group $Pbam$ with metric parameter $a$ = 755.20(1) pm, $b$ = 869.91(1) pm, $c$ = 582.42(1) pm, and $V$ = 382.62(1) 10 6 pm 3 . The Mn 3+ and Ti 4+ cations are observed to be located in the octahedral and pyramidal sites, respectively. The vibrational features in these polyhedral sites are characterized by Raman and Fourier transform infrared spectroscopes. The higher decomposition temperature of NdMnTiO 5 , compared to other $R$Mn 2 O 5 phases, is explained in terms of the higher bond strength of Ti-O bonds than those of Mn-O bonds. Temperature-dependent DC magnetic susceptibility suggests a paramagnetic to antiferromagnetic phase transition at 43(1) K. Inverse susceptibility in the paramagnetic region above 120 K follows the Curie-Weiss law, resulting in a magnetic moment of 6.33(1) μ B per formula unit. Neutron diffraction data collected at 7.5 K reveal that the magnetic moments of Nd 3+ and Mn 3+ in NdMnTiO 5 are incommensurately ordered with a propagation vector $k$ = (0, 0.238, 0.117).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Microstructural examination of interactions between chromia-based refractory and nuclear glass in a melter

This study shows the effects of nuclear waste glass production on Monofrax K-3 refractory corrosion. A continuously fed research-scale melter containing an Fe- and Ni-rich simulated nuclear waste feed with borosilicate glass-forming chemicals was cyclically melted at 1150°C and idled at 1050°C for a total of 11 weeks. Chemical maps using scanning electron microscopy show the interactions between the quenched melt and the refractory. Nanoscale X-ray-computed tomography was used for a three-dimensional visualization of certain parts of the interface. Unreacted K-3 consists of primarily corundum (Al,Cr) 2 O 3 and spinel (Fe 2+ ,Mg)(Al,Cr) 2 O 4 interlocking crystalline phases. Some of the Cr from the refractory interacts with the Ni and Fe from the melt to form a reaction layer comprising (Ni,Fe 2+ )(Cr,Fe 3+ ) 2 O 4 spinel crystals. Simultaneously, melt components (Na,Si) infiltrate into the refractory. This interaction proceeds at the expense of the integrity of the refractory structure. Intact refractory grains (e.g., (Al,Cr) 2 O 3 ) as well as the reaction layer itself can lose mechanical integrity and spall off into the melt, especially near the top of the melter. As the reaction layer can be a protective boundary for the refractory against further melt infiltration, a reduction in the reaction layer thickness allows an increase in refractory corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Corrosion behavior of Monofrax K-3 refractory in borosilicate-based model low activity waste glass melts

Owing to its good chemical and thermal durabilities at high temperatures, Monofrax K-3 refractory is widely used in nuclear waste vitrification as a lining material in melting vessels. However, the corrosion of K-3 refractory during the vitrification of nuclear waste is a serious problem because it affects the melter's safety, performance, and lifetime. Therefore, in the present study, we have focused on unearthing the impact of glass network formers, such as SiO 2 , B 2 O 3 , and Al 2 O 3 , in a model nuclear waste glass composition on the corrosion of Monofrax K-3 refractory. The corrosion tests have been performed per ASTM C621 at 1150°C for 5 days. The dimensional measurements on corroded K-3 refractory suggest that Al 2 O 3 and SiO 2 tend to reduce the refractory corrosion (neck loss), with the effect of Al 2 O 3 being significant. A corroded region on the K-3 refractory at the melt–refractory interface is observed. The corrosion occurs via a coupling of the melt infiltration induced by a capillary effect and the dissolution of Al, Mg, and Fe components from K-3 into the melt through chemical reactions. A Cr-rich layer is retained on the glass contact surface of the corroded K-3 refractory.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Surface plasmon driven near- and midinfrared photoconductivity in ligand-free ITO nanocrystal films

Semiconductor nanocrystals (NCs) offer exciting opportunities to deploy infrared optoelectronic technology in a variety of applications that are off-limits to conventional single-crystalline materials. However, the performance and stability of state-of-the-art NC-based devices strongly depend on the details of the NC surface and its passivating ligands. Here, the authors use indium tin oxide NC films stripped of organic ligands and conformally coated with Al 2 O 3 to show that absorption enabled by infrared localized surface plasmon resonances permit infrared photoconduction. For Au electrodes, these metallic NC films exhibit stable photoconductive performance over months in ambient and under electrical stress.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of O 2 addition on in-plasma photo-assisted etching of Si with chlorine

Addition of oxygen was used to control the in-plasma photo-assisted etching (PAE) of p-type Si(100) and poly-Si in a high density, inductively coupled, Faraday-shielded, Ar/Cl 2 (225/25 SCCM), 60 mTorr plasma. After etching, samples were transferred under vacuum to an UHV x-ray photoelectron spectroscopy chamber for surface analysis. Samples etched under PAE conditions (ion energies below the ionassisted etching, IAE, threshold) had a thicker surface oxide and lower [Cl] surface concentration, when compared to samples etched under IAE conditions (ion energies above the IAE threshold). PAE was found not to be affected by 0.1 or 0.25 SCCM O 2 addition, while etching stopped with more than 0.5 SCCM O 2 addition. IAE with RF power on the sample stage, resulting in -65 V self-bias, was not affected by up to 2 SCCM of oxygen addition but decreased rapidly when more than 5 SCCM O 2 was added to the plasma. These results imply that PAE may be completely suppressed, while IAE occurs unobstructed. The implications of these findings are discussed in view of applications involving continuous wave and pulsed-plasma processes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Precursor selection in hybrid molecular beam epitaxy of alkaline-earth stannates

One of the challenges of oxide molecular beam epitaxy (MBE) is the synthesis of oxides containing metals with high electronegativity (metals that are hard to oxidize). The use of reactive organometallic precursors can potentially address this issue. To investigate the formation of radicals in MBE, we explored three carefully chosen metal-organic precursors of tin for SnO 2 and BaSnO 3 growth: tetramethyltin (TMT), tetraethyltin (TET), and hexamethylditin (HMDT). All three precursors produced single-crystalline, atomically smooth, and epitaxial SnO 2 (101) films on r-Al 2 O 3 (101¯2) in the presence of oxygen plasma. The study of growth kinetics revealed reaction-limited and flux-limited regimes except for TET, which also exhibited a decrease in the deposition rate with increasing temperature above ~800 °C. Contrary to these similarities, the performance of these precursors was dramatically different for BaSnO 3 growth. TMT and TET were ineffective in supplying adequate tin, whereas HMDT yielded phase-pure, stoichiometric BaSnO 3 films. Significantly, HMDT resulted in phase-pure and stoichiometric BaSnO 3 films even without the use of an oxygen plasma (i.e., with molecular oxygen alone). Furthermore, these results are discussed using the ability of HMDT to form tin radicals and therefore assisting with Sn → Sn 4+ oxidation reaction. Structural and electronic transport properties of films grown using HMDT with and without oxygen plasma are compared. This study provides guideline for the choice of precursors that will enable the synthesis of metal oxides containing hard-to-oxidize metals using reactive radicals in MBE.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optimization of three-dimensional metamaterials for terahertz energy harvesting

This work focuses on finite element modeling (FEM) of a three-dimensional metamaterial used as an absorber for terahertz energy harvesting. The metamaterial consists of patterned pillars of an SU-8 dielectric photoresist coupled to a copper metal overlayer. Here, our study shows that the electromagnetic performance of the metamaterial is dependent on the following characteristic design parameters of the SU-8 dielectric: pillar height, bottom side length, and spacing between adjacent pillars. Using FEM, the metamaterial geometry is successfully optimized and the surface plasmon can be tuned to a peak frequency of 1.2 THz and a maximum terahertz absorption amplitude of 30%.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of processing parameters on the morphologies of complex sesquioxide thin films

Controlling and predicting the morphology of lanthanide sesquioxides in thin film form is vital to their use in current applications. In the present study, single and codeposited Sm2O3, Er2O3, and Lu2O3 thin films were grown on yttria-stabilized zirconia (8%) substrates by radio frequency magnetron sputtering at room temperature and 500 °C. The effect of two different substrate temperatures and altering the oxide cation on the structural and morphological properties of the films was analyzed. The thin films were characterized by profilometry, scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The single-component Lu2O3 and Sm2O3 films obtained were of the cubic phase, and the Er2O3 was a mix of cubic and monoclinic phases. It was observed for both the Er2O3 and Lu2O3 films that increasing the substrate temperature to 500 °C resulted in larger grained polycrystalline films. In contrast, large grained polycrystalline films were obtained at both room temperature and 500 °C for Sm2O3 and uneven granularity increased as temperature increased. Codeposition of Lu2O3 and Sm2O3, and Lu2O3 and Er2O3 resulted in a cubic bixbyite phase (the C phase of the lanthanide sesquioxide) solid solution. It was observed that the structure and morphology of the films can be controlled by manipulating deposition parameters. Both substrate temperature and altering the oxide cation contributed to changes in crystallinity and grain structure, which can modify the chemical and physical properties of the films for their applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomic layer deposition of MoO x thin films using Mo( i PrCp) 2 H 2 and O 3

Here, this work studied the growth of molybdenum oxide thin films with thermal atomic layer deposition (ALD) using Mo(iPrCp)2H2 and O3 as precursors. Growth parameters were determined by varying growth temperature and precursor dose times. ALD growth was exhibited in a temperature range of 100–200 °C. The growth per cycle ranged from 1.3 to 1.7 Å/cycle with a standard uniformity parameter of <5%. Attempts to grow films using H2O as an oxygen source showed no significant growth. Film properties were measured using spectroscopic ellipsometry, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Remote heteroepitaxy of GaN microrod heterostructures for deformable light-emitting diodes and wafer recycle

There have been rapidly increasing demands for flexible lighting apparatus, and micrometer-scale light-emitting diodes (LEDs) are regarded as one of the promising lighting sources for deformable device applications. Herein, we demonstrate a method of creating a deformable LED, based on remote heteroepitaxy of GaN microrod (MR) p - n junction arrays on c -Al 2 O 3 wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution scanning transmission electron microscopy, and the density functional theory simulations clarify how the remote heteroepitaxy is made possible through graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Knots are not for naught: Design, properties, and topology of hierarchical intertwined microarchitected materials

Lightweight and tough engineered materials are often designed with three-dimensional hierarchy and interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. We introduce a previously unexplored class of architected materials, whose components are interwoven and contain no junctions, and incorporate micro-knots as building blocks within these hierarchical networks. Tensile experiments, which show close quantitative agreements with an analytical model for overhand knots, reveal that knot topology allows a new regime of deformation capable of shape retention, leading to a ~92% increase in absorbed energy and an up to ~107% increase in failure strain compared to woven structures, along with an up to ~11% increase in specific energy density compared to topologically similar monolithic lattices. Our exploration unlocks knotting and frictional contact to create highly extensible low-density materials with tunable shape reconfiguration and energy absorption capabilities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thin film design of amorphous hafnium oxide nanocomposites enabling strong interfacial resistive switching uniformity

A design concept of phase-separated amorphous nanocomposite thin films is presented that realizes interfacial resistive switching (RS) in hafnium-oxide-based devices. The films are formed by incorporating an average of 7% Ba into hafnium oxide during pulsed laser deposition at temperatures ≤400°C. The added Ba prevents the films from crystallizing and leads to ~20-nm-thin films consisting of an amorphous HfO x host matrix interspersed with ~2-nm-wide, ~5-to-10-nm-pitch Ba-rich amorphous nanocolumns penetrating approximately two-thirds through the films. This restricts the RS to an interfacial Schottky-like energy barrier whose magnitude is tuned by ionic migration under an applied electric field. Resulting devices achieve stable cycle-to-cycle, device-to-device, and sample-to-sample reproducibility with a measured switching endurance of ≥10 4 cycles for a memory window ≥10 at switching voltages of ±2 V. Each device can be set to multiple intermediate resistance states, which enables synaptic spike-timing–dependent plasticity. The presented concept unlocks additional design variables for RS devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy’s behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m 1/2 , which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Deep Learning and Structural Imaging of Materials

Deep learning has had a transformative effect on numerous domains and is actively utilized by many scientists in data-intensive fields such as high-energy physics and cosmology. Materials science, and in particular, the structural imaging of materials with electrons and X-rays are projected to enter the age of scientific data torrents, positioning them as new application spaces for modern artificial intelligence. In this contribution, we provide a synopsis on the foundations and latest progress in deep learning and present an in-depth application of utilizing modern deep artificial neural networks in scanning transmission electron microscopy to extract structural material properties. We use this case study to expose the strengths of deep learning-based models and discuss their current limitations, in the process highlighting their potential use in other data-intensive structural imaging modalities.

Laanait, Nouamane↗
DOE OSTI2023

Engineered Wood: Sustainable Technologies and Applications

Natural wood has been used for construction, fuel, and furniture for thousands of years because of its versatility, renewability, and aesthetic appeal. However, new opportunities for wood are arising as researchers have developed ways to tune the material's optical, thermal, mechanical, and ionic transport properties by chemically and physically modifying wood's naturally porous structure and chemical composition. Such modifications can be used to produce sustainable, functional materials for various emerging applications such as automobiles, construction, energy storage, and environmental remediation. In this review, we highlight recent advancements in engineered wood for sustainable technologies, including thermal and light management, environmental remediation, nanofluidics, batteries, and structural materials with high strength-to-weight ratios. Additionally, the current challenges, opportunities, and future of wood research are discussed, providing a guideline for the further development of next-generation, sustainable wood-based materials.

36 MATERIALS SCIENCE↗