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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Structural features and the microscopic dynamics of the three-component Zr{sub 47}Cu{sub 46}Al{sub 7} system: Equilibrium melt, supercooled melt, and amorphous alloy

The structural and dynamic properties of the three-component Zr{sub 47}Cu{sub 46}Al{sub 7} system are subjected to a molecular dynamics simulation in the temperature range T = 250–3000 K at a pressure p = 1.0 bar. The temperature dependences of the Wendt–Abraham parameter and the translation order parameter are used to determine the glass transition temperature in the Zr{sub 47}Cu{sub 46}Al{sub 7} system, which is found to be T{sub c} ≈ 750 K. It is found that the bulk amorphous Zr{sub 47}Cu{sub 46}Al{sub 7} alloy contains localized regions with an ordered atomic structures. Cluster analysis of configuration simulation data reveals the existence of quasi-icosahedral clusters in amorphous metallic Zr–Cu–Al alloys. The spectral densities of time radial distribution functions of the longitudinal (C̃{sub L}(k, ω)) and transverse (C̃{sub T}(k, ω)) fluxes are calculated in a wide wavenumber range in order to study the mechanisms of formation of atomic collective excitations in the Zr{sub 47}Cu{sub 46}Al{sub 7} system. It was found that a linear combination of three Gaussian functions is sufficient to reproduce the (C̃{sub L}(k, ω)) spectra, whereas at least four Gaussian contributions are necessary to exactly describe the (C̃{sub T}(k, ω)) spectra of the supercooled melt and the amorphous metallic alloy. It is shown that the collective atomic excitations in the equilibrium melt at T = 3000 K and in the amorphous metallic alloy at T = 250 K are characterized by two dispersion acoustic-like branches related with longitudinal and transverse polarizations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structure and Properties of SiO{sub x} Films Prepared by Chemical Etching of Amorphous Alloy Ribbons

The structure and the physical properties of amorphous SiO{sub x} films prepared by chemical etching of an iron-based amorphous ribbon alloy have been studied. The neutron diffraction and also the atomicforce and electron microscopy show that the prepared visually transparent films have amorphous structure, exhibit dielectric properties, and their morphology is similar to that of opals. The samples have been studied by differential scanning calorimetry, Raman and IR spectroscopy before and after their heat treatment. It is found that annealing of the films in air at a temperature of 1273 K leads to a change in their chemical compositions: an amorphous SiO{sub 2} compound with inclusions of SiO{sub 2} nanocrystals (crystobalite) forms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural Aspects of Deformational Amorphization of Ti{sub 50}Ni{sub 25}Cu{sub 25} Crystalline Alloy under High Pressure Torsion

The evolution of the structure of the Ti50Ni25Cu25 crystalline alloy during high-pressure torsion at room temperature has been studied. The torsional moment variation curve as a function of the strain value was fixed in situ, which allowed directly observing the transition of the material from the crystalline state to the amorphous state during the HPT. It was found that the amorphization of the material in the course of the HPT begins on the grain boundaries and fragments of the crystalline phase. Amorphized boundaries form a “grain-boundary carcass” in the cells of which the high-defect nanocrystalline phase is formed. Growth of deformation leads to broadening of the “grain-boundary carcass,” loss of stability of the crystalline phase, and, as a consequence, to the phase transition “crystal → amorphous” state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Enhanced Drug Delivery by Dissolution of Amorphous Drug Encapsulated in a Water Unstable Metal–Organic Framework (MOF)

Abstract Encapsulating a drug molecule into a water‐reactive metal–organic framework (MOF) leads to amorphous drug confined within the nanoscale pores. Rapid release of drug occurs upon hydrolytic decomposition of MOF in dissolution media. Application to improve dissolution and solubility for the hydrophobic small drug molecules curcumin, sulindac, and triamterene is demonstrated. The drug@MOF composites exhibit significantly enhanced dissolution and achieves high supersaturation in simulated gastric and/or phosphate buffer saline media. This combination strategy where MOF inhibits crystallization of the amorphous phase and then releases drug upon MOF irreversible structural collapse represents a novel and generalizable approach for drug delivery of poorly soluble compounds while overcoming the traditional weakness of amorphous drug delivery: physical instability of the amorphous form.

Suresh, Kuthuru↗
DOE OSTI2011

Localized Amorphism after High-Strain-Rate Deformation in TWIP Steel

The microstructural features of shear localization, generated by a high strain rate (~105 s-1) deformation, of a twinning-induced plasticity (TWIP) steel containing about 17.5 wt. % Mn were well characterized by means of transmission electron microscopy and electron back scatter diffraction. The high deformation rate was obtained by a ballistic impact penetration test on a TWIP steel sheet. In addition to the deformation twins observed as the domain microstructural characterization of high-strain-rate deformation outside shear bands, some shear bands consisting of complex microstructures were also evidenced in the highly-deformed area. Inside the shear band, there exist a large region of amorphous phase and a smooth transition zone containing nano-crystalline (NC) phase. The grain size decreased gradually in the transition zone, changing from coarse-scale (> 100 nm) next to the fully amorphous zone to fine-scale (<10nm) adjacent to the amorphous region. The coexistence of amorphous state and fine-grained nano-crystalline phase obviously suggests that melting occurred inside the shear bands, which is corroborated by calculations showing a very high temperature rise due to the localized plastic deformation and the extremely rapid cooling rate through heat dissipation to the rest of the specimen.

Li, Nan↗
DOE OSTI2017

The amorphization of 3C-SiC irradiated at moderately elevated temperatures as revealed by X-ray diffraction

Mechanisms of radiation damage buildup in 3C-SiC remain poorly understood. Here, we use X-ray diffraction in combination with numerical simulations to study depth profiles of radiation-produced strain and lattice damage in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal increased defect recombination with increasing temperature, with a critical amorphization fluence increasing from 0.17 to 0.44 displacements per atom. The amorphization process is found to be correlated with the evolution of lattice strain. We find that, at fluences corresponding to the onset of amorphization, lattice strain is ~2% and is independent of temperature. With continuing bombardment above the onset of amorphization, the strain in the crystal bulk increases and reaches a saturation value that decreases from 7% to 5% with increasing temperature. Based on strain profiles, we compute depth profiles of the effective concentration of point defect clusters in the crystalline phase. Bombardment at higher temperatures results in lower maximum defect concentrations pointing to enhanced defect mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of silicon and oxygen dopants on the stability of hydrogenated amorphous carbon under harsh environmental conditions

Harsh environments pose materials durability challenges across the automotive, aerospace, and manufacturing sectors, and beyond. While amorphous carbon materials have been used as coatings in many environmentally-demanding applications owing to their unique mechanical, electrical, and optical properties, their limited thermal stability and high reactivity in oxidizing environments have impeded their use in many technologies. Silicon- and oxygen-containing hydrogenated amorphous carbon (a-C:H:Si:O) films are promising for several applications because of their higher thermal stability and lower residual stress compared to hydrogenated amorphous carbon (a-C:H). However, an understanding of their superior thermo-oxidative stability compared to a-C:H is lacking, as it has been inhibited by the intrinsic challenge of characterizing an amorphous, multi-component material. Here, we show that introducing silicon and oxygen in a-C:H slightly enhances the thermal stability in vacuum, but tremendously increases the thermo-oxidative stability and the resistance to degradation upon exposure to the harsh conditions of low Earth orbit (LEO). The latter is demonstrated by having mounted samples of a-C:H:Si:O on the exterior of the International Space Station via the Materials International Space Station (MISSE) mission 7b. Exposing lightly-doped a-C:H:Si:O to elevated temperatures under aerobic conditions or to LEO causes carbon volatilization in the near-surface region, producing a silica surface layer that protects the underlying carbon from further removal. In conclusion, these findings provide a novel physically-based understanding of the superior stability of a-C:H:Si:O in harsh environments compared to a-C:H.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Surface oxidation and crystallization of FeNi-Based soft magnetic nanocrystalline and amorphous nanocomposite alloys

In this work, we present characterization of surface oxidation and crystallization behavior of Metal Amorphous Nanocomposite (MANC) (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 alloys via complementary x-ray diffraction, electron microscopy, and x-ray photoelectron spectroscopy techniques. An adherent amorphous oxide of roughly 15–20 nm in thickness is observed on the wheel side of the ribbon, enriched in Fe relative to Ni and with significant content of Si and Nb as would be expected based upon a comparison of the Gibbs free energy of formation of the stable oxide phases. The amorphous character of the oxide is likely to result from the significant Si-content coupled with the amorphous and nanocrystalline character of the underlying metallic layer. Higher density of FeNi-enriched nanocrystals is also observed within ~100 nm of the wheel-side surface, presumably due to reduction in local glass former concentration. A rough, crystalline copper oxide layer is also present and forms through contact between the copper wheel and the solidifying melt during the rapid solidification process. On the air side of the ribbon, a crystalline oxide layer of ~15–20 nm is formed as well as intergranular oxidation that penetrates along the grain boundaries between highly textured surface crystallites of ~50–100 nm in size. The crystalline nature of the oxide on these surfaces is asserted to result from the lack of significant Si-content and the pre-existing surface crystallites that form during the rapid solidification process which promote a crystalline oxide surface layer. Furthermore, these results shed new insights into the details of surface oxidation and can help to inform processing and alloy composition adjustments which seek to tailor surface properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Mapping strain and structural heterogeneities around bubbles in amorphous ionically conductive Bi 2 O 3

While amorphous materials are often approximated to have a statistically homogeneous atomic structure, they frequently exhibit localized structural heterogeneity that challenges simplified models. This study uses 4D scanning transmission electron microscopy to investigate the strain and structural modifications around gas bubbles in amorphous Bi 2 O 3 induced by argon irradiation. We present a method for determining strain fields surrounding bubbles that can be used to measure the internal pressure of the gas. Compressive strain is observed around the cavities, with higher-order crystalline symmetries emerging near the cavity interfaces, suggesting paracrystalline ordering as a result of bubble coarsening. This ordering, along with a compressive strain gradient, indicates that gas bubbles induce significant localized changes in atomic packing. By analyzing strain fields with maximum compressive strains of 3%, we estimate a lower bound on the internal pressure of the bubbles at 2.5 GPa. These findings provide insight into the complex structural behavior of amorphous materials under stress, particularly in systems with gas inclusions, and offer new methods for probing the local atomic structure in disordered materials. Although considering structural heterogeneity in amorphous systems is non-trivial, these features have crucial impacts on material functionalities, such as mechanical strength, ionic conductivity, and electronic mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Fabrication of PbS nanoparticle coated amorphous carbon nanotubes: Structural, thermal and field emission properties

Graphical abstract: Simple chemical synthesis of PbS nanoparticle coated amorphous carbon nanotubes have shown better thermal stability and enhanced electron field emission properties. Highlights: {yields} PbS nanocrystals coated amorphous carbon nanotubes have been synthesized through a simple chemical route at low temperature. {yields} The composite is thermally more stable than amorphous CNTs. {yields} Composite have shown excellent cold cathode field emission property. -- Abstract: A simple chemical route for the synthesis of PbS nanoparticle coated amorphous carbon nanotubes (aCNTs) was described. The nanocomposite was prepared from an aqueous suspension of acid functionalized aCNTs, lead acetate (PbAc), and thiourea (TU) at room temperature. The phase formation and composition of the samples were characterized by X-ray diffraction and energy dispersive analysis of X-ray studies. The Fourier transformed infrared spectra analysis revealed the attachment of PbS nanoparticles on the acid functionalized aCNT surfaces. Morphology of the samples was analyzed with a field emission scanning electron microscope. UV-Vis study also confirmed the attachment of PbS nanoparticles on the walls of aCNTs. Thermal gravimetric analysis showed that the PbS coated aCNTs are more thermally stable than functionalized aCNTs. The PbS coated aCNTs showed enhanced field emission properties with a turn-on field 3.34 V {mu}m{sup -1} and the result is comparable to that of pure crystalline CNTs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Characterisation of reduced graphene oxides prepared from natural flaky, lump and amorphous graphites

Highlights: • Natural flaky, lumpy and amorphous graphites were used to synthesis rGO. • Investigation the effect of the crystal morphology on the oxidation process of GrO and characteristics of prepared rGO. • Low graphitisation degree, big specific surface area and small lateral size were beneficial to the oxidation of graphite. - Abstract: The characterisation of reduced graphene oxides (rGOs) prepared from natural flaky, lumpy, and amorphous graphites using Hummers method was investigated. The prepared graphite oxides (GrOs) and rGOs were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy, atomic force microscopy and electrochemical performance. The results showed that amorphous graphite was much easier to oxidise than lumpy and flaky graphites and was preferable for preparing single or double layer graphene because low graphitisation degree, high defect degree, high specific surface area and small crystal size were beneficial for (1) the oxidants to attack the exposed carbon atoms, (2) the intercalation of oxidants, and (3) the diffusion of oxidants between graphitic layers. In addition, rGO synthesised from amorphous graphite had the most defects and the smallest size of the in-plane sp{sup 2} domains compared to those obtained from the other two nature graphites.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Gas permeation properties of amorphous zeolitic imidazolate framework membranes made by atomic/molecular layer deposition

Amorphous metal-organic framework (MOF) membranes are desirable because they may retain some of the molecular sieving properties of their crystalline counterparts while being free of grain boundary defects, which often hinder the consistent achievement of high membrane performance. However, current methods, like melting and compression, for fabricating amorphous MOF membranes involve multi-step processes that require the formation of a crystalline membrane first, that is then amorphized, and therefore, could be challenging to scale. Here, we utilize atomic/molecular layer deposition (ALD/MLD) of diethylzinc (DEZ) and 2-methylimidazole (2mIm) to directly synthesize ultrathin amorphous zeolitic imidazolate framework (aZIF) deposits on γ-alumina-coated α-alumina supports. As the number of ALD/MLD cycles increased from 10 to 300, gas permeances decreased while ideal selectivities increased. Mixture separation factors for C3H6/C3H8, CO2/N2, and H2/C3H8 as high as 4, 37, and 194, respectively, were obtained. At 200 °C and 2.5 bar equimolar feed of H2 and C3H8, a H2/C3H8 mixture separation factor of 185 is obtained with an H2 permeance of ca. 4.15x10-8 mol/m2-s-Pa (124 GPU). Additionally, the membrane achieves a CO2/N2 mixture separation factor of 37 at 25 °C and 1 bar with a CO2 permeance of ca. 3.96x10-8 mol/m2-s-Pa (118 GPU). Considering the vast array of compositionally distinct aZIFs that can be potentially deposited by this approach, an enormously large parameter space for membrane design is emerging to be explored.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Swift heavy ion irradiation-induced amorphization of La2Ti2O7

Polycrystalline La2Ti2O7 powders have been irradiated with 2.0 GeV 181Ta ions up to a fluence of 1 × 1013 ions/cm2. Radiation-induced structural modifications were analyzed using synchrotron-based X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Raman spectroscopy and transmission electron microscopy (TEM). An increase in the amorphous fraction as a function of fluence was revealed by XRD and Raman analyses and is evidenced by the reduction in intensity of the sharp Bragg maxima from the crystalline regions. Concurrently, diffraction maxima and vibrational absorption bands broaden with the increasing amorphous fraction. The cross-section for the crystalline-to-amorphous transformation (ion tracks) was determined by quantitative analysis of XRD patterns yielding a track diameter of d = 7.2 ± 0.9 nm. Slightly larger track diameters were obtained directly from TEM images (d = 10.6 ± 0.8 nm) and SAXS analysis (d = 10.6 ± 0.3 nm). High-resolution TEM images revealed that single tracks are entirely amorphous without any outer crystalline, disordered shell as found in pyrochlore oxides of the same stoichiometry. The large ratio of ionic radii of the A- and B-site cations (rA/rB = 1.94) means that disordering over the A- and B-sites is energetically unfavorable.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A Second Amorphous Layer Underneath Surface Oxide

Abstract Formation of a nanometer-scale oxide surface layer is common when a material is exposed to oxygen-containing environment. Employing aberration-corrected analytical transmission electron microscopy and using single crystal SnSe as an example, we show that for an alloy, a second thin amorphous layer can appear underneath the outmost oxide layer. This inner amorphous layer is not oxide based, but instead originates from solid-state amorphization of the base alloy when its free energy rises to above that of the metastable amorphous state; which is a result of the composition shift due to the preferential depletion of the oxidizing species, in our case, the outgoing Sn reacting with the oxygen atmosphere.

Materials Science↗
DOE OSTI2026

Intercalation-Induced Amorphization Boosts Aqueous Magnesium-Ion Storage

The design of aqueous battery cathode materials that can store divalent ions with high capacity and satisfactory reversibility is of great technical importance and challenge. Here, we report that divalent Mg 2+ storage is facilitated by an intercalation-induced amorphization of vanadate electrode materials. Electrokinetic analyses and in situ synchrotron X-ray diffraction and absorption spectroscopy collectively demonstrate that vanadate layered materials (Li–V 3 O 8 ) undergo a structural transformation to amorphization induced by Mg 2+ intercalation, and a reversible restoration of crystalline structure upon Mg 2+ deintercalation. Debye scattering simulations suggest that intercalation-induced turbostratic disorder, especially random rotations, translational shifts, oscillatory motions, or varied interlayer spacing of adjacent V–O molecular layers, could be responsible for the observed amorphization. The highly distorted local structure, in turn, facilitates Mg 2+ intercalation across the vanadate electrode materials, responsible for nearly 3/7 of the total Mg 2+ ions intercalated. The study presented reveals an intriguing relationship between ion transport and the reversible amorphization-to-crystallization dynamics it induces, opening a paradigm for designing advanced aqueous battery electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

X-ray Scattering and O–O Pair-Distribution Functions of Amorphous Ices

The structure factor and oxygen-oxygen pair distribution functions of amorphous ices at liquid nitrogen temperature (T = 77 K) have been derived from wide-angle X-ray scattering (WAXS) up to interatomic distances of r = 23 angstrom, where local structure differences between the amorphous ices can be seen for the entire range. The distances to the first coordination shell for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA) were determined to be 2.75, 2.78, and 2.80 angstrom, respectively, with high accuracy due to measurements up to a large momentum transfer of 23 angstrom(-1). Similarities in pair-distribution functions between LDA and supercooled water at 254.1 K, HDA and liquid water at 365.9 K, and VHDA and high-pressure liquid water were found up to around 8 angstrom, but beyond that at longer distances, the similarities were lost. In addition, the structure of the high-density amorphous ices was compared to high-pressure crystalline ices IV, IX, and XII, and conclusions were drawn about the local ordering.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Additive Molar Volumes in Amorphous Ca/Sr Carbonate Solid Solutions

The development of predictive models of minor element incorporation in crystalline carbonate end products requires an understanding of the fundamental controls on metastable intermediate phase composition. In this study, we used small-angle X-ray scattering (SAXS), X-ray pair distribution function (PDF), thermogravimetric analysis (TGA), inductively coupled plasma mass spectrometry (ICP-MS), and transmission electron microscopy (TEM) to determine the composition-dependent density of an amorphous calcium–strontium carbonate (ACSC) solid solution. The amorphous calcium carbonate (ACC) and strontium carbonate (ASC) measured densities were ρ ACC = 2.19 ± 0.04 g/cm 3 and ρ ASC = 2.97 ± 0.05 g/cm 3 . Throughout our work, the experiments showed a dependence of the water content of the amorphous solid solution on the Sr mole fraction. An equation that relates the molar volume to the average cation radius, the carbonate ion radius, and the water volume was parameterized for hydrated crystalline carbonates and predicted well the molar volume of the ACSC solid solution. This finding indicates that, as for hydrated crystalline carbonates, the molar volumes of amorphous carbonates are additive and that water is a structural component of ACSC. Ab initio molecular dynamics (AIMD) simulations of the ACSC solid solutions showed strong linear correlations between calculated molar volumes and Sr and H 2 O contents, thus supporting the experimental results. In conclusion, our findings highlight the need to consider the full CaCO 3 –MeCO 3 –H 2 O ternary when quantifying metal cation incorporation in ACC.

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

Wafer-Scale Synthesis of 2D Materials by an Amorphous Phase-Mediated Crystallization Approach

The interest in the wafer-scale growth of two-dimensional (2D) materials, including transition metal dichalcogenides (TMDCs), has been rising for transitioning from lab-scale devices to commercial-scale systems. Among various synthesis techniques, physical vapor deposition, such as pulsed laser deposition (PLD), has shown promise for the wafer-scale growth of 2D materials. However, due to the high volatility of chalcogen atoms (e.g., S and Se), films deposited by PLD usually suffer from a lack of stoichiometry and chalcogen deficiency. To mitigate this issue, excess chalcogen is necessary during the deposition, which results in problems like uniformity or not being repeatable. This study demonstrates a condensed-phase or amorphous phase-mediated crystallization (APMC) approach for the wafer-scale synthesis of 2D materials. This method uses a room-temperature PLD process for the deposition and formation of amorphous precursors with controlled thicknesses, followed by a post-deposition crystallization process to convert the amorphous materials to crystalline structures. This approach maintains the stoichiometry of the deposited materials throughout the deposition and crystallization process and enables the large-scale synthesis of crystalline 2D materials (e.g., MoS 2 and WSe 2 ) on Si/SiO 2 substrates, which is critical for future wafer-scale electronics. We show that the thickness of the layers can be digitally controlled by the number of laser pulses during the PLD phase. Optical spectroscopy is used to monitor the crystallization dynamics of amorphous layers as a function of annealing temperature. The crystalline quality, domain sizes, and the number of layers were explored using nanoscale and atomistic characterization (e.g., AFM, STEM, and EDS) along with electrical characterization to explore process–structure–performance relationships. Finally, this growth technique is a promising method that could potentially be adopted in conventional semiconductor industries for wafer-scale manufacturing of next-generation electronic and optoelectronic devices.

2D electronics↗