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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Effect of chlorine and chromium on sulfur solubility in low-activity waste glass

According to an empirical sulfur solubility model developed from over 200 simulated low-activity waste (LAW) glasses, chlorine and chromium show strong effects on lowering sulfur solubility in glass. This work was aimed at understanding the mechanism behind the negative effect of chlorine and chromium on sulfur solubility. A simplified LAW glass was prepared and saturated by sodium sulfate, sodium chloride, and sodium chromate salts as single components and as mixtures with different ratios at 25 mol%, 50 mol%, and 75 mol% of sulfate mixed with chloride or chromate. A crucible-scale salt-saturation was performed by mixing the crushed glass powder with an excess amount of salts, melting at 1150 °C for one hour, and quenching. Three mixing-melting-quenching cycles were applied to determine saturation concentrations of sulfur, chromium, and chlorine incorporated into the simplified LAW glass. The glass compositions were analyzed by inductively coupled plasma–atomic emission spectroscopy, ion chromatography, and X-ray emission spectroscopy. It is proposed that the negative effect of chlorine and chromium on sulfur solubility can be explained based on the simple hypothesis that sulfur, chlorine, and chromium are present in the glass as anions competing for the voids or interstitial sites of the glass matrix, and that their solubility strongly depends on the effective size of corresponding anions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Impact of irradiation induced dislocation loops on thermal conductivity in ceramics

Experimental work aimed at understanding the role of dislocation loops in limiting phonon mediated thermal transport in ceramics is presented. Faulted dislocation loops, having diameters of a few nanometers, were introduced by irradiating a polycrystalline cerium dioxide sample with 1.6 MeV protons at 700°C. XRD analysis indicated that irradiated samples retained their crystalline structure and exhibit very little lattice expansion suggesting a low concentration of point defects. Additionally, further microstructure characterization using transmission electron microscopy revealed that interstitial type faulted dislocation loops were primarily created as expected for these irradiation conditions. Thermal conductivity of the damaged layer was measured using a modulated thermoreflectance approach. Analysis of the experimental data using the classical Klemens-Callaway approach reveals that the conductivity reduction is primarily due to dislocation loops, while point defects and voids play only a minor role. These results provide experimental confirmation that faulted loops offer a unique arrangement for displaced atoms that leads to an unusually large reduction of thermal conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2021

New Mechanism for Yield Point Phenomena

Yield point phenomena (YPP) are widely attributed to discrete dislocation locking by solute atmospheres. An alternate YPP mechanism was recently suggested by simulations of Ta single crystals without any influence of solutes or discrete dislocations. The general meso-scale (GM) simulations consist of crystal plasticity (CP) plus accounting for internal stresses of geometrically necessary dislocation content. GM predicted the YPP while CP did not, suggesting a novel internal stress mechanism. The predicted YPP varied with crystal orientation and boundary conditions, contrary to expectations for a solute mechanism. The internal stress mechanism was probed by experimentally deforming oligocrystal Ta samples and comparing the results with independent GM simulations. Strain distributions of the experiments were observed with high-resolution digital image correlation. A YPP stress–strain response occurred in the 0–2% strain range in agreement with GM predictions. Shear bands appeared concurrent with the YPP stress–strain perturbation in agreement with GM predictions. At higher strains, the shear bands grew at progressively slower rates in agreement with GM predictions. It was concluded that the internal stress mechanism can account for the existence of YPP in a wide variety of materials including ones where interstitial-dislocation interactions and dislocation transient avalanches are improbable. Furthermore, the internal stress mechanism is a CP analog of various micro-scale mechanisms of discrete dislocations such as pile-up or bow-out. It may operate concurrently with strain aging, or either mechanism may operate alone. A suggestion was made for a future experiment to answer this question.

42 ENGINEERING↗
DOE OSTI2021

A Continuum Dislocation Dynamics Crystal Plasticity Approach to Irradiated Body-Centered Cubic α-Iron

Radiation-induced embrittlement of reactor pressure vessel (RPV) steels can potentially limit the operating life of nuclear power plants. Over extended exposure to radiation doses, these body-centered cubic (BCC) irons demonstrate irradiation damage. Here, we present a continuum dislocation density (CDD) crystal plasticity model to capture the interaction among dislocations and self-interstitial atom (SIA) loops in α-iron. We demonstrate the importance of modeling cross slip using a combined stochastic Monte Carlo approach and the role of slip system strength anisotropy in capturing stochastic cross slip interactions. Through these captured interactions, the CDD crystal plasticity model can capture both the stress response and the physical evolution of dislocations on different slip system planes. Single-crystal verification experiments are used to calibrate the CDD crystal plasticity model, and a set of simplified polycrystalline simulations demonstrates the model’s ability to capture the stress response from tensile experiments on α-iron.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High temperature deuterium enrichment using TiC coated vanadium membranes

Here, the current technology for hydrogen isotope separation requires enormous capital investment and energy consumption. Palladium-based membranes exhibit hydrogen isotope selectivity and provide a continuous method of isotope enrichment but have high material costs. Here, the authors investigate the potential of titanium carbide thin films coated on vanadium as a low-cost alternative, which enabled operation at high temperatures. Protium and deuterium exhibited nominally identical solubility in TiC coated vanadium over a range of 500–700°C. Permeation tests from 600 to 700°C revealed that protium permeated faster than deuterium, with the separation factor decreasing from 1.34 to 1.15 with increasing temperature. XPS depth-profiling showed a distinct interface between the TiC layer and the V foil in as-fabricated membranes. However, post-test analysis revealed significant V diffusion through TiC and segregation to the surface. Surface limitations resulting from this degradation accounted for changes in flux and may explain why the separation factor was lower than the value of 1.42 expected from high temperature interstitial diffusion of protium/deuterium in vanadium.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Analysis of furnace contamination on superconducting radio frequency niobium using secondary-ion mass spectrometry

Detection of surface contamination on niobium materials used in superconducting radio frequency (SRF) applications is difficult due to quantitative sensitivity and near-atomic depth resolution needed. Inspection of samples known to have experienced surface contamination was found to have inconsistent nitride coverage after high-temperature nitrogen gas exposure (“doping”). Here we compare contaminating species found on samples treated in several different vacuum furnaces, both “exposed” directly in the chamber and “protected” by containment shielding from evaporative sources with “furnace caps.” Typically, furnace caps are used to impede contamination from reaching the interior surface of cavities during the high-temperature vacuum bake that immediately precedes exposure to nitrogen gas. Although, to date, little is known about the effectiveness of these caps, SIMS results showed that they were effective in limiting contamination arising from the furnace environment. Inspection of sample surfaces by SEM showed a lack of nitrides present on contaminated specimens. TEM with energy dispersive spectroscopy performed on these samples revealed that a carbon-rich layer now existed, indicating that a relatively high contaminant load prevents the nucleation and growth of surface nitrides, while thus inhibiting interstitial nitrogen uptake. Except in extreme cases, subsequent removal of the top several micrometers of the surface via electropolishing appears to effectively eliminate any strong influence on the subsequent SRF cavity performance. With the absence of furnace cleaning, carbon contamination was found to be nearly 10× higher for protected nitrogen-doped and electropolished samples, with minimal metallic contamination detected for both processes. SIMS analysis was also performed to compare the cleanliness of samples fully prepared by such nitrogen “doping” with those prepared by a related process, involving the dissolution of niobium surface oxide and diffusion of oxygen into the surface. This oxygen doping or alloying process offers attractive advantages.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Kinetic Monte Carlo simulations of aging in δ -Pu

We have developed a first-passage kinetic Monte Carlo approach for materials aging to investigate the sensitivity of void swelling to model parameters, including helium bubble density and size distribution. In addition to explicitly accounting for the spatial distribution of individual point defects, bubbles, and voids, our approach can simulate total doses equivalent to 100 years of natural aging on statistically representative volumes of materials. This technique enables us to study the effects on swelling and radiation damage evolution due to temperature and dose rate (as altered in artificially aged experiments), differences in effective interaction radii between vacancies and interstitials, and varying defect diffusion activation energies, while providing more detailed information than previous rate-equation based approaches. In conclusion, our results indicate that spatial effects that are not modeled in mean-field rate theories could play a significant role in void swelling initiation and growth for certain regimes of model parameters.

Actinides↗
DOE OSTI2020

Zero-energy bound states in the high-temperature superconductors at the two-dimensional limit

Majorana zero modes (MZMs) that obey the non-Abelian statistics have been intensively investigated for potential applications in topological quantum computing. The prevailing signals in tunneling experiments “fingerprinting” the existence of MZMs are the zero-energy bound states (ZEBSs). However, nearly all of the previously reported ZEBSs showing signatures of the MZMs are observed in difficult-to-fabricate heterostructures at very low temperatures and additionally require applied magnetic field. Here, by using in situ scanning tunneling spectroscopy, we detect the ZEBSs upon the interstitial Fe adatoms deposited on two different high-temperature superconducting one-unit-cell iron chalcogenides on SrTiO 3 (001). The spectroscopic results resemble the phenomenological characteristics of the MZMs inside the vortex cores of topological superconductors. Our experimental findings may extend the MZM explorations in connate topological superconductors toward an applicable temperature regime and down to the two-dimensional (2D) limit.

Science & Technology - Other Topics↗
DOE OSTI2022

Influence of voids on the thermal and light stability of perovskite solar cells

The formation of voids in perovskite films close to the buried interface has been reported during film deposition. These voids are thought to limits the efficiency and stability of perovskite solar cells (PSCs). Here, we studied the voids formed during operation in perovskite films that were optimized during the solution deposition process to avoid voids. New voids formed during operation are found to assemble along grain boundaries at the bottom interface, caused by the loss of residual solvent and conversion of amorphous phase to crystalline phase. Unexpectedly, the formation of these voids did not negatively affect the stability of PSCs. Decreasing the amorphous region in perovskites by thermal annealing decreased the positive iodide interstitial density, and improved the light stability of PSCs. The annealed devices maintained 90% of their initial efficiency and light soaking for 1900 hours at open circuit condition under 1-sun illumination at 50°C.

14 SOLAR ENERGY↗
DOE OSTI2024

An active, stable cubic molybdenum carbide catalyst for the high-temperature reverse water-gas shift reaction

Although technologically promising, the reduction of carbon dioxide (CO 2 ) to produce carbon monoxide (CO) remains economically challenging owing to the lack of an inexpensive, active, highly selective, and stable catalyst. We show that nanocrystalline cubic molybdenum carbide (α-Mo 2 C), prepared through a facile and scalable route, offers 100% selectivity for CO 2 reduction to CO while maintaining its initial equilibrium conversion at high space velocity after more than 500 hours of exposure to harsh reaction conditions at 600°C. The combination of operando and postreaction characterization of the catalyst revealed that its high activity, selectivity, and stability are attributable to crystallographic phase purity, weak CO-Mo 2 C interactions, and interstitial oxygen atoms, respectively. Mechanistic studies and density functional theory (DFT) calculations provided evidence that the reaction proceeds through an H 2 -aided redox mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Optical Properties of Multilayered Sol–Gel Zinc-Oxide Films

Study of structural, optical and photocatalytic properties of multilayered (1–8 layers) zinc oxide films deposited on glass substrates by sol-gel method showed, that after thermal treatment at 500°C they consist of random oriented hexagonal crystalline grains with size of 34–40 nm, forming larger particles with sizes of 100–150 nm, which do not depend on number of layers. With an increase in the number of layers, the intensity of exciton photoluminescence decreases by a factor of 10, the absorption of light in the visible and near IR ranges increases, and the efficiency of photocatalytic decomposition of the test organic dye rhodamine B increases by 10–12%. The observed changes are related to the increase in the total area of grain boundaries and to the change in the integral amount of oxygen vacancies and interstitial atoms as the number of layers increases, which makes it possible to control the properties of zinc oxide films for applications in optoelectronics, photovoltaics and photocatalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Photoluminescence Properties of ZnO Nanorods Synthesized by Different Methods

The photoluminescence properties of ZnO nanorods synthesized by the low-temperature hydrothermal and high-temperature vapor-phase methods are studied. At room temperature, the photoluminescence of ZnO nanorods synthesized by the high-temperature vapor-phase method exhibits only one highintensity ultraviolet peak at a wavelength of 382 nm. At the same time, the luminescence spectra of ZnO nanorod samples grown by the low-temperature hydrothermal method, but with the use of different chemical reagents exhibit, apart from the ultraviolet peak, a violet band or a yellow-orange band at ~401 and ~574 nm, respectively. The violet luminescence band is attributed to defects or zinc vacancy complexes, and the yellow-orange band to defects associated with interstitial oxygen.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effect of the Composition of a Carrier Gas during the Growth of a Mn delta-Layer on the Electrical and Magnetic Properties of GaAs Structures

The effect of the arsine content (from 0 to 8 μmol), supplied to a reactor together with hydrogen, on the formation of delta-doped gallium-arsenide structures by the pulsed laser sputtering of a Mn target is investigated. It is found that an arsine molar fraction of ~2.5 μmol in the reactor atmosphere during the formation of a Mn delta-doped GaAs layer allows one to obtain single-crystal epitaxial structures with the lowest layer resistance and a ferromagnetic-paramagnetic phase transition temperature of about 40 K. Increasing the arsine content to 8 μmol or the absence of arsine in a hydrogen flow leads to a significant increase in the layer resistance in the temperature range below 150 K and a decrease in the Curie temperature. In the first case, this may be due to partial compensation of the hole conductivity by donor-type defects formed as a result of an excess of arsenic on the growing surface (arsenic atoms in Ga positions or in interstitial positions). In the second case, when no arsine is supplied to the reactor, the growth surface is likely to be enriched with gallium atoms, which makes the incorporation of Mn into the Ga sublattice difficult.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High-Pressure Electrides: A Quantum Chemical Perspective

It has long been assumed that all matter will adopt simple close-packed lattices and become metallic under pressure, in accordance with the Thomas–Fermi–Dirac (TFD) model. However, this model struggles to explain pressure-driven complex structural transitions that have been observed in elements, including sodium, challenging our conventional understanding of compressed matter. Moreover, in stark contrast to the TFD model, first-principles calculations suggest that various elements and compounds become electrides under pressure. Electrides, characterized by concentrations of charge density at interstitial regions, can be thought of as ionic compounds where electrons behave as the anions. Though ambient-pressure molecular electrides have been extensively studied via experiments and computations, high-pressure electrides (HPEs) are not well-understood. The identification and characterization of HPEs have been, to date, based purely on theory, including topological analysis of the electron density and the electron localization function. Here, we review these theoretical analysis tools and suggest guidelines that can be used to classify systems as electrides. Moreover, we describe models used to rationalize the electronic structure of HPEs, drawing parallels with ambient-pressure molecular systems, and encourage the development of experimental techniques that provide evidence for the theoretically calculated charge localization.

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

Investigating the Effects of Lithium Deposition on the Abuse Response of Lithium-Ion Batteries

Li deposition at the graphitic anode is widely reported in literature as one of the leading causes of capacity fade in lithium-ion batteries (LIBs). Previous literature has linked Li deposition resulting from low-temperature ageing to diminished safety characteristics, however no current research has probed the effects of Li deposition on the abuse response of well-characterized cells. Using overtemperature testing, a relationship between increased concentrations of Li deposition and exacerbated abuse response in 1 Ah pouch cells has been established. A novel Li deposition technique is also investigated, where cells with n:p < 1 (anode-limiting) have been cycled at a high rate to exploit Li + diffusion limitations at the anode. Scanning Electron Microscopy of harvested anodes indicates substantial Li deposition in low n:p cells after 20 cycles, with intricate networks of Li(s) deposits which hinder Li + intercalation/deintercalation. Peak broadening and decreased amplitude of differential capacity plots further validates a loss of lithium inventory to Li + dissolution, and Powder X-ray Diffraction indicates Li + intercalation with staging in anode interstitial sites as the extent of Li deposition increases. A cradle-to-grave approach is leveraged on cell fabrication and testing to eliminate uncertainty involving the effects of cell additives on Li deposition and other degradation mechanisms.

25 ENERGY STORAGE↗
DOE OSTI2024

Exploring Li-Ion Transport Properties of Li 3 TiCl 6 : A Machine Learning Molecular Dynamics Study

We performed large-scale molecular dynamics simulations based on a machine-learning force field (MLFF) to investigate the Li-ion transport mechanism in cation-disordered Li 3 TiCl 6 cathode at six different temperatures, ranging from 25°C to 100°C. In this work, deep neural network method and data generated by ab − initio molecular dynamics (AIMD) simulations were deployed to build a high-fidelity MLFF. Radial distribution functions, Li-ion mean square displacements (MSD), diffusion coefficients, ionic conductivity, activation energy, and crystallographic direction-dependent migration barriers were calculated and compared with corresponding AIMD and experimental data to benchmark the accuracy of the MLFF. From MSD analysis, we captured both the self and distinct parts of Li-ion dynamics. The latter reveals that the Li-ions are involved in anti-correlation motion that was rarely reported for solid-state materials. Similarly, the self and distinct parts of Li-ion dynamics were used to determine Haven’s ratio to describe the Li-ion transport mechanism in Li 3 TiCl 6 . Obtained trajectory from molecular dynamics infers that the Li-ion transportation is mainly through interstitial hopping which was confirmed by intra- and inter-layer Li-ion displacement with respect to simulation time. Ionic conductivity (1.06 mS/cm) and activation energy (0.29eV) calculated by our simulation are highly comparable with that of experimental values. Overall, the combination of machine-learning methods and AIMD simulations explains the intricate electrochemical properties of the Li 3 TiCl 6 cathode with remarkably reduced computational time. Thus, our work strongly suggests that the deep neural network-based MLFF could be a promising method for large-scale complex materials.

Selvaraj, Selva Chandrasekaran (ORCID:000000029023↗
DOE OSTI2025

Mitigation of Pitting on Nitrogen-Doped Niobium Surfaces through Two-Step Electropolishing

Surface processing of niobium superconducting RF cavities used in particle accelerators is crucial for determining their performance. The nitrogen (N)-doping method, developed at Fermilab, enhances the cavities’ quality factor by doping the cavity’s interior surface with N atoms at 800 °C. After N-doping, electropolishing (EP) is employed to remove the niobium nitride phases and attain the desired concentration of interstitial N atoms. This study explores the effects of EP conditions on N-doped niobium samples. The samples were electropolished at 5 to 40 °C and voltages between 3 and 22 V. Different EP voltage ranges produced two types of pits, classified based on their sizes. Larger pits, linked to higher voltages, are also affected by the reaction rate. Pitting could be reduced at a lower temperature and adequate EP voltage. However, to effectively minimize gas evolution forming large-sized pitting, peeling off the top nitride layer before EP might be beneficial. This was achieved through precise low-voltage etching, forming a two-step EP process. The process involves removing the top 100–200 nm layer at a low voltage, followed by standard EP to remove the required material. This two-step EP process effectively mitigated the pitting risk associated with gas evolution on N-doped surfaces.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Linear Grains

LIGR (Linear Grains) implements a linear (Fourier mode) analysis of a shock propagating through density perturbations. It has two primary capabilities. First, it calculates the shock front distortion and post-shock flow variables (density, velocity, pressure) for single Fourier mode pairs in two dimensions (a pair of x and y modes). Second, it calculates these same quantities for a grains-like pre-shock density perturbation, which consists of a sum of many Fourier modes. This grains-like perturbation is a periodic grid of rectangles at a specifiable density and size (the grains), separated by regions of a different specifiable size and density (interstitial spaces between the grains). The single-mode analysis is based on the work of Velikovich et al., Phys. Plasmas 14 072706 (2007).

Li, GraceJ↗