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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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Revealing the synergistic effects of sequential and simultaneous dual beam irradiations in tungsten via in-situ TEM

Elucidating the synergistic effects of different energetic beams on the radiation response of nuclear materials is critical for developing an improved methodology for their evaluation when exposed to extreme environments. This article describes in-situ sequential (He implantation followed by Kr irradiation and vice-versa) and simultaneous (heavy ion Kr irradiation and He implantation) dual beam irradiations performed on tungsten at 1223 K. Dislocation loop density, average area, and total loop damage as a function of irradiation history and dose/fluence are quantified. The loop Burgers vectors and cavity damage (cavity density, size and total change in volume) are also determined at the final maximum dose for each condition. The loop damage evolution was different in all cases, with the smallest loop damage observed in the simultaneous experiment. Annihilation of Kr generated dislocation loops during He implantation in the Kr + He experiment was an unanticipated observation that may be explained by the dynamic evolution of dislocation loop sink strengths and time-dependent defect fluxes. Dislocation loop raft formation, denuded zones near extended defects, and cavity damage are compared across the different conditions. The phenomena observed and discussed in this work will stimulate further experimental and computational modeling activities leading to improved fundamental understanding of the irradiation response of nuclear materials under reactor-similar environments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Parameterization of vacancy production rate in phase-field models of fission gas bubble evolution in nuclear fuel

Phase-field modeling has increasingly been used to study microstructural evolution in fission gas bubbles in nuclear fuel to improve understanding of fission gas release. To improve computational efficiency, often only vacancies and gas atoms are included as defect species. In this case, the net effects of vacancy and interstitial production, recombination, and biased sink absorption are included as a net vacancy source, or net vacancy source combined with an effective sink. However, there has been a lack of clarity on what parameter values should be used for these approaches to best match the more complete physical picture that includes interstitials and vacancies. Here, we compare a phase-field model of void growth to analytical models for the source-only and source plus sink approach to gain insight into how the phase-field models can be parameterized effectively. The source-only approach provides greater flexibility to match growth rates determined from the full vacancy-interstitial picture. A strategy was developed for determining the value of the net vacancy source term by comparing to an analytical model that includes vacancy and interstitial production, recombination, and biased sink absorption. Finally, this strategy can be used to parameterize phase-field models of fission gas bubble growth.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Investigation of α-MnO 2 Tunneled Structures as Model Cation Hosts for Energy Storage

Future advances in energy storage systems rely on identification of appropriate target materials and deliberate synthesis of the target materials with control of their physiochemical properties in order to disentangling the contributions of distinct properties to the functional electrochemistry. Furthermore, this goal demands systematic inquiry using model materials that provide the opportunity for significant synthetic versatility and control. Ideally, a material family that enables direct manipulation of characteristics including composition, defects and crystallite size while remaining within the defined structural framework would be necessary. Accomplishing this through direct synthetic methods is desirable to minimize the complicating effects of secondary processing.

25 ENERGY STORAGE↗
DOE OSTI2018

Graphene-Supported Monometallic and Bimetallic Dimers for Electrochemical CO 2 Reduction

Bimetallic catalysts are attractive alternatives to extend the parameter space that can be tuned for support interactions and catalytic performance. In this study, we have investigated the smallest bimetallic catalysts dimers supported on defective graphene for the electrochemical reduction of CO 2 to CH 4 based on a first-principles approach and the computational hydrogen electrode model. The monometallic and bimetallic dimers formed from Group 10 (Ni, Pd, Pt) and group 11 (Cu, Ag, Au) elements are characterized by a positively charged anchoring atom occupying the vacancy site of graphene and a neutral or slightly negatively charged antenna atom sticking out from the graphene surface. The strong selective binding of these dimers ensures their high stability. Possible rate-limiting steps are identified from the full reaction pathways to generate CH4. Overall, Pt-2, AgNi, Pd-2, and AgPt are the best candidates with the lowest overpotential values of 0.37, 0.69, 0.69, and 0.76 V, respectively. It is found that the alloy effect and the interaction with support help to optimize the property. These metallic dimers, however, retain nonmonotonous property relationships that give opportunity to go beyond scaling behavior and look for a few atom catalysts that have unique properties to reduce rate-limiting potentials and improve the catalytic performance.

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

Origins of Acid-Gas Stability Behavior in Zeolitic Imidazolate Frameworks: The Unique High Stability of ZIF-71

Zeolitic imidazolate frameworks (ZIFs) are promising materials for industrial process separations, but recent literature reports have highlighted their vulnerability to acid gases (e.g., SO 2 , CO 2 , NO 2 , H 2 S), often present in practical applications. While previous work has documented the widely varying stability behavior of many ZIFs under varying (humid and dry) acid gas environments, efforts to explain or correlate these experimental observations via empirical descriptors have not succeeded. A key observation is that ZIF-71 (RHO topology) is an extraordinarily stable ZIF material, retaining both structure and porosity under prolonged humid SO 2 exposure whereas many other well-known ZIFs with different linkers and topologies (such as ZIF-8) were shown to degrade. Through a combination of hybrid quantum mechanics/molecular mechanics (QM/MM) based methods and statistical mechanical models, we successfully explain this important experimental observation via atomistic investigations of the reaction mechanism. Our holistic approach reveals an ~9 times lower average defect formation rate in ZIF-71 RHO compared to ZIF-8 SOD, leading to the conclusion that the observed experimental stability of this material rises from kinetic effects. Moreover, our analysis reveals that differing stability of the two materials is determined by the distributions of acid gas molecules, which is difficult to capture using empirical descriptors. Furthermore, our results suggest wider applicability of the present approach, toward identifying tuned functional groups and topologies that move the acid gas distributions away from more reactive sites and thus allow enhanced kinetic stability.

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

Stress-induced hydrogen self-trapping in tungsten

The molecular dynamics simulations of trapping of hydrogen atoms in tungsten are presented. The simulations reveal formation of platelet-like structures of self-trapped hydrogen induced by stresses in tungsten, in particular, those produced by dislocations, at the interstitial hydrogen concentrations ~0.3-1 at.%. The spontaneous hydrogen platelet formation in absence of dislocations and external stresses has been also observed at the higher hydrogen concentrations ~10 at.%. It is shown that the platelets can retain substantial quantities of hydrogen, exceeding trapping capacity of other non-cavity defects in tungsten. The properties of the hydrogen latelets formed in tungsten under various conditions are assessed and a formation mechanism is proposed. A model of hydrogen retention by the dislocation-induced structures is also presented, which describes retained quantities and outgassing dynamics of hydrogen in plasma exposed tungsten samples.

08 HYDROGEN↗
DOE OSTI2019

Consideration of thermal Hall effect in undoped cuprates

A recent observation of the thermal Hall effect of magnetic origin in underdoped cuprates calls for critical reexamination of low-energy magnetic dynamics in an undoped antiferromagnetic compound on square lattice, where traditional, renormalized spin-wave theory was believed to work well. Using the Holstein-Primakoff boson formalism,in this work we find that magnon-based theories can lead to finite Berry curvature in the magnon band once the Dzyaloshinskii-Moriya spin interaction is taken into account explicitly, but fail to produce nonzero thermal Hall conductivity. Assuming accidental doping by impurities and magnon scattering off of such impurity sites fails to predict skew scattering at the level of the Born approximation. Local formation of skyrmion defects is also found incapable of generating the magnon thermal Hall effect. Turning to a spinon-based scenario, we write down a simple model by adding spin-dependent diagonal hopping to the well-known π-flux model of spinons. The resulting two-band model has a Chern number in the band structure, and generates thermal Hall conductivity whose magnetic field and temperature dependencies mimic closely the observed thermal Hall signals. In disclaimer, there is no firm microscopic basis of this model and we do not claim to have found an explanation of the data, but given the unexpected nature of the experimental observation, it is hoped this work could serve as a step towards reaching some level of understanding.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Vortex Lattices in Active Nematics with Periodic Obstacle Arrays

Here, we numerically model a two-dimensional active nematic confined by a periodic array of fixed obstacles. Even in the passive nematic, the appearance of topological defects is unavoidable due to planar anchoring by the obstacle surfaces. We show that a vortex lattice state emerges as activity is increased, and that this lattice may be tuned from “ferromagnetic” to “antiferromagnetic” by varying the gap size between obstacles. We map the rich variety of states exhibited by the system as a function of distance between obstacles and activity, including a pinned defect state, motile defects, the vortex lattice, and active turbulence. We demonstrate that the flows in the active turbulent phase can be tuned by the presence of obstacles, and explore the effects of a frustrated lattice geometry on the vortex lattice phase.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microfluidic electrochemical cell for in situ structural characterization of amorphous thin-film catalysts using high-energy X-ray scattering

Porous, high-surface-area electrode architectures are described that allow structural characterization of interfacial amorphous thin films with high spatial resolution under device-relevant functional electrochemical conditions using high-energy X-ray (>50 keV) scattering and pair distribution function (PDF) analysis. Porous electrodes were fabricated from glass-capillary array membranes coated with conformal transparent conductive oxide layers, consisting of either a 40 nm–50 nm crystalline indium tin oxide or a 100 nm–150 nm-thick amorphous indium zinc oxide deposited by atomic layer deposition. These porous electrodes solve the problem of insufficient interaction volumes for catalyst thin films in two-dimensional working electrode designs and provide sufficiently low scattering backgrounds to enable high-resolution signal collection from interfacial thin-film catalysts. For example, PDF measurements were readily obtained with 0.2 Å spatial resolution for amorphous cobalt oxide films with thicknesses down to 60 nm when deposited on a porous electrode with 40 µm-diameter pores. This level of resolution resolves the cobaltate domain size and structure, the presence of defect sites assigned to the domain edges, and the changes in fine structure upon redox state change that are relevant to quantitative structure–function modeling. The results suggest the opportunity to leverage the porous, electrode architectures for PDF analysis of nanometre-scale surface-supported molecular catalysts. In addition, a compact 3D-printed electrochemical cell in a three-electrode configuration is described which is designed to allow for simultaneous X-ray transmission and electrolyte flow through the porous working electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Temperature Controlled Glass Additive Manufacturing

Glass additive manufacturing (AM) is an emerging technology with a wide range of applications in chemistry, biology, optical science, and engineering. A custom laser-based glass 3D printer was developed by a group of engineers at Los Alamos National Laboratory (LANL) and is being optimized to produce hardware for chemical processing equipment, microfluidic systems, as well as optical elements. AM glass using a filament deposition modeling (FDM) approach allows for generation of parts with high optical quality. The quality of the glass can be affected by the generation of defects such as bubbles and vaporization which affect the optical quality of the glass. The defects can also affect the mechanical performance of the glass and lead to sample cracking.

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

The Baseline Performance Reference for Irradiance in PV System Applications

This report proposes the definition of a new baseline performance reference (BPR). The definition goes beyond existing standards pertaining to photovoltaic (PV) reference cells and devices to define the response under all possible operating conditions in the field. Field evaluations using BPR devices will be more sensitive to performance anomalies than pyranometers because they track PV system power output more closely. At the same time, they will be able to detect a broader range of performance anomalies than traditional matched reference devices, which might have matching defects. The BPR definition also opens the door to new practices in resource assessment and yield prediction. Solar resource data can be collected or modeled and validated directly as BPR irradiance, and PV system simulations based on BPR irradiance need fewer assumptions and less processing to obtain the effective irradiance on modules. As a result, lower uncertainty in yield assessments can be expected.

14 SOLAR ENERGY↗
DOE OSTI2022

Dynamic Measurements of the Structural Evolution of Material Defects at the Mesoscale

This is a technical report to be published as part of the FY2021 annual overview package. We have designed experiments and developed analytical methods using images from x-ray and electron microscopy in order to quantify the behavior of crystal dislocation defects at their native nanometer-length and micro-length scales. The results of these analyses are used to directly inform theoretical physics models and guide interpretation of dark field x-ray microscopy (DFXM) images that offer spatial resolution surpassing the resolution of beamline optics. Additionally, we developed new analytical methods to automate the alignment of optics hardware used in both synchrotron and x-ray free electron laser beamline facilities. The tools and workflows developed for this project are now being deployed as proof-of-concept in reaction history analysis (RHA) for future programmatic integration.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Observation of single-defect memristor in an MoS2 atomic sheet

Non-volatile resistive switching, also known as memristor effect, where an electric field switches the resistance states of a two-terminal device, has emerged as an important concept in the development of high-density information storage, computing and reconfigurable systems. The past decade has witnessed substantial advances in non-volatile resistive switching materials such as metal oxides and solid electrolytes. It was long believed that leakage currents would prevent the observation of this phenomenon for nanometre-thin insulating layers. However, the recent discovery of non-volatile resistive switching in two-dimensional monolayers of transition metal dichalcogenide and hexagonal boron nitride sandwich structures (also known as atomristors) has refuted this belief and added a new materials dimension owing to the benefits of size scaling. Here we elucidate the origin of the switching mechanism in atomic sheets using monolayer MoS 2 as a model system. Atomistic imaging and spectroscopy reveal that metal substitution into a sulfur vacancy results in a non-volatile change in the resistance, which is corroborated by computational studies of defect structures and electronic states. These findings provide an atomistic understanding of non-volatile switching and open a new direction in precision defect engineering, down to a single defect, towards achieving the smallest memristor for applications in ultra-dense memory, neuromorphic computing and radio-frequency communication systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

First‐principles study in an inter‐granular glassy film model of silicon nitride

Abstract Based on a previously constructed intergranular glassy film ( IGF ) model for bulk silicon nitride, a large periodic model of 3864 atoms containing 2 grains of different orientations from the main bulk β‐Si 3 N 4 and 2 IGF s was fully relaxed using the ab initio density‐functional theory package VASP . The relaxed structure was then used to calculate the electronic structure, density of states, interatomic bonding, partial charge distribution, and electron localization using the OLCAO method. Analysis of the data focuses on the interfacial regions between bulk β‐Si 3 N 4 and the Si‐O‐N glass layer with different orientations. The total bond order density ( TBOD ) is evaluated in different interfacial and bulk regions. We show minor differences in the internal cohesion between crystalline grains of different facets. However, the overall charges in the bulk crystal grains and in the glassy regions are electropositive which are balanced by the negatively charged interfacial region between the two. The presence of a less rigid glassy layer is the reason for structural flexibility in ceramics without a huge penalty in the steric energy. The optimization of the interfacial structure and bonding via the creation of defective sites is the atomic origin for the existence of the IGF in silicon nitride. The insights obtained from this detailed quantum mechanical analysis of a realistic IGF model are discussed including implications on the strength, fracture toughness, and processing methods. We also discuss the potential applications of our method to other complex materials systems.

Ching, Wai‐Yim↗
DOE OSTI2026

Mesoscale atomic engineering in a crystal lattice

Controlling individual atoms using lasers, ion traps and scanning probe tips has transformed our understanding of matter and enabled breakthroughs in quantum science. Extending this control into three-dimensional (3D) solids and across mesoscopic scales, however, remains a foundational challenge. Electron irradiation in electron microscopes is known to induce atomic displacements, and atomic manipulation has been proposed and demonstrated. Yet repeated and deterministic control has remained elusive. Here, in this study, we demonstrate deterministic atomic engineering in a 3D crystal, creating ordered arrangements of more than 40,000 user-defined defects within minutes across a 150 nm × 100 nm × 13 nm volume. By steering individual Cr atoms in the magnetic semiconductor CrSBr into selected interstitial sites using an electron beam directed with sub-20-pm-scale accuracy, we create vacancy–interstitial complexes. The resulting impurity array forms a mesoscale crystal embedded within the host lattice, a new form of engineered artificial matter that remains stable at room temperature and outside the microscope. By tracking Cr atom displacements, we identify conditions under which the defect structures are predictable. Our calculations suggest that these defects form correlated impurity states with intra-defect optical transitions and inter-defect kinetic and Coulomb interactions. This establishes a generalizable platform for atomic defect engineering at mesoscopic, and potentially macroscopic, scales, opening opportunities for scalable quantum technologies, including deterministic colour-centre placement, quantum simulation of many-body lattice models and atomic-scale manufacturing.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Effects of temperature and pH on the electrochemical behaviour of alloy 600 in simulated pressurized water reactor primary water

The effects of temperature and pH on the electrochemical properties of Alloy 600 were studied in oxygenated borate buffer solutions by the measurements of open circuit potential (OCP), anodic potentiostatic polarization, Mott-Schottky analysis (MSA), and electrochemical impedance spectroscopy (EIS). At each temperature and pH, the stabilized anodic passive current density was independent of the formation potential, and the slope of the M - S plot for the passive film formed at +0.3 V OCP (OCP + 0.3 V) is positive, indicating that the passive films formed on Alloy 600 have n-type semiconductor character. With increasing temperature (in each solution), the OCP and the impedance modulus decreased, while the passive current density and the defect density calculated from MSA increased, indicating a significant reduction in corrosion resistance. With the increase in pH value, the passive current density decreased, the absolute value of impedance increased slightly, revealing a slight increase in corrosion resistance. According to the optimization of Mixed Potential Model (MPM) on the experimentally measured EIS data for Alloy 600 at OCP and +0.3 V OCP , a series of fundamental parameters related to the micro-characteristic of passive film were extracted. In the barrier layer of the passive film, the concentration of cation interstitials is much higher than that of anion vacancies, indicating that the former was a dominant defect. With increasing temperature, the linear increase in the defect density and film thickness resulted in a linear increase of the anodic current density. However, with increasing pH, the decrease of defect density and the slight increase of film thickness caused a linear reduction in anodic current density. Elevated temperature has a more significant deterioration effect on the corrosion resistance of Alloy 600 than the increased pH value. Additionally, all the kinetics parameters describing the generation of cation interstitials and oxygen vacancies at the substrate/film were obtained.

36 MATERIALS SCIENCE↗