Search NASA⌕ Search

SEARCH · Search NASA

Results for “Migration energy”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Hydrogen motion in near stoichiometric yttrium dihydride at elevated temperatures

The high-temperature motion of hydrogen in near stoichiometric yttrium dihydride (YH x , x = 1.62 and 1.87 at.%) was investigated using incoherent quasi-elastic neutron scattering and Density Functional Theory (DFT) calculations as a function of hydrogen stoichiometry. Translational motion (diffusivity) of hydrogen in yttrium dihydride was only observed in a temperature range of 1073–1173 K under vacuum environment. Here, the hydrogen motion was found to be limited to the tetrahedral sublattice, and diffusivity of hydrogen was observed to increase with decreasing hydrogen stoichiometry. The same behavior was also supported with DFT calculations. The DFT results also indicated that certain migration paths with smaller energy barriers favored H jump resulting in higher diffusivities.

08 HYDROGEN↗
DOE OSTI2020

Insights into Copper Sulfide Formation from Cu and S K edge XAS and DFT studies

An understanding of the fundamentals of the reaction between CuO with trace amounts of H 2 S to form CuS products is critical for the optimal utilization of this process in sulfur removal applications. Unfortunately, CuS is a complex material, featuring various Cu 2-x S compounds (with 0 ≤ x ≤ 1), distorted crystal phases, and varying electronic structures and coordination environments of Cu and S ions. In this work, we combine ex situ and in situ X-ray absorption spectroscopy (XAS) at S and Cu K edges, fixed bed sorption experiments, DFT simulations, and other characterization techniques to speciate the CuS products formed at different temperatures (298–383 K) and from CuO sorbents with different crystallite sizes (2.8–40 nm). The results of our analysis identify the formation of a distorted CuS layer at the surface of CuO crystals with disulfide groups with shorter Cu–S bonds and higher delocalization of the positive charge of the Cu center into (S 1– )2. This distorted CuS layer dominates the XAS signal at lower temperatures (298–323 K) and at the initial stages of sulfidation at higher temperatures (353 and 383 K) where conversion is low (<40%). First-principles atomistic simulations confirm the thermodynamic favorability of the formation of surface (S 1– )2 on both CuO (111) and ($\bar{1}11$) surfaces, providing further support for our experimental observations. Furthermore, these simulations reveal that the presence of disulfide bonds stabilized surface hydroxyl groups, leading to lower Gibbs Free Energies of their surface migration.

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

The Role of Phase Separation on Rayleigh-Plateau Type Instabilities in Alloys

Classical molecular dynamics (MD) simulations are used to investigate the role of phase separation (PS) on the Rayleigh-Plateau (RP) instability. Ni–Ag bulk structures are created at temperatures (2000 K and 1400 K) that generate different PS length scales, λ PS , relative to the RP instability length scale, λRP. Rectanguloids are then cut from the bulk structures and patterned with a perturbation of certain amplitude and wavelength, λ RP . It is found that when λ PS << λ RP (2000 K), the patterned rectanguloids break up into nanoparticles in a manner consistent with classical RP theory, whereas when λ PS << λ RP (1400 K), soluto-capillarity affects the RP instability significantly. Specifically, since Ag has a lower surface energy than Ni, Ag migrates to cover neighboring Ni regions, therefore modifying the RP instability. Thus, we demonstrate that the phase separation length scale of an immiscible alloy can be exploited to direct the assembly of functional bimetallic alloys.

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

Thermodynamic Band Gap Model for Photoinduced Phase Segregation in Mixed-Halide Perovskites

Provided is a comprehensive description of a band gap thermodynamic model, which predicts and explains key features of photosegregation in lead-based, mixed-halide perovskites. The model gives a prescription for illustrating halide migration driven by photocarrier energies. Where possible, model predictions are compared with experimental results. Free energy derivations are provided for three assumptions: (1) halide mixing in the dark, (2) a fixed number of photogenerated carriers funneling to and localizing in low band gap inclusions of the alloy, and (3) the statistical occupancy of said inclusions from a bath of thermalized photocarriers in the parent material. Model predictions include excitation intensity (I exc )-dependent terminal halide stoichiometries (x terminal ), temperature-independent x terminal , excitation intensity thresholds (I exc,threshold ) below which photosegregation is suppressed, and reduced segregation in nanocrystals as compared to thin films. Here, the model also offers insight into kinetically manipulating photosegregation rates via control of underlying mediators and rationalizes asymmetries in forward and reverse photosegregation rate constants/activation energies. What emerges is a cohesive framework for understanding ubiquitous photosegregation in mixed-halide perovskites and a rational basis by which to manage the phenomenon.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Computationally guided experimental validation of divacancy defect formation in 4H-SiC

Recent research into solid-state qubits for quantum information science has focused on optically addressable spin defects such as the negatively charged nitrogen-vacancy center in diamond and the neutrally charged divacancy (VV) in 4H-SiC as scalable quantum sensors and networking qubits. Within this context, direct investigations of the structural origin and defect formation dynamics of a sub-set of the VV center in 4H-SiC remain lacking. Here, we take a systematic experimental approach guided by predictions from first-principles simulations to gain a thorough mechanistic understanding of the VV defect formation and control in 4H-SiC. We study the effect of annealing time and temperature on VV formation in high-purity semi-insulating 4H-SiC samples following electron irradiation. Three different temperatures (1123, 1273, and 1473 K) and annealing duration (from 0.5 to 72 h) are chosen to explore VV formation in different regions. We find that samples annealed at 1273 K give the highest VV-related photoluminescence (PL) intensities, in agreement with the prediction from first-principles calculations. Furthermore, the logarithmic dependence of VV-related PL intensities on the annealing duration at 1273 K indicates that 1273 K provides sufficient thermal energy for silicon vacancy migration but not for VV migration. Together, these results suggest that efficient VV formation occurs above the V Si migration temperature and below the VV migration threshold.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Interfacial Characterization of Positive Bias Voltage Degradation in PV Modules

Degradation from high system voltage is a prevailing failure mode in fielded photovoltaic modules, and the degradation mechanism is inherently dependent on the bias polarity. Here we report the effects of positive bias. Modules under positive bias demonstrated a significant photocurrent loss caused by two routes. First, delamination and discoloration of the silicon nitride layer, leading to optical loss determined by reflectance measurements. Second, chemical discoloration of the cell gridlines and encapsulant (EVA), which is linked to an electrochemical reaction at the silver electrodes. Chemical compositional analysis using X-ray photoemission spectroscopy demonstrated that the discoloration is attributed to Ag 2 S and/or Ag 2 O. Evidence of Ag ion migration from the cell grid into the encapsulant is observed after shallow depth profiling on the EVA surface. However, Ag was not detected at the EVA/glass interface, inferring limited Ag ion transport through the EVA. The source of sulfur is believed to be ambient air, which diffused into the module through the breathable backsheet.

characterization↗
DOE OSTI2023

Utilizing high-resolution genetic markers to track population-level exposure of migratory birds to renewable energy development

With new motivation to increase the proportion of energy demands met by zero-carbon sources, there is a greater focus on efforts to assess and mitigate the impacts of renewable energy development on sensitive ecosystems and wildlife, of which birds are of particular interest. One challenge for researchers, due in part to a lack of appropriate tools, has been estimating the effects from such development on individual breeding populations of migratory birds. To help address this, we utilize a newly developed, high-resolution genetic tagging method to rapidly identify the breeding population of origin of carcasses recovered from renewable energy facilities and combine them with maps of genetic variation across geographic space (called ‘genoscapes’) for five species of migratory birds known to be exposed to energy development, to assess the extent of population-level effects on migratory birds. We demonstrate that most avian remains collected were from the largest populations of a given species. In contrast, those remains from smaller, declining populations made up a smaller percentage of the total number of birds assayed. Results suggest that application of this genetic tagging method can successfully define population-level exposure to renewable energy development and may be a powerful tool to inform future siting and mitigation activities associated with renewable energy programs.

14 SOLAR ENERGY↗
DOE OSTI2024

Investigations of Relative Stability and Distribution of Mo Species in Pore Space of Mo/ZSM-5 Systems

Reduced forms of molybdenum (Mo) carbides anchoring in pore space of zeolites are considered as activated catalysts for the methane dehydroaromatization reaction. However, the atomic structure of the active sites and their stability under reactive conditions are still not clearly understood. Herein, we employ a synergistic theoretical and experimental approach to investigate this research gap. The Raman data shows the existence of the distributed binuclear and mononuclear Mo oxides in the pores that are corroborated by the hydrogen temperature-programmed reduction experiments. The binding free energies of mono- and bi-nuclear Mo carbides in straight and sinusoidal channels and their intersections as a function of temperature and anchoring sites have been determined. The catalysts with Mo coordinated at two anchoring sites are more stable compared to those located at the rings with one Al substitution. The activation energies of the catalysts migration to adjacent rings were estimated as a function of temperature and kinetics parameters of such migrations were determined. The migration is facilitated if there is one anchoring site shared between two rings. This process can contribute to an agglomeration mechanism leading to loss of catalytic activity.

Myshakin, Evgeniy↗
DOE OSTI2023

Toward Quantum Chemical Free Energy Simulations of Platinum Nanoparticles on Titania Support

Platinum nanoparticles (Pt-NPs) supported on titania surfaces are costly but indispensable heterogeneous catalysts because of their highly effective and selective catalytic properties. Therefore, it is vital to understand their physicochemical processes during catalysis to optimize their use and to further develop better catalysts. However, simulating these dynamic processes is challenging due to the need for a reliable quantum chemical method to describe chemical bond breaking and bond formation during the processes but, at the same time, fast enough to sample a large number of configurations required to compute the corresponding free energy surfaces. Density functional theory (DFT) is often used to explore Pt-NPs; nonetheless, it is usually limited to some minimum-energy reaction pathways on static potential energy surfaces because of its high computational cost. In this work, we report a combination of the density functional tight binding (DFTB) method as a fast but reliable approximation to DFT, the steered molecular dynamics (SMD) technique, and the Jarzynski equality to construct free energy surfaces of the temperature-dependent diffusion and growth of platinum particles on a titania surface. In particular, we present the parametrization for Pt-X (X = Pt, Ti, or O) interactions in the framework of the second-order DFTB method, using a previous parametrization for titania as a basis. The optimized parameter set was used to simulate the surface diffusion of a single platinum atom (Pt 1 ) and the growth of Pt 6 from Pt 5 and Pt 1 on the rutile (110) surface at three different temperatures (T = 400, 600, 800 K). The free energy profile was constructed by using over a hundred SMD trajectories for each process. We found that increasing the temperature has a minimal effect on the formation free energy; nevertheless, it significantly reduces the free energy barrier of Pt atom migration on the TiO 2 surface and the transition state (TS) of its deposition. In a concluding remark, the methodology opens the pathway to quantum chemical free energy simulations of Pt-NPs’ temperature-dependent growth and other transformation processes on the titania support.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Temperature dependence of vacancy/self-interstitial recombination volumes in copper

We use molecular dynamics to calculate rate coefficients for recombination of vacancies with self-interstitial atoms (SIAs) in Cu at temperatures from 300 to 700 K. From these results, we calculate vacancy/SIA recombination volumes and find that they decrease from around 290 (where is one atomic volume) at 300 K to 160 at 500 K and above. By counting the number of distinct pathways by which a stable SIA may migrate to a site of spontaneous recombination with a nearby vacancy, we find a lower bound estimate of 168 for the recombination volume. We furthermore rationalize its temperature dependence based on differences between the activation energies for recombination and SIA migration. Furthermore, our work sheds light on the fundamental nature of the recombination volume and provides information that may be incorporated into multiscale models of radiation response in solids.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Uneven Strain Distribution Induces Consecutive Dislocation Slipping, Plane Gliding, and Subsequent Detwinning of Penta-Twinned Nanoparticles

Twin structures possess distinct physical and chemical properties by virtue of their specific twin configuration. However, twinning and detwinning processes are not fully understood on the atomic scale. Integrating in situ high resolution transmission electron microscopy and molecular dynamic simulations, here, we find tensile strain in the asymmetrical 5-fold twins of Au nanoparticles leads to twin boundary migration through dislocation sliding (slipping of an atomic layer) along twin boundaries and dislocation reactions at the 5-fold axis under an electron beam. Migration of one or two layers of twin planes is governed by energy barriers, but overall, the total energy, including surface, lattice strain, and twin boundary energy, is relaxed after consecutive twin boundary migration, leading to a detwinning process. In addition, surface rearrangement of 5-fold twinned nanoparticles can aid in the detwinning process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ultrasonic Jet Bat Deterrent System Advancement

General Electric Renewable Energy (GE) and the Department of Energy (DOE) worked to develop a project with an objective to increase confidence in acoustic ultrasonic bat deterrent technologies in wind turbines, by mitigating stakeholder investment risks that currently hinder the adoption of deterrent technologies. Many wind turbine sites utilize a bat conservation plan that curtail wind turbines and stop energy production. Curtailment is a known bat impact mitigation solution that has an history of environmental regulatory acceptance. To help support a solution that allows for simultaneous bat conservation and energy production with regulatory acceptance of acoustic bat deterrents, GE proposed a study to compare four treatments: control (no curtailment or deterrent), deterrent only, deterrent plus curtailment, and curtailment only. The concept was to provide a direct comparison of bat deterrent and curtailment effectiveness within the same wind farm and bat migration season. This comparison was intended to advocate for the adoption of bat deterrents with a large-scale field study by addressing customer concerns on regulatory acceptance of deterrents. The study was to be hosted at a forested habitat site during a bat migration season, by Stony Creek Energy, LLC (SCE), the owner of the Orangeville Wind Farm (OWF) in the state of New York. Included was a behavioral study plan with two turbines to monitor bat flight paths with thermal imaging cameras.

17 WIND ENERGY↗
DOE OSTI2022

Development and application of a uranium mononitride (UN) potential: Thermomechanical properties and Xe diffusion

We report that atomic-scale modeling of thermophysical and defect properties of uranium mononitride (UN) plays an important role in establishing a better understanding and improved models of UN fuel performance. Having an accurate interatomic potential is crucial for generating reliable data at finite temperatures using molecular dynamic simulations. We report a new interatomic potential for UN, based on a combination of many-body and pairwise interactions, a simple form that we later show could be easily adapted to include Xe-U and Xe-N interactions, i.e., generating a U-N-Xe interatomic potential. The potential was fitted to experimental thermal expansion and single crystal elastic constants, as well as Frenkel, Schottky, anti-Schottky, and antisite pair reaction energies from density functional theory (DFT) calculations. Using the potential, we successfully reproduced experimental lattice parameters, thermal expansion, single crystal elastic constants, and temperature dependent heat capacity. The potential also performs reasonably well in reproducing the energy of the aforementioned stoichiometric defect reactions and defect migration barriers calculated using DFT. However, the potential underestimates the energy difference between the tetrahedral and dumbbell uranium interstitials, and a more complex potential form might be needed to overcome this issue. The potential was also used to predict UN single crystal elastic constants and elastic properties at different temperatures, showing that UN becomes softer and more compressible with increasing temperature. We also compare our potential against literature data from previous empirical potentials, demonstrating similar or better behavior depending on the property of interest. To enable the simulation of Xe in UN a Buckingham potential has been fitted to DFT-derived Xe incorporation energies. The potential was then used to determine the activation energy for Xe diffusion due to various Xe-containing defects, with {XeU : VU} exhibiting the lowest activation energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Self-compensation of group-V acceptors in CdTe

Cadmium Telluride is at the core of an important thin-film technology for photovoltaics that is already commercially available, yet the CdTe-based solar cell efficiency remains limited at 22%, well below the theoretical limit of ~30%. Increasing the hole concentration is crucial for higher efficiency, and group-V elements such as As, P, and Sb are potential dopants as they are shallow acceptors. Nevertheless, group-V doped p-type CdTe often exhibits low doping activation, and the compensation source remains debated. Here, we performed hybrid density functional calculations with spin-orbit coupling to investigate possible sources of hole compensation in group-V doped CdTe. First, regarding possible self-compensation of the group-V dopants, we find that the formation of AX centers is unlikely since they are found to be unstable relative to the shallow acceptor forms. However, if the group-V dopants come in during growth (such as dimer molecules As2, P2, and Sb2), we find that the impurity atoms, which would occupy nearest neighbor sites, maintain the V-V bonds, limiting the hole density. For the native defects, our study reveals that Cd interstitial is the lowest energy donor defect in p-type CdTe. Still, it has a small migration barrier of 0.5 eV, making it highly mobile and unstable at room temperature. The Te vacancy is the next lowest formation energy donor. The migration barrier of 1.4 eV indicates that the Te vacancy is stable at room temperature. The antisite CdTe is also a donor, with low formation energy and stable at room temperature, potentially limiting the hole concentration. Our results, therefore, shed light on possible compensation centers and some guidance on how to avoid them.

14 SOLAR ENERGY↗
DOE OSTI2023

The Impact of Inherited Morphology on Sandbar Migration During Mild Wave Seasons

Sandbars are ubiquitous morphologic features found in the nearshore environment throughout the world, yet predictive capabilities of their evolution remain limited. In order to provide new insights on the relevant processes controlling sandbar morphodynamics, this study uses a 41-year record of 637 monthly cross-shore profiles from Duck, North Carolina, USA, to derive complex empirical orthogonal functions representative of the two dominant modes of sandbar migrations: offshore and onshore propagation. Interference of these two modes produces commonly observed sandbar states. While mild wave energies are traditionally assumed to drive onshore sandbar migration, the offshore mode is repeatedly seen to dominate sandbar migration in mild wave seasons following anomalously high late-winter wave energy and when the inherited morphology is composed of a single bar or terrace, as opposed to a more common two-bar state. A data-derived conceptual model is presented synthesizing the effect of antecedent morphology and wave climate chronology on interannual trends in net offshore sandbar migration.

58 GEOSCIENCES↗
DOE OSTI2022

A deep learning-based direct forecasting of CO 2 plume migration

Accurate and timely forecasts of CO 2 plume evolution in geological reservoirs are crucial for CO 2 migration detection, leakage risk assessment, and operation decision support. Conventional forecasting usually adopts a two-step strategy, first calibrating reservoir model parameters against observations using iterative inverse modeling (or history matching) and then applying the calibrated model for predictions. This method impedes real-time forecasts due to the heavy computational demand in inverse modeling and may suffer from poor prediction accuracy because of the limited observation data. In this work, we propose a deep learning-based latent space mapping framework to forecast CO 2 plume migration directly by avoiding the inverse modeling. We first use the convolutional autoencoder to map the high-dimensional complex plume extents onto low-dimensional latent space. Next, we use neural networks to learn the relationship between the observation variables and the prediction latent variables. And then for given observation data, we infer the prediction values directly. This one-step direct forecasting is computationally efficient which requires a few number of parallelizable reservoir simulations and it can provide accurate predictions with limited observations by learning the observation-prediction relationship in the reduced dimension. Therefore, our proposed method enables an in-time forecast of dynamic CO 2 plume distributions. In this work, we demonstrate the effectiveness and accuracy of our method in predicting the CO 2 plume migration using four metrics such as plume area, centroid movement distance, and plume spreading in the primary and secondary directions. And the spatio-temporal evolution patterns of plume migration under diverse geological complexities are also accurately quantified.

15 GEOTHERMAL ENERGY↗
DOE OSTI2022

Mitigating cerium migration for perfluorosulfonic acid membranes using organic ligands

Improving the electrochemical stability of proton exchange membranes is a pressing priority for heavy-duty fuel cell vehicles. The lifetime of the most widely used perfluorosulfonic acid membranes is limited by reactive free radicals generated inside the system. Cerium has been found to reduce the chemical degradation of the membranes. However, cerium migration during fuel cell operation limits the chemical durability enhancement effect expected from the radical scavenging activity of cerium. Here we investigate a wide range of organic immobilizers for cerium, measuring their suitability concerning cerium retention, radical scavenging activity, and fuel cell performance. Further, we report that partially fluorinated phosphonic acids enhance cerium retention up to 45 times and reduce fluoride emission rate by 38% compared to the commercial Nafion™ XL membrane pre-impregnated with cerium. The energetics of cerium-phosphonic acid complex systems by density functional theory calculations rationalizes effective cerium immobilization.

25 ENERGY STORAGE↗