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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Role of stacking defects on the magnetic behavior of CrCl 3

Here, in the study of van der Waals–layered magnetic materials, the properties of CrCl 3 continue to attract attention. This compound is reported to undergo antiferromagnetic ordering below ~14 K, with a ferromagneticlike region proposed to exist between 14 and 17 K. Ideally, the crystal structure is rhombohedral (R) below ~235 K, separated from a higher-temperature monoclinic (M) phase by a layer-sliding structural phase transition. However, the structural transition is often inhibited even in bulk single crystals, allowing M-type layer stacking, reported to have a 10-fold greater interlayer magnetic coupling than R-type stacking, to be present at low temperature. To clarify the effect of stacking defects on CrCl 3 , we report magnetization measurements on samples of varying crystalline quality. At low applied magnetic field, some crystals predominantly show the T N = 14 K peak, but other crystals show hysteretic behavior and a magnetization enhancement at a slightly higher temperature (14 < T ≲ 17 K.) Samples with anomalous behavior exhibit a transition around ~2 T in isothermal magnetization-field data, evidence that M-type stacking defects are the source of these anomalies. Ground powder samples are especially likely to show strongly anomalous behavior. We suggest that the anomalous behavior arises from few-layer magnetic domains that form just above T N in an environment of mixed interlayer magnetic coupling strength. We argue that the influence of M-type stacking boundaries on sublattice magnetization is already observable in reported neutron scattering data, and may be responsible for an enhancement near 17 K in reported specific heat data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Qualification of Mixing Criteria by Computational Fluid Dynamics Modeling for the 325 Building Stack Revision

Additional ventilation capacity has been designed for the 325 Building filtered exhaust stack system. The four (4) existing main facility exhaust fans are past the end of their useful life. The fans are being replaced to provide additional exhaust capacity for future growth and to provide a more robust system. Stack operations will involve running various fan combinations at any given time. The air monitoring system of the existing stack previously was found to comply with the American National Standards Institute/Health Physics Society (ANSI/HPS) N13.1-1999 standard. Full-scale, three-dimensional computational fluid dynamics (CFD) modeling was used to evaluate the modified four-fan system for compliance with the ANSI/HPS N13.1-2021 standard, which essentially is equivalent in mixing requirements to the ANSI/HPS N13.1-1999 standard (and ANSI/HPS N13.1-2011). The four mixing criteria evaluated are 1) flow angle, 2) velocity, 3) gas tracer, and 4) particle tracer. In addition to the evaluating the modified four-fan system a temporary single fan stack configuration was also evaluated with CFD modeling. The temporary stack is planned to be used while the four-fan system is being modified. Modeling of the modified four-fan design and temporary ductwork showed that flow angles, velocity uniformity, gas tracer, and particle tracer were acceptable.

42 ENGINEERING↗
DOE OSTI2023

Performance of Polymer Electrolyte Membrane Water Electrolysis Systems: Configuration, Stack Materials, Turndown and Efficiency

A cell model is developed and validated to analyze the performance of polymer electrolyte membrane water electrolysis (PEMWE) stacks and systems. It is used to characterize the oxygen evolution reaction (OER) activity on a TiO2-supported IrO2 catalyst and an unsupported IrO2 powder catalyst. Electrochemical, stack, and system thermoneutral potentials are defined and determined for isothermal and non-isothermal stack operation. Conditions are determined under which the system thermoneutral potential or flammability of H2 in the O2 anode stream limits the stack turndown and operating temperature. Performance is analyzed of a complete PEMWE system with an electrolyzer stack containing an IrO2/TiO2 anode catalyst (2 mg/cm2 Ir loading) and N117-like membrane mitigated for H2 crossover, anode balance-of-plant (BOP) components, cathode BOP system with temperature swing adsorption for H2 purification, and electrical BOP system with transformer and rectifier. At the rated power condition, defined as 2 A/cm2 at 1.9 V, 80 °C, and 30 bar H2 pressure, the stack/system efficiency is 65.3%/60.3% at beginning of life (BOL), decreasing to 59.3%/53.9% at end of life (EOL). The peak stack/system efficiency is 76.3%/70.2% at BOL, decreasing to 71.2%/65.6% at EOL. Improvements in catalyst activity and membrane are identified for a 50% increase in current to 3 A/cm2 at 1.8 V.

36 MATERIALS SCIENCE↗
DOE OSTI2023

19.32% Efficiency Polymer Solar Cells Enabled by Fine-Tuning Stacking Modes of Y-Type Molecule Acceptors: Synergistic Bromine and Fluorine Substitution of the End Groups

Here, the success of Y6-type nonfullerene small molecule acceptors (NF-SMAs) in polymer solar cells (PSCs) can be attributed to their unique honeycomb stacking style, which leads to favorable thin-film morphologies. The intermolecular interactions related to the crystallization tendency of these NF-SMAs is closely governed by their electron accepting end groups. For example, the high performance Y6 derivative L8-BO (BTP-4F) presents three types of stacking modes in contrast to two stacking modes of Y6. Hence, it is ultimately interesting to obtain more insight on the packing properties and the preferences influenced by chemical modifications such as end group engineering. This work designs and synthesizes asymmetric and symmetric L8-BO derivatives with brominated end groups and explores the stacking preferences in various modes. The asymmetric BTP-3FBr displays an optimized crystallization tendency and thin film morphology, leading to a decent power conversion efficiency (PCE) of 18.34% in binary devices and a top PCE of 19.32% in ternary devices containing 15 wt% IDIC as the second acceptor.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effect of stacking fault energy on damage microstructure in ion-irradiated CoCrFeNiMn concentrated solid solution alloys

In order to understand the effect of stacking fault energy on microstructural evolution in concentrated solid solution alloys, Kr 2+ ion irradiation was performed for FCC-type CoCrFeNiMnx alloys. During Kr 2+ ion irradiation at 500 degrees C the formation of black dots, self-interstitial atom faulted loops and perfect loops were observed, but no observable voids were found in all the alloys. The comparison of microstructural evolution among CoCrFeNiMn x (x = 0.7, 1, 1.3) alloys revealed less faulted loop number density and size in CoCrFeNiMn 1.3 . The stacking fault energy of each alloy was investigated using the deformed CoCrFeNiMn x alloys, and it was revealed that CoCrFeNiMn 1.3 had the highest stacking fault energy, which is higher value than that of 316SS. From these results, it is suggested that FeCrNiMn-based concentrated solid solution alloys could be well-designed by controlling the stacking fault energy with optimized Mn concentration as one of high radiation resistance structure materials. (C) 2020 Elsevier B.V. All rights reserved.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Hydrogen Stability and Bonding in SiN x and Al 2 O 3 Dielectric Stacks on Poly-Si/SiO x Passivating Contacts

Polycrystalline Si on SiO x passivating contacts enables some of the highest efficiency single-junction Si photovoltaic devices, but the high-temperature firing process needed for industrial metallization can significantly reduce passivation. We show that after firing, the implied open-circuit voltage, iV oc , for the Al 2 O 3 /SiN x /poly-Si/SiO x /c-Si stack is 20-30 mV higher than the SiNx/Al 2 O 3 /poly-Si/SiO x /c-Si stack and therefore provides better passivation of the SiO x /c-Si interface. Using effusion measurements and Fourier transform infrared spectroscopy, we demonstrate that more than twice as much hydrogen is retained in the dielectric up to the peak firing temperature of ~800 degrees C for Al 2 O 3 -capped structures. If the Al 2 O 3 layer is not present in the stack, after firing, the iVoc is lower by 50-100 mV compared to Al 2 O 3 /SiN x or SiN x /Al 2 O 3 stacks. These studies will inform future work on the role of dielectrics in aiding the passivation of poly-Si/SiO x passivating contacts.

08 HYDROGEN↗
DOE OSTI2024

PyFaults: A Python Toolkit for Stacking Fault Screening

PyFaults is an open-source Python library designed to model stacking fault disorder in crystalline materials and qualitatively assess the characteristic selective broadening effects in powder X-ray diffraction (PXRD). Here, the main capabilities of PyFaults are presented, including unit cell and supercell model construction, PXRD pattern calculation, assessment against experimental PXRD, and methods for rapid screening of candidate models within a set of possible stacking vectors and fault occurrence probabilities. This program aims to serve as a computationally inexpensive tool for identifying and screening potential stacking fault models in materials with planar disorder. Three diverse case studies, involving GaN, Li2MnO3 and Li3YCl6, are presented to illustrate the program functionality across a range of structure types and stacking fault modalities.

MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Red-Ox Robust SOFC Stacks for Affordable, Reliable Distributed Generation Power Systems

While SOFC systems are expected to operate reliably and with limited degradation in steady state or transient performance, SOFC stacks may ultimately fail due to the loss of structural integrity of one or several of the cells as a result of the weakening of the materials and interfaces due to physico-chemical changes that occur during continuous operation as a result of plastic and creep deformations, modification of the temperature profile, and/or degradation of the electrochemical performance of the cells. Degradation mechanisms originating from the cell components include coarsening of the microstructure over time; decomposition of materials; chemical reaction of electrode materials with electrolyte at the interface; delamination from each other; and for the anode, coking and sulfur poisoning. Of all the reliability issues that may occur for SOFCs, the main limitation for Ni-based cermet anodes (e.g., NiO-YSZ) is the poor stability during reduction-oxidation (red-ox) cycling. This project was aimed at the development of ceramic anode SOFCs based on SFCM (SrFe0.2Co0.4Mo0.4O3), which is a conductive perovskite that is red-ox stable. Additionally, the project involved the development of a red-ox robust stack. Scale up of SFCM-based cells to a large format (10 cm by 10 cm) cell size was achieved as well as a maximum power density of 0.9 W/cm 2 at 600 °C (>0.6 W/cm 2 at 0.6 V). Up to a 10-cell stack was successfully assembled and demonstrated, and cells showed similar performance in reformed, pipeline natural gas as in hydrogen. Finally, a 3-cell stack was red-ox cycled without degradation for 40 cycles at ~600 °C.

03 NATURAL GAS↗
DOE OSTI2023

Suppression of Stacking Order with Doping in 1T-TaS 2–x Se x

In 1T-TaS 2–x Se x , the charge density wave (CDW) state features a star of David lattice that expands across layers as the system becomes commensurate upon cooling. The layers can also order along the c-axis, and different stacking orders have been proposed. For this work, using neutron scattering on powder samples, we compared the stacking order previously observed in 1T-TaS 2 when the system is doped with Se. While at low temperature, a 13c layer sequence stacking was observed in TaS 2 ; this type of ordering was not evident with doping. Doping with Se results in a metallic state in which the Mott transition is suppressed, which may be linked to the absence of layer stacking.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Mechanical Characterization of Stacked Single-Crystal of Polyethylene and Monolayer MoSe 2

Polymer single crystal (SC) is a key building block of semicrystalline polymers. However, direct experimental measurement of freestanding mono-lamella polymer SC has not been demonstrated. This is, in large part, due to the difficulties associated with manipulating freestanding individual mono-lamella SC because of its extremely low rigidity and low robustness. Here, we demonstrate a new strategy to successfully suspend and test a polymer SC by using a 2D material as backing. In particular, mono-lamella polyethylene (PE) SC is stacked on monolayer MoSe 2 , and the hybrid stacks can be suspended over microholes. Nanoindentation is used to probe the suspended PE-SC/MoSe2 stacks and MoSe 2 monolayers. The results suggest the first experimentally-measured in-plane moduli of PE-SC and 2D MoSe 2 as 32 ± 3 and 237 ± 15 GPa, respectively. Such a stacked unit represents an ultrathin structure of polymer-ceramic laminate and the idea can be applied to other laminated composite systems. Therefore, this research will pave the way to accurately measure the mechanical properties of polymer SCs and their composites, as well as provide a key insight on designing composite structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge‐to‐Edge Packing and Disrupts Cofacial Stacking

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge-to-edge tiling and face-to-face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge-to-edge contacts to reorder the stability of two surface-bound 2D polymorphs. The impact on dipole-enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short-range (3.4 Å) anti-parallel dipole contacts. Despite this situation, the reduction in self-association was attributed to long-range (~6.4 Å) dipolar repulsions between π-stacked macrocycles. This work highlights our ability to control the build-up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self-assembly.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Stacking fault analysis for the early-stages of PVT growth of 4H-SiC crystals

Here, four types of stacking fault formation mechanisms are identified and discussed for early stage PVT growth of 4H-SiC crystals: Type 1: Shockley / double Shockley stacking fault formation inside the facet; Type 2: Stacking fault formation via 2D nucleation; Type 3: Frank + Shockley (S) stacking fault formation due to deflection of threading mixed dislocation (TMD) by macrosteps; Type 4: “Carrot” defect formation related to overgrowth of the terrace formed by separation of 3c/4 and c/4 step risers after deflection of a TMD by vicinal steps. The results help further reduction of defect generation in 4H-SiC substrates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Stress evolution and creep deformation in solid-oxide electrolysis cell systems – Dynamic modeling and multi-objective optimization to maximize stack life and efficiency

Here, this study develops a thermal stress model of solid-oxide electrolysis cells (SOECs) including a model for creep strain and failure probability that is integrated with a dynamic plant-wide model of a hydrogen production process. Uncertainties in key material properties of the cell are quantified to assess their impact on stress profile variability. The oxygen electrode is found to have about 10 times higher failure probability compared to the fuel electrode. The study shows that if the stack operation is not optimized, cycling operation would lead to stress build-up eventually leading to catastrophic failure. A dynamic optimization problem is set up for obtaining the optimal operational profile considering a variable hydrogen production rate. Due to the tradeoff between the efficiency and stress build-up, the dynamic optimization problem is multi-objective. It is observed that the optimizer can considerably reduce the stress build-up (i.e., can increase the stack life) albeit at the cost of a lower efficiency thus exhibiting strong tradeoffs between capital and operating costs. For example, if the stack would be replaced in 0.5 yr, specific energy requirement would be 48.5 kWh/kg H 2 while for a stack replacement time of about 6 yr, the specific energy requirement rises by about 4.2 %.

SOEC↗
DOE OSTI2023

Demonstrating imaging plate detector stacks for proton radiography using exploding pusher capsules

A new detector design has been fielded on the Omega-60 laser facility using a D 3 He backlighter capsule to radiograph a magnetized experiment. D 3 He capsules produce a low flux (~ 10 8 total yield in 4π) of protons requiring detectors with close-to single-particle sensitivity to be employed. The new detector stack consisted of both imaging plate (IP) and CR-39 to detect 14.7 MeV protons where, historically, only CR-39 has been used. IP is sensitive to significant contributions in signal from both x-rays and protons so additional filtering has to be added to attenuate the x-rays. Here, the signals and features observed from a single shot are detected by both IP and CR-39, giving confirmation that it is protons creating the signatures on the IP. Measurements of PSL/pixel are used to calculate approximate on-shot proton yields and agree with commonly measured yields. A second IP is used at the rear of the stack to measure, and subsequently remove, a background signal. The spatial resolution at the IP is limited, primarily, by a range of proton energies with varying deflections being recorded at the detector, causing potential ‘blurring’ of features. We find for this setup that the blurring effect is less than the smallest identifiable features observed at the detector, and therefore of minimal impact. A large benefit to this new stack design is that IP can be scanned and processed on much faster timescales than CR-39 allowing for prompt shot feedback. Future designs and modifications to the stack design fielded on this experiment could help improve the contrast of the radiograph on IP, as well as detecting protons produced at alternative energies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Machine-learning-aided density functional theory calculations of stacking fault energies in steel

A combined large-scale first principles approach with machine learning and materials informatics is proposed to quickly sweep the chemistry-composition space of advanced high strength steels (AHSS). AHSS are composed of iron and key alloying elements such as aluminum and manganese. A systematic exploration of the distribution of aluminum and manganese atoms in iron is used to investigate low stacking fault energies configurations using first principles calculations. To overcome the computational cost of exploring the composition space, this process is sped up using an automated machine learning tool: DeepHyper. Here our results predict that it is energetically favorable for Al to stay away from a stacking fault, but Mn atoms do not affect the stacking fault energy and can stay in the vicinity of the fault. The distribution of Al and Mn atoms in systems containing stacking faults and the effects of their interactions on the equilibrium distribution are systematically analyzed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Standardization of the Distributed Ledger Technology cybersecurity stack for power and energy applications

The global trend towards the integration of distributed energy resources is opening the doors to advanced, complex, and distributedmarketplaces. Such advanced ecosystems, where utility-owned and non utility-owned assets can contribute towards grid operations,generally require distributed communication and grid architectures, which can be supported by Distributed Ledger Technologies(DLTs). However, the potential of DLTs for long-term scalable solutions in operational technology applications has not been fullyutilized, partly due to the lack of standardization across and between different DLTs, as well as other supporting building blocks(e.g., communication protocols). This paper attempts to address this gap by proposing a DLT cybersecurity stack specificallydesigned for researchers, DLT technology developers, and end users (such as utilities). The DLT cybersecurity stack has beennotionally mapped to related cybersecurity components, namely: the Open Systems Interconnection (OSI) model, the TransmissionControl Protocol/Internet Protocol (TCP/IP) suite, and existing Smart Grid architecture frameworks. In addition, the paper discussesseveral cybersecurity implications, and demonstrates the potential uses of the DLT stack through multiple power and energy usecases. It is important to note that the stack can be also applied to the DLT use cases that are outside the power and energy domain.This work has been performed by the Cybersecurity Task Force under the IEEE P2418.5 Blockchain for Energy Standard workinggroup that is stationed under the IEEE Power and Energy Society’s Smart Buildings, Loads, and Customer Systems (SBLC)technical committee.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2026

NOCI-F Electronic Couplings in Assemblies of Indolonaphthyridine Molecules: From Dimers to the Full Stack

Key electronic processes related to molecular excitonic states of finite stacks of indolonaphthyridine molecules are analyzed via the non-orthogonal configuration interaction with fragments (NOCI-F) method. Indolonaphthyridine is an organic chromophore that can undergo several electronic photoexcitation-related intermolecular processes, such as exciton and electron transfer. The structures studied here are noncrystalline arrangements built as either ordered stacks of indolonaphthyridine or stacks extracted from molecular dynamics simulations including thermal disorder. Taking dimers or trimers from either model, we performed CASSCF and NOCI-F calculations to quantify the intermolecular electronic couplings governing singlet fission, excited singlet and triplet diffusion, and hole and electron diffusion processes. Also, comparing the results for the different models, we studied the effect of structural disorder and distortion on these couplings. Finally, we present a newly developed, advanced postanalysis tool. It takes the NOCI-F data as input to carry out a multifragment full Hamiltonian procedure that involves the complete stack, providing physical information not available from the dimer/trimer models, hence giving access to additional insight into the material’s properties.

coupling reactions↗
DOE OSTI2022

Monofluorination of Naphthyls Promotes the Cofacial π–π Stacking and Increases the Electron Mobility of Non-Planar Zinc(II) Complexes of Di(naphthylethynyl)azadipyrromethene

The homoleptic zinc(II) complex of [2,8-di(1-naphthylethynyl) 3,7-diphenyl 1,9-(4-hexylphenyl)azadipyrromethene (ZnL2) 2 ] is a promising non-planar non-fullerene acceptor for organic photovoltaic applications, but it has a relatively low electron mobility that may limit its performance. Here, we explored the fluorination of peripheral aryl groups to increase intermolecular cofacial π–π stacking interactions, which are desirable for electron transport. Here complexes with fluorine on the distal phenyls [Zn(1F-L2) 2 ], on the naphthyls [Zn(2F-L2) 2 ], and on both [Zn(3F-L2) 2 ] were synthesized and characterized. All three complexes had similar optical and electrochemical properties. The crystal packing structure of Zn(2F-L2) 2 and Zn(3F-L2) 2 revealed cofacial parallel-displaced π–π stacking between the fluorinated 1-naphthylethynyl groups. Such a cofacial orientation was not observed in Zn(L2) 2 crystals, suggesting that fluorination of the naphthyl groups promotes the cofacial π–π stacking orientation. The hole mobility increased from 1.0 × 10 –4 cm 2 V –1 s –1 for Zn(L2) 2 to 0.8–1.0 × 10 –3 cm 2 V –1 s –1 for the fluorinated complexes. Fluorination on the naphthyl groups increased the electron mobility from 4.2 × 10 –5 cm 2 V –1 s –1 for Zn(L2) 2 and Zn(1F-L2) 2 to 2.0 × 10 –4 cm 2 V –1 s –1 for Zn(2F-L2) 2 and Zn(3F-L2) 2 , consistent with cofacial π–π stacking being favorable for electron transport. The three complexes were tested in OPVs using regioregular poly(3-hexylthiophene) (P3HT) as the p-type material, and the best power conversion efficiencies were 5.2, 5.4, and 5.8% for Zn(2F-L2) 2 , Zn(1F-L2) 2 , and Zn(3F-L2) 2 , respectively, compared to 5.5% for Zn(L2) 2 . The fluorination combination found in Zn(3F-L2) 2 resulted in the best device performance. This study points to a viable strategy to increase the electron mobility and performance of non-planar zinc(II) complexes of azadipyrromethene.

36 MATERIALS SCIENCE↗