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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Elucidating a dissolution–deposition reaction mechanism by multimodal synchrotron X-ray characterization in aqueous Zn/MnO 2 batteries

Aqueous Zn/MnO 2 batteries with their environmental sustainability and competitive cost, are becoming a promising, safe alternative for grid-scale electrochemical energy storage. Here, presented as a promising design principle to deliver a higher theoretical capacity, this work offers fundamental understanding of the dissolution–deposition mechanism of Zn/β-MnO 2 . A multimodal synchrotron characterization approach including three operando X-ray techniques (powder diffraction, absorption spectroscopy, and fluorescence microscopy) is coupled with elementally resolved synchrotron X-ray nano-tomography. Together they provide a direct correlation between structural evolution, reaction chemistry, and 3D morphological changes. Operando synchrotron X-ray diffraction and spectroscopy show a crystalline-to-amorphous phase transition. Quantitative modeling of the operando data by Rietveld refinement for X-ray diffraction and multivariate curve resolution (MCR) for X-ray absorption spectroscopy are used in a complementary fashion to track the structural and chemical transitions of both the long-range (crystalline phases) and short-range (including amorphous phases) ordering upon cycling. Scanning X-ray microscopy and full-field nano-tomography visualizes the morphology of electrodes at different electrochemical states with elemental sensitivity to spatially resolve the formation of the Zn- and Mn-containing phases. Overall, this work critically indicates that for Zn/MnO 2 aqueous batteries, the reaction pathways involving Zn–Mn complex formation upon cycling become independent of the polymorphs of the initial electrode and sheds light on the interplay among structural, chemical, and morphological evolution for electrochemically driven phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Hydrogen in disordered titania: connecting local chemistry, structure, and stoichiometry through accelerated exploration

Hydrogen incorporation in native surface oxides of metal alloys often controls the onset of metal hydriding, with implications for materials corrosion and hydrogen storage. A key representative example is titania, which forms as a passivating layer on a variety of titanium alloys for structural and functional applications. These oxides tend to be structurally diverse, featuring polymorphic phases, grain boundaries, and amorphous regions that generate a disparate set of unique local environments for hydrogen. Here, we introduce a workflow that can efficiently and accurately navigate this complexity. First, a machine learning force field, trained on ab initio molecular dynamics simulations, was used to generate amorphous configurations. Density functional theory calculations were then performed on these structures to identify local oxygen environments, which were compared against experimental observations. Second, to classify subtle differences across the disordered configuration space, we employ a graph-based sampling procedure. Finally, local hydrogen binding energies and hopping kinetics are computed using exhaustive density functional theory calculations on representative configurations. Here, we leverage this methodology to show that hydrogen binding energetics are described by local oxygen coordination, which in turn is affected by stoichiometry, and form the basis of hopping kinetics and diffusion. Together these results imply that hydrogen incorporation and transport in TiO x can be tailored through compositional engineering, with implications for improving the performance and durability of titanium-derived alloys in hydrogen environments.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ferroelectric 2D antimony oxides with wide bandgaps

The first two-dimensional (2D) polymorphs of antimony dioxide, namely, γ-Sb 2 O 4 and δ-Sb 2 O 4 , are predicted using the evolutionary algorithm combined with first-principles density functional theory (DFT) calculations. Out-of-plane ferroelectricity is found in γ-Sb 2 O 4 , while in-plane ferroelectricity is found in δ-Sb 2 O 4 . The predicted dipole moments of γ-Sb 2 O 4 and δ-Sb 2 O 4 phases are 36.63 and 14.96 eÅ, respectively, implying that they can be good candidates for making ferroelectric devices. Further, the calculations show that doping with other group V elements or applying strain can lower the switching energy barriers and thus facilitate switching. Results from GW calculations show indirect band gaps of 5.51 and 3.39 eV for γ-Sb 2 O 4 and δ-Sb 2 O 4 in their monolayers, respectively. Raman spectra are calculated to facilitate the experimental investigation of the predicted structures. The existence of both in-plane and out-of-plane 2D ferroelectricity and the large band gaps make this material system particularly interesting for potential applications.

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

Evaluating the photophysical and photochemical characteristics of green-emitting cerium(III) mono-cyclooctatetraenide complexes

The photophysical and photochemical reactivity of the organometallic mono(cyclooctatetraenide)-Ce(III) complexes: [(C 8 H 8 )Ce(μ-X)(THF) 2 ] 2 X = O 3 SCF 3 - (1), Cl - (2), were studied. Here, in the course of these studies, a new polymorph of [(C 8 H 8 )Ce(μ-O 3 SCF 3 )(THF) 2 ] 2 (1) was described. Photoluminescence (PL) studies of 1 and 2 showed characteristic excitation and emission bands in the visible region, with bright green light emission under light irradiation from states corresponding to the 5d → 4f transition. Complexes 1 and 2 exhibit relatively long lifetime of 205.4 ± 0.2 and 145.8 ± 0.4 ns respectively. And the quantum yields (Φ) for 1 and 2 are 0.180 and 0.068 respectively. Electrochemical studies were performed on complexes 1 and 2 with a reversible Ce(III)/Ce(IV) redox couple recorded at $E_{1/2}$ = -1.53 V versus the Fc/Fc + for 2. Complex 1 shows an irreversible Ce(III/IV) oxidation wave. Complexes 1 and 2 revealed strongly-reducing, estimated, excited state reduction potentials ($E^*_{1/2}$) of -3.31 and -4.02 V versus the Fc/Fc + respectively, with small Stokes shifts of 0.12 eV. With their associated relatively long lifetimes, small Stokes shifts and large, negative $E^*_{1/2}$ values, both complexes were evaluated as potential photosensitisers for halogen atom transfer (XAT) using a test reaction of the dehalogenation of benzyl chloride.

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

Li-ion and Na-ion intercalation in layered MnO 2 cathodes enabled by using bismuth as a cation pillar

Low-cost batteries based on Earth-abundant materials are needed for large-scale electrical storage for the grid. Cathodes based almost entirely on Mn oxides would reduce overall battery cost but cycling of Mn oxides is often not stable. In Li-ion cells, most polymorphs of MnO 2 undergo irreversible transformation to spinel LiMn 2 O 4 during cycling, causing capacity loss. Doping MnO 2 with Bi is known to stabilize the structure, but previous reports have relied on low-crystallinity material making it impossible to pinpoint the Bi location in the structure or its mechanism. In this work, we report a series of hydrated Bi-doped layered MnO 2 compounds and characterize their structures as a function of Bi amount. Bi is shown to reside in the material interlayer, provoking higher long-range structural order even at a low doping level of 1.3%. Doped material improves the specific capacity and stability of cycling in both Li-ion and Na-ion cells. A high level of Bi doping, 4.3%, causes loss of the interlayer crystal water in non-aqueous electrolyte, and this reduces the interlayer distance. Crystal water is shown to be beneficial in a Na-ion system, while its loss improves Li-ion cycling. This provides fundamental insight into how pillaring by a heavy, multivalent cation stabilizes layered oxides.

25 ENERGY STORAGE↗
DOE OSTI2023

Shear-aligned large-area organic semiconductor crystals through extended π–π interaction

Small molecule-based organic semiconductors are of broad interest in organic field-effect transistors (OFETs) due to their potential for high crystallinity and electrical performance. The 2D molecule, TIPS-peri-pentacenopentacene (TIPS-PPP), which is the vertical extension of the 1D TIPS-pentacene (TIPS-PEN) molecule, offers a lower bandgap, higher aromaticity, and an enhanced π–π interaction with neighboring molecules in the solid state when compared to TIPS-PEN. However, an in-depth understanding of the relationship between the molecule structure, solid-state molecular packing, and the electronic properties has not been reported due to poor control over the TIPS-PPP crystallite size. In this work, we successfully engineered highly oriented large-area TIPS-PPP crystals through the solution shear coating technique. Additionally, compared with narrow ribbon-like TIPS-PEN crystals, TIPS-PPP crystals can grow centimeters long and over 500 μm wide. TIPS-PPP molecules are less susceptible to forming metastable polymorphs than TIPS-PEN molecules upon fast evaporation. The crystal structure of TIPS-PPP is also thermally stable at 250 °C. Notably, the anisotropic charge carrier mobility of TIPS-PPP crystals is resolved through fabricating bottom-gate top-contact devices, with a hole mobility of 3.1 cm 2 V -1 s -1 along the preferred packing direction. Further device optimization using top-gate bottom-contact devices improved the mobility up to 6.5 cm 2 V -1 s -1 , which is among the highest for pentacene-derivative-based organic semiconductors.

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

High-throughput and data-driven search for stable optoelectronic AMSe 3 materials

The rapid advancement in emerging optoelectronic technologies demands highly efficient, affordable, and ecofriendly materials. In this context, ternary chalcogenides, especially ternary selenides, show early promise as a material class due to their stability and remarkable electronic, optical, and transport properties. In this work, we integrate first-principles-based high-throughput computations with machine learning (ML) techniques to predict the thermodynamic stability and optoelectronic properties of 920 valency-satisfied selenide compounds. Through investigating polymorphism, our study reveals the edge-sharing orthorhombic Pnma phase (NH 4 CdCl 3 -type) as the most stable structure for most ternary selenides. High-fidelity supervised ML models are trained and tested to accelerate stability and band gap predictions. These data-driven models pin down the most influential features that dominantly control key material characteristics. The multistep high-throughput computations identify the ternary selenides with optimal direct band gaps, light carrier masses, and strong optical absorption edges. The extensive materials screening considering phase stability, toxicity, and defect tolerance, finally identifies the seven most suitable candidates for photovoltaic applications. Two of these final compounds, SrZrSe 3 and SrHfSe 3 , have already been synthesized in a single-phase form, with the latter showing an optically suitable band gap, aligning well with our findings. The non-adiabatic molecular dynamics reveal sufficiently long photoexcited charge carrier lifetimes (on the order of nanoseconds) in some of these selected selenide materials, indicating their exciting characteristics. Overall, our study suggests a robust in silico framework that can be extended to screen large datasets of various material classes for identifying promising photoactive candidates.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Influence of shape on crystal structure and optical properties of heterocyclic conjugated molecules

Organic optoelectronics are increasingly important due to their tunablilty, flexibility, and solution processability. Tuning optical properties of these materials as solids relies on the balance of weak non-covalent interactions that dictate crystal structure, but are difficult to predict. Our research aims to improve our understanding of how electrostatic interactions can direct and facilitate intramolecular interactions that dictate emergent properties of crystalline materials. This paper focuses on exploring how multi-fused thiophene ring systems that are popular in modern organic optoelectronic materials impact intramolecular interactions, while also investigating the role of molecular shape. In these examples, the shape of heterocyclic systems correlate with the crystal structures: while the bent heterocyclics show no discrete and discernable intramolecular interactions, those with bent shapes interact cofacially with one of the electron poor ArF pendants by twisting the arylene ethynylene backbone. Two of the control molecules, which bear non-fluorinated benzyl ester substituents, show intramolecular edge-face interactions, and several of these molecules show clear polymorphic behavior. Furthermore, these findings further our understanding of how discrete interactions can be altered not only by electrostatics, but also by shape, allowing for increasingly nuanced control over the crystal structures and optical properties of optoelectronic materials.

Guzmán, Elisa↗
DOE OSTI2025

Boron monoxide is a one-dimensional polymer

It was recently reported that boron monoxide (BO) is formed through the cross-linking of B 4 O 2 structural building units. Multiple theoretical phases agree with this description. Using pycnometry, multidimensional 17 O NMR spectroscopy, and plane-wave DFT calculations we determined the likely polymorph to be a one-dimensional polymer initially proposed in 1955.

Thuma, Joseph F. [Iowa State Univ., Ames, IA (Unit↗
DOE OSTI2026

High-pressure neutron powder diffraction study of an arsenolite deuterium inclusion compound: structure and formation kinetics

High-pressure variable-temperature neutron powder diffraction was employed to investigate the synthesis and structural properties of arsenolite (As 4 O 6 ), a cubic arsenic( III ) oxide polymorph, and its inclusion compound with deuterium. The compound forms with the stoichiometry As 4 O 6 ·2D 2 , consistent with earlier findings. At 295 K and 1.96(2) GPa, D 2 molecules occupy the 16c site (0, 0, 0) and are aligned along the <111> direction. The diffraction data suggest that the D 2 molecules at this site become rotationally disordered upon decompression to 0.78(2) GPa at 120 K, while no occupancy is observed at the 8a position (⅛, ⅛, ⅛) under any of the studied conditions. The kinetic data of the high-pressure inclusion compound synthesis at 1.56(2) and 1.96(2) GPa were analyzed using the Avrami model. The Avrami exponent, 0.135(16), remains invariant with pressure, demonstrating that the reaction topochemistry is unaffected by compression. Similarly, the reaction rates, 0.29(3) and 0.23(3) min −0.135 at 1.56(2) and 1.96(2) GPa, respectively, exhibit negligible pressure dependence and suggest a surprisingly low activation volume of 1.6 cm 3 mol −1 for the reaction. These results provide detailed insight into the structural dynamics and kinetics of deuterium inclusion in arsenolite under high pressure.

Guńka, Piotr A. [Warsaw University of Technology (↗
DOE OSTI2025

Alloying multiple halide perovskites on the same sublattice in search of stability and target band gaps

Single-component halide perovskites (HPs) rarely satisfy all the necessary criteria for optoelectronic applications, such as achieving an optimal band gap while maintaining high chemical and structural stability. Alloying halide perovskites has emerged as a promising strategy, not only to enhance stability but also to fine-tune their electronic and optical properties. In this work, we explore multiple degrees of freedom in alloy design, considering different substitution sublattices sites (A, B, or X in ABX3 perovskites), various chemical species (isovalent and hetero-valent elements), and multi-component compositions on a given sublattice. Using first-principles calculations based on density functional theory (DFT), we investigate how compositional variations influence the electronic (band gap) and structural properties (mixing enthalpy) of HP alloys. Our approach employs the polymorphous cell model, allowing full local relaxation which breaks local symmetry while preserving global cubic symmetry—an essential framework for accurately modeling HPs. Our results reveal that X-site mixing (halogen substitution) primarily affects the valence band maximum, allowing target band gap engineering. Additionally, variations in halogen radii introduce internal strain through octahedral distortions, influencing the mixing enthalpy. A-site substitution, while not directly contributing to the band edge states, modifies structural stability via volume effects, indirectly impacting the band gap. B-site alloying plays a dominant role in band gap modulation, leading to either positive or negative band gap bowing. Specifically, isovalent B-site mixing (Sn–Pb) induces strong positive bowing, where the alloy band gap is smaller than the average gap of parent compounds, whereas hetero-valent mixing (Cd–Pb) results in pronounced negative bowing. As an aside, we investigate the competition between the excess energy of disordered alloys vs. that of long-range ordered double perovskites of the same compositions, seeking examples of ordered phases emerging from disordered alloys. Furthermore, our findings provide fundamental insights into the electronic and structural behavior of HP alloys, offering valuable design principles for the development of stable and efficient materials for next-generation photovoltaic and optoelectronic devices.

14 SOLAR ENERGY↗
DOE OSTI2025

Advanced spectroscopic studies of (PPh 4 ) 2 [Co(N 3 ) 4 ], a field-induced single-ion magnet

The high-spin Co II complex (PPh 4 ) 2 [Co(N 3 ) 4 ] (Co-N 3 )has been investigated using advanced spectroscopic techniques [far-IR magneto-spectroscopy (FIRMS), high-frequency and high-field EPR (HFEPR), and inelastic neutron scattering (INS)] to study its zero-field-splitting (ZFS), giving spin-Hamiltonian (SH) parameters. The analysis of multi-frequency HFEPR reveals the easy-axis anisotropy with a D value of −10.39(5) cm −1 and a rhombic ratio (E/D) of 0.21(1). The magnetic properties have also been probed by direct-current (DC) magnetometry, suggesting minor differences in anisotropy from the previously reported polymorph (Co-N 3 ′). Ligand-field theory (LFT) analysis indicates that the structures of Co-N 3 and Co-N 3 ′ are closer to D 2d symmetry than other symmetries considered. Alternate-current (AC) susceptibility reveals slow magnetic relaxation under an applied field, indicating that Co-N 3 is a field-induced single-ion magnet (SIM). Here, while both Co-N 3 and Co-N 3 ′ were studied by DC magnetometry, one unusual aspect of the current work on Co-N 3 is that advanced spectroscopies HFEPR, FIRMS, and INS were used to directly observe transitions between ZFS split states, giving accurate SH parameters.

Hand, Adam T. [Univ. of Tennessee, Knoxville, TN (↗
DOE OSTI2026

Structure prediction of porous organic crystals

In this work, we explore the possibility of applying automated crystal structure prediction to reproduce the experimentally identified metastable porous polymorphs. Using our recently developed High-Throughput Organic Crystal Structure Prediction ( HTOCSP ) framework, we conducted a systematic study on five representative organic crystalline systems including hydrogen-bonded frameworks (HOFs), featured by the presence of significant porosity, in conjunction with different choices of energy models from classical, machine learning force fields, tight binding to density functional theory. Our results suggest that the current structure generation framework, with careful selection of symmetry conditions, is likely to generate rather complex and abundant metastable crystal candidates for porous crystals. In conjunction with the recent advance in universal machine learning force fields, it becomes possible to identify experimental structures as the energetically favorable candidates from a simple energy versus density analysis, thus paving the way for computational design of complex porous materials with the target systems prior to the experimental synthesis and characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thermal scattering law for ice based on neutron time-of-flight experiments carried out at the SEQUOIA spectrometer at the Oak Ridge National Laboratory

Precise estimation of neutron thermalization in moderators relies on high-fidelity thermal scattering cross-section data governed by the thermal scattering law (TSL). The Institut de Radioprotection et de Sûreté Nucléaire (IRSN) has been working on the development of improved TSL for light water ice. Many polymorphic phases of light water ice exist depending on the thermodynamic conditions. The most common type of ice at standard pressure and temperature below water freezing point (273.15 K) is ice-Ih. It is essential to have high-resolution experimental double differential data for developing and/or validating TSL for moderator materials.Existing experimental double-differential scattering data for ice-Ih are extremely sparse and of limited quality. New high-quality double-differential measurements for ice-Ih over multiple temperatures and incident neutron energies would directly support the validation and improvement of ice-Ih TSL models for criticality safety applications.Series of time-of-flight (TOF) inelastic neutron scattering experiments on ice-Ih at temperatures starting at 271 K and down to 6 K, have been carried out at the SEQUOIA spectrometer at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL), United States. The experiments have been performed for incident neutron energies, Ei= 11, 55, 160, 250, and 600 meV, to explore different excitation energies in the vibrational phonon spectrum. This paper presents the thermodynamic conditions and the details of the TOF measurements on ice-Ih and the derived phonon spectrum from the experimentally measured double differential data. A study of the variation of the phonon spectrum of ice-Ih as a function of temperature is highlighted, and a preliminary TSL evaluation is developed based on the experimental phonon spectrum.

Jaiswal, V↗
DOE OSTI2020

False metals, real insulators, and degenerate gapped metals

This paper deals with a significant family of compounds predicted by simplistic electronic structure theory to be metals but are, in fact, insulators. This false metallic state has been traditionally attributed in the literature to reflect the absence of proper treatment of electron-electron correlation (“Mott insulators”) whereas, in fact, even mean-field like density functional theory describes the insulating phase correctly if the restrictions posed on the simplistic theory are avoided. Such unwarranted restrictions included different forms of disallowing symmetry breaking described in this article. As the science and technology of conductors have transitioned from studying simple elemental metals such as Al or Cu to compound conductors such as binary or ternary oxides and pnictides, a special class of degenerate but gapped metals has been noticed. Their presumed electronic configurations show the Fermi level inside the conduction band or valence band, yet there is an “internal band gap” between the principal band edges. The significance of this electronic configuration is that it might be unstable toward the formation of states inside the internal band gap when the formation of such states costs less energy than the energy gained by transferring carriers from the conduction band to these lower energy acceptor states, changing the original (false) metal to an insulator. The analogous process also exists for degenerate but gapped metals with the Fermi level inside the valence band, where the energy gain is defined by transfer of electrons from the donor level to the unoccupied part of the valence band. We focus here on the fact that numerous electronic structure methodologies have overlooked some physical factors that could stabilize the insulating alternative, predicting instead false metals that do not really exist (note that this is in general not a physical phase transition, but a correction of a previous error in theory that led to a false prediction of a metal). Such errors include: (i) ignoring spin symmetry breaking, such as disallowing magnetic spin ordering in CuBi2O4 or disallowing the formation of polymorphous spin networks in paramagnetic LaTiO 3 and YTiO 3 ; (ii) ignoring structural symmetry breaking, e.g., not enabling energy-lowering bond disproportionation (Li-doped TiO 2 , SrBiO 3 , and rare-earth nickelates), or not exploring pseudo-Jahn–Teller-like distortions in LaMnO 3 , or disallowing spontaneous formation of ordered vacancy compounds in Ba 4 As 3 and Ag 3 Al 22 O 34 ; and (iii) ignoring spin–orbit coupling forcing false metallic states in CaIrO 3 and Sr 2 IrO 4 . The distinction between false metals vs real insulators is important because (a) predicting theoretically that a given compound is metal even though it is found to be an insulator often creates the temptation to invoke high order novel physical effects (such as correlation in d-electron Mott insulators) to explain what was in effect caused by a more mundane artifact in a lower-level mean-field band theory, (b) recent prediction of exotic physical effects such as topological semimetals were unfortunately based on the above compounds that were misconstrued by theory to be metal, but are now recognized to be stable insulators not hosting exotic effects, and (c) practical technological applications based on stable degenerate but gapped metals such as transparent conductors or electrides for catalysis must rely on the systematically correct and reliable theoretical classification of metals vs insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Templated epitaxy of TiO 2 (B) on a perovskite

The bronze-phase TiO 2 (B) has an open atomic framework that makes it a good candidate for applications in photochemical and electrochemical conversion of energy. However, the synthesis of bronze-phase TiO 2 (B) thin films on perovskite substrates, such as SrTiO 3 (STO), which is one of the most conventional versatile substrates for oxide epitaxy, has been extremely challenging owing to the preferential formation of the anatase TiO 2 over TiO 2 (B). The main reason is that the anatase TiO 2 has not only a smaller lattice mismatch than TiO 2 (B), but also a better structural symmetry match when grown on STO. Here, we demonstrate a way to circumventing this problem by using a VO 2 (B) buffer layer, yielding the growth of a high-quality single crystalline TiO 2 (B) film on a (001)-oriented STO substrate. Finally, from the resulting TiO 2 (B) film, we found that this film has a large optical bandgap of ~3.6 eV, which is close to the known theoretical value, the largest among TiO 2 polymorphs, and useful for developing high-power energy devices.

36 MATERIALS SCIENCE↗