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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Unconventional magnetic oscillations in a kagome Mott insulator

In metals, electrons in a magnetic field undergo cyclotron motion, leading to oscillations in physical properties called quantum oscillations. This phenomenon has never been seen in a robust insulator because there are no mobile electrons. We report an exception to this rule. We study a Mott insulator on a kagome lattice which does not order magnetically down to milli-Kelvin temperatures despite antiferromagnetic interactions. We observe a plateau at magnetization equal to $\frac{1}{9}$ Bohr magneton per magnetic ion, accompanied by oscillations in the magnetic torque, reminiscent of quantum oscillations in metals. The temperature dependence obeys Fermi distribution. These phenomena are consistent with a quantum spin liquid state whose excitations are fermionic spinons with a Dirac-like spectrum coupled to an emergent gauge field.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Exploring the interaction between the MW and LMC with a large sample of blue horizontal branch stars from the DESI survey

The Large Magellanic Cloud (LMC) is a Milky Way (MW) satellite that is massive enough to gravitationally attract the MW disc and inner halo, causing significant motion of the inner MW with respect to the outer halo. In this work, we probe this interaction by constructing a sample of 9866 blue horizontal branch (BHB) stars with radial velocities from the DESI spectroscopic survey out to 120 kpc from the Galactic centre. This is the largest spectroscopic set of BHB stars in the literature to date, and it contains four times more stars with Galactocentric distances beyond 50 kpc than previous BHB catalogues. Using the DESI BHB sample combined with SDSS BHBs, we measure the bulk radial velocity of stars in the outer halo and observe that the velocity in the Southern Galactic hemisphere is different by 3.7σ from the North. Modelling the projected velocity field shows that its dipole component is directed at a point 22 deg away from the LMC along its orbit, which we interpret as the travel direction of the inner MW. The velocity field includes a monopole term that is –24 km s –1 ⁠, which we refer to as compression velocity. This velocity is significantly larger than predicted by the current models of the MW and LMC interaction. This work uses DESI data from its first 2 yr of observations, but we expect that with upcoming DESI data releases, the sample of BHB stars will increase and our ability to measure the MW–LMC interaction will improve significantly.

Galaxy: evolution↗
DOE OSTI2025

Quantum Oscillations in the Heat Capacity of Kondo Insulator YbB 12

Here, we observe magnetic quantum oscillations in the heat capacity of the Kondo insulator YbB 12 . The frequency of these oscillations, 𝐹 = 700 T, agrees with that from magnetoresistance and torque magnetometry experiments for 𝜇 0 ⁢𝐻 >35 T in the Kondo insulating phase. Remarkably, the quantum-oscillation amplitudes in the heat capacity are substantial, with Δ⁢$\tilde{C}/T$ ≈ 0.5 mJ mol −1 K −2 at 0.8 K, accounting for 13% of the known linear heat-capacity coefficient 𝛾. Double-peak structures of quantum-oscillation amplitudes due to the distribution function of fermions were identified and used to determine the value of the effective mass from the heat capacity, which agrees well with that from torque magnetometry. These observations support bulk charge-neutral fermions contributing to the quantum oscillations in YbB 12 .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Thermodynamic Evidence of Fermionic Behavior in the Vicinity of One-Ninth Plateau in a Kagome Antiferromagnet

The spin-1/2 kagome Heisenberg antiferromagnets are believed to host exotic quantum entangled states. Recently, the reports of 1/9 magnetization plateau and magnetic oscillations in a kagome antiferromagnet YCu 3 ⁢(OH) 6 ⁢Br 2 ⁢[Br 𝑥 ⁢(OH) 1−𝑥 ] (YCOB) have made this material a promising candidate for experimentally realizing quantum spin liquid states. Here, we present measurements of the specific heat 𝐶 𝑝 in YCOB in high magnetic fields (up to 41.5 T) down to 0.46 K, and the 1/9 plateau feature has been confirmed. Moreover, the temperature dependence of 𝐶 𝑝 /𝑇 in the vicinity of 1/9 plateau region can be fitted by a linear in 𝑇 term which indicates the presence of a Dirac spectrum, together with a constant term, which indicates a finite density of states contributed by other spinon Fermi surfaces. Surprisingly, the constant term is highly anisotropic in the direction of the magnetic field. Additionally, we observe a double-peak feature near 30 T above the 1/9 plateau which is another hallmark of fermionic excitations in the specific heat. This combination of gapless behavior and the double-peak structure strongly suggests that the 1/9 plateau in YCOB is nontrivial and hosts fermionic quasiparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Specific ion effects on ion transport in charged polymer membranes

Selective separation of like-charged ions is a central challenge in applications such as critical mineral recovery. Electrochemical membrane–based separations offer promising pathways to address this need, but a limited fundamental understanding of ion transport in charged polymer membranes hampers the development of highly selective materials. This study elucidates the role of specific ion effects (SIEs) in ion transport through charged polymer membranes by integrating experimental measurements of ion mobility and in situ ion/ion and ion/water interactions in model charged polymer membranes with results from molecular dynamics simulations on analogous systems. We demonstrate that solvent-mediated ion interactions drive pronounced SIEs within the studied membranes, with the ion softness, i.e., the malleability of ion hydration shells, from hard/soft acid/base (HSAB) theory emerging as a key predictor of transport properties. HSAB theory also explains the observed mechanism of solvent-mediated ion interactions. Our findings offer a mechanistic framework for designing membranes with tailored ion selectivity, potentially enabling efficient separations of chemically similar ions.

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

Three-dimensional nucleation and growth of deformation twins in magnesium

At two-thirds the weight of aluminum, magnesium alloys have the potential to reduce the fuel consumption of transportation vehicles. These advancements depend on our ability to optimize the desirable versus undesirable effects of deformation twins, which are three-dimensional (3D) microstructural domains that form under mechanical stresses. Previously only characterized through surface or thin-film measurements, we here present 3D in situ characterization of deformation twinning inside an embedded grain over mesoscopic fields of view using dark-field x-ray microscopy supported by crystal plasticity finite element analysis. The results revealed the role of triple junctions on twin nucleation and the sequence and irregularity of twin growth and showed that twin-grain junctions, twin-twin junctions, and twin boundaries were the sites of localized dislocation accumulation.

Lee, Sangwon [Univ. of Michigan, Ann Arbor, MI (Un↗
DOE OSTI2025

Evidence of Completion of Milestone 4: Simulation Testbed Validated with Experimental Data

Milestone 4 is given in the SOPO as being due in quarter 5 (ending 9/11/2020) and is described thus: Milestone 4: Enhanced Simulation Testbed Validated with Experimental Data (UM, Mathieu) Simulation testbed validated with data obtained from experimental testbed, specifically, nonlinear load behaviors and communication network issues observed in the experimental testbed will be modeled in the simulation testbed. The simulation testbed should accurately capture TCL real and reactive power consumption (including during extreme events associated with nonlinear behaviors and communication network failures) to within 5% RMSE error with respect to data obtained from the experimental testbed.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2025

Examining the Impact of Local Constraint Violations on Energy Computations in DFT

ABSTRACT This work examines the impact of locally imposed constraints in Density Functional Theory (DFT). Using a metric referred to as the extent of violation index (EVI), we quantify how well exchange‐correlation functionals adhere to local constraints. Applying EVIs to a diverse set of molecules for GGA functionals reveals constraint violations, particularly for semi‐empirical functionals. We leverage EVIs to explore potential connections between these violations and errors in chemical properties. While no correlation is observed for atomization energies, a significant statistical correlation emerges between EVIs and total energies. Similarly, the analysis of reaction energies suggests weak positive correlations for specific constraints. However, definitive conclusions about error cancellation mechanisms cannot be made at this time. These observations revealed by EVIs may be useful for consideration when designing future generations of semilocal functionals.

Khanna, Vaibhav [Department of Chemistry Universit↗
DOE OSTI2026

Melting of charge density waves in low dimensions

Charge density waves (CDWs) are collective electronic states that can reshape and melt, even while confined within a rigid atomic crystal. In two dimensions, melting is predicted to be distinct, proceeding through partially ordered nematic and hexatic states that are neither liquid nor crystal. Here, we measure and explain how continuous, hexatic melting of incommensurate CDWs occurs in low-dimensional materials. As a CDW is thermally excited, disorder emerges progressively—initially through smooth elastic deformations that modulate the local wavelength and subsequently via the nucleation of topological defects. Experimentally, we track three hallmark signatures of CDW melting—azimuthal superlattice peak broadening, wavevector contraction, and integrated intensity decay.

42 ENGINEERING↗
DOE OSTI2025

Electrostatic limits on charge selectivity in ultrahigh charge density polymer membranes

Ion-exchange membranes (IEMs) with ultrahigh charge densities offer the promise of enhanced ion transport for electrochemical technologies, yet the fundamental limits of this membrane design strategy are not yet understood. In this work, we present a systematic study of bis(1-vinyl-3-imidazolium) cross-linked polymer membranes with fixed charge contents ranging from 6 to 9 mol/L[dry polymer], synthesized to isolate the effects of charge density at constant membrane water content. While ionic conductivity increases monotonically with increasing charge density, a sharp decline in charge selectivity is observed for the most densely charged membranes, defying conventional expectations. Structural, thermal, and mechanical analyses reveal a critical onset of network disruption and anomalous ion partitioning behavior in these densely charged membranes. With proper consideration of cross-linker geometry, these results are interpreted using Manning's counter-ion condensation theory, which suggests that closely packed charged cross-linkers amplify inter-chain electrostatic interactions and trigger excess counter-ion condensation. Our findings suggest that, beyond a threshold spacing between fixed charges, increased functionalization may harm rather than help charge selectivity of IEMs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

LaBr 3 : Ce self-activation analysis for measuring fast neutron fields

Measurement of the fast neutron production rate in deuterium–tritium (D–T) fusion reactions is important for applications such as active interrogation, fusion diagnostics, and borehole logging. Such measurements are typically performed by neutron activation analysis of metal foils, especially copper. Copper foil activation analysis requires efficiency and energy calibrations of the detector used to measure the foil, and it relies on the detection of 511 keV gamma rays, which are prominent in the active background when neutrons are being produced. Alternatives, such as 79m Br produced by inelastic neutron scattering on 79 Br, are limited by short half-life, low-energy gamma emission, and inability to selectively measure D–T neutrons. This work describes a novel alternative approach to measure ≳10 MeV neutron fields based on self-activation analysis of a LaBr 3 :Ce detector. The activity of 78 Br, the activation product of the 79 Br(n,2n) 78 Br reaction, is used to determine the neutron flux and infer the neutron production rate. We experimentally demonstrate the method with a cylindrical LaBr 3 :Ce crystal with a diameter and height of 3.81 cm that was placed at an ~18 cm distance from the neutron production point, at a 90° angle with respect to the deuteron beam in a D–T neutron generator. Operating voltage and current of the generator were adjusted to evaluate the technique’s performance over a nominal generator output range of approximately (1 - 9) x 10 7 n/s. The neutron output obtained from LaBr 3 :Ce activation agrees to within three standard deviations of the output obtained using copper activation. The self-activation technique can be conveniently employed in a variety of applications to simplify measurements of fast neutrons produced in D–T fusion reactions.

Active interrogationLaBr3↗
DOE OSTI2026

Rapid neutron and gamma-ray source localization using machine learning

Rapid localization of radiation sources is critical for applications including nuclear emergency response, safeguards, and security. However, conventional imaging systems such as neutron scatter cameras and Compton cameras depend on rare coincidence events, which often result in long acquisition times. In this work, we address the challenge of rapid source localization by developing a machine learning approach to predict the direction of a single radiation source using only count rates from an array of neutron and gamma-ray detectors. The proposed model is a fully connected neural network (FCNN) trained using Monte Carlo simulation data from a 252 Cf source. The model hyperparameters are optimized with a small set of routine 252 Cf measurements. We benchmarked the performance of the trained and optimized machine learning model using additional 252 Cf , 137 Cs , and PuBe measurements under laboratory conditions with varying source-detector configurations. For these measurements, the machine learning model achieved a mean localization error smaller than 30° with 3 x 10 3 system counts, corresponding to 8 s measurement time for the imaging system used in this work. In this low-statistics regime, the method outperformed traditional scatter-based imaging by more than 75% in localization accuracy for the evaluated measurement configurations. These results demonstrate that a machine learning-based approach can significantly reduce the time required for accurate single-source localization, providing a robust and computationally efficient alternative to traditional imaging systems in time-critical nuclear security and emergency response scenarios.

Gamma-ray imaging↗
DOE OSTI2025

Influence of Surface Defects on WO 3 Photoelectrodes for Catalyzing Chloride Oxidation in Water

Tungsten oxide (WO 3 ) is an n-type semiconductor due to oxygen vacancies (□ O •• in Kroger-Vink notation) or surface protonation as H x WO 3 . It is one of the few acid-stable oxides under large positive bias, which makes WO 3 ideal for interrogating the mechanism of the chloride oxidation reaction (COR). The large, positive valence band edge of ∼3 eV provides the overpotential necessary to carry out the COR, but the reaction competes with the oxygen-evolution reaction in water. The □ O •• defect density can be controlled by the atmosphere under which the material is annealed, so WO 3 films were prepared by a spin-coating method from an ammonium metatungstate precursor annealed at 500 °C under air, flowing O 2 , and flowing argon. Annealing the films in a flowing O 2 atmosphere hinders the formation of □ O ••, and annealing in Ar leads to greater surface W 6+ , likely due to expelling intercalated H + . The saturated photocurrent density (j ph ) is highest in films with the greatest concentration of W 5+ and greatest concentration of oxide defects: (0.66 mA/cm 2 annealed in air, 0.58 mA/cm 2 annealed in Ar, and 0.49 mA/cm 2 annealed in O 2 , reported at 1.5 V vs Ag/AgCl, pH 3 (before the onset of a dark reaction). The defect concentrations are determined by X-ray photoelectron spectroscopy. In all cases the Faradaic efficiency for the COR is near unity. Finally, we demonstrate that W 5d states can be probed by ligand K-edge X-ray absorption near-edge spectroscopy via pre-edge (Cl 1s → W 5d) transitions, lower in energy than the ligand-centered (Cl 1s → 4p) transition. We use this analysis to show the presence of W─Cl covalent bonds on the WO 3 films post-COR, corroborated by DFT calculations. Furthermore, this result stands in contrast to the commonly assumed mechanistic proposal invoking outer-sphere electron transfer to a physisorbed chloride ion.

Cl K-edge↗
DOE OSTI2026

Tuning Solid Electrolyte Interphase Formation before Plating Onset in Anode-Free Sodium Batteries

Sodium (Na) batteries are of growing interest due to the higher earth abundance of sodium than lithium, as well as their promising theoretical energy density when metallic Na anodes are used. However, Na plating and stripping are heavily influenced by the physicochemical properties of the solid electrolyte interphase (SEI), which is directly influenced by the solvent and salt used for the electrolyte. While most studies focus on the SEI that forms on the surface of Na metal after plating, we expand this analysis by identifying a nanoscale “pre-plating” SEI that forms on the current collector (CC) prior to the onset of Na plating. Here, we systematically investigate an array of Na salt and glyme solvents in the electrolyte and determine the associated impacts on pre-plating SEI formation on aluminum CCs. By combining analytical electrochemistry approaches with a multimodal suite of spectroscopy techniques (X-ray, infrared, and Raman), supported by density functional theory calculations, we reveal a direct correlation between the Na + coordination environment and pre-plating SEI composition. We find that longer-chain glymes produce larger proportions of organic alkoxide products in the interphase, consistent with increased Na + −glyme interactions, while the fraction of salt-derived inorganic products (e.g., NaF) correlates with Na + −anion coordination. These insights highlight the critical influence of electrolyte composition particularly solvent identity and Na + coordination on the initial SEI formation in anode-free Na batteries.

anode-free batteries↗
DOE OSTI2025

High aspect ratio organic light-emitting diodes

Reliability is particularly challenging for organic light-emitting diodes (OLEDs) used in solid-state lighting applications, because OLED lifetime is inversely proportional to luminance, and most lighting applications demand high luminance. Here we introduce a strategy to overcome this tradeoff by constructing OLEDs on a substrate with sub-mm, high aspect ratio surface texture. By creating more active OLED area per unit lighting panel area, the device current density required to generate a given panel luminance decreases. We validate this approach for fluorescent and phosphorescent OLEDs, demonstrating good thickness uniformity on corrugated substrates with area enhancement factors up to 1.4x using a standard thermal evaporator. Relative to planar controls at the same panel current density, the high aspect ratio devices achieve a 2.7-fold increase in operating lifetime and up to a 40% increase in external light extraction efficiency, indicating that this approach offers a powerful pathway to improve the efficiency and lifetime of OLED lighting.

OLED↗
DOE OSTI2025

Titanium nitride prepared by the urea-glass synthesis gives an active electrocatalyst for the oxygen reduction reaction

Rock-salt-structured titanium nitride (TiN) has emerged as a leading earth-abundant electrocatalyst for the oxygen reduction reaction (ORR). We compare TiN prepared in three ways starting from urea: the urea–glass method, by a direct reaction between urea and titanium(IV) chloride, and through a discrete monomeric complex. In the urea-glass route, a new-found [Ti 4 (µ-O) 6 (OC(NH 2 ) 2 ) 12 ] 4+ oxo-bridged titanium–urea precursor can be synthesized in a single-pot reaction at room temperature starting from titanium(IV) chloride, urea, and ethanol with a urea-to-titanium ratio of 6. Subsequent annealing of the polymeric gel that results at 750 °C in an N 2 atmosphere yields phase-pure, TiN particles on the 100 µm size scale. TiN can be deposited as an ink with PiperlON®anion exchange dispersion onto a glassy carbon rotating disk electrode (RDE), and of the three synthesis methods, the urea-glass method gives the most active ORR catalyst. The onset potential for ORR activity is −131 mV vs. Hg/HgO, and Koutecký–Levich analysis of linear-sweep voltammetry recorded at varying rotation rates supports a two-electron reduction pathway to H 2 O 2 , with a rate constant of 0.0172 cm s −1 . The higher activity is ascribed to a more oxygen-rich surface—boh defect sites and active oxygen species—afforeded by the oxo-bridged precursor, corrorborated by X-ray photoelectron spectroscopy (XPS) analysis.

Xie, Wanrui [University of Michigan, Ann Arbor, MI↗
DOE OSTI2025

Determining the complex second-order optical susceptibility in macroscale van der Waals heterobilayers

In this work, we report on the experimental characterization of the second-order susceptibility in MoSe 2 /WS 2 heterobilayers, including their hidden complex phases. To this end, we developed a heterodyne-detection scheme for second-harmonic generation and applied it to macroscale heterobilayer samples prepared using the gold-tape exfoliation method. The heterodyne scheme enabled us to distinguish the relative orientation of the crystal domains, and furthermore, it allowed us to characterize the complex phases of the susceptibility relative to a reference quartz sample. By comparing the results from the monolayer regions and the heterobilayer region over several hundred microns of the sample area, we determined that the contribution of interlayer effects to second-harmonic generation is within the experimental uncertainty arising from the sample inhomogeneity. The results here provide fundamental quantitative information necessary for the precise design of nanophotonic systems based on stacking engineering.

2D materials↗