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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Effect of Mg Content in Melt-Spun Mn–Bi–Mg–Sb–In Alloys on the Structure and Properties of Field-Annealed Magnets

Mn-Bi alloys modified with Mg and other elements were recently developed into promising rare-earth-free permanent magnets through successive melt-spinning, warm compaction, and short magnetic-field annealing. This letter reports herein on the crystal structures, texture, and magnetic properties observed in Mn 50 Bi 49-x Mg x Sb 0.5 In 0.5 alloys (x = 0, 1.5, 3.0, 4.5) throughout these processing steps. The Mg substitution favors MnBi-based intermetallic phases over the Bi- and Mn-based solid solutions and the stable α intermetallic phase over the metastable β' intermetallic phase. Magnesium increases the c/a ratio of the α phase lattice parameters for all studied x values and it increases the degree of the field-annealing-induced texture for x ≤ 3. The effect of Mg on coercivity is explained as combination of a positive one via the α phase magnetocrystalline anisotropy and a negative one via the development of texture. The effect of the substitution on the maximum energy product additionally involves the decreasing density of the alloys; the optimum x is found to be ≈3. Additionally reported are the thermal properties of selected alloys. The mechanism of field-annealing effect on the coercivity is briefly discussed.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Thermal and dynamical effects of pair production on two-temperature accretion flows

The two-temperature criterion for quasi-spherical (ion-pressure supported) accretion onto a black hole, including the effects of electron-positron pair production is studied. For an interesting range of accretion rates, Coulomb interactions between protons and pairs can cool the innermost regions of the accretion flow. The cooled plasma, assumed to possess some angular momentum, will collapse onto the equatorial plane, forming an optically thick annulus. Hysteresis effects involved in the cooling criterion are expected to lead to bistability or time dependence, which may be associated with variability in certain classes of active galactic nuclei (AGNs). Radiation from the annulus may be responsible for the EUV/soft X-ray excess observed in some AGNs.

Begelman, Mitchell C.↗
DOE OSTI2020

Ferroelastic Hysteresis in Thin Films of Methylammonium Lead Iodide

Mechanical strain can modify the structural and electronic properties of methylammonium lead iodide MAPbI 3 . The consequences of ferroelastic hysteresis, which involves the retention of structural memory upon cycles of deformation, are reported for polycrystalline thin films of MAPbI 3 . Repeatedly bent films were examined using grazing incidence wide-angle X-ray scattering (GIWAXS) to quantitatively characterize the strains and proportions of twin domains. Approximate locations for the coercive stress and saturation on the ferroelastic stress–strain curve are identified, and changes to the stress–strain curve with cyclic strain are characterized. Notably, an external stress source, such as thermal stress from the substrate or a roll-to-roll printing setup, must apply at least |50| MPa to modify the proportions of different twins. The presence of specific twin domains is found to correlate to previously reported strain and defect heterogeneity in MAPbI 3 films. Domains from differently strained twin sets interact with each other. Long-term stability testing reveals that the domain walls are highly immobile over extended periods. Nucleation of new domain walls occurs for specific mechanical strains and correlates closely with degradation. Furthermore, these results help to explain the behavior of ion migration, degradation rate, and photoluminescence in thin films under compressive and tensile strain.

Defects↗
DOE OSTI2025

Magnetocaloric effect in Mn-rich Heusler-derived alloys for room temperature-based applications

Magnetic refrigeration-based technologies rely on the magnetocaloric properties of materials and are crucial for improving energy efficiency and for supporting clean environments. However, materials possessing significant magnetocaloric properties that can be used for room temperature-based applications are still lacking. Heusler alloys (such as Mn–Ni–Ga) show giant magnetocaloric effects, which can be further improved by tuning their composition. Herein, we optimized the ratio of Ni to Ga to achieve an alloy with unique magnetocaloric properties. Here, the alloy demonstrated a substantial magnetocaloric effect, attributed to its narrow temperature range for structural and magnetic phase transitions (near room temperature with minimal hysteresis). Structural phase changes were also observed through high-resolution transmission electron microscopy. Optimum entropy changes, calculated from isothermal magnetization curves (4 Tesla magnetic field), were found to be 24.50 J kg −1 K −1 , which is higher than that of state-of-the-art alloys. Experimental demonstration of the magnetocaloric effect (refrigeration cycle) was also carried out using a thermal imaging camera. Furthermore, first-principles calculations were conducted to validate the experimental findings, specifically focusing on the compositional effects on the structural transitions and magnetic properties of the investigated MNG alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Competition of magnetocrystalline anisotropy of uranium layers and zigzag chains in UNi 0.34 Ge 2 single crystals

Structural and thermodynamic properties of single-crystalline UNi 1-x Ge 2 with x = 0.66 have been investigated by measuring magnetization, specific heat, and thermal expansion over a wide range of temperatures and magnetic fields. The measurements revealed the emergence of a long-range antiferromagnetic ordering of uranium magnetic moments below the Néel temperature T N = 45.5 (1) K and the existence of two easy axes in the studied compound, namely b and c, which correspond to the planes of the uranium zig-zag chains. A magnetic field applied along these two crystallographic directions induces in the system a first-order metamagnetic phase transition (from antiferromagnetic to field-polarized paramagnetism), and the width of the magnetic hysteresis associated with that transition reaches as much as 40 kOe at the lowest temperatures. A magnetic phase diagram developed from the experimental data showed that the metastable region associated with that magnetic hysteresis forms a funnel that narrows toward the N´eel point in a zero magnetic field. The four-layer Ising model has successfully predicted the colinear antiferromagnetic structure in UNi 0.34 Ge 2 (known from earlier reports), its magnetic phase diagram, and temperature and field variations of its magnetization. Moreover, it suggests that the first-order phase transition extends down to zero magnetic field, although it is barely detectable in the experiments performed in low magnetic fields. According to this model, the second-order phase transition occurs in the compound only in zero field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Lithium-Ion Batteries with Lithium Manganese Iron Phosphate Cathodes and Lithium Titanate Anodes: Linking Electrode Dynamics to Cell Performance

This study examines the electrochemical performance, impedance behavior, and aging mechanisms of lithium-ion cells pairing lithium manganese iron phosphate (LiMn 0.6 Fe 0.4 PO 4 , LMFP64) cathodes with lithium titanate (Li 4 Ti 5 O 12 , LTO) anodes. LMFP64 half-cells display distinct Fe and Mn redox plateaus at ∼3.5 and ∼4.1 V, respectively, and deliver excellent rate capability. Three-electrode measurements show that LMFP64 dominates cell impedance, which changes sharply across the Fe–Mn redox transition and decreases with increasing temperature (30 °C–50 °C). Voltage hysteresis arises mainly from the cathode, with higher C-rates shortening redox plateaus and broadening the transition region. Elevated temperature lowers impedance, especially near the Mn-redox and transition regions, but accelerates capacity fade. Post-cycling analyses of electrodes confirm structural stability of LMFP64 and indicate loss of lithium inventory (LLI) as the source of capacity fade. This LLI causes potential slippage between the LMFP64 and LTO electrodes, which decreases the Fe-redox plateau width. Long-term cycling highlights the critical role of electrode overhang: cathode overhang mitigates capacity fade by buffering lithium loss, whereas anode overhang cells experience faster capacity decline due to uncompensated lithium depletion. These results clarify LMFP64/LTO battery impedance evolution, thermal effects, and degradation pathways and provide insights for their applications in electric vehicles.

Area Specific Impedance↗
NASA NTRS1983

Studies in electron phenomena in MOS structures: The pulsed C-V method

The pulse hysteresis capacitance voltage (C-V) provides a straight forward technique for measuring the change of various charges in MOS structures and a tool for investigating the kinetics of various electron phenomena is developed and described. The method can be used for measuring the energy distribution and kinetics of surface states with the resolution of about 1/5 x 10 to the -9 power cm eV. Some transients in an MOS structure, particularly, the thermal generation of minority charge carriers via surface states and the relaxation of minority charge carriers supplied from the inversion layer outside the MOS structure are theoretically investigated. Analytical expressions which clearly present the physics of those electron phenomena are derived.

Kaplan, G.↗
DOE OSTI2022

Carboxylic Group Rotation and Lattice Expansion in a Co 2 (Pyrazine-2,3-Dicarboxylate) 2 (4,4'-Bipyridine) Porous Coordination Polymer Induced by CO 2 Adsorption at Ambient Temperature

Here, a Co 2 (pzdc) 2 (bpy)(H 2 O) m (pzdc: pyrazine-2,3dicarboxylate; bpy: 4,4'-bipyridine) porous coordination polymer (PCP) was studied for CO 2 uptake and concomitant structural changes at ambient temperature. Extended structural characterization included evaluation of lattice parameter changes upon CO 2 adsorption and in situ synchrotron X-ray powder diffraction data. The PCP effective pore size increased by ~2% with gas uptake over the pressure range of 1-50 atm, allowing the adsorption capacity to double. Furthermore, the hysteretic behaviors seen during CO 2 adsorption at moderate pressures are commensurate with the structural changes from synchrotron data. The adsorption and hysteresis occur with rotation of the linking carboxylate groups, and yet only minor changes in unit cell volume (ΔV ≈ 6 Å 3 ) are observed. This contrasts the findings for [Cu 2 (pzdc) 2 (bpy)] n , where a combination of pillar bpy rotations and significant lattice expansion (ΔV ≈ 68 Å(3)) takes place upon hysteretic adsorption of CO 2 . In situ high-temperature X-ray diffraction revealed that the Co(II)-based material has good thermal stability up to ca. 200° C. Finally, the CO 2 uptake also appears to be at a physisorption level, with adsorbent-adsorbate interactions that are ca. 30% stronger than what has been reported for CO 2 adsorption onto [Cu 2 (pzdc) 2 (bpy)] n .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Time-dependent THMC properties and microstructural evolution of damaged rocks in excavation damage zone

Modeling coupled thermo-hydro-mechanical-chemical (THMC) processes in host rocks near high-level nuclear waste (HLW) repositories at various time scales is an extremely challenging task. The current study integrates experimental, theoretical, and numerical methods in assessing the evolution of excavation damage zone (EDZ) over time and its implication on the long-term migration of hazardous species. Argillite and rock salt and are the focus of this study. The first part of the report presents a novel time-dependent directional microcrack damage theory for generic brittle rocks. It features detailed statistical description of the microcracks within a damaged solid, permitting a direct upscaling of microscale processes such as crack growth kinetics, crack closure/opening, sliding friction to explain the macroscopic creep, nonlinear elasticity, shear dilation, and loading-unloading hysteresis. This provides a basic platform for describing the anisotropic mechanical and transport properties of damaged rocks during excavation and subsequent THMC loadings. The model is validated and numerically implemented to Finite Element (FE) package ABAQUS through the user-defined material (UMAT) interface and have demonstrated great potential in resolving the time-dependent and anisotropic evolution of damage in the EDZ. The second part of the report presents a multi-scale experimental effort in characterizing the thermal, hydraulic, and mechanical properties of Mancos shale and Avery Island salt. For the Mancos shale, triaxial compression tests are performed at different confining pressures and temperatures to probe its thermomechanical properties relevant to HLW repositories. The obtained stress-strain data are interpreted using the proposed directional damage theory. Post-test specimens are subjected to gas permeability tests to reveal the correlation between permeability and the degree of microcracking. At microscale, temperature-controlled nanoindentation tests are performed and found a linear correlation between fracture toughness and elastic modulus from 25°C to 300°C. For Avery Island salt, we have designed and manufactured a novel relative-humidity controlled uniaxial creep device. Long-term creep tests at low stresses (< 5 MPa) are performed at different levels of relative humidity (RH). Besides confirming the much higher creep rates as one would expect through extrapolating the high-stress creep data, the results reveal that the steady-state creep rate of rock salt is strongly dependent on the ambient RH, an aspect that is often neglected in the literature. Both behaviors can be attributed to the pressure-solution creep mechanism which dominates at low stress and high RH levels. The third part of the report explores a set of numerical strategies in modeling the THMC behavior of porous geomaterials. A fully implicit, monolithic FE solution that can flexibly interface with different material models and coupling mechanisms for THMC problems is developed and verified through the ABAQUS user-defined element (UEL) interface. The scheme is used to study the THM response of a hypothetical HLW storage site with reference to an existing in-situ heater test. Strategies for integrating the UEL and the microcrack UMAT are suggested. Another numerical endeavor of this study is to implement a higher-order asymptotic homogenization method to account for the heterogeneous porous structures. The same method is then extended to perform microstructure-informed thermo-mechanical modeling of generalized continua. The above outcomes of this project provide a strong thrust towards enhancing the fundamental understanding and modeling capability of the long-term evolution of host rocks in EDZ, thus helping achieve the design goal of 1-million-year isolation of high-level nuclear wastes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Reduced coercive field in epitaxial thin film of ferroelectric wurtzite Al 0.7 Sc 0.3 N

Epitaxial ferroelectric wurtzite films exhibiting clear polarization-electric field hysteresis behavior are presented. The coercive field of this epitaxial Al 0.7 Sc 0.3 N film on the W/c-sapphire substrate is 0.4±0.3 MV cm -1 (8%) smaller than that of a conventional fiber textured film on a Pt/TiO x /SiO 2 /Si substrate, attributed to the 0.01±0.007 Å smaller c-axis lattice parameter in the epitaxial film. The strain and decrease in the coercive field most likely originate from epitaxial strain rather than the mismatch in the thermal coefficient of expansion. These results provide insight for further coercive field reduction of wurtzite ferroelectrics using epitaxial mismatch strain.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Measurement of Seebeck coefficient using a light pulse

A high-temperature (1900 K) Seebeck coefficient apparatus is described in which small thermal gradients are generated in a sample by light pulses transmitted via light pipes. By employing an analog subtraction circuit, the Seebeck coefficient is displayed directly on an X-Y recorder. This technique presents a convenient, accurate, and rapid method for measuring the Seebeck coefficient in highly doped semiconductors as a function of temperature. The nature of the resulting display (X-Y recording) is a valuable tool in determining validity of the data. A straight line results (i.e., a minimum of hysteresis) only if all potential experimental errors are minimized. Under these conditions, the error of measurements of the Seebeck coefficient is estimated to be less than + or - 1 percent.

Wood, C.↗
NASA NTRS1991

Rugged Direct-Current Transducer

Direct-current transducer withstands thermal and mechanical shocks. Operates from single, nominally 15-V power supply and nearly insensitive to both large variations in temperature and variations of as much as plus or minus 5 V in supply voltage. Its output voltage highly linear function of sensed current, with full-scale value of about 3 Vdc and offset of about 0.1 Vdc at 0 sensed current. Ruggedness of transducer due in large part to novel magnetic core, machined from solid block of nickel/iron high-permeability, low-hysteresis alloy.

Mclyman, W. T.↗
DOE OSTI2025

Synthesis, Stability, and Magnetic Properties of Antiperovskite Co 3 PdN

Experimental synthesis and characterization of theoretically predicted compounds are important steps in the materials discovery pipeline. Here, we report on the synthesis of Co 3 PdN, which was recently predicted to be a stable magnetic antiperovskite. The Co 3 PdN thin films were grown by reactive sputtering and were confirmed to form in an antiperovskite crystal structure. The thermal stability of the compound is demonstrated up to 600 K by in situ X-ray diffraction, though the phase persists at slightly higher temperatures (700 K) in an air-free magnetometer. Both ab initio calculations and magnetization measurements find Co 3 PdN to be ferromagnetic with an experimentally determined Curie temperature of T C = 560 ± 5 K. The saturation magnetization of 1.2 μ B /Co found in the experiment is slightly lower than the 1.7 μ B /Co value expected by theory. A narrow magnetic hysteresis loop with a coercive field of 100 Oe at low temperature suggests that Co 3 PdN might be useful in electronic applications requiring fast switching of the magnetization vector. While prior prediction of Co 3 PdN showed a gapped electronic band structure for each spin channel, we show that this was due to incomplete sampling of Brillouin zone paths and that band crossings exist along R-X|M and X|M-R paths. The metallic nature of Co 3 PdN is further confirmed by temperature-dependent transport measurements, which also show a considerable anomalous Hall effect. Altogether, this work represents an appreciable step toward understanding the synthesis, structure, stability, and properties of a new magnetic material.

14 SOLAR ENERGY↗
NASA NTRS2008

Application of High-Temperature Extrinsic Fabry-Perot Interferometer Strain Sensor

In this presentation to the NASA Aeronautics Sensor Working Group the application of a strain sensor is outlined. The high-temperature extrinsic Fabry-Perot interferometer (EFPI) strain sensor was developed due to a need for robust strain sensors that operate accurately and reliably beyond 1800 F. Specifically, the new strain sensor would provide data for validating finite element models and thermal-structural analyses. Sensor attachment techniques were also developed to improve methods of handling and protecting the fragile sensors during the harsh installation process. It was determined that thermal sprayed attachments are preferable even though cements are simpler to apply as cements are more prone to bond failure and are often corrosive. Previous thermal/mechanical cantilever beam testing of EFPI yielded very little change to 1200 F, with excellent correlation with SG to 550 F. Current combined thermal/mechanical loading for sensitivity testing is accomplished by a furnace/cantilever beam loading system. Dilatometer testing has can also be used in sensor characterization to evaluate bond integrity, evaluate sensitivity and accuracy and to evaluate sensor-to-sensor scatter, repeatability, hysteresis and drift. Future fiber optic testing will examine single-mode silica EFPIs in a combined thermal/mechanical load fixture on C-C and C-SiC substrates, develop a multi-mode Sapphire strain-sensor, test and evaluate high-temperature fiber Bragg Gratings for use as strain and temperature sensors and attach and evaluate a high-temperature heat flux gauge.

Piazza, Anthony↗
DOE OSTI2020

Short-range ferromagnetic order due to Ir substitutions in single-crystalline Ba(Co 1-x Ir x ) 2 As 2 (0 ≤ x ≤ 0.25)

The ternary-arsenide compound BaCo 2 As 2 was previously proposed to be in proximity to a quantum-critical point where long-range ferromagnetic (FM) order is suppressed by quantum fluctuations. In this paper we report the effect of Ir substitutions for Co on the magnetic and thermal properties of Ba(Co 1-x Ir x ) 2 As 2 (0 ≤ x ≤ 0.25) single crystals. These compositions all crystallize in an uncollapsed body-centered-tetragonal ThCr 2 Si 2 structure with space group I4/mmm. Magnetic susceptibility measurements reveal clear signatures of short-range FM ordering for x ≥ 0.11 below a nearly composition-independent characteristic temperature T cl ≈ 13 K. The small variation of T cl with x, thermomagnetic irreversibility between zero-field-cooled and field-cooled magnetic susceptibility versus T, the occurrence of hysteresis in magnetization versus field isotherms at low field and temperature, and very small spontaneous and remanent magnetizations <0.01 μ B /f.u. together indicate that the FM response arises from short-range FM ordering of FM spin clusters as previously inferred to occur in Ca(Co 1–x Ir x ) 2–y As 2 . Heat-capacity Cp(T) data do not exhibit any clear feature around Tcl, consistent with the very small moments of the FM clusters. The Cp(T) in the paramagnetic temperature regime 25–300 K is well described by the sum of a Sommerfeld electronic contribution and Debye and Einstein lattice contributions where the latter lattice contribution suggests the presence of low-frequency optic modes associated with the heavy Ba atoms in the crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Patterned Quasi-Liquid Surfaces for Condensation of Low Surface Tension Fluids

Extensive research concerns dropwise condensation of low surface tension fluids to promote energy efficiency and decarbonization in thermal energy systems. However, it is challenging as these fluids typically result in filmwise condensation. Drawing inspiration from the Namib desert beetle that enhances condensation through patterned wettability, conventional beetle-inspired surfaces excel in water condensation but flood when condensing low surface tension fluids. In this work, a patterned quasi-liquid surface is reported that achieves exceptional dropwise condensation of low surface tension fluids. The surface consists of alternating stripes with low surface energy, that is, a perfluoropolyether (PFPE) and fluorinated quasi-liquid surface (FQLS), that shows ultralow contact angle hysteresis for ethanol and hexane. Further, the PFPE stripes are slightly more slippery, acting as slippery bridges that accelerate droplet coalescence and removal. It is experimentally demonstrated that the striped PFPE-FQLS pattern exhibits a heat transfer coefficient 85%, 330%, and 550% higher than that of PFPE, fluorinated silane, and filmwise condensation, respectively. This study reveals that a high contact angle is desired to sustain dropwise condensation, irrespective of contact angle hysteresis. These findings provide a new paradigm for promoting the dropwise condensation of low surface tension fluids and offer valuable insights into surface design for energy sustainability.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structural and Chemical Evolution of Highly Fluorinated Li‐Rich Disordered Rocksalt Oxyfluorides as a Function of Temperature

Abstract Li‐rich disordered rocksalt (DRS) oxyfluorides have emerged as promising high‐energy cathode materials for lithium‐ion batteries. While a high level of fluorination in DRS materials offers performance advantages, it can only be achieved via mechanochemical synthesis, which poses challenges of reproducibility and scalability. The definition of relationships between fluorination and structural stability is required to devise alternative methods that overcome these challenges. In this study, the thermal evolution of three highly fluorinated phases, Li 2 TMO 2 F (TM = Mn, Co, and Ni), is investigated in an inert atmosphere. Diffraction and spectroscopic techniques are utilized to examine their electronic and chemical states up until conditions of decomposition. The analysis reveals that the materials phase‐separate above 400 °C, at most. It is also observed that heat‐treated DRS materials exhibit intricate changes in the local coordination of the metals, including their spin, and ordering compared to the pristine states. The changes upon annealing are accompanied by a modulation of the voltage profile, including reduced hysteresis, when used as electrodes. These results provide an in‐depth understanding of the fundamental crystal chemistry of DRS oxyfluorides in view of their promising role as the next generation of Li‐ion cathodes.

25 ENERGY STORAGE↗
DOE OSTI2026

Magnon-Magnon Interaction Induced by Dynamic Coupling in a Hybrid Magnonic Crystal

We report a combined experimental and numerical investigation of spin-wave dynamics in a hybrid magnonic crystal consisting of a CoFeB artificial spin ice (ASI) of stadium-shaped nanoelements patterned atop a continuous NiFe film separated by a 5 nm Al 2 O 3 spacer. Using Brillouin light scattering spectroscopy, we probe the frequency dependence of thermal spin waves as functions of applied magnetic field and wavevector, revealing the decisive role of interlayer dipolar coupling in the magnetization dynamics. Micromagnetic simulations complement the experiments, showing a strong interplay between ASI edge modes and backward volume modes in the NiFe film. The contrast in saturation magnetization between CoFeB and NiFe enhances this coupling, leading to a pronounced hybridization manifested as a triplet of peaks in the BLS spectra predicted by simulations and observed experimentally. This magnon−magnon coupling persists over a wide magnetic field range, shaping both the spin-wave dispersion at fixed fields and the full frequency-field response throughout the magnetic hysteresis loop. Our findings establish how ASI geometry can selectively enhance specific spin-wave wavelengths in the underlying film, thereby boosting their amplitude and identifying them as preferential channels for spin wave transmission and manipulation.

Brillouin light scattering spectroscopy↗