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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Analysis of the Switching Characteristics of MRAM Cells Based on Materials with Uniaxial Anisotropy

Magnetoresistive random access memory (MRAM) has some advantages over other types of memory. However, MRAM has one substantial drawback: the current density and magnetic field that must be applied to switch the spin-valve free layer inside an MRAM cell are too high. The dependence of the current density and switching magnetic field on the magnetic parameters of the material from which the ferromagnetic layers of a spin valve are fabricated is therefore analyzed. A comparison of the critical characteristics of a spin valve with longitudinal anisotropy shows that cobalt, iron, and alloys of them; cobalt ferroborates; and alloys of cobalt with gadolinium, are promising materials for fabricating spin valves. Bifurcation diagrams of equations that describe the valve switching process are presented and analyzed. The four optimum switching modes of a valve are selected, based on an investigation of the dynamics of the magnetization vector. The magnitudes of the external magnetic field and controlling injection current that correspond to stable MRAM cell switching are compared for a variety of materials. The switching time of an MRAM cell is estimated numerically, and the conditions for its optimum speed are determined. It is established that the most promising materials for spin-valve fabrication are Fe{sub 40}Co{sub 40}B{sub 20} and Co{sub 80}Gd{sub 20}, annealed at 300 and 200°C, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Comparative study of the spectral and structural properties of EuAl{sub 3}(BO{sub 3}){sub 4} single crystals with different morphologies

Europium alumoborate EuAl{sub 3}(BO{sub 3}){sub 4} microcrystals have been synthesized by the flux method at a temperature of 1050°C. The obtained crystals have different morphologies: both plane-faced and skeletal microcrystals have been observed. Infrared spectroscopy, cathodeluminescence, and transmission electron microscopy investigations of individual microcrystals showed that the spectral and structural characteristics of these morphological forms coincide. The obtained crystals are characterized by the rhombohedral symmetry (sp. gr. R32) with the inclusions of C2/c monoclinic phase domains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Comparative Study of the Magnetoelectric Effect in HoAl{sub 3}(BO{sub 3}){sub 4} and HoGa{sub 3}(BO{sub 3}){sub 4} Single Crystals

The comparative study of the magnetoelectric properties and magnetostriction of HoGa{sub 3}(BO{sub 3}){sub 4} and HoAl{sub 3}(BO{sub 3}){sub 4} single crystals has been carried out. The investigated compounds exhibit qualitatively similar magnetodielectric and inverse magnetoelectric ME{sub E} effects with the close absolute values, which is indicative of the weak effect of a nonmagnetic metal ion. On the contrary, the magnetostriction of the galloborate has been found to be threefold higher than that of the alumoborate. In addition, the difference between the qualitative behaviors of magnetostriction has been established: the magnetic-field dependence of magnetostriction for the alumoborate has the maximum near 70 kOe at T = 4.2 K, while the galloborate magnetostriction has no maximum and does not saturate in a field of 140 kOe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electronic Structure, Optical Properties, and Pressure Behavior of the CdB{sub 4}O{sub 7} and HgB{sub 4}O{sub 7} Compounds

Ab initio calculations of the structural, electronic, and optical properties of the CdB{sub 4}O{sub 7} and HgB{sub 4}O{sub 7} tetraborate compounds in three structural modifications with the Pbca, Cmcm, and Pmn2{sub 1} symmetry have been performed in the framework of the density functional theory using the VASP package. The calculations of the electronic band structure showed that these compounds in all the investigated modifications are dielectrics with a band gap of 2–4 eV. The calculation of the structural properties of the tetraborates under pressure showed that the phase transition between the Pbca and Pmn2{sub 1} structures in cadmium and mercury tetraborates occurs under pressures of 4.8 and 4.7 GPa, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Magnetodielectric Properties of Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4}

The magnetic and magnetodielectric properties of Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4} ferroborate with the competing Ho–Fe and Nd–Fe exchange couplings have been experimentally and theoretically investigated. Step anomalies in the magnetization curves at the spin-reorientation transition induced by the magnetic field B ║ c have been found. The spontaneous spin-reorientation transition temperature T{sub SR} ≈ 8 K has been refined. The measured magnetic properties and observed features are interpreted using a single theoretical approach based on the molecular field approximation and calculations within the crystal field model of the rare-earth ion. Interpretation of the experimental data includes determination of the crystal field parameters for Ho{sup 3+} and Nd{sup 3+} ions in Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4} and parameters of the Ho–Fe and Nd–Fe exchange couplings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental Study and Analysis of Absorption Spectra of Ni{sup 2+} Ions in Nickel Orthoborate Ni{sub 3}(BO{sub 3}){sub 2}

The results of studies of the absorption spectra of nickel orthoborate Ni{sub 3}(BO{sub 3}){sub 2} in the range of electronic d–d-transitions are reported. The obtained data are analyzed in the framework of the crystal field theory. The Ni{sup 2+} ions are located in two crystallographically nonequivalent positions 2a and 4f with point symmetry groups C{sub 2h} and C{sub 2}, respectively, surrounded by six oxygen ions forming deformed octahedra. The absorption spectra exhibit three intense bands corresponding to spin-resolved transitions from the ground state of nickel ion {sup 3}A{sub 2g} ({sup 3}F) to the sublevels of the {sup 3}T{sub 2g} ({sup 3}F), {sup 3}T{sub 1g} ({sup 3}F) and {sup 3}T{sub 1g} ({sup 3}P) triplets split by the spinorbit interaction and the rhombic component of the crystal field. At temperatures below 100 K, the spectra exhibit a thin structure, in which phonon-free lines can be distinguished. Comparison of the calculated frequencies of the zero-phonon transitions with the experimental data allows estimating parameters of the crystal field acting on the nickel ions in the 2a- and 4f-positions, as well as the parameters of electrostatic interaction between the 3d electrons and spin-orbit interaction constants.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Energy Transfer from Ce{sup 3+} to Tb{sup 3+} in Yttrium and Gadolinium Orthoborates Obtained by Hydrothermal Synthesis

We studied the structure, IR absorption spectra, the spectral characteristics of photoluminescence and morphology of cerium- and terbium-doped orthoborates of gadolinium and yttrium obtained by hydrothermal synthesis at 200°C, as well as solid solutions of orthoborates on the basis of yttrium, gadolinium, and lutetium with composition RECe{sub 0.01}Tb{sub 0.1}BO{sub 3} (RE = Lu{sub 0.5}Gd{sub 0.39}, Lu{sub 0.5}Y{sub 0.39}, and Y{sub 0.5}Gd{sub 0.39}). The X-ray diffraction spectrum of yttrium orthoborate Y{sub 1 –} {sub x} {sub –} {sub y}Ce{sub x}Tb{sub y}BO{sub 3} is described by a hexagonal lattice with space group P6{sub 3}/m, which, after annealing at 970°C, transforms into a monoclinic lattice with space group C2/c. High-temperature annealing of the studied orthoborates leads to a multiple, more than two orders of magnitude, increase in the luminescence intensity of Tb{sup 3+} ions when the samples are excited in the absorption band of cerium ions. This effect is the result of a significant increase in the concentration of Ce{sup 3+} ions in the orthoborates at high temperatures. It is shown that the luminescence of terbium ions is due to energy transfer from Ce{sup 3+} to Tb{sup 3+}, which proceeds with high efficiency (∼85%) by the mechanism of dipole-dipole interaction between cerium and terbium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Peculiarities of Phase Formation in TbBO{sub 3} during Isothermal Annealing

Detailed X-ray studies of changes in the structure of terbium orthoborate TbBO{sub 3} in the course of successive high-temperature isothermal annealing of the initial mixture in the form of an amorphous precursor and in the form of a homogenized mixture of microcrystalline Tb{sub 7}O{sub 12} and B{sub 2}O{sub 3} powders have been carried out. It is shown that the formation of TbBO{sub 3} crystals in both cases occurs through the formation of intermediate two-phase states. Particularly, the triclinic high-temperature ν-TbBO{sub 3} phase is formed already at the first crystallization stages (about 600°C) almost simultaneously with the equilibrium vaterite modification of TbBO{sub 3} (sp. gr. P63/mmc) during low-temperature annealing of an amorphous precursor, which transforms into the vaterite modification at an annealing temperature of 850°C. The phase of monoclinic terbium trioxoborate TbB{sub 3}O{sub 6} is formed at the first stages of phase formation (about 800°C) almost simultaneously with the vaterite phase when the feedstock is annealed in the form of a homogenized mixture of microcrystalline Tb{sub 7}O{sub 12} and B{sub 2}O{sub 3} powders. It also transforms into the vaterite modification at an annealing temperature of 950°, which is preserved up to the highest annealing temperatures in the experiment (1200°C). A hypothetical explanation of the formation of such two-phase states during low-temperature annealing of the feedstock and their disappearance at higher annealing temperatures is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Variation of a Defect Structure of Lithium Tetraborate (Li{sub 2}B{sub 4}O{sub 7}) in an External Electric Field

The variation of a defect structure of a lithium tetraborate single crystal under the influence of a high-strength external electric field applied along polar direction [001] has been studied by the X-ray diffraction (XDR) method. The conductivity kinetics has been measured; it is found to agree with changes in the diffraction peak parameters. Application of the electric field with the strength of 300–500 V/mm leads to a sharp broadening of the rocking curve and the increase in the integral intensity by several times, but the curve position and shape are only slightly changed. At higher electric fields from 500 to 1500 V/mm, the process of broadening the curve slows down; however, the shape asymmetry appears and the peak shifts to smaller angles, which is due to an increase in the lattice parameter along axis c. In this case, the changes become irreversible, since the distorted structure is partially recovered with a very low rate (for several months). Two types of the dependences of the rocking curves parameters variation under an external field are interpreted as the manifestation of two mechanisms of the ionic conduction due to mobile lithium (Li{sup +}) ions at low fields and oxygen vacancies (V{sub O}{sup 2+}) at higher fields. The charge carrier migration leads to an increase in the defect concentration and structural changes in a near-surface crystal region. The obtained results have practical importance from the point of view of the controlled change in the defect structure in the crystals with ionic conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation of Spectral Properties of Potassium Aluminoborate Glasses Doped with Chromium

Spectral properties of potassium aluminoborate glasses activated by various concentrations of trivalent chromium compounds are studied. The temperatures of glass transition (434°C) and bulk crystallization of the glass matrix (600°C) are determined. The heat treatment of the glass at the crystallization temperature results in the appearance of intensive narrow luminescence bands in the area of 685–715 nm that is connected with the crystallization of the LiAl{sub 7}B{sub 4}O{sub 17}:Cr{sup 3+} phase in the glass matrix; in this phase chromium is located in a highly symmetrical octahedral surrounding. Concentration dependences of lifetime and quantum yield show the existence of the concentration luminescence quenching at increasing chromium content in the glass from 0.05 to 0.2 mol %. The maximum value of quantum yield is 30%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Kinetics of Pulse Cathodoluminescence in Lithium–Gadolinium Orthoborate Crystals Doped with Cerium Impurity

The relaxation kinetics of electron excitations in single-crystal and crystal-fiber Li{sub 6}GdB{sub 3}O{sub 9} samples was studied by the time-resolved methods of pulse absorption spectroscopy and pulse cathodoluminescence under excitation with a nanosecond electron beam at 293 K. Based on the results of the numerical modeling of recombination processes, a pulse cathodoluminescence excitation mechanism was proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Polymorphism of ScBO{sub 3} at the Solid Phase Synthesis from Amorphous Precursors

Detailed X-ray studies of changes in the structure of the scandium orthoborate ScBO{sub 3} in the process of serial isothermal annealing of the initial charge in the form of amorphous precursor were carried out. It was shown that upon successive annealing of the amorphous precursor, the crystalline phase first forms at an annealing temperature of 710°C, the positions of the reflections of which do not coincide with the positions that of the known calcite structure. This phase exists in a very narrow temperature range (≈30°C) and, when the annealing temperature is increased to 750°C, it completely transfers to the known rhombohedral phase of calcite. Using the ENDEAVOR software, the cell parameters, atom positions in the cell, and the spatial symmetry group of the new phase were determined. It turned out that the new phase corresponds to the hexagonal structure of the faterite (S.G. P63/mmc), known for other orthoborates of rare-earth elements (REE).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Protocols for isolating and characterizing polysaccharides from plant cell walls: a case study using rhamnogalacturonan-II

Abstract Background In plants, a large diversity of polysaccharides comprise the cell wall. Each major type of plant cell wall polysaccharide, including cellulose, hemicellulose, and pectin, has distinct structures and functions that contribute to wall mechanics and influence plant morphogenesis. In recent years, pectin valorization has attracted much attention due to its expanding roles in biomass deconstruction, food and material science, and environmental remediation. However, pectin utilization has been limited by our incomplete knowledge of its structure. Herein, we present a workflow of principles relevant for the characterization of polysaccharide primary structure using nature’s most complex polysaccharide, rhamnogalacturonan-II (RG-II), as a model. Results We outline how to isolate RG-II from celery and duckweed cell walls and from red wine using chemical or enzymatic treatments coupled with size-exclusion chromatography. From there, we applied mass spectrometry (MS)-based techniques to determine the glycosyl residue and linkage compositions of the intact RG-II and derived oligosaccharides including special considerations for labile monosaccharides. In doing so, we demonstrated that in the duckweed Wolffiella repanda the arabinopyranosyl (Ara p ) residue of side chain B is substituted at O- 2 with rhamnose. We used electrospray-MS techniques to identify non-glycosyl modifications including methyl-ethers, methyl-esters, and acetyl-esters on RG-II-derived oligosaccharides. We then showed the utility of proton nuclear magnetic resonance spectroscopy ( 1 H-NMR) to investigate the structure of intact RG-II and to complement the RG-II dimerization studies performed using size-exclusion chromatography. Conclusions The complexity of pectic polysaccharide structures has hampered efforts aimed at their valorization. In this work, we used RG-II as a model to demonstrate the steps necessary to isolate and characterize polysaccharides using chromatographic, MS, and NMR techniques. The principles can be applied to the characterization of other saccharide structures and will help inform researchers on how saccharide structure relates to functional properties in the future.

09 BIOMASS FUELS↗
DOE OSTI2025

Evaluating High-Halide Waste Form Options for Salt-Based Nuclear Waste Simulants

In this study, waste forms were being explored for an electrochemical salt simulant, , referred to as ERV3, which is a high-LiCl/KCl salt containing simulated fission products (i.e., Sr, Cs, Nd) and Na to represent bond sodium from Experimental Breeder Reactor-II metallic fast reactor fuel. The goal was to find glassy systems that could be used to immobilize the salt in a single-step process. The envisionment of this process would be find a frit glass that could be added to the salt waste, heat treated, poured into waste canisters, and then stored for disposal. To perform this study, a literature review was conducted, the most promising seven systems were fabricated without the salt, and then mixed with salt simulant and heat treated under different processes. The criteria that were used to screen potential compositions included demonstrated alkali incorporation, could be melted at reasonably low temperature ( T ≤ 1000°C), and if the compositions had some demonstrated data for waste-form-related properties, that was a benefit. High marks were given for compositions that showed amorphous nature after slow cooling of samples containing ERV3.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Pulsed-Neutron Die-Away Response of H 2 O Targets to a D-T Generator Pulse

Pulsed-neutron die-away (PNDA) experiments were completed at Lawrence Livermore National Laboratory (LLNL). The goal of these experiments was to provide a benchmark to validate thermal neutron scattering laws of H 2 O. The experiment was conducted with a deuterium-tritium (D-T) neutron generator producing pulses of 14.1 MeV neutrons that impinged on a moderating target. The neutrons scattered and thermalized within the target and were counted as a function of time using Helium-3 ( 3 He) detectors that surrounded the target. These data provide a time-decay profile of the neutron population from which the time eigenvalue of the experiment is calculated. The time eigenvalue quantity α represents the integral parameter of interest. This report describes the measurements for H 2 O targets. The measurements were conducted over several days beginning on October 23rd, 2023. All measurements were completed at the low-scatter facility at LLNL. The evaluation identifier is FUND-LLNL-DT-H2O-PNDA-001.

3He Detectors↗
DOE OSTI2026

Pulsed-Neutron Die-Away Response of H 2 O Targets to a D-T Neutron Generator Pulse

Pulsed-neutron die-away (PNDA) experiments were completed at Lawrence Livermore National Laboratory (LLNL). The goal of these experiments was to provide a benchmark to validate thermal neutron scattering laws of H 2 O. The experiment was conducted with a deuterium-tritium (D-T) neutron generator producing pulses of 14.1 MeV neutrons that impinged on a moderating target.

3He Detectors↗
DOE OSTI2026

Understanding_the_deactivation_mechanisms_of_ethanol_conversion_over_Cu-Y_Beta_catalyst

Direct conversion of bioethanol to C₃⁺olefins is a promising pathway for sustainable aviation fuel (SAF) production, but catalyst deactivation limits long-term operation. The stability and deactivation mechanisms of multifunctional Cu–Y/Beta zeolite catalysts were investigated for ethanol-to-olefins conversion over 300 h time-on-stream in the presence of H2. Catalytic testing reveals progressive losses in ethanol conversion and C₃⁺ olefin selectivity accompanied by increased acetaldehyde formation. The catalyst testing studies correlate with a suite of characterizations of fresh, spent, and regenerated catalysts to identify the deactivation factors. The loss of Y Lewis acid sites is the primary deactivation element. Reversible acid site deactivation is caused by coke deposition, which blocks Y-derived Lewis acid sites responsible for aldol condensation, MPV reduction, and alcohol dehydration. Minor irreversible deactivation is observed and possibly results from hydrothermal dehydroxylation of Y–silanol interactions, resulting in permanent loss of Lewis acidity without zeolite framework degradation or Y aggregation. Cu sites undergo limited agglomeration into small nanoparticles but contribute insignificantly to catalyst deactivation, under the investigated time frame. Oxidative regeneration removes coke and redistributes Cu sites, leading to full recovery of the initial catalytic performance though the Y Lewis acid sites are unable to fully recover. These findings establish Lewis acid site degradation as the primary deactivation mechanism impacting long-term catalyst stability

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗