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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Magneto-optical, structural and surface properties of RIB sputtered (Bi,Ga)-substituted DyIG films

Highlights: • The dependences of properties of (Bi,Ga):DyIG films on GGG and CMZGGG substrates on the time of crystallization annealing were studied. • It was found that the films properties depend substantially on the substrate type and the time of crystallization annealing. • A minimal time of annealing to achieve the optimal parameters of the film was determined. - Abstract: The dependences of magneto-optical, structural and morphological properties of reactive ion beam sputtered (RIBS) nanoscale (Bi,Ga)-substituted DyIG [(Bi,Ga:DyIG)] films on (111) GGG and (111) CMZGGG substrates on the time of crystallization annealing were studied using Faraday effect measurements, X-ray diffraction and scanning atomic force microscopy. It was found that the roughness, degree of crystallinity and Faraday rotation angle of the films depend substantially on the substrate type and the time of crystallization annealing. It was determined a minimal time to achieve the optimal ratio between the measured magneto-optical and structural parameters of the film.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structure and photoluminescence properties of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} phosphors for solid-state lighting application

Novel phosphors of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+} and Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce{sup 3+} emission properties and the crystal structure of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7} is built and the result shows that Ce{sup 3+} ions occupy two non-equivalent Y{sup 3+} sites in the host. The codoping of Tb{sup 3+} in Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+} can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce{sup 3+}→Tb{sup 3+}. The energy transfer processes of Ce{sup 3+}–Ce{sup 3+} and Ce{sup 3+}–Tb{sup 3+} are analysed and determined to be electric dipole–dipole and dipole–quadrupole, respectively. The broad PLE spectra of Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+} and Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs. - Graphical abstract: Colour-tunable phosphors Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} with optimal quantum yield of 75.2% are synthesized and the phosphors can be served as n-UV pumped materials for LEDs. - Highlights: • Green phosphor Na{sub 2}Y{sub 2}B{sub 2}O{sub 7}:Ce{sup 3+},Tb{sup 3+} with quantum efficiency of 75.2% for n-UV application is synthesized. • The site occupation of Ce{sup 3+} in Na{sub 2}Y{sub 2}B{sub 2}O{sub 7} is investigated with the crystal structure and photoluminescence spectra. • The energy transfer of Ce{sup 3+}–Ce{sup 3+} and Ce{sup 3+}–Tb{sup 3+}, which is responsible to the tunable emitting colour of the phosphor, is demonstrated and the mechanism is studied.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structural and optical effects induced by gamma irradiation on NdPO{sub 4}: X-ray diffraction, spectroscopic and luminescence study

Highlights: • Inorganic NdPO{sub 4} crystal was grown first time using potassium polyphosphate (K{sub 6}P{sub 4}O{sub 13}) flux. • NdPO{sub 4} crystal is insoluble in water, non-hygroscopic and high radiation resistance favoring for actinides host. • Actinide immobilization can be made at 1273 K. • High yield of 1061 nm photon emission. - Abstract: Rare earth orthophosphate (NdPO{sub 4}) monazite single crystals were grown using high temperature flux growth method employing K{sub 6}P{sub 4}O{sub 13} (K{sub 6}) as molten solvent. Their structural parameters were studied using single crystal X-ray diffraction (XRD) method. The grown crystals were examined by SEM and EDX techniques for their homogeniousity and inclusion in the crystals. The influence of gamma irradiation in structural and optical absorption properties were studied by the powder XRD, FTIR and reflectance spectroscopy. The effect of gamma irradiation on luminescence properties was recorded. No significant structural change is observed up to 150 kGy gamma dose. The gamma ray induced charge trap in the crystal was saturated to 40 kGy dose. The luminescence intensity decreases with an increase in the irradiation. The emission of luminescence intensity stabilizes above 40 kGy gamma dose.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Growth of SrTiO{sub 3}(110) film by oxide molecular beam epitaxy with feedback control

By controlling the growth of complex oxide films with atomic precision, emergent phenomena and fascinating properties have been discovered, and even been manipulated. With oxide molecular beam epitaxy (OMBE) we grow high-quality SrTiO{sub 3}(110) films by evaporating Sr and Ti metals with separate controls of the open/close timing of the shutters. The incident electron beam angle of the reflective high energy electron diffraction (RHEED) is adjusted to make the (01) beam sensitive to surface chemical concentration. By monitoring such an intensity, we tune the shutter timing to synchronize the evaporation amount of Sr and Ti in real-time. The intensity is further used as a feedback control signal for automatic growth optimization to fully compensate the possible fluctuation of the source flux rates upon extended growth. A 22 nm-thick film is obtained with the precision of metal cation stoichiometry better than 0.5%.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb co-doping were prepared by sol-gel method and thermally annealed to check for the impact of phase transition on luminescence properties. Phase composition and grain sizes were examined by X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison of samples with different oxygen vacancy concentrations and different Nb concentrations confirmed the known assumption that oxygen vacancies are the main agents for tetragonal or cubic phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion luminescence intensity. Hence, ZrO{sub 2}:Er:Yb:Nb nanocrystals may show promise for upconversion applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

High energy electron diffraction instrument with tunable camera length

Ultrafast electron diffraction (UED) stands as a powerful technique for real-time observation of structural dynamics at the atomic level. In recent years, the use of MeV electrons from radio frequency guns has been widely adopted to take advantage of the relativistic suppression of the space charge effects that otherwise limit the temporal resolution of the technique. Nevertheless, there is not a clear choice for the optimal energy for a UED instrument. Scaling to beam energies higher than a few MeV does pose significant technical challenges, mainly related to the inherent increase in diffraction camera length associated with the smaller Bragg angles. In this study, we report a solution by using a compact post-sample magnetic optical system to magnify the diffraction pattern from a crystal Au sample illuminated by an 8.2 MeV electron beam. Our method employs, as one of the lenses of the optical system, a triplet of compact, high field gradients (>500 T/m), small-gap (3.5 mm) Halbach permanent magnet quadrupoles. Shifting the relative position of the quadrupoles, we demonstrate tuning the magnification by more than a factor of two, a 6× improvement in camera length, and reciprocal space resolution better than 0.1 Å –1 in agreement with beam transport simulations.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Tailored multivariate analysis for modulated enhanced diffraction

Modulated enhanced diffraction (MED) is a technique allowing the dynamic structural characterization of crystalline materials subjected to an external stimulus, which is particularly suited for in situ and operando structural investigations at synchrotron sources. Contributions from the (active) part of the crystal system that varies synchronously with the stimulus can be extracted by an offline analysis, which can only be applied in the case of periodic stimuli and linear system responses. In this paper a new decomposition approach based on multivariate analysis is proposed. The standard principal component analysis (PCA) is adapted to treat MED data: specific figures of merit based on their scores and loadings are found, and the directions of the principal components obtained by PCA are modified to maximize such figures of merit. As a result, a general method to decompose MED data, called optimum constrained components rotation (OCCR), is developed, which produces very precise results on simulated data, even in the case of nonperiodic stimuli and/or nonlinear responses. The multivariate analysis approach is able to supply in one shot both the diffraction pattern related to the active atoms (through the OCCR loadings) and the time dependence of the system response (through the OCCR scores). When applied to real data, OCCR was able to supply only the latter information, as the former was hindered by changes in abundances of different crystal phases, which occurred besides structural variations in the specific case considered. To develop a decomposition procedure able to cope with this combined effect represents the next challenge in MED analysis.

Caliandro, Rocco↗
DOE OSTI2016

Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr 2 IrO 4

Here, we report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the ${{J}_{\text{eff}}}=1/2$ states in Sr 2 IrO 4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump–hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps–1.5 ns.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Operando X-Ray Diffraction During High Temperature Electrolysis

This work presents the design, development, and deployment of an operando X-ray diffraction (XRD) system for high-temperature electrolysis (HTE), enabling real-time characterization of solid oxide electrolysis cells (SOECs) under true operational conditions. The integration of an HTE test stand within a synchrotron radiation environment, mimicking the conditions of a laboratory setup, aims to enhance our understanding of the degradation processes affecting the performance and longevity of SOECs. Utilizing a custom furnace and a high precision motor stack assembly at the Stanford Synchrotron Radiation Lightsource (SSRL), the system revealed unparalleled insights into the structural evolution of SOEC components through various operational stages, including initial heat ramp, cell reduction, fuel ramp, and wet electrolysis. Initial results demonstrate the significant impact of the initial heating and cooling on secondary phase formation within the SOEC, highlighting the utility of operando XRD for developing more efficient and durable hydrogen production technologies.

08 HYDROGEN↗
DOE OSTI2014

An electrochemical cell for in operando studies of lithium/sodium batteries using a conventional x-ray powder diffractometer

An electrochemical cell has been designed for powder X-ray diffraction studies of lithium ion batteries (LIB) and sodium ion batteries (SIB) in operando with high time resolution using a conventional powder X-ray diffractometer. The cell allows for studies of both anode and cathode electrode materials in reflection mode. The cell design closely mimics that of standard battery testing coin cells and allows obtaining powder X-ray diffraction patterns under representative electrochemical conditions. In addition, the cell uses graphite as the X-ray window instead of beryllium, and it is easy to operate and maintain. Test examples on lithium insertion/extraction in two spinel-type LIB electrode materials (Li{sub 4}Ti{sub 5}O{sub 12} anode and LiMn{sub 2}O{sub 4} cathode) are presented as well as first results on sodium extraction from a layered SIB cathode material (Na{sub 0.84}Fe{sub 0.56}Mn{sub 0.44}O{sub 2})

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optically Induced Picosecond Lattice Compression in the Dielectric Component of a Strongly Coupled Ferroelectric/Dielectric Superlattice

Above-bandgap femtosecond optical excitation of a ferroelectric/dielectric BaTiO 3 /CaTiO 3 superlattice leads to structural responses that are a consequence of the screening of the strong electrostatic coupling between the component layers. Time-resolved X-ray free-electron laser diffraction shows that the structural response to optical excitation includes a net lattice expansion of the superlattice consistent with depolarization-field screening driven by the photoexcited charge carriers. The depolarization-field-screening-driven expansion is separate from a photoacoustic pulse launched from the bottom electrode on which the superlattice is epitaxially grown. The distribution of diffracted intensity of superlattice X-ray reflections indicates that the depolarization-field-screening-induced strain includes a photoinduced expansion in the ferroelectric BaTiO 3 and a contraction in CaTiO 3 . The magnitude of expansion in BaTiO 3 layers is larger than the contraction in CaTiO 3 . The difference in the magnitude of depolarization-field-screening-driven strain in the BaTiO 3 and CaTiO 3 components can arise from the contribution of the oxygen octahedral rotation patterns at the BaTiO 3 /CaTiO 3 interfaces to the polarization of CaTiO 3 . The depolarization-field-screening-driven polarization reduction in the CaTiO 3 layers points to a new direction for the manipulation of polarization in the component layers of a strongly coupled ferroelectric/dielectric superlattice.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Exploring Charged Defects in Ferroelectrics by the Switching Spectroscopy Piezoresponse Force Microscopy

Monitoring the charged defect concentration at the nanoscale is of critical importance for both the fundamental science and applications of ferroelectrics. However, up-to-date, high-resolution study methods for the investigation of structural defects, such as transmission electron microscopy, X-ray tomography, etc., are expensive and demand complicated sample preparation. Here, with an example of the lanthanum-doped bismuth ferrite ceramics, a novel method is proposed based on the switching spectroscopy piezoresponse force microscopy (SSPFM) that allows probing the electric potential from buried subsurface charged defects in the ferroelectric materials with a nanometer-scale spatial resolution. When compared with the composition-sensitive methods, such as neutron diffraction, X-ray photoelectron spectroscopy, and local time-of-flight secondary ion mass spectrometry, the SSPFM sensitivity to the variation of the electric potential from the charged defects is shown to be equivalent to less than 0.3 at% of the defect concentration. Additionally, the possibility to locally evaluate dynamics of the polarization screening caused by the charged defects is demonstrated, which is of significant interest for further understanding defect-mediated processes in ferroelectrics.

42 ENGINEERING↗
DOE OSTI2018

Studies on Structural, Optical, Thermal and Electrical Properties of Perylene-Doped p-terphenyl Luminophors

A simple solid state reaction technique was employed for the preparation of polycrystalline luminophors of p-terphenyl containing different amounts of perylene followed by spectral characterization techniques viz. XRD, SEM, TGA-DSC, UV–Visible spectroscopy, thermo-electrical conductivity, fluorescence spectroscopy, fluorescence life time spectroscopy and temperature dependent fluorescence. X-ray diffraction profiles of the doped p-terphenyl reveal well-defined and sharp peaks indicate homogeneity and crystallinity. The SEM micrograph of pure p-terphenyl exhibit flakes like grains and then compact and finally gets separately with perylene amounts. The observed results indicate that closed packed crystal structures of doped p-terphenyl during crystal formation. The band gaps estimated from UV–visible spectroscopy decreased from 5.20 to 4.10 eV, while thermo-electrical conductivity increases with perylene content. The fluorescence spectra showed partial quenching of p-terphenyl fluorescence and simultaneously sensitization of perylene fluorescence at the excitation wavelength of p-terphenyl (290 nm) due to excitation energy transfer from p-terphenyl to perylene. The observed sensitization results are in harmony with intense blue color seen in fluorescence microscopy images and has high demand in scintillation process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Surface Modification of 304 Stainless Steel by Electro-Spark Deposition

Electro-spark deposition (ESD) is a pulsed microwelding process that is used to apply surface coatings for the repair of damaged high value and precision products or modify their surfaces for specific properties. The low heat input, minimal heat-affected zone and the ability to form metallurgical bonding of coating to substrate are major advantages of the ESD process. Many applications require the components to have excellent surface performance, such as wear and corrosion resistance. ESD technique provides an approach to modify the component surface without compromising the bulk properties. In this study, surface modifications of 304 stainless steel by ESD were investigated. Titanium carbide (TiC), tungsten carbide (WC) and molybdenum (Mo) were employed as coating materials. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) analysis were conducted to characterize the microstructure and composition of the coatings. The coatings thicknesses were all around 40 µm. The results showed that TiC and WC coatings showed a dramatic increase in the microhardness, up to 5 times. WC coating improved the wear resistance by more than 5 times, while TiC and Mo coatings also improved it by approximately 2.5 times. Electro-chemical tests were conducted to investigate the corrosion resistance of the coatings. Mo coating exhibited a significant improvement in the corrosion resistance in 5% NaCl solutions, corroding 350 times slower than stainless steel. Synchrotron x-ray diffraction was performed to investigate the microstructure changes of the Mo-coated sample. Heat treatment was also carried out to investigate the corrosion behavior of Mo-coated 304 stainless steel at elevated service temperature in air or argon.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Synthesis of Nd3BSi2O10 using a LiCl-flux method

This paper details synthesis methods that were used to fabricate phase-pure Nd3BSi2O10 using a LiCl-flux method. In this study, a variety of conditions were evaluated to find the optimal processing parameters for maximizing the Nd3BSi2O10 yield including the mass ratio of LiCl to target mass of Nd3BSi2O10 including 1:3, 1:2, 1:1, 2:1, and 6:1 as well as the soak temperature (i.e., 700, 800, or 900°C) at the 1:1 ratio. It was found that the optimal ratio of LiCl:Nd3BSi2O10 was 1:1 and the optimal heat-treatment temperature was 900°C. Product made from the 1:1 material synthesized at 900°C was recovered and fired at temperatures of 925–1350°C. After 4-h firings at temperatures of 925–1100°C, the Nd3BSi2O10 phase purity was found to be 100% with powder X-ray diffraction, but started to decompose at the longer firing times at 1100°C and higher temperatures (1350°C) at the 4-h dwell time. The durability of the Nd3BSi2O10 product was examined in flow-through conditions at pH 5.6 and 7.7 and 90°C. The release rate of Nd from the material at pH 5.6 was calculated to be 1.6×10-3 g m-2 d-1 and was determined to have a maximum release rate of Nd at pH 7.7 of 5.6×10-3 g m-2 d-1. These release rates are roughly three orders of magnitude lower than what is typically measured from glass waste forms.

Kroll, Jared O.↗
DOE OSTI2015

Facile synthesis and characterization of erythrocyte-like Y-doped PbWO{sub 4} mesocrystals and their photocatalytic activity

Novel erythrocyte-like Y-doped PbWO{sub 4} mesocrystals with average diameter and thickness of 1.5 and 0.7 μm are fabricated via a facile co-precipitation route at room temperature in the ethylene glycol (EG)-water mixed solvent. Time-dependent samples centrifuged at different times are carefully characterized by powder X-ray diffraction (pXRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectrum. The possible formation mechanism for the novel erythrocyte-like mesocrystals is proposed on the basis of these observations. The photocatalytic activity of the Y-doped PbWO{sub 4} mesocrystals is further investigated in terms of the degradation of the acid orange II under UV irradiation. This simple and environment-friendly strategy presented here offers promising route for the synthesis of other inorganic materials with unique morphologies and interesting properties. - Graphical abstract: Display Omitted - Highlights: • Novel erythrocyte-like Y-doped PbWO{sub 4} mesocrystals are firstly synthesized via a facile co-precipitation route. • The mesocrystals are assembled by small nanoparticles a common crystallographic fashion. • The erythrocyte-like mesocrystals exhibit well photocatalytic activity. • A recrystallization-growth-oriented attachment formation mechanism is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Effects of aluminum substitution on photocatalytic property of BiVO{sub 4} under visible light irradiation

Graphical abstract: Visible-light-driven Al/BiVO{sub 4} photocatalyst was prepared by a hydrothermal process. After introducing Al, the BiVO{sub 4} particles retain monoclinic scheelite structures and the ability of visible light absorption is enhanced. XPS and FTIR results reveal that the Al ions influence the local structure of the BiVO{sub 4}. The photocatalytic experiments demonstrate that the Al species incorporation can effectively enhance the photocatalytic activity of BiVO{sub 4} due to the existence of distorted VO{sub 4}{sup 3-} tetrahedron and the stronger optical absorption intensity. Highlights: Black-Right-Pointing-Pointer The visible-light-driven Al/BiVO{sub 4} photocatalysts are first prepared in our study. Black-Right-Pointing-Pointer It is found that Al is introduced into the BiVO{sub 4} lattice successfully. Black-Right-Pointing-Pointer The Al-doped BiVO{sub 4} shows a far higher photocatalytic activity than undoped BiVO{sub 4}. Black-Right-Pointing-Pointer One of the reason for the higher activity is the distorted VO{sub 4}{sup 3-} tetrahedron. Black-Right-Pointing-Pointer Another reason for the higher activity is the strong optical absorption intensity. -- Abstract: Novel visible-light-driven Al/BiVO{sub 4} photocatalysts were synthesized via a facile hydrothermal method for the first time. The samples were characterized by X-ray diffraction, N{sub 2}-sorption, UV-vis diffuse reflectance spectra, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transformed infrared spectra and X-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of methylene blue under visible light irradiation (400 nm < {lambda} <580 nm) and was compared with that of single-phase BiVO{sub 4}. The results revealed that the introduction of Al can improve photocatalytic performance greatly and different concentration of Al resulted in different photocatalytic activity. The highest activity is obtained by the sample with a doping concentration of 12 at%. The reason for the enhanced photocatalytic activities of Al/BiVO{sub 4} samples was also discussed in this paper.

36 MATERIALS SCIENCE↗