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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Corrosion Behavior of Fe-7Cr-1Mo-12Zr Metal Waste Form Alloy in Simulated Repository Environment

Metal waste forms (MWF) are solid metallic waste categorized as high-level radioactive waste generated during pyro-reprocessing of spent metallic fuels and geologically disposed off. This waste form generated requires an excellent corrosion resistance in a geological repository environment. In the present work, Fe-7Cr-1Mo-12Zr MWF alloy was developed by casting in an arc melting furnace. The x-ray diffraction analysis revealed the formation of stable phases of α-Fe solid solution and the intermetallic phases of Fe{sub 2}Zr and Fe{sub 23}Zr{sub 6}. The corrosion behavior of Fe-7Cr-1Mo-12Zr alloy was investigated using electrochemical techniques in aggressive (highly acidic with Cl{sup −}) and nominal repository pH environment. Cyclic potentiodynamic polarization studies indicated the shift in corrosion potential toward cathodic potential in highly acidic solution with Cl{sup −}. The corrosion mechanism of pitting is associated with acidified pH medium with more Cl{sup −}, whereas uniform corrosion or transpassive dissolution is resultant of mild acidity or mild alkaline medium. The passive region is wider in pH 5 and 8 when compared to pH 1 and 3. Electrochemical impedance spectroscopic (EIS) analysis revealed the lowering of passive film stability in the highly acidic medium in the presence of Cl{sup −}. The role of passive oxide layers on the corrosion resistance of the Fe-7Cr-1Mo-12Zr MWF alloy is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Understanding the Cu-Zn brass alloys using a short-range-order cluster model: Significance of specific compositions of industrial alloys

Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn a-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu 12 ]Zn 1,6 and [Zn-Cu 12 ](Zn,Cu) 6 , which explain the a-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1 st -neighbor cluster, and each cluster is matched with one to six 2 nd -neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1 st - and 2 nd -neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, therefore offering a fundamental and practical method towards composition interpretations of all kinds of alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Dragging Effect in Ag/Pd Nanocomposite Film: Generation of Bipolar Pulses

Characteristic features of the phenomenon of longitudinal photocurrent generation in Ag/Pd nanocomposite films under the obliquely incident nanosecond pulsed laser irradiation with wavelengths in the 1350–4000 nm range have been studied for the first time. Films of 20-μm thickness consisting of nanocrystals of Ag–Pd solid solution and palladium oxide (PdO) were obtained using a thick-film technology. The influence of radiation wavelength on photocurrent pulses has been studied for s- and p-polarized laser pumping. It is established that the photocurrent pulses generated by s-polarized pumping in the 1350–4000 nm wavelength range are monopolar, while p-polarized pumping can generate both mono- and bipolar pulses depending on the wavelength. The obtained results are explained by simultaneous generation of photocurrent due to the dragging effect and the surface photogalvanic effect.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Deactivation of metastable single-crystal silicon hyperdoped with sulfur

Silicon supersaturated with sulfur by ion implantation and pulsed laser melting exhibits broadband optical absorption of photons with energies less than silicon's band gap. However, this metastable, hyperdoped material loses its ability to absorb sub-band gap light after subsequent thermal treatment. We explore this deactivation process through optical absorption and electronic transport measurements of sulfur-hyperdoped silicon subject to anneals at a range of durations and temperatures. The deactivation process is well described by the Johnson-Mehl-Avrami-Kolmogorov framework for the diffusion-mediated transformation of a metastable supersaturated solid solution, and we find that this transformation is characterized by an apparent activation energy of E{sub A}=1.7 ± 0.1 eV. Using this activation energy, the evolution of the optical and electronic properties for all anneal duration-temperature combinations collapse onto distinct curves as a function of the extent of reaction. We provide a mechanistic interpretation of this deactivation based on short-range thermally activated atomic movements of the dopants to form sulfur complexes.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Order parameter and scaling behavior in BaZr{sub x}Ti{sub 1−x}O{sub 3} (0.3 < x < 0.6) relaxor ferroelectrics

We report the relaxor behavior of the zirconium doped barium titanate BaZr{sub x}Ti{sub 1−x}O{sub 3} solid solutions and discuss the temperature, frequency, and concentration dependence in terms of correlations among the polar nanoregions. The relaxor behavior is analyzed within the mean field theory by estimating the Edward-Anderson order parameter q{sub EA}. Additionally, we find that q{sub EA} calculated for the different concentrations obeys a scaling behavior q{sub EA}=1−(T/T{sub m}){sup n}, where T{sub m} are the respective dielectric maxima temperatures and n = 2.0 ± 0.1. The frequency dependence of the q{sub EA} also shows results consistent with the above mentioned picture.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Features of the Band Spectrum on the Characteristics of Stimulated Emission in Narrow-Gap Heterostructures with HgCdTe Quantum Wells

We report on the stimulated emission obtained in the wavelength range of 20.3–17.4 μm on the interband transitions at T = 8–50 K in HgCdTe quantum wells placed in a dielectric waveguide formed from wide-gap CdHgTe solid solution. Heterostructures with HgCdTe quantum wells are interesting for designing long-wavelength lasers operating in the wavelength range of 25–60 μm, which is not covered by currently available quantum cascade lasers. It is shown that the maximum temperature of stimulated emission is determined by the position of lateral maxima in the dispersion dependences in the first valence subband of the quantum well. Methods for suppressing nonradiative recombination in the structures with HgCdTe quantum wells are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Understanding the bond-energy, hardness, and adhesive force from the phase diagram via the electron work function

Properties of metallic materials are intrinsically determined by their electron behavior. However, relevant theoretical treatment involving quantum mechanics is complicated and difficult to be applied in materials design. Electron work function (EWF) has been demonstrated to be a simple but fundamental parameter which well correlates properties of materials with their electron behavior and could thus be used to predict material properties from the aspect of electron activities in a relatively easy manner. In this article, we propose a method to extract the electron work functions of binary solid solutions or alloys from their phase diagrams and use this simple approach to predict their mechanical strength and surface properties, such as adhesion. Two alloys, Fe-Ni and Cu-Zn, are used as samples for the study. EWFs extracted from phase diagrams show same trends as experimentally observed ones, based on which hardness and surface adhesive force of the alloys are predicted. This new methodology provides an alternative approach to predict material properties based on the work function, which is extractable from the phase diagram. This work may also help maximize the power of phase diagram for materials design and development.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hyperfine Interaction and Shockley–Read–Hall Recombination in Semiconductors

Experimental and theoretical studies on optical orientation and spin-dependent recombination in a semiconductor in a magnetic field under the normal incidence of circularly polarized radiation onto the sample surface are reviewed. The experiments were carried out on GaAs{sub 1 –x}N{sub x} solid solutions, in which Ga{sup 2+} interstitial displacement defects play the role of deep paramagnetic centers responsible for spin-dependent recombination. It is established that, in the investigated materials, the hyperfine interaction of a localized electron with one nucleus of the paramagnetic center remains strong even at room temperature. The theory is compared with an experiment conducted in the steady-state excitation mode and under two-pulse pump-probe conditions. An analytical formula for spin beats in a magnetic field is derived.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Influence of grain boundaries on the distribution of components in binary alloys

Based on the free-energy density functional method (the Cahn–Hilliard equation), a phenomenological model that describes the influence of grain boundaries on the distribution of components in binary alloys has been developed. The model is built on the assumption of the difference between the interaction parameters of solid solution components in the bulk and at the grain boundary. The difference scheme based on the spectral method is proposed to solve the Cahn-Hilliard equation with interaction parameters depending on coordinates. Depending on the ratio between the interaction parameters in the bulk and at the grain boundary, temperature, and alloy composition, the model can give rise to different types of distribution of a dissolved component, namely, either depletion or enrichment of the grain-boundary area, preferential grain boundary precipitation, competitive precipitation in the bulk and at the grain boundary, etc.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Homogenization Treatment and Microalloying with Mn on the Microstructure and Hot Workability of AA6060 Aluminum Alloys

The effects of a homogenization treatment and microalloying with Mn on the evolution of the microstructure and hot workability of AA6060 aluminum alloys were investigated. Various homogenization treatments with temperatures ranging from 520 to 610 °C and soaking times from 2 to 16 h were conducted. The results revealed that β-AlFeSi intermetallic was the dominant phase in the as-cast microstructure of the experimental alloys. During the homogenization, the fragmentation of intermetallics occurred and plate-like β-AlFeSi transformed into rod-like α-AlFeSi. In addition, a number of dispersoids precipitated in the 0.1Mn alloy in the temperature range of 520-580 °C. The flow stress behavior of the homogenized AA6060 alloys was mainly determined by the solid solution level. Increasing homogenization temperatures resulted in higher flow stresses owing to the increase in solute atoms in the aluminum matrix. The incremental Mn addition from 0 to 0.1% moderately increased the flow stress by up to 3%. Grain growth occurred in the alloys with low Mn contents (< 0.03Mn) during the high-temperature homogenization (580-610 °C), which resulted in a sudden decrease in the flow stresses and an irregular sample shape after the deformation. Microalloying with Mn (> 0.06%) can effectively prevent grain growth at such temperatures. For an alloy with Mn (0.1%) microalloying, homogenization at 550-580 °C for 6 h could be the optimal condition to balance the flow stress and desirable microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Reel-to-Reel Heat Treatment, Microstructure, and Superconducting Properties of Jelly-Roll Nb{sub 3}Al Superconducting Wire

In this work, we utilized the jelly-roll method to make a single-filament Nb{sub 3}Al precursor long wire, combining with a homemade reel-to-reel rapid heating and quenching (RHQ) equipment, and consequently the high-performance Nb{sub 3}Al superconducting wires had been prepared. By investigating the heating current and wire moving speed, the optimized RHQ heat treatment conditions of this Nb{sub 3}Al wire were obtained. The results suggest that the T{sub c} for the Nb{sub 3}Al superconducting wire is up to 17.4 K and the non-Cu critical current density (non-Cu J{sub c}) reaches 1238 A/mm{sup 2} at 4.2 K and 12 T, which indicates the bcc-phase Nb–Al supersaturated solid solution has already been generated. Considering the Nb{sub 3}Al precursor wire with a large thickness of Al layer, about 690 nm, such high J{sub c} is quite unexpected. The SEM analysis presents that there is still some unreacted Nb and Nb{sub 2}Al phase in the superconducting wire, which may result from the inhomogeneity of Nb and Al foils. This work implies the Nb{sub 3}Al superconducting wire is promising to the application of high-field superconducting magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Cobalt Content on Thermal, Mechanical, and Microstructural Properties of Al{sub 0.4}FeCrNiCo{sub x} (x = 0, 0.25, 0.5, 1.0 mol) High-Entropy Alloys

Al{sub 0.4}FeCrNiCo{sub x} (x = 0, 0.25, 0.5, 1.0 mol) high-entropy alloys are developed by arc melting route to investigate the effect of cobalt content on thermal, mechanical, and microstructural properties. The phase, microstructure, and chemical composition are analyzed using x-ray diffraction, transmission electron microscope, and scanning electron microscope with attached energy-dispersive x-ray spectrometer. The obtained results have shown that the Al{sub 0.4}FeCrNiCo{sub x} (x = 0-0.5 mol) high-entropy alloys form a simple FCC + BCC-type solid solution and Al{sub 0.4}FeCrNiCo{sub x=1} HEA forms a single-phase FCC structure. The compressive yield strength, microhardness, and thermal conductivity are observed to decrease from 965.22 to 233.37 MPa, 253.6 to 155.6 HV, and from 4.87 to 2.674 W/mK, respectively, whereas the electrical resistivity is observed to increase from 150.30 to 273.74 µΩ-cm with the addition of cobalt from x = 0-1 mol. Differential scanning calorimetry analysis has indicated that the Al{sub 0.4}FeCrNiCo{sub x} (x = 0, 0.25, 0.5, 1.0 mol) high-entropy alloys are thermally stable up to 1000 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structure, sintering behavior, and microwave dielectric properties of (1 − x) CaWO{sub 4}–xYLiF{sub 4} (0.02 ≤ x ≤ 0.10) ceramics

Highlights: • Structure, sinterability, and dielectric properties of CaWO{sub 4}–YLiF{sub 4} were studied. • CaWO{sub 4} can be densified (TD 97%) at 750 °C/2 h by YLiF{sub 4} doping. • Excellent microwave dielectric properties could be obtained. - Abstract: Structures and sintering behaviors of (1 − x) CaWO{sub 4}–xYLiF{sub 4} (0.02 ≤ x ≤ 0.10) ceramic have been investigated by X-ray powder diffraction (XRD), dilatometry, scanning electron microscopy (SEM) in this work. The microwave dielectric properties were measured with a network analyzer at the frequency of about 8–15 GHz. Limited solid solution could be formed within the compositional range of x < 0.1. The sintering temperature of CaWO{sub 4} could successfully be reduced to ∼750 °C/2 h by doping with small amount of YLiF{sub 4}. An optimized microwave dielectric properties with ϵ{sub r} = 10.5, Q × f = 73 000 GHz and τ{sub f} = −37.7 ppm/°C could be obtained after sintered at the 750 °C for 2 h for x = 0.04 compositions. XRD and back scattering SEM analysis indicated that the (1 − x) CaWO{sub 4}–xYLiF{sub 4} (x = 0.04) ceramic could be chemically compatible with Ag after sintering at 750 °C/2 h.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Properties of the Barium–Strontium Titanate Films Deposited onto the Silicon Substrate by rf Cathode Sputtering

Using rf cathode sputtering of a target in the oxygen atmosphere, Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} solid solution thin films have been formed on the single-crystal Si(001) cut surface and their crystal structure, microstructure, and optical characteristics have been investigated. It is shown that the films are optically anisotropic, polycrystalline, and have a c axis preferred direction perpendicular to the substrate. The a and b axes in the substrate plane have no preferred direction. It has been established that, during the synthesis, a buffer layer with a thickness of about 20 nm forms between the film and substrate, which is optically equivalent to silicon oxide.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation to the Structural, Optical, and Magnetic Properties of Synthesized Ni-Doped Anatase Nanoparticles: Essential Role of Treatment in Hydrogen on Long-Range Ferromagnetic Order

Nanocomposite powders of anatase TiO{sub 2} doped with Ni ions (TiO{sub 2}:Ni) were synthesized by facile thermal co-decomposition of a mixture of metals complexes. The X-ray diffraction (XRD) analyses using the Rietveld method confirm the formation of almost single nanocrystalline anatase structure. Anatase TiO{sub 2} incorporated with Ni ions (TiO{sub 2}:Ni) illustrated the formation of a substitutional solid solutions (SSS). The diffuse reflection spectroscopy (DRS) method used to study the optical properties of the prepared samples revealed a redshift associated with Ni doping and hydrogenation, which is explained by the creation of point defects including O-vacancies. This study showed the essential importance of hydrogenation process in order to create or boost room-temperature ferromagnetism (RT-FM). The magnetic measurements indicated that anatase TiO{sub 2} doped with 4.8 mol% Ni produce a magnetic saturation of 0.84 emu/g, which is a remarkable result compared with that related to the similar studies on doped TiO{sub 2}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Lattice thermal expansion and solubility limits of neodymium-doped ceria

Nd{sub x}Ce{sub 1−x}O{sub 2−0.5x} (x=0–1.0) powders were prepared by reverse coprecipitation-calcination method and characterized by XRD. The crystal structure of product powders transformed from single fluorite structure to the complex of fluorite and C-type cubic structure, and finally to trigonal structure with the increase of x-value. An empirical equation simulating the lattice parameter of neodymium doped ceria was established based on the experimental data. The lattice parameters of the fluorite structure solid solutions increased with extensive adoption of Nd{sup 3+}, and the heating temperature going up. The average thermal expansion coefficients of neodymium doped ceria with fluorite structure are higher than 13.5×10{sup −6} °C{sup −1} from room temperature to 1200 °C. - Graphical abstract: The crystal structure of Nd{sub x}Ce{sub 1−x}O{sub 2−0.5x} (x=0–1.0) powders transformed from single fluorite structure to the complex of fluorite and C-type cubic structure, and finally to trigonal structure with the increase of x-value.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electron scattering mechanisms in Cu-Mn films for interconnect applications

Electrical properties and corresponding structural features of Cu-Mn alloy films with potential application as barrier and interconnect layers were studied. Cu-Mn films were deposited by DC magnetron sputtering at room temperature on SiO{sub 2} substrates. Electrical resistivity measurements were made as a function of film composition and temperature. The specific resistivity varies linearly with the Mn content showing a maximum of 205 μΩcm at 80 at. % Mn. The temperature coefficient of resistance (TCR) of all alloy films is low, showing non-metallic conductivity for most compositions. Also a minimum TCR has been observed in the 40–80 at. % Mn range which was attributed to a magnetic transformation around 200–300 K. Electrical resistivity measurements are correlated with the film structure revealed by transmission electron microscopy to clarify the phase regions throughout the composition range. In the 20–40 at. % and 70–80 at. % Mn ranges, two-phase structures were identified, where Cu- or Mn-rich solid solution grains were surrounded by a thin amorphous covering layer. Based on the revealed phase regions and morphologies electron scattering mechanisms in the system were evaluated by combining the Matthiessen's rule and the Mayadas-Schatzkes theory. Grain boundary reflectivity coefficients (r = 0.6–0.8) were calculated from fitting the model to the measurements. The proposed model indicates that, in a binary system, the special arrangement of the two phases results in new scattering mechanisms. The results are of value in optimizing the various parameters needed to produce a suitable barrier layer.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Helimagnetism in CrBr 2 and CrIBr

In Cr⁢𝑋 2 (𝑋 = Br, I), a Jahn-Teller effect distorts the octahedral configuration of the anions about Cr, resulting in a ribbon chain structure. We previously observed helimagnetism in CrI 2 propagating along the ribbon chains, with an 80–90° rotation per Cr ion. Via neutron scattering, we report that CrBr 2 and the solid solution CrIBr are also helimagnetic, with Néel temperatures of 17 and 12 K, respectively, and signs of intermediate magnetic transitions in both compounds. The helical angle between spins on consecutive Cr ions along the ribbon chains increases with increasing Br substitution, from 89.7° (CrI 2 ) to 116° (CrIBr) to 147° (CrBr 2 ), possibly as a result of decreasing longer-range intrachain spin interactions with the increased electron localization of the lighter anions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗