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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Structural and magnetic properties of Sm{sub 2−x}Mn{sub x}O{sub 3} nanoparticles

Graphical abstract: - Highlights: • C-type Sm{sub 2−x}Mn{sub x}O{sub 3} (0.0 ≤ x ≤0.20) is prepared by sol–gel method. • A maximum solubility of x = 0.15 is confirmed by X-ray diffraction, Raman and infrared techniques. • Samples with x > 0.05 exhibit weak ferromagnetic properties; for x ≤ 0.05 antiferromagnetic behaviors is obtained. • Correlation between magnetic behaviors and structural and microstructural parameters is discussed. - Abstract: Mixed oxide Sm{sub 2−x}Mn{sub x}O{sub 3} (SMO), x = 0.0, 0.05, 0.10, 0.15 and 0.20 were synthesized by a sol–gel process. A single phase solid solution is formed up to x = 0.15 which confirmed by using X-ray diffraction, Raman spectroscopy and infrared techniques. Crystal structure and microstructure analyses were performed by Rietveld refinement. Preferential cationic distribution, over the two crystallographic sites 8b and 24d of space group Ia3{sup ¯}, is found for doped samples but with different extent. The r.m.s. microstrain 〈ε{sub L}{sup 2}〉{sup 1/2} depends on composition x in a systematic way emphasizing the preferential distribution. Magnetization measurements show that samples with x ≤ 0.05 have antiferromagnetic behavior, while samples with x > 0.05 exhibit a weak ferromagnetic behavior with magnetic phase transformation at 15 and 16 K for x = 0.1 and x = 0.15, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Aging Treatment on the Precipitation Behavior and Mechanical Properties of Mg-9Gd-3Y-1.5Zn-0.5Zr Alloy

Aging heat treatments of an extruded Mg-9Gd-3Y-1.5Zn-0.5Zr (wt.%) alloy at 200, 225, and 250 °C for various times were studied. The results show that dynamic recrystallization (DRX) occurred during the extrusion process and the alloy exhibited a significant aging hardening response at temperatures ranging from 200 to 225 °C. The precipitation sequence of the alloy at 225 °C was supersaturated solid solution (SSSS) → β″ (D0{sub 19}, Mg{sub 3}RE) → β′ (bco, Mg{sub 15}RE{sub 3}), where the β′ phase was the primary precipitated phase. A large amount of discontinuous lamellar-shaped 14H-structure long period stacking ordered (LPSO) phase was also observed in the α-Mg matrix before and after aging treatments. Owing to the combined strengthening effect of fine DRXed grains, β′ nanoparticles, and widespread LPSO phases, the ultimate tensile strength and tensile yield strength of the peak-aged extruded alloy reached 409 and 303 MPa, respectively. The elongation in this circumstance was ~7.1%, which was slightly lower than that of the alloy before aging treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structure and magnetism in strained Ge{sub 1-x-y}Sn{sub x}Mn{sub y} films grown on Ge(001) by low temperature molecular beam epitaxy

In this letter, we study the structural and magnetic properties of Ge{sub 1-x-y}Sn{sub x}Mn{sub y} films grown on Ge(001) by low temperature molecular beam epitaxy using X-ray diffraction, high resolution transmission electron microscopy, and superconducting quantum interference device. Like in Mn doped Ge films, Mn atoms diffuse during the growth and aggregate into vertically aligned Mn-rich nanocolumns of a few nanometers in diameter. Transmission electron microscopy observations in plane view clearly indicate that the Sn incorporation is not uniform with concentration in Mn rich vertical nanocolumns lower than the detection limit of electron energy loss spectroscopy. The matrix exhibits a GeSn solid solution while there is a Sn-rich GeSn shell around GeMn nanocolumns. The magnetization in Ge{sub 1-x-y}Sn{sub x}Mn{sub y} layers is higher than in Ge{sub 1-x}Mn{sub x} films. This magnetic moment enhancement in Ge{sub 1-x-y}Sn{sub x}Mn{sub y} is probably related to the modification of the electronic structure of Mn atoms in the nanocolumns by the Sn-rich shell, which is formed around the nanocolumns.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Local structure underlying anomalous tetragonal distortions in BiFeO{sub 3}-PbTiO{sub 3} ferroelectrics

The local structure of tetragonal BiFeO{sub 3}-PbTiO{sub 3} solid solutions featuring anomalous lattice distortions has been determined using simultaneous fitting of neutron total scattering and extended X-ray absorption fine structure data. On the local scale, the large tetragonal distortion, promoted by the displacements of the A-cations (Bi and Pb), is accommodated primarily by the [FeO{sub 6}] octahedra, even though both Fe and Ti acquire (5+1)-fold coordination. Bi cations exhibit considerably larger displacements than Pb. The combination of the A-cation displacements and the ability of M-cations to adopt 5-fold coordination is suggested as key for stabilizing the large tetragonality in BiMO{sub 3}-PbTiO{sub 3} systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Determination of the technological growth parameters in the InAs-GaAs system for the MOCVD synthesis of “Multimodal” InAs QDs

The specific features of growth in the InAs-GaAs system by the metal-organic chemical vapor deposition method are studied. The dependences of the In content of the InxGa{sub 1−x}As solid solution and of the InAs growth rate on the molar flow of In in a wide temperature range (480–700°C) are determined. The growth processes of InAs quantum dots (QDs) on GaAs with different surface misorientations are examined. The conditions are found in which InAs QDs are formed with a small number of defects and at a high density on a GaAs “sublayer” grown at a high rate. An epitaxial technique is developed for the synthesis of InAs QDs with multimodal size distribution and an extended photoluminescence spectrum, which can be effectively used in designing solar cells with QDs in the active region.

36 MATERIALS SCIENCE↗
DOE OSTI2024

In situ Formation of Platinum-Carbon Catalysts in Propane Dehydrogenation

The catalytic production of propylene via propane dehydrogenation (PDH) is a key reaction in the chemical industry. By combining operando transmission electron microscopy with density functional theory analysis, we show that the intercalation and ordering of carbon on Pt interstitials to form Pt-C solid solutions is relevant for increasing propylene production. More specifically, we found that at the point of enhanced propylene formation, the structure of platinum nanoparticles is transformed into a transient caesium chloride-type Pt-C polymorph. At more elevated temperatures, the zincblende and rock salt polymorphs seemingly coexist. When propylene production was highest, multiple crystal structures consisting of Pt and carbon were occasionally found to coexist in one individual nanoparticle, distorting the Pt lattice. Catalyst coking was detected at all stages of the reaction, but did initially not affect all particles. These findings could lead to the development of novel synthesis strategies towards tailoring highly efficient PDH catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Effect of electronic structures on catalytic properties of CuNi alloy and Pd in MeOH-related reactions

We investigated the catalytic properties of a CuNi solid solution and Pd for methanol-related reactions and associated valence electronic structures. Calculations and X-ray photoelectron spectroscopy measurements revealed that the CuNi alloy has a similar valence electronic structure to Pd and hence they exhibited similar CO selectivities in steam reforming of methanol and decomposition of methanol. Samples prepared by various processes were found to have similar CO selectivities. We conjecture that alloying of Cu and Ni dramatically alters the valence electronic structures, making it similar to that of Pd so that the alloy exhibits similar catalytic properties to Pd. First-principles slab calculations of surface electronic structures support this conjecture.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Phase Diagram and Magnetocaloric Effect of Mn{sub 2}Tb-Fe{sub 2}Tb System

Mn{sub 2}Tb-Fe{sub 2}Tb phase diagram was drawn, and the crystal structure and magnetocaloric effect of (Mn{sub 1-x}Fe{sub x}){sub 2}Tb (x ≤ 0.5) compounds at the Mn-rich side were systematically studied. X-ray diffraction demonstrates that all these Laves phase compounds crystallize in the cubic MgCu{sub 2}-type structure. The Rietveld results of XRD shows the cell volume increases with Fe content. The influence of doping effect in (Mn{sub 1-x}Fe{sub x}){sub 2}Tb (x ≤ 0.5) compounds on their magnetic and magnetocaloric properties for all solid solutions is presented. The Curie temperature (Tc) rises from 49 K (for x = 0.0) to 322 K (for x = 0.5), depending on Fe content significantly. Based on Landau’s theory, the magnetization behavior and magnetic transition were analyzed. The magnetocaloric effect (MCE) of (Mn{sub 1-x}Fe{sub x}){sub 2}Tb compounds is also discussed using the Maxwell relation, and the maximum magnetic entropy change (− ΔS{sub M}{sup Max}) approaches to 10 J kg{sup −1} K{sup −1} at x = 0 under a field ranging from 0 to 5 T. The best relative cooling power (RCP) reaches 535.03 J/kg (x = 0.1).

36 MATERIALS SCIENCE↗
DOE OSTI2015

Leaching characteristics of toxic constituents from coal fly ash mixed soils under the influence of pH

Highlights: • The impact of pH on the leaching of elements and metals from fly ash mixed soils. • Generally Ca, Cd, Mg, and Sr follows a cationic leaching pattern. • The leaching of As and Se shows an oxyanionic leaching pattern. • The leaching behavior of elements does not change based on material type. • Different fly ash types show different abilities in immobilizing trace elements. - Abstract: Leaching behaviors of Arsenic (As), Barium (Ba), Calcium (Ca), Cadmium (Cd), Magnesium (Mg), Selenium (Se), and Strontium (Sr) from soil alone, coal fly ash alone, and soil-coal fly ash mixtures, were studied at a pH range of 2–14 via pH-dependent leaching tests. Seven different types of soils and coal fly ashes were tested. Results of this study indicated that Ca, Cd, Mg, and Sr showed cationic leaching pattern while As and Se generally follows an oxyanionic leaching pattern. On the other hand, leaching of Ba presented amphoteric-like leaching pattern but less pH-dependent. In spite of different types and composition of soil and coal fly ash investigated, the study reveals the similarity in leaching behavior as a function of pH for a given element from soil, coal fly ash, and soil-coal fly ash mixtures. The similarity is most likely due to similar controlling mechanisms (e.g., solubility, sorption, and solid-solution formation) and similar controlling factors (e.g., leachate pH and redox conditions). This offers the opportunity to transfer knowledge of coal fly ash that has been extensively characterized and studied to soil stabilized with coal fly ash. It is speculated that unburned carbon in off-specification coal fly ashes may provide sorption sites for Cd resulting in a reduction in concentration of these elements in leachate from soil-coal fly ash mixture. Class C fly ash provides sufficient CaO to initiate the pozzolanic reaction yielding hydrated cement products that oxyanions, including As and Se, can be incorporated into.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Effect of Mo Doping at the B Site on Structural and Electrical Properties of Multiferroic BiFeO{sub 3}

The Mo-doped BiFe{sub 1−x}Mo{sub x}O{sub 3}, where x = 0 and 0.6, samples were synthesised by the solid-state reaction method. Admirable ferroelectric and piezoelectric properties are expected on substituting solid solutions of bulk BFO with other oxide perovskite compounds. It offers an alternative and is an environment-friendly candidate for lead-free ferroelectric and piezoelectric devices. The prepared samples were investigated by XRD, Fourier transform infrared spectroscopy (FTIR), current density (JE) measurement, PE loop tracer and field emission scanning electron microscopy to examine their crystal structure, bonding nature, current density, ferroelectric hysteresis loop and surface morphology. The Mo-doped BFO shows a change in structure, increased grain size, reduction in current density and enhancement in the PE loop on doping Mo at the Fe site.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

On the state of Mn in Mn{sub x}Zn{sub 1−x}O nanoparticles and their surface modification with isonipecotic acid

Mn-doped ZnO (Mn{sub x}Zn{sub 1−x}O) nanoparticles were synthesized by the co-precipitation method and coated with isonipecotic acid as capping ligand. The structure, composition and morphology of the resulting nanomaterial were investigated by energy disperse X-ray analysis, X-ray diffraction, and transmission electron microscopy data. Such measurements showed that the solid obtained contains 6 at% of Mn and it is formed by a highly crystalline material with 3–5 nm range of crystallite size, and only a small elongation of its cell parameter with respect to undoped ZnO wurtzite unit cell. Information on the state of manganese atom in the Mn{sub x}Zn{sub 1−x}O nanostructures formed was obtained from X-ray photoelectron (XPS) and electron energy loss (EELS) spectroscopies. XPS and EELS spectra are composed of four peaks, corresponding to two species of Mn(II) and signals from Mn(III) and Mn(IV). Such spectral data on the state of Mn in the material studied is consistent with the mapping of Mn distribution observed in recorded transmission electron microscopy images, which reveal presence of clusters of Mn atoms. Only a fraction of doping Mn atoms were found forming a solid solution with the host ZnO structure. The functionalization of the nanoparticles system with Isonipecotic acid shows that this molecule remains anchored to the nanoparticles surface mainly through its N basic site. The availability of free carboxylate groups in the capping molecule was tested by conjugation to type IV horseradish peroxidase. - Graphical abstract: State of Mn atoms in Mn-doped ZnO nanostructures prepared by the precipitation method, their capping with isonipecotic acid and subsequent conjugation to peroxidase. - Highlights: • State of manganese in manganese-doped zinc oxide nanoparticles. • Isonipecotic acid as surface modifier of ZnO nanoparticles. • Peroxidase conjugation to ZnO nanoparticles modified with isonipecotic acid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Local structure of Cu{sub x}Zn{sub 2−x}TiO{sub 4} inverse spinel

Structural and vibrational changes due to the incorporation of Cu in the Cu{sub x}Zn{sub 2−x}TiO{sub 4} inverse spinel solid solution have been investigated by X-ray diffraction, Raman spectroscopy, and ab initio calculations. Both X-ray diffraction and Raman spectroscopy show that the structure remains cubic while the unit-cell volume decreases on Cu{sup 2+} incorporation. The compositional dependencies of the Raman frequencies and linewidths indicate the incorporation of Cu{sup 2+} into tetrahedral sites. The A{sub 1g} tetrahedral mode frequency becomes independent on composition for x > 0.6. This is attributed to the limited incorporation of Cu{sup 2+} in the tetrahedral sites at Cu-rich compositions. Ab initio calculations with quasi-random structures reveal only a slight energetic preference of Cu{sup 2+} for octahedral over tetrahedral sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Low temperature synthesis of Ru–Cu alloy nanoparticles with the compositions in the miscibility gap

A complex salt [Ru(NH{sub 3}){sub 5}Cl][Cu(C{sub 2}O{sub 4}){sub 2}H{sub 2}O]—the precursor of nanoalloys combining ruthenium and copper was prepared. It crystallizes in the monoclinic space group P2{sub 1}/n. Thermal properties of the prepared salt were examined in different atmospheres (helium, hydrogen, oxygen). Thermal decomposition of the precursor in inert atmosphere was thoroughly examined and the intermediate products were characterized. Experimental conditions for preparation of copper-rich (up to 12 at% of copper) metastable solid solution Cu{sub x}Ru{sub 1−x} (based on Ru structure) were optimized, what is in sharp contrast to the bimetallic miscibility gap known for the bulk counterparts in a wide composition range. Catalytic properties of copper–ruthenium oxide composite were tested in catalytic oxidation of CO. - Highlights: • We synthesized new precursor of CuRu metastable nanoalloys. • Thermal properties of the prepared salt were examined in different atmospheres. • Thermodestruction mechanism of precursor are studied. • Cu{sub 0.12}Ru{sub 0.88} nanoalloy with the compositions in the miscibility gap is obtained. • Catalytic conversion of CO on copper–ruthenium oxide composite were examined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Effects of rare earth yttrium on microstructure and properties of Ni–16Mo–7Cr–4Fe nickel-based superalloy

Effects of rare earth yttrium on microstructure of Ni–16Mo–7Cr–4Fe alloy were examined by optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray fluorescence. M{sub 6}C phase was observed in the alloys with and without yttrium addition, and Ni{sub 17}Y{sub 2} phase existed in the alloys containing 0.05–0.43 wt.% yttrium simultaneously. The amount of Ni{sub 17}Y{sub 2} phase increased as yttrium concentration increased. When the concentration of yttrium increased to 0.43 wt.%, some multi-precipitated phase regions appeared in the form of large amount of coarse Ni{sub 3}Y phase surrounded by M{sub 6}C phase and γ phase in the alloy. Influences of rare earth yttrium on high temperature static oxidation and mechanical properties of Ni–16Mo–7Cr–4Fe alloy were also investigated. The alloy containing 0.05 wt.% yttrium showed the best oxidation resistance and mechanical properties simultaneously. The adequate concentration of yttrium at grain boundary and in the solid-solution (γ phase) and the adhesion enhancement of the outer oxidation scale to the substrate are key factors for the improvements in the mechanical properties and oxidation resistance respectively. - Highlights: • When the content of yttrium reaches to 0.43%, some multiphase regions appear. • When the content of yttrium reaches to 0.43%, some Ni{sub 17}Y{sub 2} chains appear. • The morphology of M{sub 6}C changes with increasing concentration of yttrium. • The Ni–16Mo–7Cr–4Fe alloy with 0.05% yttrium performs the best mechanical property. • The Ni–16Mo–7Cr–4Fe alloy with 0.05% yttrium performs the best oxidation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructural stability and mechanical behavior of FeNiMnCr high entropy alloy under ion irradiation

In recent years, high entropy alloys (HEAs) have attracted significant attention due to their excellent mechanical properties and good corrosion resistance, making them potential candidates for high temperature fission and fusion structural applications. However there is very little known about their radiation resistance, particularly at elevated temperatures relevant for energy applications. In the present study, a single phase (face centered cubic) concentrated solid solution alloy of composition 27%Fe-28%Ni-27%Mn-18%Cr was irradiated with 3 or 5.8 MeV Ni ions at temperatures ranging from room temperature to 700 °C and midrange doses from 0.03 to 10 displacements per atom (dpa). Transmission electron microscopy (TEM), scanning transmission electron microscopy with energy dispersive x-ray spectrometry (STEM/EDS) and X-ray diffraction (XRD) were used to characterize the radiation defects and microstructural changes. Irradiation at higher temperatures showed evidence of relatively sluggish solute diffusion with limited solute depletion or enrichment at grain boundaries. The main microstructural feature at all temperatures was high-density small dislocation loops. Voids were not observed at any irradiation condition. Nano-indentation tests on specimens irradiated at room temperature showed a rapid increase in hardness ~35% and ~80% higher than the unirradiated value at 0.03 and 0.3 dpa midrange doses, respectively. The irradiation-induced hardening was less pronounced for 500 °C irradiations (<20% increase after 3 dpa). Overall, the examined HEA material exhibits superior radiation resistance compared to conventional single phase Fe-Cr-Ni austenitic alloys such as stainless steels. Furthermore, the present study provides insight on the fundamental irradiation behavior of a single phase HEA material over a broad range of irradiation temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Formation of an 18R long-period stacking ordered structure in rapidly solidified Mg{sub 88}Y{sub 8}Zn{sub 4} alloy

The formation of the long-period stacking ordered structure (LPSO) in a Mg{sub 88}Y{sub 8}Zn{sub 4}(at%) ribbon produced by melt spinning was studied using high energy X-ray synchrotron radiation diffraction during in-situ isochronal heating and transmission electron microscopy. The microstructure of the rapidly solidified ribbons is characterised by fine magnesium grains with yttrium and zinc in solid solution and primary 18R LPSO-phase segregated at grain boundaries. Using differential scanning calorimetry, a strong exothermal peak was observed around 300 °C which was associated with the development of the 18R-type LPSO-phase in the magnesium grains. The apparent activation energy calculated using the Kissinger model was 125 KJmol{sup −1} and it is related to simultaneous diffusion of Y and Zn through magnesium basal plane. - Highlights: •The formation of the LPSO phase in rapidly solidified ribbons was studied. •The formation of the 18R LPSO starts at around 300 °C. •LPSO formation have to steps: Stacking faults along basal plane and then growth of 18R structure along the c direction.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tailoring the interfacial microstructure and mechanical strength of SiC ceramic joints using joining temperature and interlayer thickness

Highlights: • Bonding temperature could be decreased from 1600 °C to 1300 °C by inserting the Ti foil between SiC and Ta-5W. • The initial thickness interlayer and the number of interlayer had a significant influence on interface bonding. • Layered reaction layers consisting of carbides and silicide formed at the SiC/Ti/Ta-5W interfaces. • The joint strength depended mainly on the reaction layer thickness, especially the thickness of silicide layer. - Abstract: Silicon carbide ceramic joints solid state diffusion bonded by spark plasma sintering with Ti/Ta-5W/Ti multi-interlayer in the temperature range from 1250 °C to 1500 °C were investigated in detail in terms of interfacial microstructure, elemental diffusion, phase constituents, shear strength, and fracture morphology. Layered reaction layers consisting of carbides (TiC, Ti{sub 3}SiC{sub 2}, (Ta,Ti,W)C), silicide ((Ta,Ti,W){sub 5}Si{sub 3}) and Ta-rich solid solution (Ta,Ti,W) formed at the SiC/Ti/Ta-5W interfaces. It was found that joining temperature could be decreased from 1600 °C to 1300 °C by inserting the Ti foil between SiC and Ta-5W. Nevertheless, an attempt to further decrease the joining temperature to 1250 °C failed even using a thin Ti foil. The initial thickness interlayer and the number of interlayer had an influence on the interfacial diffusion bonding at SiC/Ti interface. Higher joining temperature was needed to achieve a tough interface joining for a thick interlayer compared with a thin interlayer. The increase of interlayer number also required higher joining temperature. The shear strength reached 123.5 ± 25.3 MPa for the joint diffusion bonded at 1300 °C.

36 MATERIALS SCIENCE↗