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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 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Large Scale Screening of Low Cost Ferritic Steel Designs For Advanced Ultra Supercritical Boiler Using First Principles Methods

Advanced Ultra Supercritical Boiler (AUSC) requires materials that can operate in corrosive environment at temperature and pressure as high as 760°C (or 1400°F) and 5000psi, respectively, while at the same time maintain good ductility at low temperature. We develop automated simulation software tools to enable fast large scale screening studies of candidate designs. While direct evaluation of creep rupture strength and ductility are currently not feasible, properties such as energy, elastic constants, surface energy, interface energy, and stack fault energy can be used to assess their relative ductility and creeping strength. We implemented software to automate the complex calculations to minimize human inputs in the tedious screening studies which involve model structures generation, settings for first principles calculations, results analysis and reporting. The software developed in the project and library of computed mechanical properties of phases found in ferritic steels, many are complex solid solutions estimated for the first time, will certainly help the development of low cost ferritic steel for AUSC.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Band gap engineering strategy via polarization rotation in perovskite ferroelectrics

We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2 eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Local lattice strains in the system of cubic Zn{sub 0.999}Fe{sub 0.001}S{sub x}Se{sub 1-x} (0 {<=} x {<=} 1) crystals

The structure of cubic Zn{sub 0.999}Fe{sub 0.001}S{sub x}Se{sub 1-x} (0 {<=} x {<=} 1) crystals obtained by vapor-phase chemical transport has been investigated by thermal-neutron diffraction. The diffraction patterns of these crystals are found to exhibit previously unknown diffuse-scattering effects related to local static atomic displacements in the metastable fcc lattice. It is substantiated that the tendency to form polytypes, which is characteristic to a greater extent of zinc sulfide, can be a key factor of instability in the lattice of compounds belonging to the series of anion-substituted solid solutions under study.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Oxidation model of polycrystalline lead-chalcogenide layers in an iodine-containing medium

Model concepts of control over the formation of oxide shells in the course of oxidation are confirmed on the basis of experimental results obtained in a study of the fundamental aspects of how nanostructured layers are formed upon diffusion annealing on faceted single crystals of lead chalcogenides. Auger-spectroscopic data on the distribution of the elemental composition over the thickness of layers based on lead selenide–cadmium selenide solid solutions are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Alite-ye'elimite cement: Synthesis and mineralogical analysis

Alite-ye'elimite cement is an alternative cement that combines desirable characteristics of calcium sulfoaluminate cements and Portland cement in that it shows improved strength development at early age while retaining high portlandite contents. The key problem in the clinkering process is to produce the alite-ye'elimite phase assemblage so that both phases can co-exist. In this study, a new synthesis method is proposed to achieve the coexistence of alite and ye'elimite consisting of a secondary heat treatment step at 1250 °C after regular Portland clinker firing at 1450 °C. Quantitative X-ray powder diffraction and electron microscopy were used to analyze the phase composition of clinker before and after the secondary heat treatment. The results show that ye'elimite develops during secondary heat treatment of calcium sulphate enriched clinker by reaction of C{sub 3}A and sulphate phases. Additional ferrite is formed as result of rejection of Fe originally in solid solution with C{sub 3}A during ye'elimite formation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

On the optimization of asymmetric barrier layers in InAlGaAs/AlGaAs laser heterostructures on GaAs substrates

Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost obstruction-free transport of holes and the highest possible barrier height for electrons are found. The optimal compositions of both compounds (In{sup 0.232}Al{sup 0.594}Ga{sup 0.174}As/Al{sup 0.355}Ga{sup 0.645}As) at which the flux of electrons across the barrier is at a minimum are determined with consideration for the critical thickness of the indium-containing quaternary solid solution.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Initial precipitation and hardening mechanism during non-isothermal aging in an Al–Mg–Si–Cu 6005A alloy

The characterization of precipitation and hardening mechanism during non-isothermal aging had been investigated using high resolution transmission electron microscopy for an Al–Mg–Si–Cu 6005A alloy. It was proposed that the needle-shaped β″ precipitates with a three-dimension coherency strain-field and an increased number density in the Al matrix provided the maximum strengthening effect for the Al–Mg–Si–Cu 6005A alloy. Simultaneously, it was also found that the formation and evolution of clusters in the early precipitation were associated with the vacancy binding energy, during which Si atoms played an important role in controlling the numbers density of Mg/Si co-clusters, and the excess Si atoms provided the increased number of nucleation sites for the subsequent precipitates to strengthen and improve the precipitation rate. Finally, based on the experimental observation and theoretical analysis, the precipitation sequence during the early precipitation in the Al–Mg–Si–Cu 6005A alloy was proposed as: supersaturated solid solution → Si-vacancy pairs, Mg-vacancy pairs and Mg clusters → Si clusters, and dissolution of Mg clusters → Mg atoms diffusion into the existing Si clusters → Mg/Si co-clusters → GP zone. - Highlights: • β″ precipitates provide the maximum strengthening effect for the 6005A alloy. • Si atoms play an important role in controlling the numbers of Mg/Si co-clusters. • The early aging sequence is deduced based on the solute-vacancy binding energy.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Influence of Zn on magnetocaloric effect in (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} ceramic composites

Highlights: • Synthesis of magnetic ceramic composites. • Magnetization of dual phase ceramics. • Magnetic entropy change in (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/(0.05)Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} solid solution. - Abstract: We report the magnetic and magnetocaloric properties of (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/(0.05)Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x = 0.0, 0.1, 0.3, and 0.5) ceramic composites. The composite samples with nominal compositions were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order of magnetic phase transition in the composite samples. A maximum in magnetic entropy change of ∼0.75 J/kg K at 1 T has been observed in (0.95)La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/(0.05)NiFe{sub 2}O{sub 4} sample. The values of magnetic entropy change of these composites make them attractive for potential applications. These composite samples may consider as potential material for magnetic refrigeration near room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microstructure evolution and mechanical characterization of Nd:YAG laser beam welded titanium tubes

Highlights: • Joining of thin titanium tubes using laser beam welding. • Fusion zone exhibited coarse granular like grains with serrated and irregular boundaries. • Large spherical and irregular shape pores were observed at lower welding speeds. • Misorientation angle distribution indicated substructure boundaries along with single β grain formation from double α grains. • Fusion zone strengthened by substructure boundaries, solid solution strengthening and dislocation density. - Abstract: Grade 2 titanium tubes of outer diameter 60 mm and wall thickness 3.9 mm were effectively joined by Nd:YAG laser. The welding speed was varied in five levels (2.50, 2.75, 3.00, 3.25 and 3.50 m/min). The microstructure evolution was studied using optical microscopy and advanced characterization techniques. The bead geometry changed from parallel shape to wedge shape with increased welding speed due to changes in surface tension. The macrographs showed three zones namely fusion zone, heat affected zone (HAZ) and base metal. Coarse granular structure with irregular and serrated contours was observed in the fusion zone. Acicular α grains were observed at the extreme outer edge of the fusion zone due to rapid cooling. Spherical and irregular shaped pores were observed near the centerline of the fusion zone at lower welding speeds due to large amount of entrapped gases and downward sweeping solidification front. The grain size decreased with increased welding speed due to higher cooling rate. The misorientation angle distribution map showed three distinct regions. The increase in welding speed caused an increase in low angle boundaries and a reduction in very high angle boundaries. High density of dislocations was observed in the fusion zone due to thermal stresses caused by solidification. The microhardness of the fusion zone was recorded to be higher than base metal due to substructure boundaries, solute elements and dislocations. The increase in welding speed shifted the fracture location from fusion zone to base metal and fracture mode from brittle to ductile.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Temperature-Induced structural phase transformations in Cu{sub 1.50}Zn{sub 0.30}Te and Cu{sub 1.75}Cd{sub 0.05}Te single crystals

The results of studying the temperature-induced polymorphic phase transformations in Cu{sub 1.50}Zn{sub 0.30}Te and Cu{sub 1.75}Cd{sub 0.05}Te single crystals are presented. The single crystals have been investigated in the range of 290–1100 K using X-ray diffraction analysis. The temperature dependences of the unit-cell parameters, X-ray density, and coefficients of thermal expansion for each polymorphic modification of Cu{sub 1.50}Zn{sub 0.30}Te and Cu{sub 1.75}Cd{sub 0.05}Te single crystals are presented. The influence of cationic substitution (replacement of Cu{sup 2+} with Zn{sup 2+} and Cd{sup 2+} cations) on the phase-formation processes, number of polymorphic modifications, and temperature of structural phase transition in single crystals of these solid solutions is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Characterization of Cu–Ni nanostructured alloys obtained by a chemical route. Influence of the complexing agent content in the starting solution

The influence of the amount of complexing agent added to the starting solution on the physicochemical properties of Cu–Ni nanostructured alloys obtained through a chemical route, was studied. For this purpose, three Cu–Ni nanoalloy samples were synthesized by a previously developed procedure, starting from solutions with citric acid to metal molar ratios (C/Me) of 0.73, 1.00 and 1.50. The synthesis technique consisted in preparing a precursor via the citrate-gel method, and carrying out subsequent thermal treatments in controlled atmospheres. Sample characterization was performed by scanning electron microscopy, X-ray microanalysis, X-ray diffraction, transmission electron microscopy, X-ray nanoanalysis and electron diffraction. In the three cases, copper and nickel formed a solid solution with a Cu/Ni atomic ratio close to 50/50, and free of impurities inside the crystal structure. The citric acid content of the starting solution proved to have an important influence on the morphology, size distribution, porosity, and crystallinity of the Cu–Ni alloy microparticles obtained, but a lesser influence on their chemical composition. The molar ratio C/Me = 1.00 resulted in the alloy with the Cu/Ni atomic ratio closest to 50/50. - Highlights: • We synthesize Cu–Ni nanoalloys by a chemical route based on the citrate-gel method. • We study the influence of the complexing agent content of the starting solution. • We characterize the samples by electron microscopy and X-ray techniques. • Citric acid influences the shape, size, porosity and crystallinity of the alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nanostructured crystals of fluorite phases Sr{sub 1−x}R{sub x}F{sub 2+x} and their ordering: VIII. Imperfect crystal structure of Sr{sub 0.71}Ce{sub 0.29}F{sub 2.29}

A congruently melting single crystal of nonstoichiometric phase Sr{sub 0.71}Ce{sub 0.29}F{sub 2.29} crystallizing into the CaF{sub 2} structural type (sp. gr Fm<##> } } 3 }&#x00AF;<!-- ?? --> $ /bar 3 $ 3-bar </##>m) has been studied by X-ray diffraction analysis. Vacancies in the main fluorine position 8c and interstitial anions in two 32f positions have been found. The ratio of the structural defects in the Sr{sub 0.71}Ce{sub 0.29}F{sub 2.29} solid solution corresponds to the tetrahedral configuration of the defect cluster {Sr_4_−_nCe_nF_2_6}.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Band structure engineering through orbital interaction for enhanced thermoelectric power factor

Band structure engineering for specific electronic or optical properties is essential for the further development of many important technologies including thermoelectrics, optoelectronics, and microelectronics. In this work, we report orbital interaction as a powerful tool to finetune the band structure and the transport properties of charge carriers in bulk crystalline semiconductors. The proposed mechanism of orbital interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we find that the convergence of multiple carrier pockets not only displays a strong correlation with the s-p and spin-orbit coupling but also coincides with the enhancement of power factor. Our results suggest a useful path to engineer the band structure and an enticing solid-solution design principle to enhance thermoelectric performance.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Preparation and thermophysical properties of (Sm{sub 1−x}Er{sub x}){sub 2}Ce{sub 2}O{sub 7} oxides for thermal barrier coatings

Graphical abstract: - Highlights: • These ceramic materials with fluorite structure were synthesized. • Defect points lead to their lower thermal conductivities. • The lower ionic radius of Er{sup 3+} ion leads to the reduction of thermal expansion coefficient of (Sm{sub 1−x}Er{sub x}){sub 2}Ce{sub 2}O{sub 7} oxides. - Abstract: (Sm{sub 1−x}Er{sub x}){sub 2}Ce{sub 2}O{sub 7} ceramics were synthesized by sol–gel method and sintered at 1600 °C for 10 h in air. The influence of Er{sub 2}O{sub 3}-substitution on the phase structure and thermophysical properties of Sm{sub 2}Ce{sub 2}O{sub 7} was investigated. The phase structures of these ceramics were identified by X-ray diffraction showing that all synthesized ceramics have fluorite-type structure. The measurements for thermophysical properties of these ceramics show that their thermal conductivities and thermal expansion coefficients remarkably decreased through Er-substitution. However, the thermal expansion coefficients were higher than that of YSZ and their thermal conductivities were much lower than that of 8YSZ. The excellent thermophysical property implies that these solid solutions are potential materials for the ceramics layer in thermal barrier coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hierarchical domain structure of lead-free piezoelectric (Na{sub 1/2} Bi{sub 1/2})TiO{sub 3}-(K{sub 1/2} Bi{sub 1/2})TiO{sub 3} single crystals

We report a unique hierarchical domain structure in single crystals of (Na{sub 1/2}Bi{sub 1/2})TiO{sub 3}-xat. %(K{sub 1/2}Bi{sub 1/2})TiO{sub 3} for x = 5 and 8 by transmission electron microscopy (TEM). A high density of polar nano-domains with a lamellar morphology was found, which were self-assembled into a quadrant-like configuration, which then assembled into conventional ferroelectric macro-domains. Studies by high resolution TEM revealed that the polar lamellar regions contained a coexistence of in-phase and anti-phase oxygen octahedral tilt regions of a few nanometers in size. Domain frustration over multiple length scales may play an important role in the stabilization of the hierarchy, and in reducing the piezoelectric response of this Pb-free piezoelectric solid solution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Magnetoabsorption in narrow-gap HgCdTe epitaxial layers in the terahertz range

The magnetoabsorption and photoconductivity spectra are investigated in the terahertz (THz) range at a temperature of T = 4.2 K for n-Hg{sub 1−x}Cd{sub x}Te bulk epitaxial layers of various compositions (both semiconductor and semimetallic) grown by molecular-beam epitaxy. Within the framework of the Kane 8 · 8 model, the electron and hole Landau levels are calculated. It is shown that, in contrast to the results of previous investigations, all observed resonance lines are related to transitions between the Landau levels of free carriers (the cyclotron resonance in the conduction band and the transitions between heavy-hole and electron Landau levels), which is evidence of the high purity and structural perfection of the samples. The possibility of using zero-gap Hg{sub 1−x}Cd{sub x}Te solid solutions as THz photodetectors tunable by magnetic field is shown.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Element Composition Variation in Lead Zirconate Titanate upon the Ion-Plasma Deposition: Experiment and Simulation

The element composition modification is experimentally studied in PZT thin films obtained via the RF magnetron sputtering with variable working gas pressure. The experimental data were interpreted through the statistic simulation of thermalization and diffusion of sprayed Pb, Zr, and Ti atoms during the ion-plasma deposition of PZT thin films. The simulation data are shown to adequately describe (within the limits of 5%) the change in element composition at various pressures of the gas environment. The study conducted enables one to produce PZT thin films with a set element composition, which is essential for optimizing the electric and physical properties of solid solutions at the morphotropic phase boundary.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effects of Zn addition on the age hardening behavior and precipitation evolution of an Al-Mg-Si-Cu alloy

Highlights: • The Zn addition enhances the age hardening response of Al-Mg-Si-Cu alloy. • The major of Zn remains in the Al matrix during artificial aging at 170 °C. • The Zn addition prompts the formation of solute clusters, GP zones and β″ precipitates. - Abstract: The effects of Zn on the age hardening behavior and corresponding microstructure of an Al-0.9Mg-0.8Si-0.2Cu (wt%) alloy were investigated by hardness testing, transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP). During aging for up to 8 h at 170 °C (peak hardness condition), the addition of Zn does not alter the precipitation sequence of the Al-Mg-Si alloy, which can be expressed as: supersaturated solid solution → solute clusters → GP zones → β″. The Zn does not significantly partition into clusters or precipitates, and the majority of Zn remains in the Al matrix, prompting the formation of solute clusters during the early stage of aging and subsequently stimulating the transformation from solute clusters to GP zones to β″ precipitates. The characterization of precipitation evolution caused by Zn addition correlates well with the observed enhanced age hardening response.

36 MATERIALS SCIENCE↗