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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Luminescence, structure and antiferroelectric-type phase transition in Ca8ZnEu(PO4)7

Highlights: • Thermal, dielectric and luminescence properties were obtained for Ca{sub 8}ZnEu(PO{sub 4}){sub 7}. • Ca{sub 8}ZnEu(PO{sub 4}){sub 7} belongs to antiferroelectric with T{sub c} = 836 K. • First-order antiferroelectric/paraelectric phase transitions have been found. • Influence of composition on the luminescence properties has been shown. • Structure of Ca{sub 8}ZnEu(PO{sub 4}){sub 7} was refined by the Rietveld method. - Abstract: Photoluminescence excitation and emission spectra of new phosphate Ca{sub 8}ZnEu(PO{sub 4}){sub 7} have been investigated. The influence of the composition on the luminescence intensity has been shown. The substitution of Zn{sup 2+} for Ca{sup 2+} in Ca{sub 9}Eu(PO{sub 4}){sub 7} with the formation of Ca{sub 8}ZnEu(PO{sub 4}){sub 7} leads to the increased emission intensity {sup 5}D{sub 0} → {sup 7}F{sub 2} by about 1.5 times and to decreased number of bands from three to one in the range of {sup 5}D{sub 0} → {sup 7}F{sub 0} transition. Conditions of preparation do not influence the luminescent properties and distribution of Eu{sup 3+} cations in the structure. DSC, SHG data and dielectric spectroscopy reveal that Ca{sub 8}ZnEu(PO{sub 4}){sub 7} belongs to antiferroelectrics (T{sub c} = 836 K). The first-order antiferroelectric/paraelectric transformations are accompanied by a changing symmetry (R3-barC to R3-barm). The structure of Ca{sub 8}ZnEu(PO{sub 4}){sub 7} (sp. gr. R3-barc) was refined by the Rietveld method. The Zn{sup 2+} cations occupy the M5 site. The Eu{sup 3+} and Ca{sup 2+} ions are located in the M1 and M3 sites of β-Ca{sub 3}(PO{sub 4}){sub 2}-type structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Fast-decaying plant litter enhances soil carbon in temperate forests but not through microbial physiological traits

Abstract Conceptual and empirical advances in soil biogeochemistry have challenged long-held assumptions about the role of soil micro-organisms in soil organic carbon (SOC) dynamics; yet, rigorous tests of emerging concepts remain sparse. Recent hypotheses suggest that microbial necromass production links plant inputs to SOC accumulation, with high-quality (i.e., rapidly decomposing) plant litter promoting microbial carbon use efficiency, growth, and turnover leading to more mineral stabilization of necromass. We test this hypothesis experimentally and with observations across six eastern US forests, using stable isotopes to measure microbial traits and SOC dynamics. Here we show, in both studies, that microbial growth, efficiency, and turnover are negatively (not positively) related to mineral-associated SOC. In the experiment, stimulation of microbial growth by high-quality litter enhances SOC decomposition, offsetting the positive effect of litter quality on SOC stabilization. We suggest that microbial necromass production is not the primary driver of SOC persistence in temperate forests. Factors such as microbial necromass origin, alternative SOC formation pathways, priming effects, and soil abiotic properties can strongly decouple microbial growth, efficiency, and turnover from mineral-associated SOC.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Tautomerism unveils a self-inhibition mechanism of crystallization

Abstract Modifiers are commonly used in natural, biological, and synthetic crystallization to tailor the growth of diverse materials. Here, we identify tautomers as a new class of modifiers where the dynamic interconversion between solute and its corresponding tautomer(s) produces native crystal growth inhibitors. The macroscopic and microscopic effects imposed by inhibitor-crystal interactions reveal dual mechanisms of inhibition where tautomer occlusion within crystals that leads to natural bending, tunes elastic modulus, and selectively alters the rate of crystal dissolution. Our study focuses on ammonium urate crystallization and shows that the keto-enol form of urate, which exists as a minor tautomer, is a potent inhibitor that nearly suppresses crystal growth at select solution alkalinity and supersaturation. The generalizability of this phenomenon is demonstrated for two additional tautomers with relevance to biological systems and pharmaceuticals. These findings offer potential routes in crystal engineering to strategically control the mechanical or physicochemical properties of tautomeric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Constraining multi-field inflation using the SPHEREx all-sky survey power spectra

Abstract We investigate how well the SPHEREx all-sky survey can constrain local primordial non-Gaussianity beyond the parameterf NL using galaxy power spectra. We forecast joint constraints on the parametersf NL ,g NL andτ NL obtained assuming a simple two-field curvaton model of inflation. The parametersf NL andg NL characterise the squeezed limits of the primordial bispectrum and trispectrum respectively, and lead to a characteristic scale-dependence of the galaxy bias that increases out to arbitrarily large scales. Values of the parameterτ NL > (6/5f NL ) 2 cause the galaxy power spectrum to have a stochastic component which also increases out to arbitrarily large scales. Our MCMC forecasts indicate that SPHEREx can provide joint constraints on any two of the three parametersf NL ,g NL andτ NL . Due to strong degeneracies among these parameters, measurements of the galaxy power spectra alone may not be sufficient to jointly constrain all three. Constraints onf NL ,g NL andτ NL obtained from galaxy power spectrum observations depend on the modelling of underlying nuisance parameters. We study the robustness of our forecast constraints to modelling choices and note that even with relatively conservative modelling assumptions, SPHEREx galaxy power spectra can provide strong evidence of local non-Gaussianity, even if the particular values off NL andg NL cannot be measured precisely.

Astronomy & Astrophysics↗
DOE OSTI2021

encore : an O ( N g2) estimator for galaxy N -point correlation functions

ABSTRACT We present a new algorithm for efficiently computing the N-point correlation functions (NPCFs) of a 3D density field for arbitrary N. This can be applied both to a discrete spectroscopic galaxy survey and a continuous field. By expanding the statistics in a separable basis of isotropic functions built from spherical harmonics, the NPCFs can be estimated by counting pairs of particles in space, leading to an algorithm with complexity $\mathcal {O}(N_\mathrm{g}^2)$ for Ng particles, or $\mathcal {O}(N_\mathrm{FFT}\log N_\mathrm{FFT})$ when using a Fast Fourier Transform with NFFT grid-points. In practice, the rate-limiting step for N > 3 will often be the summation of the histogrammed spherical harmonic coefficients, particularly if the number of radial and angular bins is large. In this case, the algorithm scales linearly with Ng. The approach is implemented in the encore code, which can compute the 3PCF, 4PCF, 5PCF, and 6PCF of a BOSS-like galaxy survey in ${\sim}100$ CPU-hours, including the corrections necessary for non-uniform survey geometries. We discuss the implementation in depth, along with its GPU acceleration, and provide practical demonstration on realistic galaxy catalogues. Our approach can be straightforwardly applied to current and future data sets to unlock the potential of constraining cosmology from the higher point functions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

How Hydrologic Connectivity Regulates Water Quality in River Corridors

Abstract Downstream flow in rivers is repeatedly delayed by hydrologic exchange with off‐channel storage zones where biogeochemical processing occurs. We present a dimensionless metric that quantifies river connectivity as the balance between downstream flow and the exchange of water with the bed, banks, and floodplains. The degree of connectivity directly influences downstream water quality — too little connectivity limits the amount of river water exchanged and leads to biogeochemically inactive water storage, while too much connectivity limits the contact time with sediments for reactions to proceed. Using a metric of reaction significance based on river connectivity, we provide evidence that intermediate levels of connectivity, rather than the highest or lowest levels, are the most efficient in removing nitrogen from Northeastern United States’ rivers. Intermediate connectivity balances the frequency, residence time, and contact volume with reactive sediments, which can maximize the reactive processing of dissolved contaminants and the protection of downstream water quality. Our simulations suggest denitrification dominantly occurs in riverbed hyporheic zones of streams and small rivers, whereas vertical turbulent mixing in contact with sediments dominates in mid‐size to large rivers. The metrics of connectivity and reaction significance presented here can facilitate scientifically based prioritizations of river management strategies to protect the values and functions of river corridors.

Harvey, Jud↗
DOE OSTI2021

Exploring the Effects of Piston Bowl Geometry and Injector Included Angle on Dual-Fuel and Single-Fuel RCCI

Abstract Reactivity control compression ignition (RCCI) is a low-temperature combustion technique that has been proposed to meet the current demand for high thermal efficiency and low engine-out emissions. However, its requirement of two separate fuel systems (i.e., a low-reactivity fuel system and a high-reactivity fuel system) has been one of its major challenges in the last decade. This leads to the single-fuel RCCI concept, where the secondary fuel (reformates of diesel) is generated from the primary fuel (diesel) through catalytic partial oxidation reformation. Following the in-depth analysis of the reformate fuel (reformates of diesel) and its benefit as the low-reactivity fuel with diesel, the effects of the start of injection (SOI) timing of diesel and the energy-based blend ratio were also studied in detail. In this study, the effects of piston profile and the injector included angles were experimentally examined using both conventional fuel pairs (gasoline—diesel and natural gas—diesel) and reformate RCCI. A validated computational fluid dynamics (CFD) model was also used for a better understanding of the experimental trends. Comparing a reentrant bowl piston with a shallow bowl piston at a constant compression ratio and SOI, the latter showed better thermal efficiency, regardless of the fuel combination, due to its 10% lower surface area for the heat transfer. Comparing the 150-degree included angle and 60-degree included angle on the shallow bowl piston, the latter showed better combustion efficiency, regardless of the fuel combination, due to its earlier combustion phasing (at constant SOI timing). The effect was particularly prominent on reformate RCCI because of its incredibly high diluent concentration, which retards the combustion further for the 150-deg injector. Later, using convergecfd, seven different injector included angles were studied at a constant SOI. With the change in injector included angle, the region of the cylinder targeted by the fuel spray varies significantly, and it was found to have a significant impact on the combustion efficiency and the engine-out emissions. As the injector included angle changed from 60-deg to 150-deg, the combustion efficiency increased by 15% and the CO, NOx, and HC emissions decreased by 96%, 70%, and 86%, respectively.

Engineering↗
DOE OSTI2013

Reliability of temperature determination from curve-fitting in multi-wavelength pyrometery

Abstract This paper examines the reliability of a widely used method for temperature determination by multi-wavelength pyrometry. In recent WDM experiments with ion-beam heated metal foils, we found that the statistical quality of the fit to the measured data is not necessarily a measure of the accuracy of the inferred temperature. We found a specific example where a second-best fit leads to a more realistic temperature value. The physics issue is the wavelength-dependent emissivity of the hot surface. We discuss improvements of the multi-frequency pyrometry technique, which will give a more reliable determination of the temperature from emission data.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Abstract for CRADA between National Energy Technology Laboratory and OCO Chem

The National Energy Technology Laboratory (NETL) and OCO Chem (Participant) will collaborate in the development and scaling of electrochemical technologies that convert carbon dioxide (CO 2 ) into formic acid. This CO 2 -derived product is an industrially relevant chemical with various agricultural and industrial applications, as well as an emerging liquid hydrogen carrier 53 g of H 2 per liter. The use of formic acid as a liquid hydrogen carrier eliminates the challenges of long-distance H 2 transport and storage, which could lead to additional use as a precursor in the “green” energy and chemical sectors. Conventional formic acid production relies on carbon-intensive processes that use fossil fuel-derived starting materials. The collaboration will facilitate the deployment of technologies that convert captured CO 2 , water, and excess renewable electricity into carbon-neutral formic acid. The anticipated results will reduce the carbon footprint of conventional industrial processes, allow more sustainable use of our Nation’s fossil energy resources, and advance NETL’s ongoing CO 2 utilization efforts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Mutually Reinforced Polymer–Graphene Bilayer Membranes for Energy‐Efficient Acoustic Transduction

Abstract Graphene holds promise for thin, ultralightweight, and high‐performance nanoelectromechanical transducers. However, graphene‐only devices are limited in size due to fatigue and fracture of suspended graphene membranes. Here, a lightweight, flexible, transparent, and conductive bilayer composite of polyetherimide and single‐layer graphene is prepared and suspended on the centimeter scale with an unprecedentedly high aspect ratio of 10 5 . The coupling of the two components leads to mutual reinforcement and creates an ultrastrong membrane that supports 30 000 times its own weight. Upon electromechanical actuation, the membrane pushes a massive amount of air and generates high‐quality acoustic sound. The energy efficiency is ≈ 10–100 times better than state‐of‐the‐art electrodynamic speakers. The bilayer membrane's combined properties of electrical conductivity, mechanical strength, optical transparency, thermal stability, and chemical resistance will promote applications in electronics, mechanics, and optics.

Khan, Assad U.↗
DOE OSTI2022

Comparative Analysis of the Near‐ and Far‐Field Optical Response of Thin Plasmonic Nanostructures

Abstract Nanostructures made of metallic materials support collective oscillations of their conduction electrons, commonly known as surface plasmons. These modes, whose characteristics are determined by the material and morphology of the nanostructure, couple strongly to light and confine it into subwavelength volumes. Of particular interest are metallic nanostructures for which the size along one dimension approaches the nanometer or even the subnanometer scale, since such morphologies can lead to stronger light–matter interactions and higher degrees of confinement than regular three‐dimensional nanostructures. Here, the plasmonic response of metallic nanodisks of varying thicknesses and aspect ratios is investigated under far‐ and near‐field excitation conditions. It is found that, for far‐field excitation, the strength of the plasmonic response of the nanodisk increases with its thickness, as expected from the increase in the number of conduction electrons in the system. However, for near‐field excitation, the plasmonic response becomes stronger as the thickness of the nanodisk is reduced. This behavior is attributed to the higher efficiency with which a near‐field source couples to the plasmons supported by thinner nanodisks. The results of this work advance the understanding of the plasmonic response of thin metallic nanostructures, thus increasing their potential for the development of novel applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Tailoring the Local Environment of Platinum in Single‐Atom Pt 1 /CeO 2 Catalysts for Robust Low‐Temperature CO Oxidation

Abstract A single‐atom Pt 1 /CeO 2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over‐stabilization of Pt 2+ in a highly symmetric square‐planar Pt 1 O 4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt 2+ by thermal‐shock (TS) synthesis leads to a highly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO 2 to generate Pt single atoms in an asymmetric Pt 1 O 4 configuration. Owing to this unique coordination, Pt 1 δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low‐temperature performance. CO oxidation reactivity on the Pt 1 /CeO 2 _TS catalyst was retained under oxidizing conditions.

Jiang, Dong↗
DOE OSTI2023

Cracked Film Lithography with CuGaO x Buffers for Bifacial CdTe Photovoltaics

Abstract Bifacial CdTe solar cells with greater power density than the monofacial baselines are demonstrated by using a CuGaO x rear interface buffer that passivates while reducing sheet resistance and contact resistance. Inserting CuGaO x between the CdTe and Au increases mean power density from 18.0 ± 0.5 to 19.8 ± 0.4 mW cm −2 for one sun front illumination. However, coupling CuGaO x with a transparent conductive oxide leads to an electrical barrier. Instead, CuGaO x is integrated with cracked film lithography (CFL)‐patterned metal grids. CFL grid wires are spaced narrowly enough (≈10 µm) to alleviate semiconductor resistance while retaining enough passivation and transmittance for a bifacial power gain: bifacial CuGaO x /CFL grids generate 19.1 ± 0.6 mW cm −2 for 1 sun front + 0.08 sun rear illumination and 20.0 ± 0.6 mW cm −2 at 1 sun front + 0.52 sun rear—the highest reported power density at field albedo conditions for a scaled polycrystalline absorber.

14 SOLAR ENERGY↗
DOE OSTI2013

Magnetic structures in RNi₄B (R=Nd, Tb, Ho, Er)

Neutron diffraction has been performed on RNi₄B (R=Nd, Tb, Ho, Er) polycrystals. The orthorhombic structure for NdNi₄B and the CeCo₄B structure type (hexagonal) for TbNi₄B and HoNi₄B are confirmed. Our data also show that this last structure is currently the best approximant for ErNi₄B. The RNi₄B (R=Nd, Tb, Ho, Er) order ferromagnetically at respectively 11.0, 18.1, 6.2 and 10.0 K. The crystal electric field (CEF) interaction controls the magnetic anisotropy in this series leading to an easy axis ~30 deg above the basal plane in RNi₄B (R=Nd, Tb, Ho) and parallel to the c-axis in ErNi₄B at 1.6 K. The RNi₄B (R=Nd, Tb, Ho) display a spin re-orientation below T c which arises from a competition between the second order term and the higher order terms of the CEF hamiltonian. - Graphical abstract: Simplified magnetic structure in NdNi₄B and full magnetic structure in RNi₄B (R=Tb, Ho). Variation with temperature of the easy magnetization axis direction (angle with c-axis) showing a spin re-orientation. Highlights: • RNi₄B (R=Nd, Tb, Ho, Er) polycrystals were inductively melted. • Neutron diffraction confirms they all order ferromagnetically. • The magnetization easy axis is parallel to the c-axis in ErNi₄B. • The RNi₄B (R=Nd, Tb, Ho) display a spin re-orientation below T c . • Their easy axis tilts from the c-axis at T c to ~30 deg above the basal plane at 1.5 K.

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

Crystal structure and magnetic properties of the Ba{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, Pb{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, and Pb{sub 3}TeCo{sub 3}V{sub 2}O{sub 14} langasites

We report the structural and magnetic characterizations of Ba{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, Pb{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, and Pb{sub 3}TeCo{sub 3}V{sub 2}O{sub 14}, compounds that are based on the mineral dugganite, which is isostructural to langasites. The magnetic part of the structure consists of layers of Co{sup 2+} triangles. Nuclear and magnetic structures were determined through a co-refinement of synchrotron and neutron powder diffraction data. In contrast to the undistorted P321 langasite structure of Ba{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, a complex structural distortion yielding a large supercell is found for both Pb{sub 3}TeCo{sub 3}P{sub 2}O{sub 14} and Pb{sub 3}TeCo{sub 3}V{sub 2}O{sub 14}. Comparison of the three compounds studied along with the zinc analog Pb{sub 3}TeZn{sub 3}P{sub 2}O{sub 14}, also characterized here, suggests that the distortion is driven by Pb{sup 2+} lone pairs; as such, the Pb compounds crystallize in a pyroelectric space group, P2. Magnetic susceptibility, magnetization, and heat capacity measurements were performed to characterize the magnetic behavior. All three compounds become antiferromagnetic with Néel temperatures T{sub N}≈21 K (Ba{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}), ≈13 K (Pb{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}), and ≈8 K (Pb{sub 3}TeCo{sub 3}V{sub 2}O{sub 14}), and they exhibit magnetic transitions at high applied magnetic fields, suggesting intrinsically complex magnetic behavior for tetrahedrally coordinated d{sup 7} Co{sup 2+} in this structure type. - Graphical abstract: Ba{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, Pb{sub 3}TeCo{sub 3}P{sub 2}O{sub 14} and Pb{sub 3}TeCo{sub 3}V{sub 2}O{sub 14} exhibit a triangles-of-triangles arrangement of the magnetic cations. Despite the Pb-induced crystallographic distortion, all of these materials exhibit competing antiferromagnetic and ferromagnetic interactions that lead to complex high field magnetism. - Highlights: • Nuclear and magnetic structures of Ba{sub 3}TeCo{sub 3}P{sub 2}O{sub 14}, Pb{sub 3}TeCo{sub 3}P{sub 2}O{sub 14} and Pb{sub 3}TeCo{sub 3}V{sub 2}O{sub 14}. • Structural characterization shows complex Pb-induced distortion. • Distortion puts Pb-compounds into space group that allows potential multiferroicity. • Magnetic characterization shows competing magnetic interactions. • Triangles of triangles motif results in complex high-field magnetic behavior.

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

Cu-doping effect on dielectric properties of organic gel synthesized Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ}

Copper doped-Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ} samples were synthesized by an organic gel assisted citrate process. X-ray diffraction of compositions with x=0.002, 0.005, 0.01, 0.02 and 0.04 does not reveal any change of hexagonal perovskite structure on doping. The effects of Cu-doping on the microstructure and dielectric properties were investigated. Cu doping modifies the electrical properties at the level of the impedance characteristics of both grain and grain boundary and to understand these different behaviours, we have carried out high-resolution transmission electron microscopy analysis. Among the Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ} specimens studied, the composition x=0.002 shows a permittivity (ε′{sub r}) higher than the undoped compound and a lower loss tangent (tanδ) over several orders of magnitude of frequency. - Graphical abstract: Highlighting of many stacking faults (intergrowths) in substituted compounds with x>0.01 (right picture), which could explain the different dielectric properties observed in these compounds. However compounds with x>0.01 remain with a better stacking sequence as we can see on the left picture. Display Omitted - Highlights: • High permittivity of the Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ}. • Substitution leads to a mixed oxidation state for manganese: Mn{sup 4+}/Mn{sup 3+}. • Creation of oxygen vacancies which are responsible for stacking faults. • Highlighting relationship between Cu substitution and dielectric properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Thermoelectric properties of Fe and Al double substituted MnSi{sub γ} (γ~1.73)

Two series of Fe and Al double substituted MnSi{sub γ} chimney ladders with a nominal valence electron count, VEC=14 per transition metal were prepared (γ=1.75). Simultaneous replacement of Mn with Fe and Si with Al yielded the Mn{sub 1−x}Fe{sub x}Si{sub 1.75−x}Al{sub x} series while the second Mn{sub 1−x}Fe{sub x}Si{sub 1.75–1.75x}Al{sub 2x} series follows the pseudo-binary between MnSi{sub 1.75} and FeAl{sub 2}. Scanning electron microscopy and elemental mapping revealed that ~60% of the nominal Al content ends up in the product with the remainder lost to sublimation, and that up to 7% Al can be substituted in the main group sublattice. Profile analysis of X-ray powder diffraction data revealed gradual changes in the cell metrics, consistent with the simultaneous substitution of Fe and Al in a fixed ratio. All samples are p-type with VEC≈13.95 from the structural data and ~1×10{sup 21} holes cm{sup −3} from variable temperature Seebeck measurements. The substituted samples have lower electrical resistivities (ρ{sub 300} {sub K}=2–5 mΩ cm) due to an improved microstructure. This leads to increased thermoelectric power factors (largest S{sup 2}/ρ=1.95 mW m{sup −1} K{sup −2}) compared to MnSi{sub γ}. The thermal conductivity for the Mn{sub 0.95}Fe{sub 0.05}Si{sub 1.66}Al{sub 0.1} sample is 2.7 W m{sup −1} K{sup −1} between 300 and 800 K, and is comparable to literature data for the parent material. - Graphical abstract: The crystal structure, microstructure and thermoelectric properties of Fe and Al double substituted MnSi{sub γ} (γ~1.73) have been investigated. - Highlights: • Up to 7% Al can be substituted in MnSi{sub γ} when co-doped with Fe. • Improved microstructure and reduced electrical resistivities for Al substituted samples. • Largest power factor 1.95 mW m{sup −1} K{sup −2} and best estimated ZT=0.5.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

High elongation achieved by band-like distribution of reinforcements in aluminum matrix composites

Highlights: • The high elongation of composites with high reinforcement content has been achieved by band-like distribution of ABO. • The band-like distribution of ABO could lead to more homogenous strain distribution by scattering the damages. • The cracks played a key role in the strain non-localization process, but have negligible contribution to the tensile strain. • A model of the relationship between the ductility enhancement and the band-like distribution of ABO was established. • The residual stresses induced by band-like distribution of ABO were theoretically calculated and experimentally measured. - Abstract: Ductile aluminum matrix composites reinforced by Al{sub 18}B{sub 4}O{sub 33} whisker (ABO) with band-like distribution (Band-like Aluminum Matrix Composites, BAMCs) were fabricated by powder metallurgy and extrusion followed by annealing. The cracks tend to nucleate in the ABO-rich bands, but the band-like structure induces compressive residual stress then suppresses the crack propagation and improves the strain transferring ability in the BAMCs. The denser and smaller cracks formed in the BAMCs with higher ABO volume fraction during tensile test. These cracks play an important role in the strain non-localization process, but have negligible contribution to the tensile strain.

36 MATERIALS SCIENCE↗