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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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Spontaneous Emission and Lasing of a Two-Wavelength Quantum-Cascade Laser

The results of experiments on the fabrication (by molecular-beam epitaxy) and investigation of the heterostructures of a two-frequency quantum-cascade laser produced on the basis of a heteropair of In{sub 0.53}Ga{sub 0.47}As/Al{sub 0.48}In{sub 0.52}As solid solutions on an InP substrate are presented. The heterostructures contained quantum cascades emitting at a wavelength of 9.6 μm and cascades emitting at a wavelength of 7.6 μm. The high structural quality of the fabricated heterostructures is shown. The spontaneous emission and lasing spectra are investigated and the multimodal laser generation of stripe lasers at a wavelength of 7.6 μm is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Thermodynamic Assessment of LiCl-KCl-PuCl{sub 3} Ternary System

Pyroprocessing in LiCl-KCl molten salt is being considered as an alternative to the PUREX for the used nuclear fuel treatment. As more and more spent fuel is reprocessed, the composition of molten salt electrolyte changes, which alters the thermodynamic properties of the system and subsequently requires the adjustment of operation conditions. In order to optimize the system design and carefully operate it, thermodynamic assessment of actinides and lanthanides in LiCl-KCl molten salt is needed. Even though several systems have been assessed recently, such as LiCl-KCl-CeCl{sub 3} and LiCl-KCl-UCl{sub 3}, as one of the major actinides in pyro-processing, PuCl{sub 3} in LiCl-KCl hasn't been calculated. In present work, LiCl- KCl-PuCl{sub 3} is being considered and studied. Sub-binary systems of LiCl-PuCl{sub 3} and LiCl-KCl system was calculated firstly by using two-sublattice model based on the CALPHAD (Calculation of Phase Diagram) theory. The result indicates both of LiCl-PuCl{sub 3} and LiCl-KCl show simple eutectic properties and no solid solution is found. This research will help to predict the properties in electro-refiner when the concentration of elements in LiCl- KCl molten salt electrolyte changes during pyro-processing. Currently, binary system of KCl-PuCl{sub 3} is also being assessed and after that, phase diagram of ternary system of LiCl-KCl-PuCl{sub 3} will be calculated to provide a whole sight of the properties of PuCl{sub 3} in LiCl-KCl eutectic salt. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Effect of Cu Interlayer on the Microstructure and Strength for Brazing of Tungsten/316L Steel

Brazing is an effective technique for joining tungsten and steel. However, the high residual stresses are produced due to the different coefficients of thermal expansions between tungsten and steel. Compared with the direct brazing with BNi-2 foil filler, BNi-2/Cu/ BNi-2 multiple interlayer was used as filler to minimize the residual stresses between tungsten and 316L steel. The brazing experiments were conducted at 1050 °C for 25 min using Cu foils with different thickness. The results show that tungsten and 316L steel have been successfully joined by brazing. The intermetallic compound of NiW formed at the W/BNi-2 interface, which was detrimental to the strength of the joint. The microhardness of different diffusion zones is higher than that of the substrates owing to the formation of intermetallic compound and solid solution. All specimens of shear testing fractured at the W/BNi-2 interface close to W substrate, and the average strength of joints was 197, 275 and 268 MPa with multiple interlayer thickness of 0.2 , 0.1 and 0.05 mm copper foil, respectively, while the average strength of joints was 143 MPa with BNi-2 foil filler. The significant increase in the joint shear strength can be ascribed to the Cu foil in the multiple interlayer because of with excellent plasticity and toughness.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of microstructure on the thermoelectric performance of La{sub 1−x}Sr{sub x}CoO{sub 3}

We present a case where the microstructure has a profound effect on the thermoelectric properties of oxide compounds. Specifically, we have investigated the effect of different sintering treatments on La{sub 1−x}Sr{sub x}CoO{sub 3} samples synthesized using the Pechini method. We found that the samples, which are dense and consist of inhomogeneously-mixed grains of different size, exhibit both higher Seebeck coefficient and thermoelectric figure of merit than the samples, which are porous and consist of grains with almost identical size. The enhancement of Seebeck coefficient in the dense samples is attributed to the so-called “energy-filtering” mechanism that is related to the energy barrier of the grain boundary. On the other hand, the thermal conductivity for the porous compounds is significantly reduced in comparison to the dense compounds. It is suggested that a fine-manipulation of grain size ratio combined with a fine-tuning of porosity could considerably enhance the thermoelectric performance of oxides. - Graphical abstract: The enhancement of the dimensionless thermoelectric figure ZT of merit is presented for two equally Sr-doped LaCoO3 compounds, possessing different microstructure, indicating the effect of the latter to the thermoelectric performance of the La{sub 1−x}Sr{sub x}CoO{sub 3} solid solution. - Highlights: • Electrical and thermal transport properties are affected by the microstructure in La{sub 1−x}Sr{sub x}CoO{sub 3} polycrystalline materials. • Coarse/fine grain size distribution enhances the Seebeck coefficient. • Porosity reduces the thermal conductivity in La{sub 1−x}Sr{sub x}CoO{sub 3} polycrystalline samples. • The combination of large/small grain ratio distribution with the high porosity may result to the enhancement of the thermoelectric performance of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo

Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L1{sub 2} structure. The fully Cr-ordered alloyed L1{sub 2} phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Phase transitions, dielectric properties, and vibrational study of stannates perovskites Sr{sub 1−x}Er{sub x}SnO{sub 3−δ}

Graphical abstract: The diffuseness of the phase transition of the Sr{sub 1−x}Er{sub x}SnO{sub 3−δ} enhances with the increasing of erbium content. These compounds were found to undergo phase transitions with increasing temperature. - Highlights: • Substitution Sr/Er in the alkaline earth cage modifies the thermally induced disorder. • Two phase transitions have been observed by DSC. • The dielectric constant increases with erbium substitution. • Dielectric loss increases exponentially with temperature. • The conductivity contribution is mainly due to hopping process. - Abstract: A polycrystalline stannates perovskites Sr{sub 1−x}Er{sub x}SnO{sub 3−δ} (x = 0.00, 0.01 and 0.03) were synthesized by sol–gel method and their vibrational properties were investigated using Raman scattering. The substitution of Er in the Sr site, results in a slight change of the position of the Raman spectrum bands. The differential scanning calorimetry (DSC) shows two phase transitions at 532 K and 634 K for Sr{sub 0.99}Er{sub 0.01}SnO{sub 3−δ}. The dielectric behavior of each solid solution (x = 0.01 and x = 0.03) has been studied as a function of temperature and frequency and has confirmed the observed phase transitions. The diffuseness of the phase transitions of these materials enhances with the increasing of erbium content. The dielectric constant showed a strong increase near the phase transitions temperature which value depends with frequency. This phenomenon is usually observed in relaxor materials. The conduction and the dielectric relaxation are attributed to hopping of electrons among Sn{sup 2+} and Sn{sup 4+} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Formation of Nanosized Surface Layers of 03Kh17N12M2 Stainless Steel by Implantation of N{sup +} Ions

Accumulation of nitrogen in nanosized surface layers of 03Kh17N12M2 stainless steel has been detected upon N{sup +} ion implantation up to 14 at % together with metal nitrides, mainly of chromium nitride CrN and interstitial solid solution. It has been demonstrated that N{sup +} ion implantation accompanied by preliminary irradiation by Ar{sup +} and O{sup +} ions decreases maximum nitrogen concentration by at least two times. It is assumed that this is stipulated by segregation to surface layers of iron atoms upon irradiation by Ar{sup +} ions as well as formation of chromium oxide Cr{sub 2}O{sub 3} and chromium hydroxide CrOOH upon irradiation by O{sup +} ions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Synthesis of 0.1% & 0.2% neodymium doped barium zirconium titanate (BaZr{sub 0.2}Ti{sub 0.8}O{sub 3}) and study of their dielectric behaviour

Efforts have been made to ease process of producing widely used multilayered ceramics of Barium Zirconium Titanium Oxides and study their dielectric behaviour and structural properties. For this purpose, adequate proportions of Barium Carbonate, Zirconium Oxide and Titanium Oxide were taken and hand milled for 2 hours. Neodymium composition of the order of 0.1% and 0.2% was used for doping to weight percentage of BaZr0.2Ti0.8O3. The samples were authenticated using raw data obtained from Bruker AXS D8 advance Copper KL alpha source XRD equipment. Further, the samples were studied for their phase transition, composition, single phase perovskite structure using XRD technique. The technique has also been applied to know formation of stable homogeneous solid solution from XRD parameters. The other physical parameters like the morphology, micro structural information, crystal arrangements and topography have also been observed through SEM. The SEM has revealed information related to grain size development and composition of sample with fine agglomerates. For complete study of the compounds the atomic and weight composition has also been examined by Electron Dispersive Spectroscopy patterns. The comparison has been made with other works on ceramics at various frequencies and has yielded very interesting results.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Spectroscopy and tunable continuous-wave operation of Cr{sup 2+}:Zn{sub 1-x}Mg{sub x}Se single crystal around 2.5 μm

Hexagonal single crystals of the Cr{sup 2+}:Zn{sub 1-x}Mg{sub x}Se solid solution are grown by the Bridgman – Stockbarger technique. We study their optical and photoluminescent characteristics and determine the temperature dependences of the photoluminescence kinetics within the range 5 – 440 K. The crystals possess a broad gain band in the range from 2 to 3.5 μm and exhibit a weak quenching of luminescence with a quantum yield exceeding 80% at room temperature. Tunable continuous-wave oscillation is demonstrated in the region of 2.5 μm. (lasers)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Preparation and Thermal Expansion of Calcium Iron Zirconium Phosphates with the NaZr{sub 2}(PO{sub 4}){sub 3} Structure

Ca{sub 0.5(1+} {sub x)}Zr{sub 2–x}Fe{sub x}(PO{sub 4}){sub 3} phosphates have been synthesized by a sol–gel process. The individual compounds and solid solutions obtained crystallize in the NaZr{sub 2}(PO{sub 4}){sub 3} structure (trigonal symmetry, sp. gr. R3̄). Using high-temperature X-ray diffraction, we have determined their thermal expansion parameters in the temperature range from 25 to 800°C. With increasing x, the magnitudes of their linear thermal expansion coefficients and thermal expansion anisotropy decrease. Most of the synthesized phosphates can be rated as low-thermal-expansion compounds and can be regarded as materials capable of withstanding thermal “stress.”.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Luminescence Properties of GaInAsP Layers with Graded Composition–Depth Profiles Grown on InP Substrates

Luminescence properties of epilayers of Ga{sub 1 –x}In{sub x}As{sub y}P{sub 1 –y} (GaInAsP) solid solutions with graded content of Group V elements (Δy up to 0.08 over a total thickness of about 1 μm) were studied at 77 and 300 K. The photoluminescence (PL) spectra of GaInAsP epilayers with large Δy values were broadened. The GaInAsP epilayers of low crystalline perfection exhibited either no PL emission or showed PL spectra characteristic of transitions involving impurity energy levels.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Microsphere LiMn 0.6 Fe 0.4 PO 4 /C cathode with unique rod-like secondary architecture for high energy lithium ion batteries

LiMn x Fe 1-x PO 4 /C is considered a promising next-generation cathode material with significant commercial potential, inheriting the safety of LiFePO 4 while offering higher energy densities. However, the extremely low conductivity and the Jahn-Teller effect induced by Mn 3+ limit its practical capacity and rate performance. Effective modifications can be achieved through particle nanonization and uniform carbon coating. Here, in this work, we synthesized microspherical LiMn 0.6 Fe 0.4 PO 4 /C cathode materials using a hydrothermal method combined with spray drying carbon coating. The cathode material exhibits a microsphere structure composed of aggregated nanorods with a uniform 3 nm carbon coating, showing good dispersibility, small specific surface area and high tap density. In-situ diffraction analysis showed that expanding the single-phase solid solution region during (de)lithiation can reduce the energy barrier for electron transport, improve the kinetics of the (dis)charge process, and enhance both cycling and rate performance. The initial capacity at 0.1C can reach 155 mAh/g, and the capacity remains at 133.5 mAh/g with a retention rate of 97.1 % after 300 cycles. The synergistic effect of particle nanonization and uniform carbon coating endows the LiMn x Fe 1-x PO 4 /C material with excellent electrochemical performance.

25 ENERGY STORAGE↗
DOE OSTI2016

Enhanced damage resistance and novel defect structure of CrFeCoNi under in situ electron irradiation

Defect production and growth in CrFeCoNi, a single-phase concentrated solid solution alloy, is characterized using in situ electron irradiation inside a transmission electron microscope operated at 400–1250 kV and 400 °C. All observed defects are interstitial-type, either elliptical Frank loops or polygonal (mostly rhombus) perfect loops. Both forms of loops in CrFeCoNi exhibit a sublinear power law of growth that is > 40 times slower than the linear defect growth in pure Ni. Lastly, this result shows how compositional complexity impacts the production of Frenkel pairs and the agglomeration of interstitials into loops, and, thus, enhances the radiation tolerance.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Abnormal thermal conductivity in tetragonal tungsten bronze Ba{sub 6−x}Sr{sub x}Nb{sub 10}O{sub 30}

Ba{sub 6−x}Sr{sub x}Nb{sub 10}O{sub 30} solid solution with 0 ≤ x ≤ 6 crystallizes in centrosymmetric tetragonal “tungsten bronze” structure (space group P4/mbm). We report on the x dependence of thermal conductivity of polycrystalline samples measured in the 2–400 K temperature interval. Substitution of Sr for Ba brings about a significant decrease in thermal conductivity at x ≥ 3 accompanied by development of a low-temperature (T ≈ 10–30 K) “plateau” region reminiscent of a glass-like compounds. We explain this behaviour based on a size-driven site occupancy and atomic displacement parameters associated with an alkaline earth atomic positions in the title compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of composition on electrical properties of lead-free Bi{sub 0.5}(Na{sub 0.80}K{sub 0.20}){sub 0.5}TiO{sub 3}-(Ba{sub 0.98}Nd{sub 0.02})TiO{sub 3} piezoelectric ceramics

Lead-free piezoelectric ceramics with the composition of (1-x)Bi{sub 0.5}(Na{sub 0.80}K{sub 0.20}){sub 0.5}TiO{sub 3}-x(Ba{sub 0.98}Nd{sub 0.02})TiO{sub 3} or (1-x) BNKT-xBNdT (with x = 0-0.20 mol fraction) have been synthesized by a conventional mixed-oxide method. The compositional dependence of phase structure and electrical properties of the ceramics were systemically studied. The optimum sintering temperature of all BNKT-BNdT ceramics was found to be 1125 Degree-Sign C. X-ray diffraction pattern suggested that BNdT effectively diffused into BNKT lattice during sintering to form a solid solution with a perovskite structure. Scanning electron micrographs showed a slight reduction of grain size when BNdT was added. It was found that BNKT-0.10BNdT ceramic exhibited optimum electrical properties ({epsilon}{sub r} = 1716, tan{delta} = 0.0701, T{sub c} = 327 Degree-Sign C, and d{sub 33} = 211 pC/N), suggesting that this composition has a potential to be one of a promising lead-free piezoelectric candidate for dielectric and piezoelectric applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Rearrangement of Electroluminescence Spectra in Type-II n-InAs/n-InAsSbP Heterostructures

Single heterostructures of type II n{sup +}-InAs/n{sup 0}-InAs{sub 0.59}Sb{sub 0.16}P{sub 0.25}, based on an intentionally undoped epitaxial layer with an electronic type of conductivity are obtained by metalorganic vapor phase epitaxy (MOVPE). In the heterostructure, a transition layer of modulated composition is formed near the heterointerface in the bulk of the quaternary solid solution. The existence of a radiative recombination channel due to the presence of localized hole states in quantum wells formed in the transition layer near the heterointerface is shown. It is demonstrated that the maximum of the intensity of the electroluminescence spectrum of the heterostructure under study is rearranged when a forward external bias is applied. The results of this study can be used in the development of tunable light-emitting diodes operating in the midinfrared range of 2–4 μm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Determination of Some Photoluminescence Parameters of Ca(Al{sub x}Ga{sub 1 –x}){sub 2}S{sub 4}:Eu{sup 2+}

We synthesized a solid solution of Ca(Al{sub x}Ga{sub 1 – x}){sub 2}S{sub 4} activated with europium ions Eu{sup 2+}. The photoluminescence spectra and photoluminescence excitation spectra of the crystals at 300 K for x = 0.2 are measured. The dependence of the luminescence intensity on the temperature in the range of 10–300 K is investigated. Based on the experimental results, the redshift, the Stokes shift, the activation energy, and the lifetime of the Eu{sup 2+} ions are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental Liquidus Studies of the Pb-Fe-Si-O System in Equilibrium with Metallic Pb

Phase equilibria of the Pb-Fe-Si-O system have been investigated at 943 K to 1773 K (670 °C to 1500 °C) for oxide liquid in equilibrium with liquid Pb metal and solid oxide phases: (a) quartz, tridymite, or cristobalite; (b) (fayalite + tridymite) or (fayalite + spinel); (c) spinel (Fe{sub 3}O{sub 4}); (d) complex lead-iron silicates (melanotekite PbO·FeO{sub 1.5}·SiO{sub 2}, barysilite 8PbO·FeO·6SiO{sub 2}, 5PbO·FeO{sub 1.5}·SiO{sub 2}, and 6PbO·FeO{sub 1.5}·SiO{sub 2}); (e) lead silicates (Pb{sub 2}SiO{sub 4}, Pb{sub 11}Si{sub 3}O{sub 17}); (f) lead ferrites (magnetoplumbite Pb{sub 1+x}Fe{sub 12−x}O{sub 19−x} solid solution range); and (g) lead oxide (PbO, massicot). High-temperature equilibration on primary phase or iridium substrates, followed by quenching and direct measurement of Pb, Fe, and Si concentrations in the phases with the electron probe X-ray microanalysis, has been used to accurately characterize the system in equilibrium with Pb metal. All results are projected onto the PbO-“FeO”-SiO{sub 2} plane for presentation purposes. The present study is the first systematic characterization of liquidus over a wide range of compositions in this system in equilibrium with metallic Pb.

36 MATERIALS SCIENCE↗