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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Photoluminescence spectroscopy of Cr 3+ in β-Ga 2 O 3 and (Al 0.1 Ga 0.9 ) 2 O 3

Alloying β-Ga 2 O 3 with Al 2 O 3 to create (Al x Ga 1–x ) 2 O 3 enables ultra-wide bandgap materials suitable for applications deep into ultraviolet. In this work, photoluminescence (PL) spectra of Cr 3+ were investigated in monoclinic single crystal β-Ga 2 O 3 , and 10 = mol. % Al 2 O 3 alloyed with β-Ga 2 O 3 , denoted β-(Al 0.1 Ga 0.9 ) 2 O 3 or AGO. Temperature-dependent PL properties were studied for Cr 3+ in AGO and β-Ga 2 O 3 from 295 to 16 K. For both materials at room temperature, the red-line emission doublet R 1 and R 2 occurs at 696 nm (1.78 eV) and 690 nm (1.80 eV), respectively, along with a broad emission band at 709 nm (1.75 eV). Here, the linewidths for AGO are larger for all temperatures due to alloy broadening. For both materials, the R-lines blue-shift with decreasing temperature. The (lowest energy) R 1 line is dominant at low temperatures due to the thermal population of the levels. For temperatures above ~50 K, however, the ratio of R 2 to R 1 peak areas is dominated by nonradiative combination.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Communication—Dissolution and Passivation of a Ni-Cr-Fe-Ru-Mo-W High Entropy Alloy by Elementally Resolved Electrochemistry

The formation and dissolution of the passive film on a novel NiCrFeRuMoW high entropy alloy in H 2 SO 4 was measured with atomic emission spectroelectrochemistry. Passivation involved Cr and Ru enrichment, whether passivation was achieved spontaneously at open circuit or by potentiostatic step into the passive domain. The other elements, Ni, Fe, Mo, and W, dissolved at rates approximately proportional to their bulk concentrations. The air formed film showed only a Cr enrichment. Excellent corrosion resistance properties were indicated by spontaneous passivation, the low passive current in the polarization curve, and the absence of detectable elemental dissolution during the active peak.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Supercontinuum generation in oxide and semiconductor materials (InP, Si, GaN, GaAs, PbMoO 4 , YVO 4 , ZGP, TiO 2 , diamond) pumped by radiation of the Cr:ZnS fs-MOPA system

Ultrashort light sources in the middle-infrared range are highly beneficial for applications such as gas molecular spectroscopy, remote sensing, atmospheric science, medical treatments, and light–matter interaction studies. Ultrafast lasers utilizing chromium-doped ZnS/Se (Cr:ZnS/Se) have proven to be robust and stable solutions within this spectral region. Nonlinear spectral broadening is fundamentally important, as it pushes the pulse duration limits imposed by the bandwidth of laser media. In this study, we demonstrate the spectral broadening and supercontinuum generation in several bulk materials, including InP, Si, GaN, GaAs, PbMoO 4 , YVO 4 , diamond, and TiO 2 , using pump radiation with up to 4 W average power centered at 2.35 µm from a Cr:ZnS femtosecond MOPA system. Some of the investigated materials have excellent potential as effective media for middle-infrared supercontinuum generation, demonstrating the feasibility of developing a single-cycle pulse middle-infrared laser system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Single-pass Cr:ZnSe amplifier for broadband infrared undulator radiation

An amplifier based on a highly-doped chromium zinc-selenide (Cr:ZnSe) crystal is proposed to increase the pulse energy emitted by an electron bunch after it passes through an undulator magnet. The primary motivation is a possible use of the amplified undulator radiation emitted by a beam circulating in a particle accelerator storage ring to increase the particle beam’s phase-space density—a technique dubbed optical stochastic cooling (OSC). This paper uses a simple four energy level model to estimate the single-pass gain of Cr:ZnSe and presents numerical calculations combined with wave-optics simulations of undulator radiation to estimate the expected properties of the amplified undulator wave-packet.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Kerr-lens mode-locked Cr:ZnS oscillator reaches the spectral span of an optical octave

We report, to the best of our knowledge, the first super-octave femtosecond polycrystalline Cr:ZnS laser at the central wavelength 2.4 µm. The laser is based on a non-polarizing astigmatic X-folded resonator with normal incidence mounting of the gain element. The chromatic dispersion of the resonator is controlled with a set of dispersive mirrors within one third of an optical octave over 2.05–2.6 µm range. The resonator’s optics is highly reflective in the range 1.8–2.9 µm. The components of the oscillator’s output spectrum at the wavelengths 1.6 µm and 3.2 µm are detected at –60 dB with respect to the main peak. Average power of few-cycle Kerr-lens mode-locked laser is 1.4 W at the pulse repetition frequency 79 MHz. That corresponds to 22% conversion of cw radiation of Er-doped fiber laser, which we used for optical pumping of the Cr:ZnS oscillator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

350 mJ electro-optically Q-switched 2.79 µm Cr:Er:YSGG MOPA

We report on developing three flashlamp-pumped electro-optically Q-switched Cr:Er:YSGG lasers with the Q-switch based on a La 3 Ga 5 SiO 14 crystal. The “short” laser cavity was optimized for high peak power applications. In this cavity, 300 mJ output energy in 15 ns pulses at a 3 Hz repetition rate was demonstrated with pump energy below 52 J. However, several applications, such as Fe:ZnSe pumping in a gain-switched regime, require longer (∼ 100 ns) pump pulse duration. We developed a 2.9 m long laser cavity that delivers 190 mJ of output energy in 85 ns pulses for these applications. We also demonstrated the Cr:Er:YSGG MOPA system producing 350 mJ output energy at 90 ns pulse duration and 47.5 J of pumping, corresponding to an amplification factor of 3.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Cross-section of electrical impact excitation in bulk n-type monocrystalline Al:Cr:ZnSe

Middle-infrared luminescence of bulk Al:Cr:ZnSe crystal under direct electrical excitation of Cr 2+ , 5 E− 5 T 2 transition, is reported. Effective cross-section of electrical excitation was estimated based on comparative luminescence measurements under electrical and optical (1560 nm) excitations. Calculation of the threshold current density for lasing under electrical excitation of this material was also performed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

4D evolution of Cr 23 C 6 precipitates in neutron-irradiated and annealed HT-UPS steel observed via synchrotron micro-computed tomography

High-temperature-ultrafine precipitate strengthened (HT-UPS) steel is a potential structural material for advanced nuclear reactors; however, its irradiation response is not well understood. This research provides insight into irradiation-induced effects, such as precipitate evolution mechanisms and four-dimensional morphological evolution, in HT-UPS steel using synchrotron micro-computed tomography. Identical specimens were characterized pre-irradiation and post-irradiation following neutron exposure up to 0.3 displacements per atom at 600 °C. Irradiation effects were also differentiated from the annealing response of precipitates. Following neutron irradiation, the average Cr 23 C 6 precipitate size reduced, affected by the synergy of nucleation and growth, ballistic dissolution, and inverse coarsening, which was observed at fluences an order of magnitude lower than previously observed. Annealing at 600 °C for 32 h increased the average Cr 23 C 6 precipitate size and decreased the phase fraction, attributed to precipitate coarsening. The precipitate morphology evolution and resultant mechanisms can be utilized to parameterize and validate microstructural models simulating radiation damage or annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

AmeriFlux FLUXNET-1F CR-Fsc Filadelfia sugar cane cropland

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CR-Fsc Filadelfia sugar cane cropland. This is the FLUXNET version of the carbon flux data for the site CR-Fsc Filadelfia sugar cane cropland produced by applying the standard ONEFlux (1F) software. Site Description - The research site is located in a sugar cane cropland generally harvested in December. Sugarcane is irrigated(furrow irrigation) sporadically only during the dry season (January-April).Crop height varies from 0m to 4m.

Johnson, Mark [University of British Columbia]↗
DOE OSTI2024

Mechanical creep testing and characterization of Cr coated Zircaloy

Zirconium based cladding has been developed for use in light water reactor fuel applications due to the material’s desirable low neutron scattering cross section. To help improve corrosion resistance in accident conditions, such as a loss of coolant accident (LOCA), a chromium coating can be applied to the outer diameter of the Zircaloy tube. Cladding strength at reactor relevant temperatures is important for the structural performance. Stress relaxation creep testing was performed on Cr coated Zircaloy-4 to measure strain rate as a function of stress for 350 and 650°C. These were performed at both 5 ± 1 % and 7.5 ± 1 % strain. The lower temperature provides results near normal operating temperature, while the higher temperature provides results relevant to off-normal conditions where recrystallization will take place. Characterization was also performed to analyze the structure of the Cr coating and Zircaloy-4 as well as the interface between the two.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Effect of Silicon on High Temperature Oxidation of Fe-Cr-Si Alloys in Carbon Dioxide Environments

Supercritical carbon dioxide offers the potential for efficient and sustainable power generation. Identifying materials that can be used to construct the high temperature portions of the cycle is a barrier to developing this technology. Various Fe-Cr alloys have been identified as promising construction materials due to a favorable combination of high temperature strength, commercial availability, and cost. The effect of minor alloying elements, particularly Si, has been shown to significantly impact the oxidation and carburization processes for these alloys after relatively short duration exposures in hot carbon dioxide. The long-term impact is less understood, making it challenging to predict performance of real components that will be in service for many years. The objectives in this project are to better understand the long-term oxidation and carburization behavior of Fe-Cr alloys and the important role of Si; to enhance the existing body of literature on the long-term exposure of alloys to hot carbon dioxide; and enable lifetime predictions for future supercritical carbon dioxide power cycle components.

Menna, Valerie↗
DOE OSTI2025

The Effect of Thermal Aging on the Performance of High-Cr Ni-based Alloys in Primary Water Environment

Nickel-based Alloy 690, and the associated weld Alloys 52 and 152, are used for nozzle penetrations in replacement heads for pressurized water reactor (PWR) vessels. They are chosen for their excellent overall resistance to general corrosion and environmental degradation, primarily stress corrosion cracking (SCC). However, many of the existing PWRs are expected to operate beyond their first or second license renewal (e.g., 40 to 60 years or beyond 60 years). Hence, the thermal stability of Ni-Cr alloys is a potential concern for the long-term performance of both existing and advanced nuclear power plants. Moreover, Ni-Cr alloys are being considered for high-level radioactive waste disposal containers that will be required to contain the waste for at least 10,000 years.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Microstructure, electrical resistivity, and tensile properties of neutron-irradiated Cu–Cr–Nb–Zr

High strength, high conductivity copper alloys that can resist creep at high temperatures are one of the primary candidates for efficient heat exchangers in fusion reactors. Cu–Cr–Nb–Zr (CCNZ) alloys, which were designed to improve the strength and creep life of ITER Cu–Cr–Zr (CCZ) reference alloys, have been found to have comparable electrical conductivity and tensile properties to CCZ alloys. The measured creep rupture times for these improved alloys is about ten times higher than the ITER reference alloys at 90–125 MPa at 500 °C. However, the effects of neutron irradiation on these alloys, and the ensuing material properties, have not been studied; thus, their utility in a fusion reactor environment is not well understood. This study characterizes the room temperature mechanical and electrical properties of a neutron-irradiated CCNZ alloy and compares them to a neutron-irradiated ITER reference heat sink CCZ alloy. Tensile specimens were neutron irradiated in the High Flux Isotope Reactor (HFIR) to 5 dpa between 250 °C and 325 °C. Post-irradiation characterization included electrical resistivity measurements, hardness, and tensile tests. Microstructural evaluation used scanning electron microscopy, energy dispersive x-ray spectroscopy, and atom probe tomography to characterize the irradiation-produced changes in the microstructure and investigate the mechanistic processes leading to post-irradiation properties. Transmutation calculations were validated with composition measurements from atom probe data and used to calculate contributions to the increased electrical resistivity measured after irradiation. Comparisons with CCZ alloys in the same irradiation heat found that the post-irradiated CCNZ and CCZ alloys had comparable electrical resistivity. Although CCNZ alloys suffered more irradiation hardening than CCZ, the overall tensile behavior deviated very little from non-irradiated values in the temperature range studied.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nematic Fluctuations in the Non-Superconducting Iron Pnictide BaFe 1.9-x Ni 0.1 Cr x As 2

The main driven force of the electronic nematic phase in iron-based superconductors is still under debate. Here, we report a comprehensive study on the nematic fluctuations in a non-superconducting iron pnictide system BaFe 1.9-x Ni 0.1 Cr x As 2 by electronic transport, angle-resolved photoemission spectroscopy (ARPES), and inelastic neutron scattering (INS) measurements. Previous neutron diffraction and transport measurements suggested that the collinear antiferromagnetism persists to x = 0.8, with similar Néel temperature TN and structural transition temperature Ts around 32 K, but the charge carriers change from electron type to hole type around x = 0.5. In this study, we have found that the in-plane resistivity anisotropy also highly depends on the Cr dopings and the type of charge carriers. While ARPES measurements suggest possibly weak orbital anisotropy onset near Ts for both x = 0.05 and x = 0.5 compounds, INS experiments reveal clearly different onset temperatures of low-energy spin excitation anisotropy, which is likely related to the energy scale of spin nematicity. These results suggest that the interplay between the local spins on Fe atoms and the itinerant electrons on Fermi surfaces is crucial to the nematic fluctuations of iron pnictides, where the orbital degree of freedom may behave differently from the spin degree of freedom, and the transport properties are intimately related to the spin dynamics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Surface Electronic Structure of Cr Doped Bi 2 Se 3 Single Crystals

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi 2-x Cr x Se 3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi 2 Se 3 . These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis of Nano-Oxide Precipitates by Implantation of Ti, Y and O Ions in Fe-10%Cr: Towards an Understanding of Precipitation in Oxide Dispersion-Strengthened (ODS) Steels

The properties of oxide dispersion-strengthened steels are highly dependent on the nature and size distribution of their constituting nano-oxide precipitates. A fine control of the processes of synthesis would enable the optimization of pertinent properties for use in various energy systems. This control, however, requires knowledge of the precise mechanisms of nucleation and growth of the nanoprecipitates, which are still a matter of debate. In the present study, nano-oxide precipitates were produced via the implantation of Y, Ti, and O ions in two different sequential orders in an Fe-10%Cr matrix that was subsequently thermally annealed. The results show that the oxides that precipitate are not necessarily favoured thermodynamically, but rather result from complex kinetics aspects related to the interaction between the implanted elements and induced defects. When Y is implanted first, the formation of nanoprecipitates with characteristics similar to those in conventionally produced ODS steels, especially with a core/shell structure, is evidenced. In contrast, when implantation starts with Ti, the precipitation of yttria during subsequent high-temperature annealing is totally suppressed, and corundum Cr 2 O 3 precipitates instead. Moreover, the systematic involvement of {110} matrix planes in orientation relationships with the precipitates, independently of the precipitate nature, suggests matrix restriction effects on the early stages of precipitation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of Production Bias on Radiation-Induced Segregation in Ni-Cr Alloys

We present an in-depth investigation into the Radiation-Induced Segregation (RIS) phenomenon in Ni-Cr alloys. All the pivotal factors affecting RIS such as surface’s absorption efficiency, grain size, production bias, dose rate, temperature, and sink density were systematically studied. Through comprehensive simulations, the individual and collective impacts of these factors were analyzed, enabling a refined understanding of RIS. A notable finding was the significant influence of production bias on point defects’ interactions with grain boundaries/surfaces, thereby playing a crucial role in RIS processes. Production bias alters the neutrality of these interactions, leading to a preferential absorption of one type of point defect by the boundary and consequent establishment of distinct surface-mediated patterns of point defects. These spatial patterns further result in non-monotonic spatial profiles of solute atoms near surfaces/grain boundaries, corroborated by experimental observations. In particular, a positive production bias, signifying a higher production rate of vacancies over interstitials, drives more Cr depletion at the grain boundary. Moreover, a temperature-dependent production bias must be considered to recover the experimentally reported dependence of RIS on temperature. The severity of radiation damage and RIS becomes more pronounced with increased production bias, dose rate, and grain size, while high temperatures or sink density suppress the RIS severity. Model predictions were validated against experimental data, showcasing robust qualitative and quantitative agreements. The findings pave the way for further exploration of these spatial dependencies in subsequent studies, aiming to augment the comprehension and predictability of RIS processes in alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Presence of Induced Weak Ferromagnetism in Fe-Substituted YFe x Cr 1–x O 3 Crystalline Compounds

Fe-substituted YFe x Cr 1–x O 3 crystalline compounds show promising magnetic and multiferroic properties. Here we report the synthesis and characterization of several compositions from this series. Using the autocombustion route, various compositions (x = 0.25, 0.50, 0.6, 0.75, 0.9, and 1) were synthesized as high-quality crystalline powders. In order to obtain microscopic and atomic information about their structure and magnetism, characterization was performed using room temperature X-ray diffraction and energy dispersion analysis as well as temperature-dependent neutron diffraction, magnetometry, and 57 Fe Mössbauer spectrometry. Rietveld analysis of the diffraction data revealed a crystallite size of 84 (8) nm for YFeO 3 , while energy dispersion analysis indicated compositions close to the nominal compositions. The magnetic results suggested an enhancement of the weak ferromagnetism for the YFeO 3 phase due to two contributions. First, a high magnetocrystalline anisotropy was associated with the crystalline character that favored a unique high canting angle of the antiferromagnetic phase (13°), as indicated by the neutron diffraction analysis. This was also evidenced by the high magnetic hysteresis curves up to 90 kOe by a remarkable high critical coercivity value of 46.7 kOe at room temperature. Second, the Dzyaloshinskii–Moriya interactions between homogenous and heterogeneous magnetic pairs resulted from the inhomogeneous distribution of Fe 3+ and Cr 3+ ions, as indicated by 57 Fe Mössbauer studies. Together, these results point to new methods of controlling the magnetic properties of these materials.

36 MATERIALS SCIENCE↗