Search NASA⌕ Search

SEARCH · Search NASA

Results for “Transitional”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Phase transition dynamics in one-dimensional halide perovskite crystals

Triiodide perovskites CsPbI 3 , CsSnI 3 , and FAPbI 3 (where FA is formamidinium) are highly promising materials for a range of optoelectronic applications in energy conversion. However, they are thermodynamically unstable at room temperature, preferring to form low-temperature (low-T) non-perovskite phases with one-dimensional anisotropic crystal structures. While such thermodynamic behavior represents a major obstacle toward realizing high-performance devices based on their high-temperature (high-T) perovskite phases, the underlying phase transition dynamics are still not well understood. In this work, we use in situ optical micro-spectroscopy to quantitatively study the transition from the low-T to high-T phases in individual CsSnI 3 and FAPbI 3 nanowires. We reveal a large blueshift in the photoluminescence (PL) peak (~38 meV) at the low-T/high-T two-phase interface of partially transitioned FAPbI 3 wire, which may result from the lattice distortion at the phase boundary. Compared to the experimentally derived activation energy of CsSnI 3 (~1.93 eV), the activation energy of FAPbI 3 is relatively small (~0.84 eV), indicating a lower kinetic energy barrier when transitioning from a face-sharing octahedral configuration to a corner-sharing one. Further, the phase propagation rate in CsSnI 3 is observed to be relatively high, which may be attributed to a high concentration of Sn vacancies. Our results could not only facilitate a deeper understanding of phase transition dynamics in halide perovskites with anisotropic crystal structures, but also enable controllable manipulation of optoelectronic properties via local phase engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The iron spin transition of deep nitrogen-bearing mineral Fe3N1.2 at high pressure

Abstract Nitrogen is an essential element for life, one of the most abundant volatiles in the atmosphere, and an important component in the Earth’s interior, where iron nitride is an essential host of deep nitrogen. Here, we investigate the pressure-induced electronic spin-pairing transition of iron in siderazot (Fe3N1.2) at pressures up to 45.8 GPa at room temperature, using diamond-anvil cell techniques coupled with synchrotron X-ray emission spectroscopy. The integrated intensity of the satellite emission peak (K′β) decreases upon compression but remains unchanged at pressures greater than 30.5 GPa. In other words, the high-spin to low-spin transition of iron in Fe3N1.2 starts immediately at very low pressures and completes at ~30.5 GPa. The iron spin transition completion pressures increase with the nitrogen concentration of hexagonal close-packed iron nitrides (i.e., Fe3N1.2, Fe7N3, and Fe2N). Moreover, the identity and concentration of light elements in binary iron-rich compounds such as Fe3N, Fe3C, Fe3P, Fe3S, Fe7C3, and Fe7N3, together with their crystal structure, could affect the iron spin transition pressures. The spin transition of iron-rich alloys could alter the bonding nature and the physical properties, including the thermal and electrical conductivity, thereby influencing the thermal state and evolution of planetary interiors.

Geochemistry & Geophysics↗
DOE OSTI2020

Coupling of Laminar-Turbulent Transition with RANS Computational Fluid Dynamics

This project combines several new concepts to create a boundary layer transition prediction capability that is suitable for analyzing modern hypersonic flight vehicles. The first new concept is the use of ''optimization'' methods to detect the hydrodynamic instabilities that cause boundary layer transition; the use of this method removes the need for many limiting assumptions of other methods and enables quantification of the interactions between boundary layer instabilities and the flow field imperfections that generate them. The second new concept is the execution of transition analysis within a conventional hypersonics CFD code, using the same mesh and numerical schemes for the transition analysis and the laminar flow simulation. This feature enables rapid execution of transition analysis with less user oversight required and no interpolation steps needed.

42 ENGINEERING↗
DOE OSTI2026

Quantum enabled precision measurements of the 229Th nuclear isomer transition (final report)

The existence of the nuclear isomer transition in thorium-229 was first inferred from keV lines in the gamma spectrum of uranium-233 decay more than 40 years ago. Over the years, the value of the transition energy has been refined with indirect measurements using nuclear physics techniques, and the current evidence points to transition energy in the laser-accessible vacuum ultra-violet region of the spectrum. At the start of this project, the two best measurements of the transition energy were 7.8±0.5 eV and 8.28±0.17 eV from high precision gamma ray spectroscopy and kinetic energy of internal conversion electrons, respectively. This project aimed to reduce the uncertainty in the transition energy to 10 meV using direct calorimetric measurements of the decay energy with superconducting nanowire single photon detectors (SNSPDs). Specifically, the method that was pursued was to generate thorium-229 in the excited isomer state by the alpha decay of uranium-233, embed the excited state thorium into an SNSPD, then detect the energy released when the isomer deexcites.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

HATS-71b: A Giant Planet Transiting an M3 Dwarf Star in TESS Sector 1

We report the discovery of HATS-71b, a transiting gas giant planet on a P=3.7955 day orbit around a G=15.35 mag M3 dwarf star. HATS-71 is the coolest M dwarf star known to host a hot Jupiter. The loss of light during transits is 4.7%, more than in any other confirmed transiting planet system. The planet was identified as a candidate by the ground-based HATSouth transit survey. It was confirmed using ground-based photometry, spectroscopy, and imaging, as well as space-based photometry from the NASA Transiting Exoplanet Survey Satellite mission (TIC 234523599). Combining all of these data, and utilizing Gaia DR2, we find that the planet has a radius of 1.024±0.018 R{sub J} and mass of 0.37 ±0.24 M{sub J} (95% confidence upper limit of <0.80 M{sub J}), while the star has a mass of 0.4861±0.0060 M{sub ⊙} and a radius of 0.4783±0.0060 R{sub ⊙}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

TESS Hunt for Young and Maturing Exoplanets (THYME). II. A 17 Myr Old Transiting Hot Jupiter in the Sco-Cen Association

We present the discovery of a transiting hot Jupiter orbiting HIP 67522 (T {sub eff} ∼ 5650 K; M {sub *} ∼ 1.2M {sub ⊙}) in the 10–20 Myr old Sco-Cen OB association. We identified the transits in the TESS data using our custom notch filter planet search pipeline and characterize the system with additional photometry from Spitzer; spectroscopy from SOAR/Goodman, SALT/HRS, LCOGT/NRES, and SMARTS/CHIRON; and speckle imaging from SOAR/HRCam. We model the photometry as a periodic Gaussian process with transits to account for stellar variability and find an orbital period of 6.9596{sub −0.000015}{sup +0.000016} days and radius of 10.02{sub −0.53}{sup +0.54} R {sub ⊕}. We also identify a single transit of an additional candidate planet with radius 8.01{sub −0.71}{sup +0.75} R {sub ⊕} that has an orbital period of ≳23 days. The validated planet HIP 67522b is currently the youngest transiting hot Jupiter discovered and is an ideal candidate for transmission spectroscopy and radial velocity follow-up studies, while also demonstrating that some young giant planets either form in situ at small orbital radii or else migrate promptly from formation sites farther out in the disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

TOI-811b and TOI-852b: New Transiting Brown Dwarfs with Similar Masses and Very Different Radii and Ages from the TESS Mission

We report the discovery of two transiting brown dwarfs (BDs), TOI-811b and TOI-852b, from NASA’s Transiting Exoplanet Survey Satellite mission. These two transiting BDs have similar masses but very different radii and ages. Their host stars have similar masses, effective temperatures, and metallicities. The younger and larger transiting BD is TOI-811b at a mass of M {sub b} = 59.9 ± 13.0M {sub J} and radius of R {sub b} = 1.26 ± 0.06R {sub J}, and it orbits its host star in a period of P = 25.16551 ± 0.00004 days. We derive the host star’s age of 93{sub −29}{sup +61} Myr from an application of gyrochronology. The youth of this system, rather than external heating from its host star, is why this BD’s radius is relatively large. This constraint on the youth of TOI-811b allows us to test substellar mass–radius evolutionary models at young ages where the radius of BDs changes rapidly. TOI-852b has a similar mass at M {sub b} = 53.7 ± 1.4M {sub J} but is much older (4 or 8 Gyr, based on bimodal isochrone results of the host star) and is also smaller with a radius of R {sub b} = 0.83 ± 0.04R {sub J}. TOI-852b’s orbital period is P = 4.94561 ± 0.00008 days. TOI-852b joins the likes of other old transiting BDs that trace out the oldest substellar mass–radius evolutionary models where contraction of the BD’s radius slows and approaches a constant value. Both host stars have a mass of M {sub ⋆} = 1.32M {sub ⊙} ± 0.05 and differ in their radii, T {sub eff}, and [Fe/H], with TOI-811 having R {sub ⋆} = 1.27 ± 0.09R {sub ⊙}, T {sub eff} = 6107 ± 77 K, and [Fe/H] = + 0.40 ± 0.09 and TOI-852 having R {sub ⋆} = 1.71 ± 0.04R {sub ⊙}, T {sub eff} = 5768 ± 84 K, and [Fe/H] = + 0.33 ± 0.09. We take this opportunity to examine how TOI-811b and TOI-852b serve as test points for young and old substellar isochrones, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Relativistic Hybrid Stars with Sequential First-order Phase Transitions in Light of Multimessenger Constraints

In this work, we consider the properties of compact stars in which quark matter has low- and high-density phases that are separated by a first-order phase transition. Thus, unlike the commonly considered case of a single phase transition from hadronic to quark matter, our models of hybrid stars contain sequential phase transitions from hadronic matter to low- and then to high-density quark matter phases. We extend our previous study of the parameter space of hybrid stars with a single phase transition to those with sequential phase transitions, taking into account the constraints on the mass and radius of neutron stars from the NICER experiment, the experimental inferences of the neutron skin thickness of the lead nucleus by the PREX-II experiment, and constraints on the tidal deformability from the gravitational-wave event GW170817. We determine the range of the masses for which both twin and triplet configurations, i.e., identical-mass stars with two and three different values of radii, arise.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Regional Analysis for an Economically and Environmentally Viable Transition to Heavy-Duty Vehicles with Alternative Powertrains

The transportation sector is responsible for a significant portion of greenhouse gas emissions. Within the sector, truck freight is responsible for a third of the associated emissions. Alternative powertrains are seen as a viable approach to significantly reduce these emissions. Prior to making a large-scale transition, it is important to consider the following questions: will the power grid support a transition to alternative powertrains?; will the transition truly reduce carbon emissions?; and will the transition impose an unnecessary economic burden on companies within the industry? The answer to these questions, however, can vary by geography, maturity/capacity of the energy distribution network or predicted vehicle load. We focus on the latter two questions, investigating the variation in estimated total cost of ownership and carbon emissions across the United States at the zip code level for both heavy-duty battery electric vehicles and heavy-duty fuel cell electric vehicles. As a benchmark, we compare estimated emissions and costs of alternative powertrain vehicles to that of conventional heavy-duty vehicles powered by diesel internal combustion engines. This work highlights areas with electric grids primed for a transition to alternative powertrain vehicles, such as the Pacific Northwest, and areas that require further infrastructure investment in renewables, such as many of the Mountain states, Missouri, and Florida. Additionally, this work illustrates the current advantages in carbon emissions of battery electric vehicles compared to fuel-cell electric vehicles, while providing insights into required regional investments for narrowing the gap.

Goulet, Nate [ORNL] (ORCID:0000000237314965)↗
DOE OSTI2024

Measuring Sustainability of Solar Modules for Energy Transition: Mass, Energy, and Circularity

Transition to a carbon-free energy system is crucial for global decarbonization and underpins Circular Economy (CE) goals. Photovoltaic (PV) technology is required for Energy Transition, but manufacturing and circular pathways can be material, energy, and carbon-intensive. Therefore, we need a prioritization of sustainability strategies for PV evolution and lifecycle management in the context of Energy Transition. This study employs a suite of quantitative metrics to compare different proposed sustainability strategies for PV modules on their ability to achieve Energy Transition. Proposals for sustainable PV range from high-yield, high-efficiency paradigms, to short-lived and fully recyclable, to long-lasting, indestructible modules. We leverage a global decarbonization deployment schedule through 2100 with the open-source PV in Circular Economy (PV ICE) tool to quantify the impacts of different evolving module design scenarios covering the range of proposed sustainability strategies. First, modules are compared on effective capacity and required replacements to meet and maintain decarbonization capacity targets through 2100. We demonstrate the effects of lifetime, degradation, and reliability on effective capacity. Next, we quantify and compare virgin material demands and lifecycle wastes, examining the impacts of lifetime and recycling rates. Finally, and critically for renewable energy technologies, we quantify the energy demands required to achieve the decarbonization capacity targets and calculate energy balance metrics (net energy, energy return on investment). These results are then summarized into a metric matrix, demonstrating tradeoffs and the importance of longevity. Our suite of mass and energy metrics provides stakeholders and decision-makers with quantitative data on circular economy choices for PV in the energy transition, enabling informed evaluation of tradeoffs of different PV module designs and CE pathways.

circular economy↗
DOE OSTI2022

Intentional and Responsible Energy Transitions: Integrating Design Choices in the Pursuit of Carbon-Neutral Futures

The transitions of energy systems to carbon neutrality are among is one of the most ambitious, complex, uncertain, significant, and transformative projects in human history. They will therefore demand extraordinarily thoughtful, informed, and careful leadership. In recent years, this project has reached an important turning point, with widespread agreement to decarbonize energy systems by 2050. We argue that the next step is to engage leaders in doing the work necessary to achieve that goal. Specifically, we argue that regional leaders, across sectors, should build collaborative initiatives to intentionally and responsibly design and advance regional energy transitions. These transitions will entail navigating uncertain and unknown terrain, requiring diverse organizations and communities to work together to chart and construct potential pathways, assess their implications, and collectively work to make progress. To address these challenges, we recommend adopting region-first, anticipatory, justice-oriented approaches. In such approachesthis process, regions can collaboratively identify, deliberate, design, and navigate toward endpoints along complex and shifting pathways that recognize that design will matter. Efuture energy systems will deeply shape and be shaped by the futures of both societies and economies. Transitions will therefore need to be inclusive, to provide broad public input into both how to proceed with transitions and the goals that guide their design.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2023

Electronic Coupling of Metal–to–Insulator Transitions in Nickelate–Based Heterostructures

In rare earth nickelates, the metal-to-insulator transition observed as a function of temperature can be described using an electronic and a structural order parameter. The electronic one is linked to the electronic disproportionation observed below the transition temperature and the structural one characterizes the breathing mode that develops in the low temperature phase. Here SmNiO 3 /NdNiO 3 superlattices are grown with insulating LaAlO 3 spacer layers to study the unusual coupling of metal-to- insulator transitions observed at SmNiO 3 /NdNiO 3 interfaces and determine the role of the two order parameters. Temperature-dependent transport measurements reveal that a single unit cell of LaAlO 3 inserted between SmNiO 3 and NdNiO 3 leads to a complete decoupling of the metal-to-insulator transitions suggesting that the order parameter controlling the coupling is the electronic one.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Communities in energy transition: exploring best practices and decision support tools to provide equitable outcomes

Abstract The U.S. coal industry has been in a state of decline for the past decade, a trend ushered by flat electricity demand, increased regulatory pressure, and market competition from cost-competitive clean energy sources. The receding economic viability of the coal industry has been acutely felt by the communities with immediate economic ties to coal-fired generation. With the energy transition underway, the question of how to engage communities as stakeholders in the decision-making process and address their needs through an equitable and just transition remains unresolved. To that end, this paper explores the economic, environmental, and social challenges presented by the energy transition at the community level, highlighting four case studies from transitioning coal-dependent communities across the United States to ultimately identify best practices in coal plant decommissioning processes. This paper weaves these community-identified best practices into two support tools—a decommissioning checklist and a redevelopment decision-making framework—that can be used to engage communities in the power plant retirement decision, the site reclamation phase, and eventual redevelopment of the site and revitalization of the surrounding community.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2026

Fragile-to-strong transition in liquid As 2 S 3 under pressure: The effect of melt metallization

The well-known classification of glass-forming melts into fragile and strong liquids has several notable exceptions, including water, silica, and certain phase-change materials (PCMs). These exceptional fluid systems exhibit a fragile-to-strong transition (FST) upon cooling: a transformation from a high-temperature liquid with fast atomic dynamics, low viscosity, and low flow activation energy, to a viscous supercooled melt with high energy barriers near the glass transition temperature T g . This behavior is critically important for non-volatile memories, photonic tensor cores, reconfigurable metamaterials, and other devices, that use PCMs, enabling nanosecond-scale crystallization in the fragile regime and long data retention in the strong regime near or below T g . A significant structural transformation is expected between these two viscosity regimes, along with a semiconductor-metal (SC-M) transition upon heating, driven by high internal pressure and associated density increase. By applying high external pressure to the canonical low-conducting chalcogenide melt As 2 S 3 , we observed both the FST and the SC-M transition, occurring simultaneously within the same domain of the P, T−phase space. These findings suggest that the FST is not limited to a few exceptional liquids but is a common phenomenon, at least in systems that exhibit melt metallization within specific regions of their P, T−phase diagrams.

first-principles molecular dynamics↗
DOE OSTI2025

Field-tunable BKT and quantum phase transitions in spin-$\frac{1}{2}$ triangular lattice antiferromagnet

Quantum magnetism is one of the most active fields for exploring exotic phases and phase transitions. The recently synthesized Na 2 BaCo(PO 4 ) 2 (NBCP) is an ideal material incarnation of the spin-$\frac{1}{2}$ easy-axis triangular lattice antiferromagnet (TLAF). Experimental evidence shows that NBCP hosts the spin supersolid state with a giant magnetocaloric effect. Theory further predicts that magnetic fields can drive NBCP through Berezinskii-Kosterlitz-Thouless (BKT) and other richer quantum phase transitions. However, detecting these transitions is challenging, as they onset at ultralow temperatures near 60 mK and require high magnetization sensitivity. Using a newly developed gradient force magnetometer in a dilution refrigerator, we mapped the magnetic susceptibility phase diagram down to 30 mK. Our results provide a more comprehensive and accurate understanding of BKT melting of spin supersolidity and several field-tunable quantum phase transitions, which establish NBCP as a model platform for frustrated magnetism and highlight potential applications of its giant magnetocaloric effects.

BKT transition↗
DOE OSTI2021

Structural Phase Transitions of NbO 2 : Bulk versus Surface

The metal to insulator transition of NbO 2 has been predicted to be a result of a structural phase transition (SPT) governed by Peierls physics. However, direct observation of the SPT using experimental techniques is still restricted by the extremely high transition temperature (810 °C) and the proclivity for NbO 2 to oxidize into Nb 2 O 5 above 400 °C when exposed to air. In this work, we address these issues and employ temperature-dependent X-ray spectroscopy to describe the SPT of NbO 2 from the bulk to surface. Temperature-dependent extended X-ray absorption fine structure spectroscopy (T-EXAFS) reveals a gradual weakening of the bulk Nb dimers over a large temperature range, which is indicative of a second-order Peierls mechanism. From these measurements, we determine the critical dimer distance to be 2.77 Å. Our T-EXAFS observations are supported by density functional theory of the phonon dispersion and the electronic density of states of NbO 2 , which conclude that the dimerization is responsible for the insulating phase. The dimerization does not extend to the topmost layers, where an oxygen rich surface reconstruction is preferred irrespective of temperature even in extremely reducing environments; changes in the low-energy electron diffraction patterns are attributed to oxygen concentration and are independent of the underlying bulk phase transitions of NbO 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

In Situ Imaging of an Anisotropic Layer-by-Layer Phase Transition in Few-Layer MoTe 2

Understanding the phase transition mechanisms in two-dimensional (2D) materials is a key to precisely tailor their properties at the nanoscale. Molybdenum ditelluride (MoTe 2 ) exhibits multiple phases at room temperature, making it a promising candidate for phase-change applications. Here, we fabricate lateral 2H–T d interfaces with laser irradiation and probe their phase transitions from micro- to atomic scales with in situ heating in the transmission electron microscope (TEM). By encapsulating the MoTe 2 with graphene protection layers, we create an in situ reaction cell compatible with atomic resolution imaging. We find that the T d -to-2H phase transition initiates at phase boundaries at low temperatures (200–225 °C) and propagates anisotropically along the b-axis in a layer-by-layer fashion. We also demonstrate a fully reversible 2H-T d -2H phase transition cycle, which generates a coherent 2H lattice containing inversion domain boundaries. Furthermore, our results provide insights on fabricating 2D heterophase devices with atomically sharp and coherent interfaces.

2D materials↗
DOE OSTI2020

Phase Transition in a Memristive Suspended MoS 2 Monolayer Probed by Opto- and Electro-Mechanics

Semiconducting monolayers of a 2D material are able to concatenate multiple interesting properties into a single component. Here, by combining opto-mechanical and electronic measurements, we demonstrate the presence of a partial 2H–1T' phase transition in a suspended 2D monolayer membrane of MoS 2 . Electronic transport shows unexpected memristive properties in the MoS 2 membrane, in the absence of any external dopants. A strong mechanical softening of the membrane is measured concurrently and may only be related to the 2H–1T' phase transition, which imposes a 3% directional elongation of the topological 1T' phase with respect to the semiconducting 2H. We note that only a few percent 2H–1T' phase switching is sufficient to observe measurable memristive effects. Our experimental results combined with first-principles total energy calculations indicate that sulfur vacancy diffusion plays a key role in the initial nucleation of the phase transition. Our study clearly shows that nanomechanics represents an ultrasensitive technique to probe the crystal phase transition in 2D materials or thin membranes. Lastly, a better control of the microscopic mechanisms responsible for the observed memristive effect in MoS 2 is important for the implementation of future devices.

2D materials↗