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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Improved Crystal Quality by Detached Solidification in Microgravity

The goals of our work on detached solidification have been to: Develop a complete understanding of all of the phenomena of detached solidification; Make it possible to achieve detached solidification reproducibly; Increase crystallographic perfection through detached solidification. Specifically, we aimed in this project to: Identify a system and develop methods that would allow viewing of the melt surface and convection in the melt during detached solidification in microgravity; Improve understanding of the origination and evolution of detachment through experiments and theoretical treatments; Achieve detachment on earth. The project resulted in 14 publications, 15 presentations, completion of 2 Ph.D. theses, and completion of 2 M.S. theses. Two additional papers are currently being reviewed for publication. Copies of most of the papers are attached as appendices. Among the accomplishments are: Achievement of detached solidification of InSb on earth and determination of the conditions favoring detachment on earth. Development of a new method for coating the interior of silica growth ampoules with transparent boron nitride, which yields the high contact angles for semiconductor melts that favor detachment. Development of a new coating for the interior of Pyrex ampoules yielding very high contact angles for water and molten organic compounds. Development of a material-balance model for steady detached solidification that provides greatly improved insight into the process, both in microgravity and on earth. Dimensionless parameters were found that clarify the role of operating conditions and physical properties. The reason for the occurrence of two steady states was clarified, along with their relative stability. Observation of periodic gas tubes during directional solidification of water and organic compounds. Gas bubbles did not propagate around the periphery to yield full detachment. Failure to obtain detachment is attributed to the ready plastic deformation of these materials, so that the frozen material continues to adhere to the ampoule wall during cooling.

Regel, Liya L.↗
NASA NTRS2000

Estimation of the oxalate content of foods and daily oxalate intake

BACKGROUND: The amount of oxalate ingested may be an important risk factor in the development of idiopathic calcium oxalate nephrolithiasis. Reliable food tables listing the oxalate content of foods are currently not available. The aim of this research was to develop an accurate and reliable method to measure the food content of oxalate. METHODS: Capillary electrophoresis (CE) and ion chromatography (IC) were compared as direct techniques for the estimation of the oxalate content of foods. Foods were thoroughly homogenized in acid, heat extracted, and clarified by centrifugation and filtration before dilution in water for analysis. Five individuals consuming self-selected diets maintained food records for three days to determine their mean daily oxalate intakes. RESULTS: Both techniques were capable of adequately measuring the oxalate in foods with a significant oxalate content. With foods of very low oxalate content (<1.8 mg/100 g), IC was more reliable than CE. The mean daily intake of oxalate by the five individuals tested was 152 +/- 83 mg, ranging from 44 to 352 mg/day. CONCLUSIONS: CE appears to be the method of choice over IC for estimating the oxalate content of foods with a medium (>10 mg/100 g) to high oxalate content due to a faster analysis time and lower running costs, whereas IC may be better suited for the analysis of foods with a low oxalate content. Accurate estimates of the oxalate content of foods should permit the role of dietary oxalate in urinary oxalate excretion and stone formation to be clarified. Other factors, apart from the amount of oxalate ingested, appear to exert a major influence over the amount of oxalate excreted in the urine.

NASA Discipline Regulatory Physiology↗
NASA NTRS2006

Thermodynamic Analysis of Dual-Mode Scramjet Engine Operation and Performance

Recent analytical advances in understanding the performance continuum (the thermodynamic spectrum) for air-breathing engines based on fundamental second-law considerations have clarified scramjet and ramjet operation, performance, and characteristics. Second-law based analysis is extended specifically in this work to clarify and describe the performance characteristics for dual-mode scramjet operation in the mid-speed range of flight Mach 4 to 7. This is done by a fundamental investigation of the complex but predictable interplay between heat release and irreversibilities in such an engine; results demonstrate the flow and performance character of the dual mode regime and of dual mode transition behavior. Both analytical and computational (multi-dimensional CFD) studies of sample dual-mode flow-fields are performed in order to demonstrate the second-law capability and performance and operability issues. The impact of the dual-mode regime is found to be characterized by decreasing overall irreversibility with increasing heat release, within the operability limits of the system.

Riggins, David↗
NASA NTRS2001

Challenges and Lessons Learned in the Application of Autonomy to Space Operations

NASA's Space Operations Management Office (SOMO) is working toward a goal of providing an integrated infrastructure of mission and data services for space missions undertaken by NASA enterprises. A significant portion of this effort is focused on reducing the cost of these services. We are interested in the potential of autonomy to reduce operations costs. SOMO services support space missions, but are not part of the mission objectives; therefore the level of acceptable risk is very low. In fact, SOMO could be effective ly prevented from applying autonomy if customers merely perceive it as adding risk to their mission(s). We are interested in this workshop from the standpoint of understanding what can be done to realize the potential cost savings due to autonomy while maintaining acceptable risk and serving the needs of our customers. We would like to present our lessons learned so far in adopting autonomy and automation, which we think will contribute to clarifying the challenges facing the use of such technology. SOMO provides services to a diverse and ambitious set of mission customers. Many of these missions are groundbreaking missions for which communications, data, and other operations requirements sometimes cannot be clearly articulated early in the program. This motivates a need for systems that are robust in the face of unanticipated situations so that customer missions are not unreasonably constrained or impacted by "shortcomings" in SOMO services. One of SOMO's primary goals is to realize a paradigm in which SOMO acts as a service provider to organizations that fly space missions for NASA, other government agencies, and even the commercial sector. These organizations purchase SOMO services "by the pound" as customers. We have to provide systems that are not experiments themselves, but rather stable bases from which to do bold experiments. To this end, SOMO also seeks to work closely with industry to see that robust autonomy technology gets infused into products and services for the space industry and beyond. The potential for application of these technologies spans space-based communications networks (e.g. TDRSS) and ground-based assets including communication and tracking antenna systems, data networks, and control centers. There are several problems that are candidates for the application of autonomy, if it can be made reliable enough, including: antenna control, antenna scheduling, communication link scheduling and operation, navigation, attitude determination, fault detection, isolation, and reconfiguration (for spacecraft or ground assets), and mission-level planning and scheduling. Some attempts have been made to apply autonomy and automation in these areas in the past with varying degrees of success. We will present relevant case histories and the lessons inferred from them. Combining this past experience with anticipated future needs, we can clarify the challenges that must be met in order to realize the benefits of autonomy.

Forrest, David J.↗
NASA NTRS2012

Coincident Observation of Lightning using Spaceborne Spectrophotometer and Ground-Level Electromagnetic Sensors

The present study aims at assessing a possible new way to reveal the properties of lightning flash, using spectrophotometric data obtained by FORMOSAT-2/ISUAL which is the first spaceborne multicolor lightning detector. The ISUAL data was analyzed in conjunction with ground ]based electromagnetic data obtained by Duke magnetic field sensors, NLDN, North Alabama Lightning Mapping Array (LMA), and Kennedy Space Center (KSC) electric field antennas. We first classified the observed events into cloud ]to ]ground (CG) and intra ]cloud (IC) lightning based on the Duke and NLDN measurements and analyzed ISUAL data to clarify their optical characteristics. It was found that the ISUAL optical waveform of CG lightning was strongly correlated with the current moment waveform, suggesting that it is possible to evaluate the electrical properties of lightning from satellite optical measurement to some extent. The ISUAL data also indicated that the color of CG lightning turned to red at the time of return stroke while the color of IC pulses remained unchanged. Furthermore, in one CG event which was simultaneously detected by ISUAL and LMA, the observed optical emissions slowly turned red as the altitude of optical source gradually decreased. All of these results indicate that the color of lightning flash depends on the source altitude and suggest that spaceborne optical measurement could be a new tool to discriminate CG and IC lightning. In the presentation, we will also show results on the comparison between the ISUAL and KSC electric field data to clarify characteristics of each lightning process such as preliminary breakdown, return stroke, and subsequent upward illumination.

Adachi, Toru↗
NASA NTRS2013

Human Spaceflight Technology Needs - A Foundation for JSC's Technology Strategy

Human space exploration has always been heavily influenced by goals to achieve a specific mission on a specific schedule. This approach drove rapid technology development, the rapidity of which adds risks as well as provides a major driver for costs and cost uncertainty. The National Aeronautics and Space Administration (NASA) is now approaching the extension of human presence throughout the solar system by balancing a proactive yet less schedule-driven development of technology with opportunistic scheduling of missions as the needed technologies are realized. This approach should provide cost effective, low risk technology development that will enable efficient and effective manned spaceflight missions. As a first step, the NASA Human Spaceflight Architecture Team (HAT) has identified a suite of critical technologies needed to support future manned missions across a range of destinations, including in cis-lunar space, near earth asteroid visits, lunar exploration, Mars moons, and Mars exploration. The challenge now is to develop a strategy and plan for technology development that efficiently enables these missions over a reasonable time period, without increasing technology development costs unnecessarily due to schedule pressure, and subsequently mitigating development and mission risks. NASA's Johnson Space Center (JSC), as the nation s primary center for human exploration, is addressing this challenge through an innovative approach in allocating Internal Research and Development funding to projects. The HAT Technology Needs (TechNeeds) Database has been developed to correlate across critical technologies and the NASA Office of Chief Technologist Technology Area Breakdown Structure (TABS). The TechNeeds Database illuminates that many critical technologies may support a single technical capability gap, that many HAT technology needs may map to a single TABS technology discipline, and that a single HAT technology need may map to multiple TABS technology disciplines. The TechNeeds Database greatly clarifies understanding of the complex relationships of critical technologies to mission and architecture element needs. Extensions to the core TechNeeds Database allow JSC to factor in and appropriately weight JSC Center Core Technology Competencies, and considerations of Commercialization Potential and Partnership Potential. The inherent coupling among these, along with an appropriate importance weighting, has provided an initial prioritization for allocation of technology development research funding for JSC. The HAT Technology Needs Database, with a core of built-in reports, clarifies and communicates complex technology needs for cost effective human space exploration such that an organization seeking to assure that research prioritization supports human spaceflight of the future can be successful.

Stecklein, Jonette M.↗
NASA NTRS2013

Spacecraft Parachute Recovery System Testing from a Failure Rate Perspective

Spacecraft parachute recovery systems, especially those with a parachute cluster, require testing to identify and reduce failures. This is especially important when the spacecraft in question is human-rated. Due to the recent effort to make spaceflight affordable, the importance of determining a minimum requirement for testing has increased. The number of tests required to achieve a mature design, with a relatively constant failure rate, can be estimated from a review of previous complex spacecraft recovery systems. Examination of the Apollo parachute testing and the Shuttle Solid Rocket Booster recovery chute system operation will clarify at which point in those programs the system reached maturity. This examination will also clarify the risks inherent in not performing a sufficient number of tests prior to operation with humans on-board. When looking at complex parachute systems used in spaceflight landing systems, a pattern begins to emerge regarding the need for a minimum amount of testing required to wring out the failure modes and reduce the failure rate of the parachute system to an acceptable level for human spaceflight. Not only a sufficient number of system level testing, but also the ability to update the design as failure modes are found is required to drive the failure rate of the system down to an acceptable level. In addition, sufficient data and images are necessary to identify incipient failure modes or to identify failure causes when a system failure occurs. In order to demonstrate the need for sufficient system level testing prior to an acceptable failure rate, the Apollo Earth Landing System (ELS) test program and the Shuttle Solid Rocket Booster Recovery System failure history will be examined, as well as some experiences in the Orion Capsule Parachute Assembly System will be noted.

Stewart, Christine E.↗
NASA NTRS2022

Cloud Adjustments From Large-Scale Smoke–Circulation Interactions Strongly Modulate the Southeastern Atlantic Stratocumulus-to-Cumulus Transition

Smoke from southern Africa blankets the southeastern Atlantic Ocean from June to October, producing strong and competing aerosol radiative effects. Smoke effects on the transition between overcast stratocumulus and scattered cumulus clouds are investigated along a Lagrangian (air-mass-following) trajectory in regional climate and large eddy simulation models. Results are compared with observations from three recent field campaigns that took place in August 2017: ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES), CLouds and Aerosol Radiative Impacts and Forcing: Year 2017 (CLARIFY), and Layered Atlantic Smoke Interactions with Clouds (LASIC). The case study is set up around the joint ORACLES–CLARIFY flight that took place near Ascension Island on 18 August 2017. Smoke sampled upstream on an ORACLES flight on 15 August 2017 likely entrained into the marine boundary layer later sampled during the joint flight. The case is first simulated with the WRF-CAM5 regional climate model in three distinct setups: (1) FireOn, in which smoke emissions and any resulting smoke–cloud–radiation interactions are included; (2) FireOff, in which no smoke emissions are included; (3) RadOff, in which smoke emissions and their microphysical effects are included but aerosol does not interact directly with radiation. Over the course of the Lagrangian trajectory, differences in free tropospheric thermodynamic properties between FireOn and FireOff are nearly identical to those between FireOn and RadOff, showing that aerosol–radiation interactions are primarily responsible for the free tropospheric effects. These effects are non-intuitive: in addition to the expected heating within the core of the smoke plume, there is also a “banding” effect of cooler temperature (∼1–2 K) and greatly enhanced moisture (>2 g kg−1) at the plume top. This banding effect is caused by a vertical displacement of the former continental boundary layer in the free troposphere in the FireOn simulation resulting from anomalous diabatic heating due to smoke absorption of sunlight that manifests primarily as a few hundred meters per day reduction in large-scale subsidence over the ocean. A large eddy simulation (LES) is then forced with free tropospheric fields taken from the outputs for the WRF-CAM5 FireOn and FireOff runs. Cases are run by selectively perturbing one variable (e.g., aerosol number concentration, temperature, moisture, vertical velocity) at a time to better understand the contributions from different indirect (microphysical), “large-scale” semi-direct (above-cloud thermodynamic and subsidence changes), and “local” semi-direct (below-cloud smoke absorption) effects. Despite a more than 5-fold increase in cloud droplet number concentration when including smoke aerosol concentrations, minimal differences in cloud fraction evolution are simulated by the LES when comparing the base case with a perturbed aerosol case with identical thermodynamic and dynamic forcings. A factor of 2 decrease in background free tropospheric aerosol concentrations from the FireOff simulation shifts the cloud evolution from a classical entrainment-driven “deepening–warming” transition to trade cumulus to a precipitation-driven “drizzle-depletion” transition to open cells, however. The thermodynamic and dynamic changes caused by the WRF-simulated large-scale adjustments to smoke diabatic heating strongly influence cloud evolution in terms of both the rate of deepening (especially for changes in the inversion temperature jump and in subsidence) and in cloud fraction on the final day of the simulation (especially for the moisture “banding” effect). Such large-scale semi-direct effects would not have been possible to simulate using a small-domain LES model alone.

southeast Atlantic Ocean↗
DOE OSTI2021

GRIP: Constraint-based Explanation of Missing Answers for Graph Queries

Abstract: A useful feature in graph query engines is to clarify “Why certain entities (nodes, attribute values or edges) are missing” in query answers. This task is even more challenging when the relevant data is already missing in the underlying data source. Missing data, on the other hand, can be inferred by enforcing data constraints for graphs. We demonstrate GRIP, a system that exploits data constraints to clarify missing answers for graph queries. (1) Constraint-based ex- planation. Given a desired yet missing entity in the query answer, GRIP ensures to generate finite and minimal sequences of data con- strains (an “explanation”) that should be consecutively enforced to ?? to ensure its occurrence for the same query. (2) Answering “why” and“how” questions. Users can query GRIP with both“Why”(“Why” the element is missing) and “How” questions (“How” to refine the graph to include the missing answer). GRIP engine supports run- time generation of explanations by incrementally maintaining a set of bi-directional search trees. (3) Interactive exploration. GRIP provides a user-friendly GUI to support interactive ad visual exploration of explanations, including both automated generation and step-by-step inspection of graph manipulations.

graphs↗
DOE OSTI2022

Plant Cell Growth and Cell Wall Enlargement

Irreversible cell enlargement begins with cell wall loosening which induces wall stress relaxation, leading to cell water uptake and cell enlargement. Growing cell walls consist of a cohesive network of cellulose microfibrils embedded in hydrophilic pectins and cellulose-binding hemicelluloses. Models of the growing cell wall are provisional hypotheses about how these wall polymers interact to make a strong yet extensible wall. Recent results clarify how wall strength, plasticity and elasticity depend mostly on the stretching, straightening and sliding of cellulose microfibril networks in the wall. Passive sliding of cellulose microfibrils is facilitated by nonenzymic proteins named expansins while various enzymes modify pectins and hemicelluloses, altering their interactions with each other and with cellulose. Growth cessation is correlated with reduced expression of genes that promote wall loosening as well as changes in the direction of cellulose deposition and the structure of matrix polysaccharides, leading to a less extensible cell wall.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Identifying Photoinduced Dipolar Polarization and Orbit–Orbit Interaction between Excitons in Organic–Inorganic Hybrid Perovskites

Abstract Photoinduced polarization and orbit–orbit interaction are important issues in hybrid perovskites toward developing optoelectronic functionalities. This paper identifies that photoinduced polarization occurs in hybrid perovskites with mixed‐cation methylammonium (MA)/formamidinium (FA) (MA x FA (1− x ) PbI 3 ) by measuring bulk polarization at 1 MHz in a magnetic field. Interestingly, when the internal dipole moment is increased upon increasing the MA:FA ratio, the photoinduced dipolar polarization can be substantially enhanced, clarifying the controversial issue of whether photoexcitation can induce a dielectric polarization within dipolar polarization regime in hybrid perovskites. Furthermore, upon increasing photoinduced dipolar polarization, it is found that the intrinsic orbit–orbit interaction between excitons can be increased, revealed by monitoring photocurrent change (Δ J sc ) upon switching the photoexcitation between linear and circular polarizations. This presents that organic cations are directly involved in the orbit–orbit interaction within band structures. Clearly, the studies provide an insightful understanding of the dipole moment effects on photoinduced dipolar polarization and orbit–orbit interaction between excitons in hybrid perovskites toward controlling the optoelectronic properties.

Dou, Yixuan↗
DOE OSTI2024

Ionic‐Liquid‐Gating‐Induced Hydrogenation in Epitaxial Strontium Ferrite

Abstract Incorporating hydrogen into complex oxides holds promise for discovering exotic phenomena and novel functionalities by promoting couplings between ion and lattice/charge/spin/orbital degrees of freedom. Here, electrolyte gating‐driven hydrogenation is investigated in epitaxial brownmillerite SrFeO 2.5 thin films in which the hydrogenation‐induced lattice distortion is qualitatively different from its counterpart SrCoO 2.5 . The achievable lattice expansion in hydrogenated SrFeO 2.5 is weaker than in SrCoO 2.5 and primarily occurs along the normal of the stacked octahedral FeO 6 and tetrahedral FeO 4 layers. Upon the substitution of Fe with Co, the lattice expansion monotonically increases with increase of Co/Fe ratio, implying an intrinsic difference in accommodating hydrogen between Fe‐ and Co‐based brownmillerites. Moreover, a net magnetic moment in hydrogenated SrFeO 2.5 films is observed above room temperature, which gradually weakens with the increase of Co substitution, suggesting a stronger canted magnetism in Fe‐based hydrogenated brownmillerites. This work clarifies the electrolyte gating‐driven hydrogenation mechanisms in brownmillerite SrFeO 2.5 epitaxial thin films and those with Co substitution, particularly the deterministic role of Co/Fe ratio in the evolution of structure and properties upon hydrogenation.

Chemistry↗
DOE OSTI2020

Criteria for Realizing Room-Temperature Electrical Transport Applications of Topological Materials

The unusual electronic states found in topological materials can enable a new generation of devices and technologies, yet a long-standing challenge has been finding materials without deleterious parallel bulk conduction. This can arise either from defects or thermally activated carriers. In this study, the criteria that materials need to meet to realize transport properties dominated by the topological states, a necessity for a topological device, are clarified. This is demonstrated for 3D topological insulators, 3D Dirac materials, and 1D quantum anomalous Hall insulators, though this can be applied to similar systems. The key parameters are electronic bandgap, dielectric constant, and carrier effective mass, which dictate under what circumstances (defect density, temperature, etc.) the unwanted bulk state will conduct in parallel to the topological states. As these are fundamentally determined by the basic atomic properties, simple chemical arguments can be used to navigate the phase space to ultimately find improved materials. This will enable rapid identification of new systems with improved properties, which is crucial to designing new material systems and push a new generation of topological technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Third Dimension of Ferroelectric Domain Walls

Abstract Ferroelectric domain walls are quasi‐2D systems that show great promise for the development of nonvolatile memory, memristor technology, and electronic components with ultrasmall feature size. Electric fields, for example, can change the domain wall orientation relative to the spontaneous polarization and switch between resistive and conductive states, controlling the electrical current. Being embedded in a 3D material, however, the domain walls are not perfectly flat and can form networks, which leads to complex physical structures. In this work, the importance of the nanoscale structure for the emergent transport properties is demonstrated, studying electronic conduction in the 3D network of neutral and charged domain walls in ErMnO 3 . By combining tomographic microscopy techniques and finite element modeling, the contribution of domain walls within the bulk is clarified and the significance of curvature effects for the local conduction is shown down to the nanoscale. The findings provide insights into the propagation of electrical currents in domain wall networks, reveal additional degrees of freedom for their control, and provide quantitative guidelines for the design of domain‐wall‐based technology.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Elastic Lattice Enabling Reversible Tetrahedral Li Storage Sites in a High-Capacity Manganese Oxide Cathode

The key to breaking through the capacity limitation imposed by intercalation chemistry lies in the ability to harness more active sites that can reversibly accommodate more ions (e.g., Li + ) and electrons within a finite space. However, excessive Li-ion insertion into the Li layer of layered cathodes results in fast performance decay due to the huge lattice change and irreversible phase transformation. Here, in this study, an ultrahigh reversible capacity is demonstrated by a layered oxide cathode purely based on manganese. Through a wealth of characterizations, it is clarified that the presence of low-content Li 2 MnO 3 domains not only reduces the amount of irreversible O loss; but also regulates Mn migration in LiMnO 2 domains, enabling elastic lattice with high reversibility for tetrahedral sites Li-ion storage in Li layers. This work utilizes bulk cation disorder to create stable Li-ion-storage tetrahedral sites and an elastic lattice for layered materials, with a reversible capacity of 600 mA h g –1 , demonstrated in th range 0.6–4.9 V versus Li/Li + at 10 mA g –1 . Admittedly, discharging to 0.6 V might be too low for practical use, but this exploration is still of great importance as it conceptually demonstrates the limit of Li-ions insertion into layered oxide materials.

25 ENERGY STORAGE↗
DOE OSTI2022

Direct Exciton Harvesting from a Bound Triplet Pair

Abstract Singlet fission is commonly defined as the generation of two triplet excitons from a single absorbed photon. However, ambiguities within this definition arise due to the complexity of the various double triplet states that exist in SF chromophores and the corresponding interconversion processes. To clarify this process, singlet fission is frequently depicted as sequential two‐step conversion in which a singlet exciton decays into a bound triplet‐pair biexciton state that dissociates into two “free” triplet excitons. However, this model discounts the potential for direct harvesting from the coupled biexciton state. Here, it is demonstrated that individual triplet excitons can be extracted directly from a bound triplet pair. It is demonstrated that due to the requirement for geminate triplet–triplet annihilation in intramolecular singlet fission compounds, unique spectral and kinetic signatures can be used to quantify triplet‐pair harvesting yields. An internal quantum efficiency for triplet exciton transfer from the triplet pair of >50%, limited only by the solubility of the compounds is achieved. The harvesting process is not dependent on the net multiplicity of the triplet‐pair state, suggesting that an explicit, independent dissociation step is not a requirement for using triplet pairs to do chemical or electrical work.

Chemistry↗
DOE OSTI2025

Atomistic Mechanisms of the Crystallographic Orientation‐Dependent Cu 1.8 S Conductive Channel Formation in Cu 2 S‐Based Memristors

Achieving multiple types of resistive switching in a single material with controlled ionic motion is a key challenge in neuromorphic computing, traditionally addressed by combining materials with distinct switching behaviors. Here, Cu 2-x S is identified as a promising candidate to overcome this limitation due to its hierarchical phase transitions. Using in situ biasing experiments, reversible and non-reversible phase transitions (and resistive switching) are demonstrated in γ-Cu 2 S by controlling the compliance current. The formation of parallel high-digenite Cu 1.8 S channels, orientated along the γ-Cu 2 S [201] crystallographic direction, drives the nonvolatile resistive switching. These channels emerge via an intermediate δ-Cu 2 S phase and are stabilized at room temperature by residual strains, alongside β-Cu 2 S phase. In conclusion, the work clarifies the complex, electrically triggered phase transformations in γ-Cu 2 S, and highlights the potential of Cu 2-x S as a versatile material for neuromorphic computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Phase Synergy Enables Low‐Power Ferroelectric Switching in HfO 2 Epitaxial Films

HfO 2 -based ferroelectric materials have emerged as leading candidates for next-generation non-volatile memory technologies, owing to their nanoscale robust ferroelectricity and complementary metal–oxide–semiconductor (CMOS) compatibility. However, challenges and debates persist in advancing and comprehensively understanding their ferroelectric behavior. In particular, conventional approaches typically regard non-ferroelectric phases as detrimental and primarily focus on suppressing their formation, yet overlooking their potentially synergistic contributions—particularly those of the tetragonal (T) phase. Here, we unambiguously clarify the beneficial role of the T-phase and introduce a phase-boundary engineering strategy that deliberately harnesses it to enhance ferroelectricity in HfO 2 films. By stabilizing optimal coherent boundaries between ferroelectric orthorhombic (O) and T phases in epitaxial La-doped HfO 2 films, we achieve significant improvements in ferroelectric properties—doubling the remanent polarization (P r ∼ 30 µC/cm 2 ) and substantially reducing the coercive field (E c ∼ 3 MV/cm) by 30% compared to low-La doped samples without such boundaries. Atomic-scale electron microscopy reveals the structural nature of the atomically sharp, coherent O–T boundaries. Combined with deep-learning enhanced molecular dynamics simulations, our results unravel that these boundaries facilitate intermediate polarization states that lower the switching energy barrier. Consequently, phase coexistence shifts from an inherent drawback to a tunable design element, offering a broadly applicable route to ultra-low-power HfO 2 -based nanoelectronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗