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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

CoSn-type NiIn1–xSbx (0 ≤ x ≤ 0.17): Site-Selective Substitution, Electronic Structure, Chemical Bonding, and Structural Transformation

CoSn-type intermetallic compounds have emerged as a model platform for Kagome-derived flat-band physics, where subtle chemical perturbations can strongly influence electronic structure and phase stability. Here, we present a combined experimental and theoretical study of Sb-substitution in CoSn-type NiIn1–xSbx (0 ≤ x ≤ 0.17) to elucidate the interplay between site selectivity, solubility limit, chemical bonding, and electronic structure. Rietveld refinements on Neutron powder diffraction data confirmed the selective Sb-substitution at the electron-rich In2 (2d) site forming the honeycomb substructure, while the In1 (1a) site within the Kagome layer remains exclusively occupied by In. Density functional theory (DFT) calculations revealed that pristine CoSn-type NiIn hosts Ni 3d-dominated flat bands near the Fermi level (EF), originating from the Kagome-like Ni substructure. Partial replacement of In by Sb within the honeycomb layer alters these flat-band features below EF, reducing the density of states and suppressing the flat-band topology near the Fermi level. Orbital-resolved electronic structure and chemical-bonding analyses show that Sb-substitution enhances Ni-p-block (In/Sb) covalency and optimizes charge compensation, stabilizing the CoSn-type structure up to the solubility limit x ≈ 0.17. Beyond the limit, the higher-Sb compositions show satellite reflections consistent with an incommensurately modulated phase. These results establish a link between site-selective chemical substitution, bonding optimization, and flat-band electronic structure evolution, providing fundamental insights into how chemical substitution influences the electronic properties of Kagome-based intermetallic compounds.

Roy, Nilanjan [National Institute of Technology Si↗
NASA NTRS1987

COSMIC

The design goals of the COSMIC spaceborne telescope array concept are outlined. These include a high degree of structural stiffness, a wide field of view, and a broad wavelength band. These properties directly enhance the scientific productivity and technical reliability of the array. If a sufficiently stiff structure can be designed, COSMIC can operate as a phased array; if the structure relaxes before it can be rephased on a reference star, it degrades to a coherent array. The COSMIC engineering study suggests that passively-stabilized, phased arrays are feasible.

Traub, Wesley A.↗
NASA NTRS2004

Effect of Sintering on Mechanical and Physical Properties of Plasma-Sprayed Thermal Barrier Coatings

The effect of sintering on mechanical and physical properties of free-standing plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings (TBCs) was determined by annealing them at 1316 C in air. Mechanical and physical properties of the TBCs, including strength, modes I and II fracture toughness, elastic modulus, Poisson s response, density, microhardness, fractography, and phase stability, were determined at ambient temperature as a function of annealing time ranging from 0 to 500 h. All mechanical and physical properties, except for the amount of monoclinic phase, increased significantly in 5 to 100 h and then reached a plateau above 100 h. Annealing resulted in healing of microcracks and pores and in grain growth, accompanying densification of the TBC s body due to the sintering effect. However, an inevitable adverse effect also occurred such that the desired lower thermal conductivity and good expansivity, which makes the TBCs unique in thermal barrier applications, were degraded upon annealing. A model was proposed to assess and quantify all the property variables in response to annealing in a normalized scheme. Directionality of as-sprayed TBCs appeared to have an insignificant effect on their properties, as determined via fracture toughness, microhardness, and elastic modulus measurements.

Choi, Sung R.↗
DOE OSTI2025

Enhancing stability, magnetic anisotropy, and coercivity of manganese aluminum: Machine learning, ab initio , and micromagnetic modeling

The binary manganese aluminum (MnAl) alloy with L⁢1 0 crystal structure is a promising rare earth (RE) element-free permanent magnetic material because of its exceptional magnetic properties. However, experimentally synthesizing it in a stable bulk form is extremely challenging. Here, in this study, an alternative method of stabilizing the material, a pathway for experimental synthesis and validation, is proposed and theoretically verified. This is done by partially substituting Mn and Al sites with Fe and Ni and identifying its enhanced phase stability, saturation magnetization density, magnetic anisotropy, and coercivity from density functional theory (DFT), machine learning (ML) crystal graph convolution neural network (CGCNN), and micro-magnetic modeling. When considering a fixed 50% Ni, the magnetic anisotropy increases with the increasing Fe content but decreases the formation energy. The calculated formation energies, elastic constants, and phonon frequencies demonstrate that the binary and quaternary compositions are stable. Most importantly, in 50% Fe and Ni-substituted-equiatomic phase, magnetic anisotropy constants and saturation magnetization density increase by 56% and 23% as compared to the MnAl. Further, the coercivity of the equiatomic phase predicted with micro-magnetic modeling is higher by 17% than the parent compound.

Bhandari, Churna [Ames National Laboratory, and Io↗
NASA NTRS2007

Effects of Exposures on Superalloys for Space Applications

The industry is demanding longer term service at high temperatures for nickel-base superalloys in gas turbine engine as well as potential space applications. However, longer term service can severely tax alloy phase stability, to the potential detriment of mechanical properties. Cast Mar-M247LC and wrought Haynes 230 superalloys were exposed and creep tested for extended times at elevated temperature. Microstructure and phase evaluations were then undertaken for comparisons.

Gabb, Tim↗
NASA NTRS2005

Multicomponent, Rare-Earth-Doped Thermal-Barrier Coatings

Multicomponent, rare-earth-doped, perovskite-type thermal-barrier coating materials have been developed in an effort to obtain lower thermal conductivity, greater phase stability, and greater high-temperature capability, relative to those of the prior thermal-barrier coating material of choice, which is yttria-partially stabilized zirconia. As used here, "thermal-barrier coatings" (TBCs) denotes thin ceramic layers used to insulate air-cooled metallic components of heat engines (e.g., gas turbines) from hot gases. These layers are generally fabricated by plasma spraying or physical vapor deposition of the TBC materials onto the metal components. A TBC as deposited has some porosity, which is desirable in that it reduces the thermal conductivity below the intrinsic thermal conductivity of the fully dense form of the material. Undesirably, the thermal conductivity gradually increases because the porosity gradually decreases as a consequence of sintering during high-temperature service. Because of these and other considerations such as phase transformations, the maximum allowable service temperature for yttria-partially stabilized zirconia TBCs lies in the range of about 1,200 to 1,300 C. In contrast, the present multicomponent, rare-earth-doped, perovskite-type TBCs can withstand higher temperatures.

Miller, Robert A.↗
NASA NTRS2004

Thermal Conductivity and Water Vapor Stability of Ceramic HfO2-Based Coating Materials

HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2-15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications will also be discussed.

Zhu, Dong-Ming↗
DOE OSTI2026

Temperature‐Dependent Crystallization in Two‐Step Perovskite Deposition Revealed by In Situ GIWAXS and Machine Learning‐Guided Analysis

The performance and stability of perovskite solar cells are strongly governed by the crystallization behavior of their active layer. In two-step sequential deposition, early-stage film formation plays a decisive role in determining final phase purity and device quality. Guided by a data-driven analysis of nearly 39 000 devices in the FAIR perovskite database, we identified solvent-mediated quenching and thermal processing as key variables affecting power conversion efficiency (PCE), particularly in two-step fabrication. Here, to investigate these effects in real time, we designed and implemented a custom-built, temperature-controlled spin-coating system, enabling precise thermal modulation during precursor deposition. Using this platform, we performed in situ GIWAXS measurements to study the crystallization dynamics of FA 0.5 MA 0.5 PbI 3 films over a temperature range of 30°C–90°C. Our results reveal a non-monotonic relationship between spin-coating temperature and α-phase formation, governed by the interplay between precursor interdiffusion, PbI 2 crystallinity, and δ-phase suppression. The custom thermal control enabled us to isolate and quantify these competing effects during the earliest stages of film formation, providing mechanistic insight into how spin-coating temperature governs both phase purity and kinetic pathways in two-step perovskite systems. Temperature-dependent SEM and photovoltaic device measurements further demonstrate that early-stage crystallization pathways directly translate into differences in morphology, charge-transport continuity, and device performance. These findings inform targeted strategies for optimizing deposition protocols to balance rapid nucleation, phase stability, and device performance.

Saadawy, Ahmed [King Fahd University of Petroleum ↗
NASA NTRS2013

Calcium-Magnesium-Aluminosilicate (CMAS) Reactions and Degradation Mechanisms of Advanced Environmental Barrier Coatings

The thermochemical reactions between calcium-magnesium-aluminosilicate- (CMAS-) based road sand and several advanced turbine engine environmental barrier coating (EBC) materials were studied. The phase stability, reaction kinetics and degradation mechanisms of rare earth (RE)-silicates Yb2SiO5, Y2Si2O7, and RE-oxide doped HfO2 and ZrO2 under the CMAS infiltration condition at 1500 C were investigated, and the microstructure and phase characteristics of CMAS-EBC specimens were examined using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Experimental results showed that the CMAS dissolved RE-silicates to form crystalline, highly non-stoichiometric apatite phases, and in particular attacking the silicate grain boundaries. Cross-section images show that the CMAS reacted with specimens and deeply penetrated into the EBC grain boundaries and formed extensive low-melting eutectic phases, causing grain boundary recession with increasing testing time in the silicate materials. The preliminary results also showed that CMAS reactions also formed low melting grain boundary phases in the higher concentration RE-oxide doped HfO2 systems. The effect of the test temperature on CMAS reactions of the EBC materials will also be discussed. The faster diffusion exhibited by apatite and RE-doped oxide phases and the formation of extensive grain boundary low-melting phases may limit the CMAS resistance of some of the environmental barrier coatings at high temperatures.

Ahlborg, Nadia L.↗
NASA NTRS2019

Ka-band Phase Measurement System for SWOT Mission

The KaRIn (Ka-band radar interferometer) instrument for SWOT (surface water ocean topography) mission faces unique challenges in terms of phase stability and group delay stability requirements to achieve centimeter level accuracy for height measurements. Conventional altimetry assumes nadir point return and measures a single range. SWOT will require additional angle of arrival information to provide swath coverage. Errors in differential phase and common group delay can both act as primary sources of systematic errors in determining the height using interferometric data. The ground support equipment (GSE) necessary for the performance requirements verification gets a fraction of the error allocation from the instrument. A phase measurement system capable of measuring millidegrees and working with pulsed excitation is developed and the preliminary results are described in this paper.

Esteban-Fernandez, Daniel↗
DOE OSTI2026

Equation of state for Hf, Ta, W, Re, Os, Ir, Pt, and Au to multi-terapascal pressures from density-functional theory

We present the zero-temperature equation of state (pressure dependence of compression) and phase stability predictions for the 5d-transition metals obtained from all-electron density-functional theory (DFT) calculations. The results compare favorably with experiments but extend beyond current experimental capabilities to 10 TPa. Our study reveals phase changes that are explained from the calculated electronic structure. The cubic face-centered and body-centered structures (fcc and bcc), together with two-, three-, and four-layered hexagonal structures, play major roles under compression. The results’ dependence on the electron exchange and correlation in the DFT approach is investigated, and it is shown that the impact of the choice, while significant at lower pressures, diminishes in the terapascal regime. We further illustrate that the normal parabolic trends in atomic volume and bulk modulus with atomic number, due to the occupation of bonding and anti-bonding 5d states, break down at TPa pressures, suggesting drastically different chemical bonding at these extreme conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1992

A new ordered tetragonal phase in the Ti3Al+Nb system

Results are reported from an experimental study of phase stability in a plasma-sprayed Ti3Al+Nb alloy using TEM and electron diffraction techniques. The alloys was produced from Ti3Al+Nb powder via an inductively coupled plasma deposition process. Evidence was found for the ordering of the B2 phase to a structure similar to the DO3-type phase, but with a tetragonal distortion. An ordered tetragonal phase (T) is proposed to account for these observations, and the existence of the B2 - T ordering transformation in the Ti3Al+Nb system is suggested. The T phase can be regarded as a DO3-like phase with a tetragonal distortion. The tegragonality c0/a0 is approximately equal to 1.02, and a0 equals 0.65 +/-0.01 nm.

Hsiung, L. M.↗
DOE OSTI2025

Enhanced Ion Transport and Molecular Packing Stability in Asymmetric 2D Nanostructured π‐Conjugated Thieno[3,2‐b]Thiophene‐Based Liquid Crystal

Organic semiconductors based on liquid crystal (LC) molecules have attracted increasing interest. Here, in this work, two linear LCs based on 2,5‐bis(thien‐2‐yl)thieno[3,2‐b]thiophene (BTTT) mesogen are designed and synthesized, including BTTT/dEO3 with two symmetrically attached tri(ethylene oxide) groups and BTTT/mEO6 with one asymmetrically attached hexa(ethylene oxide) group. These two molecules have comparable functional‐group compositions but different molecular geometries, leading to their moderately different material performances. Both LCs show smectic mesophases with relatively low transition temperatures as confirmed by differential scanning calorimetry and polarized optical microscopy. A combination of experimental grazing incidence wide‐angle X‐ray scattering and molecular dynamics (MD) simulations reveals a herringbone packing motif of BTTT segments in both LCs while a smaller molecular tilt angle in BTTT/mEO6. Ionic conductivities are measured by doping LCs with different amounts of ionic dopants, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). BTTT/mEO6 shows better smectic phase stability to higher LiTFSI doping ratios. Both LCs exhibit similar ionic conductivities in the smectic phases, but BTTT/mEO6 outperforms BTTT/dEO3 by a factor of three in the amorphous phase at higher temperatures. MD simulations, performed to examine the ion solvation environment, reveal that BTTT/mEO6 is more efficient in coordinating Li‐ions and screening their interactions with TFSI‐ions which further promote ionic transport.

grazing incidence wide-angle X-ray scattering↗
NASA NTRS1990

Cable delay compensator for microwave signal distribution over optical fibers

The basic principles of microwave fiber-optic systems are outlined with emphasis on fiber-optic cable delay compensators (CDC). Degradation of frequency and phase stability is considered, and it is pointed out that the long-term stability of a fiber-optic link is degraded by group delay variations due to temperature fluctuations in the optical fiber and low-frequency noise characteristics of the laser. A CDC employing a voltage-controlled oscillator to correct for phase variations in the optical fiber is presented, and the static as well as dynamic closed-loop analyses of the fiber-optic CDC are discussed. A constructed narrow-band fiber-optic CDC is shown to reduce phase variations caused by temperature fluctuations by a factor of 400. A wide-band CDC utilizing a temperature-controlled coil of fiber to compensate for phase delay is also proposed.

Primas, Lori E.↗
NASA NTRS1976

DSN research and technology support

Continuing testing and refinement of the remote controlled, unattended automated pulsar observing station is noted, along with routine pulsar observations of 22 pulsars. Radar observations of geostationary satellite are discussed. Current status of the 400-kW X-band radar is reported along with routine automatic testing of the stability-reliability of the DSS 13 maser-receiver noise adding radiometer combination. A failure in the Faraday rotation receiving system is noted along with discussion in some detail of the activities of the high power transmitter maintenance facility. Continuation of receiver phase stability testing, specifically the effects of temperature on coaxial cables, is discussed and results reported. A demonstration at full power of the microwave power transmission facility is noted and routine support of the planetary radio astronomy experiment is discussed. Transmission of master clock synchronization signals to overseas DSN stations is also reported.

Jackson, E. B.↗
DOE OSTI2025

Mg-Ion Conduction in Antiperovskite Solid Electrolytes Revealed by 25 Mg Ultrahigh Field NMR and First-Principles Calculations

Magnesium-ion batteries hold the potential to outperform the energy density of lithium-ion batteries, given the divalent charge carried by each Mg 2+ cation, but remain in an early stage of development. Here, in this study, 25 Mg solid-state nuclear magnetic resonance (ssNMR) is used to gain insight into the local structure and Mg-ion dynamics of candidate Mg-ion solid electrolytes, the antiperovskites Mg 3 SbN and Mg 3 AsN. Using the highest available magnetic field (35.2 T) for high-resolution solid-state NMR, the largest 25 Mg quadrupole coupling constants (C Q ) yet measured of up to 22 MHz are reported and corroborated by first-principles calculations. Predicted C Q values are shown to correlate with the antiperovskite’s tolerance factor; thus, 25 Mg NMR linewidths can report on lattice distortions and phase stability of these antiperovskites. Variable-temperature 25 Mg NMR spectra demonstrate changes at elevated temperatures, ascribed to Mg-ion motional effects. 25 Mg T 1 relaxometry measurements at ultrahigh field reveal a lower activation energy for the more distorted Mg 3 AsN phase, matching computational predictions of a lower energy barrier for Mg 2+ ion migration and suggesting that additional scrutiny of antiperovskites as Mg-ion conductors is warranted. Given the inherent challenges of 25 Mg NMR, this work demonstrates the benefits of combining ultrahigh field NMR spectroscopy, advanced pulse sequences, modern signal processing, and first-principles calculations to facilitate NMR of quadrupolar nuclei as a tool to probe the local structure and ion dynamics in beyond-Li battery materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Integrated optical frequency division for microwave and mmWave generation

Abstract The generation of ultra-low-noise microwave and mmWave in miniaturized, chip-based platforms can transform communication, radar and sensing systems 1–3 . Optical frequency division that leverages optical references and optical frequency combs has emerged as a powerful technique to generate microwaves with superior spectral purity than any other approaches 4–7 . Here we demonstrate a miniaturized optical frequency division system that can potentially transfer the approach to a complementary metal-oxide-semiconductor-compatible integrated photonic platform. Phase stability is provided by a large mode volume, planar-waveguide-based optical reference coil cavity 8,9 and is divided down from optical to mmWave frequency by using soliton microcombs generated in a waveguide-coupled microresonator 10–12 . Besides achieving record-low phase noise for integrated photonic mmWave oscillators, these devices can be heterogeneously integrated with semiconductor lasers, amplifiers and photodiodes, holding the potential of large-volume, low-cost manufacturing for fundamental and mass-market applications 13 .

Science & Technology - Other Topics↗
NASA NTRS1988

A digitally implemented phase-locked loop detection scheme for analysis of the phase and power stability of a calibration tone

A digital phase-locked loop (PLL) scheme is described which detects the phase and power of a high SNR calibration tone. The digital PLL is implemented in software directly from the given description. It was used to evaluate the stability of the Goldstone Deep Space Station open loop receivers for Radio Science. Included is a derivative of the Allan variance sensitivity of the PLL imposed by additive white Gaussian noise; a lower limit is placed on the carrier frequency.

Densmore, A. C.↗