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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

RF transient analysis and stabilization of the phase and energy of the proposed PIP-II LINAC

Here, this paper describes a recent effort to develop and benchmark a simulation tool for the analysis of RF transients and their compensation in an H- linear accelerator. Existing tools in this area either focus on electron LINACs or lack fundamental details about the LLRF system that are necessary to provide realistic performance estimates. In our paper we begin with a discussion of our computational models followed by benchmarking with existing beam-dynamics codes and measured data. We then analyze the effect of RF transients and their compensation in the PIP-II LINAC, followed by an analysis of calibration errors and how a Newton’s Method based feedback scheme can be used to regulate the beam energy to within the specified limits.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Microstructure and mechanical properties of V–4Ti–4Cr alloy as a function of the chemical heat treatment regimes

The regularities of the formation of a heterophase structure and mechanical properties of V–4Ti–4Cr alloy as a function of thermomechanical and chemical heat treatments are studied. The regimes of thermomechanical treatment which provide the formation of a heterophase structure with a homogeneous volume distribution of oxycarbonitride nanoparticles with a size of about 10 nm and an increase in the volume content and thermal stability of this phase and which provide an increase in the temperature of alloy recrystallization are developed. The formation of the heterophase structure results in a substantial (up to 70%) increase in the short-term high-temperature strength of the alloy at T = 800°C. The increase in the strength is achieved while keeping a rather high level of plasticity.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Composition Effects on Phase Formation and Stability

In this report, results from experimental studies of the composition dependence of nucleation are presented. A model for nucleation that takes simultaneous account of the interfacial attachment processes at the growing cluster interface and diffusion into the region surrounding the developing cluster is presented and numerical results are discussed.

Kelton, Kenneth F.↗
DOE OSTI2017

Creating Binary Cu–Bi Compounds via High-Pressure Synthesis: A Combined Experimental and Theoretical Study

Exploration beyond the known phase space of thermodynamically stable compounds into the realm of metastable materials is a frontier of materials chemistry. The application of high pressure in experiment and theory provides a powerful vector by which to explore this uncharted phase space, allowing discovery of complex new structures and bonding in the solid state. We harnessed this approach for the Cu–Bi system, where the realization of new phases offers potential for exotic properties such as superconductivity. This potential is due to the presence of bismuth, which, by virtue of its status as one of the heaviest stable elements, forms a critical component in emergent materials such as superconductors and topological insulators. To fully investigate and understand the Cu–Bi system, we welded theoretical predictions with experiment to probe the Cu–Bi system under high pressures. By employing the powerful approach of in situ X-ray diffraction in a laser-heated diamond anvil cell (LHDAC), we thoroughly explored the high-pressure and high-temperature (high-PT) phase space to gain insight into the formation of intermetallic compounds at these conditions. We employed density functional theory (DFT) calculations to calculate a pressure versus temperature phase diagram, which correctly predicts that CuBi is stabilized at lower pressures than Cu11Bi7, and allows us to uncover the thermodynamic contributions responsible for the stability of each phase. Detailed comparisons between the NiAs structure type and the two high-pressure Cu–Bi phases, Cu11Bi7 and CuBi, reveal the preference for elemental segregation within the Cu–Bi phases, and highlight the unique channels and layers formed by ordered Cu vacancies. The electron localization function from DFT calculations account for the presence of these “voids” as a manifestation of the lone pair orientation on the Bi atoms. Our study demonstrates the power of joint experimental–computational work in exploring the chemistry occurring at high-PT conditions. The existence of multiple high-pressure-stabilized phases in the Cu–Bi binary system, which can be readily identified with in situ techniques, offers promise for other systems in which no ambient pressure phases are known to exist.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A theoretical investigation of the effect of Ga alloying on thermodynamic stability, electronic-structure, and oxidation resistance of Ti 2 AlC MAX phase

We present a systematic investigation of thermodynamic stability, phase-reaction, and chemical activity of Al containing disordered Ti 2 (Al-Ga)C MAX phases using machine-learning driven high-throughput framework to understand the oxidation resistance behavior with increasing temperature and exposure to static oxygen. The A-site (at Al) disordering of Ti 2 AlC with Ga shows significant change in the chemical activity of Al with increasing temperature and exposure to static oxygen, which is expected to enable surface segregation of Al, thereby, the formation of Al 2 O 3 and improved oxidation resistance. We performed in-depth convex hull analysis of ternary Ti-Al-C, Ti-Ga-C, and Ti-Al-Ga-C based MAX phase, and provide detailed contribution arising from electronic, chemical and vibrational entropies. The thermodynamic analysis shows change in the Gibbs formation enthalpy (ΔG form ) at higher temperatures, which implies an interplay of temperature-dependent enthalpy and entropic contributions in oxidation resistance Ga doped Ti 2 AlC MAX phases. A detailed electronic structure and chemical bonding analysis using crystal orbital Hamilton population method reveal the origin of change in phases stability and in oxidation resistance in disorder Ti2(Al 1-x Ga x )C MAX phases. Our electronic structure analysis correlate well with the change in oxidation resistance of Ga doped MAX phases. We believe our study provides a useful guideline to understand to role of alloying on electronic, thermodynamic, and oxidation related mechanisms of bulk MAX phases, which can work as a precursor to understand oxidation behavior of twodimensional MAX phases, i.e., MXenes (transition metal carbides, carbonitrides and nitrides).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Shape Dependence of Pressure-Induced Phase Transition in CdS Semiconductor Nanocrystals

Understanding structural stability and phase transformation of nanoparticles under high pressure is of great scientific interest, as it is one of the crucial factors for design, synthesis, and application of materials. Even though high-pressure research on nanomaterials has been widely conducted, their shape-dependent phase transition behavior still remains unclear. Examples of phase transitions of CdS nanoparticles are very limited, despite the fact that it is one of the most studied wide band gap semiconductors. Here we have employed in-situ synchrotron wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) to investigate the high-pressure behaviors of CdS nanoparticles as a function of particle shapes. We observed that CdS nanoparticles transform from wurtzite to rocksalt phase at elevated pressure in comparison to their bulk counterpart. Phase transitions also vary with particle shape—rod-shaped particles show a partially reversible phase transition and the onset of the structural phase transition pressure decreases with decreasing surface-to-volume ratios, while spherical particles undergo irreversible phase transition with relatively low phase transition pressure. Additionally, TEM images of spherical particles exhibited sintering-induced morphology change after high-pressure compression. Calculations of the bulk modulus reveals that spheres are more compressible than rods in the wurtzite phase. These results indicate that the shape of the particle plays an important role in determining their high-pressure properties. Our study provides important insights into understanding of the phase-structure-property relationship, guiding future design and synthesis of nanoparticles for promising applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the structural stability of crystalline ceria phases in undoped and acceptor-doped ceria materials under in situ reduction conditions

The reduction of pure and Sm-doped ceria in hydrogen has been studied by synchrotron-based in situ X-ray diffraction to eventually prove or disprove the presence of crystalline cerium hydride (CeH x ) phases and the succession of potential structural phase (trans)formations of reduced cerium oxide phases during heating-cooling cycles up to 1273 K. Despite a recent report on the existence of bulk and surface CeH x phases during reductive treatment of pure CeO 2 in H 2 , structural analysis by Rietveld refinement as well as additional 1 H-NMR spectroscopy did not reveal the presence of any crystalline CeH x phase. Rather, a sequence of phase transformations during the re-cooling process in H 2 has been observed. In both samples, the reduced/defective fluorite lattice undergoes at first a transformation into a bixbyite-type lattice with a formal stoichiometry Ce 0.58 3+ Ce 0.42 4+ O 1.71 and Sm 0.15 3+ Ce 0.39 3+ Ce 0.46 4+ O 1.73 , before a transformation into rhombohedral Ce 7 O 12 takes place in pure CeO 2 . This phase is clearly absent for the Sm-doped material. Finally, a triclinic Ce 11 O 20 phase appears for both materials, which can be recovered to room temperature, and on which a phase mixture of bixbyite Ce 0.66 3+ Ce 0.34 4+ O 1.67 , rh-Ce 0.60 3+ Ce 0.40 4+ O 1.70 and tri-Ce 0.48 3+ Ce 0.52 4+ O 1.76 (for pure CeO 2 ) or bixbyite Sm 0.15 3+ Ce 0.47 3+ Ce 0.38 4+ O 1.69 and tri-Sm 0.15 3+ Ce 0.31 3+ Ce 0.54 4+ O 1.77 (for Sm-doped CeO 2 ) prevails. The absence of the rhombohedral phase indicates that Sm doping leads to the stabilization of the bixbyite phase over the rhombohedral one at this particular oxygen vacancy concentration. It is worth noting that recent work proves that hydrogen is indeed incorporated within the structures during the heat treatments, but under the chosen experimental conditions it has apparently no effect on the salient structural principles during reduction.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Stabilization of Miscible Aqueous Phases via Diffusion‐Controlled Multifunctional Nanoparticle‐Ligand Complexation

Liquid‐in‐liquid structuring by harnessing miscible aqueous domains can be achieved by inducing thermodynamically defined phase separation using aqueous solutions of incompatible solutes, where immiscibility is dictated by the concentrations of the solutes. For instance, in aqueous two‐phase systems (ATPSs), the interfacial tension between the two different aqueous solutions is so small that it stabilizes the phase‐separated domains, but not their shape, thus falling short of designing tunable, robust structures. Here, we introduce a diffusion‐controlled strategy that enables liquid‐in‐liquid compartmentalization absent a thermodynamically defined interface or bulk liquid‐liquid phase separation using a barrier formed in situ at the initial contact boundary of an aqueous dispersion of multifunctional nanoparticles and a solution of multifunctional ligands in pure water or a water/alcohol mixture. The nanoparticles and ligands are entropically driven to disperse uniformly but interact at the initial contact boundary more rapidly than bulk mixing, forming a layer that establishes a barrier akin to a semi‐permeable membrane and allows the formation of tubular compartments. A wealth of opportunities is enabled by the proposed technique, where examples in separations, soft electronic devices, and ultralight porous electromagnetic shielding materials are shown.

cryogels↗
DOE OSTI2020

Order-disorder versus displacive transitions in Jahn-Teller active layered materials

Large anharmonic vibrations often play a crucial role in dynamically stabilizing crystalline phases whose structures are unstable at low temperature. Although the average structure of such phases can be measured through diffraction experiments, their local structure remains a challenge to characterize and understand. Dynamically stabilized phases are often classified as order/disorder or displacive based on the qualitative nature of their local structure. A robust understanding of how chemistry determines this distinction in behavior, however, is lacking. This article presents a parametric study of an anharmonic vibrational model that describes the transition from a cooperative to a noncooperative Jahn-Teller distortion in layered oxides—a class of materials widely used in Li-ion and Na-ion batteries. The results illustrate how the shape of the energy landscape determines the extent to which the high-temperature phase has order/disorder vs displacive character. In this work, we find that the nature of the high-temperature phase is determined by a competition between the strength of the elastic coupling between Jahn-Teller distortions at nearby sites and the energy scale driving the Jahn-Teller distortion. A comparison of the model to energy landscapes calculated with density-functional theory suggests that the high-temperature phases of the Jahn-Teller active layered compounds LiNiO 2 , NaNiO 2 , LiMnO 2 , and NaMnO 2 exhibit order/disorder character.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Activity and Stability of (Pr 1-x Nd x ) 2 NiO 4 as Cathodes for Solid Oxide Fuel Cells: Part V. In Situ Studies of Phase Evolution

This study is to complement an early report (the manuscript is attached for review purpose) on the role of interlayer on activity and performance stability in praseodymium nickelates. The aforementioned report showed a remarkable 48% increase in power density while switching from common GDC interlayer to a new interlayer chemistry (PGCO). Furthermore, a stable long-term performance was linked with suppressed reaction between the cathode and PGCO interlayer. In this article, we report in situ studies of the phase evolution. The high energy XRD studies at a synchrotron source showed fully suppressed phase transition in praseodymium nickelates with PGCO interlayer, while the electrodes on the GDC interlayer undergo substantial phase transformation. Furthermore, in operando and post-test XRD analyses shown fully suppressed structural changes in electrodes operated in full cells at 750°C and 0.80 V for 500 hours. SEM-EDS analysis showed that the formation of PrO x at the cathode-interlayer interface may play a role in a decrease of mechanical integrity of the interfaces, due to thermal expansion mismatch, leading to a local stress between the two phases. Furthermore, phase evolution at a narrow interface may propagate toward the electrode bulk, leading to structural changes Q1 and performance degradation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Ultra-stable, low phase noise dielectric resonator stabilized oscillators for military and commercial systems

EPSD has designed, fabricated and tested, ultra-stable, low phase noise microwave dielectric resonator oscillators (DRO's) at S, X, Ku, and K-bands, for potential application to high dynamic range and low radar cross section target detection radar systems. The phase noise and the temperature stability surpass commercially available DROs. Low phase noise signals are critical for CW Doppler radars, at both very close-in and large offset frequencies from the carrier. The oscillators were built without any temperature compensation techniques and exhibited a temperature stability of 25 parts per million (ppm) over an extended temperature range. The oscillators are lightweight, small and low cost compared to BAW & SAW oscillators, and can impact commercial systems such as telecommunications, built-in-test equipment, cellular phone and satellite communications systems. The key to obtaining this performance was a high Q factor resonant structure (RS) and careful circuit design techniques. The high Q RS consists of a dielectric resonator (DR) supported by a low loss spacer inside a metal cavity. The S and the X-band resonant structures demonstrated loaded Q values of 20,300 and 12,700, respectively.

Mizan, Muhammad↗
DOE OSTI2013

Ion-beam-induced magnetic and structural phase transformation of Ni-stabilized face-centered-cubic Fe films on Cu(100)

Metastable face-centered cubic (fcc) Fe/Cu(100) thin films are good candidates for ion-beam magnetic patterning due to their magnetic transformation upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni for stabilizing the fcc γ phase. The amount of Ni necessary to stabilize nonmagnetic, transformable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phase diagram revealing the transformable region is presented.

36 MATERIALS SCIENCE↗