Search NASA⌕ Search

SEARCH · Search NASA

Results for “dynamic diffraction”

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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Interfacial Void Formation and Self-Healing in Oxide Scales on Al-containing High-Entropy Alloy

The exceptional high-temperature oxidation resistance of Al-containing high-entropy alloys (HEAs) is often attributed to the formation of a protective α-Al 2 O 3 scale. However, the dynamic, atomic-scale mechanisms governing the stability of this scale—including interfacial void formation and the often-postulated but rarely visualized “self-healing” capacity—remain poorly understood. Herein, we reveal the complex evolution of the triple-layer oxide scale on an Al 10 CoCrFeNi HEA through combined electron microscopy and diffraction study. We show that interfacial voids are an inherent consequence of the scaling process, originating from two distinct mechanisms: the Kirkendall effect at the interface between the γ-Al 2 O 3 /α-Al 2 O 3 and alloy driven by cationic diffusion imbalance and volumetric contraction due to phase transformations at the spinel/Cr 2 O 3 interface. Crucially, we provide microstructural evidence consistent with an intrinsic self-healing response. This process is driven by coupled inward diffusion of oxygen and outward diffusion of metal cations, leading to the in-situ formation of transient θ-Al 2 O 3 and spinel phases that partially fill and seal the voids. Here, these results provide atomic-scale insights into the phase evolution, defect formation, and self-repair of oxide scales in HEAs—highlighting pathways to enhance their oxidation resistance in extreme environments.

High-entropy alloy↗
DOE OSTI2024

Six-Letter DNA Nanotechnology: Incorporation of Z-P Base Pairs into Self-Assembling 3D Crystals

Artificially expanded genetic information systems (AEGIS) were developed to expand the diversity and functionality of biological systems. Recent experiments have shown that these expanded DNA molecular systems are robust platforms for information storage and retrieval as well as useful for basic biotechnologies. In tandem, nucleic acid nanotechnology has seen the use of information-based “semantomorphic” encoding to drive the self-assembly of a vast array of supramolecular devices. To establish the effectiveness of AEGIS toward nanotechnological applications, we investigated the ability of a six-letter alphabet composed of A:T, G:C and synthetic Z:P (Z, 6-amino-3-(1'-β- D-2'-deoxy ribofuranosyl)-5-nitro-(1H)-pyridin-2-one; P, 2-amino-8-(1'- β-D-2'-deoxyribofuranosyl)-imidazo-[1,2a]-1,3,5-triazin-(8H)-4-one) base pairs to engage in 3D self-assembly. We found that crystals could be programmably assembled from AEGIS oligomers. We conclude that unnatural base pairs can be used for the topological self-assembly of crystals. We anticipate the expansion of AEGISbased nucleic acid nanotechnologies to enable the development of novel nanomaterials, high-fidelity signal cascades, and dynamic nanoscale devices.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Phenyl Ring Dynamics in a Tetraphenylethylene-Bridged Metal-Organic Framework: Implications for the Mechanism of Aggregation-Induced Emission

Molecules that exhibit emission in the solid state, especially those known as aggregation-induced emission (AIE) chromophores, have found applications in areas as varied as light-emitting diodes and biological sensors. Despite numerous studies, the mechanism of fluorescence quenching in AIE chromophores is still not completely understood. To this end, much interest has focused on understanding the low-frequency vibrational dynamics of prototypical systems, such as tetraphenylethylene (TPE), in the hope that such studies would provide more general principles toward the design of new sensors and electronic materials. We hereby show that a perdeuterated TPE-based metal–organic framework (MOF) serves as an excellent platform for studying the low-energy vibrational modes of AIE-type chromophores. In particular, we use solid-state 2 H and 13 C NMR experiments to investigate the phenyl ring dynamics of TPE cores that are coordinatively trapped inside a MOF and find a phenyl ring flipping energy barrier of 43(6) kJ/mol. DFT calculations are then used to deconvolute the electronic and steric contributions to this flipping barrier. Finally, we couple the NMR and DFT studies with variable-temperature X-ray diffraction experiments to propose that both the ethylenic C=C bond twist and the torsion of the phenyl rings are important for quenching emission in TPE, but that the former may gate the latter. To conclude, we use these findings to propose a set of design criteria for the development of tunable turn-on porous sensors constructed from AIE-type molecules, particularly as applied to the design of new multifunctional MOFs.

Shustova, Natalia B↗
DOE OSTI2016

{sup 1}H and {sup 19}F spin-lattice relaxation and CH{sub 3} or CF{sub 3} reorientation in molecular solids containing both H and F atoms

The dynamics of methyl (CH{sub 3}) and fluoromethyl (CF{sub 3}) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state {sup 1}H and {sup 19}F spin-lattice relaxation experiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF{sub 3} reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance (NMR) time scale) to investigate CF{sub 3} reorientation occurring on the NMR time scale. The effects of {sup 19}F–{sup 19}F and {sup 19}F–{sup 1}H spin-spin dipolar interactions on the complicated nonexponential NMR relaxation provide independent inputs into determining a model for CF{sub 3} reorientation. As such, these experiments provide much more information than when only one spin species (usually {sup 1}H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH{sub 3} and CF{sub 3} reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components.

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

Dynamic, Adaptive, Systems and Materials: Complex, Simple and Emergent Behaviors

This program has been funded by DoE/BES for twenty years. It has moved into and out of various subjects as it has developed, but it has retained its focus on complexity and complex systems. The project has evolved in the following way: Self-Assembly and Biomimetic Self-Assembly: All self-assembling systems depend upon a minimum of two types of interaction: a repulsion and an attraction. For the familiar molecular systems, attractive interactions are typically hydrogen bonds and electrostatic interactions. Repulsive interactions include steric effects, hydrophobic effects (in biological systems), and charge-charge repulsion. We have expanded this repertoire to include surface interactions, magnetic interactions, and others. I list these systems in the order in which we have explored them: i) A key emphasis in current work is in understanding how the movement of ions in a magnetic field (the Lorentz effect) interacts with catalytic systems. We have demonstrated that an acceleration in rate of reduction of CO 2 to CO can be accomplished by applying an external magnetic field. This acceleration is largely due to the application of the Lorentz effect on mass transport at the catalyst’s surface. ii) We have also extensively explored the influence of electrostatics, as exhibited in self-assembling systems, by tribocharging. iii) Another key system involves surface tension effects; examples include interactions between heavy particles floating at a liquid-air interface, and interacting by changes in surface area; interactions of bubbles and bubble rafts, behaviors of bubble trains in microfluidic networks, and behaviors of microorganisms in constraining environments. iv) This work has intentionally de-emphasized biological systems; but it does include some work on protein-ligand interactions and interactions among microorganisms. v) We have also explored applications of some of these effects, these explorations include bubble rafts as diffraction gratings, exploration of the structures that can be obtained by tribocharging and uses of these structures in exploring nucleation and melting of crystals. vi) Although not a major focus of this work, several other topics have emerged and offer opportunities for future work. These include the behavior of bubble trains and bubble rafts in microfluidic systems. A particularly interesting example is the formation of bubble trains that repeat in the alteration of large and small bubbles according to rules we do not presently understand, but are uniquely large-period oscillating systems. These systems offer a new route into understanding the instabilities of the type represented by oscillations. vii) We have also begun exploratory projects on magnetic levitation (especially to determine molecular density), and information storage (in molecules). Magnetic Levitation: Self-assembling and biomimetic systems require both attraction and repulsion. We have used electrostatics (tribocharging), interfacial free-energies (surface tension and related forces) and others. Potential uses include reconfigurable diffraction gratings and liquid lenses; exploration of mechanisms in tribocharging; tunneling in EGaIn junctions; and bubble trains (especially in micro-fluidic systems). Examples of systems representing these topics is included in the following papers: Complexity: Disks rotating at a water-air interface; Benard-Marangoni effects; Vortex-Crystals from spinning magnetic disks (Marangoni effects); EGaIn Electrode to study quantum tunneling; Self-Assembly of electrostatically-charged metallic spheres (electrets); Dynamically reconfigurable lens; Using computational designs of ligands for enzymes; Electrostatic self-assembly by tribocharging; Monodisperse bubble trains in microchannel systems; Inverted dripping faucet; Flames; Printing of micro-organisms to regenerate the “ink” of printing device; Using micro-organisms to move loads (“microoxen”); Motion of bacterial swarms near surfaces; Making monodisperse particles in microfluidic systems; Coding/decoding of information stored in droplet trains in microfluidic networks; Magnetic levitation; and Information storage. i) Tribocharging. The change in focus of this work on electrets from the fundamentals of charging to applications of these materials in studying self-assembly using electrostatic interactions. ii) Bubbles in Microchannels. The realization that systems of bubbles in microchannels represented a major opportunity to study complexity in a very tractable system, and the development of a semi-quantitative theory of this subject. iii) Flames. The growth of “flames” remains an exploratory subject for the research, although their currently relatively little active work involving it ongoing. iv) Systems with Microorganisms. The removal of work in biological systems from this project. Based on work supported in this program, we now have a significant project on the development of microfluidic tools for studying C. elegans (a nematode), but this work was not appropriate for a program focused on complexity, and we developed separate support for it. (It is, however, an example of successful seeding of a new area by BES.) The work on electrets has gone through a period in which a part of the program was the subject of a MURI; the focus of this work was to develop materials that did not charge electrostatically on friction or contact. The MURI is now over, and the work on dynamic self-assembly (supported by BES) is the major focus. “Flames” has also enjoyed synergistic support, in terms of a project supported by DARPA on flame suppression (in the absence of extinguishing agents, using acoustic and electrostatic interactions). This work was helpful in understanding some of the basics of flames, but is entirely distinct from the BES focus in complexity. A growing interest is in the Lorentz effect. The Lorentz effect is the force exerted on charged particles (electrons, ions, charged molecules) when they move through a perpendicular magnetic field. The Lorentz effect is almost ubiquitous in modern technology: examples of applications include electric motors, dynamos, cathode ray tubes, many batteries, and most systems that control electrical currents with magnetic forces. We have begun to explore the Lorentz effect in electrochemical systems and heterogeneous catalytic systems involving charged organic species and inorganic ions. This work is still at an early stage, but initial studies that Lorentz effects can be large when ions move through magnetic fields, or magnetic fields move in the presence of ions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effect of Ion Irradiation on Nanocrystallization and Surface Relief of a Ribbon from Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} Alloy

Using the methods of X-ray diffraction and atomic force microscopy, the process of crystallization of an amorphous Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} alloy irradiated with accelerated Ar{sup +} ions is investigated. It is found out that an irradiation by the Ar{sup +} ions with the energy 30 keV at the ion current density 300 μA/cm{sup 2} (fluence 3.75·10{sup 15} cm{sup –2}, irradiation time ~2 s, ion-beam short-duration heating up to 350°С, which is 150°С lower than the thermal crystallization threshold) results in a complete crystallization of this amorphous alloy (throughout the bulk of a 25 μm ribbon) followed by precipitation of solid solution crystals of α-Fe(Si), close in its composition to Fe{sub 80}Si{sub 20}, stable phase of Fe{sub 3}Si, and metastable hexagonal phases. By the methods of atomic force and scanning tunneling microscopy it is shown that nanocrystallization caused by ion irradiation is accompanied by surface relief changes both on the irradiated and unirradiated sides of the Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} alloy ribbon at the depth exceeding by a factor of 10{sup 3} that of the physical ion penetration for this material. The data obtained, taking into account a significant temperature decrease and multiple acceleration of the crystallization process, serve an evidence of the radiation-dynamic influence of accelerated ions on the metastable amorphous medium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Effects of interlayer confinement and hydration on capacitive charge storage in birnessite

Nanostructured birnessite exhibits high specific capacitance and nearly ideal capacitive behaviour in aqueous electrolytes, rendering it an important electrode material for low-cost, high-power energy storage devices. The mechanism of electrochemical capacitance in birnessite has been described as both Faradaic (involving redox) and non-Faradaic (involving only electrostatic interactions). To clarify the capacitive mechanism, we characterized birnessite’s response to applied potential using ex situ X-ray diffraction, electrochemical quartz crystal microbalance, in situ Raman spectroscopy and operando atomic force microscope dilatometry to provide a holistic understanding of its structural, gravimetric and mechanical responses. These observations are supported by atomic-scale simulations using density functional theory for the cation-intercalated structure of birnessite, ReaxFF reactive force field-based molecular dynamics and ReaxFF-based grand canonical Monte Carlo simulations on the dynamics at the birnessite–water–electrolyte interface. We show that capacitive charge storage in birnessite is governed by interlayer cation intercalation. We conclude that the intercalation appears capacitive due to the presence of nanoconfined interlayer structural water, which mediates the interaction between the intercalated cation and the birnessite host and leads to minimal structural changes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Photocarrier-induced persistent structural polarization in soft-lattice lead halide perovskites

The success of the lead halide perovskites in diverse optoelectronics has motivated considerable interest in their fundamental photocarrier dynamics. Here, in this work, we report the discovery of photocarrier-induced persistent structural polarization and local ferroelectricity in lead halide perovskites. Photoconductance studies of thin-film single-crystal CsPbBr 3 at 10 K reveal long-lasting persistent photoconductance with an ultralong photocarrier lifetime beyond 10 6 s. X-ray diffraction studies reveal that photocarrier-induced structural polarization is present up to a critical freezing temperature. Photocapacitance studies at cryogenic temperatures further demonstrate a systematic local phase transition from linear dielectric to paraelectric and relaxor ferroelectric under increasing illumination. Our theoretical investigations highlight the critical role of photocarrier–phonon coupling and large polaron formation in driving the local relaxor ferroelectric phase transition. Our findings show that this photocarrier-induced persistent structural polarization enables the formation of ferroelectric nanodomains at low temperature, which suppress carrier recombination and offer the possibility of exploring intriguing carrier–phonon interplay and the rich polaron photophysics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Low-Dimensional Network Formation in Molten Sodium Carbonate

Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (F-x(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to Fx(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example similar to 55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na+ ions.

Wilding, Martin C.↗
DOE OSTI2018

Large spontaneous polarization in polar perovskites of PbTiO 3 -Bi(Zn 1/2 Ti 1/2 )O 3

PbTiO 3 –Bi(Zn 1/2 Ti 1/2 )O 3 is considered to be a promising high-ferroelectric performance material in the Pb/Bi-based perovskite family. In the present study, a whole set of (1 – x )PbTiO 3 – x Bi(Zn 1/2 Ti 1/2 )O 3 (0 ≤ x ≤ 1) solid solutions have been prepared by the conventional solid-state and high-pressure vs. high-temperature methods. The effect of Bi(Zn 1/2 Ti 1/2 )O 3 on the crystal structure has been investigated by synchrotron X-ray powder diffraction. Unlike most PbTiO 3 -based perovskites, the present system exhibits a continuously enhanced tetragonality (c/a) and large spontaneous polarization (PS) properties. The enhanced c/a is ascribed to the large spontaneous polarization displacements induced by the strong Pb/Bi–O hybridization and coupling interactions between Ti/Zn and Pb/Bi cations, which can be evidenced from the lattice dynamics study and first-principles calculations. Accordingly, the T C ( i.e., x = 0.5) is expected to be approximately 1000 °C if its perovskite structure can be stabilized. In conclusion, the present study provides a route to obtain large-PS in PbTiO 3 -based ferroelectric materials by introducing isostructural perovskites with strong polarity.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis and characterization of new fluoride-containing manganese vanadates A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F

Large single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO{sub 4}F{sub 2} building blocks. The A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains of edge-sharing MnO{sub 4}F{sub 2} units running along the a-axis, and interconnected through V{sub 2}O{sub 7} pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn{sup 2+} indicated that Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} is antiferromagnetic with a Neél temperature, T{sub N}=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}. Mn{sub 2}(VO{sub 4})F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn{sup 2+}. These interpenetrating chains are additionally connected through isolated VO{sub 4} tetrahedra to form the condensed structure. - Graphical abstract: New vanadate fluorides A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}(VO{sub 4})F have been synthesized hydrothermally. Upon cooling, the one-dimensional Mn(II) substructure results in antiferromagnetic ordering. Display Omitted - Highlights: • Single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}, (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown hydrothermally. • The use of fluoride mineralizers in the synthesis led to the formation of new compounds without OH{sup −} groups. • The structure of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} features zigzag chains of MnO{sub 4}F{sub 2} units. • Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} exhibits antiferromagnetic ordering with a Neel temperature of ~3 K. • Mn{sub 2}VO{sub 4}F possesses a condensed framework structure with disordered fluorine atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Using electron energy-loss spectroscopy to measure nanoscale electronic and vibrational dynamics in a TEM

Electron energy-loss spectroscopy (EELS) can measure similar information to x-ray, UV–Vis, and IR spectroscopies but with atomic resolution and increased scattering cross-sections. Recent advances in electron monochromators have expanded EELS capabilities from chemical identification to the realms of synchrotron-level core-loss measurements and to low-loss, 10–100 meV excitations, such as phonons, excitons, and valence structures. EELS measurements are easily correlated with electron diffraction and atomic-scale real-space imaging in a transmission electron microscope (TEM) to provide detailed local pictures of quasiparticle and bonding states. This perspective provides an overview of existing high-resolution EELS (HR-EELS) capabilities while also motivating the powerful next step in the field—ultrafast EELS in a TEM. Ultrafast EELS aims to combine atomic-level, element-specific, and correlated temporal measurements to better understand spatially specific excited-state phenomena. Ultrafast EELS measurements also add to the abilities of steady-state HR-EELS by being able to image the electromagnetic field and use electrons to excite photon-forbidden and momentum-specific transitions. We discuss the technical challenges ultrafast HR-EELS currently faces, as well as how integration with in situ and cryo measurements could expand the technique to new systems of interest, especially molecular and biological samples.

Chemistry↗
DOE OSTI2020

Lattice Dynamics of Sb 2 Se 3 from Inelastic Neutron and X-Ray Scattering

The lattice dynamics of orthorhombic Sb 2 Se 3 is studied by a combination of inelastic neutron and 121 Sb nuclear inelastic scattering giving access to the total and Sb partial density of phonon states (DPS). The Se partial DPS is determined from the difference between the total and Sb partial DPS. The total DPS is determined at 39, 150, and 300 K, and an analysis of the temperature-induced mode shifts in combination with low-temperature powder diffraction data is provided. Using an earlier reported theoretical approach, the corresponding total and partial DPS of Sb 2 Se 3 are calculated by first-principles calculations. Herein, a detailed analysis of the Grüneisen parameter, element-specific and bulk Debye temperatures, and the mean force constants as derived from the experimental data and discrete Fourier transform calculations is provided. In general, the calculations underestimate the strength of the covalent Sb-Se bonds.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Ergodicity reflected in macroscopic and microscopic field-dependent behavior of BNT-based relaxors

The effect of heterovalent B-site doping on ergodicity of relaxor ferroelectrics is studied using (1 − y)(0.81Bi{sub 1/2}Na{sub 1/2}TiO{sub 3}-0.19Bi{sub 1/2}K{sub 1/2}TiO{sub 3})-yBiZn{sub 1/2}Ti{sub 1/2}O{sub 3} (BNT-BKT-BZT) with y = (0.02;0.03;0.04) as a model system. Both the large- and small-signal parameters are studied as a function of electric field. The crystal structure is assessed by means of neutron diffraction in the initial state and after exposure to a high electric field. In order to measure ferroelastic domain textures, diffraction patterns of the poled samples are collected as a function of sample rotation angle. Piezoresponse force microscopy (PFM) is employed to probe the microstructure for polar regions at a nanoscopic scale. For low electric fields E < 2 kV·mm{sup −1}, large- and small-signal constitutive behavior do not change with composition. At high electric fields, however, drastic differences are observed due to a field-induced phase transition into a long-range ordered state. It is hypothesized that increasing BZT content decreases the degree of non-ergodicity; thus, the formation of long-range order is impeded. It is suggested that frozen and dynamic polar nano regions exist to a different degree, depending on the BZT content. This image is supported by PFM measurements. Moreover, PFM measurements suggest that the relaxation mechanism after removal of the bias field is influenced by surface charges.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Influence of Water, Vacuum, and Temperature on Surface Conditions of a Zeolite‐based Molecular Sieve

Molecular sieves such as zeolite-based materials are ubiquitous in industrial separation processes. However, there is a significant gap in understanding the surface properties and adsorption mechanisms for commercial zeolites, as most research focuses on pure zeolite powders rather than industrially relevant forms. Here, this work addresses this gap in understanding by employing advanced characterization techniques, including positron annihilation spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, liquid nitrogen sorption, and Fourier-transform infrared spectroscopy, to investigate the adsorption and desorption behavior of water in commercial zeolite 13X. Our research reveals insights into the pore-filling mechanisms, the impact of material binders on adsorption properties, and the dynamics of hydration and drying processes for zeolites. Monitoring changes on a minute scale allowed the distinction between fast and slow processes leading to sample drying. The identification of positronium bound to Na + ions indicated that water molecules remain in the vicinity of Na + ions after air-drying zeolite 13X. These findings highlight the importance of various environmental conditions in restoring zeolite properties to baseline after hydration, with significant implications for optimizing industrial processes. This work sets the direction for further research aimed at developing more efficient and robust separation techniques.

Beads Binder↗
DOE OSTI2023

On the role of methyl groups in the molecular architectures of mesophase pitches

The role of methyl groups on the liquid–crystal structure of mesophase pitches was investigated by combining experimental characterizations and atomic-scale computational modeling, using three pitches synthesized from different precursors. Of the three pitches, C-9 alkyl benzene and naphthalene-based pitches have 13 and 7 methyl groups per average polyaromatic hydrocarbon, respectively. By contrast, mesophase produced from a coal-tar pitch has about one methyl group. The coal tar–based mesophase pitch is hydrogen deficient or more aromatic compared with C-9 alkyl benzene- and naphthalene-based pitches. Additionally, X-ray diffraction data showed that average coherent domain sizes of C-9 alkyl benzene (3.7 nm) and naphthalene-based (3.6 nm) pitches with more methyl groups are larger than that of coal tar–based mesophase (2.4 nm). Based on the identified features, the influence of the methyl group on the layering structures was investigated via molecular dynamics simulations. The results revealed that methyl groups are critical in mesophase layering in C-9 alkyl benzene- and naphthalene-based pitches, by reducing CH-π interaction. However, similar alignment could be achieved without the same degree of methyl substitutions for the coal tar-based pitch because of stronger π-π interaction than the other precursors. The insights from this study contribute to our understanding of the formation of conventional mesophase pitch and have implications for the processing of coal-derived materials. In conclusion, this knowledge is vital to produce valuable products like carbon fiber and graphite from pitches.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Fast attenuation of high-frequency acoustic waves in bicontinuous nanoporous gold

We studied the formation and attenuation of GHz elastic waves in free-standing nanoporous gold films by MeV ultrafast electron diffraction and finite element simulations. By tracing the evolution of the high frequency acoustic waves in time domain, we found that the bicontinuous nanoporous structure in nanoporous gold films results in three-dimensionally acoustic response with low coherence, leading to fast attenuation of the elastic waves in comparison with solid gold films. The morphologically dominated dynamics indicates the nanoporosity plays an important role in the high-frequency acoustic energy relaxation, which shines a light on the applications of dealloyed nanoporous materials in nanodevices and sensors as GHz and THz acoustic filters and dampers.

36 MATERIALS SCIENCE↗