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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Formation and energetics of amorphous rare earth (RE) carbonates in the RE 2 O 3 –CO 2 –H 2 O system

Amorphous materials are of interest in the genesis of crystalline solids. They are often the first to precipitate from supersaturated solutions and are in the nanometer size range, transforming into a nanocrystalline metastable phase, and then to thermodynamically stable phases. One must seek knowledge of the composition, structure, thermodynamics, kinetics, and reaction pathways that relate the amorphous and crystalline phases. The subject of this study is the amorphous phases in the system RE 2 O 3 -CO 2 –H 2 O (RE- La, Nd, Dy,Yb). They were synthesized via direct precipitation and urea hydrolysis, and characterized by powder XRD, DTA with mass spectrometric analysis of the evolved gases. Phases have the non-stoichiometric composition RE 2 O 3 ·xCO 2 ·yH 2 O (1 < x < 3, 3 < y <7), which is different from that of crystalline simple carbonates and hydroxycarbonates. Thus we consider them to be amorphous precursors, rather than amorphous carbonates. High temperature oxide melt solution calorimetry in molten sodium molybdate solvent was used to derive their enthalpies of formation from oxides and elements. Increase of energetic stability per mole of RE 2 O 3 compounds occurs in the order: RE 2 O 3 → 2RE(OH)3→ 2REO(OH) → RE 2 O 2 CO 3 → Amorphous precursor → 2(REOHCO 3 ) → RE 2 (CO 3 ) 3 ·yH 2 O. We calculated the enthalpies of possible transformations of amorphous precursors to crystalline phases and conclude that thermodynamics determines the dependence of the crystallizing products on the temperature and partial pressure of CO 2 and H 2 O. Amorphous precursors are clearly intermediate in the synthesis, and ternary phases containing both H 2 O and CO 2 compete with each other in terms of thermodynamic stability. The energy landscape obtained here will allow one to directly synthesize specific products and control their functionality.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

X-ray Amorphous Materials in Soils from the Antarctica Dry Valleys: Insights into Aqueous Alteration Processes on Mars

The CheMin XRD instrument onboard the Curiosity rover has discovered abundant quantities of X-ray amorphous materials (25-40 wt. %) in windblown deposits and sedimentary rocks on Mars. The large amounts of X-ray amorphous materials on Mars is surprising because these materials are usually not found in large abundances in terrestrial soils. We have previously identified short-range ordered or X-ray amorphous materials in Antarctica Dry Valleys (ADV) soils. The ADV are one of the driest and coldest environments on Earth and provide an ideal process analog environment for Mars. The objective of this study was to further characterize the chemistry and mineralogy of ADV soils, specifically to quantify and characterize the X-ray amorphous materials. Two soils were characterized from different elevations in the ADV - a low elevation, coastal, subxerous soil in Taylor Valley and a high elevation, ultraxerous soil in University Valley. Rietveld analysis of XRD patterns generated with a CheMin-like analog instrument indicated up to 40 and 15 wt. % X-ray amorphous materials in the Taylor and University Valley soils, respectively. The high abundance of X-ray amorphous materials in Taylor Valley is surprising for one of the driest places on Earth. These materials may have been physically and chemical altered during soil formation, however, the limited interaction with water and low temperatures may have resulted in the formation of “immature” X-ray amorphous or SRO materials. Perhaps, a similar process contributes to the formation of the high content of X-ray amorphous materials detected on Mars.

Antarctica↗
DOE OSTI2021

A medium-range structure motif linking amorphous and crystalline states

Amorphous materials have no long-range order, but there are ordered structures at short range (2–5 Å), medium range (5–20 Å) and even longer length scales. While regular and semiregular polyhedra are often found as short-range ordering in amorphous materials, the nature of medium-range order has remained elusive. Consequently, it is difficult to determine whether there exists any structural link at medium range or longer length scales between the amorphous material and its crystalline counterparts. Moreover, an amorphous material often crystallizes into a phase of different composition, with very different underlying structural building blocks, further compounding the issue. Here, we capture an intermediate crystalline cubic phase in a Pd-Ni-P amorphous alloy and reveal the structure of the medium-range order, a six-membered tricapped trigonal prism cluster (6M-TTP) with a length scale of 12.5 Å. We find that the 6M-TTP can pack periodically to several tens of nanometres to form the cube phase. Our experimental observations provide evidence of a structural link between the amorphous and crystalline phases in a Pd-Ni-P alloy at the medium-range length scale and suggest that it is the connectivity of the 6M-TTP clusters that distinguishes the crystalline and amorphous phases. These findings will shed light on the structure of amorphous materials at extended length scales beyond that of short-range order.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Size Effects in the Thermal Conductivity of Amorphous Polymers

Manipulating thermal conductivity through nanoengineering is of critical importance to advance technologies, such as soft robotics, artificial skin, wearable electronics, batteries, thermal insulation, and thermoelectrics. Here, by examining amorphous polymers, including polystyrene, polypropylene, polyethylene, and ethylene vinyl alcohol, using molecular dynamics simulations, we find that the thermal conductivities of amorphous polymers can be reduced below their amorphous limit by size effects. Size-dependent thermal transport in amorphous materials is decomposed into crystalline, crystalline-to-amorphous, and amorphous regimes. In the amorphous regime, the mean free path of propagating heat carriers can range from tens of nanometers to more than 100 nm, contributing 16%–36% of the total thermal conductivity. A two-channel model that combines no size effect (i.e., difusons and locons) and size effect (i.e., propagons) is proposed to account for size-dependent thermal conductivity. We also find that the presence of charged molecules in polymers can significantly affect the thermal conductivity and its size effects due to electrostatic interactions. Overall, this work provides insights into the thermal conductivity of amorphous polymers that will have a broad impact on the nano- and chemical engineering of polymers for various energy-related applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Suppressed paramagnetism in amorphous Ta 2 O 5 − x oxides and its link to superconducting-qubit performance

Amorphous-oxide layers in thin-film capacitors are linked to reduced transmon-qubit T 1 coherence times. Ta -based capacitors outperform Nb -based ones, suggesting that amorphous Ta 2 O 5 − x is less lossy than Nb 2 O 5 − x . We investigate the microscopic features of these amorphous oxides using ab initio molecular dynamics and density functional theory, revealing the origins of the superior performance of Ta 2 O 5 − x . We establish that oxygen deficiency is less likely to occur in amorphous Ta 2 O 5 − x than in Nb 2 O 5 − x for 0 ≤ x ≤ 0.25 and that for a given oxygen deficiency x , metal Ta — Ta bond formation is enhanced. Such bonds, which are accommodated by structural flaws in the amorphous network, capture electrons better than in amorphous Nb 2 O 5 − x . These thermochemical differences quench or highly suppress magnetic moments in amorphous Ta 2 O 5 − x and eliminate a potential source of quasiparticles and magnetic flux noise. We also show that hyperfine couplings between Nb nuclei and local magnetic moments in Nb 2 O 5 − x can form “two-level systems” (TLSs) or “two-level fluctuators” with energy splittings of 100–1000 MHz or higher. This reveals a TLS mechanism in amorphous Nb 2 O 5 − x oxide layers that is likely inactive in Ta 2 O 5 − x . Our work provides a fundamental understanding of the materials chemistry and limitations imposed by native oxides of superconducting qubits that can be used to guide materials selection and processing.

Pritchard, P. Graham [Northwestern U.] (ORCID:0000↗
NASA NTRS1994

The contribution of vapor deposition to amorphous rims on lunar soil grains

Recent analysis analytical electron microscope study of lunar soils showed that the approximately 60-nm-wide amorphous rims surrounding many lunar soils grains exhibit distinct compositional differences from their hosts. On average, the amorphous rim compositions reflect the local bulk soil composition with the exceptions of Si and S, which are enriched relative to the bulk soil. These chemical trends led us to propose that the amorphous rims were in fact deposits of impact-generated vapors produced during regolith gardening, a hypothesis that runs contrary to the generally accepted view that the rims are produced through amorphization of the outer parts of mineral grains by interaction with the solar wind. Analytical data are reported for amorphous rims on individual minerals in lunar soils in order to show that the magnitude of the chemical differences between rim and host are so great that they require a major addition of foreign elements to the grain surfaces. The average composition of amorphous rims is listed as a function of host mineralogy as determined in microtone thin sections using energy-dispersive X-ray spectrometry in the transmission electron microscope. As the host mineral becomes chemically more complex, the chemical differences are not as clear. The average rim compositions are remarkably similar and are independent of the host grain mineralogy. Whether there are 'sputtering' or radiation effects superimposed on the vapor-deposited material can be debated. We do not explicitly exclude the effects of radiation damage as a contributing factor to the formation of amorphous rims; we are merely emphasizing the major role played by condensed vapors in the formation of amorphous rims on lunar soil grains.

Keller, L. P.↗
NASA NTRS2013

Characterizing the Phyllosilicates and Amorphous Phases Found by MSL Using Laboratory XRD and EGA Measurements of Natural and Synthetic Materials

The Curiosity Rover landed on the Peace Vallis alluvial fan in Gale crater on August 5, 2012. A primary mission science objective is to search for past habitable environments, and, in particular, to assess the role of past water. Identifying the minerals and mineraloids that result from aqueous alteration at Gale crater is essential for understanding past aqueous processes at the MSL landing site and hence for interpreting the site's potential habitability. X-ray diffraction (XRD) data from the CheMin instrument and evolved gas analyses (EGA) from the SAM instrument have helped the MSL science team identify phases that resulted from aqueous processes: phyllosilicates and amorphous phases were measure in two drill samples (John Klein and Cumberland) obtained from the Sheepbed Member, Yellowknife Bay Fm., which is believed to represent a fluvial-lacustrine environment. A third set of analyses was obtained from scoop samples from the Rocknest sand shadow. Chemical data from the APXS instrument have helped constrain the chemical compositions of these secondary phases and suggest that the phyllosilicate component is Mg-enriched and the amorphous component is Fe-enriched, relatively Si-poor, and S- and H-bearing. To refine the phyllosilicate and amorphous components in the samples measured by MSL, we measured XRD and EGA data for a variety of relevant natural terrestrial phyllosilicates and synthetic mineraloids in laboratory testbeds of the CheMin and SAM instruments. Specifically, Mg-saturated smectites and vermiculites were measured with XRD at low relative humidity to understand the behavior of the 001 reflections under Mars-like conditions. Our laboratory XRD measurements suggest that interlayer cation composition affects the hydration state of swelling clays at low RH and, thus, the 001 peak positions. XRD patterns of synthetic amorphous materials, including allophane, ferrihydrite, and hisingerite were used in full-pattern fitting (FULLPAT) models to help determine the types and abundances of amorphous phases in the martian rocks and sand shadow. These models suggest that the rocks and sand shadow are composed of approx 30% amorphous phases. Sulfate-adsorbed allophane and ferrihydrite were measured by EGA to further understand the speciation of the sulfur present in the amorphous component. These data indicate that sulfate adsorbed onto the surfaces of amorphous phases could explain a portion of the SO2 evolution in the Rocknest SAM data. The additional constraints placed on the mineralogy and chemistry of the aqueous alteration phases through our laboratory measurements can help us better understand the nature of the fluids that affected the different samples and devise a history of aqueous alteration for the Sheepbed Member of the Yellowknife Bay Fm. at Gale crater.

Rampe, Elizabeth B.↗
NASA NTRS2017

The Amorphous Composition of Three Mudstone Samples from Gale Crater: Implications for Weathering and Diagenetic Processes on Mars

The Mars Science Laboratory rover, Curiosity, is exploring the lowermost formation of Gale crater's central mound. Within this formation, three samples named Marimba, Quela, and Sebina have been analyzed by the CheMin X-ray diffractometer and the Alpha Particle X-ray Spectrometer (APXS) to determine mineralogy and bulk elemental chemistry, respectively. Marimba and Quela were also analyzed by the SAM (Sample Analysis at Mars) instrument to characterize the type and abundance of volatile phases detected in evolved gas analyses (EGA). CheMin data show similar proportions of plagioclase, hematite, and Ca-sulfates along with a mixture of di- and trioctahedral smectites at abundances of approximately 28, approximately 16, and approximately 18 wt% for Marimba, Quela, and Sebina. Approximately 50 wt% of each mudstone is comprised of X-ray amorphous and trace crystalline phases present below the CheMin detection limit (approximately 1 wt%). APXS measurements reveal a distinct bulk elemental chemistry that cannot be attributed to the clay mineral variation alone indicating a variable amorphous phase assemblage exists among the three mudstones. To explore the amorphous component, the calculated amorphous composition and SAM EGA results are used to identify amorphous phases unique to each mudstone. For example, the amorphous fraction of Marimba has twice the FeO wt% compared to Quela and Sebina yet, SAM EGA data show no evidence for Fe-sulfates. These data imply that Fe must reside in alternate Fe-bearing amorphous phases (e.g., nanophase iron oxides, ferrihydrite, etc.). Constraining the composition, abundances, and proposed identity of the amorphous fraction provides an opportunity to speculate on the past physical, chemical, and/or diagenetic processes which produced such phases in addition to sediment sources, lake chemistry, and the broader geologic history of Gale crater.

Achilles, C. N.↗
NASA NTRSDate not supplied

Characterizing Martian X-ray Amorphous Materials through Terrestrial Analogs

X-ray amorphous materials (i.e., lacking long-range crystallographic order) have been identified on the martian surface from orbit and in-situ. Initial models of orbital IR spectral data identified volcanic glasses [e.g., 1], but subsequent interpretations suggested that amorphous silicates are dominantly secondary in nature and formed from water-rock interactions [e.g., 2-4]. ThermalIR spectra from the Mini-Thermal Emission Spectrometer on the Spirit rover show evidence for the amorphous secondary product opaline silica[e.g., 5].X-ray diffraction (XRD) measurements by the CheMin instrument on the Mars Science Laboratory rover have identified 20-70 wt.% amorphous materials in every sample analyzed in Gale crater to date [e.g., 6]. Mass balance calculations using CheMin results and bulk elemental measurements by the Alpha Particle X-ray Spectrometer suggest the amorphous component in Gale crater is variably enriched in Si, Fe, and S[e.g., 7,8].The compositions are not consistent with pure volcanic glass, indicating water must have been involved in the formation of amorphous materials in Gale crater. We seek to better constrain the conditions under which amorphous materials on Mars formed by studying the composition and short-range atomic order of amorphous materials in terrestrial analog environments via XRD and transmission electron microscopy (TEM).

E. B. Rampe↗
NASA NTRSDate not supplied

Characterizing Martian X-Ray Amorphous Materials Through Terrestrial Analogs

X-ray amorphous materials (i.e., lacking long-range crystallographic order) have been identified on the martian surface from orbit and in-situ. Initial models of orbital IR spectral data identified volcanic glasses [e.g., 1], but subsequent interpretations suggested that amorphous silicates are dominantly secondary in nature and formed from water-rock interactions [e.g., 2-4]. Thermal IR spectra from the Mini-Thermal Emission Spectrometer on the Spirit rover show evidence for the amorphous secondary product opaline silica [e.g., 5]. X-ray diffraction (XRD) measurements by the CheMin instrument on the Mars Science Laboratory rover have identified 20-70 wt.% amorphous materials in every sample analyzed in Gale crater to date [e.g., 6]. Mass balance calculations using CheMin results and bulk elemental measurements by the Alpha Particle X-ray Spectrometer suggest the amorphous component in Gale crater is variably enriched in Si, Fe, and S [e.g., 7,8]. The compositions are not consistent with pure volcanic glass, indicating water must have been involved in the formation of amorphous materials in Gale crater. We seek to better constrain the conditions under which amorphous materials on Mars formed by studying the composition and short-range atomic order of amorphous materials in terrestrial analog environments via XRD and transmission electron microscopy (TEM).

E B Rampe↗
NASA NTRSDate not supplied

High Resolution Imaging and Analysis of Terrestrial Impact Glass: Amorphous Materials, Phyllosilicates and Everything in Between

Introduction: Impact cratering is one of the most ubiquitous geologic processes shaping the surface of all solid bodies in our solar system. Impacts are also a major source of clay minerals, poorly crystalline clay-like phases and amorphous (i.e., lacking long-range atomic order) materials on Earth and Mars. Phyllosilicates and amorphous materials have consistently formed a major component (~20-70 wt%) of every single drilled rock and soil sample in Gale Crater on Mars, as determined by the CheMin instrument on Curiosity. The origin of the amorphous component is speculative, but could be primary impact or volcanic-produced glass(es) deposited via aeolian or fluvial processes, secondary aqueous alteration products or chemical precipitates; it is likely to be a combination of all three possibilities. Efforts to determine the composition of these materials across the rover’s traverse through Gale Crater are ongoing. Naturally occurring amorphous phases are found in a variety of environments on Earth, and terrestrial analogue studies may help shed light on how they may have formed on Mars. Primary and altered impact glass are likely widespread on Mars and may have contributed to the amorphous component found throughout Gale Crater. In its pristine, unaltered state, impact glass (i.e., melt glass) is considered amorphous. However, truly unaltered glass is rarely preserved in crater fill impactites as it quickly alters in the post-impact environ-ment, commonly forming a mixture of hydrated aluminosilicate phases whose structures are not always discernable at the microscale (i.e., they may be amorphous or contain short-range order). These phases are part of an incredibly complex group of materials; differences in their composition and crystalline structure (or lack thereof) and genetic relationship to the more well-crystalline clay minerals are often only discernable at the nanoscale, beyond the resolution of traditional X-ray diffractometers (XRD) and scanning electron microscopes/microprobes (SEM/EPMA) alone. In this contribution, we summarize recent results from ongoing characterization of clay minerals, poorly crystalline clay-like phases, and amorphous materials preserved in altered terrestrial impact glass from the Chicxulub (~66 Ma) and Ries (~15 Ma) impact structures. This work has been performed using a combination of high-resolution transmission electron microscopy (HR-TEM), SEM, microprobe/EPMA, Raman spectroscopy and XRD.

Impact crater↗
DOE OSTI2024

Method for electrochemical transformation of amorphous material to crystalline material

A method for converting amorphous boron nitride to crystalline boron nitride, the method comprising immersing the amorphous boron nitride into anhydrous molten magnesium chloride maintained within a temperature range of 720° C.-820° C. while the amorphous boron nitride is cathodically polarized at a voltage within a range of −2.2V to −2.8V for a period of time of at least 2 minutes to result in conversion of the amorphous boron nitride to the crystalline form. Also described herein is a method for converting an amorphous carbon material to a crystalline carbon material, the method comprising immersing said amorphous carbon material into anhydrous molten magnesium chloride maintained within a temperature range of 780° C.-820° C. while the amorphous carbon material is cathodically polarized at a voltage within a range of −2.2V to −2.8V for a period of time of at least 2 minutes to result in conversion of the amorphous carbon material to the crystalline form.

Bagri, Prashant↗
DOE OSTI2025

Pressure-driven density match nucleates metastable r8 phases from amorphous Si and Ge

The pressure–temperature phase behavior of covalent disordered solids such as amorphous silicon and germanium is complex. Questions remain on possible glass transitions, on polyamorphism via amorphous–amorphous transitions, on connections with liquid–liquid transitions, on structure-behavior relationships, and on their potential as precursor for novel methods for material discovery. Here we demonstrate experimentally the nucleation of a metastable, four-fold coordinated rhombohedral r8 phase from pure amorphous silicon and germanium upon room temperature compression at pressures below 10 GPa. Accompanying theory reveals a strong pressure-driven distortion of the bond angle transforming the starting tetrahedral low-density amorphous network to a distorted four-fold coordinated medium-density state. This state is of lower density than metallic high-density networks, resembles the crystalline r8 phase and initiates its nucleation. Our finding shows that polyamorphism is not the only possible transformation mode for these amorphous solids and that instead nucleation of interesting functional phases at potentially useful pressures is possible. Such novel access modes to metastable structures are critical for future exploitability and could be useful for other tetrahedral materials including carbon, where the related (bc8) post-diamond phase remains elusive. Our observed density match between an amorphous and a metastable crystalline phase clearly allows for a new phase transition pathway, while corresponding theory demonstrates how carefully validated atomistic simulations can guide prediction, discovery and synthesis of novel material structures.

Materials discovery↗
DOE OSTI2024

Structure, bonding and electronic characteristics of amorphous Se

Ovonic threshold switching (OTS) selector can effectively improve the storage density and suppress the leakage current of advanced phase-change memory. As a prototypical OTS material, amorphous GeSe is widely investigated. But the attentions paid to amorphous Se (i.e., the functional constituent in amorphous GeSe) is very limited up to now. Here, in this work, we have explored the structure, bonding and electronic characteristics of amorphous Se using ab initio molecular dynamics simulations. The results reveal that the Se atoms in amorphous Se tend to form the 2-coordinated configurations, and they connect with each other to form the long chains. The fraction of vibrational density of state located in high frequency range is relatively large, and the formation energy of Se-Se bond is as large as 4.44 eV, hinting that the Se-Se bonds in chains possess a high stability. In addition, the mid-gap state related to the OTS behavior is also found in the amorphous Se despite of the small proportion. Our findings enrich the knowledge of the amorphous Se, which contributes to the applications of Se-based OTS selectors.

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

Amorphization and Crystallization of Hexanitroazobenzene (HNAB) Using Conventional DSC and Flash DSC

Abstract The present work presents results from an investigation of the glass transition and crystallization behaviors of HNAB tested over more than five orders of magnitude of cooling rate from 0.005 °C/s to 600 °C/s (0.3 to 36000 °C/min) by a combination of conventional and Flash differential scanning calorimetry (DSC). The work quantifies the influence of the thermal amorphization route on the properties of this high explosive. Cooling rates faster than 100 °C/s (6000 °C/min) result in amorphous HNAB as expected from prior work, but we also find that amorphization of the HNAB occurs at cooling rates slower than 0.008 °C/s (0.5 °C/min). The behavior of the amorphous HNAB made by slow cooling is compared with that of amorphous HNAB made by fast cooling, as well as with that made by solvent casting in terms of glass transition temperature, apparent activation energy of glass transition, and dynamic fragility parameter m . Besides, the non‐isothermal crystallization response as a function of cooling rate is also reported. The thermal stability and decomposition energy of amorphous HNAB are compared with those of the crystalline counterpart, being similar heats of decomposition of 3295 and 3392 J/g, respectively; suggesting that the amorphous HNAB will have similar thermal stability and chemical energy to the crystalline form.

Koh, Yung P.↗
DOE OSTI2021

Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys

Amorphous complexions in nanocrystalline metals have the potential to improve mechanical properties and radiation tolerance, as well as resistance to grain growth. In this study, the stability of amorphous complexions in binary and ternary Cu-based alloys is investigated by observing the effect of cooling rate from high temperature on the occurrence of amorphous-to-ordered complexion transitions. Bulk Cu-Zr and Cu-Zr-Hf alloy samples were annealed to induce boundary premelting and then quenched through a procedure that induces a gradient of local cooling rate through the sample height. Amorphous complexion thickness distributions were found to be invariant to local cooling rate in the Cu-Zr-Hf alloy, demonstrating enhanced stability of the amorphous complexion structure compared to the Cu-Zr alloy, which had thinner amorphous complexions in the regions that were slowly cooled. The experimental results are used to construct time-temperature-transformation diagrams for the amorphous-to-ordered complexion transition in both the binary and ternary alloys, enabling a deeper understanding of the influence of cooling rate and grain boundary chemistry on complexion transitions. In conclusion, the critical cooling rate necessary to avoid complexion transitions in the ternary alloy is found to be at least three orders of magnitude slower than that for the binary alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A High Energy X-ray Diffraction Study of Amorphous Indomethacin

Amorphous pharmaceuticals often possess a wide range of molecular conformations and bonding arrangements. The x-ray pair distribution function (PDF) method is a powerful technique for the characterization of variations in both intra-molecular and inter-molecular packing arrangements. Here, the x-ray PDF of amorphous Indomethacin is shown to be particularly sensitive to the preferred orientations of the chlorobenzyl ring found in isomers in the crystalline state. In some cases, the chlorobenzyl ring has no preferred torsional angle in the amorphous form, while in others evidence of distinct isomer orientations are observed. Amorphous samples with no preferred torsion angles of the chlorobenzyl ring are found to favor enhanced inter-molecular hydrogen bonding, and this is reflected in the intensity of the first sharp diffraction peak. These significant variations in structure rule out amorphous Indomethacin as a possible standard for x-ray PDF measurements. At high humidity, time resolved PDF's for >40 h reveal water molecules forming hydrogen bonds with Indomethacin molecules. Finally, a simple linear hydrogen bond model indicates that water molecules in the wet amorphous form have similar hydrogen bond strengths to those found between Indomethacin dimers or chains in the dry amorphous form.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Orientation-dependent mutual crystalline and amorphous order in a single phase solid

Amorphous materials distinguish themselves from crystalline materials by lacking long-range order while retaining structural order at the local scale (2–5 Å). However, the complexity in topological and chemical order prevents current characterization tools from fully unveiling the structure in disordered materials. Consequently, the nature of medium-range order in amorphous materials has remained elusive. The Zachariasen and crystal competing models have been proposed to describe disordered phases and have both been verified through synthesis and characterization. The main difference between them is thought to be whether the amorphous phase shows medium-range order. Here we demonstrate a form of organized inorganic matter that is amorphous in two dimensions, while exhibiting long-range order and a high degree of crystallinity in the third. The structure consists of periodically stacked 2-dimensional amorphous Nb-W-O monolayers without long-range in-plane order. The unique periodic and therefore crystalline stacking along one principal axis enables direct imaging and revealed that the amorphous Nb-W-O monolayers formed in agreement with the Zachariasen model for 2 dimensions. Our findings show that the gap between crystalline and amorphous materials does not only depend on medium-range order but can also apply to principal dimensions within the same solid.

Nanowires↗