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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Mechanisms of Three-Dimensional Solid-Phase Epitaxial Crystallization of Strontium Titanate

Strontium titanate (SrTiO 3 , STO) is a complex metal oxide with a cubic perovskite crystal structure. Due to its easily described and understood crystal structure in the cubic phase, STO is an ideal model system for exploring the mechanistic details of solid-phase epitaxy (SPE) in complex oxides. SPE is a crystallization approach that aims to guide crystal growth at low homologous temperatures to achieve targeted microstructures. Beyond planar thin films, SPE can also exploit the addition of a chemically inert, noncrystallizing, amorphous obstacle in the path of crystallization to generate complex three-dimensional structures. The introduction of this mask fundamentally alters the SPE process, inducing a transition from two- to three-dimensional geometries and from vertical to lateral crystal growth under the influence of the crystal/mask/amorphous boundary. Using a combination of molecular dynamics simulations and experiments, we identify several unique phenomena in the nanoscale growth behaviors in both conventional (unmasked) and masked SPE. Examining conventional SPE of STO, we find that crystallization at the interface is strongly correlated to, and potentially driven by, density fluctuations in the region of the amorphous STO near the crystalline/amorphous interface with a strong facet dependence. In the masked case, we find that the crystalline growth front becomes nonplanar near contact with the mask. We also observe a minimum vertical growth requirement prior to lateral crystallization. Both phenomena depend on the relative bulk and interfacial free energies of the three-phase (crystal/mask/amorphous) system.

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

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH) 4 – ) or dimeric (Al 2 O(OH) 6 2– ) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH) 4 – and Al 2 O(OH) 6 2– anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K 2 [Al 2 O(OH) 6 ], Rb 2 [Al 2 O(OH) 6 ], and Cs[Al(OH) 4 ]·2H 2 O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al 2 O(OH) 6 2– anions, while the third contains the monomeric Al(OH) 4 – anion. Here, comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

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

Role of Surface Features on the Initial Dissolution of CH 3 NH 3 PbI 3 Perovskite in Liquid Water: An Ab Initio Molecular Dynamics Study

In this study, the degradation of CH 3 NH 3 PbI 3 (MAPbI 3 ) hybrid organic inorganic perovskite (HOIP) by water has been the major issue hampering its use in commercial perovskites solar cells (PSCs) as MAPbI 3 HOIP have been known to easily degrade in the presence of water molecules. However, even though there have been numerous studies investigating this phenomenon, there is still no consensus on the mechanisms of initial stages of dissolution. Here, we attempt to consolidate differing mechanistic interpretations previously reported in the literature through the use of the first-principles constrained ab-initio molecular dynamics (AIMD) to study the mechanisms, kinetics, and thermodynamics that accompany the degradation of MAPbI 3 HOIP in liquid water. We consider not only the dissolution of the species found on the pristine MAPbI 3 HOIP surfaces, but also the dissolution from defect sites to imitate the successive degradation steps, and propose a sequence of events in the initial phase of MAPbI 3 HOIP dissolution. By comparing the dissolution free energy barrier between surface species of different surficial types, we find that the dominant dissolution mechanisms of surface species varies widely based on the specific surface features adjacent to the dissolving ion. The high sensitivity of dissolution mechanism to surface features has contributed to the many dissolution mechanisms proposed in the literature. In contrast, the dissolution free energy barriers are mainly determined by the dissolving species rather than the type of surfaces, and the type of surfaces the ions are dissolving from are inconsequential toward the dissolution free energy barrier. However, the presence of surface defects such as vacancy sites are found to significantly lower the dissolution free energy barriers. Based on the estimated dissolution free energy barriers from different types of surfaces that we investigated in this study, we proposed that the dissolution of MAPbI 3 HOIP in liquid water originates from surface defect sites that propagate laterally along the surface layer of the MAPbI 3 HOIP crystal.

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

Moving beyond the constraints of chemistry via crystal structure discovery with isotropic multiwell pair potentials

The rigid constraints of chemistry-dictated by quantum mechanics and the discrete nature of the atom-limit the set of observable atomic crystal structures. What structures are possible in the absence of these constraints? Here, we systematically crystallize one-component systems of particles interacting with isotropic multiwell pair potentials. We investigate two tunable families of pairwise interaction potentials. Our simulations self-assemble a multitude of crystal structures ranging from basic lattices to complex networks. Sixteen of the structures have natural analogs spanning all coordination numbers found in inorganic chemistry. Fifteen more are hitherto unknown and occupy the space between covalent and metallic coordination environments. The discovered crystal structures constitute targets for self-assembly and expand our understanding of what a crystal structure can look like.

crystal structures↗
DOE OSTI2024

Halide Perovskites Breathe Too: The Iodide–Iodine Equilibrium and Self-Doping in Cs 2 SnI 6

The response of an oxide crystal to the atmosphere can be personified as breathing-a dynamic equilibrium between O 2 gas and O 2– anions in the solid. We characterize the analogous defect reaction in an iodide double-perovskite semiconductor, Cs 2 SnI 6 . Here, I 2 gas is released from the crystal at room temperature, forming iodine vacancies. The iodine vacancy defect is a shallow electron donor and is therefore ionized at room temperature; thus, the loss of I2 is accompanied by spontaneous n-type self-doping. Conversely, at high I 2 pressures, I 2 gas is resorbed by the perovskite, consuming excess electrons as I 2 is converted to 2I – . Halide mobility and irreversible halide loss or exchange reactions have been studied extensively in halide perovskites. However, the reversible exchange equilibrium between iodide and iodine [2I – (s) ↔ I 2(g) + 2e – ] described here has often been overlooked in prior studies, though it is likely general to halide perovskites and operative near room temperature, even in the dark. An analysis of the 2I – (s) /I 2(g) equilibrium thermodynamics and related transport kinetics in single crystals of Cs 2 SnI 6 therefore provides insight toward achieving stable composition and electronic properties in the large family of iodide perovskite semiconductors.

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

Observation of an Orientational Glass in a Superlattice of Elliptically-Faceted CdSe Nanocrystals

Extensive prior work has shown that colloidal inorganic nanocrystals coated with organic ligand shells can behave as artificial atoms and, as such, form superlattices with different crystal structures and packing densities. Although ordered superlattices present a high degree of long-range positional order, the relative crystallographic orientation of the inorganic nanocrystals with respect to each other tends to be random. Recent works have shown that superlattices can achieve orientational alignment through combinations of nanocrystal faceting and ligand modification, as well as selective metal particle attachment to particular facets. These studies have focused on the assembly of high-symmetry nanocrystals, such as cubes and cuboctahedra. In this work, we study the assembly of elliptically faceted CdSe/CdS core/shell nanocrystals with one distinctive crystallographic orientation along the major elliptical axis. We show that the nanocrystals form an unexpectedly well-ordered translational superlattice, with a degree of order comparable to that achieved with higher-symmetry nanocrystals. Additionally, we show that, due to the particles' faceted shape, the superlattice is characterized by an orientational glass phase in which only certain orientations are possible due to entropically frustrated crystallization. In this phase, the nanocrystals do not exhibit a local orientational ordering but rather have distinct orientations that emerge at different locations within the same domain. The distinct orientations are a result of a facet-to-facet lock-in mechanism that occurs during the self-assembly process. These facet-to-facet alignments force the nanocrystals to tilt on different lattice planes forming different projections that we termed apparent polydispersity. Our experimental realization of an orientational glass phase for multifaceted semiconducting nanocrystals can be used to investigate how this phase is formed and how it can be utilized for potential optical, electrical, and thermal transport applications.

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

Quantifying the Relevance of Long-Range Forces for Crystal Nucleation in Water

Understanding nucleation from aqueous solutions is of fundamental importance in a multitude of fields, ranging from materials science to biophysics. The complex solvent-mediated interactions in aqueous solutions hamper the development of a simple physical picture, elucidating the roles of different interactions in nucleation processes. In this study, we make use of three complementary techniques to disentangle the role played by short- and long-range interactions in solvent-mediated nucleation. Specifically, the first approach we utilize is the local molecular field (LMF) theory to renormalize long-range Coulomb electrostatics. Second, we use well-tempered metadynamics to speed up rare events governed by short-range interactions. Third, the deep learning-based State Predictive Information Bottleneck approach is employed in analyzing the reaction coordinate of the nucleation processes obtained from the LMF treatment coupled with well-tempered metadynamics. We find that the two-step nucleation mechanism can largely be captured by the short-range interactions, while the long-range interactions further contribute to the stability of the primary crystal state under ambient conditions. Furthermore, by analyzing the reaction coordinate obtained from the combined LMF-metadynamics treatment, we discern the fluctuations on different time scales, highlighting the need for long-range interactions when accounting for metastability.

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

Sculpting 2D Crystals via Membrane Contractions before and during Solidification

When phospholipids crystallize within the otherwise fluid membranes of giant unilamellar vesicles, the resulting molecularly thin “2D” solids exhibit great variety in their morphology evolution. For example, within membranes containing moderate amounts of the crystallizing component, crystals grow with a fixed morphology depending on vesicle size. Conversely for membranes containing large amounts of the crystallizing species, we find small compact crystals on vesicles of all sizes. However, on large vesicles, growing crystals sprout flower petals that lengthen progressively. These behaviors result from two combined mechanisms: first, like other 2D solids, the shear rigidity of phospholipid crystals renders them intolerant to morphologies with nonzero Gaussian curvature. As a result and especially at elevated membrane tension, the cost of bending elasticity is reduced at the expense of line energy by the formation of flowers as opposed to compact crystals. Second, the composition-dependent tension rise during cooling relaxes via water permeation of the membrane with a time constant scaling as R2. The amount of crystal formed for a small decrease in temperature determines this composition-dependent increase in stress from thermal contractions versus solidification. Surface Evolver computations were motivated using the predicted tension evolution to develop a processing space that maps to experimental observations for initial and growing crystal morphology. Important variable groups are identified, including a scaled ratio of bending to line energy, a vesicle-size-independent group for membrane contractions, and a time constant for stress relaxation. Though processing stresses ultimately relax, the crystal morphology persists well beyond the processing window.

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

Toward In Situ Synchrotron Mapping of Crystal Selection Processes during Crystal Growth

In this work, we present an automated and rapid method for non-destructive mapping of crystal grains in a rod-shaped sample. The approach was designed for application to in situ float-zone crystal growth experiments at an x-ray synchrotron source, but could be useful in other applications. The methods have been tested on a TiO 2 boule grown in an optical float zone furnace. The approach applies a statistical filter to polycrystalline diffraction patterns on 2D detectors to rapidly determine the degree of powder-quality 1of the signal. When larger crystals emerge in the growth, their position, size and shape can be tracked using an automated blob-tracking algorithm that follows individual Bragg peaks as a function of position in a grid-scan, even when multiple crystals are contributing spots to diffraction images. This method is found to be robust as the same crystal shape can be independently reconstructed using different sets of Bragg reflections. Image segmentation methods are then used to map out the polycrystalline grains. We also note that other information about crystal quality, such as mosaicity or strain state, may be inferred and mapped from the intensity variation of the Bragg peaks at different locations within the sample.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Observation of [VCu1–Ini2+VCu1–] Defect Triplets in Cu-Deficient CuInS2

Copper indium disulfide (CuInS2) is a semiconductor with a direct energy band gap of 1.53 eV, an optimal value for highly efficient thin-film solar cells. But it has reached only ~ 11 % power conversion efficiency, far less than the theoretically achievable value of ~ 30 %. The cause of this low performance is not understood. A single crystal grown from 1 mol% Cu-deficient melt was studied, using atomic resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and electron dispersive spectroscopy (EDS). While the bulk crystal is exactly stoichiometric CuInS2, it contains nanometer-thick, structurally coherent, Cu-deficient interphases that form along rotational twin boundaries in the {112} plane. Transition zones from bulk crystal to interphase are observed, where In is seen to move from its normal site InIn in the chalcopyrite structure to a tetrahedral interstitial site Ini, while Cu remains in its normal CuCu position. Two InIn rows of the bulk crystal merge into one row of Ini, causing excess Ini in the interphase. The concentrations of CuCu and Ini reflect a ratio of Cu vacancies, VCu, to excess Ini of ~ 2. Their relative lattice positions, and the high electrical resistivity of the crystal, suggests that VCu and excess Ini ‘precipitate’ as self-compensating, electrically neutral, [VCu1- Ini2+ VCu1-] defect triplets. This is the first atomic-level observation of the ordered defect that has been invoked as the basic structural modifier in chalcopyrite compound homologs. The interphases introduce an optical gap of 1.47 eV. Electron trapping in band tail states, evident from a photoconductivity exponent of 0.54, is the likely cause of an unusually low electron mobility of 0.1 cm2V-1s-1. The overall result is that making CuInS2 slightly copper-poor inserts nanometer-thick layers of the interphase into the bulk crystal. This study shows that apparently conflicting results of the effect of Cu deficiency on CuInS2 thin-film solar cells may be resolved by analyzing structure and composition at nanometer spatial resolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Exploring the influence of transition metals on f-element bonding

The United States aims to triple its nuclear energy production by 2050, which will result in increased uranium usage and spent nuclear fuel generation. This highlights the need for a comprehensive understanding of actinide coordination chemistry, which is crucial for the extraction, processing, purification, and fabrication of uranium-based fuels. Moreover, it is vital for the reprocessing or safe disposal of nuclear waste and effective remediation efforts. Achieving this successfully requires an in-depth understanding of f-electron behavior, as “the role of 5f electrons in bond formation remains a fundamental topic in actinide chemistry”. Introducing a second metal into the system can increase structural dimensionality and diversify structural architecture. Heterometallic systems can also alter material properties, such as magnetic and spectroscopic characteristics, luminescence, and actinide mobility. Additionally, secondary transition metals, even when present only in the second coordination sphere and not directly coordinated, can influence the electron density at the actinyl metal center. In this study, uranium heterometallic single crystals were synthesized by incorporating transition metals such as iron(III), iron(II), nickel(II), manganese(II), copper(I), and cobalt(II). The crystals were formed using 2,6-pyridine dicarboxylic acid and other structurally similar ligands with varying functional groups. The synthesized crystals were analyzed using an extensive array of analytical and computational characterization techniques, including single crystal X-ray diffraction, Raman and infrared spectroscopy, and density functional theory calculations.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2021

Scaling up of High-Performance Single Crystalline Ni-rich Cathode Materials (CRADA 509)

This is a collaborative effort between Battelle Memorial Institute as manager and operator of Pacific Northwest National Laboratory (PNNL) and Albemarle Corporation (“Participant”) to develop and scale up an innovative and low-cost synthesis approach for preparing high-performance single crystalline Ni-rich cathode materials, i.e., LiNi0.8Mn0.1Co0.1O2 (NMC811) and LiNi0.9Mn0.05Co0.05O2 (NMC90) for next-generation LIBs. At the end of this project, the team will (1) develop a cost-effective synthesis approach for preparing single crystalline MNC811 (>200 mAh/g) and NMC90 (>210 mAh/g) by using advanced lithium salts, (2) address the performance issues of single crystals prepared from large-scale synthesis, and (3) demonstrate the processing/scaling up capabilities of up to 1 kg/batch of high-performance NMC811 and NMC90 single crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Crystal structure of hexachlorothallate within a caesium chloride–phosphotungstate lattice Cs 9 (TlCl 6 )(PW 12 O 40 ) 2 ·9CsCl

Crystal formation of caesium thallium chloride phosphotungstates, Cs 9 (TlCl 6 )(PW 12 O 40 ) 2 ·9CsCl showcases the ability to capture and crystallize octahedral complexes via the use of polyoxometalates (POMs). The large number of caesium chlorides allows for the POM [α-PW 12 O 40 ] 3- to arrange itself in a cubic close-packing lattice extended framework, in which the voids created enable the capture of the [TlCl 6 ] 3- complex.

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

Synthesis and Structural Characterization of 2′‐Deoxy‐2′‐Methoxy‐ L ‐Cytidine Nucleic Acids

Abstract We report here for the first time the synthesis of a novel 2′‐methoxy‐modified L‐cytidine analog and its phosphoramidite, as well as its incorporation into oligonucleotides via solid‐phase synthesis. Our measure the thermostability of the modified L‐nucleic acids by UV‐melting studies, and find out the 2′‐methoxy‐derivatization enhances the thermostability of the L‐duplexes. Consistent with the thermostability result, our X‐ray crystal structure study reveals that the 2′‐methoxy‐L‐deoxycytidine forms the Watson‐Crick base pair with L‐guanosine virtually as the mirror‐image fashion of native pair. This novel chemically modified L‐cytidine provides a useful biochemical and structural strategy to create mirror‐image nucleic acid molecules with expanded functionalities.

2′-Methoxy↗