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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Orientational Order in Spin-Cast Lead-Iodide Perovskite Nanocrystal Solids

Combined synthetic control over size and composition renders colloidal lead-halide perovskite nanocrystals a tunable platform for high-efficiency optoelectronic applications. However, the properties and operational stability of devices based on nanocrystal solids are often dictated by the method of the evaporation-induced assembly. Ubiquitous slow evaporation techniques can produce highly ordered nanocrystal domains but limit the prospects for scalable fabrication of continuous device layers, calling for investigation of approaches to more rapidly form ordered perovskite nanocrystal solids. Here, we study orientationally ordered lead-iodide perovskite nanocrystal solids prepared by conventional spin coating with molecular additives (excess ligand) to enhance ordering within the arrays. In situ X-ray scattering measurements reveal that orientational ordering occurs rapidly upon solvent removal during spin coating and can be further enhanced by manipulating the spin speed. We vary the additive ligand length and explore trade-offs between ordering and layered perovskite impurity formation. Arrays treated with the intermediate-length octylamine ligand exhibit increased in-plane electronic conductivity, suggesting orientational ordering and internanocrystal electronic coupling can be enhanced by the treatment. In conclusion, these results highlight the prospects of establishing long-range order in lead-halide perovskite nanocrystal solids by using simple and fast coating methods.

14 SOLAR ENERGY↗
DOE OSTI2024

Generic Behavior of Ultrastability and Anisotropic Molecular Packing in Codeposited Organic Semiconductor Glass Mixtures

Vapor-deposited glass mixtures of organic semiconductors commonly serve as active layers in organic electronic devices, whose lifetime and performance are strongly influenced by the stability and structure of these mixed glasses. Here, we study the stability and anisotropic molecular packing of six co-deposited organic semiconductor glass mixtures with 50:50 weight ratio, by differential scanning calorimetry and spectroscopic ellipsometry. We also find that all six binary systems exhibit high kinetic stability and significantly reduced enthalpy relative to the corresponding liquid-cooled glassy mixtures (ultrastable behavior), even for systems where the glass transition temperatures of the components differ by more than 90 K. Furthermore, we demonstrate that the birefringence of a co-deposited glass mixture, a measure of its anisotropic packing, can be predicted from the birefringence of glasses of the two pure components. These results for stability and structure are expected to be applicable to other co-deposited organic semiconductor glass mixtures, so long as the two components mix well in the glass and individually can form ultrastable glasses. Therefore, our findings are significant for designing novel electronic devices with enhanced device lifetime and increased operational efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unraveling the Growth Mechanism of Strongly Confined CsPbBr 3 Perovskite Quantum Dots under Thermodynamic Equilibrium Control

Size-confined lead halide perovskite quantum dots (PQDs) are promising materials for optoelectronic devices. Large quantities of PQDs with high ensemble uniformity are often needed for device fabrication. The thermodynamic-equilibrium-controlled synthesis can produce PQDs with good size and shape uniformity. Unfortunately, scaling up this synthesis often produces unwanted perovskite nanoplatelets (NPLs). To date, the PQD and NPL growth mechanism under thermodynamic equilibrium control remains unexplored. We discovered that the growth of size-confined CsPbBr 3 PQDs is mediated by ultrasmall (~ 2.4 nm) metastable nanoclusters. These nanoclusters can eventually grow into PQDs when sufficient Cs-precursors are provided. Otherwise, the unreacted nanoclusters will self-assemble and fuse into NPLs during the synthesis and/or PQD purification. Furthermore, by controlling the homogeneous growth of nanoclusters, strongly confined (≤ 5 nm) PQDs with high size uniformity can be produced at the gram scale.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

(NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 , a Vacancy-Ordered Three-Dimensional Tin(II) Perovskite-Derived Semiconductor

Ordering vacancies in hybrid Sn(II) halide semiconductors provides a strategy for preventing uncontrolled oxidation and formation of mobile holes. In this study, we report the structure and optical and electronic properties of (NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 , a vacancy-ordered perovskite derivative with three-dimensional inorganic connectivity. The crystal structure resembles that of a Dion–Jacobson layered perovskite derivative, but with [SnI 5 ] square pyramids bridging the layers. UV–vis diffuse reflectance spectroscopy reveals a sharp onset of light absorption at 1.86(1) eV with the photoluminescence emission maximum at 1.90(1) eV. However, the maximum excitation occurs from 3.42 to 3.81 eV (325 to 370 nm), revealing a significant Stokes shift of 1.3 eV. The electronic properties determined from dark and time-resolved microwave conductivity measurements reveal a minimum carrier mobility of 4.3 × 10 –2 cm 2 V –1 s –1 and a maximum carrier density of 5.96 × 10 16 cm –3 , a uniquely low value for a hybrid Sn(II) halide semiconductor. The transport behavior in combination with first-principles calculations of the electronic band structure and dielectric permittivity suggest polaron-mediated electronic transport, yet the photogenerated carriers have a fast and fluence-dependent nonradiative recombination rate, suggestive of localized “defect-like” states at the band edge. The observed photoluminescence is most consistent with single-ion-like behavior of an asymmetric Sn(II) environment. Together, these results suggest that defect ordering presents a strategy for the reduction of mobile charge carriers at equilibrium.

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

Supramolecular Assembly of Multielement Ribbon-like Structures Derived from Halide Perovskites

Halide perovskites are crucial materials with broad applications owing to their exceptional optoelectronic properties. Vacancy-ordered double perovskites, featuring highly tunable transition metal sites, enable controllable optoelectronic properties through multielement compositional design. Here, in this study, we introduced 18-crown-6 into the vacancy-ordered double perovskites system and developed two-dimensional ribbon-like single crystals (18C6@K) 2 {PtSnTeIrRe} 1 Cl 6 via an antisolvent supramolecular assembly method, demonstrating morphology modulation through multielement composition design. The crystals crystallize in the centrosymmetric space group $P\bar{1}$. The dumbbell-shaped structural units (crown ether@A)2MX6 pack along a and b axes to form a 2-dimensional (2D) monolayer, and these monolayers further stack along the c axis to generate the ribbon-like single crystals. Energy-dispersive X-ray spectroscopy (EDX) qualitatively confirmed the uniform distribution of the five transition metals throughout the crystal, while inductively coupled plasma atomic emission spectroscopy (ICP–AES) quantitatively verified their atomic ratios. We further investigated the origin of the morphology, distinct from the previously reported cube-like single crystals with the $R\bar{3}$ space group. When acetonitrile was used as the solvent, three-dimensional crystals with $R\bar{3}$ symmetry were obtained, whereas dimethylformamide (DMF) was essential for forming two-dimensional ribbon-like single crystals. The essential role of DMF could be ascribed to its capability to maintain a higher concentration of the building blocks. Moreover, Ir 4+ and Pt 4+ cations also played critical roles in inducing the two-dimensional ribbon-like morphology. The three-element (18C6@K) 2 {PtSnTe}1Cl 6 single crystals exhibited bright yellow emission under 375 nm laser excitation, demonstrating the tunability of optoelectronic properties of this class of material.

Zhu, Heqing [University of California, Berkeley, C↗
DOE OSTI2026

Site-Selective Doping and Oxidation State Control of Copper in Gold Nanorods

We report the synthesis of plasmonic gold–copper nanostructures with tunable copper spatial distribution and oxidation state. Au–Cu alloy shells were deposited in aqueous solution onto colloidal gold nanorods that functioned as seeds, and the resulting shell morphology was found to depend strongly on the nanorod aspect ratio. For relatively fat gold nanorods (16 x 31 nm), Au–Cu growth was preferentially localized near the rod midsections, forming belt-like structures, whereas for skinnier nanorods (9 x 32 nm), Au–Cu growth produced patchy surface coverage around the entire rod. The shell thickness was tuned from 1 to 4 nm; upon air exposure, thicker shells exhibited a higher Cu(I) fraction compared to the initial shell. Incorporation of the Au–Cu shell led to pronounced shifts in the plasmonic features of the gold nanorods. These tunable plasmonic Au–Cu nanorods provide a materials basis for Cu-based plasmonic materials in the context of electrochemical CO₂ reduction.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Dithionite Inhibits Iron(III) (Hydr)oxide Formation during Olivine Dissolution Advancing Simultaneous CO 2 Mineralization and Nickel Recovery

Increasing CO 2 concentration poses significant global challenges, impacting both environmental and human health. As we strive for a carbon-neutral energy technology transition, the demand for critical elements (e.g., nickel and cobalt) continues to increase, while high-grade ores are depleting. Combining CO 2 mineralization with the recovery of critical elements from low-grade ores offers an innovative solution. Olivine, a magnesium-rich ultramafic with trace amounts of critical elements, is a promising mineral; however, its impurities, such as iron (Fe(III)), hinder the dissolution of Ni and Mg from olivine, reducing its carbonation and critical element recovery. Here, to address this challenge, this study examined Ni dissolution from San Carlos olivine at high temperatures and high CO 2 pressure. We found that iron(III) (hydr)oxide layers impeded olivine dissolution; however, with sodium dithionite (Na 2 S 2 O 4 ), a reducing agent, olivine dissolution is significantly improved by preventing iron(III) (hydr)oxide formation. With Na 2 S 2 O 4 , within 24 h, Mg and Ni dissolution from olivine increased 2.85-fold and 2.66-fold, respectively, compared to samples without Na 2 S 2 O 4 . After seven cycles, with solutions replaced every 24 h, 98.9% of the total Mg and 84.6% of the total Ni were recovered. This approach enhances olivine’s CO 2 mineralization and improves the sustainability of critical element supply.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Lignin-Derived Magnetic Activated Carbons for Effective Methylene Blue Removal

Large-scale environmental remediation of polluted water requires an effective and recyclable adsorbent produced from an abundant, low-cost, and renewable feedstock via a simple processing procedure. In this work, we demonstrate that lignin-derived magnetic activated carbons (mACs) uniquely satisfy these five criteria for (i) high-performance adsorption, (ii) high regeneration efficiency, (iii) feedstock economic and environmental viability, (iv) single-step processing and (v) large-scale production. The mACs are synthesized via an efficient co-carbonization and activation with simultaneous impregnation of ferric sulfate. Here, the Langmuir model closely fits the adsorption of methylene blue (MB) by mACs within the temperature range of 298–323 K, where the adsorption capacity increases as temperature increases. This capacity increased from 55.0 mg g -1 to 220.2 mg g -1 with the presence of magnetic nanoparticles. In addition, the magnetite nanoparticles on the ACs surface significantly improve its recycling ability with the removal percentage above 95% after four cycles for 5:1 mAC.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Structural Features of Zirconium-Based Metal–Organic Frameworks Affecting Radiolytic Stability

Metal–organic frameworks (MOFs) NU-1000 and UiO-66 are herein exposed to two different gamma irradiation doses and dose rates and analyzed to determine the structural features that affect their stability in these environments. MOFs have shown promise for the capture and sensing of off-gases at civilian nuclear energy reprocessing sites, nuclear waste repositories, and nuclear accident locations. However, little is understood about the structural features of MOFs that contribute to their stability levels under the ionizing radiation conditions present at such sites. This study is the first of its kind to explore the structural features of MOFs that contribute to their radiolytic stability. Both NU-1000 and UiO-66 are MOFs that contain Zr metal-centers with the same metal absorption cross section. However, the two MOFs exhibit different linker connectivities, linker aromaticities, node densities, node connectivities, and interligand separations. In this study, NU-1000 and UiO-66 were exposed to high (423.3 Gy/min, 23 min, and 37 s) and low (0.78 Gy/min, 4320 min) dose rates of 60 Co gamma irradiation. NU-1000 displayed insignificant radiation damage under both dose rates due to its high linker connectivity, low node density, and low node connectivity. However, low radiation dose rates caused considerable damage to UiO-66, a framework with lower aromaticity and smaller interligand separation. Finally, results suggest that chronic, low-radiation environments are more detrimental to Zr MOF stability than acute, high-radiation conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Stabilization of Photocatalytically Active Uranyl Species in a Uranyl–Organic Framework for Heterogeneous Alkane Fluorination Driven by Visible Light

When photoactivated, the uranyl ion is a robust oxidant capable of abstracting hydrogen atoms from nonactivated C–H bonds. Yet, the highly reactive singly reduced [U V O 2 ] + intermediate is unstable with respect to disproportionation to the uranyl dication and insoluble tetravalent uranium phases, which limits the usage of uranyl ions as robust photocatalysts. Herein, we demonstrate that photoactivated uranyl ions can be stabilized by immobilizing and separating them spatially in a uranyl–organic framework heterogeneous catalyst, NU-1301. The visible-light-photoactivated uranyl ions in NU-1301 demonstrated longer-lived U(V) and radicals than those in homogeneous counterparts, as evidenced by X-ray photoelectron spectroscopy and time-dependent electron paramagnetic resonance, leading to higher turnovers and enhanced stability for the fluorination of nonactivated alkanes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Bridging the Transuranics with Uranium(IV) Sulfate Aqueous Species and Solid Phases

Isolating isomorphic compounds of tetravalent actinides (i.e., Th IV , U IV , Np IV , and Pu IV ) improve our understanding of the bonding behavior across the series, in addition to their relationship with tetravalent transition metals (Zr and Hf) and lanthanides (Ce). Similarities between these tetravalent metals are particularly illuminated in their hydrolysis and condensation behavior in aqueous systems, leading to polynuclear clusters typified by the hexamer [M IV 6 O 4 (OH) 4 ] 12+ building block. Prior studies have shown the predominance and coexistence of smaller species for Th IV (monomers, dimers, and hexamers) and larger species for U IV , Np IV , and Pu IV (including 38-mers and 70-mers). We show here that aqueous uranium(IV) sulfate also displays behavior similar to that of Th IV (and Zr IV ) in its isolated solidphase and solution speciation. Two single-crystal X-ray structures are described: a dihydroxide-bridged dimer (U 2 ) formulated as U 2 (OH) 2 (SO 4 ) 3 (H 2 O) 4 and a monomer-linked hexamer framework (U-U 6 ) as (U(H 2 O) 3.5 ) 2 U 6 O 4 (OH) 4 (SO 4 ) 10 (H 2 O) 9 . These structures are similar to those previously described for ThIV. Moreover, cocrystallization of monomer and dimer and of dimer and monomer–hexamer phases for both Th IV (prior) and U IV (current) indicates the coexistence of these species in solution. Because it was not possible to effectively study the sulfate-rich solutions via X-ray scattering from which U 2 and U-U 6 crystallized, we provide a parallel solution speciation study in low sulfate conditions, as a function of the pH. Raman spectroscopy, UV–vis spectroscopy, and small-angle X-ray scattering of these show decreasing sulfate binding, increased hydrolysis, increased species size, and increased complexity, with increasing pH. Furthermore, this study describes a bridge across the first half the actinide series, highlighting U IV similarities to Th IV , in addition to the previously known similarities to the transuranic elements.

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

Prediction of Solution Behavior via Calorimetric Measurements Allows for Detailed Elucidation of Polyoxometalate Transformation

The solution behavior of a polyoxometalate cluster, LiNa-U 24 Pp 12 (Li 24 Na 24 [(UO 2 O 2 ) 24 (P 2 O 7 ) 12 ]) that consists of 24 uranyl ions, peroxide groups, and 12 pyrophosphate linkers, was successfully predicted based on new thermodynamic results using a calorimetric method recently described for uranyl peroxide nanoclusters (UPCs), molybdenum blues, and molybdenum browns. The breakdown of LiNa-U 24 Pp 12 and formation of U 24 (Li 24 [UO 2 O 2 OH] 24 ) was monitored in situ via Raman spectroscopy using a custom heating apparatus. A combination of analytical techniques confirmed the simultaneous existence of U 24 Pp 12 and U 24 midway through the conversion process and U 24 as the single end product. The application of a molecular weight filter resulted in a complete and successful separation of UPCs from solution and, in conjunction with DOSY results, confirmed the presence of large intermediate cluster building blocks.

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

Volatilized Molten Salts: An Alternative Avenue for Synthesizing Single-Phase Perovskites

Single phase La 0.8 Sr 0.2 MnO 3 (LSM) and core-shell La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF)-LSM have been synthesized using a volatilized mol-ten salt synthesis (vMSS) method for the first time with a LiCl-KCl eutectic. While deleterious to LSM formation when the MSS takes place in the liquid phase, LiCl-KCl eutectic successfully facilitates LSM formation when volatilized. Specifically, KCl evaporates before LiCl and promotes formation of LSM via the gaseous phase. As time progresses, LiCl volatilizes and contributes negatively to Sr retention in the perovskite phase in accordance with Lux-Flood chemistry and to product phase purity. The vMSS is therefore a way to obviate the more immediate restrictions of Lux-Flood chemistry in the liquid phase. LiCl-KCl eutectic can also be used to successfully synthesis core-shell LSCF-LSM nanoparticles in times as short as 1 hour at 600 °C. These results demonstrate the surprising versatility and flexibility of the MSS method to synthesize numerous potential energy relevant materials with greater ease than previously thought.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Assembly of Uranyl Peroxides from Ball Milled Solids

Mechanochemistry enables transformations of highly insoluble materials such as uranium dioxide or the mineral studtite [(UO 2 )(O 2 )(H 2 O) 2 ]·(H 2 O) 2 into uranyl triperoxide compounds that can subsequently assemble into hydroxide-bridged uranyl peroxide dimers in the presence of lithium hydroxide. Dissolution of these solids in water yields uranyl peroxide nanoclusters including U 24 , Li 24 [(UO 2 )(O 2 )(OH)] 24 . Insoluble uranium solids can transform into highly soluble uranyl peroxide phases in the solid state with miniscule quantities of water. Furthermore, such reactions are potentially applicable to uranium processing in the front and back end of the nuclear fuel cycle.

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

Gamma-Ray-Induced Formation of Uranyl Peroxide Cage Clusters

Aqueous solutions of lithium uranyl triperoxide, Li 4 [UO 2 (O 2 ) 3 ] (LiUT), were irradiated with gamma rays at room temperature and found to form the uranyl peroxide cage cluster, Li 24 [(UO 2 )(O 2 )(OH)] 24 (Li–U 24 ). Raman spectroscopy and 18 O labeling were used to identify the Raman-active vibrations of LiUT. With these assignments, the concentration of LiUT was tracked as a function of radiation dose. A discrepancy between monomer removal and cluster formation suggests that the reaction proceeds by the assembly of an intermediate. Non-negative matrix factorization was used to separate Raman spectra into components and resulted in the identification of a unique intermediate species. Much of the conversion appears to be driven by water radiolysis products, particularly the hydroxyl radical. Furthermore, this differs from the 18 O-labeled copper-catalyzed formation of U 24 , which progresses at a steady rate with no observation of intermediates. Li–U 24 in solution decomposes at high radiation doses resulting in a solid insoluble product similar to Na-compreignacite, Na 2 (UO 2 ) 6 O 4 (OH) 6 ·7H 2 O, which contains uranyl oxyhydroxy sheets.

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

Solution-Processable Copper Halide Based Hybrid Materials Consisting of Cationic Ligands with Different Coordination Modes

Here, using cationic ligands containing both aromatic and aliphatic coordination sites, we have synthesized and structurally characterized five new CuX-based hybrid materials consisting of anionic inorganic motifs that also form coordinate bonds with the cationic organic ligands. As a result of the unique bonding nature at the inorganic/organic interfaces, these compounds demonstrate strong resistance toward heat and can be readily processed in solution. They emit light in the visible region ranging from cyan to yellow color, with the highest photoluminescence quantum yield (PLQY) reaching 71%. The influence of the different coordination modes of the ligands on their emission behavior was investigated employing both experimental and theoretical methods, which have provided insight in understanding structure–property relationships in these materials and guidelines for tuning and enhancing their chemical and physical properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Fe 0.6 Pd 0.4 Te 2 : A New Polymorph of FeTe 2 and PdTe 2 Stable at Ambient Pressure

Whereas pyrite space group is a high pressure polymorph of FeTe 2 , here we report pyrite-type single crystal Fe 0.6 Pd 0.4 Te 2 prepared using Pd substitution on Fe atomic site with ambient pressure crystal growth methods. Here, Fe 0.6(1) Pd 0.4(1) Te 2 single crystals show metal behavior above 15 K abided by Bloch-Grüneisen relation, and display resistivity upturn below 15 K due to disorder-related scattering of correlated electronic states.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

The Role of the Organic Solvent Polarity in Isolating Uranyl Peroxide Capsule Fragments

Uranyl peroxide capsules are a fascinating class of polyoxometalates (POMs), discovered only in the 21st century. Understanding the reactivity between peroxide, alkali cations, and uranyl in alkaline solutions is important in nuclear science disciplines including mineralogy, nuclear energy, and legacy nuclear wastes. In this work, we have developed a general procedure to isolate different fragments of the uranyl-peroxide POM capsules, using organic solvents to partially remove K + salts from crude solids of the monomer building block UO 2 (O 2 ) 3 4– (K–U 1 ), leading to stabilization of these reactive fragments. Higher polarity organic solvents remove more K + salts from the crude solid, owed to higher solubility, resulting in more extensive linking of uranyl peroxide building units. By this strategy we have isolated and structurally characterized a dimer K 6 [(UO 2 ) 2 (O 2 ) 4 (OH) 2 ]·7H 2 O (K–U 2 ) and a hexamer face frequently observed in the capsules, K 12 [(UO 2 ) 6 (O 2 ) 9 (OH) 6 ]$·x$H 2 O(K–U 6 ). Comparing experimental and computed Raman spectra shows that these intermediates crystallize by a solid-to-solid transformation, via polymerization of the monomer building block. By small-angle X-ray scattering (SAXS), we track the conversion of the fragments to POM capsules; the reaction rate increases from K–U 1 (days) < K–U 2 (hours) < K–U 6 (instantaneous). This study provides a general synthetic procedure to isolate metastable uranyl peroxide oligomers and control the oligomerization, which will be later applied to systems with the heavier alkalis that are even less stable.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗