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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Role of Ammonium Hydroxide on Glucose Oxidase Immobilized in Metal–Azolate Framework-7 Enzyme Activity

Enzymes are nature’s catalysts, but their instability outside native environments limits practical applications. Metal–organic frameworks (MOFs) offer a promising platform for enzyme immobilization, enhancing stability, and reusability through their tunable porosity and crystallinity. While ZIF-based MOFs have been extensively studied, metal azolate framework-7 (MAF-7) remains largely unexplored for biomimetic mineralization. Its hydrophilic character makes it a promising alternative for enzyme encapsulation; however, the role of essential basic modulators such as ammonium hydroxide (NH 4 OH) on enzyme structure and function has not been investigated. Here, in this study, we examine the NH 4 OH mediated synthesis of glucose oxidase within MAF-7 using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cryogenic transmission electron microscopy (cryo-TEM), and enzyme assays. Our results show that NH 4 OH modulates crystal morphology, enzyme activity, and nucleation behavior, with higher concentrations leading to partial enzyme denaturation and reduced catalytic performance. By integrating time-resolved cryo-TEM with activity assays, we uncover how modulator concentration impacts early stage crystallization and enzyme folding, a mechanistic insight not previously demonstrated in MOF systems. These findings highlight modulator chemistry as a critical, underexplored variable in MOF synthesis, advancing rational design strategies for enzyme@MOFs (E@MOF) beyond ZIFs and toward more tunable, biocompatible frameworks like MAF-7.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Thin-Film Deposition and Characterization of a Sn-Deficient Perovskite Derivative Cs 2 SnI 6

In this work, we describe details of a two-step deposition approach that enables the preparation of continuous and well-structured thin films of Cs 2 SnI 6 , which is a one-half Sn-deficient 0-D perovskite derivative (i.e., the compound can also be written as CsSn 0.5 I 3 , with a structure consisting of isolated SnI 6 4- octahedra). The films were characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), UV-Vis spectroscopy, photoluminescence (PL), photoelectron spectroscopy (UPS, IPES, XPS) and Hall effect measurements. UV-Vis and PL measurements indicate that the obtained Cs 2 SnI 6 film is a semiconductor with a band gap of 1.6 eV. This band gap was further confirmed by the UPS and IPES spectra, which were well reproduced by the calculated density of states with the HSE hybrid functional. The Cs 2 SnI 6 films exhibited n-type conduction with a carrier density of 6(1) × 10 16 cm -3 and mobility of 2.9(3) cm 2 /V·s. While the computationally-derived band structure for Cs 2 SnI 6 shows significant dispersion along several directions in the Brillouin zone near the band edges, the valence band is relatively flat along the $Γ$–X direction, indicative of a more limited hole minority carrier mobility compared to analogous values for the electrons. The ionization potential (IP) and electron affinity (EA) were determined to be 6.4 and 4.8 eV, respectively. The Cs 2 SnI 6 films show some enhanced stability under ambient air, compared to methylammonium lead (II) iodide perovskite films stored under similar conditions; however, the films do decompose slowly, yielding a CsI impurity. We discuss these findings in the context of suitability of Cs 2 SnI 6 for photovoltaic and related optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

First 14-Layer Twinned Hexagonal Perovskite Ba 14 Mn 1.75 Ta 10.5 O 42 : Atomic-Scale Imaging of Cation Ordering

Formation of hexagonal perovskite with mixed cubic and hexagonal stacking of AO 3 layers becomes more and more difficult when the number of layers in the stacking repeating unit increases. So far, the highest number of layers reported for twinned hexagonal perovskite is 12, with alternative 5 consecutive cubic layers and one hexagonal layer in the (ccccch) 2 sequence. Here, we present the unexpected formation of a 14-layer twinned hexagonal perovskite with a stacking sequence (cccccch) 2 for the BaO 3 layers on the Ba 14 Mn 1.75 Ta 10.5 O 42 (Ba 8 MnTa 6 O 24 ) composition, the first example of twinned hexagonal perovskite with a periodicity exceeding 12-layers. The B-cation and vacancy distributions are characterized by multiple efficient and complementary techniques including neutron and synchrotron powder diffraction, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging, and electron energy loss spectroscopy (EELS) and X-ray energy dispersive spectroscopy (EDS) elemental mapping. Atomic-resolution STEM-HAADF imaging and EELS/EDS elemental mapping enables direct observation of high-spin d 5 Mn 2+ cation ordering in the d 0 Ta 5+ host, thus demonstrating the great potential of this technique for probing cation ordering and performing structure determination. Moreover, atomic mapping allows for the observation of local defect structure variants, which can be a powerful tool for future new material design. The large high-spin Mn 2+ cation and Ta-vacancy pair formation in face-sharing octahedral sites play key roles on both the stabilization of this 14-layer twinned hexagonal perovskite structure and the Mn 2+ ordering in the central corner-sharing octahedral (CSO) positions within the five-consecutive CSO layers. Here, compared with the 8-layer twinned Ba 8 ZnTa 6 O 24 material, the low quality factor in microwave frequency and enhanced ultraviolet and visible light absorption of Ba 14 Mn 1.75 Ta 10.5 O 42 as well as the photocatalytic activity on water splitting are discussed in terms of the presence of high-spin Mn 2+ cations in the structure.

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

Crystallization and Phase Transformations of Aluminum (Oxy)hydroxide Polymorphs in Caustic Aqueous Solution

Gibbsite, bayerite, and boehmite are important aluminum (oxy)hydroxide minerals in nature and have been widely deployed in various industrial applications. They are also major components in caustic nuclear wastes stored at various U.S. locations. Knowledge of their crystallization and phase transformation processes contributes to understanding their occurrence and could help optimize waste treatment processes. While it has been reported that partial conversion of bayerite and gibbsite to boehmite occurs in basic solutions at elevated temperatures, systematic studies of factors affecting the phase transformation as well as the underlying reaction mechanisms are non-existent, particularly in highly alkaline solutions. We explored the effects of sodium hydroxide concentrations (0.1~3 M), reaction temperature (60~100 ?) and aluminum concentrations (0.1~1 M) on the crystallization and transformation of these aluminum (oxy)hydroxides. Detailed structural and morphological characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectrometry revealed that these processes depend largely on the reaction temperature and the Al/OH- ratio. When 1 = Al/OH- = 2.5, the reactions favor formation of high crystallinity precipitates, whereas at Al/OH- ratio ? 2.5 precipitation ceases unless the Al concentration is higher than 1 M. We identified pseudoboehmite, bayerite and gibbsite as intermediate phases to bayerite, gibbsite and boehmite, respectively, all of which transform via dissolution-reprecipitation. Gibbsite transforms to boehmite in both acidic and weak caustic environments at temperatures above 80 oC. However, a ‘bar-shaped’ gibbsite morphology dominates in highly caustic environments (3 M NaOH). The findings enable a robust basis for selection of various solid phases by tuning the reaction conditions.

aluminum (oxy)hydroxide polymorphs, crystallizatio↗
DOE OSTI2018

Single-Doped and Multidoped Transition-Metal (Mn, Fe, Co, and Ni) ZnO and Their Electrocatalytic Activities for Oxygen Reduction Reaction

The electrochemical oxygen reduction reaction (ORR) is the limiting half-reaction of fuel cells, which is mediated by using platinum-based catalysts. Hence, the development of low-cost, active ORR catalysts is highly required to make fuel cell technology commercially available. In this report, transition-metal (TM; Mn, Fe, Co, and Ni) single-doped and multidoped (MD) ZnO nanocrystals (ZNs) were prepared for use as ORR catalysts using a simple precipitation method. The effects of single doping and multidoping on the structure, morphology, and properties of the TM-doped ZNs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence, X-ray photoelectron microscopy, electron paramagnetic resonance, and Raman and photoluminescence (PL) spectroscopies. The XRD results reveal that synthesized ZnO samples retained a pure hexagonal wurtzite crystal structure, even at high levels of multidoping (nominal 20%). SEM analyses show that the morphology of the prepared ZNs varies with the doping elements, doping mode, and amounts of doping. The observation of peak shifting and peak intensity changes in Raman studies confirms the presence of dopants in ZnO. The PL investigation reveals that the incorporation of dopants into the ZnO structure increases the oxygen vacancies within the materials. The highest oxygen vacancies were present in Mn-doped ZnO and 15% MD ZnO among the single-doped and MD samples, respectively. Linear-sweep voltammetry studies conclude that doped ZnO shows enhanced ORR activity compared to the undoped samples. The Mn-doped ZnO and 15% MD ZnO exhibited the highest ORR activity among the prepared single-doped and MD ZN samples, respectively. In comparison, single doping showed better ORR activity than the multidoping system. The enhanced ORR activity of the synthesized ZN materials correlates with the amount of oxygen vacancies present in the samples. Finally, the enhanced activity of TM-doped ZnO suggests that these materials can be used as potential, low-cost electrocatalysts for ORR in fuel cell technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Unraveling Gibbsite Transformation Pathways into LiAl-LDH in Concentrated Lithium Hydroxide

The intercalation of lithium (Li+) ions into metallic hydroxides (e.g. gibbsite, Al(OH)3) facilitates the synthesis of layered double hydroxides. Caustic environments, such as in lithium hydroxide (LiOH) solutions, present additional pathways beyond the intercalation of ions, specifically dissolution/precipitation processes. Herein, the phase transformation Al(OH)3 to lithium aluminum hydroxide dihydrate, Li[Al(OH)3)]2OH•2H2O in partially deuterated LiOH solutions is tracked through multinuclear, magic angle spinning, high-field nuclear magnetic resonance spectroscopy (27Al and 6Li MAS-NMR) , X-ray diffraction, and scanning electron microscopy of harvested solids. At high magnetic fields (19.975 T), 27Al MAS-NMR enabled detection and quantification of the reactive interface between Al(OH)3 and Li[Al(OH)3)]2OH•2H2O. 6Li MAS-NMR spectra collected on the harvested solids exhibited exchange mediated narrowing as the reaction time progressed, consistent with transport of Li+ ions between the interface and the bulk Li[Al(OH)3)]2OH•2H2O. Complimentary in-situ 27Al MAS-NMR at lower magnetic fields (7.046 T) utilized unique rotors capable of simultaneous resolution of solution and solid state Al-species in caustic environments. The reaction between Al(OH)3 (0.5 M) and LiOH (3 M) initially exhibited greater dissolution and formation of Al(OH)4- than the precipitation. Over several hours, the supersaturated Al(OH)4- solution precipitated Li[Al(OH)3)]2OH•2H2O. Simultaneous, in-situ observations of the solid component tracked the formation of Li[Al(OH)3)]2OH•2H2O evident by an increase in signal and narrowing of the Oh resonance. These results provides insight into Al precipitation in alkaline media with applications ranging from the reduction of Al content in Hanford site, high-level radioactive waste (HLRW) to the precipitation of LDH materials for application as catalyst materials, drug delivery devices, and ion-ion exchangers.

Graham, Trenton R.↗
DOE OSTI2017

Atomic Structure of Submonolayer NaCl Grown on Ag(110) Surface

In this work, we report results on the growth of an NaCl film on Ag(110) under ultrahigh vacuum conditions. At room temperature, low-energy electron diffraction and scanning tunneling microscopy show that the NaCl film forms a (4×1) superstructure. At RT, the film consists of small-sized islands that coalesce into larger islands at 410 K. These large islands preserve the (4×1) superstructure and cover the entire surface. The apparent heights obtained from the STM images show that the initial thickness of the NaCl islands is one atomic layer, and they present a very small height corrugation. The density functional theory calculations, with and without the inclusion of van der Waals effects, confirm the coexistence of two domains in agreement with the observed structure.

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

Gaseous Iodine Sorbents: A Comparison between Ag-Loaded Aerogel and Xerogel Scaffolds

The general properties of aluminosilicate aerogels and xerogels with silver nanoparticles as sorbents for capturing iodine gas [I2(g)] were investigated. The structures, morphologies, compositions, and pore structures of aerogel and xerogel were compared using powder X-ray diffraction (PXRD), scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, as well as specific surface area (SSA) and pore size analyses. The as-made aerogels, xerogels, and heat-treated aerogels were impregnated with Ag by aqueous ion exchange using AgNO3 solutions, and PXRD patterns showed the presence of nanocrystalline Ag0 after Ag-impregnation. Iodine loadings of aerogels and xerogels were 0.33–0.41 g g-1. The Ag-impregnated aerogels without heat-treatment showed an 8 mass% higher iodine loading than Ag-impregnated xerogels and 3 mass% higher than heat-treated Ag-impregnated aerogels. All gels after iodine uptake showed the presence of AgI, indicating chemisorption of iodine to silver. The SSA values of the as-made gels were 419–598 m2 g-1 but decreased significantly to 34–120 m2 g-1 after Ag-impregnation and iodine uptake processes. Overall, changes in physical and chemical properties of aerogels and xerogels after iodine uptake were similar, and the difference in iodine loading capacities of the aerogels and xerogels was not significant while the synthesis process of xerogel is more practical because it does not require supercritical drying.

aerogel, xerogel, iodine capture↗
DOE OSTI2020

Luminescent Properties of DOBDC Containing MOFs: The Role of Free Hydroxyls

A novel metal–organic framework (MOF), Mn-DOBDC, has been synthesized in an effort to investigate the role of both the metal center and presence of free linker hydroxyls on the luminescent properties of DOBDC (2,5-dihydroxyterephthalic acid) containing MOFs. Co-MOF-74, RE-DOBDC (RE–Eu and Tb), and Mn-DOBDC have been synthesized and analyzed by powder X-ray diffraction (PXRD) and the fluorescent properties probed by UV–Vis spectroscopy and density functional theory (DFT). Mn-DOBDC has been synthesized by a new method involving a concurrent facile reflux synthesis and slow crystallization, resulting in yellow single crystals in monoclinic space group C2/c. Mn-DOBDC was further analyzed by single-crystal X-ray diffraction (SCXRD), scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), and photoluminescent emission. Results indicate that the luminescent properties of the DOBDC linker are transferred to the three-dimensional structures of both the RE-DOBDC and Mn-DOBDC, which contain free hydroxyls on the linker. In Co-MOF-74 however, luminescence is quenched in the solid state due to binding of the phenolic hydroxyls within the MOF structure. Finally, Mn-DOBDC exhibits a ligand-based tunable emission that can be controlled in solution by the use of different solvents.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Examining Metal Identity and Proximity Effects on Acetylene Hydrogenation with Azolate-Based MOFs

Liquid organic hydrogen carriers (LOHCs) are an attractive fuel source due to their compatibility with existing transportation methods and ease of use. However, they suffer from sluggish (de)hydrogenation kinetics. One promising platform for developing next-generation catalysts is metal–organic frameworks (MOFs), which can enable systematic interrogation into the influence of metal identity and spatial arrangement. In this study, the effect of the coordination environment was investigated using Ni- and Co-based azolate MOFs: MFU-4l-OH (M x Zn 5–x (OH) 4 (BTDD) 3 ; x = 4 for M = Co and x = 3 for M = Ni, H 2 BTDD = bis(1H-1,2,3-triazolo[4,5-b][4′,5′-i])dibenzo[1,4]dioxin), composed of single-site nodes, and M(OH) 2 BBTA (M = Ni, Co; H 2 BBTA = 1H,5H-benzo(1,2-d:4,5-d’)bistriazole), composed of extended chain-type nodes. The catalysts were characterized by isotherms, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS) analysis. Acetylene hydrogenation activity under steady state conditions (150 °C, 1:1 C 2 H 2 :H 2 ) revealed higher turnover frequencies (TOFs) up 1.17 × 10 –2 mol C 2 H 2 mol −1 Ni min −1 and 1.98 × 10 –3 mol C 2 H 2 mol −1 Co min −1 for Ni-MFU-4l-OH and Co-MFU-4l-OH, respectively, compared to their BBTA analogues. However, the Co-based MOFs, particularly Co 2 (OH) 2 -BBTA, exhibited greater selectivity (up to 19%) for the fully hydrogenated ethane product. Isosteric heat of adsorption (Q st ) measurements for ethylene and ethane revealed that the BBTA framework had stronger binding to the products than MFU-4l. Furthermore, these findings demonstrate that metal identity and coordination environment may modulate acetylene hydrogenation performance, leading to design principles for tuning LOHC hydrogenation catalysts.

catalysts↗
DOE OSTI2019

Charge Transfer Dynamics of Phase-Segregated Halide Perovskites: CH 3 NH 3 PbCl 3 and CH 3 NH 3 PbI 3 or (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n -1 Pb n I 3 n +1 Mixtures

Lead halide perovskites present a versatile class of solution-processable semiconductors with highly tunable bandgaps that span ultraviolet, visible, and near-infrared portions of the spectrum. We explore phase-separated chloride and iodide lead perovskite mixtures as candidate materials for intermediate band applications in future photovoltaics. X-ray diffraction and scanning electron microscopy reveal that deposition of precursor solutions across the MAPbCl 3 /MAPbI 3 composition space affords quasi-epitaxial cocrystallized films, in which the two perovskites do not alloy but instead remain phase-segregated. First-principle calculations further support the formation of an epitaxial interface and predict energy offsets in the valence band and conduction band edges that could result in intermediate energy absorption. The charge dynamics of variable mixtures of the relatively narrow bandgap (1.57 eV) MAPbI 3 perovskite and wide bandgap (3.02 eV) MAPbCl 3 are probed to map charge and energy flow direction and kinetics. Time-resolved photoluminescence and transient absorption measurements reveal charge transfer of photoexcited carriers in MAPbCl 3 to MAPbI 3 in tens of picoseconds. The rate of quenching can be further tuned by replacing MAPbI 3 with two-dimensional Ruddlesden-Popper (BA) 2 (MA) n-1 Pb n I 3 n +1 (n = 3, 2, and 1) perovskites, which also remain phase-separated.

2D perovskites↗
DOE OSTI2016

Aerobic Epoxidation of Olefin by Platinum Catalysts Supported on Mesoporous Silica Nanoparticles

Here, we report platinum catalysts for the efficient aerobic oxidation of olefins to form epoxides and/or derived glycol monoethers. The catalysts, diaqua and dichloro PtII complexes supported by the ligand di(2-pyridine)methanesulfonate (dpms), are most active when they are covalently tethered to mesoporous silica nanoparticles (MSNs). Supporting the molecular Pt complexes on the MSNs prevents bimolecular catalyst deactivation. Using this strategy, turnovers > 40,000 are achieved for the aerobic oxidation of norbornene in 2,2,2-trifluoroethanol. The position of the tether and the nature of other ligands in the metal co-ordination sphere (aqua, hydroxo or chloro) are illustrated to affect the catalyst activity. The new MSN-supported Pt materials were characterized by NMR spectroscopy, nitrogen physisorption, powder X-ray diffraction (PXRD), scanning electron mi-croscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA).

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

Surfactant Engineering and Its Role in Determining the Performance of Nanoparticulate Organic Photovoltaic Devices

The fabrication of organic photovoltaics (OPVs) from non-hazardous nanoparticulate (NP) inks offers considerable promise for the development of ecofriendly large-scale printed solar modules. However, the typical NP core-shell morphology (driven by the different donor/acceptor affinities for the surfactant used in NP synthesis) currently hinders the photovoltaic performance. As such, surfactant engineering offers an elegant approach to synthesizing a more optimal intermixed NP morphology and hence an improved photovoltaic performance. In this work, the morphology of conventional sodium dodecyl sulfate (SDS) and 2-(3-thienyl) ethyloxybutylsulfonate (TEBS)-stabilized poly(3-hexylthiophene) (P3HT) donor:phenyl-C 61 -butyric acid methyl ester (PC 61 BM) acceptor NPs is probed using scanning transmission X-ray microscopy, UV-vis spectroscopy, grazing-incidence X-ray diffraction, and scanning electron microscopy. While the SDS-stabilized NPs exhibit a size-independent core-shell morphology, this work reveals that TEBS-stabilized NPs deliver an intermixed morphology, the extent of which depends on the particle size. Consequently, by optimizing the TEBS-stabilized NP size and distribution, NP-OPV devices with a power conversion efficiency that is ~50% higher on average than that of the corresponding SDS-based NP-OPV devices are produced.

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

Hybrid molecular beam epitaxy of germanium-based oxides

Abstract Germanium-based oxides such as rutile GeO 2 are garnering attention owing to their wide band gaps and the prospects of ambipolar doping for application in high-power devices. Here, we present the use of germanium tetraisopropoxide (GTIP), a metal-organic chemical precursor, as a source of germanium for the demonstration of hybrid molecular beam epitaxy for germanium-containing compounds. We use Sn 1- x Ge x O 2 and SrSn 1- x Ge x O 3 as model systems to demonstrate our synthesis method. A combination of high-resolution X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy confirms the successful growth of epitaxial rutile Sn 1- x Ge x O 2 on TiO 2 (001) substrates up to x = 0.54 and coherent perovskite SrSn 1- x Ge x O 3 on GdScO 3 (110) substrates up to x = 0.16. Characterization and first-principles calculations corroborate that germanium occupies the tin site, as opposed to the strontium site. These findings confirm the viability of the GTIP precursor for the growth of germanium-containing oxides by hybrid molecular beam epitaxy, thus providing a promising route to high-quality perovskite germanate films.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Single-step One-pot Synthesis of TiO 2 Nanosheets Doped with Sulfur on Reduced Graphene Oxide with Enhanced Photocatalytic Activity

A hybrid photocatalyst based on anatase TiO 2 was designed by doping TiO 2 with sulfur and incorporating reduced graphene oxide (TiO 2 -S/rGO hybrid), with an aim to narrow the band gap to potentially make use of visible light and decrease the recombination of excitons, respectively. This TiO 2 -S/rGO hybrid was successfully synthesized using a one-pot hydrothermal method via single-step reaction. The structure and morphology of the TiO 2 -S/rGO hybrid catalyst was carefully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Its photocatalytic reactivity was evaluated by the degradation of methyl blue. The results showed that both the doping of sulfur and the introduction of rGO worked as designed, and the TiO 2 -S/rGO hybrid exhibited high photocatalytic activity under simulated sunlight. Finally, considering both the facile and scalable reaction to synthesize TiO 2 -S/rGO hybrid, and its excellent photocatalytic performance, such TiO 2 -S/rGO hybrids are expect to find practical applications in environmental and energy sectors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Water dissociation on Mn(1×1)/Ag(100)

In this work we utilize experimental and simulation techniques to examine the molecular level interaction of water with a MnO(1×1) thin film deposited onto Ag(100). The formation of MnO(1×1)/Ag(100) was characterized by low energy electron diffraction and scanning tunneling microscopy. Density functional theory (DFT) shows MnO(1×1) is thermodynamically more stable than MnO(2×1) by –0.4 eV per MnO. Upon exposure to 2.5 Torr water vapor at room temperature, X-ray photoemission spectroscopy results show extensive surface hydroxylation attributed to reactivity at MnO(1×1) terrace sites. DFT calculations of a water monomer on MnO(1×1)/Ag(100) show the dissociated form is energetically more favorable than molecular adsorption, with a hydroxylation activation barrier 0.4 eV per H 2 O. Lastly, these results are discussed and contrasted with previous studies of MgO/Ag(100) which show a stark difference in behavior for water dissociation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

CuCr 2 O 4 particle growth and evolution across sol–gel routes and calcination profiles

CuCr 2 O 4 spinel is a candidate coating material for central receivers in concentrating solar power to protect structural alloys against high temperature oxidation and related degradation. Coating performance and microstructure of dip-coated and sintered coatings is dictated by the initial particle size of the CuCr 2 O 4 and sintering temperature, but can be compromised by particle agglomeration. Here in this study, sub-micron particles were synthesised through the Pechini and modified Pechini sol–gel methods. Phase composition was confirmed via X-ray diffraction. Particle growth during calcination of the nanoparticles at different temperatures (650°C, 750°C, 850°C) and times (between 1 and 24 h) was measured via laser diffraction and scanning electron microscopy. The modified Pechini method displayed evidence of smaller particle sizes and greater agglomeration. The kinetics of particle growth observed are consistent with a diffusion limited inhibited grain growth model.

36 MATERIALS SCIENCE↗