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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

In-situ characterization and quantification of melt pool variation under constant input energy density in laser powder bed fusion additive manufacturing process

Size and shape of a melt pool play a critical role in determining the microstructure in additively manufactured metals. However, it is very challenging to directly characterize the size and shape of the melt pool beneath the surface of the melt pool during the additive manufacturing process. Here, we report the direct observation and quantification of melt pool variation during the laser powder bed fusion (LPBF) additive manufacturing process under constant input energy density by in-situ high-speed high-energy x-ray imaging. We show that the melt pool can undergo different melting regimes and both the melt pool dimension and melt pool volume can have orders-of-magnitude change under a constant input energy density. Our analysis shows that the significant melt pool variation cannot be solely explained by the energy dissipation rate. We found that energy absorption changes significantly under a constant input energy density, which is another important cause of melt pool variation. Our further analysis reveals that the significant change in energy absorption originates from the separate roles of laser power and scan speed in depression zone development. The results reported here are important for understanding the laser powder bed fusion additive manufacturing process and guiding the development of better metrics for processing parameter design.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Synthesis and Characterization of Nanocrystalline Fe{sub (100−x)}Ni{sub (x)} Alloy Powders by Auto-combustion and Hydrogen Reduction

Nanocrystalline Fe{sub 90}Ni{sub 10,} Fe{sub 70}Ni{sub 30} andFe{sub 50}Ni{sub 50} alloy powders were successfully synthesized using a simple auto-combustion route followed by hydrogen reduction. The experimental work consisted of two steps, where the first step was auto-combustion and, the second step was reduction of the combusted powders. Citric acid was used as fuel during combustion, and citrate to nitrate ratio (C/N) was maintained at 0.3. NiFe{sub 2}O{sub 4} and Fe{sub 2}O{sub 3} phase formation occurred in obtained powders. Obtained powders were reduced in a hydrogen atmosphere at 700 °C/1 h for alloy formation. X-ray diffraction results revealed the presence of BCC α-(Fe,Ni) and FCC γ-(Fe,Ni) phases in reduced powders. Rietveld refinement technique was used to confirm α-(Fe,Ni) and γ-(Fe,Ni) phases with Im-3 m and Fm-3 m space groups, respectively. The Fe{sub 50}Ni{sub 50} powder has been found to have a single γ-(Fe,Ni) phase. Crystallite size of synthesized powders was calculated using the Scherrer equation and transmission electron microscopic analysis, which has been found < 50 nm. The nanocrystalline powders of all three compositions have shown soft magnetic nature with high saturation magnetization (Ms) and low coercivity (Hc). Effect of composition on the phase formation, microstructure and magnetic behavior was investigated. This rapid and simple process for attaining nanoparticles of Fe-Ni alloys with high Ms is expected to be useful in potent applications such as sensors, biomedical applications and electromagnetic wave absorbers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Photoluminescence, thermoluminescence and defect centres in Y2O3 and Y2O3:Tb3+ under 100 MeV swift Ni8+ ion beam irradiation

Highlights: • XRD showed decrease of crystallite size after ion irradiated. • Electron spin resonance reveals the presence of F, F{sup +} and O{sub 2}{sup −} centres. • SHI irradiated Y{sub 2}O{sub 3}:Tb{sup 3+} exhibits purity of intense green emission and long life time. • The Tb{sup 3+} doped Y{sub 2}O{sub 3} shows a linear, greater TL efficiency, longer life time and less fading under SHI irradiation. - Abstract: Y{sub 2}O{sub 3} and Y{sub 2}O{sub 3}:Tb{sup 3+} powders, synthesized via the solution combustion method, were studied in order to determine the effect of 100 MeV swift Ni{sup 8+} ions on the photoluminescence (PL), thermoluminescence (TL) and swift ion beam induced defects. Synthesized materials were characterized by X-ray powder diffraction, electron spin resonance, PL intensity, decay measurements and TL. Cubic structures were observed in both the pristine and ion irradiated materials. The ion irradiated materials exhibited smaller crystallite sizes than that of the pristine material. PL peaks in the visible region were identified at 485, 542, 582 and 621 nm due to the {sup 5}D{sub 4}→{sup 7}F{sub 3,4,5,6} transition of Tb{sup 3+}. The PL intensity showed an increase up to 3 × 10{sup 10} ions cm{sup −2} and then a significant decrease with a further increase in the ion fluence. The recorded time resolved PL at an ion irradiated fluence of 3 × 10{sup 10} ions cm{sup −2}, exhibited an increase in the life time of the material. TL glow curves were obtained for the samples irradiated with a swift Ni{sup 8+} ion beam. These glow curves showed a peak at 518 K with a shoulder peak at 473 K and its intensity linearly increased upto a fluence of 1 × 10{sup 11} ions cm{sup −2}. Whereas, the undoped sample showed peaks at 421 and 662 K and its intensity sub-linearly increased upto a fluence of 1 × 10{sup 11} ions {sup −2}. TL efficiency values of the Y{sub 2}O{sub 3}:Tb{sup 3+} sample, irradiated by a 100 MeV Ni{sup 8+} ion beam, have been measured relative to the undoped Y{sub 2}O{sub 3} sample and were found to be 1.34. The Tb{sup 3+} doped sample exhibited a less fading effect under the swift heavy ion beam.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

AFRL Additive Manufacturing Modeling Series: Challenge 1, Characterization of Residual Strain Distribution in Additively-Manufactured Metal Parts Using Energy-Dispersive Diffraction

A machine component fabricated by additive manufacturing (AM) of metal powders often possesses steep residual stress gradients with significant magnitudes due to large temperature gradients that transpire within a localized area during fabrication. These processing-induced residual stresses can cause distortion of the part, and if they are of significant magnitude, they could induce cracking of the component, degrade printability, and/or diminish subsequent mechanical performance. The ability to predict these residual stresses imparted by AM is an important step in permeating AM technology for advanced manufacturing. Calibration and validation of AM process models used for prediction are, therefore, a critical step in understanding the origin and mitigating the challenges associated with residual stresses inherent to the AM process. In the present work, the residual strain distributions in components with simple geometries fabricated by a laser powder bed fusion (LBPF) process were characterized non-destructively using energy-dispersive X-ray diffraction in support of the US Air Force Research Laboratory Additive Manufacturing Modeling Challenge Series Groeber et al. (JOM 70:441-448, 2018). The measurement setup and approach are described in detail so that the data can be used as a benchmark to calibrate and validate models for the prediction of macro-scale residual stresses due to the LPBF process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Characterization of multi-material 316L-Hastelloy X fabricated via laser powder-bed fusion

The aim of this work is to provide firsthand knowledge of 316 L stainless steel (316 L) and Hastelloy X (HX) multi-material processing via laser powder bed fusion (PBF). Specifically, microstructure of the interface is studied using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Surface metrology is performed to characterize the resulting surface roughness at the interface followed by tensile and flexural testing of multi-material samples to characterize the mechanical properties of the interfaces. Results showed that use of proper process parameters for each individual material led to formation of a compositional gradient at the interface that stretched for 240 μm (10–12 layers) with no evidence of cracking or porosity. The interface exhibited higher surface roughness compared to 316 L or HX as measured by arithmetic mean height, Sa, and maximum valley depth, Sv, parameters. During tensile testing, samples failed in the 316 L region away from the interface, with comparable yield strength, ultimate strength, and ductility. Finally, it was concluded that the “naturally” formed interface created a compositional gradient which was defect free due to similar values of coefficient of thermal expansion, input energy density, and different Marangoni numbers of the materials.

316L stainless Steel↗
DOE OSTI2023

Rapid AI-based Dissection of Ashes using Raman and XRF Spectroscopy (RADAR-X)

Waste-to-energy (WTE) facilities incinerate ~35 million tons of municipal solid waste annually in the United States. The incineration process reduces the mass and the volume of the waste fraction by over 75 and 95%, respectively. The fraction left after incineration remains as ash residues and is referred to as WTE ash, compromising of bottom and fly ash. In the United States, ~10 million tons of WTE ashes are generated annually and predominantly landfilled because of the lack of secondary end-use pathways. This incurs a significant financial burden (landfilling costs) on U.S. WTE facilities and also results in the loss of materials to the landfill. The primary objective of this research is to understand better the elemental and mineralogical composition of WTE ashes from diverse origins and find composition dependent upcycling pathways for diverting these ashes from landfills. This primary objective was addressed through three research tasks –(Task I) An AI-led Multi-Modal Approach for Compositional Analysis, (Task II) Developing a Dissolution-Based Test for Real Time Analysis, and (Task III) Establishing composition-dependent end uses. The chemical composition of WTE ash is dependent on two factors, i.e., the input waste composition and the operational parameters of a WTE facility (combustion conditions). Amongst these two factors, the input waste composition will likely show spatial and temporal variation. As a result, the chemical composition of WTE ash will also fluctuate. To understand the spatial and temporal variation in WTE ash composition, in Task I, we collected 128 ash samples (62 bottom ash and 66 fly ash samples) from 11 WTE facilities located in 11 U.S. states and characterized them via X-ray Fluorescence, powder X-ray Diffraction, and Raman Spectroscopy. The findings from this extensive characterization work indicated that the key elements in WTE fly ashes are Ca, Cl (greater than 10 wt. %), Si, S, K, Zn ( between 1 and 10 wt. %), Mg, Al, P, Ti, Fe, Cu, Br, and Pb (between 0.1 and 1 wt. %). Similarly, the key elements in WTE bottom ash fraction finer than 45μm are Ca (greater than 10 wt. %), Mg, Al, Si, S, Cl, K, Ti, Fe, Zn (between 1 and 10 wt. %), P, V, Cr, Mn, Cu, Br, and Pb (between 0.1 and 1 wt. %). Here, we note that the dominant fraction of WTE bottom ash is the coarse fraction. The coarse WTE bottom ash fraction (rich in silicon) was not characterized in this study because of excessive grinding requirements and their unsuitability as a supplementary cementitious material due to their coarse nature. The elements in WTE bottom ashes are present as calcite, anhydrite, vaterite, hydroxyapatite, quartz, bassanite, gehlenite, akermanite, hydrocalumite, and portlandite. Similarly, the mineralogical species present in WTE fly ashes are calcium chloride hydroxide, halite, calcite, anhydrite, sylvite, hydrocalumite, vaterite, hannebachite, quartz, and bassanite. Temporal variation in ash composition may also result in significant fluctuations in chemical compositions. Therefore, a WTE facility may need to monitor the ash composition (elemental and mineralogical composition) in real time. In Task I, we evaluated the possibility of using a portable X-ray fluorescence (XRF) spectrometer to monitor the elemental composition in real-time. Specifically, we collected XRF data on identical specimens via a portable XRF spectrometer (low-end) and a lab-based benchtop XRF spectrometer (high-end). The collected data was used to train an A.I. algorithm (portable XRF data as an input and benchtop XRF data as an output) to predict accurate elemental composition using portable XRF data. Finally, we developed a 2-minute photobleaching protocol to monitor the mineralogical characteristics of WTE ashes via Raman spectroscopy. Overall, the activities in Task I improved our understanding of ash composition and developed techniques to monitor elemental and mineralogical composition in near real-time. Based on the findings of Task I, we find that WTE ashes exhibit wide variability in mineralogy. For ICP-based elemental analysis, all the mineralogical species in WTE ashes must be brought into solution. This is traditionally accomplished with acid digestion using a combination of multiple acids. However, acid digestion with multiple acids is time-consuming and often fails to ensure complete digestion of the ash matrix. To address this limitation, in Task II, we developed an alkali-fusion-based digestion protocol using a combination of lithium tetraborate, lithium metaborate, and their combinations as possible alkali fluxes for digesting WTE ashes entirely and rapidly. The validity of the developed method was evaluated on two standard ash specimens, i.e., SRM 1633c coal fly ash and BCR-176R incineration fly ash specimen. The findings suggest that the developed protocol can ensure complete digestion of elements such as Al, Ba, Ca, Cr, Cu, Mg, Mn, P, Sr, V, Zn, Be, K, and rare earth elements. The recent changes in the energy market towards renewables and increased metal recycling have resulted in reduced supplies of supplementary cementitious materials (coal fly ash and slag). Therefore, in Task III, we evaluated the possibility of employing WTE ashes as SCMs. As the chemical composition of WTE ashes varies temporally (on an hourly basis), there was also a need to develop tests that can evaluate the suitability of material to act as supplementary cementitious material rapidly, i.e., in a few minutes. Therefore, in Task II, we also developed a rapid test to assess the suitability of a material to act as an SCM in 5 minutes. This represents a significant advance over the state-of-the-art R 3 test, which takes ~144 hours. This test was initially validated on amorphous aluminosilicates, such as calcined clays, and could be extended to evaluate other industrial by-products, such as WTE ashes. In Task III, we evaluated the possibility of employing WTE ashes for two applications, i.e., as an SCM and a lime substitute for clay stabilization. The findings from Task I indicated that WTE ashes are enriched in chlorine and, therefore, cannot be used directly as an SCM due to corrosion-related risks and altered hydration kinetics. Accordingly, we developed an ash treatment protocol to reduce the solubility of chlorine-containing species in WTE ashes. The developed treatment protocol also immobilized lead in certain mineral forms. As a result of the treatment, WTE ashes can be used as SCMs without any corrosion or heavy metal leaching concerns. The second application examined in this study was clay stabilization. WTE ashes are calcium-rich and can be an adequate lime replacement for clay stabilization. Our findings reveal that the sum of the concentrations of Ca(OH) 2 and CaClOH controls the clay stabilization capability of WTE ashes. In summary, in this work, we evaluated the elemental and mineralogical characteristics of U.S. WTE ashes from diverse origins and developed tests to evaluate the chemical characteristics of these ashes in real time through a portable XRF and a benchtop Raman spectrometer. Based on the chemical characteristics of these ashes, we developed an ash treatment process to enable the use of WTE ashes as an SCM and also evaluated the possibility of employing these ashes for clay stabilization. Overall, the findings from this work enables the diversion of WTE ashes from landfills for multiple end-uses, i.e., as an SCM or a lime substitute for clay stabilization.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Synthesis and physical properties of a new layered ferromagnet Cr 1.21 Te 2

Single crystals of a new layered compound, Cr 1.21 Te 2 , were synthesized via a vapor transport method. The crystal structure and physical properties were characterized by single crystal and powder x-ray diffraction, temperature- and field-dependent magnetization, zero-field heat capacity, and angle-resolved photoemission spectroscopy. Cr 1.21 Te 2 , containing two Cr sites, crystalizes in a trigonal structure with a space group P-3 (No. 147). The Cr site in the interstitial layer is partially occupied. Physical property characterizations indicate that Cr 1.21 Te 2 is metallic with hole pockets at the Fermi energy and undergoes a ferromagnetic phase transition at ~ 173 K. The magnetic moments align along the c axis in the ferromagnetic state. Based on low-temperature magnetization, the spin stiffness constant, D, and spin excitation gap, Δ , were estimated according to Bloch's law to be D = 94 ± 17 meV Å 2 and Δ = 0.45 ± 0.33 meV, suggesting its possible application as a low dimensional ferromagnet.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High pO(2) Floating Zone Crystal Growth of the Perovskite Nickelate PrNiO3

Single crystals of PrNiO3 were grown under an oxygen pressure of 295 bar using a unique high-pressure optical-image floating zone furnace. The crystals, with volume in excess of 1 mm(3), were characterized structurally using single crystal and powder X-ray di ff raction. Resistivity, specific heat, and magnetic susceptibility were measured, all of which evidenced an abrupt, first order metal-insulator transition (MIT) at similar to 130 K, in agreement with previous literature reports on polycrystalline specimens. Temperature-dependent single crystal di ff raction was performed to investigate changes through the MIT. Our study demonstrates the opportunity space for high fugacity, reactive environments for single crystal growth specifically of perovskite nickelates but more generally to correlated electron oxides.

floating zone method↗
DOE OSTI2019

Structural and Magnetic Properties of La-Substituted M-Type Hexagonal Sr–Ni Ferrites Synthesized by Ball-Milling-Assisted Ceramic Process

Sr{sub 0.5}Ni{sub 0.5}La{sub x}Fe{sub 12 − x}O{sub 19} (x = 0, 0.08, 0.16, and 0.24) hexaferrites have been synthesized by ball-milling-assisted ceramic process. The calcined samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and vibrating sample magnetometry (VSM). XRD reveals that all samples consist of the main M-type hexagonal Sr ferrite phase and a low amount of rhombohedral Fe{sub 2}O{sub 3} as secondary phase, and a continuous increase of the hexagonal lattice parameters with substitution content (x). Magnetic characterization indicates that all Sr{sub 0.5}Ni{sub 0.5}La{sub x}Fe{sub 12 − x}O{sub 19} samples have a hard magnetic property. Substitution of Fe{sup 3+} ions by La{sup 3+} ions can obviously improve the specific saturation magnetization, remanence, magnetic moment, and effective anisotropy constant. Specific saturation magnetization, remanence, and the magnetic moment reach a maximum at x= 0.24 and calcination temperature of 1050 {sup ∘}C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

CHARACTERIZATION ON ANISOTROPIC THERMAL CONDUCTIVITY FOR BIG AREA ADDITIVE MANUFACTURING WITH POLYMERS

Additive manufacturing with polymers has been used mainly for prototyping. A recent development of Big Area Additive Manufacturing (BAAM) at Oak Ridge National Laboratory has opened its applications in the mold and die industry. A numerical simulation and prediction for a mold heating performance requires accurate anisotropic thermal properties of the printed material, which are challenging to obtain, and often requires the use of multiple techniques. The transient plane source (TPS) technique has been widely used due to its ability to measure the thermal properties of an extensive range of materials (solids, liquids, powder). Despite the capability to characterize thermal conductivity k of isotropic and anisotropic materials, the measurements of latter materials are limited to the cases, where the samples have the same thermal conductivity k along x- and y-axis that form the radial plane. In this work, the method for a characterization of k in all three dimensions is developed, and the application of TPS is extended to the determination of thermal properties along the x-, y-, and z-axis individually. The materials are represented by additively manufactured polymers including polylactic acid (PLA) and styrene maleic anhydride (SMA). The developed method consists of (1) a determination of the heat capacity of the polymers by means of TPS in combination with the developed in this work data analysis procedure, (2) a machining three types of cylindrical samples from the same material, with the height corresponding either to x-, y-, or z-direction of printing, and (3) a determination of axial thermal conductivity employing anisotropic model and using previously determined heat capacity

Trofimov, Artem↗
DOE OSTI2020

Structure and stability of alkali gallates structurally reminiscent of hollandite

Abstract Single crystals of CsGa 7 O 11 , RbGa 7 O 11 , and RbGa 4 In 5 O 14 were grown from alkali halide melts and their structures were characterized by single crystal and powder X‐ray diffraction. CsGa 7 O 11 and RbGa 7 O 11 adopt the same structure type, reminiscent of the hollandite structure type, as it contains nearly rectangular channels made up of two dimers of edge‐sharing GaO 6 octahedra, and two corner‐sharing octahedron/tetrahedron pairs. The structure of RbGa 4 In 5 O 14 is more complex and is comprised of indium octahedra, gallium trigonal bipyramids, and gallium tetrahedra, and contains similar sized tunnels as CsGa 7 O 11 and RbGa 7 O 11 . CsGa 7 O 11 and RbGa 4 In 5 O 14 were further characterized by TGA, ion exchange experiments, and DFT studies revealing that both structures are thermodynamically stable up to 850°C; however, CsGa 7 O 11 decomposes to GaO(OH) xH 2 O when heated in warm aqueous solutions. CsGa 7 O 11 undergoes ion exchange in both an aqueous solution of RbCl and a RbNO 3 melt, as predicted by DFT studies, where the ion exchange is more extensive in the RbNO 3 melt.

Juillerat, Christian A.↗
DOE OSTI2021

Local-Distance Seismic Event Relocation and Relative Magnitude Estimation, Applications to Mining Related Seismicity in the Powder River Basin, Wyoming

Recent efforts to characterize small ( M w < 3 ) seismic events at local distances have become more important because of the increased observation of human-triggered and induced seismicity and the need to advance nuclear explosion monitoring capabilities. The signals generated by low-magnitude seismic sources necessitate the use of nearby short-period observations, which are sensitive to local geological heterogeneity. Local to near-regional distance ( < 300 km ) surface and shear waves can dominate short-period observations from small, shallow seismic sources. In this work, we utilize these observations to estimate precise, relative locations and magnitudes of ~ 700 industrial mining events in Wyoming, using nearly 360,000 observations. The precise, relative location estimates (with formal location uncertainty estimates of less than 1 km) collapse a diffuse collection of mining events into discrete clusters associated with individual blasting operations. We also invert the cross-correlation amplitudes to estimate precise, relative moment magnitude estimates, which help validate and identify disparities in the event sizes reported by regional network catalogs. Joint use of multiple phases allows for the inclusion of more seismic events due to the increase in the number of observations. In some cases, using a single phase allowed us to relocate only 50% of the original reported seismic events within a cluster. Combining shear- and surface-wave phases increased the number of events to above 90% of the original events, allowing us to characterize a broader range of event sizes, source to station distances, and event distributions. This analysis takes a step toward making a fuller characterization of small industrial seismic events observed at local distances.

58 GEOSCIENCES↗
DOE OSTI2020

Long-range and local crystal structures of the S r 1 - x C a x Ru O 3 perovskites

Here, the crystal structures of the Sr 1–x Ca x RuO 3 (0 ≤ x ≤ 1) perovskites are investigated using both long-range and local structural probes. High-resolution synchrotron powder x-ray-diffraction characterization at ambient temperature shows that the materials have orthorhombic long-range crystal structures to high precision, and we support previous work showing that Ca 2+ substitution for Sr 2+ primarily changes the tilting of rigid corner-sharing RuO 6 octahedra at their shared oxygen vertices. X-ray pair-distribution function analysis for SrRuO 3 , CaRuO 3 , and one intermediate composition show them to display monoclinic symmetry at the local level; when averaged over different domain orientations this yields orthorhombic symmetry in the long range, and no long-range or local phase transitions are observed between 80 and 300 K for materials with intermediate compositions. High-resolution transmission electron microscopy shows that the Sr/Ca distribution is random at the nanoscale. Lastly, we plot magnetic characteristics such as the ferromagnetic T c , Curie-Weiss theta, effective moment, and ambient temperature susceptibility vs the octahedral tilt and unit-cell volume.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Multi-modal surface analysis of porous films under operando conditions

Practical catalysts with a porous framework, such as zeolites, host catalytic reactions at active sites engrained in the pores and channels of the scaffold. The mechanism of interaction at these active sites, defining catalyst performance, remains elusive, in large part, due to the lack of surface characterization methods available for thick films or powders. Here, we present thin film analogs of practical catalysts that allow for the implementation of surface characterization tools, including advanced microscopy and operando spectroscopy methodologies. Specifically, we investigated bilayer silica, MFI nanosheets, and UiO-66 thin films using a multi-modal approach addressing film growth, characterization, and gas adsorption aimed at understanding catalytic activity, reactivity, and selectivity properties, as defined by molecular-level changes in the reaction mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Thorium Metal‐Organic Framework with Outstanding Thermal and Chemical Stability

Abstract A new thorium metal‐organic framework (MOF), Th(OBA) 2 , where OBA is 4,4′‐oxybis(benzoic) acid, has been synthesized hydrothermally in the presence of a range of nitrogen‐donor coordination modulators. This Th‐MOF, described herein as GWMOF‐13, has been characterized by single‐crystal and powder X‐ray diffraction, as well as through a range of techniques including gas sorption, thermogravimetric analysis (TGA), solid‐state UV/Vis and luminescence spectroscopy. Single‐crystal X‐ray diffraction analysis of GWMOF‐13 reveals an interesting, high symmetry (cubic Ia d ) structure, which yields a novel srs‐a topology. Most notably, TGA analysis of GWMOF‐13 reveals framework stability to 525 °C, matching the thermal stability benchmarks of the UiO‐66 series MOFs and zeolitic imidazolate frameworks (ZIFs), and setting a new standard for thermal stability in f‐block based MOFs.

Carter, Korey P.↗
DOE OSTI2018

Magnetic Properties of Co-doped Bismuth Oxide (δ-Bi{sub 2}O{sub 3}) at Low Temperature

The (Bi{sub 2}O{sub 3}){sub 1−x−y}(Gd{sub 2}O{sub 3}){sub x}(Lu{sub 2}O{sub 3}){sub y} material compounds were prepared by using the solid-state reaction technique under normal air conditions. The heat treatments of the ternary samples were performed firstly at 800 °C for 48 h and then at 750 °C for 100 h. The structural, morphological, and magnetic properties of the materials were characterized by X-ray powder diffraction (XRD), scanning electron microscope, and a Quantum Design PPMS-9T system, respectively. From the XRD results, it was found that the phases of all of the samples consisted of the fluorite-type face-centered cubic δ-Bi{sub 2}O{sub 3} phase. It was observed that the microstructure of the samples is uniformly distributed on the samples’ surface. The temperature dependence of magnetization (M–T) measurements showed that the magnetization rose sharply at the critical temperature. The calculated critical temperature values vary from 22.19 to 56.61 K for the samples. All of the samples displayed the paramagnetic behavior. The paramagnetic behavior started from 300 K to very low temperature which varied from 22.19 to 56.61 K. The coercive rise on the magnetization below 22.19 K or 56.61 K with decreasing temperature causes a phase transformation in the δ-Bi{sub 2}O{sub 3} system. This sudden increment was considered as a ferromagnetic or ferrimagnetic phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Morphology, UV–visible and ellipsometric studies of sodium lithium orthovanadate

Sodium lithium orthovanadates were prepared by the classic ceramic method technique. Structure, phase purity, composition, and morphology were characterized by X-ray powder diffraction, infrared spectroscopy, energy dispersive spectroscopy, scanning-electron microscopy and atomic force microscopy. The optical properties of Na{sub x}Li{sub 1−x}CdVO{sub 4} (x = 0.5, 1) compounds prepared were recorded at room temperature using ultra-visible and ellipsometric spectroscopies in the spectral range (200–800) nm. The average reflectance of the pellets showed high reflectivity (over 80%) in the visible spectrum. The UV–Vis absorption bands are assigned to the charge transfer from the oxygen ligands to the central vanadium atom inside the [VO{sub 4}]{sup 3−} groups in the orthovanadate compounds. The optical band gaps E{sub g} of both samples are evaluated using Kubelka–Munk function. The analysis of the data revealed the existence of optical allowed direct transition for Na{sub x}Li{sub 1−x}CdVO{sub 4} (x = 0.5, 1). Spectroscopic ellipsometry measurements have been performed on Na{sub x}Li{sub 1−x}CdVO{sub 4} (x = 0.5, 1) specimens and their optical properties were analyzed using the Cauchy model.

77 NANOSCIENCE AND NANOTECHNOLOGY↗