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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The u 3 si 2 -H system

U 3 Si 2 is of interest to the nuclear industry as a candidate fuel material due to its high uranium density and high thermal conductivity. However, it has been observed to react with hydrogen, resulting in material decrepitation. As a result, it is important to understand the thermodynamics of the U 3 Si 2 -H system. In this study, the thermodynamics of the hydrogen absorption reaction of USi were determined experimentally using Sievert’s gas absorption and related to crystallographic evolution with hydrogen content using X-ray diffraction. Experimentally-determined thermodynamic parameters were compared with results from density functional theory modeling. Results from this study were also compared with those determined in previous work. Sievert’s gas absorption results were used to develop the pressure-composition-temperature (PCT) curves of the U 3 Si 2 -H system. It was found that the hydride phase exhibited a maximum stoichiometry between U 3 Si 2 H 1.8 and U 3 Si 2 H 2 . The two-phase region for hydride formation from U 3 Si 2 exhibited a miscibility gap with a critical temperature between 623 and 673 K, as calculated from the PCT curves. Analysis of the PCT curves also showed that both the enthalpy and entropy of the hydrogen absorption reaction increased with hydrogen content but were lower than the values for uranium trihydride formation from uranium metal. The enthalpy of reaction for hydrogen absorption was calculated to range between -86.9 and -94.8 kJ mol -1 , while the entropy of reaction was calculated to range between 101.9 and 138.8 J mol -1 K -1 . Furthermore, DFT modeling of the thermoydnamic stability of the USi hydride phases yielded a decomposition temperature of U 3 Si 2 H 2 of approximately 600 K, which was consistent with the experimental results. Similarly, the DFT-calculated enthalpy and entropy of reaction to form USiH were determined to be -106.5kJ mol and 121.8J mol -1 K -1 , respectively, which were both in close agreement with the experimentally-determined values.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Hard exclusive $\pi^{+}n$ electro production beam spin asymmetries off the proton in the GPD and TDA regimes

Hard exclusive \pi^{+} π + n electro-production can be used to gain access to the 3D nucleon structure. The QCD factorisation mechanism in the “nearly forward region” ( t/Q^{2} t / Q 2 small) allows a description by Generalized Parton Distributions (GPDs), while for the “nearly backward” kinematic region ( u/Q^{2} u / Q 2 small) a description based on nucleon to pion transitions (TDAs) is available. The paper presents a measurement of single beam spin asymmetries to extract the A^{\sin\phi}_{LU} A L U sin ϕ moments and the related cross section ratio \sigma_{LT^\prime}/\sigma_{0} σ L T ′ / σ 0 from the hard exclusive \pi^{+} π + channel off the unpolarized hydrogen target in a wide range of kinematics based on data taken with the CLAS spectrometer at Jefferson Lab. In addition, under forward angles a detailed multidimensional study will be presented based on CLAS12 data and compared to theoretical predictions.

Diehl, Stefan↗
DOE OSTI2021

Uranium nitride (UN) pellets with controllable microstructure and phase – fabrication by spark plasma sintering and their thermal-mechanical and oxidation properties

Dense uranium mononitride (UN) pellets with controlled microstructures and tailored grain size from large-grained to a few microns are synthesized by spark plasma sintering (SPS) combined with high energy ball milling. The impacts of the sintering conditions on fuel microstructure, grain size, physical density, and phase behavior are systematically investigated, and the thermal-mechanical properties and oxidation behavior of the SPS densified UN pellets are characterized. Higher sintering temperatures and longer ball milling durations and thus finer starting UN powders promote sintering and densification, and dense UN pellets above 95% theoretical density can be achieved by SPS at 1873 K for 10 min. UN phase purity is maintained in the SPS-densified pellets sintered at a lower temperature and short duration. A phase heterogeneity with secondary UO 2 or uranium sesquinitride (U 2 N 3 ) occurs for the UN pellets sintered at higher temperatures using finer UN powders. The hardness and fracture toughness of the SPS-densified UN pellets increase with smaller grain sizes and higher densities to 7.9 GPa and 3.5 MPa m 1/2 , respectively. Furthermore, both small (1–2 μm) and large grain-sized (30–50 µm) UN pellets exhibit good thermal conductivity. Dynamic oxidation testing by a thermogravimetric analyzer in air shows that the onset temperature for oxidation varies with microstructure and phase heterogeneity of the SPS densified UN pellets. Particularly, the smaller-grained (micron-sized) UN pellets containing uranium oxides and U 2 N 3 display lower weight gain and significantly-reduced oxidation kinetics, and full oxidation completes at a temperature above 1173 K when tested with a ramp rate of 10 K/min.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unusual Base Pair between Two 2-Thiouridines and Its Implication for Nonenzymatic RNA Copying

2-Thiouridine (s 2 U) is a nucleobase modification that confers enhanced efficiency and fidelity both on modern tRNA codon translation and on nonenzymatic and ribozyme-catalyzed RNA copying. We have discovered an unusual base pair between two 2-thiouridines that stabilizes an RNA duplex to a degree that is comparable to that of a native A:U base pair. High-resolution crystal structures indicate similar base-pairing geometry and stacking interactions in duplexes containing s 2 U:s 2 U compared to those with U:U pairs. Notably, the C=O···H–N hydrogen bond in the U:U pair is replaced with a C=S···H–N hydrogen bond in the s 2 U:s 2 U base pair. The thermodynamic stability of the s 2 U:s 2 U base pair suggested that this self-pairing might lead to an increased error frequency during nonenzymatic RNA copying. However, competition experiments show that s 2 U:s 2 U base-pairing induces only a low level of misincorporation during nonenzymatic RNA template copying because the correct A:s 2 U base pair outcompetes the slightly weaker s 2 U:s 2 U base pair. In addition, even if an s 2 U is incorrectly incorporated, the addition of the next base is greatly hindered. This strong stalling effect would further increase the effective fidelity of nonenzymatic RNA copying with s 2 U. Our findings suggest that s 2 U may enhance the rate and extent of nonenzymatic copying with only a minimal cost in fidelity.

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

C–H Bond Activation via U(II) in the Reduction of Heteroleptic Bis(trimethylsilyl)amide U(III) Complexes

Reduction of (C 5 Me 5 ) 2 U III (NR 2 ) and (C 5 Me 5 )U III (NR 2 ) 2 (R = SiMe 3 ) with potassium graphite in the presence of 2.2.2-cryptand (crypt) generates dark solutions that have UV-visible spectra consistent with time-dependent density functional theory (TDDFT) calculations on the U(II) products, [(C 5 Me 5 ) 2 U II (NR 2 )] - and [(C 5 Me 5 )U II (NR 2 ) 2 ] - . However, the solutions quickly change color and form the U(III) C–H bond activation products [K(crypt)][(C 5 Me 5 ) 2 U III (CH 2 SiMe 2 NSiMe 3 –κC,κN)], 1, and [K(crypt)][(C 5 Me 5 )U III (NR 2 )(CH 2 SiMe 2 NSiMe 3 –κC,κN)], 2, that were identified by X-ray crystallography. DFT calculations on the putative [(C 5 Me 5 ) 2 U II (NR 2 )] - and [(C 5 Me 5 )U II (NR 2 ) 2 ] - complexes revealed 5f 3 6d 1 ground state electron configurations as previously found in isolable [(C 5 H 4 SiMe 3 ) 3 U II ] - , which indicated that these low symmetry heteroleptic complexes are reasonable precursors for new U(II) complexes.

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

The effect of Ti content on age hardening and mechanical properties of uranium-titanium alloys

Here, the effect of Ti content on age hardening and the resulting mechanical properties are described for -quenched U-Ti alloys containing 0.3 wt.% to 2.0 wt.%Ti. Age hardening occurs between ~250°C and ~450°C. Overaging occurs at higher temperatures by cellular decomposition. Age hardening kinetics suggest that different mechanisms occur depending on Ti content and initial microstructure. Strengthening in 'a acicular martensites begins by the formation of Ti clusters which evolve into thin U 2 Ti disc shaped precipitates and later mature into continuous U 2 Ti rods beginning at peak hardness. The mechanism of hardening in 'b banded martensite is more elusive, as significant hardening occurs where atomic mobility is lower than that required for precipitate formation, similar to that reported for age hardening in ''b banded martensite in U-6%Nb. The activation energy for aging varies with Ti content and microstructure. In fully martensitic alloys containing 0.75% to 2.0%Ti it is in the vicinity of ~44 kcal/mole (184 kJ/mole). But it is lower in alloys containing less than 0.6%Ti where quenched microstructures are less than fully martensitic. Tensile ductility is high prior to aging, decreases with age hardening, is effectively zero at peak hardness, and remains low in overaged conditions. Attractive combinations of strength and ductility are best obtained in alloys containing 0.6% to 1.0%Ti which have been partially aged to fractional hardening levels no greater than ~0.6. This corresponds to the very early stages of aging, associated with clustering and the earliest stages of U 2 Ti disc formation. Alloys containing 0.45%Ti or less are not as responsive to age hardening. Alloys containing 1.5% and 2.0%Ti can be aged to higher strengths, but extreme quench rate sensitivity prevents them from being effectively heat treated in realistic section thicknesses.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Raman spectroscopy of uranium nitride kernels

Uranium nitride is an advanced fuel candidate for a wide variety of advanced nuclear reactors. This work summarizes the first characterization of UN kernels by Raman spectroscopy. First-principles density functional theory calculations were performed to predict the Raman spectra of uranium sesquinitride (U 2 N 3 ), uranium dinitride (UN 2 ), uranium mononitride (UN), uranium monocarbide (UC), as well as U-N-C (UN 1-x C x ) and a U-N-C-O mixture. Further, a core–shell structure was identified by scanning electron microscopy and Raman spectroscopy imaging. A signal at ~500 cm -1 was identified on the periphery of the core-shell structure, possibly corresponding to U 2 N 3 and/or UN 2 . This signal broadens and shifts to 470 cm -1 because of the formation of UNC, UNCO or U 2 N 3+x structures. The culmination of this work demonstrates the feasibility of using Raman spectroscopy to identify variations in composition and phases in UN kernels.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Enhanced steam oxidation resistance of uranium nitride nuclear fuel pellets

Here, the steam oxidation resistance of UN and UN-(20 vol%)ZrN fuel pellets is evaluated to enhance understanding of steam corrosion mechanisms in advanced nuclear fuel materials. In situ neutron diffraction shows the modified UN fuel pellets form a (U 0.77 ,Zr 0.23 )N solid-solution and the sole crystalline oxidation product detected in bulk is (U 0.77 ,Zr 0.23 )O 2 . U 2 N 3 is not detected in significant quantities during the steam oxidation of UN or (U 0.77 ,Zr 0.23 )N and stable lattice parameters show that hydriding does not take place. Steam oxidation rates, obtained via sequential Rietveld refinement show how (U 0.77 ,Zr 0.23 )N has a higher activation energy (79 ± 1 kJmol -1 vs. 50 ± 5 kJmol -1 ), higher onset temperature (430 °C vs. 400 °C) and slower reaction rates for steam oxidation up to 616 °C, than pure UN. Throughout, both UN and (U 0.77 ,Zr 0.23 )N exhibit linear (non-protective) oxidation kinetics, signifying that degradation of the fuel pellets is caused by the evolution of gaseous products at the interface followed by oxide scale spallation. This quantitative and mechanistic understanding of material degradation enables better defined operating regimes and points towards (U,Zr)N solid solutions as a promising strategy for the design of advanced nuclear fuel materials with enhanced steam corrosion resistance.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Phase-field simulations of intergranular fission gas bubble behavior in U 3 Si 2 nuclear fuel

U 3 Si 2 is a potential accident-tolerant fuel that shows promise due to its high thermal conductivity and higher uranium density relative to UO 2 . However, its swelling and fission gas release behavior in light water reactor (LWR) conditions is relatively unknown. To provide mechanistic insight and determine parameters for engineering-scale fuel performance modeling of pellet-form U 3 Si 2 , phase-field simulations of the growth, interconnection, and venting of intergranular fission gas bubbles were performed. The fractional coverage of the grain boundary and the fraction of bubble area that is vented were calculated as a function of time. From the simulation data, the fractional grain boundary coverage at saturation, an important parameter needed in engineering-scale modeling of swelling and fission gas release, was determined. Multiple simulations were run to determine the uncertainty in the calculated value. Finally, the effect of model assumptions and input parameters that are not well known was evaluated. Simulation results are compared to related theoretical and computational work. Based on the simulation results, a value of 0.60 for the fractional grain boundary coverage at saturation is recommended for U 3 Si 2 fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Solid-state phase transitions of two quaternary metallic fuel alloys (U-2.5Mo-2.5Ti-5.0Zr and U-1.5Mo-1.5Ti-7.0Zr in wt. %)

This study focuses on the solid-state phase transitions of two quaternary fuel alloys for fast reactors: U-1.5Mo-1.5Ti-7.0Zr (U-MT7Z) and U-2.5Mo-2.5Ti-5.0Zr (U-MT5Z). Here, the phase transitions were determined by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). To identify the high temperature phases, the alloys were annealed at 873K, 948K, 1023K, and 1123K (all under 72 hours). Combining those characterizations, the phase transitions are determined. In U-MT7Z, there is one phase transition observed, and it is ascribed to α + U 2 Ti → γ transition. In U-MT5Z, two transitions are found. The first transition is α → γ, while the second is U 2 Ti → γ. The γ phase onset temperature of U-MT5Z is lower than that of U-MT7Z due to the higher Mo content.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Oxidation kinetics of SPS-densified U 3 Si 2 fuels—Microstructure impact

Here, U 3 Si 2 is a potential candidate for accident tolerant fuels because of its high uranium density and excellent thermal conductivity in comparison to UO 2 . However, U 3 Si 2 suffers from oxidation, steam corrosion, and subsequent disintegration/pulverization. The detailed investigation of kinetics that incorporates fundamental treatment of oxidation of U 3 Si 2 is scarcely reported, and the oxidation mechanisms have not been fully elucidated. In this paper, the oxidation behavior of microcrystalline (mc - ) and nanocrystalline (nc - ) U 3 Si 2 have been systematically investigated using a thermogravimetric analysis (TGA) apparatus through a series of isothermal and non-isothermal kinetic studies. The isothermal kinetic study with a model-fitting approach indicates oxidation activation energy of 85 kJ/mol for dense mc - U 3 Si 2 and 96.4 kJ/mol for nc - U 3 Si 2 pellets, while the isoconversional approach leads to an activation energy in the range of 70–85 kJ/mol for mc - U 3 Si 2 and 75–86 kJ/mol for nc - U 3 Si 2 with three most common model-free methods, including Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods. The derivation of oxidation activation energies using both isothermal and isoconversional methods highlights the approach to evaluate the oxidation resistance of nuclear materials using TGA quantitatively and makes it possible to compare among various nuclear fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on U(Al5Fe)2 by Materials Project

UFe2Al10 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. U is bonded in a 8-coordinate geometry to four equivalent Fe and sixteen Al atoms. All U–Fe bond lengths are 3.41 Å. There are a spread of U–Al bond distances ranging from 3.10–3.60 Å. Fe is bonded in a 10-coordinate geometry to two equivalent U and ten Al atoms. There are a spread of Fe–Al bond distances ranging from 2.52–2.70 Å. There are five inequivalent Al sites. In the first Al site, Al is bonded in a 12-coordinate geometry to one U, two equivalent Fe, and nine Al atoms. There are a spread of Al–Al bond distances ranging from 2.61–3.00 Å. In the second Al site, Al is bonded in a 2-coordinate geometry to one U, two equivalent Fe, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.58–2.80 Å. In the third Al site, Al is bonded in a 2-coordinate geometry to two equivalent U, two equivalent Fe, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.71–2.79 Å. In the fourth Al site, Al is bonded in a 2-coordinate geometry to two equivalent U, two equivalent Fe, and eight Al atoms. Both Al–Al bond lengths are 2.68 Å. In the fifth Al site, Al is bonded in a 2-coordinate geometry to two equivalent U, two equivalent Fe, and eight Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Photodissociation and Infrared Spectroscopy of U + (CO 2 ) n , UO + (CO 2 ) n , and UO 2+ (CO 2 ) n Cation-Molecular Complexes

Laser vaporization of uranium in a pulsed supersonic expansion of carbon dioxide is used to produce complexes of the form U + (CO 2 ) n , UO + (CO 2 ) n , and UO 2+ (CO 2 ) n . These ions are selected in a reflectron time-offlight mass spectrometer and studied with visible laser photodissociation and tunable infrared laser photodissociation spectroscopy in the region of the CO 2 antisymmetric stretch. The dissociation patterns and spectroscopy of these ions indicate that CO 2 ligands are intact molecules. Although reaction products that form oxide-carbonyl or oxalate species are predicted to be stable, there is no direct evidence in the frequency range studied for the formation of these species. There is no clear indication for the coordination numbers for singly charged uranium and its oxide complexes with CO 2 . However, there is strong support in the vibrational patterns for an eight-coordinate complex of the doubly charged UO 2+ species, i.e., UO 2+ (CO 2 ) 8 .

Cluster chemistry↗
DOE OSTI2023

Energetics of oxidation and formation of uranium monocarbide

To enable better implementation of uranium monocarbide (UC) as an advanced nuclear fuel for future high-temperature reactors, it is essential to have a thorough knowledge of its thermal and thermodynamic properties under reactor operational conditions. In this work, we studied thermal bulk oxidation of UC by simultaneous thermal analysis consisting of thermogravimetric analysis – differential scanning calorimetry coupled with evolved gas mass spectrometry (TGA-DSC-MS), and we examined the thermodynamic stability of UC using high temperature oxide melt drop solution calorimetry. Further, in air, our studied UC sample (which contains ~5 mol% UO 2 ) was found to undergo a step-wise thermal oxidation process consisting of consecutive oxidations and thermal decomposition reactions: 0.95UC·0.05UO 2 → UO 3 ·0.29(C x O y ) + 0.66CO 2 → UO 3 ·0.20(C x O y ) + 0.09CO 2 → UO 3 ·0.03(C x O y ) + 0.17CO 2 → U 3 O 8 + 0.03CO 2 + 0.166O 2 . DSC was further used to determine the enthalpies of reactions associated with this series of oxidation reactions. Synchrotron X-ray diffraction (XRD) and extended X-ray absorption spectroscopy (EXAFS) were performed to characterize both the long- and short-range structures of UC. The standard enthalpy of formation (ΔH° f ) of UC was determined to be –50.7 ± 10.8 kJ/mol·atom, in good agreement with previous values measured by bomb calorimetry. Lastly, the enthalpic landscape of U-C compounds, including UC, U 2 C 3 , and α-UC 1.94 , were established based on the enthalpy normalized per mole atom, which suggests that U-C phases are thermodynamically stable at lower C/U ratios.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

U–C Bond Insertion, Ring-Opening, and C–H Activation in a Uranium Bis(diisopropylamino)cyclopropenylidene (BAC) Adduct

Reaction of [U(NR 2 ) 3 ] (R = SiMe 3 ) with 1 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) in Et 2 O results in the formation of [(NR 2 ) 3 U(BAC)] (1), which can be isolated in modest yields. Thermolysis of 1 in C 6 D 6 at 85 °C results in the formation of the ring-opened U(IV) product, [(NR 2 ) 2 U{N(R)(SiMe 2 CH=C(NiPr 2 )C(NiPr 2 )=CH)}] (2), which can be isolated in low yields. Mechanistic studies suggest that the formation of 2 proceeds via dissociation of BAC from 1 to regenerate [U(NR 2 ) 3 ], which converts into [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] at the elevated temperatures. BAC then inserts into the U–C bond of [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] to generate a cyclopropenyl intermediate, which undergoes ring opening and C–H activation to afford the final product, 2. We hypothesize that the ring-opening generates an unobserved carbene intermediate. Notably, thermolysis of a 1:1 mixture of independently prepared [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] and BAC results in clean formation of 2, providing strong support for the proposed mechanism. The formulations of both 1 and 2 were confirmed by X-ray crystallography. Finally, theoretical calculations indicate that the hypothesized uranium carbene intermediate features strong U–C bonding, potentially with some carbyne character in the electronic structure.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Materials Data on U(Al5Ru)2 by Materials Project

URu2Al10 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. U is bonded in a 10-coordinate geometry to four equivalent Ru and sixteen Al atoms. All U–Ru bond lengths are 3.45 Å. There are a spread of U–Al bond distances ranging from 3.15–3.63 Å. Ru is bonded in a 10-coordinate geometry to two equivalent U and ten Al atoms. There are a spread of Ru–Al bond distances ranging from 2.58–2.74 Å. There are five inequivalent Al sites. In the first Al site, Al is bonded in a distorted linear geometry to two equivalent U and two equivalent Ru atoms. In the second Al site, Al is bonded in a 2-coordinate geometry to one U and two equivalent Ru atoms. In the third Al site, Al is bonded in a distorted bent 120 degrees geometry to two equivalent U and two equivalent Ru atoms. In the fourth Al site, Al is bonded in a distorted bent 120 degrees geometry to two equivalent U and two equivalent Ru atoms. In the fifth Al site, Al is bonded in a 12-coordinate geometry to one U and two equivalent Ru atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(SiNi5)2 by Materials Project

UNi10Si2 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. U is bonded in a 8-coordinate geometry to sixteen Ni and four equivalent Si atoms. There are a spread of U–Ni bond distances ranging from 2.67–3.09 Å. All U–Si bond lengths are 3.16 Å. There are four inequivalent Ni sites. In the first Ni site, Ni is bonded in a 8-coordinate geometry to one U, eleven Ni, and two equivalent Si atoms. There are a spread of Ni–Ni bond distances ranging from 2.42–2.96 Å. Both Ni–Si bond lengths are 2.54 Å. In the second Ni site, Ni is bonded in a 1-coordinate geometry to one U, eleven Ni, and two equivalent Si atoms. There are a spread of Ni–Ni bond distances ranging from 2.48–2.71 Å. Both Ni–Si bond lengths are 2.40 Å. In the third Ni site, Ni is bonded in a 2-coordinate geometry to two equivalent U, nine Ni, and two equivalent Si atoms. There are four shorter (2.44 Å) and one longer (2.83 Å) Ni–Ni bond lengths. Both Ni–Si bond lengths are 2.50 Å. In the fourth Ni site, Ni is bonded to two equivalent U, eight Ni, and two equivalent Si atoms to form distorted NiU2Si2Ni8 cuboctahedra that share corners with four equivalent SiU2Ni10 cuboctahedra, corners with ten equivalent NiU2Si2Ni8 cuboctahedra, edges with two equivalent SiU2Ni10 cuboctahedra, edges with four equivalent NiU2Si2Ni8 cuboctahedra, faces with four equivalent SiU2Ni10 cuboctahedra, and faces with six equivalent NiU2Si2Ni8 cuboctahedra. Both Ni–Ni bond lengths are 2.40 Å. Both Ni–Si bond lengths are 2.30 Å. Si is bonded to two equivalent U and ten Ni atoms to form distorted SiU2Ni10 cuboctahedra that share corners with six equivalent SiU2Ni10 cuboctahedra, corners with eight equivalent NiU2Si2Ni8 cuboctahedra, edges with three equivalent SiU2Ni10 cuboctahedra, edges with four equivalent NiU2Si2Ni8 cuboctahedra, a faceface with one SiU2Ni10 cuboctahedra, and faces with eight equivalent NiU2Si2Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(Zn10Os)2 by Materials Project

UOs2Zn20 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. U is bonded in a 4-coordinate geometry to sixteen Zn atoms. There are four shorter (3.10 Å) and twelve longer (3.13 Å) U–Zn bond lengths. Os is bonded to twelve Zn atoms to form OsZn12 cuboctahedra that share corners with six equivalent OsZn12 cuboctahedra, edges with eighteen equivalent ZnUZn10Os cuboctahedra, and faces with six equivalent ZnUZn10Os cuboctahedra. There are six shorter (2.54 Å) and six longer (2.81 Å) Os–Zn bond lengths. There are three inequivalent Zn sites. In the first Zn site, Zn is bonded in a 2-coordinate geometry to two equivalent U and twelve equivalent Zn atoms. All Zn–Zn bond lengths are 3.04 Å. In the second Zn site, Zn is bonded in a distorted linear geometry to two equivalent Os and six equivalent Zn atoms. There are two shorter (2.69 Å) and four longer (2.83 Å) Zn–Zn bond lengths. In the third Zn site, Zn is bonded to one U, one Os, and ten Zn atoms to form distorted ZnUZn10Os cuboctahedra that share corners with fifteen equivalent ZnUZn10Os cuboctahedra, edges with two equivalent ZnUZn10Os cuboctahedra, edges with three equivalent OsZn12 cuboctahedra, a faceface with one OsZn12 cuboctahedra, and faces with fifteen equivalent ZnUZn10Os cuboctahedra. There are a spread of Zn–Zn bond distances ranging from 2.64–2.92 Å.

36 MATERIALS SCIENCE↗