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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Spectroscopic characterization of neptunium(VI), plutonium(VI), americium(VI) and neptunium(V) encapsulated in uranyl nitrate hexahydrate

The coordination of crystalline products resulting from the co-crystallization of Np(VI), Pu(VI), Am(VI), and Np(V) with uranyl nitrate hexahydrate (UNH) has been revealed through solid-state spectroscopic characterization via diffuse reflectance UV-Vis-NIR, SEM-EDS, and extended X-ray absorption fine structure (EXAFS). Density functional and multireference wavefunction calculations were performed to analyze the An(VI/V)O 2 (NO 3 ) 2 ·2H 2 O electronic structures and to help assign the observed transitions in the absorption spectra. EXAFS show a similar coordination between the U(VI) in UNH and Np(VI) and Pu(VI); while Am resulted in a similar coordination to Am(III), as reduction of Am(VI) occurred prior to EXAFS data being obtained. Here, the co-crystallization of the oxidized transuranic species—penta- and hexavalent—with UNH, represents a significant advance from not only a practical standpoint in providing an elegant solution for used nuclear fuel recycle, but also as an avenue to expand the fundamental understanding of the 5f electronic behavior in the solid-state.

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

Near-infrared C-term MCD spectroscopy of octahedral uranium (V) complexes

C-term magnetic circular dichroism (MCD) spectroscopy is a powerful method for probing d–d and f–f transitions in paramagnetic metal complexes. However, this technique remains underdeveloped both experimentally and theoretically for studies of U(V) complexes of Oh symmetry, which have been of longstanding interest for probing electronic structure, bonding, and covalency in 5f systems. In this study, C-term NIR MCD of the Laporte forbidden f–f transitions of [UCl 6 ] - and [UF 6 ] - are reported, demonstrating the significant fine structure resolution possible with this technique including for the low energy Γ 7 → Γ 8 transitions in [UF 6 ] - . The experimental NIR MCD studies were further extended to [U(OC 6 F 5 ) 6 ] - , [U(CH 2 SiMe 3 ) 6 ] - , and [U(NC(tBu)(Ph)) 6 ] - to evaluate the effects of ligand-type on the f–f MCD fine structure features. Theoretical calculations were conducted to determine the Laporte forbidden f–f transitions and their MCD intensity experimentally observed in the NIR spectra of the U(V) hexahalide complexes, via the inclusion of vibronic coupling, to better understand the underlying spectral fine structure features for these complexes. These spectra and simulations provide an important platform for the application of MCD spectroscopy to this widely studied class of U(V) complexes and identify areas for continued theoretical development.

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

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

Addition of [UI 2 (THF) 3 (μ-OMe)] 2 ·THF (2·THF) to THF solutions containing 6 equiv. of K[C 14 H 10 ] generates the heteroleptic dimeric complexes [K(18-crown-6)(THF) 2 ] 2 [U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)] 2 ·4THF (1 18C6 ·4THF) and {[K(THF) 3 ][U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)]} 2 (1 THF ) upon crystallization of the products in THF in the presence or absence of 18-crown-6, respectively. Both 1 18C6 ·4THF and 1 THF are thermally stable in the solid-state at room temperature; however, after crystallization, they become insoluble in THF or DME solutions and instead gradually decompose upon standing. X-ray diffraction analysis reveals 1 18C6 ·4THF and 1 THF to be structurally similar, possessing uranium centres sandwiched between bent anthracenide ligands of mixed tetrahapto and hexahapto ligation modes. Yet, the two complexes are distinguished by the close contact potassium-arenide ion pairing that is seen in 1 THF but absent in 1 18C6 ·4THF, which is observed to have a significant effect on the electronic characteristics of the two complexes. Structural analysis, SQUID magnetometry data, XANES spectral characterization, and computational analyses are generally consistent with U(IV) formal assignments for the metal centres in both 1 18C6 ·4THF and 1 THF , though noticeable differences are detected between the two species. For instance, the effective magnetic moment of 1 THF (3.74 μ B ) is significantly lower than that of 1 18C6 ·4THF (4.40 μ B ) at 300 K. Furthermore, the XANES data shows the U L III -edge absorption energy for 1 THF to be 0.9 eV higher than that of 1 18C6 ·4THF, suggestive of more oxidized metal centres in the former. Of note, CASSCF calculations on the model complex {[U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)] 2 } 2– (1*) shows highly polarized uranium–arenide interactions defined by π-type bonds where the metal contributions are primarily comprised by the 6d-orbitals (7.3 ± 0.6%) with minor participation from the 5f-orbitals (1.5 ± 0.5%). These unique complexes provide new insights into actinide–arenide bonding interactions and show the sensitivity of the electronic structures of the uranium atoms to coordination sphere effects.

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

Ring-opening of a thorium cyclopropenyl complex generates a transient thorium-bound carbene

The reaction of [Cp 3 ThCl] with in situ generated 1-lithium-3,3-diphenylcyclopropene results in the formation of [Cp 3 Th(3,3-diphenylcyclopropenyl)] (1), in good yields. Thermolysis of 1 results in isomerization to the ring-opened product, [Cp 3 Th(3-phenyl-1H-inden-1-yl)] (3) via a hypothesized carbene intermediate. This transformation represents a new mode of reactivity of 3,3-diphenylcyclopropene with the actinides, improving our ability to use this reagent as a carbene source. Here, a combined DFT and 13 C{ 1 H} NMR analysis of 1 shows a spin–orbit induced downfield shift at C α due to participation of the 5f orbitals in the Th–C bond.

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

Room temperature crystal field splitting of curium resolved by circularly polarized luminescence spectroscopy

Coordination of Cm(III) with a chiral decadentate ligand N,N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]-1,2-diaminocyclohexane (tpadac) generated complexes with strong luminescence allowing for the unprecedented measurement of well-resolved Cm(III) circularly polarized luminescence spectra. Quantitative resolution of the electronic structure of the [Cm(tpadac)][K] complexes was achieved at room temperature, highlighting the strength of the combination of luminescence and circularly polarized luminescence spectroscopies to unravel the fundamental electronic structure of Cm(III). These results are a clear demonstration that these spectroscopies are powerful yet simple tools for the fundamental understanding of electronic structure, which opens the door to future investigations of other Cm(III) complexes in geometries relevant to nuclear applications, and even other 5f-elements.

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

Unveiling the covalency of versatile Pu(iii)-N bonds in a unique plutonium(iii) complex

A trivalent plutonium–pyrazinyl–tetrazolate complex Na 2 [Pu(Hdtp)(dtp) 2 (H 2 O) 4 ]·9H 2 O (Pu_dtp, H 2 dtp = 2,3-di-1H-tetrazol-5-ylpyrazine) was synthesized through metathesis reaction of plutonium bromide and Na 2 (dtp)·2H 2 O in water. This structure is particularly notable among complexes formed by trivalent f-elements and the dtp 2− ligand in aqueous media. In contrast to other trivalent f-elements, including all Ln 3+ (with the exception of Pm 3+ ) and Cm 3+ , preferentially coordinated with eight water molecules rather than the nitrogen donors of the dtp 2− ligand, Pu 3+ exhibits a distinct affinity for nitrogen coordination. This observation provides strong evidence that the 5f electrons in Pu 3+ are more delocalized than other studied trivalent f-elements. In Pu_dtp, three distinct Pu(III)–N bonds are present: one Pu(III)–N5 from pyrazinyl, one Pu(III)–N4 from the least electronegative nitrogen in the tetrazolate, and three Pu(III)–N1/N2/N3 from the most electronegative nitrogens in the tetrazolate. Experimental Pu(III)–N bond lengths, Wiberg bond indices (WBI), natural localized molecular orbitals (NLMO), quantum theory of atoms in molecules (QTAIM), and energy decomposition analysis (EDA), reveal a covalency trend: Pu(III)–N from the most electronegative nitrogen in tetrazolate > Pu(III)–N from the least electronegative nitrogen in tetrazolate > Pu(III)–N from pyrazinyl. This trend arises from the increased negative charge on the most electronegative nitrogen atoms in the tetrazolate ring, enhancing electrostatic Pu–N1/N2/N3 interactions. These stronger electrostatic interactions lead to shorter bond lengths, thereby enhancing orbital overlap and greater covalency, compared to the less electronegative nitrogen in tetrazolate (Pu–N4) and the neutral pyrazinyl nitrogen (Pu–N5).

Bai, Zhuanling [Colorado School of Mines, Golden, ↗
DOE OSTI2025

Multiple oxidation states of uranium stabilized by an O , N , O -ligand

Elements of the 5f row maintain a wide variety of oxidation states that have been exploited in synthesis, catalysis, and separations. Herein, we describe the complexation of an O,N,O chelator, ExPh, with uranium in the (IV) and (VI) (uranyl) oxidation states. These two uranium complexes, U(IV)ExPh and UO 2 ExPh, respectively, were characterized in the solid state via single-crystal X-ray diffraction (SC-XRD) analysis. Electrochemical studies using cyclic voltammetry were employed to investigate the multiple redox events associated with the U(IV) complex. Spectro-electrochemical analysis of U(IV)ExPh provided spectroscopic evidence of a stable U(V) species. Chemical oxidation of U(IV)ExPh allowed isolation of the U(V) complex, U(V)ExPh. All three stable uranium complexes produced in this study were characterized via IR, UV-vis and NMR spectroscopies, and micro-spectrophotometry. On the other hand, efforts to reduce U(IV)ExPh to the corresponding U(III) species or produce this putative complex directly from ExPh failed to yield an isolable product. The stabilization of three formal oxidation states of uranium, coupled with previous lanthanide-row results, paves the way for studies of ExPh and its analogues in minor actinide chemistry.

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

Measurement of Local Magnetic Fields in Actinide Tetrafluorides

Fluorine-19 magnetic shielding tensors have been measured in a series of actinide tetrafluorides (AnF4) by solid state nuclear magnetic resonance (NMR) spectroscopy. Tetravalent actinide centers with 0 to 8 valence electrons can form tetrafluorides with the same unit cell, making these compounds an attractive choice for a systematic study of the variation in electronic structure across the 5f row of the Periodic Table. Pronounced deviations from predictions based on localized valence electron models have been detected by these experiments, which suggests that this approach may be used as a quantitative probe of electronic correlations.

Walter, Eric D.↗
DOE OSTI2023

A guided ion beam investigation of UO 2 + thermodynamics and f orbital participation: Reactions of U + + CO 2 , UO + + O 2 , and UO + + CO

A guided ion beam tandem mass spectrometer was employed to study the reactions of U + + CO 2 , UO + + O 2 , and the reverse of the former, UO + + CO. Reaction cross sections as a function of kinetic energy over about a three order of magnitude range were studied for all systems. The reaction of U + + CO 2 proceeds to form UO + + CO with an efficiency of 118% ± 24% as well as generating UO 2 + + C and UCO + + O. The reaction of UO + + O 2 forms UO 2 + in an exothermic, barrierless process and also results in the collision-induced dissociation of UO + to yield U + . In the UO + + CO reaction, the formation of UO 2 + in an endothermic process is the dominant reaction, but minor products of UCO + + O and U + + (O + CO) are also observed. Analysis of the kinetic energy dependences observed provides the bond energies, D 0 (U + –O) = 7.98 ± 0.22 and 8.05 ± 0.14 eV, D 0 (U + –CO) = 0.73 ± 0.13 eV, and D 0 (OU + –O) = 7.56 ± 0.12 eV. The values obtained for D 0 (U + –O) and D 0 (OU + –O) agree well with the previously reported literature values. To our knowledge, this is the first experimental measurement of D 0 (U + –CO). Furthermore, an analysis of the oxide bond energies shows that participation of 5f orbitals leads to a substantial increase in the thermodynamic stability of UO 2 + relative to ThO 2 + and especially transition metal dioxide cations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

The bond energy of UN + : Guided ion beam studies of the reactions of U + with N 2 and NO

In this work, a guided ion beam tandem mass spectrometer was used to study the reactions of U + with N 2 and NO. Reaction cross sections were measured over a wide range of energy for both systems. In each reaction, UN + is formed by an endothermic process, thereby enabling the direct measurement of the threshold energy and determination of the UN + bond dissociation energy. For the reaction of U + + N 2 , a threshold energy (E 0 ) of 4.02 ± 0.11 eV was measured, leading to D 0 (UN + ) = 5.73 ± 0.11 eV. The reaction of U + + NO yields UO + through an exothermic, barrierless process that proceeds with 94 ± 23% efficiency at the lowest energy. Analysis of the endothermic UN + cross section in this reaction provides E 0 = 0.72 ± 0.11 eV and, therefore, D 0 (UN + ) = 5.78 ± 0.11 eV. Averaging the values obtained from both reactions, we report D 0 (UN + ) = 5.76 ± 0.13 eV as our best value (uncertainty of two standard deviations). Combined with precise literature values for the ionization energies of U and UN, we also derive D 0 (UN) = 5.86 ± 0.13 eV. Both bond dissociation energies agree well with high-level theoretical treatments in the literature. The formation of UN + in reaction of U + with NO also exhibits a considerable increase in reaction probability above ~3 eV. Theory suggests that this may be consistent with the formation of UN + in excited quintet spin states, which we hypothesize are dynamically favored because the number of 5f electrons in reactants and products is conserved.

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

Magnetic, transport and thermal properties of δ-phase UZr 2

Here, polycrystals of hexagonal δ-phase UZr 2 have been synthesised and studied by means of heat capacity, magnetic susceptibility, magnetisation, electrical resistivity, magnetoresistance, thermoelectric power, thermal conductivity measurements, for the first time, at temperatures from 1.8 to 300 K and in magnetic fields up to 8 T. The weak temperature dependence of the magnetic susceptibility and the small value of both Seebeck (0.75 μV/K at room temperature) and of the Sommerfeld coefficient (13.5 mJ mol –1 K –2 ) point to 5f-electrons in this material having a delocalised nature. The electrical resistivity and magnetoresistance indicate the presence of significant electronic disorder in δ-UZr 2 , consistent with the disorder in its crystal structure. Density functional theory calculations have been performed and compared to experimental results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Comment on ‘Resonant inelastic x-ray scattering from U 3 O 8 and UN’

In a recent manuscript, Lawrence Bright et al (2023 J. Phys.: Condens. Matter 35 175501) reported the resonant inelastic x-ray scattering spectra of U 3 O 8 , as well as UN. Their goal was to identify electronic multiplets associated with a 5f 1 configuration with ground state 2 F 5/2 . Complete active space self-consistent field with spin–orbit coupling (CASSCF-SOC) predicted that 2 F 5/2 transitions should be observable at 190 and 328 meV. However, these energies were not accessible in their experiment. Here they suggested that the recent inelastic neutron scattering results of Miskowiec et al (2021 Phys. Rev. B 103 205101) could have been sensitive to these transitions. Here we show that transitions of this possible origin appear in that dataset near 198, 262, 362, and potentially 448 meV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Advances in actinide thin films: synthesis, properties, and future directions

Actinide-based compounds exhibit unique physics due to the presence of 5f electrons, and serve in many cases as important technological materials. Targeted thin film synthesis of actinide materials has been successful in generating high-purity specimens in which to study individual physical phenomena. These films have enabled the study of the unique electron configuration, strong mass renormalization, and nuclear decay in actinide metals and compounds. The growth of these films, as well as their thermophysical, magnetic, and topological properties, have been studied in a range of chemistries, albeit far fewer than most classes of thin film systems. This relative scarcity is the result of limited source material availability and safety constraints associated with the handling of radioactive materials. Here, we review recent work on the synthesis and characterization of actinide-based thin films in detail, describing both synthesis methods and modeling techniques for these materials. Further, we review reports on pyrometallurgical, solution-based, and vapor deposition methods. We highlight the current state-of-the-art in order to construct a path forward to higher quality actinide thin films and heterostructure devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Electronic correlation induced expansion of Fermi pockets in δ-plutonium

Plutonium is a critically important material as the behavior of its 5f electrons stands midway between the metalliclike itinerant character of the light actinides and localized atomic-core-like character of the heavy actinides. The δ phase of plutonium (δ-Pu), whereas still itinerant, has a large coherent Kondo peak and strong electronic correlations coming from its near-localized character. Here, using sophisticated Gutzwiller wave function and dynamical mean-field theory correlated theories, we study the Fermi surface and associated mass renormalizations of δ-Pu together with calculations of the de Haas–van Alphen frequencies. We find a large (~200%) correlation induced volume expansion in both the hole and the electron pockets of the Fermi surface in addition to an intermediate mass enhancement. All of the correlated electron theories predict, approximately, the same hole pocket placement in the Brillouin zone, which is different from that obtained in conventional density-functional band-structure theory, whereas the electron pockets from all theories are in, roughly, the same place.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Topological band and superconductivity in UTe 2

UTe 2 is a likely spin-triplet superconductor that also exhibits evidence for chiral Majorana edge states. A characteristic structural feature of UTe 2 is inversion-symmetry related pairs of U atoms, forming rungs of ladders. Here we show how each rung's two sublattice degrees of freedom play a key role in understanding the electronic structure and the origin of superconductivity. In particular, DFT + U calculations generically reveal a topological band near the chemical potential originating from a band inversion associated with 5f electrons residing on these rungs, necessitating a microscopic description that includes these rung degrees of freedom. Furthermore, we show that a previously identified strong ferromagnetic interaction within a U-U rung leads to a pseudospin-triplet superconducting state that accounts for a nonzero polar Kerr angle, the observed magnetic field-temperature phase diagrams, and nodal Weyl fermions. Finally, our analysis may also be relevant for other U-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Machine learning study of magnetism in uranium-based compounds

Actinide and lanthanide-based materials display exotic properties that originate from the presence of itinerant or localized f electrons and include unconventional superconductivity and magnetism, hidden order, and heavy-fermion behavior. Due to the strongly correlated nature of the 5f electrons, magnetic properties of these compounds depend sensitively on applied magnetic field and pressure, as well as on chemical doping. However, precise connection between the structure and magnetism in actinide-based materials is currently unclear. In this investigation, we established such structure-property links by assembling and mining two datasets that aggregate, respectively, the results of high-throughput density functional theory simulations and experimental measurements for the families of uranium- and neptunium-based binary compounds. Various regression algorithms were utilized to identify correlations among accessible attributes (features or descriptors) of the material systems and predict their cation magnetic moments and general forms of magnetic ordering. Descriptors representing compound structural parameters and cation f-subshell occupation numbers were identified as most important for accurate predictions. The best machine learning model developed employs the random forest regression algorithm. It can predict both spin and orbit moment size with root-mean-square error of 0.17 μ B and 0.19 μ B , respectively. Lastly, the random forest classification algorithm is used to predict the ordering (paramagnetic, ferromagnetic, and antiferromagnetic) of such systems with 76% accuracy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The insufficiency of the charge transfer model for resonant $\text{XES}$ in $\text{UF}$ 4

Recently, it was suggested that the single-electron charge transfer model (ligand 2p to Uranium 5f transition) could be used to explain the U M 4,5 Resonant X-ray Emission Spectroscopy (XES) of uranium dioxide (UO 2 ) and uranium tetrafluoride (UF 4 ). Here in this report, it is shown that this model produces results inconsistent with a joint consideration of both of the bandgaps of UO 2 and UF 4 and is thus insufficient to explain the observed behavior. An alternative Raman-based model is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba8B5N10F by Materials Project

Ba8(BN2)5F crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are seventeen inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to six N3- atoms to form edge-sharing BaN6 octahedra. There are a spread of Ba–N bond distances ranging from 2.85–2.97 Å. In the second Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.22 Å. In the third Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form distorted BaN5F octahedra that share corners with three BaN4F2 octahedra and edges with two equivalent BaN5F octahedra. The corner-sharing octahedra tilt angles range from 53–72°. There are a spread of Ba–N bond distances ranging from 2.78–3.10 Å. The Ba–F bond length is 2.71 Å. In the fourth Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.25 Å. In the fifth Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.23 Å. In the sixth Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.19 Å. In the seventh Ba2+ site, Ba2+ is bonded in a 3-coordinate geometry to six N3- atoms. There are a spread of Ba–N bond distances ranging from 2.72–3.23 Å. In the eighth Ba2+ site, Ba2+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Ba–N bond distances ranging from 2.76–3.15 Å. In the ninth Ba2+ site, Ba2+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.09 Å. In the tenth Ba2+ site, Ba2+ is bonded to four N3- and two equivalent F1- atoms to form BaN4F2 octahedra that share corners with two equivalent BaN5F octahedra and edges with six BaN6 octahedra. The corner-sharing octahedra tilt angles range from 53–72°. There are a spread of Ba–N bond distances ranging from 2.81–2.88 Å. There are one shorter (2.71 Å) and one longer (2.78 Å) Ba–F bond lengths. In the eleventh Ba2+ site, Ba2+ is bonded to four N3- and two equivalent F1- atoms to form BaN4F2 octahedra that share corners with two equivalent BaN5F octahedra and edges with six BaN4F2 octahedra. The corner-sharing octahedra tilt angles range from 56–72°. There are a spread of Ba–N bond distances ranging from 2.82–2.85 Å. There are one shorter (2.70 Å) and one longer (2.75 Å) Ba–F bond lengths. In the twelfth Ba2+ site, Ba2+ is bonded to six N3- atoms to form edge-sharing BaN6 octahedra. There are a spread of Ba–N bond distances ranging from 2.86–2.95 Å. In the thirteenth Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form a mixture of edge and corner-sharing BaN5F octahedra. The corner-sharing octahedral tilt angles are 66°. There are a spread of Ba–N bond distances ranging from 2.82–2.97 Å. The Ba–F bond length is 2.69 Å. In the fourteenth Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form BaN5F octahedra that share a cornercorner with one BaN5F octahedra and edges with six BaN4F2 octahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Ba–N bond distances ranging from 2.82–2.91 Å. The Ba–F bond length is 2.71 Å. In the fifteenth Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form distorted BaN5F octahedra that share corners with three BaN4F2 octahedra and edges with two equivalent BaN5F octahedra. The corner-sharing octahedra tilt angles range from 56–72°. There are a spread of Ba–N bond distances ranging from 2.78–3.11 Å. The Ba–F bond length is 2.69 Å. In the sixteenth Ba2+ site, Ba2+ is bonded in a 3-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.70–3.24 Å. In the seventeenth Ba2+ site, Ba2+ is bonded to six N3- atoms to form edge-sharing BaN6 octahedra. There are a spread of Ba–N bond distances ranging from 2.82–3.03 Å. There are ten inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.35 Å) and one longer (1.36 Å) B–N bond length. In the second B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. In the third B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. Both B–N bond lengths are 1.35 Å. In the fourth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. In the fifth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.36 Å) B–N bond length. In the sixth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. Both B–N bond lengths are 1.35 Å. In the seventh B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.36 Å) B–N bond length. In the eighth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.35 Å) and one longer (1.36 Å) B–N bond length. In the ninth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. In the tenth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. There are twenty inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the second N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the third N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the fourth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the fifth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the sixth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the seventh N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the eighth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the ninth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the tenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the eleventh N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the twelfth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the thirteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the fourteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the fifteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the sixteenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the seventeenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the eighteenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the nineteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the twentieth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded to four Ba2+ atoms to form corner-sharing FBa4 tetrahedra. In the second F1- site, F1- is bonded to four Ba2+ atoms to form corner-sharing FBa4 tetrahedra.

36 MATERIALS SCIENCE↗