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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

In-plane multi-q magnetic ground state of Na 3 Co 2 SbO 6

We report Na 3 Co 2 SbO 6 is a potential Kitaev magnet with a monoclinic layered crystal structure. Recent investigations of the C3-symmetric sister compound Na 2 Co 2 TeO 6 have uncovered a unique triple-q magnetic ground state, as opposed to a single-q (zigzag) one, prompting us to examine the influence of the reduced structural symmetry of Na 3 Co 2 SbO 6 on its ground state. Neutron diffraction data obtained on a twin-free crystal reveal that the ground state remains a multi-q state, despite the system's strong non-C 3 -symmetric anisotropy. This robustness of multi-q orders suggests that they are driven by a common mechanism in the honeycomb cobaltates, such as interactions beyond the bilinear order. Spin-polarized neutron diffraction results show that the ordered moments are entirely in plane, with each staggered component orthogonal to the propagating wave vector. The inferred ground state appears more compatible with the so-called XXZ easy-plane anisotropy than the Kitaev anisotropy, and features unequal ordered moments reduced by strong quantum fluctuations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Direct observation of the exotic β – γ – α decay mode in the T z = – 1 nucleus Na 20

The exotic β – γ – α decay mode of 20 Na has been directly observed for the first time in the Day-one experiment at the Beijing Radioactive Ion-beam Facility. The 20 Na source was produced by using a 100-MeV proton beam bombarding a stack of microporous MgO thick target and delivered as an intense mass separated beam after online ionization. A high-efficiency simultaneous measurement of β, γ, and α transitions enables the β-delayed γ – γ and α – γ coincidence spectroscopy. Here three β – γ – α exotic decay sequences in 20 Na are discovered, which expands the rare decay modes observed in β decay. Moreover, a β – α –decay sequence to the 6130-keV 3 – state of 16 O is observed, which is likely through the 12367-keV 1 + state in 20 Ne. The experimentally deduced B(F) and B(GT) are compared to the shell-model calculation, the allowed β transition strengths can be well accounted for by using sd shell-model space interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

First measurement of proton decay from a transfer reaction to 21 Na

Decay protons from excited states in Na 21 populated through a previously reported Mg 24 ( p , α ) Na 21 transfer reaction [Cha et al. , Phys. Rev. C 96 , 025810 (2017) ] were analyzed to extract the proton branching ratios of the energy levels. Additionally, by utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched Mg 24 solid targets, the decay protons were detected in coincidence with α particles from the ( p , α ) reaction using a silicon strip detector array. Proton decay branching ratios of several Na 21 levels were deduced for the p 0 and p 1 decay channels to the ground and first excited states in Ne 20 , respectively.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurement of the Ne 18 ( α , p ) Na 21 reaction with the ANASEN active-target detector system at E c . m . = 2.5 – 4 MeV

The 18 Ne(α,p) 21 Na reaction plays a significant role in Type-I X-ray bursts. It is a major path in the breakout from the hot-CNO cycles to the synthesis of heavier elements in the αp- and rp-processes. An experiment to determine the cross section of this reaction was performed with the ANASEN active-target detector system, determining the cross section at energies between 2.5 and 4 MeV in the center-of-mass frame. The measured cross sections for reactions populating the ground state in 21 Na are consistent with results obtained from the time-inverse reaction, but significantly lower than the previously published experimental data of direct measurements. The total cross sections are also compared with those derived from indirect methods and statistical-model calculations. Furthermore, this experiment establishes a new experimental data set on the excitation function of the 18 Ne(α,p) 21 Na reaction, revealing the significance of the excited states' contributions to the total reaction cross section and allowing us to separate the contribution of the (α,2p) reaction. The impact of the measured cross section on thermal reaction rates is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Disorder-Enriched Magnetic Excitations in a Heisenberg-Kitaev Quantum Magnet Na 2 ⁢Co 2 ⁢TeO 6

Using optical magnetospectroscopy, we investigate the magnetic excitations of Na 2 ⁢Co 2 ⁢TeO 6 in a broad magnetic field range (0 T ≤ B ≤ 17.5 T) at low temperature. Our measurements reveal rich spectra of in-plane magnetic excitations with a surprisingly large number of modes, even in the high-field spin-polarized state. Theoretical calculations find that the Na-occupation disorder in Na 2 ⁢Co 2 ⁢TeO 6 plays a crucial role in generating these modes. Our Letter demonstrates the necessity to consider disorder in the spin environment in the search for Kitaev quantum spin liquid states in practicable materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Magnetism and T-x phase diagrams of Na- and Ag-substituted EuCd 2 As 2

EuCd 2 As 2 is an antiferromagnetic semimetal, that can host non-trivial topological properties, depending upon its magnetic state and excitations. Here, we report the synthesis and characterization of Eu(Cd 1-x Ag x ) 2 As 2 and Eu 1-y Na y Cd 2 As 2 , and study the evolution and nature of magnetic order with doping. Temperature-substitution phase diagrams are constructed from the electrical resistance and magnetic susceptibility data. We observe a splitting of the magnetic transition into two different transitions, and the gradual increase in one of the transition temperatures with Agand Na-substitution. The other transition remains more or less independent of doping. Further, we show that a magnetic state with a net ferromagnetic moment is stabilized by both Ag and Na doping and this can be explained by considering the changes in band filling due to substitution as suggested by density functional theory (DFT) calculations. We thus show that chemical substitution and the subsequent changes in band filling could be a pathway to tune the magnetic ground state and to stabilize a ferromagnetic phase in EuCd 2 As 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Insights into Na + Diffusion in Silicon Modules under Operating Conditions: Measuring Low Concentrations by D-SIMS

Sodium induced shunting under an electric field is a challenging reliability issue in crystalline Si solar modules. The source of this Potential-Induced Degradation of the Shunting type (PID-s) is well understood and its influence on power loss has been intensively studied based on phenomenological models on cell or module level relating the experimental power-loss to stressing parameters (time, temperature, voltage). However, little is known about the Na ion migration kinetics, responsible for PID on a microscopic level, and its quantitative relation to the efficiency degradation. In this paper we present our investigations of sodium ion migration in Ethylene-Vinyl Acetate (EVA) and silicon through Dynamic Secondary Ion Mass Spectroscopy (D-SIMS). Each sample was annealed at field relevant temperatures from 60-90 °C to address typical migration mechanisms of common PV installations. Analysis of the SIMS migration profiles revealed a diffusivity constant D 0,EVA = 0.09 ± 0.14 cm 2 /s and an activation energy E A,EVA = 0.85 ± .04 eV for Na in EVA and diffusivities higher than extrapolated literature values in silicon (D 0,Si = (3.03 ± 2.42)x10 -5 cm 2 /s, and E A,Si = 0.98 ± 0.02 eV). The new insight will be included in a drift-diffusion based degradation model accounting for the partition coefficient across all relevant interfaces. This model can assist in predicting PID-failure in the field based on the given model stack and the diffusion of Na + through each material. Furthermore, this tool can be used for process optimization as well as material selection significantly reducing the cost and time to validate a technology.

14 SOLAR ENERGY↗
DOE OSTI2021

Effects of Al:Si and (Al+Na):Si ratios on the static corrosion of sodium‐boroaluminosilicate glasses

Abstract Understanding alteration mechanisms of borosilicate glasses in aqueous media is essential to nuclear waste performance assessments to ensure radioisotopes are contained for extended durations. Aluminum is typically added to glass compositions to reduce the extent of alteration. However, previous work on 7‐day durability tests has suggested that Al has a nonlinear relationship with extent of alteration. The effects of Al:Si and (Al+Na):Si substitutions on glass durability were evaluated using series of glasses based on the International Simple Glass corroded in static conditions up to 13 months in deionized water at 90°C. The alteration behavior was determined by measurement of element release in solution. The ⁓7‐day alteration trends across the series were consistent with predicted trends. The 13‐month results indicated overall alteration decreased as Al:Si ratios increased and was unaffected by changes in (Al+Na):Si except for the glass with the highest (Al+Na):Si ratio (ISG‐A23N), which completely altered within 14 days. Frequent sampling and in situ Raman measurements of solutions revealed ISG‐A23N experienced several distinguishable alteration rate regimes within 7 days, forming a ⁓100 µm alteration layer and a NaSiAlO 4 zeolite.

Reiser, Joelle T.↗
DOE OSTI2022

Thermal dynamics of P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode materials for sodium ion batteries studied by in situ analysis

Cobalt-free layered Na 0.67 Ni 0.33 Mn 0.67 O 2 is an attractive cathode material for sodium ion batteries. The thermal stability of cathode materials is crucial to their practical applications. In the current work, we investigate structural and morphological evolution in P2-type Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode materials during annealing via in situ synchrotron X-ray diffraction and transmission electron microscopy. Insights are obtained from the two complementary in situ characterizations (at different length scales) in term of the thermal stability of P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode materials. Here, the results indicate that the hexagonal P2 phase remains unchanged during the heat treatment process, and thermally driven expansion/contraction of lattice parameters exhibit an anisotropic character in the a and c directions. In addition, interfaces/grain boundaries play an important role in the structural stability, which leads to the distinct morphological evolution between the polycrystalline and single-crystal particles.

25 ENERGY STORAGE↗
DOE OSTI2023

Vitrification of Hanford Tank 241-AP-105 Waste at 7 M Na and Equivalent Simulant

Hanford Site nuclear waste is to be vitrified at the Waste Treatment and Immobilization Plant (WTP), which is a part of the safe and efficient retrieval, treatment, and disposal mission of the U.S. Department of Energy Office of River Protection. Hanford tank 241-AP-105 (referred to herein as AP-105) is one of the initial Hanford radioactive tank wastes planned to be processed and vitrified. A portion of AP-105 waste was retrieved by Washington River Protection Solutions, LLC (WRPS) and transferred to Pacific Northwest National Laboratory (PNNL). The waste went through dilution by Columbia River water to reach a target sodium (Na) concentration of 7 M, solids filtration, and cesium removal by ion exchange. A glass composition was calculated from the Kim et al. glass models to satisfy the WTP baseline requirements based on the as-received sample and the target dilution to 7 M, from which a simulant was calculated and glass forming chemical (GFC) additions were determined to form a liquid/solids mixture called melter feed. To prepare for the processing of the 7 M Na AP-105 waste melter feed and learn about the production expectations, the melter feed simulant of 7 M Na AP-105 waste was processed in a non-radioactive, continuous laboratory-scale melter (CLSM) system.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Effect of Cationic (Na + ) and Anionic (F – ) Co-Doping on the Structural and Electrochemical Properties of LiNi 1/3 Mn 1/3 Co 1/3 O 2 Cathode Material for Lithium-Ion Batteries

Elemental doping for substituting lithium or oxygen sites has become a simple and effective technique to improve the electrochemical performance of layered cathode materials. Compared with single-element doping, this work presents an unprecedented contribution to the study of the effect of Na + /F – co-doping on the structure and electrochemical performance of LiNi 1/3 Mn 1/3 Co 1/3 O 2 . The co-doped Li 1-z Na z Ni 1/3 Mn 1/3 Co 1/3 O 2-z F z (z = 0.025) and pristine LiNi 1/3 Co 1/3 Mn 1/3 O 2 materials were synthesized via the sol–gel method using EDTA as a chelating agent. Structural analyses, carried out by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, revealed that the Na + and F – dopants were successfully incorporated into the Li and O sites, respectively. The co-doping resulted in larger Li-slab spacing, a lower degree of cation mixing, and the stabilization of the surface structure, which substantially enhanced the cycling stability and rate capability of the cathode material. The Na/F co-doped LiNi 1/3 Mn 1/3 Co 1/3 O 2 electrode delivered an initial specific capacity of 142 mAh g –1 at a 1C rate (178 mAh g –1 at 0.1C), and it maintained 50% of its initial capacity after 1000 charge–discharge cycles at a 1C rate.

25 ENERGY STORAGE↗
DOE OSTI2020

Proton Decay of 21 Na for 20 Ne Energy Levels

The 24 Mg(p,α) 21 Na transfer reaction has been previously studied for a spectroscopic study of 21 Na. In this follow-up analysis, the proton decays of the excited states of the radionuclide 21 Na, which were measured simultaneously, are reported. By investigating the coincidence between the reaction α-particles and decay protons, we were able to identify three groups of events that are associated with the energy levels in 20 Ne. The 20 Ne excitation energy plot was obtained as a result. Here, the four lowest known energy levels in 20 Ne (the ground state and excited states at E x = 1.633, 4.247 and 4.966 MeV) were clearly observed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Materials Data on Na(CuS)4 by Materials Project

Na(CuS)4 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Na1+ is bonded to six equivalent S2- atoms to form NaS6 octahedra that share corners with six equivalent CuS4 tetrahedra and edges with six equivalent NaS6 octahedra. All Na–S bond lengths are 2.93 Å. There are two inequivalent Cu+1.75+ sites. In the first Cu+1.75+ site, Cu+1.75+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with three equivalent NaS6 octahedra, corners with three equivalent SCu3S tetrahedra, and corners with six equivalent CuS4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. There are three shorter (2.33 Å) and one longer (2.34 Å) Cu–S bond lengths. In the second Cu+1.75+ site, Cu+1.75+ is bonded in a trigonal planar geometry to three equivalent S2- atoms. All Cu–S bond lengths are 2.23 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Cu+1.75+ and one S2- atom to form SCu3S tetrahedra that share corners with three equivalent CuS4 tetrahedra and corners with six equivalent SCu3S tetrahedra. The S–S bond length is 2.11 Å. In the second S2- site, S2- is bonded in a 7-coordinate geometry to three equivalent Na1+ and four Cu+1.75+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(Nd2Se3)4 by Materials Project

Na(Nd2Se3)4 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Na1+ is bonded to eight Se2- atoms to form distorted NaSe8 hexagonal bipyramids that share corners with eight equivalent NdSe8 hexagonal bipyramids, edges with four equivalent NdSe8 hexagonal bipyramids, and faces with eight NdSe8 hexagonal bipyramids. There are four shorter (3.03 Å) and four longer (3.27 Å) Na–Se bond lengths. There are three inequivalent Nd+2.88+ sites. In the first Nd+2.88+ site, Nd+2.88+ is bonded to eight Se2- atoms to form distorted NdSe8 hexagonal bipyramids that share corners with two equivalent NaSe8 hexagonal bipyramids, corners with six NdSe8 hexagonal bipyramids, edges with four NdSe8 hexagonal bipyramids, a faceface with one NaSe8 hexagonal bipyramid, and faces with seven NdSe8 hexagonal bipyramids. There are a spread of Nd–Se bond distances ranging from 2.97–3.23 Å. In the second Nd+2.88+ site, Nd+2.88+ is bonded to eight Se2- atoms to form distorted NdSe8 hexagonal bipyramids that share corners with eight NdSe8 hexagonal bipyramids, edges with four NdSe8 hexagonal bipyramids, faces with two equivalent NaSe8 hexagonal bipyramids, and faces with six NdSe8 hexagonal bipyramids. There are a spread of Nd–Se bond distances ranging from 3.00–3.23 Å. In the third Nd+2.88+ site, Nd+2.88+ is bonded to eight Se2- atoms to form distorted NdSe8 hexagonal bipyramids that share corners with eight NdSe8 hexagonal bipyramids, edges with two equivalent NaSe8 hexagonal bipyramids, edges with two equivalent NdSe8 hexagonal bipyramids, and faces with eight NdSe8 hexagonal bipyramids. There are a spread of Nd–Se bond distances ranging from 2.99–3.21 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to one Na1+ and five Nd+2.88+ atoms to form a mixture of distorted corner, edge, and face-sharing SeNaNd5 octahedra. The corner-sharing octahedra tilt angles range from 14–52°. In the second Se2- site, Se2- is bonded to one Na1+ and five Nd+2.88+ atoms to form a mixture of distorted corner, edge, and face-sharing SeNaNd5 octahedra. The corner-sharing octahedra tilt angles range from 19–50°. In the third Se2- site, Se2- is bonded to six Nd+2.88+ atoms to form a mixture of distorted corner, edge, and face-sharing SeNd6 octahedra. The corner-sharing octahedra tilt angles range from 16–52°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(ScI3)2 by Materials Project

Na(ScI3)2 is beta Vanadium nitride-derived structured and crystallizes in the trigonal P31c space group. The structure is three-dimensional. Na1+ is bonded to six I1- atoms to form NaI6 octahedra that share corners with six equivalent ScI6 octahedra and edges with three equivalent ScI6 octahedra. The corner-sharing octahedra tilt angles range from 47–49°. There are three shorter (3.25 Å) and three longer (3.29 Å) Na–I bond lengths. There are two inequivalent Sc+2.50+ sites. In the first Sc+2.50+ site, Sc+2.50+ is bonded to six I1- atoms to form ScI6 octahedra that share corners with six equivalent NaI6 octahedra and faces with two equivalent ScI6 octahedra. The corner-sharing octahedra tilt angles range from 47–49°. All Sc–I bond lengths are 2.93 Å. In the second Sc+2.50+ site, Sc+2.50+ is bonded to six I1- atoms to form ScI6 octahedra that share edges with three equivalent NaI6 octahedra and faces with two equivalent ScI6 octahedra. There are three shorter (2.93 Å) and three longer (2.94 Å) Sc–I bond lengths. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted T-shaped geometry to one Na1+ and two Sc+2.50+ atoms. In the second I1- site, I1- is bonded in a distorted T-shaped geometry to one Na1+ and two Sc+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(Sm2Se3)4 by Materials Project

Na(Sm2Se3)4 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Na1+ is bonded to eight Se2- atoms to form distorted NaSe8 hexagonal bipyramids that share corners with eight equivalent SmSe8 hexagonal bipyramids, edges with four equivalent SmSe8 hexagonal bipyramids, and faces with eight SmSe8 hexagonal bipyramids. There are four shorter (2.99 Å) and four longer (3.25 Å) Na–Se bond lengths. There are three inequivalent Sm+2.88+ sites. In the first Sm+2.88+ site, Sm+2.88+ is bonded to eight Se2- atoms to form distorted SmSe8 hexagonal bipyramids that share corners with two equivalent NaSe8 hexagonal bipyramids, corners with six SmSe8 hexagonal bipyramids, edges with four SmSe8 hexagonal bipyramids, a faceface with one NaSe8 hexagonal bipyramid, and faces with seven SmSe8 hexagonal bipyramids. There are a spread of Sm–Se bond distances ranging from 2.93–3.21 Å. In the second Sm+2.88+ site, Sm+2.88+ is bonded to eight Se2- atoms to form distorted SmSe8 hexagonal bipyramids that share corners with eight SmSe8 hexagonal bipyramids, edges with two equivalent NaSe8 hexagonal bipyramids, edges with two equivalent SmSe8 hexagonal bipyramids, and faces with eight SmSe8 hexagonal bipyramids. There are a spread of Sm–Se bond distances ranging from 2.95–3.18 Å. In the third Sm+2.88+ site, Sm+2.88+ is bonded to eight Se2- atoms to form distorted SmSe8 hexagonal bipyramids that share corners with eight SmSe8 hexagonal bipyramids, edges with four SmSe8 hexagonal bipyramids, faces with two equivalent NaSe8 hexagonal bipyramids, and faces with six SmSe8 hexagonal bipyramids. There are a spread of Sm–Se bond distances ranging from 2.96–3.21 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to one Na1+ and five Sm+2.88+ atoms to form a mixture of distorted corner, edge, and face-sharing SeNaSm5 octahedra. The corner-sharing octahedra tilt angles range from 14–43°. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to one Na1+ and five Sm+2.88+ atoms. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to six Sm+2.88+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(CoO2)3 by Materials Project

Na(CoO2)3 crystallizes in the triclinic P1 space group. The structure is three-dimensional. Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.28–2.92 Å. There are three inequivalent Co+3.67+ sites. In the first Co+3.67+ site, Co+3.67+ is bonded to five O2- atoms to form distorted CoO5 trigonal bipyramids that share a cornercorner with one CoO6 octahedra, corners with three equivalent CoO4 tetrahedra, and edges with two equivalent CoO6 octahedra. The corner-sharing octahedral tilt angles are 36°. There are a spread of Co–O bond distances ranging from 1.75–2.21 Å. In the second Co+3.67+ site, Co+3.67+ is bonded to four O2- atoms to form CoO4 tetrahedra that share corners with four equivalent CoO6 octahedra and corners with three equivalent CoO5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 33–71°. There are a spread of Co–O bond distances ranging from 1.79–1.96 Å. In the third Co+3.67+ site, Co+3.67+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with four equivalent CoO4 tetrahedra, a cornercorner with one CoO5 trigonal bipyramid, and edges with two equivalent CoO5 trigonal bipyramids. There are a spread of Co–O bond distances ranging from 1.86–2.02 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Na1+ and three Co+3.67+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+ and two Co+3.67+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+, two Co+3.67+, and one O2- atom. The O–O bond length is 1.47 Å. In the fourth O2- site, O2- is bonded to one Na1+ and three Co+3.67+ atoms to form distorted corner-sharing ONaCo3 tetrahedra. In the fifth O2- site, O2- is bonded to one Na1+ and three Co+3.67+ atoms to form distorted corner-sharing ONaCo3 tetrahedra. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+, two Co+3.67+, and one O2- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(WO3)2 by Materials Project

Na(WO3)2 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Na1+ is bonded to twelve equivalent O2- atoms to form NaO12 cuboctahedra that share corners with twelve equivalent NaO12 cuboctahedra and faces with eight equivalent WO6 octahedra. All Na–O bond lengths are 2.76 Å. W+5.50+ is bonded to six equivalent O2- atoms to form WO6 octahedra that share corners with six equivalent WO6 octahedra and faces with four equivalent NaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All W–O bond lengths are 1.95 Å. O2- is bonded in a distorted square co-planar geometry to two equivalent Na1+ and two equivalent W+5.50+ atoms.

36 MATERIALS SCIENCE↗