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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Electronic bonding transitions in oxide glass above two megabar pressures

Inelastic x-ray scattering (IXS) of B 2 O 3 glass up to ∼2.2 Mbar reveals electronic bonding transitions in oxide glasses. B -edge IXS identifies the high-energy feature above ∼1.4 Mbar and a gradual increase in its intensity toward ∼2.2 Mbar, indicating the formation of hypervalent boron via electron polarization to oxygen atoms. The pressure-driven high energy shifts in O -edge IXS indicate pronounced electronic dispersion that increases upon densification of amorphous oxides above ∼2 Mbar. The extent of the energy shifts and enhanced polarization correlate with increasing atomic radius of cation in oxide glass, establishing the role of cation radius in electronic structures of amorphous oxides under compression. The results elucidate the electronic mechanisms behind the structural transformation in low- oxide glasses, where transitions to highly coordinated cations are hindered well above 1 Mbar, providing the origin of incompressibility of low- amorphous oxide under multi-Mbar compression. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

X-ray Crystal Structure of Thorium Tetrahydroborate, Th(BH 4 ) 4 , and Computational Studies of An(BH 4 ) 4 (An = Th, U)

Here the crystal structure of Th(BH 4 ) 4 is described. Two of the four BH 4 – ions are terminal and tridentate (κ 3 ), whereas the other two bridge between neighboring Th IV centers in a κ 2 ,κ 2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH 4 – groups by 14 Th–H bonds. The six boron atoms describe a distorted octahedron in which the κ 3 -BH 4 – ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An(BH 4 ) 4 (An = Th, U) were also investigated by DFT. The geometries of [An(BH 4 ) 6 ] 2– , [An3(BH 4 ) 16 ] 4– , and [An 5 (BH 4 ) 26 ] 6– fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th(BH 4 ) 6 ] 2– units are predicted to feature 16-coordinate Th IV centers.

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

Materials Data on Ta36B4C35 by Materials Project

Ta26C25Ta9C8TaBC(B)2BC1 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of two boron molecules; one BC1 sheet oriented in the (0, 0, 1) direction; one Ta26C25 sheet oriented in the (0, 0, 1) direction; one Ta9C8 sheet oriented in the (0, 0, 1) direction; and one TaBC sheet oriented in the (0, 0, 1) direction. In the BC1 sheet, B3+ is bonded in a trigonal planar geometry to three equivalent C4- atoms. All B–C bond lengths are 1.83 Å. C4- is bonded in a distorted trigonal planar geometry to three equivalent B3+ atoms. In the Ta26C25 sheet, there are eighteen inequivalent Ta+3.56+ sites. In the first Ta+3.56+ site, Ta+3.56+ is bonded in a 3-coordinate geometry to three equivalent C4- atoms. There are one shorter (2.14 Å) and two longer (2.15 Å) Ta–C bond lengths. In the second Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 1°. All Ta–C bond lengths are 2.23 Å. In the third Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are five shorter (2.25 Å) and one longer (2.26 Å) Ta–C bond lengths. In the fourth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. All Ta–C bond lengths are 2.25 Å. In the fifth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.24 Å) and three longer (2.26 Å) Ta–C bond lengths. In the sixth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.24 Å) and three longer (2.25 Å) Ta–C bond lengths. In the seventh Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the eighth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the ninth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the tenth Ta+3.56+ site, Ta+3.56+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the eleventh Ta+3.56+ site, Ta+3.56+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) Ta–C bond lengths. In the twelfth Ta+3.56+ site, Ta+3.56+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the thirteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the fourteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the fifteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) Ta–C bond lengths. In the sixteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the seventeenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.23 Å) and two longer (2.24 Å) Ta–C bond lengths. In the eighteenth Ta+3.56+ site, Ta+3.56+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Ta–C bond lengths are 2.25 Å. There are fifteen inequivalent C4- sites. In the first C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the third C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fourth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the fifth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the sixth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the seventh C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the eighth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the ninth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the tenth C4- site, C4- is bonded to six equivalent Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) C–Ta bond lengths. In the eleventh C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the twelfth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the thirteenth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fourteenth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifteenth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. All C–Ta bond lengths are 2.25 Å. In the Ta9C8 sheet, there are nine inequivalent Ta+3.56+ sites. In the first Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are five shorter (2.24 Å) and one longer (2.25 Å) Ta–C bond lengths. In the second Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Ta–C bond distances ranging from 2.23–2.26 Å. In the third Ta+3.56+ site, Ta+3.56+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Ta–C bond lengths are 2.26 Å. In the fourth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifth Ta+3.56+ site, Ta+3.56+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. In the sixth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) Ta–C bond lengths. In the seventh Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.23 Å) and four longer (2.24 Å) Ta–C bond lengths. In the eighth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.24 Å) and two longer (2.25 Å) Ta–C bond lengths. In the ninth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. There are eight inequivalent C4- sites. In the first C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the third C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. All C–Ta bond lengths are 2.24 Å. In the fourth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. All C–Ta bond lengths are 2.24 Å. In the fifth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the sixth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the seventh C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the eighth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the TaBC sheet, Ta+3.56+ is bonded in a single-bond geometry to one C4- atom. The Ta–C bond length is 2.08 Å. B3+ is bonded in a trigonal planar geometry to three equivalent C4- atoms. There are a spread of B–C bond distances ranging from 1.81–1.85 Å. C4- is bonded to one Ta+3.56+ and three equivalent B3+ atoms to form corner-sharing CTaB3 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V2(B24C)3 by Materials Project

(VB4C)2(B)60B4C crystallizes in the orthorhombic P222 space group. The structure is one-dimensional and consists of one hundred and twenty boron molecules; two tetraborylmethane molecules; and four VB4C ribbons oriented in the (1, 0, 0) direction. In each VB4C ribbon, V3+ is bonded in a linear geometry to two equivalent C4- atoms. Both V–C bond lengths are 2.51 Å. There are two inequivalent B+0.08+ sites. In the first B+0.08+ site, B+0.08+ is bonded in a single-bond geometry to one C4- atom. The B–C bond length is 1.64 Å. In the second B+0.08+ site, B+0.08+ is bonded in a single-bond geometry to one C4- atom. The B–C bond length is 1.64 Å. C4- is bonded in a 4-coordinate geometry to two equivalent V3+ and four B+0.08+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

First DIII-D-West hybrid scenario similarity experiments for iter-relevant long-pulse operation

For the first time, similarity experiments between DIII-D and WEST were performed in the ITER "hybrid-like" regime during dedicated campaigns in April and May 2025. The matched parameters include elongation, triangularity, ion ∇B drift direction toward the X-point, qprofile, and core normalized physics quantities in terms of normalized pressure, normalized gyroradius, electron collisionality, ratio of ion to electron temperature, T i /T e . Core transport physics is explored with different aspect ratio (R/a) values (typically 3 at DIII-D and 5 on WEST). DIII-D explored high-beta conditions (electromagnetic effect) with low torque injection (~0 ± 0.5 N•m) using high heating power (up to 6 MW NBI and 2 MW ECRH powers), while scanning the heating mix (ion vs electron), beta, T i /T e , core radiation via controlled tungsten injection using the Laser Blow-Off system. WEST extended operation toward long-duration pulses using its actively cooled tungsten divertor, achieving dominated electron heating regimes with reduced tungsten contamination. Boron impurity injection were scanned on WEST to control edge conditions and core performance. It is found that core confinement improves-manifested by higher electron temperature, total energy content, neutron rate, and ion temperatureunder conditions of low separatrix density, consistent with previous observations [Bourdelle et al., Nucl. Fusion 63 (2023) 056021]. Conditions for Hmode access and for ion heating in electron-dominated regimes in both WEST and DIII-D will be discussed and compared. The ratio of the thermal energy confinement time (τ E ) to the volume-averaged electron-ion collisional heat exchange time (τ e-i ) is a key parameter to enhance ion heating and potentially facilitate H-mode access in electron-heated regimes. These first-of-a-kind coordinated DIII-D and WEST experiments provide a unique multi-machine dataset to validate predictive models and to optimize ITER hybrid-scenario performance under diverse core and edge conditions.

DIII-D↗
DOE OSTI2020

Materials Data on Ni3Te(MoO7)6 by Materials Project

Te(MoO4)6(NiO6)3 is T-50 Boron-derived structured and crystallizes in the trigonal R-3c space group. The structure is zero-dimensional and consists of eighteen NiO6 clusters and six Te(MoO4)6 clusters. In each NiO6 cluster, Ni is bonded in an octahedral geometry to six O atoms. There are a spread of Ni–O bond distances ranging from 1.81–1.85 Å. There are three inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Ni atom. In the second O site, O is bonded in a single-bond geometry to one Ni atom. In the third O site, O is bonded in a single-bond geometry to one Ni atom. In each Te(MoO4)6 cluster, Mo is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Mo–O bond distances ranging from 1.73–2.34 Å. Te is bonded in an octahedral geometry to six equivalent O atoms. All Te–O bond lengths are 1.96 Å. There are four inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Mo atom. In the second O site, O is bonded in a bent 120 degrees geometry to two equivalent Mo atoms. In the third O site, O is bonded in a single-bond geometry to one Mo atom. In the fourth O site, O is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mo and one Te atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spherical trihedral metallo-borospherenes

The discovery of borospherenes unveiled the capacity of boron to form fullerene-like cage structures. While fullerenes are known to entrap metal atoms to form endohedral metallofullerenes, few metal atoms have been observed to be part of the fullerene cages. Here we report the observation of a class of remarkable metallo-borospherenes, where metal atoms are integral parts of the cage surface. We have produced La 3 B 18 - and Tb 3 B 18 - and probed their structures and bonding using photoelectron spectroscopy and theoretical calculations. Global minimum searches revealed that the most stable structures of Ln 3 B 18 - are hollow cages with D 3h symmetry. The B 18 -framework in the Ln 3 B 18 - cages can be viewed as consisting of two triangular B6 motifs connected by three B 2 units, forming three shared B 10 rings which are coordinated to the three Ln atoms on the cage surface. These metallo-borospherenes represent a new class of unusual geometry that has not been observed in chemistry heretofore.

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

Materials Data on B9C by Materials Project

B9C crystallizes in the triclinic P1 space group. The structure is zero-dimensional and consists of ten boron molecules, one tetraborylmethane molecule, and one B4C cluster. In the B4C cluster, there are four inequivalent B+0.33+ sites. In the first B+0.33+ site, B+0.33+ is bonded in a single-bond geometry to one C3- atom. The B–C bond length is 1.85 Å. In the second B+0.33+ site, B+0.33+ is bonded in a single-bond geometry to one C3- atom. The B–C bond length is 1.58 Å. In the third B+0.33+ site, B+0.33+ is bonded in a single-bond geometry to one C3- atom. The B–C bond length is 1.52 Å. In the fourth B+0.33+ site, B+0.33+ is bonded in a single-bond geometry to one C3- atom. The B–C bond length is 1.59 Å. C3- is bonded in a 4-coordinate geometry to four B+0.33+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaGaBiB2O7 by Materials Project

CaGaBBiO6BO crystallizes in the tetragonal P-42_1m space group. The structure is three-dimensional and consists of four boron monoxide molecules and one CaGaBBiO6 framework. In the CaGaBBiO6 framework, Ca2+ is bonded to six O2- atoms to form distorted CaO6 octahedra that share a cornercorner with one CaO6 octahedra, a cornercorner with one BO4 tetrahedra, corners with two equivalent GaO4 tetrahedra, and edges with two equivalent BO4 tetrahedra. The corner-sharing octahedral tilt angles are 74°. There are a spread of Ca–O bond distances ranging from 2.24–2.66 Å. There are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to four equivalent O2- atoms to form GaO4 tetrahedra that share corners with four equivalent CaO6 octahedra and corners with four equivalent BO4 tetrahedra. The corner-sharing octahedral tilt angles are 67°. All Ga–O bond lengths are 1.91 Å. In the second Ga3+ site, Ga3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Ga–O bond lengths are 1.89 Å. B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share a cornercorner with one CaO6 octahedra, a cornercorner with one BO4 tetrahedra, corners with two equivalent GaO4 tetrahedra, and edges with two equivalent CaO6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of B–O bond distances ranging from 1.43–1.55 Å. Bi3+ is bonded in a 1-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.13–2.90 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to one Ca2+, one Ga3+, one Bi3+, and one O2- atom. The O–O bond length is 1.59 Å. In the second O2- site, O2- is bonded in a water-like geometry to two equivalent Bi3+ atoms. In the third O2- site, O2- is bonded in a 1-coordinate geometry to one Ca2+, one B3+, and two equivalent Bi3+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+, one Ga3+, one B3+, and one Bi3+ atom. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

f-Element complexes with benzyl and cyclohexyl substituted trihydroborates

Actinide complexes containing the simplest borohydrides (BH 4 ) 1- and (MeBH 3 ) 1- can exhibit remarkably highly volatility, which creates unique hazards and handling challenges, especially when making measurements on solid samples under vacuum. Here we describe efforts to prepare new actinide borohydride complexes with attenuated volatility by adding bulkier benzyl (Bn) and cyclohexyl (Cy) substituents to boron. Reactions of ThCl 4 , UI 3 (thf) 4 , and NdI 3 with the mixed alkali metal salt Li/K(BnBH 3 )(thf) n yielded Th(BnBH 3 ) 4 (thf) 2 , U(BnBH 3 ) 4 (thf) 2 , and K[Nd(BnBH 3 ) 4 ], respectively. Notable amongst these, the reaction with UI 3 (thf) 4 proceeds via oxidation of U(III) to U(IV) despite the presence of reducing borohydride ligands. Similarly, reactions of the same metal halides with four equivalents of Li(CyBH 3 )(Et 2 O) n yielded Th(CyBH 3 ) 4 , U(CyBH 3 ) 4 (thf) 2 , and [Li(Et 2 O) 3 ][Nd(CyBH 3 ) 4 ]. Single crystal X-ray diffraction studies of the M(BnBH 3 ) 4 (thf) 2 complexes with M = Th and U confirmed their formulations. Furthermore, the complexes have approximate D 2d point group symmetry and adopt bicapped hexagonal antiprismatic coordination geometries with axial thf ligands and κ 3 -BnBH 3 ligands bound in the equatorial plane. K[Nd(BnBH 3 ) 4 ] and [Li(Et 2 O) 3 ][Nd(CyBH 3 ) 4 ], which were prepared for comparison to U(III) complexes that were unsuccessfully targeted, were also structurally characterized to reveal complex anions with tetrahedral arrangements of trihydroborate ligands bound to Nd(III). Crystals obtained for Th(CyBH 3 ) 4 and U(CyBH 3 ) 4 (thf) 2 were not suitable for XRD studies, but 1 H and 11 B NMR spectra were consistent with their formulations. Collectively, these complexes represent rare examples of structurally characterized f-element trihydroborate complexes with carbon substituents other than methyl.

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

Materials Data on TiMoAs2 by Materials Project

TiMoAs2 is T-50 Boron-derived structured and crystallizes in the orthorhombic Pmc2_1 space group. The structure is three-dimensional. Ti4+ is bonded to six As3- atoms to form distorted TiAs6 pentagonal pyramids that share corners with eight equivalent MoAs6 octahedra, corners with four equivalent TiAs6 pentagonal pyramids, edges with four equivalent MoAs6 octahedra, edges with two equivalent TiAs6 pentagonal pyramids, and faces with two equivalent TiAs6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 42–56°. There are a spread of Ti–As bond distances ranging from 2.51–2.78 Å. Mo2+ is bonded to six As3- atoms to form distorted MoAs6 octahedra that share corners with four equivalent MoAs6 octahedra, corners with eight equivalent TiAs6 pentagonal pyramids, edges with two equivalent MoAs6 octahedra, edges with four equivalent TiAs6 pentagonal pyramids, and faces with two equivalent MoAs6 octahedra. The corner-sharing octahedral tilt angles are 53°. There are a spread of Mo–As bond distances ranging from 2.53–2.71 Å. There are two inequivalent As3- sites. In the first As3- site, As3- is bonded in a 6-coordinate geometry to four equivalent Ti4+ and two equivalent Mo2+ atoms. In the second As3- site, As3- is bonded in a 1-coordinate geometry to two equivalent Ti4+ and four equivalent Mo2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Metastable piezoelectric group-IV monochalcogenide monolayers with a buckled honeycomb structure

Multiple two-dimensional materials are being naïvely termed stable on the grounds of displaying phonon dispersions with no negative frequencies and of not collapsing on molecular dynamics calculations at fixed volume. But, if these phases do not possess the smallest possible structural energy, how does one understand and establish their actual meta stability? To answer this question, twelve two-dimensional group-IV monochalcogenide monolayers (SiS, SiSe, SiTe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, and PbTe) with a buckled honeycomb atomistic structure—belonging to symmetry group P3m1—displaying an out-of-plane intrinsic electric polarization are shown to be metastable by three independent methods. First, we uncover a coordination-preserving structural transformation from the low-buckled honeycomb structure onto the lower-energy Pnm2 1 (or Pmmn for PbS, PbSe, and PbTe) phase to estimate energy barriers E B that must be overcome during such structural transformation. Using the curvature of the local minima and E B as inputs to Kramers escape formula, large escape times are found, implying the structural metastability of the buckled honeycomb phase (with the exception of PbS and PbSe, these phases display escape times ranging from 700 years to multiple times the age of the universe and can be considered “stable” for practical purposes in that relative sense). The second demonstration is provided by phonon dispersion relations that include the effect of long-range Coulomb forces and display no negative vibrational modes. The third and final demonstration of structural metastability is furnished by room-temperature ab initio molecular dynamics for selected compounds. Here, the magnitude of the electronic band gap evolves with chemical composition. Different from other binary two-dimensional compounds such as transition metal dichalcogenide monolayers and hexagonal boron nitride monolayers which only develop an in-plane piezoelectric response, the twelve group-IV monochalcogenide monolayers with a buckled honeycomb structure also display out-of-plane piezoelectric properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on LiB12PC by Materials Project

LiB6CP(B)6 crystallizes in the orthorhombic Ima2 space group. The structure is zero-dimensional and consists of twenty-four boron molecules and four LiB6CP clusters. In each LiB6CP cluster, Li1+ is bonded in a distorted single-bond geometry to one C4- and one P3- atom. The Li–C bond length is 2.74 Å. The Li–P bond length is 2.68 Å. There are four inequivalent B+0.50+ sites. In the first B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one C4- atom. The B–C bond length is 1.67 Å. In the second B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one P3- atom. The B–P bond length is 1.91 Å. In the third B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one C4- atom. The B–C bond length is 1.66 Å. In the fourth B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one P3- atom. The B–P bond length is 1.91 Å. C4- is bonded in a tetrahedral geometry to one Li1+, three B+0.50+, and one P3- atom. The C–P bond length is 1.87 Å. P3- is bonded in a 5-coordinate geometry to one Li1+, three B+0.50+, and one C4- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs3Zr7BCl20 by Materials Project

Cs3Zr7Cl20B crystallizes in the trigonal R-3c space group. The structure is three-dimensional and consists of six boron molecules and one Cs3Zr7Cl20 framework. In the Cs3Zr7Cl20 framework, Cs1+ is bonded to twelve Cl1- atoms to form distorted CsCl12 cuboctahedra that share corners with four equivalent CsCl12 cuboctahedra, corners with six equivalent ZrCl5 square pyramids, edges with four equivalent CsCl12 cuboctahedra, edges with two equivalent ZrCl5 square pyramids, edges with two equivalent ZrCl5 trigonal bipyramids, and faces with two equivalent ZrCl5 square pyramids. There are a spread of Cs–Cl bond distances ranging from 3.62–4.07 Å. There are two inequivalent Zr2+ sites. In the first Zr2+ site, Zr2+ is bonded to five Cl1- atoms to form ZrCl5 square pyramids that share corners with three equivalent CsCl12 cuboctahedra, corners with five equivalent ZrCl5 square pyramids, an edgeedge with one CsCl12 cuboctahedra, and a faceface with one CsCl12 cuboctahedra. There are a spread of Zr–Cl bond distances ranging from 2.56–2.81 Å. In the second Zr2+ site, Zr2+ is bonded to five Cl1- atoms to form ZrCl5 trigonal bipyramids that share edges with six equivalent CsCl12 cuboctahedra. There are three shorter (2.39 Å) and two longer (2.47 Å) Zr–Cl bond lengths. There are five inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent Cs1+ and two equivalent Zr2+ atoms. In the second Cl1- site, Cl1- is bonded in a 2-coordinate geometry to one Cs1+ and two equivalent Zr2+ atoms. In the third Cl1- site, Cl1- is bonded in a distorted single-bond geometry to three equivalent Cs1+ and one Zr2+ atom. In the fourth Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent Cs1+ and two equivalent Zr2+ atoms. In the fifth Cl1- site, Cl1- is bonded in a distorted single-bond geometry to two equivalent Cs1+ and one Zr2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SiB11H10C4F11 by Materials Project

BSiC3H9FB5CHF5(FB1)5 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of twenty boron monofluoride molecules, four B5CHF5 clusters, and four BSiC3H9F clusters. In each B5CHF5 cluster, there are five inequivalent B+1.91+ sites. In the first B+1.91+ site, B+1.91+ is bonded in a distorted bent 120 degrees geometry to one C4- and one F1- atom. The B–C bond length is 1.72 Å. The B–F bond length is 1.37 Å. In the second B+1.91+ site, B+1.91+ is bonded in a distorted bent 120 degrees geometry to one C4- and one F1- atom. The B–C bond length is 1.73 Å. The B–F bond length is 1.37 Å. In the third B+1.91+ site, B+1.91+ is bonded in a distorted bent 120 degrees geometry to one C4- and one F1- atom. The B–C bond length is 1.72 Å. The B–F bond length is 1.37 Å. In the fourth B+1.91+ site, B+1.91+ is bonded in a distorted bent 120 degrees geometry to one C4- and one F1- atom. The B–C bond length is 1.72 Å. The B–F bond length is 1.37 Å. In the fifth B+1.91+ site, B+1.91+ is bonded in a distorted bent 120 degrees geometry to one C4- and one F1- atom. The B–C bond length is 1.72 Å. The B–F bond length is 1.37 Å. C4- is bonded in a 1-coordinate geometry to five B+1.91+ and one H1+ atom. The C–H bond length is 1.09 Å. H1+ is bonded in a single-bond geometry to one C4- atom. There are five inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one B+1.91+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one B+1.91+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one B+1.91+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one B+1.91+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one B+1.91+ atom. In each BSiC3H9F cluster, B+1.91+ is bonded in a single-bond geometry to one F1- atom. The B–F bond length is 1.45 Å. Si4- is bonded in a trigonal pyramidal geometry to three C4- and one F1- atom. All Si–C bond lengths are 1.85 Å. The Si–F bond length is 1.96 Å. There are three inequivalent C4- sites. In the first C4- site, C4- is bonded to one Si4- and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the second C4- site, C4- is bonded to one Si4- and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the third C4- site, C4- is bonded to one Si4- and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. There are nine inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. F1- is bonded in a bent 150 degrees geometry to one B+1.91+ and one Si4- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Post-closure Nuclear Criticality Safety Evaluations for Disposition of Criticality Control Overpacks at the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) is a geological repository in southern New Mexico that provides for disposal of transuranic (TRU) wastes from atomic energy defense activities. The Sandia National Laboratories (Sandia) Report, Consideration of Nuclear Criticality When Disposing of Transuranic Waste at the Waste Isolation Pilot Plant, addresses nuclear criticality safety based on the projected inventory characteristics for the initial compliance certification application of WIPP in 1996. As the inventory, waste forms, and disposal package designs change, revised or new analyses are necessary to demonstrate acceptability for these configurations within the WIPP safety basis and compliance with 10,000-year post-closure standards of the US Environmental Protection Agency (EPA). Saylor and Scaglione evaluated criticality control overpacks (CCOs) in 2017 based on conservative assumptions for post-closure repository structural conditions with resulting effects on containers and container spacing, The Saylor and Scaglione evaluation of CCOs addressed a single waste configuration that represents the Surplus Plutonium Disposition Program’s dilute and dispose waste form and composition. This initial CCO study demonstrated that 50 grams of boron carbide (B 4 C) per CCO is sufficient to ensure post-closure criticality safety based on a well-mixed waste composition, and Oak Ridge National Laboratory (ORNL) subsequently determined that this amount of B 4 C does not require constraints on moisture or plastic present as moderator. The Saylor and Scaglione analysis conservatively assumes repository room closure that eliminates all space between fissile gram equivalent (FGE) 239 Pu masses. The close-packed array was selected based on limited availability of repository salt creep modeling results at that time. In 2019, Brickner provided additional evaluations for pipe overpack containers (POCs), building on the conservative basis provided by Saylor and Scaglione. Brickner’s 2019 analysis made use of new geomechanical data for post-closure spacing that rely on advances in repository modeling as documented in the work by Reedlunn and Bean. This current CCO evaluation for generic waste materials expands on earlier work performed at ORNL and includes evaluation of CCOs across a much broader range of possible waste compositions and geometries. This evaluation is intended to provide input for the required feature, event and process (FEP) screening to determine if post-closure criticality must be included as an event in the 10,000-year regulatory evaluation. As such, the approach to modeling post-closure criticality presented in this report has been coordinated with the Sandia team responsible for FEP screening. The resulting analysis supports disposition of fissile materials in the CCO containing up to 380 FGE 239 Pu and expands conditions acceptable for disposal of fissile material in CCOs. This evaluation builds on the methodology of Saylor and Scaglione and Brickner, using the most recently available geomechanical data for CCO spacing under salt creep compaction scenarios provided by Reedlunn and Bean. The broad range of fissile material configurations analyzed in this report are intended to account for configurations that may occur during the post-closure disposal time period, and it also includes waste configurations that are not physically possible to support analysis of conditions that influence neutron fluence.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Materials Data on Mg(SiB6)2 by Materials Project

MgB12Si2 crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of sixteen boron molecules and four Mg(B4Si)2 clusters. In each Mg(B4Si)2 cluster, Mg2+ is bonded in a distorted bent 150 degrees geometry to two Si4- atoms. There are one shorter (2.45 Å) and one longer (2.64 Å) Mg–Si bond lengths. There are six inequivalent B+0.50+ sites. In the first B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one Si4- atom. The B–Si bond length is 2.08 Å. In the second B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one Si4- atom. The B–Si bond length is 2.07 Å. In the third B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one Si4- atom. The B–Si bond length is 2.17 Å. In the fourth B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one Si4- atom. The B–Si bond length is 2.00 Å. In the fifth B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one Si4- atom. The B–Si bond length is 2.00 Å. In the sixth B+0.50+ site, B+0.50+ is bonded in a single-bond geometry to one Si4- atom. The B–Si bond length is 2.07 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 5-coordinate geometry to one Mg2+ and four B+0.50+ atoms. In the second Si4- site, Si4- is bonded in a 4-coordinate geometry to one Mg2+ and four B+0.50+ atoms.

36 MATERIALS SCIENCE↗