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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

RbB 3 Si 3 : An Alkali Metal Borosilicide that is Metastable and Superconducting at 1 atm

The stability, electronic structure and potential superconductivity in AB 3 Si 3 (A = Na, K, Rb, and Cs) compounds that assume the clathrate-based sodalite structure whose frameworks consists of covalent B-Si bonds is investigated via first-principles calculations. This structure type has recently been predicted in a number of high temperature superconducting hydrides, but these are only stable under megabar pressures. Herein, we predict a novel superconducting phase, RbB 3 Si 3 , that could be synthesized under pressures that are a factor of ten smaller, ~10 GPa, and quenched to atmospheric conditions. Electron-phonon coupling calculations predict that RbB 3 Si 3 possesses a superconducting critical temperature, T c , of 14 K at 1 atm. Here, the dynamic stability of RbB 3 Si 3 and CsB 3 Si 3 at ambient pressure can be explained by considering the chemical pressure exerted on the B-Si framework that is caused by the size effect of the alkali metal atom.

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

Materials Data on RbB(CN)2 by Materials Project

RbB(CN)2 crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional. Rb1+ is bonded in a square co-planar geometry to four equivalent N3- atoms. There are two shorter (2.90 Å) and two longer (3.04 Å) Rb–N bond lengths. B3+ is bonded in a linear geometry to two equivalent C1+ atoms. Both B–C bond lengths are 1.44 Å. C1+ is bonded in a distorted linear geometry to one B3+ and one N3- atom. The C–N bond length is 1.20 Å. N3- is bonded in a distorted trigonal non-coplanar geometry to two equivalent Rb1+ and one C1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbB(CN)4 by Materials Project

Rb(CN)4B crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional and consists of four boron molecules and one Rb(CN)4 framework. In the Rb(CN)4 framework, Rb1+ is bonded in a 8-coordinate geometry to eight equivalent N3- atoms. There are four shorter (3.11 Å) and four longer (3.33 Å) Rb–N bond lengths. C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. N3- is bonded in a distorted single-bond geometry to two equivalent Rb1+ and one C2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbB by Materials Project

BRb is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Rb is bonded to six equivalent B atoms to form a mixture of edge and corner-sharing RbB6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Rb–B bond lengths are 3.34 Å. B is bonded to six equivalent Rb atoms to form a mixture of edge and corner-sharing BRb6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Superconductivity in CH 4 and BH – 4 containing compounds derived from the high-pressure superhydrides

Inspired by the synthesis of the high-pressure Fm3m LaH 10 superconducting superhydride, systematic density functional theory (DFT) calculations are performed to study ternaries that could be derived from it by replacing two of the hydrogen atoms with boron or carbon and varying the identity of the electropositive element. Though many of the resulting alkali-metal and alkaline-earth MC 2 H 8 phases are predicted to be dynamically stable at mild pressures, their superconducting critical temperatures (T c s) are low because their metallicity results from the filling of an electride-like band. Substitution with a trivalent element leads to phases with substantial metal d- character at the Fermi level whose T c s are typically above 40 K. Here, among the MB 2 H 8 phases examined, KB 2 H 8 , RbB 2 H 8 and CsB 2 H 8 are predicted to be dynamically stable at very mild pressures, and their stability is rationalized by a DFT-Chemical Pressure analysis that elucidates the role of the M atom size. Quantum anharmonic effects strongly affect the properties of KB 2 H 8 , the highest predicted T c compound, near 10 GPa, but molecular dynamics simulations reveal it would decompose below its T c at this pressure. Nonetheless, at ca. 50 GPa KB 2 H 8 is predicted to be thermally stable with a superconducting figure of merit surpassing that of the recently synthesized LaBeH 8 .

36 MATERIALS SCIENCE↗