RbB₃Si₃: An Alkali Metal Borosilicide that is Metastable and Superconducting at 1 atm

Abstract

The stability, electronic structure, and potential superconductivity in AB3Si3 (A = Na, K, Rb, and Cs) compounds that assume a clathrate-based sodalite structure whose framework consists of covalent B–Si bonds are 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, RbB3Si3, that could be synthesized under pressures that are smaller by a factor of 10, ∼10 GPa, and quenched to atmospheric conditions. Electron–phonon coupling calculations predict that RbB3Si3 possesses a superconducting critical temperature, T c, of 14 K at 1 atm. The dynamic stability of RbB3Si3 and CsB3Si3 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.

Conventional High-Temperature Superconductivity in Metallic, Covalently Bonded, Binary-Guest C–B Clathrates

“…19 The superconducting properties of a few borocarbide clathrates stuffed with two different metal atoms have also been studied theoretically. 16−18 In the silicon analogues, Pm3̅ n RbB 3 Si 3 was thermodynamically stable with respect to the elemental phases between 7 and 35 GPa, and it remained metastable at 1 atm with an estimated T c of 14 K. 33 CSP coupled with high-throughput calculations have uncovered analogous clathrate cages, but with inequivalent C:B ratios, identifying I4/mmm CaB 2 C 4 and SrB 4 C 2 stoichiometry structures as superconductors with T c s of 2 and 19 K, respectively, while SrB 2 C 4 and BaB 2 C 4 were predicted to possess superior mechanical properties with Vickers Hardnesses, H v s, of 44 and 41 GPa, respectively, 34 though they were not on the convex hull. 12 We note that metal-doped clathrates with pure carbon frameworks are also predicted to exhibit high-T c superconductivity 23,24 (for example, sodalite-like NaC 6 with a predicted T c above 100 K 35 ); however, non-B-doped carbon clathrates have not been produced to date.…”

Cage Adaption by High-Pressure Synthesis: The Clathrate-I Borosilicide Rb8B8Si38

“…Nevertheless, subsequent attempts to prepare further boron-containing clathrate-I phases remained unsuccessful at ambient pressure. At this stage, the synthesis strategy was reconsidered by taking into account the beneficial effect of elevated pressures as evidenced by the recent preparation of the borosilicide LiBSi 2 comprising a [Si 2 B – ] n framework of four-bonded atoms and the theoretical prediction of quenchable sodalite-type RbB 3 Si 3 …”

“…At this stage, the synthesis strategy was reconsidered by taking into account the beneficial effect of elevated pressures as evidenced by the recent preparation of the borosilicide LiBSi 2 comprising a [Si 2 B − ] n framework of four-bonded atoms 18 and the theoretical prediction of quenchable sodalite-type RbB 3 Si 3 . 19 In the scope of the present work, the influence of highpressure conditions on the formation of a clathrate-I borosilicide is investigated. We find that high-pressure synthesis grants access to the clathrate-I Rb 8 B 8 Si 38 showing remarkable thermal stability.…”

Rational Design of Superconducting Metal Hydrides via Chemical Pressure Tuning

“…Because these distortions lower the density of states at the Fermi level, thereby decreasing the T c , it is important to understand their origin. The Density Functional Theory-Chemical Pressure (DFT-CP) method, [31] which has been applied successfully to explain the stability and structural distortions in a plethora of complex inorganic materials, [32][33][34] visualizes the internal stresses inherent in crystal structures as a consequence of steric constraints. It is therefore the ideal technique to analyze how chemical substitution affects the structures the superconducting metal hydrides adopt.…”