Prediction of novel boron–carbon based clathrates

Abstract

Clathrates are inclusion compounds featured with host framework cages and trapped guest atoms or small molecules. Recently, the first boron-carbon (B-C) clathrate SrB3C3 was successfully synthesized at high pressures near...

Computational Screening and Stabilization of Boron-Substituted Type-I and Type-II Carbon Clathrates

“…For example, the occupation of trivalent guest atoms results in the formation of semiconducting materials such as LaB 3 C 3 , 67 distorted ScB 3 C 3 is predicted to be ferroelectric with a high polarization density, 68 and other guest atom combinations may be used to tune the density of states at the Fermi level to produce superconductors with high transition temperatures approaching ∼100 K. 51,53,55,69 In addition, metastable clathrates with different boron contents such as SrB 2 C 4 and LaB 4 C 2 have been investigated computationally at 50 GPa. 54 The experimental realization of type-VII C−B clathrates validates the stabilization principle based on boron substitution and suggests that other carbon clathrate structure types might be realized using the same approach. Indeed, previous calculations of model type-I and type-II systems demonstrate boron stabilization conceptually; however, no thermodynamically stable substitution schemes have been identified for structures other than type-VII.…”

“…Increased stability with pressure is consistent with other sp 3 structures including diamond and type-VII C−B clathrates. [51][52][53][54][55]57,65,67,68,80 Both cases with Li in the large cages and Mg in the large cages for type-II clathrate are an exception from this trend and are destabilized with increased pressure. The small sizes of the Li and Mg cations may not be sufficient to stabilize clathrates at high pressure when only the large cages are occupied, and these phases become destabilized with increased compression.…”

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

“…The superconducting properties of a few borocarbide clathrates stuffed with two different metal atoms have also been studied theoretically. − In the silicon analogues, Pm 3̅ 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 . CSP coupled with high-throughput calculations have uncovered analogous clathrate cages, but with inequivalent C:B ratios, identifying I 4/ 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, though they were not on the convex hull . We note that metal-doped clathrates with pure carbon frameworks are also predicted to exhibit high- T c superconductivity , (for example, sodalite-like NaC 6 with a predicted T c above 100 K); however, non-B-doped carbon clathrates have not been produced to date.…”

Exploration of AB3Si3 (A = Na/K/Rb/Cs) compounds under moderate pressure

“…16 Subsequently, superconductivity was confirmed through experiments 17 and density functional theory (DFT) calculations. 16,18 This discovery inspired numerous studies on related materials, [19][20][21][22][23] extending even to quaternary borocarbides by substituting different guest atoms. 16,24,25 Silicon-based materials, as the closest neighbor of carbon in elemental group IVA, are also extensively studied.…”