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

Abstract

Inspired by the synthesis of XB3C3 (X = Sr, La) compounds in the bipartite sodalite clathrate structure, density functional theory (DFT) calculations are performed on members of this family containing up to two different metal atoms. A DFT-chemical pressure analysis on systems with X = Mg, Ca, Sr, Ba reveals that the size of the metal cation, which can be tuned to stabilize the B–C framework, is key for their ambient-pressure dynamic stability. High-throughput density functional theory calculations on 105 Pm3̅ symmetry XYB6C6 binary-guest compounds (where X, Y are electropositive metal atoms) find 22 that are dynamically stable at 1 atm, expanding the number of potentially synthesizable phases by 19 (18 metals and 1 insulator). The density of states at the Fermi level and superconducting critical temperature, T c , can be tuned by changing the average oxidation state of the metal atoms, with T c being highest for an average valence of +1.5. KPbB6C6, with an ambient-pressure Eliashberg T c of 88 K, is predicted to possess the highest T c among the studied Pm3̅n XB3C3 or Pm3̅ XYB6C6 phases, and calculations suggest it may be synthesized using high-pressure high-temperature techniques and then quenched to ambient conditions.

Superconductivity in the doped polymerized fullerite clathrate from first principles

“…Indeed ab initio DFT simulations performed on the strontium and barium doped carbon-boron clathrates yield T c 's of 40 K and 43 K, respectively, at room pressure [11]. Furthermore, an increase in T c up to 88 K was predicted in this class of compounds for the potassium-lead binary-guest clathrate [6,12].…”

Structure, Stability and Superconductivity of N-doped Lutetium Hydrides at kbar Pressures

“…Thus, with reported T c s of the superhydrides reaching temperatures not uncommon for a typical winter-day in upstate New York, the focus of research changed to predicting and synthesizing materials that could maintain high T c s, but at lower pressures, with the ultimate goal of realizing superconductivity at ambient temperature and pressure. As the structures and superconducting properties of the binary hydrides had been exhaustively searched with no such candidate found, computations turned towards predicting ternary hydrides that remained dynamically stable to pressures below 100 GPa [27][28][29], or boron-carbon analogues of the superhydrides that were stable at 1 atm [30].…”

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

“…15 This clathrate is a hole conductor and the first member of the borocarbide analog family of clathrate hexahydrides. 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 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.…”

“…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. For example, B can be introduced into metal silicides to form a typical clathrate-I K 7 B 7 Si 39 , where small metals/ions may be accommodated in the clathrate cage.…”