Superconductive Sodium Carbides with Pentagon Carbon at High Pressures

Abstract

The design of metal-bearing carbon-based materials with unique structures and intriguing properties is highly desirable in the fields of physics, chemistry, and materials science.Here, within swarm-intelligence structure search and first-principles computations, we uncovered several hitherto unknown sodium carbides (i.e., Na 4 C, Na 3 C 2 , NaC, Na 2 C 3 , and NaC 2 ) under high pressure. Intriguingly, the C atom arrangement reveals multiple structure evolution behavior with increased carbon content, from isolated anions in Na 4 C, tetramers in Na 3 C 2 , extended chains in NaC, pentagonal rings in Na 2 C 3 , to eventually hexagonal rings in NaC 2 . Among predicted phases, the superconducting critical temperature T c of NaC 2 could approach ∼42 K at 80 GPa, which is slightly higher than the T c of 39 K in the highest phonon-mediated superconductivity of MgB 2 at ambient pressure. This work offers insights into the reaction of carbides containing alkali metals and paves the way for the future investigation of high superconductivity in metal carbide systems.

Emerging Yttrium Phosphides with Tetrahedron Phosphorus and Superconductivity under High Pressures

“…Such case is also observed in Y hydrides [47,48] and P6/mmm NaC 2 . [67] In addition, further study illustrates that the bandgaps of known P2 1 /m YP 5 exhibit gradually decrease with increasing pressure (Figure S12a). Furthermore, the electronic band structure and PDOS of P2 1 /m YP 5 at higher pressure of 8 GPa show that it becomes a metallic phase (Figure S12b and S12c).…”

Atomic-Scale Pentagraphene Ribbons Stabilized with Alkali Metals under Moderate Pressures

“…The Pnma phase possesses a larger equilibrium cell volume than Cmcm (inset of Figure b). However, at ambient pressure, M 2 C 3 favors the Pnma phase with much lower total energy than that of the Cmcm phase . The enthalpy difference of the Pnma phase for M 2 C 3 f.u.…”

“…However, at ambient pressure, M 2 C 3 favors the Pnma phase with much lower total energy than that of the Cmcm phase. 42 The enthalpy difference of the Pnma phase for M 2 C 3 f.u. with respect to Cmcm is defined by ΔH = [H(Pnma) − H(Cmcm)]/5.…”

High-Tc superconductivity of polyhydride Rb2MgH18 with a layered hydrogen structure at high pressure

“…The structure searches for Rb x Mg y H z (x = 1-2, y = 1-2, z = 1-4, 6, 8-10, 12, 16, 18, 24, 28) at 100, 200, and 300 GPa were carried out using a particle-swarm optimization algorithm implemented in the CALYPSO software, [45][46][47] which has been successfully applied to various high-pressure systems. [48][49][50][51][52][53] Simulated cells containing up to 62 atoms were adopted. The total number of searched structures in this work was around 151 000.…”