Predicting a metallic carbon allotrope: Pop-graphite via Na–C compounds.

The article focuses on the theoretical prediction and characterization of a novel layered carbon allotrope named pop-graphite, derived from a high-pressure sodium–carbon compound NaC₃. Pop-graphite features a unique penta–octa–penta (pop) carbon ring framework and remains stable under ambient conditions after sodium removal, exhibiting metallic conductivity, intrinsic single-gap superconductivity driven by electron–phonon coupling involving carbon p_z orbitals, and enhanced mechanical flexibility compared to conventional graphite. The proposed synthesis involves forming NaC₃ at pressures above 10.8 GPa followed by sodium degassing, facilitated by low sodium migration energy barriers, suggesting experimental feasibility. These findings expand the understanding of graphite-like carbon allotropes and highlight pop-graphite's potential applications in energy storage and electronic devices.