Emergent Superhardness and Superconductivity in a Hexagonal ZnC10.

Superhard materials typically rely on strong localized covalent bonds, which suppress electronic delocalization and thus hinder metallicity or superconductivity. Here, we propose a strategy to overcome this limitation by introducing Zn atoms into a hexagonal diamond framework. We predict a metastable ZnC10 compound that adopts a hexagonal diamond-like framework (space group P63/mcm) under ambient conditions. The Zn atoms are coordinated by six carbon atoms in a hexagonal framework, which introduces additional electronic states near the Fermi level and enables phonon-mediated superconductivity, while the strong sp3 C-C covalent network preserves the mechanical rigidity. As a result, ZnC10 simultaneously exhibits superhardness (calculated Vickers hardness of 45.8 GPa) and superconductivity (transition temperature ∼3.5 K). These findings establish hexagonal diamond-based frameworks as promising structural templates and provide an effective strategy for the design of multifunctional superhard carbon materials.