Ultrahigh strength of cage-like polymeric nitrogen surpassing diamond under high pressure

We report first-principles predictions of a cage-like polymeric nitrogen phase (cage-N) composed of interlocked N10 clusters stabilized by mixed sp2/sp3 hybridization. Under high pressure, cage-N exhibits exceptional mechanical performance, including an ideal compressive strength of 343 GPa at a pressure of 300 GPa, ∼33% higher than that of diamond. This ultrahigh strength arises from the synergistic interplay between its three-dimensional covalent framework and hybridized bonding topology, which enables isotropic stress accommodation and dynamic electronic rearrangement. These results establish cage-N as a promising non-carbon ultrahard material and provide a bonding-driven route toward designing superhard frameworks under extreme conditions.