Uniaxiality‐Induced Reduced‐Pressure Synthesis of Ultrahard Paracrystalline Diamond

Abstract Synthesizing fully sp 3 ‐bonded non‐crystalline carbon remains a long‐standing challenge due to the intrinsic instability of the sp 3 bond at ambient pressure. Recently, paracrystalline diamond, a new‐form sp 3 ‐bonded non‐crystalline carbon consisting of sub‐nanometer‐sized paracrystallites, has been synthesized from face‐centered cubic C 60 at 30 GPa, which has attracted attention due to its unique structural features and excellent physical properties. However, the ultrahigh synthesis pressure of paracrystalline diamond poses an obstacle to its large‐scale production and applications. In this study, paracrystalline diamond is synthesized at an exceptionally low pressure (16 GPa) via inducing uniaxiality at high‐pressure and high‐temperature conditions, thereby breaking through the temperature‐pressure phase diagram of C 60 . By combining structural characteristics and advanced molecular dynamics simulation, the remarkable reduction of synthesis pressure is attributed to the fact that the symmetry of the C 60 cage is broken due to the uniaxiality, which further allows the C 60 cage to collapse at much lower pressures. This work reveals the critical role of uniaxiality in the reduced‐pressure synthesis of paracrystalline diamond, which may provide a potent methodological strategy for the development of novel low‐cost high‐pressure materials.