Uniaxiality-Induced Reduced-Pressure Synthesis of Ultrahard Paracrystalline Diamond

Y Pan and XH Yuan and Y Cheng and BY Xu and SC Liu and ZT Wang and SD Wang and K Hu and SC Zhu and QJ Li and MS Wang and ZD Liu and H Tang and BB Liu, ADVANCED MATERIALS, 37 (2025).

DOI: 10.1002/adma.202500037

Synthesizing fully sp3-bonded non-crystalline carbon remains a long- standing challenge due to the intrinsic instability of the sp3 bond at ambient pressure. Recently, paracrystalline diamond, a new-form sp3-bonded non-crystalline carbon consisting of sub-nanometer-sized paracrystallites, has been synthesized from face-centered cubic C60 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 C60. 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 C60 cage is broken due to the uniaxiality, which further allows the C60 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.

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