Amorphous Diamond – A High-Pressure Superhard Carbon Allotrope

Carbon has long been a rich and active research area offering exciting discoveries of new allotropes including both crystalline and disordered structures such as buckyballs, carbon nanotubes, graphene and diamond-like amorphous carbon with numerous and exciting potential in technological applications.

A team that includes CDAC student Yu Lin and researchers from Stanford University and Carnegie has observed a new carbon allotrope with a fully sp3-bonded amorphous structure and diamond-like strength by compressing glassy carbon above 40 gigapascals. The initially all sp2-bonded glassy carbon was found to gradually transform to a fully sp3-bonded tetrahedral carbon framework while preserving its amorphous structure. This high pressure carbon allotrope demonstrated its exceptional hardness by sustaining an extremely large pressure difference which has never been observed in any material besides diamond. The findings expand the wealth of pure carbon allotropes and open exciting possibilities for potential applications using pressure-hardened superhard amorphous solids. The results of this study was published in Physical Review Letters [Y. Lin et al., Phys. Rev. Lett. 107, 175504 (2011)].