"Amorphous Diamond: A High-Pressure Superhard Carbon Allotrope"

Yu Lin: Li Zhang, Ho-kwang Mao, Paul Chow, Yuming Xiao, Maria Baldini, Jinfu Shu, and Wendy L. Mao; Phys. Rev. Lett., 10/19/11.

Additional Authors: Li Zhang, Ho-kwang Mao, Paul Chow, Yuming Xiao, Maria Baldini, Jinfu Shu, and Wendy L. Mao

Abstract:

Compressing glassy carbon above 40 GPa, we have observed a new carbon allotrope with a fully sp3-bonded amorphous structure and diamondlike strength. Synchrotron x-ray Raman spectroscopy revealed a continuous pressure-induced sp2-to-sp3 bonding change, while x-ray diffraction confirmed the perseverance of noncrystallinity. The transition was reversible upon releasing pressure. Used as an indenter, the glassy carbon ball demonstrated exceptional strength by reaching 130 GPa with a confining pressure of 60 GPa. Such an extremely large stress difference of >70  GPa has never been observed in any material besides diamond, indicating the high hardness of this high-pressure carbon allotrope.