Superhard monoclinic polymorph of carbon.
We report a novel phase of carbon possessing a monoclinic C2/m structure (8 atoms/cell) identified using an ab initio evolutionary structural search. This polymorph, which we call M-carbon, is related to the (2x1) reconstruction of the (111) surface of diamond and can also be viewed as a distorted (through sliding and buckling of the sheets) form of graphite. It is stable over cold-compressed graphite above 13.4 GPa. The simulated x-ray diffraction pattern and near K-edge spectroscopy are in satisfactory agreement with the experimental data [W. L. Mao, Science 302, 425 (2003)10.1126/science.1089713] on overcompressed graphite. The hardness and bulk modulus of this new carbon polymorph are calculated to be 83.1 and 431.2 GPa, respectively, which are comparable to those of diamond.
Li
Quan
Q
State Key Lab of Superhard Materials, Jilin University, Changchun 130012, China.
Ma
Yanming
Y
Oganov
Artem R
AR
Wang
Hongbo
H
Wang
Hui
H
Xu
Ying
Y
Cui
Tian
T
Mao
Ho-Kwang
HK
Zou
Guangtian
G