Bonding changes in compressed superhard graphite.
Compressed under ambient temperature, graphite undergoes a transition at approximately 17 gigapascals. The near K-edge spectroscopy of carbon using synchrotron x-ray inelastic scattering reveals that half of the pi-bonds between graphite layers convert to sigma-bonds, whereas the other half remain as pi-bonds in the high-pressure form. The x-ray diffraction pattern of the high-pressure form is consistent with a distorted graphite structure in which bridging carbon atoms between graphite layers pair and form sigma-bonds, whereas the nonbridging carbon atoms remain unpaired with pi-bonds. The high-pressure form is superhard, capable of indenting cubic-diamond single crystals.
Mao
Wendy L
WL
Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA. wmao@chicago.edu
Mao
Ho-kwang
HK
Eng
Peter J
PJ
Trainor
Thomas P
TP
Newville
Matthew
M
Kao
Chi-chang
CC
Heinz
Dion L
DL
Shu
Jinfu
J
Meng
Yue
Y
Hemley
Russell J
RJ