title: Bonding changes in compressed superhard graphite.
abstract: 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.
authors.affiliation: Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA. wmao@chicago.edu
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Mao
authors.forename: Ho-kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Eng
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Trainor
authors.forename: Matthew
authors.initials: M
authors.lastname: Newville
authors.forename: Chi-chang
authors.initials: CC
authors.lastname: Kao
authors.forename: Dion L
authors.initials: DL
authors.lastname: Heinz
authors.forename: Jinfu
authors.initials: J
authors.lastname: Shu
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley