Bonding Changes in Compressed Superhard Graphite

• DOI: 10.1126/science.1089713
• Publication Date: 2003-10-16T21:09:09Z
• Authors: Wendy L. Mao; Ho-kwang Mao; Peter J. Eng; Thomas P. Trainor; Matthew Newville; Chi-chang Kao; Dion L. Heinz; Jinfu Shu; Yue Meng; Russell J. Hemley
• Keywords: 02 engineering and technology; 0210 nano-technology

Compressed under ambient temperature, graphite undergoes a transition at ∼17 gigapascals. The near K-edge spectroscopy of carbon using synchrotron x-ray inelastic scattering reveals that half of the π-bonds between graphite layers convert to σ-bonds, whereas the other half remain as π-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 σ-bonds, whereas the nonbridging carbon atoms remain unpaired with π-bonds. The high-pressure form is superhard, capable of indenting cubic-diamond single crystals.