Bonding Changes in Compressed Superhard Graphite

• Published in: Science (American Association for the Advancement of Science) Vol. 302; no. 5644; pp. 425 - 427
• Main Authors: Mao, Wendy L., Mao, Ho-kwang, Eng, Peter J., Trainor, Thomas P., Newville, Matthew, Kao, Chi-chang, Heinz, Dion L., Shu, Jinfu, Meng, Yue, Hemley, Russell J.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 17.10.2003; The American Association for the Advancement of Science
• Subjects: Ambient temperature; Anvils; Atoms; Carbon; Chemical properties; Chemistry; Climate; Conceptual Tempo; Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Energy; Estimators; Exact sciences and technology; Gaskets; Grade Point Average; Graphite; Hydrostatics; Observation; Physics; Pressure; Spectroscopy; Structure of solids and liquids; crystallography; Wave diffraction; X ray diffraction; United States; X-ray scattering; Phase transformations; Hydrostatic pressure; Graphite; Chemical bonds; Hard materials; Experimental study; High pressure
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1089713

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.