Abstract
Amorphous diamond, formed by high-pressure compression of glassy carbon, is of interests for new carbon materials with unique properties such as high compressive strength. Previous studies attributed the ultrahigh strength of the compressed glassy carbon to structural transformation from graphite-like sp2-bonded structure to diamond-like sp3-bonded structure. However, there is no direct experimental determination of the bond structure of the compressed glassy carbon, because of experimental challenges. Here we succeeded to experimentally determine pair distribution functions of a glassy carbon at ultrahigh pressures up to 49.0 GPa by utilizing our recently developed double-stage large volume cell. Our results show that the C-C-C bond angle in the glassy carbon remains close to 120°, which is the ideal angle for the sp2-bonded honey-comb structure, up to 49.0 GPa. Our data clearly indicate that the glassy carbon maintains graphite-like structure up to 49.0 GPa. In contrast, graphene interlayer distance decreases sharply with increasing pressure, approaching values of the second neighbor C-C distance above 31.4 GPa. Linkages between the graphene layers may be formed with such a short distance, but not in the form of tetrahedral sp3 bond. The unique structure of the compressed glassy carbon may be the key to the ultrahigh strength.
Highlights
Carbon is known to display numerous allotropes, such as graphite, diamond, fullerenes, carbon nanotubes, and glassy carbon, because of its flexibility to form chemical bonds with sp, sp2, and sp3-hybridizations
In situ synchrotron X-ray Raman spectroscopy (XRS) measurement for the type-I Glassy carbon (GC) showed a decrease of π-bonding feature with increasing pressure and its eventual disappearance at 44.4 GPa5
Optical Raman spectroscopy measurement for the type-I GC showed a weakening of the G-band (~1600 cm−1) feature at high pressures, which was interpreted as the result of the sp2-sp[3] structural transformation at high pressures[6]
Summary
Carbon is known to display numerous allotropes, such as graphite, diamond, fullerenes, carbon nanotubes, and glassy carbon, because of its flexibility to form chemical bonds with sp-, sp2-, and sp3-hybridizations. We determined g(r) of the type-I GC at high-pressure conditions up to 49.0 GPa under room temperature by utilizing our recently developed double-stage large volume cell[11,12] combined with a multi-angle energy dispersive X-ray diffraction (EDXD) technique[13].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
