Compressed glassy carbon maintaining graphite-like structure with linkage formation between graphene layers

Area of Science:

• Materials Science
• Condensed Matter Physics
• High-Pressure Science

Background:

• Amorphous diamond, derived from compressed glassy carbon, exhibits remarkable strength.
• Previous theories suggested a transformation to sp³-bonded structures, but lacked direct experimental evidence.

Purpose of the Study:

• To experimentally determine the bond structure of glassy carbon under ultrahigh pressures.
• To investigate the structural changes responsible for the high compressive strength of compressed glassy carbon.

Main Methods:

• Utilized a newly developed double-stage large volume cell.
• Experimentally determined pair distribution functions of glassy carbon at pressures up to 49.0 GPa.

Main Results:

• Glassy carbon maintained a graphite-like sp²-bonded structure with bond angles near 120° up to 49.0 GPa.
• Graphene interlayer distances decreased significantly, approaching second-neighbor C-C distances above 31.4 GPa.
• Evidence suggests layer linkages, not tetrahedral sp³ bonds, form at high pressures.

Conclusions:

• The ultrahigh strength of compressed glassy carbon is attributed to its retained graphite-like structure and interlayer interactions, not a transition to sp³ bonding.
• This finding challenges previous assumptions about the structural basis of amorphous diamond's strength.