Amorphous diamond: a high-pressure superhard carbon allotrope

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Carbon allotropes exhibit diverse structures and properties.
• High-pressure synthesis is key to discovering novel materials.
• Understanding pressure-induced phase transitions is crucial for materials development.

Purpose of the Study:

• To synthesize and characterize a new carbon allotrope under high pressure.
• To investigate the pressure-induced bonding changes in glassy carbon.
• To evaluate the mechanical properties and potential applications of the new material.

Main Methods:

• High-pressure compression of glassy carbon above 40 GPa.
• Synchrotron X-ray Raman spectroscopy for analyzing bonding states.
• X-ray diffraction to assess structural changes and crystallinity.
• Mechanical testing using the synthesized material as an indenter.

Main Results:

• A novel, fully sp(3)-bonded amorphous carbon allotrope was synthesized.
• Continuous reversible pressure-induced sp(2)-to-sp(3) bonding transition observed.
• The material maintained non-crystalline structure up to 130 GPa.
• Exceptional strength demonstrated, with a stress difference exceeding 70 GPa.

Conclusions:

• High-pressure compression of glassy carbon yields a unique amorphous allotrope with diamond-like mechanical properties.
• The reversible sp(3)-bonded amorphous phase represents a significant advancement in carbon materials science.
• This discovery opens avenues for developing ultra-hard materials for demanding applications.