Crystal structure of cold compressed graphite.

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Graphite is a common carbon allotrope, but its behavior under high pressure is complex.
• Experimental observations of graphite under pressure show features not fully explained by current models.

Purpose of the Study:

• To identify novel carbon allotropes stable under high pressure.
• To explain experimental data from high-pressure graphite studies.
• To characterize the properties of a newly discovered carbon allotrope.

Main Methods:

• Systematic structural search using computational methods.
• Density Functional Theory (DFT) calculations for structural and electronic properties.
• Analysis of predicted X-ray diffraction and Raman spectra.

Main Results:

• Discovery of a new carbon allotrope, Z-carbon, with Cmmm symmetry.
• Z-carbon predicted to be more stable than graphite above 10 GPa.
• Z-carbon is composed of pure sp(3) bonds, explaining experimental spectra.
• Predicted Z-carbon is a transparent, wide band-gap semiconductor with diamond-like hardness.

Conclusions:

• Z-carbon represents a stable high-pressure phase of carbon.
• The transition from graphite to Z-carbon involves graphene sheet sliding and buckling.
• Z-carbon's unique properties offer potential for new material applications.