The crystal structure of cold compressed graphite

TL;DR

This paper predicts a new carbon allotrope called Z-carbon, more stable than graphite above 10 GPa, with unique structural, electronic, and mechanical properties, matching experimental data under high pressure.

Contribution

The study introduces Z-carbon, a novel stable carbon allotrope under high pressure, with detailed structural, electronic, and mechanical characterization, supported by systematic computational analysis.

Findings

Z-carbon is more stable than graphite above 10 GPa.

Z-carbon matches experimental X-ray and Raman spectra features.

Z-carbon is a transparent wide band gap semiconductor with diamond-like hardness.

Abstract

Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp3 bonds and is the only carbon allotrope which provides an excellent match to unexplained features in experimental X-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to Z-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that Z-carbon is a transparent wide band gap semiconductor with a hardness comparable to diamond.