New Superhard Carbon Phases Between Graphite and Diamond

TL;DR

This paper proposes two new superhard carbon allotropes, H-carbon and S-carbon, which are more stable than previous models and could serve as intermediate phases between graphite and diamond, supported by first-principles calculations.

Contribution

The paper introduces two novel carbon phases, H-carbon and S-carbon, with superior stability and electronic properties, expanding the understanding of intermediate superhard carbon allotropes.

Findings

H-carbon and S-carbon are more stable than previous models.

Their bulk moduli are comparable to diamond.

Transition pressures align with experimental data.

Abstract

Two new carbon allotropes (H-carbon and S-carbon) are proposed, as possible candidates for the intermediate superhard phases between graphite and diamond obtained in the process of cold compressing graphite, based on the results of first-principles calculations. Both H-carbon and S-carbon are more stable than previously proposed M-carbon and W-carbon and their bulk modulus are comparable to that of diamond. H-carbon is an indirect-band-gap semiconductor with a gap of 4.459 eV and S-carbon is a direct-band-gap semiconductor with a gap of 4.343 eV. The transition pressure from cold compressing graphite is 10.08 GPa and 5.93 Gpa for H-carbon and S-carbon, respectively, which is in consistent with the recent experimental report.