D-carbon: A New sp3 Carbon Allotrope

TL;DR

This paper introduces D-carbon, a new stable sp3 carbon allotrope with exceptional hardness and stability, identified through ab initio calculations, and suggests potential synthesis pathways from diamond.

Contribution

The study discovers and characterizes a new stable sp3 carbon phase, D-carbon, with superior stability and properties compared to previous models, and explores its synthesis route.

Findings

D-carbon is more stable than T6 structure.

D-carbon has a Vickers hardness of 86.58 GPa.

D-carbon exhibits a band gap of 4.33 eV.

Abstract

We have investigated the structural, mechanical and electronic properties of D-carbon by ab initio calculations, a new phase of crystalline sp3 carbon (pace group D2h5, Pmma-orthorhombic). Total-energy calculations demonstrate that D-carbon is energetically more favorable than previously proposed T6 structure. State-of-the-art theoretical calculations show that this new phase is dynamic, mechanical, and thermal stable at zero pressure, and more stable than graphite beyond 63.7 GPa. Importantly, the calculations reveal that D-carbon possesses high Vickers hardness (86.58 GPa) and bulk modulus (369 GPa), which are comparable to diamond. D-carbon is a semiconductor with a band gap of 4.33 eV, lower than diamond's gap (5.47 eV). The simulated X-ray diffraction pattern is in satisfactory agreement with the previously experimental data in chimney or detonation soot, suggesting its possible presence in the specimen. Equally important, the possible transition path from diamond to D-carbon has been investigated, indicating a possible approach to synthesize this new phase.