A metallic superhard boron carbide: first-principles calculations

Area of Science:

• Materials Science
• Computational Chemistry
• Solid State Physics

Background:

• Boron-carbon compounds (BC3) are of interest for their unique electronic and mechanical properties.
• Previous theoretical studies have proposed various BC3 structures, but experimental synthesis remains challenging.

Purpose of the Study:

• To predict and characterize a novel monoclinic BC3 phase (M-BC3) using first-principles calculations.
• To investigate the stability, electronic, and mechanical properties of the predicted M-BC3 structure.
• To compare theoretical predictions with experimental data to aid in material identification.

Main Methods:

• First-principles calculations were employed to determine the total energy, elastic constants, and phonon frequencies.
• Density Functional Theory (DFT) was used for electronic structure calculations.
• Raman spectral calculations were performed for comparison with experimental results.

Main Results:

• A stable monoclinic BC3 (M-BC3) phase was predicted, featuring alternating metallic BC and insulating C layers, resulting in two-dimensional conductivity.
• The calculated phase transition pressure from graphite-like BC3 to M-BC3 is 9.3 GPa.
• The theoretical Vickers hardness of M-BC3 is 43.8 GPa, suggesting it is a potentially superhard material.

Conclusions:

• The predicted M-BC3 phase is dynamically and mechanically stable.
• M-BC3 exhibits promising properties for potential applications as a superhard material with 2D conductivity.
• Experimental BC3 crystals may contain a mixture of M-BC3 and Pmma-b phases, as indicated by Raman spectral analysis.