A pressure-induced superhard SiCN₄ compound uncovered by first-principles calculations

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Design

Background:

• Silicon-carbon-nitride (Si-C-N) compounds are promising candidates for superhard materials due to their unique properties.
• Previous research had synthesized only limited Si-C-N stoichiometries (SiCN, Si2CN4, SiC2N4).

Purpose of the Study:

• To theoretically investigate the existence and properties of novel Si-C-N compounds.
• To explore the structural stability and potential superhard characteristics of predicted SiCN4 phases.

Main Methods:

• First-principles structural prediction using particle swarm optimization.
• Calculation of enthalpy differences to determine phase stability under pressure.
• Analysis of dynamic stability via phonon dispersion calculations.
• Estimation of Vickers hardness using elastic modulus.

Main Results:

• A new SiCN4 compound was theoretically identified with three distinct crystal structures: P41212, Fdd2, and R3̄.
• Pressure-induced phase transitions were predicted from P41212 to Fdd2 at 2 GPa, and to R3̄ at 249 GPa.
• The Fdd2 and R3̄ phases are thermodynamically stable above 41 GPa and dynamically stable within their respective pressure ranges.
• Calculated band gaps range from 3.72 to 4.37 eV, and estimated Vickers hardness exceeds 40 GPa, indicating superhard potential.

Conclusions:

• The theoretical discovery of SiCN4 expands the landscape of Si-C-N materials.
• High pressure stabilizes novel SiCN4 phases with predicted superhard properties.
• These findings offer crucial insights for future experimental synthesis and applications of Si-C-N superhard materials.