Corrugation-Stabilized Layers and Stacking-Selected Ground State in Layered Graphitic C₃N₄.

Area of Science:

• Materials Science
• Computational Chemistry
• Solid State Physics

Background:

• Graphitic carbon nitride (C₃N₄) displays structural polymorphism due to flexible heptazine networks.
• Corrugated monolayers are favored over planar sheets, but the bulk ground state of C₃N₄ remains uncertain due to unexplored interlayer stacking effects.

Purpose of the Study:

• To systematically investigate the intralayer corrugation and interlayer stacking effects on the bulk ground state of graphitic C₃N₄.
• To identify the most stable crystalline phase of graphitic C₃N₄.

Main Methods:

• Performed a comprehensive structural search combining intralayer corrugation and interlayer stacking within an NX-network framework.
• Utilized first-principles optimization for approximately one hundred candidate structures.
• Conducted phonon calculations and simulated X-ray diffraction for stability and characterization.

Main Results:

• Layer corrugation is the primary stabilization factor, with interlayer stacking providing additional energy gains.
• Stacking of the P3₂1 monolayer leads to the P3̅c1 phase, which is energetically more favorable than the commonly assumed Pbca structure.
• Phonon calculations confirmed the dynamic stability of the P3̅c1 phase.

Conclusions:

• A two-step stabilization mechanism involving corrugation and stacking governs the bulk structure of graphitic C₃N₄.
• The P3̅c1 phase is identified as a strong candidate for the lowest-energy bulk graphitic C₃N₄.
• Simulated X-ray diffraction patterns can distinguish the P3̅c1 phase from the Pbca structure.