In Situ Transmission Electron Microscopy Reveals the Thickness-Dependent Thermal Decomposition Mechanisms of C3N5 Flakes

C₃N₅ materials have received wide interest due to their enormous potential in optoelectronic and catalytic applications; however, their thermal instability under high-temperature conditions remains a critical challenge preceding practical implementations. In this context, the microscopic understanding of their structural decomposition mechanisms at high temperatures is imperative. In this work, we systematically investigate the thermal decomposition behaviors of C₃N₅ flakes via in situ transmission electron microscopy. Our atomic-scale observations reveal thickness-dependent thermal decomposition mechanisms for C₃N₅ flakes; these thin C₃N₅ flakes initially decompose to form small amorphous carbon nanoparticles (NPs), which subsequently grow and crystallize, while thick C₃N₅ flakes only precipitate amorphous carbon NPs on their surface and largely maintain their original structure under the same heating conditions. These two decomposition behaviors can be attributed to discrepancies in atomic bonding and particle diffusion according to the thickness of the C₃N₅ flakes. The findings provide fundamental insights into the thermal stability of C₃N₅ flakes and may offer indispensable guidance for designing stable C₃N₅-based materials.