Shock-induced phase transition of g-C₃N₄ to a new C₃N₄ phase

In this study, phase transition of graphitic carbon nitride (g-C₃N₄) was investigated using the shockwave compression technique. Firstly, the shock Hugoniot data of g-C₃N₄ were obtained using a bore propellant gun and a light gas gun under impact velocities of 1.208-4.982 km/s, revealing one phase transition pressure of g-C₃N₄ at 22.4 GPa. Then, a series of shock recovery experiments was carried out with a pressure range of 17.0-62.1 GPa. The recovered samples were characterized by various techniques, including X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The measured d-values of the recovered samples were compared with those from the previous reported results, revealing a new carbon nitride phase synthesized by the shockwave compression technique. The new phase is indexed as a triclinic cell with a = 0.481 nm, b = 0.353 nm, c = 0.285 nm, α = 67.52°, β = 100.75°, γ = 106.47°, and V_cell= 0.043 nm³. EDX and XPS spectra reveal the existence of C and N elements with an atomic ratio of 0.754, also confirming the presence of a new C₃N₄ phase obtained via a g-C₃N₄ phase transition induced by shockwave compression with a pressure range of 29.3-62.1 GPa. These sample results are in good agreement with the shock Hugoniot data.