First-Principles Calculations of Phase Transition and Stability of Si₂CN₄ under High Pressure

A pressure-induced phase transition and stability in Si₂CN₄ polymorphs under high pressure are studied by first-principles calculations. The result shows that the phase transition pressure of α- and β-Si₂CN₄ to the cubic spinal phase is 29.9GPa and 27.5GPa predicted by thermodynamic method respectively. Under ambient condition, all of the three Si₂CN₄ polymorphs are metastable with positive formation enthalpy. Unlike the stability of Si₃N₄ polymorphs, α-Si₂CN₄ is more stable than the β phase.