First-principles calculations of phase transition and stability of si 2CN 4 under High Pressure

A pressure-induced phase transition and stability in Si 2CN 4 polymorphs under high pressure are studied by first-principles calculations. The result shows that the phase transition pressure of α- and β-Si 2CN 4 to the cubic spinal phase is 29.9 GPa and 27.5 GPa predicted by thermodynamic method respectively. Under ambient condition, all of the three Si 2CN 4 polymorphs are metastable with positive formation enthalpy. Unlike the stability of Si 3N 4 polymorphs, α-Si 2CN 4 is more stable than the β phase. © 2009 Chinese Physical Society and IOP Publishing Ltd.