Elastic and structural instability of cubic Sn<SUB>3</SUB>N<SUB>4</SUB> and C<SUB>3</SUB>N<SUB>4</SUB> under pressure

We use in situ high-pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride (γ-Sn3N4) under pressure up to 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B0) is 149(±1.2) GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic, and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa [ M. Huang and Y. P. Feng J. Appl. Phys. 96 4015 (2004)]. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions