Interesting physical properties of the new spinel phase of Si3N4 and C3N4

The physical properties of the new high-pressure spinel phase of Si3N4 and C3N4 were studied by first-principles calculations. The presence of Si at the octahedral site and the elongated Si-N bonds under pressure have a profound effect on many properties of Si3N4 including lowering the compressibility, decreasing the direct band gap and effective mass, increasing the static dielectric constants, and enhancing covalent bonding. The last effect is explained by calculating the bond order and number of bonds. Possible routes of synthesis at lower pressure and potential applications are suggested.