The stability, electronic properties, and hardness of SiN2 under high pressure

The structures of silicon nitride (SiN2) under high pressures have been predicted using the developed particle swarm optimization algorithm for crystal structure prediction. The pyrite SiN2 can be synthesized above 17 GPa, and the current thermodynamical calculations reveal that the pyrite-type structure is the most stable up to 100 GPa. No imaginary phonon frequencies in the whole Brillouin zone indicate the pyrite SiN2 is dynamically stable. Strikingly, the mechanical analyses show the pyrite SiN2 displays a behavior very similar to isotropy and high bulk modulus, shear modulus, and high simulated hardness indicate its very incompressible and superhard nature (63 GPa), which was driven by the strong covalent Si-N bonds and localized nonbonding.