A new phase in the binary iron nitrogen system?--The prediction of iron pernitride, FeN2

Among numerous different AB(2) structures with the hypothetical composition FeN(2), the structures lying lowest in energy have been determined by a series of density-functional electronic-structure calculations. The most likely FeN(2) phase crystallizing in the space group R3m must be considered an iron pernitride incorporating binuclear N-N units (d=1.275 Å) with an anionic charge of 2-. This high-pressure magnetic phase with a bulk modulus of about 192 GPa and an iron saturation moment of approximately 1.68 μ(B) should already form at a pressure of 17 GPa at an assumed reaction temperature of 1000 K. Besides bonding Fe-N interactions, antibonding N-N and Fe-Fe interactions exist in the crystal structure.