Prediction of spinel structure and properties of single and double nitrides

Lattice constants, bulk moduli, band gaps, electronic bonding, and the stability of 20 new nitrides with spinel structure are studied by first-principles calculations. Double nitrides AB(2)N(4) are found to be stable when the counterparts BA(2)N(4) are metastable except for TiZr2N4. The four single nitrides C3N4, Si3N4 Ge3N4, and Sn3N4 have direct band gaps at the Gamma point ranging from 1.14, to 3.45 eV while Zr3N4 and Ti3N4 have small indirect gaps. For double nitrides, both metallic and insulating band structures are possible. The total bond orders of the stable double nitrides are larger than those of Constituent single nitrides. Among them, CSi2N4 shows exceptionally strong covalent bonding and a large bulk modulus. A simple scaling law based on bond lengths can describe the bulk moduli of these spinel nitrides quite well.