Predicted stability, structures, and magnetism of 3d transition metal nitrides: the M4N phases

Abstract

The 3d transition metal nitrides M₄N (Sc₄N, Ti₄N, V₄N, Cr₄N, Mn₄N, Fe₄N, Co₄N, Ni₄N, and Cu₄N) have unique phase relationships, crystal structures, and electronic and magnetic properties. Here we present a systematic density functional theory (DFT) study on these transition metal nitrides, assessing both the I-M₄N phase and the II-M₄N phase, which differ in ordering of the N atoms within the face-centered cubic (FCC) framework of metal atoms. The calculations showed that for M = Mn, Fe, Co and Cu, the I-M₄N phases with perfect metal sub-lattices are favored, while for M = Sc–Cr, and Ni, the II-M₄N phases with distorted metal sub-lattices are favored. We predict that several currently not existing II-M₄N phases may be synthesized experimentally as metastable phases. From Bader charge analysis the M₄N phases are found to be ionic with significant metal–metal bonding. I-M₄N with M = Cr to Ni are magnetic, while II-M₄N with M = Cr and Ni are non-magnetic. The calculations revealed unusually high local magnetic moments and high spin-polarization ratios of the M1 atoms in I-M₄N (M = Cr to Ni). The origin of magnetism and lattice distortion of the M₄N phases is addressed with the Stoner criterion. Detailed information about the relative stability, structures, chemical bonding, as well as the electronic and magnetic properties of the phases are of interest to a wide variety of fields, such as chemical synthesis, catalysis, spintronics, coating technology, and steel manufacturing.