Theoretical calculations on the structures, electronic and magnetic properties of binary 3d transition metal nitrides

Abstract

The electronic structures of a number of binary 3d transition metal and iron nitrides, some of which still need to be synthesized, have been investigated by means of spin-polarized first principles band structure calculations ( TB-LMTO-ASA). The chemical bonding in all compounds has been clarified in detail through the analysis of total and local densities-of-states (DOS ) and crystal orbital Hamilton populations (COHP). The binary transition metal nitride set includes ScN, TiN, VN, CrN, MnN, FeN, CoN and NiN, both in the sodium chloride as well as in the zinc blende structure type. Antibonding metal-metal interactions for higher electron counts are significantly weaker in the zinc blende type, thus favoring this structural alternative for the later transition metal nitrides.For binary iron nitrides, the stoichiometric phases a◊-Fe 16 N 2 , c∞-Fe 4 N, e-Fe 3 N, f-Fe 2 N as well as the recently synthesized (rf-sputtering) non-stoichiometric compounds c◊-FeN 0.91 and c+-FeN 0.5-0.7 have been investigated. There is experimental evidence that c◊-FeN 0.91 adopts the zinc blende structure type while c+-FeN 0.5-0.7 should crystallize in a defect sodium chloride type structure. For the stoichiometric phases, most numerical theoretical data are consistent with the measured ground state properties ( lattice parameters and magnetic moments) whenever experimentally available. The general trends concerning iron-nitrogen and iron-iron bonding have been elucidated; the role of nitrogen vacancies were simulated by a number of model calculations. It appears that potentially antibonding interactions are the source of local structural distortions in all of these phases.For c◊-FeN 0.91 , theory supports the proposed metallic zinc blende structure with a theoretical lattice parameter of 421 pm for the exact 151 composition. With respect to c+-FeN 0.5-0.7 in the defect NaCl structure type, we arrive at theoretical lattice constants between 389 and 398 pm, somewhat depending upon the nitrogen content.

Electronic structure and magnetism of equiatomic FeN

“…It is suggested that other unknown effects should be responsible for the extraordinarily larger lattice constant observed for FeN with NaCl structure. Eck et al [10] have estimated the equilibrium lattice constant for defected FeN and obtained a rather smaller a th . Up to date, no theoretical investigations on FeN film has been reported.…”

“…It may therefore be, as suggested in Refs. [9,10], that the experimental NaCltype FeN with a=4.5Å is not in stable state due to unknown effects, such as the effect of the surface.…”

“…Most recently, Eck et al [10] performed band structure calculations using tight-binding-linearmuffin-tin-orbitals (TB-LMTO) method within the atomic-sphere-approximation (ASA) and investigated structural and electronic properties of both FeN structures by analyzing density of states (DOS) and crystal orbital Hamilton population (COHP). They concluded that the zinc blende structure should be more stable because of the weaker antibonding Fe-Fe interactions below the Fermi level.…”

Synthesis, structure and properties of new functional oxynitride ceramics

“…The GaON nanowires were assumed to be grown by the catalytic behavior of Ni or Co, which precipitated during ammonolysis due to the instability of their nitrides. 64) One-dimensional growth occurred because the metal precipitates obstruct isotropic two-dimensional growth of GaON in the hexagonal c-plane. The nanowire did not grow by VLS growth.…”

Processing of dielectric oxynitride perovskites for powders, ceramics, compacts and thin films

“…The thermal stability of several types of metal nitrides and oxynitrides has been well studied. Transition metal nitrides gradually become unstable with an increase in their antibonding electronic contribution 15 . For example, a powder of α"-Fe 16 N 2 was prepared by ammonolysis of α-Fe powder at a very low temperature because of the thermally unstable chemical bonds between iron and nitrogen 16 .…”