Transition metal-based double nitrides

Abstract

This paper reviews the formation of seve:ral transition metal based double nitrides. The metallic nature of the nitrides has been used as the basis for understanding their properties and structure. At 3 GPa and 1673 K normally covalent GaN with a wurtzite structure reacts with NbN to form cubic (Nb1_xGax)N solid solutions (x:;;; 0.15). Ga was found in a distorted octahedral environment. In reactions with nitrogen at 1273 K, alkaline earth metals (A) formed stoichiometric compounds of ANiN with nickel and A3MN3 with metals (M = V, Cr, Fe, Co). These compounds had [NiNj2-infinite linear chains and [MN316-trigonal planar units. Covalent nature was very important in understanding the bonding between M and N in these alkaline earth transition metal nitrides. The type of structural unit depended on the number of d-electrons. Rf-sputter deposition as well as high pressure synthesis was useful for preparing metastable transition metal nitrides and their solid solutions. (Til_xAlx)N solid solutions and a new compound FeN with zinc blende type structure were obtained by rf-sputtering. 9.1 Introduction Transition metal nitrides have been attracting much attention as high temperature ceramics, magnetic materials, superconductors, and catalysts. Most are simple binary compounds in which the transition metals are close-packed and where nitrogen resides in octahedral interstitial sites between the metal atoms. The rock salt NaCI structure and hexagonal WC structure are typical crystalline forms for these simple transition metal nitrides. Nitrides with the same structure type can form homogeneous solid solutions MI_xM'xN for a wide range of X.I Other double metal nitrides have been limited to the anti-perovskite phases (e.g. Fe3AIN) and the Nowotny phases (e.g Nb3AIN2). In these compounds nitrogen atoms also sit in octahedral interstitial sites formed by transition metals. The t2g orbitals of the transition metals overlap to form metallic bonds and the e~ orbitals interact with nitrogen to form covalent bonds through d 2 sp hybridization. I Chemical bonds in metal nitrides are rich in variety. Alkaline and alkaline earth metals form ionic bonds to nitrogen in compounds such as S. T. Oyama (ed.), The Chemistry of Transition Metal Carbides and Nitrides