L Journal of Alloys and Compounds 317–318 (2001) 237–244 www.elsevier.com / locate / jallcom Layered ternary transition metal nitrides; synthesis, structure and physical properties a, a a a * Duncan H. Gregory , Paul M. O’Meara , Alexandra G. Gordon , Daniel J. Siddons , a a b b Alexander J. Blake , Marten G. Barker , Thomas A. Hamor , Peter P. Edwards a School of Chemistry, University of Nottingham, Nottingham NG72RD, UK b School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Abstract Two-dimensional structures are an emerging class of materials within nitride chemistry. We report here our systematic studies of two groups of these layered compounds: 1 Lithium transition metal compounds, Li h M N (M5Co, Ni, Cu, h5Li vacancy) and 2 32x 2y y x ternary transition metal nitrides of general formulation AMN (A5alkaline earth metal, M5Ti, Zr, Hf). Compounds in class 1 are based 2 on the hexagonal Li N structure, unique to nitrides. Compounds in group 2, by contrast, crystallise with oxide structures (a-NaFeO or 3 2 KCoO ). Specific and unusual synthetic methods have been developed to reproducibly prepare these compounds. Compounds in series 1 2 1 contain ordered or disordered Li vacancies at increased levels relative to the parent Li N, itself a Li fast ion conductor. Nitrides in series 3 2 should be nominally diamagnetic ( S50), yet magnetic measurements reveal behaviour seemingly inconsistent with this assumption.  2001 Elsevier Science B.V. All rights reserved. Keywords: Nitrides; Synthesis; Structure; Diffraction 1. Introduction ing from structures unique to nitrides (principally Li N or 3 subnitride derivatives). In either case, knowledge of rela- After several decades of dedicated research, advances in tively well-characterised analogue or parent systems can be the chemistry of inorganic nitrides have accelerated exploited to (a) establish a degree of structural predictabili- dramatically over the last 5–10 years. Transition metal ty, (b) begin to modify and manipulate composition, compounds illustrate many of the reasons why nitride structure and also, therefore physical properties of po- chemistry is receiving increased attention. Exhibiting a tential new materials. particularly rich and unexpected valence behaviour, they Materials of stoichiometry ABX are well-known in 2 already display evidence of both curious and useful oxides and chalcogenides. The 2-D structural nature of electronic behaviour [1–3]. many of these materials is intrinsic to their properties (e.g. An emerging structural class within nitride chemistry are batteries, electronic materials). Nitride ABX examples 2 two dimensional, layered materials. Intriguing examples now embrace alkali metal–transition metal and mixed already exist within nominally simple binary systems such transition metal systems. Alkaline earth metal compounds, I II I II as A –N and A –N (A 5Li, A 5Ca, Sr, Ba). For example, however, are still relatively rare. ABN nitrides are, in 2 Li N, crystallising with a unique layered structure [4,5], is some cases, non-stoichiometric (e.g. Li W N ) [6] 3 0.84 1.16 2 the only stable alkali metal nitride. Also, Sr N and Ba N with potential for (de)intercalation chemistry (e.g. 2 2 (‘excess electron’, anti -CdCl -type subnitrides) are the Li MoN ) [7]. Many of the studied materials are 2 12x 2 most stable nitrides of strontium and barium whereas metallic and paramagnetic, whereas some show more ‘Sr N ’ and ‘Ba N ’ are ill-defined. Layered ternary unexpected and exciting behaviour (e.g. Ca TaN ) [8]. 3 2 3 2 x 2 nitrides broadly follow two patterns in terms of their By contrast, manipulation of the Li N parent structure 3 crystal chemistry: those adopting structures with known via substitution of transition metals is not an entirely recent analogues (chiefly from oxide chemistry) and those evolv- phenomenon. Originally, research into nominal Li MN 32x x (M5Co, Ni, Cu) systems was performed over 50 years ago [9,10]. Solid solutions of limited range (typically x,0.5) *Corresponding author. E-mail address: Duncan.Gregory@Nottingham.ac.uk (D.H. Gregory). were observed with retention of the Li N structure. 3 0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388(00)01340-2