Chemical Composition of Lithiated Nitrodonickelates Li 3- xy Ni x N: Evidence of the Intermediate Valence of Nickel Ions from Ion Beam Analysis and Ab Initio Calculations.

Lamellar lithiated nitridonickelates have been investigated from both experimental and theoretical points of view in a wide range of compositions. In this study, we show that the nickel ion in lamellar lithiated nitridonickelates adopts an intermediate valence close to +1.5. This solid solution can therefore be written Li 3-1.5 x Ni x N with 0 ≤ x ≤ 0.68. Attempts to introduce more nickel into these phases systematically lead to the presence of the endmember of the solid solution, Li 1.97 Ni 0.68 N, with metallic nickel as an impurity. The LiNiN phase has never been observed, and first-principles calculations suggested that all the structural configurations tested were mechanically unstable.