Preparation, crystallographic, spectroscopic and magnetic characterization of low-valency nitridometalates Li2[(Li1-xMx)N] with M = Cu, Ni

Thermogravimetric and difference thermal analyses show that the reactions of lithium nitride with the transition metals Cu and Ni under molecular nitrogen to form phases Li-2[(Li1-xMxI)N] take place above 673 K. The maximum weight gains are reached at 926 K and 968 K for M = Cu and Ni, respectively At higher temperatures, the ternary phases Li-2[(Li1-xMxI)N] decompose, limiting the substitutional level x. In the temperature range of 773 K -873 K, the successful synthesis of Li-2[(Li1-xNixI)N] (0 < x less than or equal to 0.85(l)) single phase products is demonstrated. Maximum substitution obtained for the Cu phases is x(max) = 0.43(l). The dependence of the lattice parameters of the hexagonal unit cell on x is almost linear. The magnetic moment of M strongly depends on x. At low x the magnetic moments in phases with M = Ni are presumably enhanced by orbital effects. A decrease Of mu(eff) with x to mu(eff)(x = 1) --> 0 is explained by delocalization of the magnetic moments and by the gradual formation of a metal for the hypothetical compound Li-2[NiN] (x = 1). XAS spectroscopy at the transition metal K-edges shows that Cu and Ni principally correspond to d(10) and d(9)-configurations, respectively.