Stoichiometry and defect structure control in the ternary lithium nitridometalates Li_3-x-yNi_xN

A comprehensive study of the system Li_3-x-yNi_xN has investigated systematically the way in which synthesis parameters can be utilized to control stoichiometry and structure. Powder neutron diffraction and SQUID magnetometry have been used to characterize several representative compounds (with 0 < x < 1) in the ternary phase system. The results show that processing conditions such as reaction time and temperature have profound effects on the levels of lithium vacancies (y) that, in a manner similar to lithium nitride (Li₃N) itself, are randomly distributed across lithium sites within the hexagonal [Li_2-yN] planes. Nickel occupies the interplanar site with lithium irrespective of the doping level, x, or the synthesis conditions applied. The magnetic behavior evolves from localized Curie-Weiss-type to delocalized Pauli paramagnetic with increased nickel substitution levels. The concentration of lithium vacancies, however, appears to have no profound effect on the magnetic and electronic properties. The results suggest that increasing y at constant x most probably leads to the formation of holes in bands with nitrogen 2p character rather than in localized nickel 3d bands.