NMR study on the motion of Li + defects and the magnetic behavior in Li xNiO 2

Abstract

The motion of Li + defects and the magnetic behavior have been investigated by 7Li-NMR technique. The spin–lattice relaxation time T 1, the spin–spin relaxation time T 2 and the Knight shift K were measured in delithiated Li x NiO 2 from 4.2 to 650 K. The motional narrowing observed in delithiated samples above 200 K indicates that a remarkable motion of Li + defects exists. A contribution from a development of the magnetic correlation between Ni 3+ spins appeared in T 1 −1 and K below 100 K in LiNiO 2. The increase for T 1 −1 and K at low temperatures was strongly suppressed with decreasing x. This implies that nonmagnetic Ni 4+ ion produced by vacancies would cut off the magnetic correlation between inter/intra-Ni layer. The increase of vacancies promotes the motion of Li + defects and substantially varies the magnetic behavior. The magnetic relaxation process arising from Ni 3+ spins which is dominant at low temperatures changes into a relaxation process based on the motion of Li + defects with increasing temperature.