Nuclear magnetic relaxation rates and line-widths were determined for the 7Li and 93Nb resonances in the layered compound. The Li long-range hopping rate was determined as a function of temperature. Rotating-sample experiments showed that the frequency dependence of the Li spin-lattice relaxation rate at low resonant frequencies resulted from cross relaxation to the quadrupole-broadened 93Nb spins. An important aspect of the cross relaxation was a large frequency variation of the 93Nb transitions which resulted from the diffusion of Li vacancies. The 93Nb relaxation rates were shown to support both the cross relaxation and the Li hopping interpretations. In the presence of high magnetic fields, cross-relaxation was suppressed and the 7Li and 93Nb spin-lattice relaxation rates differed by 3 orders of magnitude. The frequency and temperature dependences of the high-field relaxation rates indicated that the relaxation mechanisms were not associated with diffusive Li motion. In the case of both Li and Nb, almost linear temperature dependences of T1-1 resulted from interactions with conduction electrons. The electrons were believed to be due to the acceptor-like behavior of Li vacancies. A much lower 7Li relaxation rate reflected the existence of a much smaller electron density (at the Fermi surface) at Li sites than at Nb sites. Sample-to-sample variations in the Li ion mobility and in the Nb relaxation rate were suggested to reflect variations in the Li deficiency of the material.

A.F.McDowell, D.M.Snyderman, M.S.Conradi, B.G.Silbernagel, A.M.Stacy: Physical Review B, 1994, 50[21], 15764-74