Lithium diffusion in spinel Li4 Ti5 O12 and LiTi2 O4 films detected with 8Li β-NMR.

Diffusion of Li+ in (111) oriented thin films of the spinels Li4 Ti5 O12 and LiTi2 O4 has been studied with 8Li β-detected NMR in the temperature range between5 and 310 K. In Li4 Ti5 O12, the spin-lattice relaxation rate (1/T1) versus temperature shows a clear maximum around 100 K (=Tmax) which we attribute to magnetic freezing of dilute Ti3+ local magnetic moments, consistent with the results of magnetization and muon spin relaxation (μ+ SR) measurements. The decrease in 1/T1 with temperature above T max indicates that Li+ starts to diffuse with a thermal activation energy (Ea) of 0.11(1) eV. In LiTi2 O4, on the contrary, as temperature increases from 200 K, 1/T1 increases monotonically up to 310 K. This suggests that Li also starts to diffuse above 200 K with Ea = 0.16 (2) eV in LiTi2 O4. Comparison with conventional Li-NMR on Li4 Ti5 O12 implies that both β-NMR and μ+ SR sense short-range Li motion, i.e., a jump diffusion of Li+ to the nearest neighboring sites. [ABSTRACT FROM AUTHOR]