Magnetism and lithium diffusion in Li_xCoO_2 by a muon-spin rotation and relaxation (μ~+SR) technique

摘要

Microscopic magnetism of the electrochemically Li-deintercaleted Li_xCoO_2 powders has been investigated by muon-spin rotation and relaxation (μ~+SR) spectroscopy in the temperature (T) range between 10 and 300 K. Weak transverse-field μ~+SR measurements indicate that localized moments appear in LiCoO_2 below 60 K, while both Li_(0.53)CoO_2 and Li_(0.04)CoO_2 are paramagnetic even at 10 K. Zero-field μ~+SR measurements for the samples with x = 0.53 and 0.04 show that the field distribution width (Δ) due to randomly oriented nuclear magnetic moments of ~7Li and ~(59)Co decreases monotonically with increasing T up to 250 K, and then it decreases steeper (increasing slope (dΔ/dT)) above 250 K. Because the muon hopping rate (v) is almost T independent for Li_(0.53)CoO_2 below 300 K, the decrease in Δ suggests that the time scale of Li~+ diffusion in Li_xCoO_2 is within a microsecond scale.