Milling effect on the local structure, site occupation, and site migration in aluminum substituted lithium manganese oxides

摘要

Li-7 and Al-27 MAS-NMR, magnetic susceptibility, and complex impedance measurements have been performed to study the local structure and electrical resistivity in AI doped spinel LiMn2-xAlxO4 (x = 0, 0.05) exposed to a ball-milling process. The milling process decreased the effective magnetic moment of the Mn species, arising from the appearance of Mn4+, and lead to the suppression of the antiferromagnetic correlation. A hopping time and an activation energy for hopping charge carrier, estimated from electrical resistivity, relatively became larger above milling time of 2.5 h. Li-7 and Al-27 MAS-NMR spectra were dependent on milling time, and changes in the spectrum intensities were related to the distribution of Al/Li site occupation. Consequently, we concluded that structural disorder caused by the moderate milling process stimulated a migration of Al3+ ions from the 8a site to the 16d one and the increase of Li+ ions at the 8a site on the diffusion pathway. Such a mutual site migration between the 8a and 16d site for Li+ and Al3+ ions would be favorable to Li+ ion diffusion in the milled samples.