Power law behaviors of electrical conductivities in lithium manganese oxides

Complex impedance measurements have been performed to study electrical conducting behaviors of LiMn2O4 exposed to milling. The electrical conductivity of non-milled LiMn2O4 deviated from a typical exponent power law behavior σ(ω) = σ(0) + Aω ^ n with the exponent n = 1 and obeyed the power law with 0.6 < n < 0.8. On the other hand, in the samples exposed to milling, n decreased down to 0.3 with an increase in temperature. The temperature dependence of the ratio (log A)/n was discussed to investigate an aspect of the diffusion pathway and the activation energy barrier profile for hopping conduction. A decrease in the ratio (log A)/n was observed in milled LiMn2O4 samples. It would be related to a decrease in the number of the effective channels of the diffusion pathway due to degradation of the activation energy barrier structure. It seems that the lattice disorder induced by milling would be disadvantageous to the carrier hopping process at high temperatures in the milled LiMn2O4 samples.