Electrical transport properties in ＄LiMn_{2}O_{4}＄, ＄Li_{0..95}Mn_{2}O_{4}＄, and ＄LiMn_{1.95}B_{0.05}O_{4}＄ (B=Al or Ga) around room temperature

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In order to identify the carrier responsible for the electrical transport at room temperature in ＄LiMn_{2}O_{4}＄ from the viewpoint of practical applications as a cathode material, the bulk conductivity measurements by complex-plane impedance analyses have been carried out on ＄LiMn_{2}O_{4}＄ ,＄Li_{0.95}Mn_{2}O_{4}＄, and ＄LiMn_{1.95}B_{0.05}O_{4} (B=Al^{3} or Ga^{3+}＄ together with the measurements of four-probe dc conductivities and dielectric relaxation processes, because these are two candidates for the carrier, a Li ion or a nonadiabatic small polaron of an ＄e_{g}＄ electron on ＄Mn^{3+}＄. The comparison of the ionic conductivity estimated numerically from the parameters obtained experimentally for the Li-diffusion in ＄LiMn_{2}O_{4}＄ with the bulk conductivity indicates that the Li-diffusion seems difficult to play the primary role in the electrical conduction. Instead, a hopping-process of nonadiabatic small polarons of ＄e_{g}＄ electrons is likely to dominate predominantly the electrical transport properties. The dielectric relaxation process, and the activation energies and the pre-exponential factors of the bulk conductivities in ＄Li_{0.95}Mn_{2}O_{4}＄ and ＄LiMn_{1.95}B_{0.05}O_{4}＄ are explained self-consistently in terms of the polaronic conduction.
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