The electrical transport properties of La 1−x Sr x CoO 3 (0.03 x 0.07) have been investigated using complex-plane impedance analysis and dielectric measurements with measurements of four-probe dc conductivities and magnetic susceptibilities. The temperature dependencies of the bulk conductivities obtained by impedance analysis, and dielectric relaxation processes provide evidence of the hopping conduction below 60 K, which is remarkably different from the hopping conduction in LaCoO 3 , despite the degree of doping with Sr being very small. The features in the low-doping range are: (i) the emergence of the hopping conduction at markedly lower temperatures in comparison with the case for non-doped LaCoO 3 ; (ii) the abrupt reduction of the activation energy required for the conduction, 0.042 eV at x = 0.03 to 0.021 eV at x = 0.07, from 0.34 eV for LaCoO 3 ; and (iii) a progressive decrease in the activation energy with increasing x. The difference in conduction behaviour between La 1−x Sr x CoO 3 and LaCoO 3 is due to the alternation of the spin state of Co 3+ caused by the Sr doping. The results have been discussed in terms of a process of hopping of small polarons localized by the electron-lattice interaction in tandem with the electron-magnon interaction.
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