Abstract
In the present investigation detailed structural, electrical, magnetic and thermoelectric measurements on bulk samples of Li-doped La1−xLixMnO3+δ (0.05 ≤ x ≤ 0.3) manganites have been done. The samples are synthesized by wet-chemical mixing route and XRD analysis using Rietveld refinement revealed single phase behaviour upto Li-concentration x = 0.25. All the samples in the present series show ferromagnetic behaviour while metallic behaviour is shown by the samples upto Li concentration x = 0.2. Beyond x = 0.2 the sample (i.e., La0.75Li0.25MnO3) show insulating behaviour for the entire temperature range accompanied by charge-order transition around T = 225 K. The low temperature resistivity data are best fitted by ρ(T) = ρ0 + ρ4.5T 4.5 + C/sinh2(hυs/2kBT), where C is a constant. Such behaviour might be an indication of the small-polaron coherent motion which involves a relaxation due to a soft optical phonon mode that is strongly coupled to the carriers. Thermoelectric power (TEP) measurements reveal interesting results showing a colossal value of −340 μV/K around 25 K for the CO sample in the present series. The probable mechanism responsible for the observed large TEP has been discussed here.
Published Version
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