Resistivity, giant magnetoresistance and thermopower in La0.7Sr0.3MnO3 showing a large difference in temperatures corresponding to the ferromagnetic transition and the insulator - metal transition

La 0.7 Sr 0.3 MnO 3 samples prepared by heating the precursor gel at different temperatures in the 873 – 1473 K range show nearly the same ferromagnetic transition temperature (T c ≈ 392±4 K), but the insulator-metal like transition temperatures (T p ) are significantly lower (≈ 170 K) than the corresponding T c s in the samples annealed at lower temperatures (873 K and 1073 K). Magnetoresistance shows a peak only in the sample where T p ≈ T c . Thermopower (S) is large and negative for the samples annealed at lower temperatures, but it is low, exhibiting a change of sign with temperature for the sample annealed at 1473 K.