Abstract
We report the results of electrical resistivity, magnetic susceptibility andthermoelectric power measurements on the stoichiometric hole-dopedLa0.8Ca0.2MnO3 andelectron-doped La0.8Ce0.2MnO3 manganites. The resistivity and thermopower data show a metal–insulator phase transitionfor both samples. Magnetic susceptibility measurement confirms that both the samplesundergo a transition from paramagnetic to ferromagnetic phase at defined Curie temperaturesTc = 240 K(La0.8Ca0.2MnO3) and263 K (La0.8Ce0.2MnO3). The electrical resistivity data are then theoretically analysed within the framework of theclassical electron–phonon model of resistivity, i.e. the Bloch–Gruneisen model. Detailed analysisof the electrical resistivity of electron- and hole-doped manganites suggests that besides theelectron–phonon effect another possibility for the change in carrier density arises due to thepresence of electron correlation in the metallic system. From the thermopowerS(T) results, we suggest that its behaviour is determined by competition among the severaloperating scattering mechanisms for the heat carriers and a balance between carrierdiffusion and phonon drag contributions in the polycrystalline samples of hole-dopedLa0.8Ca0.2MnO3 andelectron-doped La0.8Ce0.2MnO3 manganites.
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