Study on Electric Resistivity and Thermoelectric Power in (La0.8Ca0.2)MnO3-y

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Abstract
Electric resistivities and thermoelectric powers of the system (La 0.8 Ca 0.2 )MnO 3- y were measured in several samples with y less than 0.07, in which the amounts of the oxygen deficiencies y were carefully controlled. The electrical conduction at T > T c ( T c denotes the magnetic transition temperature) is of an activation type, while at T < T c , it changes from a degenerate type to an activation type with increasing y . The thermoelectric power at T > T c is proportional to 1/ T in all samples and that at T < T c shows a metalic behavior in the samples with y =0.00 and 0.025. The activation energy estimated from the electric resistivity at T > T c is about three times larger than that estimated from the thermoelectric power. These experimental results are discussed on the basis of the conventional semiconductor model.