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

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.