Magnetoresistance and Microstructure of Manganite Ceramics La_0.6Sr_0.4MnO₃ Sintered with Various Oxide Additives

Abstract

We investigated the change in magnetoresistive properties with the change in microstructure of manganite ceramics with nominal chemical composition of La_0.6Sr_0.4MnO₃ by sintering them with various additives. SiO₂, CuO, V₂O₅, or Bi₂O₃ were selected as the additives. The average size of grains of the ceramic samples with additives increased in comparison with that of the sample without additives. The result indicates liquid phase sintering for the samples with additives. The samples with additives have a perovskite-phase and various second phases, and their lattice constants were slightly different from those of the sample without additives. It is supposed for the samples with additives except the sample containing CuO that the ratio of La/Sr changes with the addition of the above oxides. It is also supposed that Cu was introduced to the B-sites of the perovskite-type structure, which is confirmed by the fact that the ferromagnetic transition temperature of the sample is 13 K lower than that of the sample without additives. The differences in the chemical compositions between the sample without additives and those with additives were roughly estimated to be within 10%. The temperature dependences of the electric resistivity and magnetoresistance of the samples were different from each other. The results were thought to originate from the difference in the microstructure from the slight difference in the chemical composition of the perovskite-phase in the samples.