Abstract: La_(1-x)Sr_xCoO_3 has been studied by XPS. It is showed that the La 3d_(5/2) spectrum is a doublet. The peak of higher one of BE is assigned to a shake-up satellite, which results from that 2p electrons of oxygen transfer to the empty 4f orbital of lanthanum. The ratio R of the intensity of shake-up satellite to parent peak is a measure of covalency of La—O.R, and hence the covalency of La—O increases with the increasing stronium content, The R is called COVALENT FACTOR. It was found that if stronium was partly substituted for the place of lanthanum, it would influence the covalency of La—O. The covalency of Co—O decreases with the increase of stronium content, while ionicity of Co—O increases, which results in a change of reducing temperature of cobalt in La_(1-x)Sr_xCoO_3.
We succeeded in explaining the reasons of both segregation of lanthanum of LaCoO_3 and no segregation when stronium was partly substituted for the place of lanthanum.