用XPS对La1-xSrxCoO3的研究

本文用XPS对La_(1-x)Sr_xCoO_3进行了研究, 发现在La_(1-x)Sr_xCoO_3中La 3d_(5/2)的伴峰与主峰之比可以做为La-O共价性的量度。此比值R定义为“共价性因子”。我们利用成键共价性和离子性这个概念解释了La在LaCoO_3中的表面偏析以及锶部分取代镧的位置后, 阻止了La_(1-x)Sr_xCoO_3中镧的偏析, 并且说明了随x增加钴还原温度升高的原因。

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF La1-xSrxCoO3

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.