X-ray photoelectron spectroscopy investigation on chemical states of oxygen on surfaces of mixed electronic–ionic conducting La0.6Sr0.4Co1 yFeyO3 ceramics

The chemical state of oxygen on the surfaces of mixed electronic–ionic conducting La0.6Sr0.4Co1 yFeyO3 ceramics was characterized by X-ray photoelectron spectroscopy (XPS). It was ascertained that there are five different kinds of oxygen on the ceramic surfaces, including lattice oxygen (OL), chemisorbed oxygen (OC) in the forms of O2 , O , and O2 , and oxygen in hydroxyl environment (OH). The concentration of OC þ OH relative to total detected oxygen enhanced with the increase of Co/ Fe ratio. In order to examine the relation between the chemical states of oxygen on the surfaces and the electrical nature of the ceramics, the mixed electronic–ionic conducting properties were investigated. At an identical measuring temperature, the electronic conductivity and ionic conductivity of La0.6Sr0.4Co1 yFeyO3 ceramics tended to rise with the increase of Co/Fe ratio. It was considered that the mixed electronic–ionic conducting properties are responsible for the complex chemical states of oxygen on the ceramic surfaces. # 2004 Elsevier B.V. All rights reserved.