<i>In-Situ</i>EELS Analysis of Cobalt Valence in La_1-xSr_xCoO_3-y

Abstract Transition and rare earth metal elements have played a vital role in synthesis of functional and smart materials because of their unique electronic structures and mixed valences. Experimental measurement of the valence states is thus important for understanding the mechanism which drives the functional properties. Lai1.xSrxCoO3-y(LSCO), for example, is an ionic conductor with potential applications in fuel cells and many other fields. In this type of materials, the anion deficiency is directly associated with the ratio of Co2+/Co3+ (or Co3+/Co4+) present in the specimen. It is known that the anion deficiency of the material depends on the operation temperature, but a direct measurement of anion deficiency is a challenge to existing microscopy techniques. In this paper, we present the in-situ analysis of Co valence in LSCO using electron energy-loss spectroscopy (EELS) in a transmission electron microscope. LSCO thin films (with x = 0.5) were grown on polished MgO(00l) substrate by liquid source metal-organic chemical vapor deposition (MOCVD) method [1].