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L4.09 - Oxygen Surface Exchange Kinetics in Epitaxial Thin Films Studied by Time-Resolved X-Ray Diffraction 
Date/Time:
April 23, 2014   11:30am - 12:00pm
 
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The study of the kinetics of oxygen exchange in transition metal oxides is of increasing relevance for understanding the fundamental mechanisms for oxygen reduction and evolution reactions (ORR/OER) of oxide catalysts as well as for novel cathode materials for intermediate-temperature solid oxide fuel cell (SOFC) technology.In most transition metal oxide materials the variation in the oxygen stoichiometry produced by oxygen exchange with the atmosphere is often accompanied by subtle cell volume changes. Generally, the incorporation of charged defects (oxygen vacancies or interstitials) is expected to cause a cell expansion from the equilibrium intrinsic cell because of variations in the radii of the transition metal ions as well as Coulomb repulsion between those defects. Any slight variation in the oxygen content would proportionally result in a measurable volume increase. The ability to dynamically follow the cell volume variations allows establishing a direct correlation with oxidation/reduction kinetics. In this talk we will describe recent development of a new methodology to analyze oxygen surface kinetics in epitaxial thin films by using X-ray diffraction time-resolved measurements in conventional lab diffractometer [1]. With this technique we have been able to measure average cell parameter changes as small as 0.1 ppm in a time scale of a few seconds in a variety of SOFC cathode materials like La2NiO4+d, GdBaCo2O5+d and Ba0.5Sr0.5Co0.8Fe0.3O3-d, as well as in epitaxial bilayers. We will describe the usefulness of this methodology as complementary to other well-established techniques such as Electric Conductivity Relaxation (ECR) and 18O Isotopic Exchange Depth Profiling (IEDP) experiments. [1] R. Moreno, P. García, J. Zapata, J. Roqueta, J. Chaigneau and J. Santiso, Chem. Mater. 25 (2013) 3640-3647
 


 
 
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