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Intern: Ryan Haggerty, UCSB Mentor: Eric Toberer Faculty Supervisor: Ram Seshadri Department: Materials Research Laboratory

THE EFFECT OF NONSTOICHIOMETRY ON THE CRYSTAL STRUCTURE OF La0.5Sr0.5CoO3-x

The ceramic La0.5Sr0.5CoO3-x has the ability to form with varying amounts of oxygen while retaining its perovskite structure. As the temperature is raised, the diffusion of atoms in the crystal lattice becomes more favorable. Oxygen vacancies move through the lattice of La0.5Sr0.5CoO3-x to form an equilibrium with the oxygen partial pressure at each interface. This is known as oxygen ion conduction. The combination of oxygen ion and electrical conductivity makes La0.5Sr0.5CoO3-x an ideal cathode material in solid oxide fuel cells. Bulk samples of La0.5Sr0.5CoO3-x with varying x have been prepared by solid state synthesis. The concentration of oxygen vacancies has been determined through oxidation reduction titrations. The structure of the samples was then characterized using powder X-ray diffraction in order to find a relation between the structural properties and the amount of oxygen vacancies in the material. These studies complement existing work on magnetron-sputtered thin film samples of the same material.

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