Ordered and Disordered Defects in Perovskite Related Structures With An Emphasis on Superconducting Oxides

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This research is a continuation of ongoing investigation of the defect structure and electrical properties of the perovskite- related oxide ceramics. Materials in the lanthanum-copper oxide system will be investigated during this grant period. Experimental techniques, such as equilibrium electrical conductivity at constant oxygen activity and constant chemical composition, coulombic titration, electron microscopy (including selected area diffraction, dark field imaging, and latticing, will be used to give quantitative information on defect concentrations, conduction mechanisms, and on the defect ordering that occurs in some of these materials. A domain model at the nanostructure level has been proposed to explain the observed behavior of partially-oxidized, acceptor-doped, members of the related strontium-iron-titanium oxide system. These materials are remarkably similar to the superconducting oxides in both compositional and structural type. An improved understanding of the nature of the defect structure and its relation to electrical properties of these materials will lead to an improved understanding of the mechanisms of superconductivity.