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Dissertation Abstract

Dissertation by Christopher T. Jones
Dissertation Title: Hybrid High Temperature Superconductor / Conducting Polymer Systems

Hybrid systems of high-temperature superconductors and conducting polymers have been assembled and their properties assayed. Studies were conducted on several systems including bilayer thin film assemblies, particle composites, and intercalation materials. Crucial to the preparation of these ceramic / polymer composites is the availability of a pristine high-temperature superconductor surface and the identification of new synthetic methods that are capable of combining in an intimate manner these two different phases of electronic material. Surface corrosion and crystallographic orientation of the superconductor are found to be important variables which influence the polymer / cuprate charge transfer characteristics. To prepare many of the polymer composites described herein electrodeposition methods were employed. In this context, self-assembled monolayers were found to dramatically affect growth and the surface morphology of electrochemically deposited polypyrrole on bulk and thin film superconductors of YBa₂Cu₃O_7-x. Conductivity experiments were performed to measure the temperature dependence of resistivity, superconducting transition temperature, and critical currents before and after polymer deposition as well as before and after polymer doping. Modulation of the transition temperature in superconducting / conducting polymer bilayer assemblies was accomplished by oxidative and reductive doping of the conducting polymer. These bilayer systems were used to create a “molecular switch” for lowering and raising the transition temperature of the superconductor. As another method for preparing composite polymer / superconductor structures, the intercalation of polypyrrole into the lattice of various Bi Sr Ca Cu O phases was accomplished by vapor phase exposure of iodine intercalated Bi Sr Ca Cu O with pyrrole monomer. X-ray powder diffraction was used to assess the structural changes which occur upon pyrrole exposure. Likewise, an increase of a 3.5 Å in the distance between adjacent bismuth oxide layers was noted following this treatment. Furthermore, scanning electron microscopy was used to characterize the surface properties of these systems. These studies have given insight into the synthesis and properties of hybrid superconductor / conducting polymer assemblies.