GROWTH AND PROPERTIES OF EPITAXIAL FERROELECTRIC SUPERCONDUCTOR HETEROSTRUCTURES/

Epitaxial trilayer heterostructures of YBa2Cu3O7-delta/BaXSr1-XTiO3/YB a2Cu3O7-delta, with x=0.25-0.90, were grown on silicon-on-sapphire buf fered with CeO2 and Y-ZrO2. The top and bottom YBa2Cu3O7-delta films w ere c-axis oriented, micro-crack free and had superconducting transiti ons T-c's in the range 86-90K. A thin antidiffusion layer of SrTiO3 (d approximate to 70 Angstrom) between YBa2Cu3O7-delta and BaXSr1-XTiO3 improved the quality of the top superconducting film. The maximum valu es of the permittivity of the BaXSr1-XTiO3 layers were observed around the Curie temperatures of corresponding bulk monocrystals. The dielec tric permittivity of the BaXSr1-XTiO3 (x=0.25-0.75) layers depended st rongly (approximate to 20%) on an applied voltage (+/-2.5 V) at temper atures around 77 K. The dielectric loss of the thin films was much hig her than for corresponding bulk crystals.