High-Tc superconductor-polymer composites: YB2Cu3O7−x-polyester polymer and YBa2Cu3O7−x-Teflon

The YBa2Cu3O7−x (YBCO) superconductor powder-polyester polymer (Polimal 109) and YBCO-Teflon composites were investigated. The volume fraction of YBCO powder ranged from 0.05 to 0.8. D.c. electrical conductivity of the composites increased exponentially with increase of YBCO volume content. The I–V characteristics showed transition from ohmic to highly nonohmic behaviour at electric field intensities of about 100 V/cm. Although these composites do not show zero resistance below the superconducting transition temperature Tc of YBCO, the intrinsic diamagnetic properties of superconductor are observed. The magnetic field shielding effect indicates the superconducting transition at 90 K. The investigated composites have, at liquid nitrogen temperature, levitation properties similar to those of ceramic superconductors. The levitation force is proportional to the YBCO volume content.