EXTRINSIC CONDUCTING AND SUPERCONDUCTING POLYMER SYSTEMS .4. SUPERCONDUCTING PROPERTIES OF YBACUO COMPOSITES BASED ON PVDF/PS/CARBON BLACK AND PVDF/PS/COPPER POLYMER SYSTEMS

摘要

In this work, the critical temperature (T-c) of a series of polymeric superconducting systems is determined which, sintered or not, are obtained through the incorporation of the superconducting ceramic YBaCuO into two extrinsic conducting polymer systems: PVDF/PS/carbon black and PVDF/PS/copper. In addition, the diamagnetic characteristics of these systems are studied on the basis of susceptibility measurements as a function of temperature. As regards the unsintered systems and according to the experimental results, copper-based composites can be termed as insulating materials and the samples with the highest carbon black content as reaching metalliclike conductivities. In no case, however, is an abrupt leap in conductivity observed as a function of temperature, indicating the superconducting nature of these systems from an electrical point of view. On the contrary, magnetic susceptibility measurements as a function of temperature detect in all cases a superconducting transition, i.e., a shift in the critical temperature range, bringing it close to that of pure YBaCuO (approximate to 100 K). After sintering, the samples retained their original shape as well as reasonable mechanical properties. The electrical conductivity study confirmed the absence of superconductivity as a consequence of polymer combustion during sintering and thereby implying the disappearance of the orthorhombic phase of YBaCuO, which X-ray evidence proved to be accountable for superconductivity in this ceramic material. (C) 1996 John Wiley & Sons, Inc. [References: 16]