MECHANICAL AND SUPERCONDUCTING PROPERTIES OF BIPBSRCACUO-PE AND BIPBSRCACUO-MGO COMPOSITES

In this work it is shown that the inherently weak mechanical propertie s of monolithic high-temperature superconductors can be improved by pr ocessing the superconductor into a composite. Both polyethylene (PE) a nd MgO were used to prepare a composite material with BiPbSrCaCuO (BSC CO) superconductors. Three-point bending tests were conducted on monol ithic BSCCO, 50 vol% BSCCO-PE and 50 vol% BSCCO-MgO particulate compos ites. As expected, the PE composites exhibited an increased ductility in comparison with the monolithic material and a decreased flexural mo dulus, while the flexural strength remains comparable with that of mon olithic BSCCO. Although the presence of a resistive percolation path c ould be demonstrated at and below room temperature, zero resistivity a t T < T-c was not observed and the magnetic expulsion force diminished after processing. Magnetic measurements show that this is due to poor intergrain coupling. In contrast to the PE composites, the BSCCO-MgO composites can be re-sintered after mixing. This provides an opportuni ty for the material to regain the intergrain couplings and results in the recovery of zero resistivity at 110 K and in magnetic expulsion du e to intergrain currents. Mechanical measurement on the MgO composites showed a decrease in ductility, an increased flexural modulus and a c omparable flexural strength.