Study on annealing treatment and Sr/Ca ratio for Pb-Sr-Y-Ca-Cu-O ceramics with 1212 structure

The annealing effects of “1212” lead cuprate in a Pb-Sr-Y-Ca-Cu-O system were investigated. Samples with a nominal composition of (Pb 0.7 Cu 0.3 )Sr 2 (Y 1- x Ca x )Cu 2 O y ( x =0.4-0.7) were annealed at various temperatures in oxygen. The x =0.5 sample, which was annealed at 800°C and then quenched, exhibited the highest T c (zero resistivity) of 48 K. It was found that there were three different types, two tetragonal phases and one orthorhombic phase, in the “1212” of x =0.5. It was considered that the phase transformation was caused by different oxygen contents. Samples with a nominal composition of (Pb 0.7 Cu 0.3 )Sr 2+ z (Y 0.5 Ca 0.5- z )Cu 2 O y ( z =±0.3) were also prepared. Deviation from z =0.0 in the composition induced degradation of the superconductivity.