The effects of calcium content and silver doping on superconductivity of (Pb0.5Cd0.5)Sr-2(Y1-xCax)Cu2O7-delta (0.3 <= x <= 0.5)

The effects of silver addition and calcium content (0.3 less than or equal to x less than or equal to 0.5) on the structural, thermal and superconduct ing properties of (Pb0.5Cd0.5)Sr-2(Y1-xCax)Cu2O7-delta have been studied. A 10 mol% Ag2O addition leads to the formation of phase-pure superconductor together with metallic silver but without impurities. The lattice constants and cell volume of the superconducting phase in the composite increase wit h the increasing calcium content. The silver-free superconductors show only onset of superconductivity (T-c,T- (onset)). As the Ca content increases, T-c,T- onset increases from 30 to 43 K (for x = 0.3-0.5) and the resistivit y behaviour before T-c changes from semiconducting to metallic in nature. A ddition of silver helps in oxygen transport, leading to the observation of zero resistance in the composites. Appreciable rise in T-c,T- onset to 57 K was found for the composite with x = 0.4. The melting point of the composi te is less than that of the corresponding parental superconductor. The pres ent study suggests the optimum calcium content of the (Pb0.5Cd0.5)-1212 sup erconductor to be around x = 0.4. For low values of the calcium content, a small amount of silver seems to substitute into the lattice of the supercon ductor.