Structural and superconducting properties of Hg0.75Re0.25Ba2-xSrxCa2Cu3O8+delta superconductors grown by sol-gel and sealed quartz tube synthesis

The structural and superconducting properties of Hg0.75Re0.25Ba2-xSrxCa2Cu3 O8+delta (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) grown by sol-gel and sealed qua rtz tube synthesis were investigated through XRD, EDX, and micro-Roman anal ysis. They show that the efficiency of c-axis reduction caused by the Sr su bstitution depends on the environment in the (Hg, M)-O layer. The rhenium d oping produces a more rigid block that limits the Sr substitution in the Ba site more than other reported doping cations, such as lead. Superconductin g properties measurements show that the irreversibility line (IL) values de crease with increasing Sr substitution. Moreover, the IL line measurements also show that the vortex lines have a 3D behavior for all the samples with ft values in the range 2.1-1.9. Finally, resistivity measurements under hi gh pressure indicate an overdoped regime for these samples. (C) 2001 Academ ic Press.