Superconductor-Insulator Transition in Composite Granular (1−n)Gd123-nPr123 and (1−m)Gd123-mPrBa123

Abstract

Granular composite samples of GdBa2Cu3O7−δ (Gd123), PrBa2Cu3O7−δ (Pr123), and Pr0.5Ba0.5Ba2Cu3O7−δ (PrBa123) have been prepared by the solid state reaction technique. The characterization of samples has been done by SEM and XRD measurements. We have investigated the effect of Pr123 and PrBa123 insulating grains on the superconductor-insulator transition and the normal state resistivity of the (1−n)Gd123-nPr123 and (1−m)Gd123-mPrBa123 systems. The dominant diffusion of Pr ions onto the neighboring Gd123 grains in (1−n)Gd123-nPr123 causes high rate of suppression of superconductivity similar to the chemical-doped GdPr123 system. For (1−m)Gd123-mPrBa123 system, the suppression rate is slower and we have superconducting sample with Tcmid = 41 K for the second phase of m = 0.6 sample. Comparison of the superconductor-insulator and metal-insulator transitions in the granular samples and the chemical substituted GdPr123 indicates optimization of the superconducting state in (1−n)Gd123-mPrBa123 relative to (1−n)Gd123-nPr123 and GdPr123 systems. The more stable characteristic of PrBa123 relative to Pr123, when they are mixed with Gd123 grains, makes PrBa123 more suitable for any superconductor-insulator application. The mechanism of suppression of superconducting state for Pr123 has been discussed by comparison of experimental results against the hole filling and hole localization models presented for the insulating Pr123.