Clustering process of the cuprate phase in Ag-added BPSCCO composites

Abstract

The clustering of cuprate grains in sintered composites of Ag-added (Bi, Pb)–Sr–Ca–Cu–O (Tc≈110 K) has been investigated in particular reference to the percolation process. The material consists of two phases: metallic grains of Ag and superconducting cuprate-grains of (Bi, Pb)2Sr2Ca2Cu3Ox (2223 phase). The resistivity ρ at 77 K is a decreasing function of Ag-volume fraction f, the contribution from the superconducting clusters being concealed. However, when the temperature T is further lowered enough, ρ changes stepwise into an increasing function, showing the obvious contribution from the superconducting clusters. This transition is realized when the superconducting weak-link is enhanced by lowering T, and is featured by the two dimensional character of the percolation process of the cuprate clusters.