The percolation limit and weak link effects on the superconducting phase transition in high temperature superconductors

The parameters controlling the intergranular percolating network of the new class of high temperature superconductors have been studied using a novel method to control specimen composition as the percolation limit is approached. The form of the resistive transition in two-phase composites formed from Y2BaCuO5 and YBa2Cu3O7-δ is shown to be complex and that processes occuring in each of a number of temperature ranges are discussed. Microbridges formed from these materials show characteristics which are determined by the weak-link structure and display features related to the resistive transition of the bulk material.