TEMPERATURE-DEPENDENCE OF CRITICAL CURRENTS IN YBA2CU3O7-DELTA CERAMICS

The temperature dependence of critical currents in YBa2Cu3O7-delta superconducting ceramics have been studied following the Ginzburg-Landau theory and the de Gennes proximity effects for a superconductor-normal-conductor interface. Based on an S/N/S weak-link model, critical currents as a function of temperature have been calculated and a model able to describe different kinds of I(c)-T characteristics in 1:2:3 ceramics has been developed. A set of four YBa2Cu3O7-delta ceramic samples has been prepared for experimental studies. These samples were annealed under different conditions. Critical currents as a function of temperature have been measured in a high-heat-transfer system. I(c)-T characteristics ranging from a quadratic temperature dependence to a temperature dependence of the Josephson-tunneling type have been observed. The experimental I(c)-T characteristics fit very well theoretical predictions which include the effects of randomness in the thickness of the nonsuperconducting barriers and the boundary conditions for tbe samples.