TEMPERATURE AND MAGNETIC-FIELD DEPENDENCE OF THE CRITICAL CURRENT-DENSITY OF YBCO WITH FINE GRAINS

We measured the critical current of thin strips of sintered YBCO deposited by electrophoresis or sedimentation on an Ag substrate. The typical granulometry of deposited samples was about 1 μm. The critical current of the samples was measured as a function of the temperature (from the transition temperature down to LHe) and of the magnetic field. The current density versus temperature and magnetic field behavior shows a number of interesting features. The current increases quadratically on decreasing temperature and the half width of the I versus B curves increases slightly, with a value in agreement with the junction size. We show that these effects can be explained in the framework of BCS theory, by modelling the material as a network of weak links with small dimensions having a normal barrier. © 1990.