CRITICAL CURRENT DISTRIBUTIONS IN YBA2CU3O7-X CERAMICS

V-I curves of ten polycrystalline YBa2Cu3O7-x samples have been measured over a broad current range (< 10 A) in the temperature interval 78K-90K and at magnetic fields H < 60 Oe. Critical current density of our samples ranged from 20-250 A/cm2 (78K, H = O) which enabled us to single out the two regimes with different mechanisms limiting the measured critical current. A detailed study of the critical current distributions within the samples has also been performed. The temperature and magnetic field dependences of the parameters extracted from the critical current distribution (CCD) curves (i.e. the most probable, average and maximum critical current respectively) have been analysed. A rather successful fit of experimental CCD curves to the log-normal distribution has been performed and the relation between the CCD curve and the microstructure of the samples has been pointed out.