CRITICAL STATE IN THE Y-Ba-Cu-O CERAMICS

The temperature and field dependences of the Y-Ba-Cu-O ceramics susceptibility have been studied both experimentally and theoretically. These dependence have been used to reconstruct the temperature dependence of the critical current (j c (T) = j c (0)(1 − T/T c1 )3/2, j c (0) = 340 A/cm 2, T c1 = 94.6 K ) and the distribution of the granules with respect to the superconducting transition temperature (with the maximum at T c2 = 95.3 K and ∆T = 1.1 K ). Within the critical state concept diamagnetic response of the granular superconductors at fundamental and multiple frequencies has been calculated. The calculation results are in good agreement with the experimentally obtained susceptibility dependences and explain the different dependences of the diamagnetic response on the magnitude of the d.c. field and the amplitude of a.c. field.