CORRELATION BETWEEN THE ELECTRIC-FIELD EFFECT AND WEAK-LINK TYPE IN YBA2CU3-XOY AND YBA2CU3-XOY AG-X HIGH-T-C SUPERCONDUCTING CERAMICS/

An experimental study is reported of the effect of an electric field E less than or equal to 120 MV/m and of temperature T on the critical c urrent I-c and I-V characteristics of yttrium-based high-T-c supercond ucting ceramics. The materials studied were copper-deficient ceramics, YBa2Cu3 - xOy (D samples), and YBa2Cu3 - xOy/Ag-x ceramics [S samples with silver present in amounts equal to the copper deficiency (0 less than or equal to x less than or equal to 0.4)]. It has been establish ed that in D samples at 77 K, the electric field increases I-c and red uces substantially R for I > I-c, whereas in S samples no field effect is observed. Measurements of the I-c(T) dependence near the critical temperature showed that they can be described for all samples by a rel ation of the type I-c = const(1 - T/T-c)(alpha), where alpha approxima te to 1 for the D samples, and alpha approximate to 2 for the S sample s. The results obtained suggest that the electric-field effect correla tes with the existence in the ceramic of SIS-type weak links at grain boundaries. (C) 1998 American Institute of Physics.