CRITICAL-CURRENT DENSITY ENHANCEMENT BY PHASE-DECOMPOSITION OF YBA2CU4O8 INTO YBA2CU3O7-DELTA AND CUO

Bulk YBa2Cu4O8 (Y-124) is prepared from YBa2Cu3O7-delta (Y-123) and Cu O by a powder-metallurgical method. The superconducting features of th e Y-124, in particular critical current densities and activation energ ies, are measured resistively using a four-probe technique and magneti cally using a Faraday magnetometer. In a second step the Y-124 is deco mposed at high temperatures. The intragranular critical current densit y is measured at different annealing times, t(A), in order to determin e and discuss the characteristics of the j(c)(t(A)) curves.