LOW-FIELD BEHAVIOR OF CRITICAL-CURRENT IN SM1-X-BA2-CU3-O7-DELTA CERAMIC SUPERCONDUCTOR(X)

The transport critical current I(c) carried by ceramic Sm1-xBa2-Cu3+x- O7-delta (SBCO) superconducting samples (prepared by the coprecipitati on technique using organic carbonate in the presence of stable polymer ) in low magnetic fields (0-100 Oe) have been investigated at differen t temperatures close to the critical transition temperature T(c). A si gnificant reduction of the transport current-carrying capacity has bee n observed for magnetic fields smaller than the lower critical field H (cl). A semilog plot of the field dependence of the transport critical current density J(ct) reveals a well-defined field value H(c)' charac teristic of a crossover between regions dominated by the inter- and in tragranular effects. Microwave measurements show evidence of a reducti on in the total number of weak links between the network of the superc onducting grain structure for Cu-rich-SBCO samples. The enhancement of J(tc) for Cu-rich SBCO samples is due to the increase in hole concent ration caused by partial replacement of Sm by Cu which caused physical densification between the network of superconducting grain structure in SBCO.