INDUCTIVE MEASUREMENTS OF INTERGRANULAR CRITICAL CURRENTS IN CERAMIC RINGS - A COMPARISON BETWEEN SINTERED AND MELT PROCESSED Y-BASED, BI-BASED AND TL-BASED SUPERCONDUCTORS

A comparative study of superconducting properties at T = 77 K and T = 4.2 K was made between ceramics prepared by conventional sintering techniques and ceramics which were melt processed. The field dependence of the critical current was determined by means of an inductive method. Using ring shaped samples the intergranular currents can be unambiguously separated from the intragranular currents since the magnetic flux shielded by the screening current circulating in the ring is monitored instead of the magnetization. Values for j(c) obtained this way are in good agreement with results from resistive measurements of the same sample. Except for Bi2Sr2CaCu2O8+delta all our sintered materials show weak link behaviour. Melt processing was favourable for Tl2Sr2Ca2Cu3O10+delta and especially for Bi2Sr2CaCu2O8+delta, but led to poor intergrain current densities in YBCO.