AN OPTIMUM HEATING PROGRAM FOR FABRICATING MTG BI1.6PB0.4SR2CA2CU3OY SUPERCONDUCTORS

Following our recent report on the successful fabrication of ''station ary'' MTG Bi1.6Pb0.4Sr2Ca2Cu3O(y) pellets in a simple tube furnace, we have tried many heating programs with various ''crystal growth starti ng temperatures'', T(s), and sintering temperatures, T(e); the samples are sintered for 20-40 h before quenching in air. It is found that T( s)-T(e) should be rather narrow to produce good MTG samples, and the t ypical value of J(c) is enhanced from 100 A cm-2 (for a polycrystallin e sample) to about 3 x 10(3) A cm-2 for our good ones. SEM and TEM res ults indicate that the samples are full of packs which contain highly oriented mica-like layers.