SUPERCONDUCTIVE CRITICAL-TEMPERATURE DEPRESSION IN THE (BI,PB)2SR2CA2CU3O10+DELTA(2223) PHASE BY POSTSINTER QUENCHING

Changes in Tc resulting from variations in the post-sintering cooling rate, from liquid quenching to slow air cooling, were investigated for the 2223 phase in the Bi-Pb-Sr-Ca-Cu-O system with a nominal composition of Bi1.6Pb0.4Sr2Ca3Cu4Ox. Complex ac susceptibility measurements were used to identify the critical temperatures of the high-Tc, 2223 and the low-Tc, 2212 phases, as well as those of the bulk material. Tc of the granular 2223 phase decreased from 107 K to 93 K after fast quenching. Similar treatment, however, raised Tc of the 2212 phase from 63 K to 80 K. The opposing behaviors of these two superconducting phases, associated with variations in oxygen stoichiometry resulting from different cooling rates, and their effects on bulk Tc values are discussed. © 1990.