FORMATION OF HIGH-T-C PHASES OF THE SYSTEM BI-PB-SR-CA-CU-O IN A FLUXED KCL MELT

The influence of the conditions of synthesis and annealing on the rati o of the volumes and the temperature T-c(n) at which transition to the superconducting state begins is investigated on the basis of diamagne tic susceptibility measurements and x-ray phase analysis for bismuth 2 212 and 2223 phases obtained from solution in a KCl melt. It is found that the value of T-c(n) for the 2212 phase decreases as the temperatu re and the holding time are increased in synthesis. The 2212-2223 tran sition in the fluxed KCl melt takes place in the presence of an oxygen deficiency, and the width of the transition interval to the supercond ucting state of the 2223 phase depends on the cooling rate of the flux ed melt after isothermal holding and also on subsequent annealing in a ir. Temperatures T-c(n) = 107 K,90 K, and 20 K are observed for unanne aled crystals of the 2223 phase with average dimensions 50 X 50 mu m. Air annealing leads to oxygen saturation of their lattice, and T-c(n) = 107 K throughout the entire structure of the crystal. (C) 1997 Ameri can Institute of Physics.