THE LOCAL VARIATION OF CA2PBO4 IN THE CORE OF (PH,BI)(2)SR2CA2CU3OX SUPERCONDUCTING TAPES DURING THERMAL-PROCESSING WITH DIFFERENT HEATING RATES

We present the results of an investigation into the variation in the a mount of the secondary phase, Ca2PbO4, during the thermal processing o f silver-sheathed (Pb,Bi)2Sr2Ca2Cu3Ox tapes. It has been found that, a fter an initial fast decrease in Ca2PbO4, there is an incubation perio d, of 20 hours for heating rate 2 degrees C/hr and 30 hours for heatin g rate of 60 degrees C/hr, during which the amounts of both (Pb,Bi)222 3 and Ca2PbO4 remain unchanged. After this period the amount of Ca2PbO 4 phase decreases simultaneously with the increase of (Pb,Bi)2223 phas e.