Rapid Formation of the 110 K Phase in BI-Pb-Sr-Ca-Cu-O through Freeze-Drying Powder Processing

Three techniques for processing Bi‐Pb‐Sr‐Ca‐Cu‐O (BPSCCO) powders were investigated: dry‐mixing, sol‐gel formation, and freeze‐drying. It was found that sintering for 120 h at 850°C is required to form nearly single‐phase (Bi,Pb)2Sr2Ca2Cu3O10‐y by dry‐mixing, whereas sintering for 30 h at 840°C was sufficient to form the 110 K (2223) phase when freeze‐drying was used. The sol‐gel route was found to be intermediate in efficiency between these two techniques. Freeze‐drying provided highly reactive, intimately mixed, and carbon‐free precursors. The presence of carbonates in the uncalcined powders was the major cause of phase segregation and sluggishness of the 110 K phase formation.