Effect of Lead Loss and Sheath Structure on Phase Formation and Alignment in (Bi,Pb)₂Sr₂Ca₂Cu₃O_10+δ/Ag Composite Conductors

The effects of metallic constituent evaporation and sheath structure on grain growth and alignment in silver‐sheathed (Bi,Pb)₂Sr₂Ca₂Cu₃O_10+δ (Bi‐2223)/Ag composites have been investigated by inductively coupled plasma/atomic emission spectroscopy (ICP/AES), X‐ray diffraction, scanning electron microscopy, and energy dispersive X‐ray spectroscopy. Specimens of Bi‐2223/Ag composites fabricated by the oxide‐powder‐in‐tube technique were peeled (opened) lengthwise to expose the ceramic powder core, and then heat‐treated in 0.075 atm of oxygen for selected temperatures and times. The results were compared with those for as‐processed samples with closed silver sheaths treated under identical conditions. ICP/AES analysis indicated that lead was the only metallic element to undergo substantial evaporation during annealing of opened samples. The lead‐release process in parallel with the Bi‐2223 formation reaction had an activation energy of ∼25 kJ/mol. Lead loss from the opened samples resulted in incomplete conversion to Bi‐2223. The combined results show that the silver sheath effectively prevents evaporative lead loss, preserves and promotes densification, and induces texturing of the layered phases.