Thermostability and decomposition of the (Bi,Pb)2Sr2Ca2Cu3O10 phase in silver-clad tapes

Abstract
The stability of the Bi2−x Pb x Sr2Ca2Cu3O10 (Pb‐2223) phase contained in silver‐sheathed oxide‐powder‐in‐tube specimens has been investigated by x‐ray diffraction,transmission electron microscopy, and energy dispersive x‐ray analysis.Silver tubes loaded with Pb‐2223 precursor powders were processed into tapes using established metallurgical techniques. The tapes were heat‐treated in a specially designed equilibration apparatus at selected temperatures (800–845 °C) for a range of times (10–5500 min) and quenched in liquid gallium held at ∼40 °C. The results showed that the Pb‐2223 phase is stable in a limited temperature interval between 810 and 830 °C in 7.5% oxygen. At 800 °C, this phase decomposes to Bi2Sr2CaCu2O8 (2212), Ca2PbO4, and CuO; while at temperatures ≥840 °C it partially melts with precipitation of Bi2Sr2CuO6 (2201) and Ca2CuO3. The effects of the silvercladding on the Pb‐2223 phase stability and microstructure are also discussed.