A study of the competitive reactions occuring during the heat treatment of silver-sheathed Bi1.8Pb0.4Sr2.0Ca2.2Cu3.0Oy aerosol spray pyrolysis powder

Abstract The phase conversion reactions that occur when a fine, micron-size powder of overall composition Bi 1.8 Pb 0.4 Sr 2.0 Ca 2.2 Cu 3.0 O y (2223) is heat treated in a silver tube have been studied. We find that non-superconducting phases, particularly alkaline earth cuprates, grow more readily than the desired 2223 phase, because the activation energy for their growth (∼300 kJ/mole in air) is about a factor of five less than for the Bi 2 Sr 2 CaCu 2 O x (2212) to 2223 conversion (∼1.5 MJ/mole). A reduced oxygen partial pressure (7.5% O 2 /Ar) is found to favor the 2223 phase and CuO. The reaction to 2223 occurs preferentially at the Ag interface; continued growth occurs preferentially from the initial 2223 interface plates. The study shows that an aligned 2223 microstructure requires a smooth Ag-oxide interface and very close attention to thermal processing.