Reaction Sequencing During Processing of the 123 Superconductor

This paper presents reaction sequencing studies conducted for two precursors to the 123 superconductor in air and helium environments. In air, the reactants in both precursor systems produce an intermediate 123 phase at 1000 K without going through the BaCuO{sub 2} and Y{sub 2}BaCuO{sub 5} intermediate phases, observed in earlier work with mixed powder precursors. In helium, the fully developed 123 tetragonal phase is formed at temperatures as low as 880 K, but it also decomposes to Y{sub 2}BaCuO{sub 5}, BaCu{sub 2}O{sub 2}, and BaCuO{sub 2}; the extent of decomposition depends on the temperature. The 123 tetragonal phase completely decomposes by 1075 K, but it can be reformed if the atmosphere is switched back to air at a temperature above 950 K.