Melt processing of the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ superconductor in oxygen and argon atmospheres

Solidification and subsequent annealing of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O/sub 2/ and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutectic structure of Bi/sub 2/Sr/sub 3-x/Ca/sub x/O/sub y/ and Cu/sub 2/O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi/sub 2.15/Sr/sub 2/Ca/sub 0.85/Cu/sub 2/O/sub y/.<>