Superconducting critical transitions with an onset at 112 K and zero resistance at 107 K are obtained within the Bi-Sr-Ca-Cu-O system. The synthesis and formation of the 110-K superconducting phase using the 85-K material as a precursor is explained. The 110-K phase grows from the 85-K phase such that the resulting faceted crystal (a pseudomorph) can contain some of the 85-K phase in the core. With such a microstructure our magnetic data can be simply explained. A major structural difference between the 85- and 110-K materials is that the 85-K material can grow (relatively) large single crystals having long-range order whereas the 110-K material has only intermediate-range order (cryptocrystalline) of about 100-200 Å.

• Received 29 February 1988

DOI:https://doi.org/10.1103/PhysRevB.38.2504