We have demonstrated the presence of a single-phase solid solution for the ${\mathrm{Bi}}_2{\mathrm{Sr}}_{3-x}{\mathrm{Ca}}_x{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ superconductor, in the $1.25\le x\le 2.0$ range. The lattice parameters and melting points vary monotonically with $x$, both increasing towards the Sr-rich composition. This monotonic variation of the lattice parameters extends into the $0.8\le x\le 2.2$ range, but the material is multiphased outside the $1.25\le x\le 2.0$ limit. Superconducting onsets in the ranges of 70-89 and 108-118 K have been obtained; however, the exact results are very sensitive to processing parameters. Magnetization measurements indicate high intragranular current densities ($J_c$) at 5 K of ∼5×${10}^6$ A/${\mathrm{cm}}^2$. The actual transport $J_c$ is low (≅ 70 A/${\mathrm{cm}}^2$ at 4 K) and exhibits a strong field dependence similar to the behavior of the Y${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ superconductor.

• Received 21 March 1988

DOI:https://doi.org/10.1103/PhysRevB.38.757