(${\mathrm{Yb}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$) (${\mathrm{Ba}}_{0.8}$${\mathrm{Sr}}_{0.2}$${)}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{z}}$ (0≤x≤0.4) solid solutions of the ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{z}}$ (‘‘1:2:3’’) -type structure were successfully synthesized. The solid-solution samples were characterized with respect to the oxygen content, crystal structure, and superconducting properties. The ‘‘fully oxygenated’’ samples with z∼0.8 were prepared employing postannealing at high oxygen partial pressure atmosphere [P(${\mathrm{O}}_2$)=400 atm]. The samples had orthorhombic unit cells and showed bulk superconductivity. The superconducting transition temperatures (${\mathit{T}}_{\mathit{c}}$’s) ranged from 80 to 32 K, depending on the Ca content. Samples with x=0.1 and 0.3, and various oxygen contents (0.36≤z≤0.89 for x=0.1 and 0.10≤z≤0.78 for x=0.3) were prepared by employing quenching and annealing techniques. For (${\mathrm{Yb}}_{0.7}$${\mathrm{Ca}}_{0.3}$) (${\mathrm{Ba}}_{0.8}$${\mathrm{Sr}}_{0.2}$${)}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{z}}$, as the oxygen content z decreased, ${\mathit{T}}_{\mathit{c}}$ increased from 40 K first, then peaked at 82 K at z=0.56, and decreased down to 48 K at z=0.10. The relationship between ${\mathit{T}}_{\mathit{c}}$ and the hole concentration in the ${\mathrm{CuO}}_2$ sheet, ${\mathit{p}}_{\mathrm{sheet}}$, was obtained. ${\mathit{T}}_{\mathit{c}}$ was maximum at ${\mathit{p}}_{\mathrm{sheet}}$=0.18 for both samples with x=0.1 and 0.3.

• Received 15 January 1991

DOI:https://doi.org/10.1103/PhysRevB.44.2341