The structural and superconducting properties of (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}\mathrm{-}\mathit{y}}$${\mathrm{Ca}}_{\mathit{y}}$${\mathrm{Hf}}_{\mathit{x}}$)${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{z}}$ samples are investigated using resistivity, ac susceptibility, and dc magnetization measurements. The effect of increasing the Hf concentration in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{z}}$ lowers the oxygen content and decreases ${\mathit{T}}_{\mathit{c}}$. The substitution of Ca for Y in (${\mathrm{Y}}_{0.85\mathrm{-}\mathit{y}}$${\mathrm{Ca}}_{\mathit{y}}$${\mathrm{Hf}}_{0.15}$)${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{z}}$ provides proper matching between the ionic radius and valence of ${\mathrm{Y}}^{3+}$ (0.89 Å) and the average ionic radius and valence of ${\mathrm{Hf}}^{4+}$ (0.78 Å) and ${\mathrm{Ca}}^{2+}$ (0.99 Å). As the Ca content increases, the ${\mathit{T}}_{\mathit{c}}$ increases from y=0 (74 K) to y=0.15–0.20 (compensated oxides) having ${\mathit{T}}_{\mathit{c}}$ of 84.5–85.5 K. Magnetization measurements on powdered Hf-doped samples exhibit pronounced M(H) hysteresis loops indicative of extensive flux pinning and enhanced critical currents.

• Received 18 October 1993

DOI:https://doi.org/10.1103/PhysRevB.49.6299