Superconductivity and oxygen ordering in (Ca,Ba,La)Cu3O7−δ

Magnetization measurements on polycrystalline samples with nominal composition ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{\mathit{x}}$ ${\mathrm{Ba}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{La}}_{\mathit{x}}$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (x=0.0, 0.05, 0.10, 0.50, and 1.0) show that only samples with x=1.0 or 0.0 contain a single superconducting phase. Gas evolution experiments on (Ca,Ba,La)${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (x=1.0, δ∼0.07) reveal the presence of an oxygen phase that is indistinguishable from the oxygen chain structure of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (x=0.0, δ∼0.05); however, the total amount of evolved oxygen is very different between the two phases. These studies suggest that two phases coexist in (Ca,Ba,La)${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$: a superconducting phase in which ${\mathrm{La}}^{3+}$ ions occupy the ${\mathrm{Y}}^{3+}$ sites, and a second nonsuperconducting phase where ${\mathrm{Ca}}^{2+}$ ions occupy the ${\mathrm{Y}}^{3+}$ sites.