Superconductivity and antiferromagnetism in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{1+\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_{6\pm \mathrm{\delta }}$ and ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CaCu}}_2$${\mathrm{O}}_{6\pm \mathrm{\delta }}$

L${\mathrm{a}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_6$ can be made superconducting by doping Ca or Sr in the form of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$(Sr,Ca${)}_{\mathit{x}}$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{6+\mathrm{\delta }}$ and by synthesis under high ${\mathrm{O}}_2$ pressures of more than 4 atm. Superconducting properties of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{1+\mathit{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{6\pm \mathrm{\delta }}$ (0.08≤x≤0.25) and ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{6\pm \mathrm{\delta }}$ (0.07≤x≤0.23) as functions of composition (x) and oxygen partial pressure during synthesis (${\mathit{P}}_{\mathrm{O}2\mathrm{}}$ up to 400 atm) were investigated by measuring their electrical resistivity and magnetic susceptibility. In both compounds, the superconducting transition temperature (${\mathit{T}}_{\mathit{c}}$) increased with increasing x and ${\mathit{P}}_{\mathrm{O}2\mathrm{}}$, and showed almost the same maximum ${\mathit{T}}_{\mathit{c}}$ (zero) of about 51 K at the solubility limit of Ca or Sr in La (x≊0.25) with ${\mathit{P}}_{\mathrm{O}2\mathrm{}}$ at 400 atm, although at a lower ${\mathit{P}}_{\mathrm{O}2\mathrm{}}$, ${\mathit{T}}_{\mathit{c}}$ (zero) was higher in a Sr-doped compound than that of a Ca- doped compound. Nonsuperconducting or weakly superconducting ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{1+\mathit{x}}$ ${\mathrm{Cu}}_2$