Bulk superconducting ${\mathrm{Y}}_2$${\mathrm{Ba}}_4$${\mathrm{Cu}}_7$${\mathrm{O}}_{15\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ prepared in oxygen at 1 atm

Synthesis of bulk ${\mathrm{Y}}_2$ ${\mathrm{Ba}}_4$ ${\mathrm{Cu}}_7$ ${\mathrm{O}}_{15\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ high-${\mathit{T}}_{\mathit{c}}$ superconductors at atmospheric pressure, without the addition of alkali rate enhancers, is reported. The superconducting transition temperature for ${\mathrm{Y}}_2$ ${\mathrm{Ba}}_4$ ${\mathrm{Cu}}_7$ ${\mathrm{O}}_{15\mathrm{-}\mathrm{\delta }}$ is shown to depend on oxygen stoichiometry, with the resistive onset observed above 90 K. The ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ phase has zero resistance ${\mathit{T}}_{\mathit{c}}$ close to 80 K. A modified Y-Ba-Cu-O P-T phase diagram is presented.