Superconductivity under high pressure of ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$${)}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (M=Fe, Co, Al, Cr, Ni, and Zn)

A survey of the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (1:2:3) and related superconductors as a function of pressure p(≤17 kbar) was made. Well-characterized samples, among them fully oxidized and oxygen-reduced 1:2:3 and Cu-substituted ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{M}}_{\mathit{x}}$ ${)}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (M=Fe, Co, Al, Cr, Ni, and Zn), were prepared according to published methods. Small pieces (∼100 mg) of the samples were measured for superconductivity using an ac mutual inductance method. For ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ little pressure dependence is observed (${\mathit{dT}}_{\mathit{c}}$/dp=-0.01±0.02 K/kbar), in agreement with most previous work. However, with substitutions M=Fe, Co, or Al, a significant positive pressure dependence of ${\mathit{T}}_{\mathit{c}}$ is observed, increasing with increasing M content. For M=Zn and Ni there is little pressure dependence of ${\mathit{T}}_{\mathit{c}}$. For an oxygen-reduced sample (δ=0.2)${\mathit{T}}_{\mathit{c}}$ increases with pressure.