Pressure dependence of $T_c$ to 17 GPa with and without relaxation effects in superconducting ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$

Hydrostatic high-pressure studies to 17 GPa were carried out on superconducting ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$ over the full range of oxygen content x. The observed bell-shaped $T_c\mathrm{}\left(P\right)\mathrm{}$ dependences are found to depend markedly on the temperature at which the pressure is changed. The time-dependent relaxation processes are studied using both $T_c$ and the electrical resistivity at 298 K as probes. The activation volume for oxygen diffusion is determined from the pressure-dependent activation energy and compared with estimates from a simple hard-sphere model.