Stoichiometry and pressure dependence of Tc of YBa2Cu3Ox

We report on the systematic investigation of the pressure dependence of the transition temperature $\drm T_{\rm c}/ \drm p$ of ${\rm YBa}_2{\rm Cu}_3{\rm O}_x$ as a function of the oxygen content x. The samples from the 60 K plateau have shown a pressure dependence $\drm T_{\rm c}/ \drm p$ in the order of 0.4–0.5 K/kbar. Giant pressure effects have been found for the oxygen stoichiometries $x= 6.7-6.8$. Most astonishingly, the 90 K samples have revealed a variety of pressure effects systematically changing with the oxygen content. We have found a correlation of structural parameters and $\drm T_{\rm c} /\drm p$ in the oxygen range $x= 6.8-7$