Some diffusive properties of oxygen in Y-Ba-Cu-O systems

We have studied the diffusive properties of oxygen in Y-Ba-Cu-O systems at 940 $^{\circ}$C by measurements of the resistive response time $\tau$ of the samples subjected to the step-like increase of the oxygen pressure $\Delta p_{{\rm O}_2}\sim 1$ to 5 bars. The superconducting (SC) transition widths $\Delta T_{\rm c}$ plotted versus inverse diffusion constant $D^{-1}\sim\tau$ obey the universal linear dependence. The characteristic protruded tail of the real part of AC susceptibility which exhibits the feature at 86 K is absent in samples with the nominal composition Y$_3$Ba$_3$Cu$_6$O$_x$ (Y-336) in the regime $\tau < 3$ s as result of weakly connected grains of YBa$_2$Cu$_3$O$_{7-\delta}$ (Y-123) nucleated from decomposed Y-336 phase