Oxygen intercalation homogeneity and electrical transport in superconductingBa2YCu3O7−δcrystals

The intercalation of oxygen in twinned single crystals of ${\mathrm{Ba}}_2\mathrm{Y}{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ occurs by diffusion along basal $a-b$ planes, as shown by time-dependent resistivity measurements at elevated temperatures. Separation of the oxygen-deficient 60-K phase in crystals annealed in ${\mathrm{O}}_2$ is revealed by an anomalous temperature dependence of the resistance along the $c$ direction. Susceptibility analysis shows that oxygenation and the sharpness of the superconducting transition can be enhanced significantly, with no change in $T_c$, by $F$-ion implantation followed by rediffusion of oxygen.