Diffusion of oxygen in superconductingYBa2Cu3O7−δceramic oxides

We have used in situ resistivity measurements to monitor the diffusion of oxygen in and out of the ceramic oxide $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. The study of out-diffusion of oxygen was carried out by annealing the oxide in ambient helium at constant heating rates and at constant temperatures. The rate of out-diffusion of oxygen has been found to be independent of $\delta$, and the resistivity changes linearly with time during isothermal anneals. Assuming that the rate of out-diffusion is surface reaction limited, we have determined a surface barrier of 1.7 eV. The study of in-diffusion of oxygen was performed by annealing the oxygen-deficient oxide ($\delta =0.38\mathrm{}$) in ambient oxygen. The in-diffusion rate was found to depend strongly on $\delta$; we have determined the activation energies of the process at $\delta =0.38\mathrm{}$ and $\delta =0\mathrm{}$ to be 0.5 eV and 1.3 eV, respectively. The diffusivity of oxygen for $\delta =0\mathrm{}$ has been determined to be $D=0.035\mathrm{}\exp (-1.3\mathrm{} \mathrm{eV}/kT)$ ${\mathrm{cm}}^2$/sec. Combining the kinetic data and published structural information, we have examined a vacancy mechanism and a twinning mechanism for anisotropic diffusion of oxygen in the CuO layer between the BaO layers.