Oxygen diffusion in epitaxial ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ thin films

In situ resistance changes of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ thin films during deposition were investigated at four different substrate temperatures in the 560–700 °C range. The shapes of the resistance curves with time and the measurement of deposition rates clearly indicated that the film grew epitaxially on the (100)${\mathrm{SrTiO}}_3$ substrate at 700 °C. Isothermal oxygen diffusion along the c-axis direction into the epitaxially grown ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ thin films was investigated by monitoring in situ resistance changes in the 450–600 °C range; the apparent diffusion coefficients were (3.1–6.3)×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^2$/s. An Arrhenius plot of the diffusion coefficients in the 450–550 °C range gave an activation energy of 0.33 eV for oxygen diffusion plus a tetragonal-orthorhombic phase transition.