Desorption of oxygen from ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ films studied by Raman spectroscopy

Phonons of laser-deposited ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$ films on MgO(100) substrates are investigated in a Raman setup as a function of laser power density. Investigations of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ films allow us to study oxygen out-diffusion, where the onset of out-diffusion is indicated by the appearance of disorder-induced modes in the Raman spectra. At a pressure of 5×${10}^{\mathrm{-}6}$ mbar the temperature threshold of the out-diffusion is (490±15) K. With increasing oxygen pressure the observed temperature thresholds rise only moderately in contrast to the behavior expected from the ${\mathit{p}}_{\mathrm{ox}}$-T phase diagram of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$. Even at 1 bar oxygen partial pressure out-diffusion is observed and tetragonal sites with x=0 develop. These observations can be explained by photon-stimulated desorption of oxygen. Investigations of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$ films allow us to study oxygen in-diffusion. In 1 bar oxygen we observe competing oxygen fluxes due to thermally activated diffusion and photon-stimulated desorption. From these measurements we determine an upper bound of the thermal activation energy of the oxygen in-diffusion into ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$ films of (0.19±0.01) eV. © 1996 The American Physical Society.