Room-temperature oxygen diffusion and ordering inYBa2Cu3O7−ystudied with time-resolved Raman spectroscopy

Abstract

Oxygen diffusion and ordering is studied in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals as a function of time after oxygen is ejected from the surface with a strong laser pulse. Features in the Raman spectra that are sensitive to oxygen concentration and disorder are monitored by time-resolved spectroscopy. The experiments clearly show that room-temperature diffusion takes place from the bulk ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ into the oxygen-depleted ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathit{y}}$ surface. There appear to be a fast (τ1 min) lifetime to the observed features. We suggest that diffusion in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathit{y}}$, which is shown to proceed via hopping of oxygen along vacancy positions, may be aided by anharmonic features of the lattice in addition to the chemical potential gradient at the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathit{y}}$ (surface)–${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ (bulk) interface.