Electrical conductivity relaxation studies of oxygen transport in epitaxial YBa2Cu3O7-δ thin films

The oxygen transport behavior in c-axis-oriented YBa₂Cu₃O_7-δ films has been investigated by means of electrical conductivity relaxation measurements. The oxygen surface exchange coefficients have been determined from the out- and in-diffusion when the oxygen partial pressure was switched between pO₂ = 0.01 atm and 0.02 atm at temperatures of 773 K to 873 K. The results are described by a model in which oxygen molecules dissociated at two different surface sites, diffuse rapidly along the grain boundaries which act as "chimneys." The bulk stoichiometry then adjusts by fast diffusion in the ab-planes. The overall transport kinetics are limited by the surface reactions. The activation energy for both surface exchange controlled processes are ∼ 1.0 eV. An understanding of the effects of grain boundaries on the transport properties of thin YBCO films is important for the potential application of these materials.