A low-frequency internal friction peak was observed at 200 °C for sintered ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ bar specimens annealed at different temperatures between 400 and 650 °C. This peak is interpreted in terms of diffusional jumps of oxygen atoms in the basal planes between sublattice sites ${\mathrm{O}}_{\mathrm{A}}$((1/2, 0,0) and ${\mathrm{O}}_{\mathrm{B}}$(0,(1/2,0). These two sites are not crystallographically equivalent in orthorhombic symmetry. Oxygen diffusivity for planar diffusion in the basal planes was derived on the basis of a one-dimensional random-walk process, which yields: D=((1/4)$d^2$$C_B$/($C_A$+$C_B$)ν ${\nu }_0$ exp(-$H_B$/kT) =$D_0$exp(-$H_B$/kT), where $H_B$=$H_A$+ΔE. The parameters $C_A$, $C_B$, ${\nu }_0$, and $H_A$ are evaluated from internal friction data for the specimens of known oxygen deficiency x and ΔE, the poten- tial energy difference between sites ${\mathrm{O}}_{\mathrm{A}}$ and ${\mathrm{O}}_{\mathrm{B}}$, from Boltzmann’s distribution law $C_A$/$C_B$=exp(-ΔE/kT). The preexponential factor $D_0$=3.5×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^2$/sec and the activation energy of the 200 °C internal-friction peak $H_A$=1.03 eV are both temperature insensitive. By contrast, ΔE is temperature dependent; it is 0.23 eV at 400 °C and decreases as the temperature is raised, vanishing at 670 °C, the temperature of the orthorhombic-to-tetragonal transition temperature at which ${\mathrm{O}}_{\mathrm{A}}$ and ${\mathrm{O}}_{\mathrm{B}}$ sites become indistinguishable. Non-Arrhenius behavior exists between the oxygen diffusivity and the diffusion temperature in this type of diffusion mechanism.

• Received 30 January 1989

DOI:https://doi.org/10.1103/PhysRevB.40.4549