OXYGEN SELF-DIFFUSION COEFFICIENT IN THE SUPERCONDUCTOR YBA2CU3O7-DELTA FROM INTERNAL-FRICTION MEASUREMENTS

The internal friction of YBa2Cu3O7-δ is measured at 7.8, 40, and 144 kHz as a function of temperature (from 300 to 1100 K) and oxygen partial pressure. At 40 kHz a marked damping peak occurs at ∼800 K which is attributable to oxygen hopping in the basal plane. The oxygen diffusion coefficient calculated from the hopping relaxation time is in good agreement with other estimates yielding an activation enthalpy, h m=1.07±0.05 eV and D0=1.8×10-4 cm2/s. At a critical value of δ∼0.25 the diffusion coefficient begins to rise rapidly similar to the occurrence of a fast-ion transition.