New anelastic relaxation effect in Y-Ba-Cu-O at low temperature: A Snoek-type peak due to oxygen diffusion

Internal friction and resonant frequency measurements have been carried out in YBa2Cu3O7-x; after oxygen outgassing the material becomes semiconducting YBa2Cu3O6 and the anelastic processes observed in the superconducting samples are suppressed. Instead, a new intense effect appears: The process is thermally activated (shifting from 56 to 75 K when the frequency changes from 1.1 to 17.4 kHz) with an activation energy Es=0.11 eV, and is only 25% broader than a single relaxation time process. It is attributed to the stress-induced hopping of residual free oxygen and the derived diffusion coefficient is D=4×10-4exp(-0.11 eVkT) cm2/sec, which extrapolated to room temperature is comparable with that of hydrogen in transition metals.