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 $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$; after oxygen outgassing the material becomes semiconducting Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$ 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 $E_s=0.11\mathrm{}$ 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 $D=4\mathrm{}\times {10}^{-4\mathrm{}}\exp (-0.11\mathrm{} \frac{\mathrm{eV}}{\mathrm{kT}})$ ${\mathrm{cm}}^2$/sec, which extrapolated to room temperature is comparable with that of hydrogen in transition metals.