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 $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$; 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 ${E}_{s}=0.11$ 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 $D=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\mathrm{exp}(\ensuremath{-}0.11 \frac{\mathrm{eV}}{\mathrm{kT}})$ ${\mathrm{cm}}^{2}$/sec, which extrapolated to room temperature is comparable with that of hydrogen in transition metals.

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