Internal friction and resonant frequency measurements have been carried out in YBa₂Cu₃O_7-x; after oxygen outgassing the material becomes semiconducting YBa₂{Cu}₃O₆ 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 eV/kT) cm²/sec, which extrapolated to room temperature is comparable with that of hydrogen in transition metals.
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Cannelli et al. (1988) studied this question.
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