Internal friction due to oxygen relaxation in superconducting YBa2Cu3O7−δ above Tc

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Abstract
YBa2Cu3O7−δ has an internal friction peak near 210 °C measured at 1.18 Hz. The shift in the temperature of this peak with frequency as measured with different internal friction techniques indicates that the relaxation process has an average activation energy of 1.14 ± 0.05 eV and a pre-exponential factor, τ0 = 1.5 × 10−13s (log τ0 = −12.82 ± 0.23). The peak height decreases during annealing at above 375 °C in helium and increases when annealed in oxygen. The mechanism for the relaxation is believed to be the stress-induced motion of oxygen atoms in the Cu–O plane. Detailed analysis shows that the internal friction peak is determined by a spectrum of activation energies; this spectrum is a symmetrical single peak 0.12 eV wide at half-height. Models for the relaxation are considered and the resulting diffusivities are compared to tracer diffusion results.