Oxygen out diffusion in polycrystalline YBa2Cu3O7-x investigated by internal friction measurements

The anelastic behavior of YBa2Cu3O7-x (0.1 < x < 0.5) during out diffusion of oxygen has been studied in the (300-900)K range by the vibrating reed technique. To test the samples complementary X-ray diffraction analyses, SEM observations, thermogravimetric and resistivity measurements, have been performed. The anelasticity spectrum in samples with x < 0.2 shows two peaks P01, P02 at approximately 550 and 700 K at 500 Hz. The relaxation strength of P01, which was an activation energy of roughly 1.2 eV, increases strongly when x increases up to 0.44 ± 0.02, whereas, P02 strongly decreases. The dynamic modulus shows an anomalous trend at temperatures higher than 770 K perhaps indicative of the ortho-tetra transition. Isothermal measurements of the dynamic modulus have shown an exponential behavior similar to the one experienced by in-situ resistivity measurements. In this paper some hypothesis on the mechanisms giving rise to the observed peaks and to the dynamic modulus behavior in terms of oxygen content, structural changes, and thermally activated diffusional jumps are presented