it is suggested that the variation of the internal friction (IF) characteristics of a single-phase YBCO specimen resulting from an increase of oxygen deficiency d is associated either with an ordeiing diffusioii process between iayers, or with an order/disorder diffusion process in the Cu (2) plane. The experimental results are explained in the light of these oxygen-vacancy migration processes. The essential connections between high-T, superconductivity, electric behaviour and oxygen-vacancy ordering are discussed.

The anelastic relaxation of lithium tantalate crystal is studied by using a multifunction inverted torsion pendulum. A relaxation internal friction (IF) peak is observed in the temperature range 100 degrees C to 350 degrees C and the orientation, domain and oxygen-deficiency effects on the IF peak are studied. The activation energy of this process is determined to be 1.26+or-0.02 eV and the IF peak is shown to be associated with the stress-induced anelastic motion of the electric domain boundaries.