The temperature and oscillation frequency dependences of internal friction and shear modulus of superconducting YBa2Cu3O7- delta specimens are measured using a multifunction internal-friction torsion pendulum to study the degree of ordering and the migration of oxygen deficiency sites in the superconductor YBa2Cu3O7- delta . It is found that relaxation is most likely to occur in units where one oxygen site is surrounded by four barium ions rather than along the O-Cu-O chain. This indicates that an internal-friction study provides a powerful way of investigating the relaxation process of oxygen atoms as well as the degree of ordering of oxygen deficiencies in relation to superconductivity features.

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.

Internal friction (IF) measurement techniques are used to study high-T, superconducting cuprates. IF peaks associated with oxygen deficiency are located over a temperature range from room temperature to 623 K at frequencies from to 5 Hz. IF characteristics, i.e. activation energies, relaxation stength and ordering critical temperature, are investigated in relation to the orthorhombic-to-tetragonal transition, superconducting properties and electrical behaviour with progressively increasing oxygen deficiency, achieved through appropriate thermal cycling. Relationships between these properties are discussed and it is suggested that a fundamental connection exists between the migration of oxygen vacancies and the onset of superconductivity.