Dynamics of oxygen and phase transitions in the 123 ceramic superconductors by anelastic relaxation measurements

The existing measurements of elastic energy dissipation and modulus on RBa 2 Cu 3 O 6+x have been reviewed and the possible mechanisms have been discussed taking into account the whole range of temperatures and O stoichiometries. Most of the processes have been correlated with the dynamics of O in the CuO x planes: those above room temperature to jumps of O bound in chains and ordered domains, and those at low temperature with hops between off-centre positions within the chains. Free oxygen in the diluted tetragonal phase has a mobility which is anomalously high for an oxide. Phase transformations are observed both above and below room temperature, and have been discussed in connection with the relaxation processes.