Oxygen mobility and phase transformation in RBa2Cu3O6+x

The anelastic relaxation processes in RBa2Cu3O6+x observed above room temperature and those attributable to O diffusion have been reviewed, taking into account the whole range of O stoichiometries. The thermally activated processes have been correlated with the dynamics of O in the CuOx planes. The processes above room temperature have been explained in terms of jumps of O bound in chains and ordered domains. Instead, the only stable process in the dilute tetragonal phase occurs below 100 K and it has been attributed to the jumps of free oxygen; the resulting free oxygen mobility is anomalously high. The possible connection between O ordering and some observed phase transformations has been discussed. (orig.)