Oxygen mobility and phase transformations in RBa2Cu3O6+x

The anelastic relaxation processes in RBa2Cu306+X observed above room temperature and those attributable to 0 diffusion have been reviewed. taking into account the whole range of 0 stoichiometries. The thermally activated processes have been correlated with the dynamics of 0 in the CuOx planes. The processes above room temperature have been explained in terms of jumps of 0 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 0 ordering and some observed phase transformations has been discussed.