MOBILITY AND ORDERING OF THE OXYGEN IONS IN SEMICONDUCTING AND INSULATING YBA2CU3O6+X

Elastic energy loss experiments were made in order to investigate the O mobility and reordering in the CuOx planes of YBa2Cu3O6+x at the low est values of x. The height of a dissipation peak with an activation e nergy of 0.11 eV, attributed to jumps of isolated oxygens, has been sh own to decrease both after severe degassing treatments in vacuum and a fter several months of room temperature ageing. The apparent inconsist ency between the high mobility of free O and the slow reordering kinet ics is discussed. The repulsive Coulomb interaction between the isolat ed O ions is proposed to have a major influence on their aggregation p robability, and consequently on the fraction of free O at equilibrium and on the time necessary for reaching it.