Elastic energy-loss experiments were performed on Cu3Ba2YO6+x samples in order to investigate O mobility on CuOx planes, for x-values which were close to zero. The height of a peak with an activation energy of 0.11eV, which had previously been attributed to jumps of isolated O atoms (Snoek effect), was shown to decrease after severe de-gassing treatments in vacuum or after several months of room-temperature aging. Attention was focused on the apparent paradox that the extremely high mobility of isolated O atoms contrasted with the slow re-ordering kinetics and relatively high fractions of isolated O atoms which were estimated from the height of the dissipation peak below 100K. An explanation was proposed, in order to resolve these inconsistencies, which was based upon Coulomb repulsion between isolated O ions. It was estimated that the binding energy of an O atom to a chain was equal to about 0.25eV in the highly dilute tetragonal phase. An alternative interpretation was expressed in terms of polaron hopping for the same 0.11eV relaxation process.

G.Cannelli, R.Cantelli, F.Cordero, N.Piraccini, F.Trequattrini, M.Ferretti: Physical Review B, 1994, 50[22], 16679-83