OXYGEN MOBILITY IN YBA2CU3O7-DELTA

The aim of this experimental study is to characterize the oxygen mobil ity in CuO confined planes in the high T-c superconductor YBaCuO by me ans of a very low frequency mechanical spectroscopy technique allowing measurements in a temperature range where the oxygen concentration re mains stable. For oxygen-rich specimens corresponding to the orthorhom bic I phase we observe a single relaxation peak. The measured activati on energy E(I) varies between 0.8 and 1.3 eV and is a complex function of the oxygen concentration. For less rich oxygen contents a second r elaxation peak is observed coexisting with the first peak. Its energy E(TII) is about 1.10 eV, independent of the concentration. A model of oxygen jumps in CuO planes is proposed to explain these results.