Fast oxygen mobility in tetragonal YBa2Cu3O7-x by anelastic relaxation measurements

Evidence of a very high mobility of the isolated O atoms in the Cu(1)-O basal planes of tetragonal YBa2Cu3O6.2 is reported. The jumps of the isolated O atoms between the O(4) and O(5) positions are expected to give rise to a well detectable anelastic relaxation process, and a recently reported elastic energy dissipation peak in YBa2Cu3O6.2 (63 K, 1.1 kHz) was attributed to this mechanism, resulting in an O diffusion coefficient in the basal plane of 4 × 10-4exp(-0.11 eV kT) cm2/sec. Measurements are produced here which show that all anelastic processes above room temperature in orthorhombic YBa2Cu3O7-x disappear in YBa2Cu3O6.2, confirming that the low temperature peak is indeed due to the diffusion of the free oxygen