Evidence was found for a very high mobility of isolated O atoms in the Cu(1)-O basal planes of the tetragonal material, Cu3Ba2YO6.2. Jumps of isolated O atoms between the O(4) and O(5) positions were expected to give rise to an easily detectable anelastic relaxation process. A recently reported elastic energy dissipation peak (63K, 1.1kHz) had been attributed to this mechanism. From this, it was deduced that O diffusion in the basal plane could be described by:

D (cm2/s) = 0.0004 exp[-0.11(eV)/kT]

The present measurements showed that all of the anelastic processes which occurred above room temperature, in orthorhombic Cu3Ba2YO7, disappeared in Cu3Ba2YO6.2. This confirmed that the low-temperature peak was due to the diffusion of free O.

G.Cannelli, R.Cantelli, F.Cordero, M.Ferretti, F.Trequattrini: Solid State Communications, 1991, 77[6], 429-31