The internal friction peaks in YBa2Cu3O6+x above room temperature mark the phase transformations of the system

The YBa2Cu3O6+x system exhibits internal friction peaks above room temperature. These peaks are thermally activated. When the system is fully oxygenated (x=1), one peak only is detected. At a lower oxygen content, x<0.8, this peak change in shape and position and a new one can be contemporarily detected. These peaks are reasonably linked with the crystal phases of the system. We present a sequence of measures taken on the same sample, where the evolution of these peaks is shown. (orig.)