THE INTERNAL-FRICTION PEAKS IN YBA2CU3O6-TEMPERATURE MARK THE PHASE-TRANSFORMATIONS OF THE SYSTEM(X ABOVE ROOM)

The YBa2Cu3O6+x system exhibits internal friction peaks above room tem perature. These peaks are thermally activated. When the system is full y oxygenated (x=1), one peak only is detected. At a lower oxygen conte nt, 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 c rystal phases of the system. We present a sequence of measures taken o n the same sample, where the evolution of these peaks is shown.