ANELASTIC MEASUREMENTS OF DEFECTS RELATED TO SUBSTITUTIONAL PR IN Y0.7PR0.3BA2CU3O6+X

We measured the elastic energy dissipation of Y0.7Pr0.3Ba2Cu3O6+x betw een 50 and 930 K at various O concentrations. All the features observe d in RBa(2)Cu(3)O(6+x) were substantially reproduced in the partially Pr substituted sample. In addition, a new dissipation peak was observe d around 400 K (0.7 kHz), due to a relaxation process with an activati on energy of similar to 0.8 eV. The peak width is about twice that of a single relaxation process, and its intensity is maximum when most of oxygen is removed from the CuOx planes. It is proposed that the proce ss involves a configuration of three O atoms around a same Cu(1), whic h is supposed to be stable only in a cell containing a Pr ion.