LOCAL DISORDER IN THE OXYGEN ENVIRONMENT AROUND PR IN Y1-ZPRXBA2CU3O7AS MEASURED BY X-RAY-ABSORPTION FINE-STRUCTURE

We present K-edge x-ray absorption fine structure (XAFS) data, for and the local structure of several Y1-xPrxBa2Cu3O7 alloys. Most of the Pr substitutes onto well ordered Y sites. The amplitude of the first Pr- O peak is greatly reduced when compared to the first Y-O peak. Fits to standards suggest that some oxygen atoms around the Pr become disorde red. Most of the Pr-O distances are about 2.45 Angstrom, but 15-40% of them are in a somewhat broadened peak at about 2.27 Angstrom. The exi stence and the size of these two bond lengths is consistent with a hyb ridization of Pr3+, Pr4+, and (Pr3+ - hole-in-the-ligand) bonds and a formal valence of about 3.33+ for the Pr ion.