ELECTRONIC STRUCTURAL DIFFERENCES OF RBA2CU3O6.1 (R=Y, PR AND ND) SINGLE-CRYSTALS PROBED BY SOFT-X-RAY ABSORPTION-SPECTROSCOPY

A systematic polarization dependent O1s-NEXAFS study of large RBa2Cu3O 6.1 (R = Y, Pr and Nd) single crystals has been performed using the no n-surface sensitive fluorescence yield detection method. The results s how the energetic position, symmetry and density of empty p (hybrid) s tates on the oxygen sites. The density of empty Pr4f-O2p and Nd4f-O2p hybrid states for PrBa2Cu3O6.1 and NdBa2Cu3O6.1 just above E(F) is ver y low, but large for the energy range 3-8 eV above E(F). As the energe tic position and density of these empty states appears to be almost id entical, there is no evidence for differences between the Pr4f-O2p and Nd4f-O2p hybridization. For these tetragonal materials this result in dicates that the Pr valence value is very close to the valence value o f the Nd ions, that is 3+. In addition, this suggests that the average Pr-O bond length in PrBa2Cu3O6 is not as short as reported for PrBa2C u3O7 and therefore that the Pr4f-O2p hybridization is possibly differe nt in the two cases.