Valence determination as a function of doping in PrBa2Cu3O7

We present results of x-ray absorption near edge spectra (XANES), neutron powder diffraction, and resonant x-ray diffraction on samples of PrBa2Cu3O7-delta and Pr1-xCaxBa2Cu3O7. The data are obtained as a function of the doping levels of oxygen and Ca. There are significant changes in the Pr L-3 XANES spectra with changes in oxygen or Ca concentrations, indicating that the Pr electronic properties are affected by doping. The resonant x-ray scattering experiments show that the changes observed occur on Pr ions incorporated in the PrBa2Cu3O7-delta structure, and are not the result of changes to a Pr-containing impurity phase. A quantitative model, based on Literature precedent, is used to extract Pr valences from the data, although the XANES cannot distinguish between models involving charge transfer and those involving hybridization. The results are compared with data obtained from Pb2Sr2Pr1-xCaxCu3O8. The implications of these experiments are discussed in view of the exceptional magnetic and electronic properties of PrBa2Cu3O7-delta.