Electronic states in rare-earth 1:2:3 oxides: Photoemission and Raman studies

X-ray photoemission spectra (XPS) and Raman measurements of Y1-xEuxBa2Cu3O7 and Eu1-xPrxBa2Cu3O7 are compared to those of Y1-xPrxBa2Cu3O7. It is shown that, with increasing x, the binding energies of the Ba core levels of Eu1-xPrxBa2Cu3O7 shift towards higher values as in Y1-xPrxBa2Cu3O7, while those of Y1-xEuxBa2Cu3O7 do not, despite similar changes in Ba-O interatomic distances in the latter two systems. Raman measurements of Y1-xPrxBa2Cu3O7 show a frequency increase of the Ba and apical-oxygen modes with increasing x, but a much smaller frequency increase in Y1-xEuxBa2Cu3O7. The XPS and Raman results reflect changes in the Ba-O hybridization and correlate with both the suppression of superconductivity in both Y1-xPrxBa2Cu3O7 and Eu1-xPrxBa2Cu3O7, and with the retention of superconductivity in Y1-xEuxBa2Cu3O7. © 1991 The American Physical Society.