A CORE AND VALENCE LEVEL PHOTOEMISSION-STUDY OF Y1-XPRXBA2CU3O7

Core and valence level photoemission spectra of the 123 oxides Y1-xPrxBa2Cu3O7 have been measured over the complete composition range 0 < x < 1. Ceramic samples were cleaned in situ in the spectrometer UHV system by annealing in oxygen to yield clean surfaces whose atomic composition mirrored that of the bulk. No major variations in core level binding energies as a function of composition parameter were apparent. Comparison of Pr 3d core level spectra of BaPrO3 and BaPr2O4 with those of PrBa2Cu3O7 suggest a Pr(III) valence state in the 123 compound. There was a progressive increase with Pr doping in the intensity of the photoemission structure excited with 21.2 eV radiation in the upper part of the valence band. This observation is discussed in relation to the Pr 4f/O 2p mixing thought to be responsible for the metal to non-metal transition in this system.