Copper valency and anion p band holes in the perovskite superconductor YBa2Cu3O7

Abstract Results of photoelectron spectroscopy studies on a molecular Cu (III) complex are compared with those of the perovskite type high T c superconductor YBa 2 Cu 3 O 7 . The evidence from the Cu 2p core level spectra is compatible in terms of formal valency assignments with a model that involves the presence of trivalent copper with strongly covalent Cu/O interaction as the minority Cu component. Attempts to obtain a spectroscopic prove for the simultaneous existence of anion p band holes (critical valence state model) turned out to be inconclusive as a consequence of surface effects.