X-ray photoelectron spectroscopic study of the high-Tc superconductor YBa2Cu3O7 –x: evidence for Cu3+ and surface oxygen excess

Abstract

Samples of the superconducting oxide YBa₂Cu₃O_{7 –x}, prepared by conventional powder processing routes, have been studied by X-ray photoelectron spectroscopy. The quenched material shows considerable surface excess of oxygen; comparison with Y–Cu–O preparations indicate that the oxygen excess is associated with the presence of barium. High-T_c oxide preparations which were introduced into the spectrometer immediately after removal from the furnace gave unequivocal evidence for the presence of Cu³⁺.