Correlation of superconductivity with ‘‘oxygen dimer’’ peak in photoelectron spectra from YBa2Cu3−xCoxO7−y

Abstract

X-ray photoelectron spectroscopy of YBa2Cu3−xCoxO7−y (0<x<0.4) shows a systematic change in the O 1s and Cu 2p3/2 regions as a function of x. Three peaks in the O 1s spectra at 528.5, 531, and 532.7 eV are seen for x=0 which are assigned to O2−, O1−, and O2−2 ions, respectively. As x is increased, the relative intensity of the O2−2 or O1− to the O2− peak decreases and the Cu2+ fraction increases showing a correlation with the decrease in the superconducting transition temperature. The result is interpreted in terms of Co ions substituting for the Cu ions in the chain with the Co ion in octahedral coordination.