X-ray-photoelectron-spectroscopy evidence for peroxide in 1:2:3 copper oxides containing disordered or excess oxygen

Abstract

The x-ray-photoelectron-spectroscopy of several layered oxides provide no Cu(2p) evidence for Cu(III), but exhibit an extra O(1s) peak where direct contact between oxygen atoms occurs within the Cu(1) planes of the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ structure. The extra peak has a binding energy typical of that for a peroxide ion (${\mathrm{O}}_2$ ${)}^2$. This observation, in conformity with earlier prediction, provides compelling evidence for holes in the O 2p bands of the high-$T_c$ copper-oxide superconductors.