“…Previous works on O 1s spectra of YBC sintered pellets also showed signals that could be decomposed into many peaks. 17,20,23,24 The main peak (E b D 528 eV) corresponds to bonding with Y, Ba and Cu in the superconducting phase, whereas the 530.4 eV peak can be related to the change of composition at surfaces or interfaces as discussed previously. Surface species close to BaO or Cu 2 O are expected because O 1s binding energies for these oxides are given at…”