We have studied the x-ray-absorption near-edge spectra of EuBa2(Cu1-yZny)3O7 as a function of Zn and O content. There is clear evidence for the development of Cu1+ ions as the O content is reduced to levels sufficient to suppress superconductivity. However, there is no effect on the electronic state of the Cu ion as the Zn content is increased and superconductivity vanishes. We tentatively conclude that the suppression of superconductivity is in both cases due to the preferred occupancy of certain planes by nonmagnetic (filled d subshell) atoms, as proposed in YBa2Cu3O6 on the basis of neutron scattering.
Physical Review B (Condensed Matter) 38(4), pp.2930-2933