A spectroscopic study on the existence of Cu³⁺ OR O^2-₂ in the superconducting YBa₂Cu_3-xCo_xO_7±δ phase

YBa₂Cu_3-xCo_xO_7±δ (x = 0.1 and 1.0) samples were prepared by thermal decomposition of nitrates in order to investigate the peroxide-ion which may exist in the Cu(1) plane between Ba layers. In the YBa₂Cu₃O₇ structure, peroxide-ion due to oxygen dimerization may be formed both (1) by the disordering of the oxygen in the Cu(1) plane and (2) by the introduction of oxygen in excess of O_6.5. These requirements for peroxide formation are satisfied in the system YBa₂Cu_3-xCo_xO_7±δ (x = 0.1 and 1.0). From iodometric titration, the oxygen content for tetragonal YBa₂Cu_3-xCo_xO_7±δ (x = 0.1 and 1.0) was determined to be 6.93 and 7.26 with superconducting (T_c = 56 K) and semiconducting behavior, respectively. Compared with the typical oxygen binding energy of peroxides (B.E. = 533 eV) in the X-ray photoelectron spectra, no peroxide-ions were stabilized in the YBa₂Cu_3-xCo_xO_7±δ lattice. In addition, colorimetric analysis also supports the absence of peroxide-ion in the YBa₂Cu_3-xCo_xO_7±δ system even at high cobalt concentration.