XANES study on the evolution among different copper species, Cu^I, Cu^II and Cu^III, in CuBa₂YCu₂O_6+z upon oxygen loading

X-ray absorption near-edge structure (XANES) spectroscopy at the Cu L-edge is applied to follow the gradual formation of CU^II and Cu^III species from Cu^I with increasing amount of excess oxygen, z, in Cu(1) Ba₂ YCu(2)₂ O_6+z. For the study, a series of samples with precisely controlled oxygen contents was prepared utilizing the temperature-controlled oxygen-depletion (TCOD) annealing technique in the sample synthesis and employing coulometric titration for accurate oxygen-content analysis. It may be concluded that at low amounts of excess oxygen, z, Cu(1)^I in the charge reservoir tends to be first oxidized to Cu(1)^II rather than directly to Cu(1) ^III, suggesting that complete chain formation does not occur at low oxygen contents.