XANES study on the evolution among different copper species, Cu~(I), Cu~(II) and Cu~(III), in CuBa_(2)YCu_(2)O_(6+z) upon oxygen loading

摘要

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 the Cu~(I) species with increasing amount of excess oxygen, z, in Cu(1)Ba_(2)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.