X-ray absorption spectroscopic study on Bi₂Sr₂Ca_1-xY_xCu₂O _8+δ (x = 0-1)

The X-ray absorption near edge spectra for Bi₂Sr₂Ca_1-xY_xCu₂O _8+δ (x = 0-1) have been investigated at Cu K- and Bi L_III-edges. Upon the substitution of Y for Ca, overall edge of Cu K-edge XANES spectra shifts towards the lower energy side, indicating the decrease of the formal Cu valence state. The more detailed fine structure was studied from the second-derivative Cu K-edge XANES spectra, and it was suggested that the Cu-O bond distance increases with the substitution of Y³⁺ for Ca²⁺. There is no noticeable energy shift in Bi L_III-edge XANES spectra. This is not consistent with the previously reported results. But in our case, invariant spectra upon the substitution of Y might be due to the charge transfer along the Cu-O-Bi bond as well as the amount of the incorporated excess oxygen. The Cu K-edge EXAFS spectra for the present compounds showed average Cu-O bond distance to increase upon the substitution of Y, which is consistent with the Cu K-edge XANES results.