Hole states in Eu0.9–xPrxCa0.1BaSrCu3O7–δ studied by X-ray absorption spectroscopy

Abstract

The hole states located on different oxygen sites have been investigated in Eu_0.9 – xPr_xCa_0.1BaSrCu₃O_7 – δ with increasing Pr³⁺ substitution by high-resolution oxygen K-edge and copper L-edge X-ray absorption spectra. The results reveal that the hole states are depleted systematically by the substitution and in turn lead to a reduction in T_c. However, the rate at which the depletion occurs is lower in Eu_0.9 – xPr_xCa_0.1BaSrCu₃O_7 – δ compared to that in Y_1 – xPr_xBa₂Cu₃O_7 – δ and Dy_1 – xPr_xBa₂Cu₃O_7 – δ. This is due to the partial substitution of Ba²⁺ by Sr²⁺ ions and R (rare earth element) by Ca²⁺ ions in the present case. The depletion of hole states gives evidence in support of the hole-depletion models based on Pr 4f–O 2p_π hybridization. The possible reasons for the anomalous behavior of Pr³⁺ ions in RBa₂Cu₃O_7 – δ are also discussed.