Hole states in Eu_(0.9-x)Pr_xCa_(0.1)BaSrCu_3O_(7-#delta#) studied by X-ray absorption spectroscopy

摘要

The hole states located on different oxygen sites have been investigated in Eu_(0.9-x)Pr_xCa_(0.1)BaSrCu_3O_(7-#delta#) with increasing Pr~(3+) 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 deletion occurs is lower in Eu_(0.9-x)Pr_xCa_(0.1)BaSrCu_3O_(7-#delta#) compared to that in Y_(1-x)Pr_xBa_2Cu_3O_(7-#delta#) and Dy(1-x)Pr_xBa_2Cu_3O_(7-#delta#). This is due to the partial substitution of Ba~(2+) by Sr~(2+) ions and R (rare earth element) by Ca~(2+) 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_(#pi#) hybridization. The possible reasons for the anomalous behavior of Pr~(3+) ions in RBa_2Cu_3O_(7-#delta#) are also discussed.