O K-edge and Cu L-23-edge XANES study on the concentration and distribution of holes in the (Pb2/3Cu1/3)(3)Sr-2(Y, Ca) Cu2O8+z superconductive phase - art. no. 184507

By means of high-resolution O K-edge and Cu L-23-edge x-ray:absorption near -edge-structure spectroscopy continuous increase of the CuO2-plane hole con centration with increasing Ca-substitution level has been established for t he superconductive, oxygen-depleted (z approximate to0) (Pb2/3Cu1/3)(3)Sr-2 (Y1-xCax)Cu2O8+z. [(Pb2/3Cu1/3)-3212] phase with a three-layer PbO-Cu-PbO c harge-reservoir block. For the O K-edge absorption, a pre-edge peak at simi lar to 528.3 eV is seen, originating from the. excitation of the O 1s elect ron to the O 2p hole state located in the CuO2 plane. With increasing Ca-su bstitution level, the intensity of this peak continuously increases within the substitution range studied, i.e., 0 less than or equal tox less than or equal to0.5. Consistently, with increasing x, the shoulder on the high-ene rgy side of the main absorption peak at similar to 932.0 eV in the Cu L-23- edge spectra, i.e., a feature typically assigned to formally trivalent copp er, enhances. From the Cu L-23-edge spectra it was furthermore confirmed th at the charge-reservoir copper remains in the monovalent state, indicating that the holes created through Ca substitution are directed solely into the superconductive CuO2 plane. In terms of increasing the CuO2-plane hole con centration, Ca substitution;vas found to work more efficiently in (Pb2/3Cu1 /3)-3212 as compared to, e.g., the related Bi-2212 phase.