Cu K-Edge Study of (Tl_(0.5)Pb_(0.5))Sr_2Ca_(1-x)Y_xCu_2O_(7-δ)

Near-edge x-ray-absorption spectra at the Cu K-edge has been measured for (Tl_(0.5)Pb_(0.5))Sr_2Ca_(1-x)Y_xCu_2O_(7-δ) compound series. It is found that both the intensity of the quadruple 1s → 3d transition feature and the edge-energy decrease with increasing x. Our results show that the Cu valence decreases slightly with the substitution of Ca^(+2) by Y^(+3). This result, together with recent O K-edge result the O-2p holes are reduced by the substitution, indicates that electronic charge is transferred into the entire CuO_2 layers by the Y^(+3) for Ca^(+2) substitution.