Photoemission Study of Bi2Nd0.5Ca2.5Cu2Oy and Bi2(La,Pr)0.5Ca2.5Cu2Oy Superconductors

X-ray photoelectron spectra (XPS) of Cu 2p have been studied for oxygen- and air-sintered samples of Bi2(La,Pr)0.5Ca2.5Cu2Oy and Bi2Nd0.5Ca2.5Cu2Oy. We estimated the number of Cu 3d electrons, n d , and charge transfer energy, Δ, from these results. We point out the possibility that the difference of T C between these compounds with the same doped hole concentrations is associated with the difference of n d . The role of the Cu 3d – O2p charge transfer in superconductivity is discussed.