XPS Study on the Electronic Structure of Bi2Sr2Ca1-xNdxCu2Oy

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Abstract
XPS core level and valence band spectra of sintered Bi2Sr2Ca1-x Nd x Cu2O y which manifests a superconducting to semiconducting phase change around x=0.5 have been measured. The fraction of Cu1+ to the total Cu ions evaluated from Cu2p spectra amounts to 7% in Bi2Sr2CaCu2O y , but decreases to 0% with increasing Nd content. From Ca2p, Sr3d, Nd3d, Bi4f and O1s spectra, it is inferred that Ca2+ and Sr2+ are mixed and distributed over both Ca and SrO layers, whereas Nd3+ and Sr2+ are rather separate. From the valence band spectra, a finite density of states at E F is deduced for Ca-rich oxides, but it diminishes in Bi2Sr2NdCu2O y . The analysis of ionic configurations based on the mixed valencies of copper and oxygen ions gives a consistent account of the above spectra and the superconductor to semiconductor transition.