Site Occupancies of Sr and Ca Ions in Bi₂(Sr_1-xCa_x)₃Cu₂O_y Studied by Photoemission Core-Level Spectroscopy

Abstract

The range of Sr/Ca substitution for the formation of a superconducting 2212 phase in sintered Bi 2 (Sr 1- x Ca x ) 3 Cu 2 O y has been examined by X-ray powder diffraction. It has been found that the 2212 monophase is formed in the range 1/3≤ x ≤0.6. X-ray photoelectron spectra (XPS) of Sr3 d and Ca2 p core levels of these samples can be decomposed into higher- and lower-binding-energy components. They are attributable to Sr and Ca ions occupying the cation sites of SrO and Ca layers of the 2212 phase. The interrelation between the two spectral components of each ion and the two kinds of occupation sites is examined, and the distribution probabilities of the Sr and Ca ions on these sites are evaluated.