Comparative photoemission studies of Bi_2-xPb_xSr₂Ca_n-1Cu_nO_2n+4+y (n = 2, 3)

Abstract

XPS and UVPES studies of Bi2212, BiPb2212 and BiPb2223 have been carried out. Shifts in various core levels are observed as we move from Bi2212 to BiPb2223. Core level shifts indicate that the main oxidation states of Bi and Pb are III and IV, respectively, in all the three compounds. The Pb4f core lines show two components indicating their inequivalent sites. The mixed occupancy of Ca and Sr is clearly shown in the spectra. The decrease in ionic character from two to three CuO₂ layer bismuth cuprates is explained on the basis of satellite to main line intensity ratio and the energy separation between the main line and satellite of the Cu2p core level. The valence band moves towards the Fermi level in BiPb2223 as compared to Bi2212. Our results are compared with band structure calculations of Bi2212 and we suggest possible reasons for the ambiguities of O2s resonant photoemission in Bi2212.