Effect of gamma-irradiation on the electronic structure of (Bi_1.65Pb_0.35)Sr₂Ca₂Cu₃O₁₀ superconductor

An XPS investigation was carried out on (Bi_1.65Pb_0.35)Sr₂Ca₂Cu₃O₁₀ superconductors, in an effort to study the effect of gamma-irradiation. There is no significant change in the binding energies of Bi 4f, Ca 2p, Cu 2p, O 1s, Pb 4f, and Sr 3p core levels up to the gamma dose of 50 Mrad. However, for the gamma dose of 60 Mrad, the Bi 4f region shows two sets of spin-orbit split levels, one set at about 1.3 eV lower and the other at about 1.7 eV higher binding energies than that of the low-dose samples. Furthermore, for this high-dose sample, (i) the O 1s region clearly shows the evidence of the removal of O by gamma irradiation and (ii) the Cu 2p region shows no satellite, which is typical of Cu²⁺ valence states and a low energy shoulder that is a signature of Cu¹⁺ valence states, in contrast to the low-dose samples. These observations suggest a reduction of hole-concentration in the Cu-O planes through the O removal at a gamma dose between 50 and 60 Mrad.