Substitution sites of Pb and Y in Bi₂Sr₂Ca₁Cu₂O_8+δ : X-ray photoelectron diffraction as fingerprinting tool

The substitution site of Y and Pb in the cuprate-type high temperature superconductor Bi₂Sr₂Ca₁Cu₂O_8+δ is determined in a very direct and unambiguous way by means of angle-scanned x-ray photoelectron diffraction (XPD). Using XPD as a fingerprinting tool, we conclude that Y occupies the Ca sites and Pb the Bi sites, respectively. Furthermore, low-energy electron diffraction data unequivocally show the presence of the incommensurate lattice modulation which is known for pure Bi2212, but not for sufficiently Pb doped Bi2212. We can, therefore, attribute the reappearance of the modulation directly to the Y doping.