Bismuth Valence in a $Tl_{0.7}Bi_{0.3}Sr_{1.6}Ba_{0.4}CaCu_{2}O_{y}$ Superconductor from X-Ray Photoemission Spectroscopy

The X-ray electron photoemission spectra of a $Tl_{0.7}Bi_{0.3}Sr_{1.6}Ba_{0.4}CaCu_2O_{y}$ superconductor were measured with $Al K_{α}$ and $Mg K_{α}$ radiation at room temperature. The Bi 4f spectrum was compared to the same spectra of $Bi_{1.75}Pb_{0.35}Sr_{1.9}Ca_{2.05}Cu_{3.05}O_{y}$ and $Tl_{0.6}Pb_{0.4}Sr_{1.6}Ba_{0.4}Ca_2Cu_3O_{y}$ superconductors. In Bi,Pb-based superconductor only one type of $Bi^{3+}$ ions is present. The Bi 4f spectrum in the Tl,Bi-superconductor consists of two contributions due to the different valences. The component from $Bi^{5+}$ lines is in higher binding energy than from $Bi^{3+}$. The ratio of trivalent $Bi^{3+}$ to pentavalent $Bi^{5+}$ bismuth ions was calculated from decomposition of the spin-orbit split spectrum of the Bi 4f photoelectrons. The conclusion is that Bi is present in trivalent and in pentavalent form and the ratio of $Bi^{3+}$ to $Bi^{5+}$ is 1.87 ± 0.02.