Bismuth Valence in a Tl0.7Bi0.3Sr1.6Ba0.4CaCu2Oy Superconductor from X-Ray Photoemission Spectroscopy

The X-ray electron photoemission spectra of a Tl0.7Bi0.3Sr1.6Ba0.superconductor were measured with Al K(alpha) and Mg K(alpha) radiation at room temperature. The Bi 4f spectrum was compared to the same spectra of Bi1.75Pb0.35Sr1.9Ca2.05Cu3.05Oy and Tl0.6Pb0.4Sr1.6Ba0.4Ca2Cu3Oy superconductors. In Bi,Pb-based superconductor only one type of Bi3+ ions is present. The Bi 4f spectrum in the Tl,Bi-superconductor consists of two contributions due to the different valences. The component from Bi5+ lines is in higher binding energy than from Bi3+. The ratio of trivalent Bi3+ to pentavalent Bi5+ 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 Bi3+ to Bi5+ is 1.87 +- 0.02.