Bismuth Valence in a Tl_0.7Bi_0.3Sr_1.6Ba_0.4CaCu₂O_ySuperconductor from X-Ray Photoemission Spectroscopy

Abstract

The X-ray electron photoemission spectra of a Tl 0.7 Bi 0.3 Sr 1.6 Ba 0.4 CaCu 2 O y superconductor were measured with Al K and Mg K 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 2 Cu 3 O 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.