Electronic structure study of the formal oxidation state of bismuth in copper-oxide superconductors containing Bi-O double layers

Abstract

Tight-binding band electronic structure calculations were performed on the various structures of the Bi 4O 8 double layer found in Bi-based copper-oxide superconductors. With respect to the Fermi level, the position of the Bi 6p-block bands of the BiO double layers is strongly affected by distortion around Bi atoms and by insertion of extra oxygen atoms in the BiO double layer. Our results show that the bottom of the Bi 6p-block bands lies more than 1.0 eV above the Fermi level, so that the formal oxidation state appropriate for Bi is +3. The observation of previous band structure studies that the bottom of the Bi 6p-block bands lies below the Fermi level is a direct consequence of using an ideal structure for the BiO double layer.