Ionic energy levels and hole formation in high temperature superconductors

Madelung potentials of some fluoride and oxide compounds were calculated by direct summation. A new method is devised for constructing energy level diagrams for high temperature superconductors. The method depends on an effective electron affinity for oxygen in the solid, derived from known band gaps in oxide compounds. The levels are related to charge distribution, defects and processing parameters. The diagrams show instabilities in the crystal structures of Bi2Sr2Ca2Cu3O10 and Tl2Ba2Ca2Cu3O10 and demonstrate how holes are formed. (orig.)