COMMON EXCITONIC MECHANISM FOR CuO2 AND BiO3 BASED PEROVSKITES

BiO 3 based high Tc oxides are studied and compared to CuO 2 based ones. Both are described by a general Hamiltonian and studied by perturbation theory in the hopping energy. It is shown that a common polarization mechanism can give rise to pairing of the O holes added to the antiferromagnetic or disproportionated semiconducting states. The necessary conditions are: proximity of the M(Cu or Bi) and O levels, a gap in the electronic spectrum of the system and important nearest-neighbor M-O repulsion.