Abstract
Based upon the experimental evidences and inferences, the almost filled σ-electron band embedded in the extended two-dimensional or one-dimensional square planar [CuO4]-bonding system is identified to be the unique high T c superconductivity possible band, because it is a pseudo-inner orbital, muffled and isolated from the outer phonon systems by the other filled, localized orbitals. A high Debye temperature θD=770-800K is evaluated for the [CuO4]-bonding system. An ideal structural model for (Ba2Y)Cu3O7, which explains the orthorhombic constants and the high pressure behavors of T c of this material is proposed.