Investigation of Chemical Bond Properties and Moessbauer Spectroscopy in YBa2 Cu3O7

Chemical bond properties of YBa2Cu3O7 were studied by using the average band-gap model. The calculated resuits show that the covalency of Cu(1)-O bond is 0. 406, and one of Cu(2) -O is 0.276. Moessbauer isomer shifts of ^57Fe in Y-123 were calculated by the chemical surrounding factor h,defined by covalency and electronic polarizability.The charge-state and site of Fe were determined. The relation between the coupling constant of electron-phonon interaction and covalency is employed to explain that the Cu(2)-O plane is more important than the Cu(1)-O chain on the super-conductivity in the Y-123 compounds.