OPTICAL-ABSORPTION SPECTRA OF GD2BACOO5 AND Y2BACOO5

The marked differences found in the optical spectra of the brown colou red Gd2BaCoO5 and the green coloured Y2BaCoO5 oxides, have been explai ned taking into account the different crystal structures' that they pr esent. While Gd2BaCoO5 shows orthorhombic symmetry, space group Immm, with the cobalt located at distorted octahedral coordination (CoO6), t he Y2BaCoO5 crystallizes with orthorhombic symmetry, space group Pnma, in which the cobalt is surrounded by five oxygen atoms, forming disto rted square pyramids (CoO5) which have C4v as point symmetry.