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 pre sent. While Gd2BaCoO5 shows orthorhombic symmetry, space group Immm, w ith the cobalt located at distorted octahedral coordination (CoO6), th e Y2BaCoO5 crystallizes with orthorhombic symmetry, space group Pnma, in which the cobalt is surrounded by five oxygen atoms, forming distor ted square pyramids (CoO5) which belong to the C4v group symmetry.