Optical Absorption Spectra of Gd2BaCoO5 and Y2BaCoO5

The marked differences found in the optical spectra of the brown coloured Gd₂BaCoO₅ and the green coloured Y₂BaCoO₅ oxides, have been explained taking into account the different crystal structures that they present. While Gd₂BaCoO₅ shows orthorhombic symmetry, space group Immm, with the cobalt located at distorted octahedral coordination (CoO₆), the Y₂BaCoO₅ crystallizes with orthorhombic symmetry, space group Pnma, in which the cobalt is surrounded by five oxygen atoms, forming distorted square pyramids (CoO₅) which have C_4V as point symmetry.