STRUCTURAL PARAMETERS AND ELECTRON DIFFERENCE DENSITY IN Y2BACUO5

Diyttrium barium copper(II) pentoxide, Y2BaCuO5, M(r) = 458.7, orthorhombic, Pnma, a = 12.188 (2), b = 5.662 (2), c = 7.132 (2) angstrom, V = 492.17 (3) angstrom3, z = 4, D(x) = 6.19 Mg m-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 36.633 mm-1, F(000) = 812, T = 298 K, final R = 0.059, wR = 0.028 for 2758 unique reflections. The structural parameters for the nonsuperconducting 'green phase' Y2BaCuO5 were redetermined and the electron density compared with that for the high-T(c) superconductor YBa2Cu3O7-delta. The DELTArho topography near Cu in Y2BaCuO5 resembles that near Cu2 in YBa2Cu3O7-delta, which has similar coordination. It differs markedly from that near Cul, which coordinates with disordered 0 atoms. The similarity of both coordination and electron density for the Cu atom in the green phase with those for Cu2 in the high-T(c) compound is consistent with both atoms being in the + 2 oxidation state.